The Effect Of Mechanical Vibration (113 Hz Applied to ... effect of mechanical...The Effect Of Mechanical Vibration (113 Hz Applied to Maxillary First Premolars) On Root Resorption

The Effect Of Mechanical Vibration (113 Hz Applied to Maxillary First

Premolars) On Root Resorption Associated With Orthodontic Force: A

Micro-CT Study.

Johnathan L.E. Grove, (BDSc Western Australia) Discipline of Orthodontics

Faculty of Dentistry University of Sydney

Australia

A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Clinical Dentistry (Orthodontics)

October 2011

The Effect Of Mechanical Vibration (113 Hz Applied to Maxillary First Premolars) On Root Resorption Associated With Orthodontic Force: A Micro-CT Study.

By Johnathan Grove Page 3

Declaration

Candidate Certification

This is to certify that the candidate carried out the work in this

thesis, in the Orthodontic Department, University of Sydney, and it

has not been submitted to any other University or Institution for a

higher degree.

Johnathan Grove

------------------------------------------------

Johnathan L.E. Grove



Dedication

To my mum Lynn and dad Don, for all your love, patience, and

encouragement over the years. Without you I would not be

where I am today. Thank you for always being only a phone call

away!

To my beautiful Adriana, for all your love and support. You

always manage to bring a smile to my face. Thank you for

sharing this journey with me!

To all my friends and family, thank you for simply

understanding!

“All men by nature desire to know”

(Aristotle)



Acknowledgements

My sincere thanks and gratitude is expressed to the following:

Professor M Ali Darendeliler, Head of Department, Discipline of Orthodontics, University of

Sydney for his supervision and support throughout this thesis

Professor Tamer Turk, Associate Professor Selma Elekdag-Turk, and their team, Department

of Orthodontics, Ondokuz Mayis University for their collaboration with this study, and their

assistance in the collection of the sample

Dr Carmen Gonzales, Senior Lecturer, Discipline of Orthodontics, University of Sydney for

her supervision of the project

Dr Oyku Dalci, Lecturer, Discipline of Orthodontics, University of Sydney for her welcome

advice and supervision of the project

Mr Dennis Dwarte, Australian Centre for Microscopy and Microanalysis, University of

Sydney, for his help with the micro-CT and VG Studio Max

Associate Professor Peter Petocz, Department of Statistics, Macquarie University Sydney, for

his help and suggestions regarding the statistical analysis of the project



Associate Professor Allan Jones, Australian Centre for Microscopy and Microanalysis,

University of Sydney, for his help with the micro-CT, VG Studio Max and CHull2D

To the previous orthodontic postgraduate students from the Department of Orthodontics at

the University of Sydney for their hard work, effort, and guidance which have helped shape

this research

Finally, to my friends and colleagues at the department, especially Drs Daniel Tan, Riaan

Foot, Saad Al-Mozany, and Tiffany Huang, for their continuous support and friendship over

the last three years, and for taking this new life-step with me



Abbreviations

2D Two dimensional 3D Three dimensional AAC Acellular afibrillar cementum AEFC Acellular extrinsic fibre cementum AIFC Acellular intrinsic fibre cementum BMP Bitmap cAMP Cyclic adenosine monophosphate CIFC Cellular intrinsic fibre cementum CEJ Cemento-enamel junction CMSC Cellular mixed stratified cementum FEM Finite element model GIC Glass ionomer cement HERS Hertwig’s epithelial root sheath Hz Hertz IL-1 Interleukin-1 IL-1b Interleukin-1beta Micro-CT Micro computed tomography MM Millimeters NSAID Non-steroidal anti-inflammatory drug OIIRR Orthodontically induced inflammatory root resorption OPG Osteoprotegrin OTM Orthodontic tooth movement PA Periapical radiograph PDL Periodontal ligament PEMF Pulsed electromagnetic field PTH Parathyroid hormone RANK Receptor activator of nuclear factor kappa beta RANKL Receptor activator of nuclear factor kappa beta ligand SEM Scanning electron microscopy TEM Transmission electron microscopy TIFF Tagged image file format TMA Beta-titanium molybdenum alloy TNF Tumour necrosis factor TNFRSF11A Tumour necrosis factor receptor super-family 11alpha TRAP Tartrate resistant acid phosphotase µE Micro strain WBV Whole body vibration XMT X-ray microtomography



Table of Contents: Declaration ................................................................................................................................. 3

Dedication .................................................................................................................................. 4

Acknowledgements .................................................................................................................... 5

Abbreviations ............................................................................................................................. 7

1 Introduction ..................................................................................................................... 12

2 Review of the Literature .................................................................................................. 16

2.1 Cementum ............................................................................................................... 16

2.1.1 Definition & Role of Cementum......................................................................... 16

2.1.2 Classification & Types of Cementum ................................................................. 17

2.1.3 Development of Cementum .............................................................................. 20

2.1.4 Composition & Components .............................................................................. 21

2.1.4.1 Organic matrix ............................................................................................ 22

2.1.4.2 Mineral component .................................................................................... 22

2.2 Root Resorption & Orthodontically Induced Inflammatory Root Resorption ......... 23

2.2.1 Definition ........................................................................................................... 24

2.2.2 History ................................................................................................................ 24

2.2.3 Incidence & Prevalence...................................................................................... 25

2.2.4 Classification ...................................................................................................... 27

2.2.5 Grading ............................................................................................................... 29

2.2.6 Aetiology ............................................................................................................ 29

2.2.6.1 Biological Risk Factors................................................................................. 30

2.2.6.1.1 Genetic factors ....................................................................................... 30

2.2.6.1.2 Environmental factors ............................................................................ 32

2.2.6.2 Dental Risk Factors ..................................................................................... 36

2.2.6.2.1 Pre-existing resorption ........................................................................... 36

2.2.6.2.2 History of trauma ................................................................................... 36

2.2.6.2.3 Dental morphology, anomalies, and agenesis ....................................... 37

2.2.6.2.4 Endodontic treatment ............................................................................ 38

2.2.6.2.5 Periodontal status .................................................................................. 38

2.2.6.2.6 Specific tooth type vulnerability ............................................................ 39

2.2.6.2.7 Severity & type of malocclusion ............................................................ 39

2.2.6.2.8 Alveolar bone density & turnover rate .................................................. 40

2.2.6.2.9 Dental age & stage of root development .............................................. 41



2.2.6.3 Mechanical Risk Factors ............................................................................. 41

2.2.6.3.1 Treatment duration ................................................................................ 41

2.2.6.3.2 Type & extent of tooth movement ........................................................ 42

2.2.6.3.3 Force magnitude & duration .................................................................. 43

2.2.6.3.4 Appliances & treatment techniques ...................................................... 45

2.2.6.3.5 Extraction versus non-extraction ........................................................... 46

2.2.6.3.6 Transplanted teeth ................................................................................. 46

2.2.7 Diagnosis of Root Resorption ............................................................................ 46

2.2.7.1 Location of OIIRR ........................................................................................ 48

2.2.8 Pathogenesis & Mechanisms of Root Resorption ............................................. 48

2.2.8.1 Histopathology ........................................................................................... 50

2.2.8.2 Biochemistry ............................................................................................... 51

2.2.8.3 Resorptive Resistance ................................................................................. 52

2.2.8.4 Repair .......................................................................................................... 53

2.2.9 Prognosis, Prevention, & Management of OIIRR............................................... 54

2.2.9.1 Prevention .................................................................................................. 55

2.2.9.2 Management .............................................................................................. 56

2.3 Research Methodologies for Evaluation of OIIRR ................................................... 57

2.3.1 Radiography ....................................................................................................... 57

2.3.2 Serial Sectioning & Light Microscopy ................................................................. 59

2.3.3 Scanning Electron Microscopy ........................................................................... 59

2.3.4 X-ray Micro-Tomography ................................................................................... 60

2.3.4.1 SkyScan 1172 Desktop X-ray Micro-Tomograph ........................................ 61

2.3.4.2 Previous Dental Research Using Micro-CT Technology .............................. 62

2.4 Vibration .................................................................................................................. 64

2.4.1 Whole Body Vibration ........................................................................................ 66

2.4.2 Vibration & Dentistry ......................................................................................... 67

2.4.2.1 Rate of Tooth Movement ........................................................................... 67

2.4.2.1.1 Acceledent Device .................................................................................. 69

2.4.2.2 Pain Control ................................................................................................ 70

3 References ....................................................................................................................... 72

4 Manuscript ....................................................................................................................... 99

4.1 Abstract .................................................................................................................. 101

4.2 Introduction & Literature Review .......................................................................... 102

4.3 Material and Methods ........................................................................................... 104



4.3.1 Sample .............................................................................................................. 104

4.3.2 Appliance design .............................................................................................. 106

4.3.3 Specimen collection ......................................................................................... 107

4.3.4 Sample Analysis ................................................................................................ 107

4.3.5 Statistical Analysis ............................................................................................ 109

4.4 Results .................................................................................................................... 109

4.5 Discussion............................................................................................................... 111

4.6 Conclusions ............................................................................................................ 115

4.7 Acknowledgement ................................................................................................. 116

4.8 References ............................................................................................................. 117

4.9 List of Figures ......................................................................................................... 126

Figure 1: Intra-oral views, and schematic design, of the 0.017” x 0.025” TMA spring..................................................................................................................................... 126

Figure 2: Oral B HummingBird unit with modified tip ............................................... 126

Figure 3: Total resorption volume per tooth ............................................................. 127

Figure 4: Overall resorption volume per surface ....................................................... 127

Figure 5: Overall resorption volume per vertical thirds ............................................ 128

Figure 6: a) Graph of resorption volume per subject (vibration versus non-vibration), with line of best fit (dotted line = equal amounts of resorption, vib & non-vib). b) Regression graph with line of best fit showing the relationship between the effect of vibration and the amount of resorption experienced on the non-vibration side per subject. ....................................................................................................................... 128

Figure 7: Regression graphs, with lines of best fit, showing the relationship per subject between the effect of vibration (Improvement) and the amount of resorption experienced on the a) Buccal, b) Mesial, c) Palatal, and d) Distal, aspects. .............. 129

Figure 8: Regression graphs, with lines of best fit, showing the relationship per subject between the effect of vibration (Improvement) and the amount of resorption experienced on the a) Cervical, b) Middle, and c) Apical, aspects. ........................... 130

4.10 List of Tables .......................................................................................................... 131

Table I: Total volume of root resorption per tooth ................................................... 131

Table II: Total volume of root resorption per experimental group ........................... 131

Table III: Total volume of root resorption per tooth surface .................................... 131

Table IV: Total volume of root resorption per vertical third ..................................... 132

Table V: Paired Differences ........................................................................................ 132

Table VI: Regression analysis – Comparing overall non-vibration & overall improvement with vibration ...................................................................................... 133

Table VII: Regression analyses per tooth surface – Comparing non-vibration & the improvement with vibration. ..................................................................................... 133



Table VIII: Regression analyses per vertical third – Comparing non-vibration & the improvement with vibration ...................................................................................... 134

5 Future Directions ........................................................................................................... 135

6 Appendices ..................................................................................................................... 138

6.1 Appendix: Index for Qualitative Assessment of Root Resorption ......................... 138

6.2 Appendix: Sample distribution and split-mouth study design .............................. 139

6.3 Appendix: Specimen collection procedure ............................................................ 139

6.4 Appendix: SkyScan 1172 desktop x-ray micro-tomograph .................................... 140

6.5 Appendix: Images from VGStudio Max .................................................................. 140

6.6 Appendix: Data – Total resorption per tooth ........................................................ 141

6.7 Appendix: Data – Total resorption per tooth surface ........................................... 142

6.8 Appendix: Data – Total resorption per vertical third ............................................. 143



1 Introduction

Orthodontic tooth movement (OTM) occurs as a result of the mechanical stimulus,

produced by a force applied to the crown of a tooth, and the biological response of the

periodontium1. There are three fundamental biologic responses associated with application

of orthodontic force, including bone apposition, bone resorption, and root resorption.

The occurrence of root resorption was first mentioned in 18562, and has been

described as a physiological or pathological process that involves the active breakdown and

destruction of formed tooth structure3, specifically mineralised and non-mineralised

cementum and mineralised dentine4, 5. Physiological resorption occurs naturally and can be

seen in the deciduous dentition during the process of tooth eruption. Pathological

resorption involves either internal resorption within the canal, or external resorption of the

root surface.

Although the link between root resorption and orthodontic force was first suggested

by Ottolengui6 in 1914, the relationship is still not well understood. It appears external root

resorption occurs during orthodontic tooth movement in association with the removal of

hyalinised tissue resulting from local injury to the periodontal ligament (PDL)4 i.e.

orthodontic force. Brezniak and Wasserstein7 suggested the application of an orthodontic

force induces an inflammatory reaction within the PDL which is essential to tooth

movement and is also fundamental to root resorption. They described this orthodontic

force induced root resorption as Orthodontically Induced Inflammatory Root Resorption

(OIIRR), and concluded it is an undesirable and unavoidable consequence of orthodontic

treatment7-10.



The incidence of OIIRR varies within the literature ranging from a greater than 90%

occurrence of root resorption in histological studies11-13 to incidences of 0% - 100% in

radiographic studies14-20. More recently, the incidence of root resorption in adults has been

reported as 25% - 76% after at least 12 months of treatment21-25, while in adolescents the

incidence has been reported as 5% - 18%16, 22, 26, 27. Root resorption has also been reported

in untreated teeth increasing in conjunction with age, suggesting some degree of loss of

root structure can be considered normal11, 28.

The aetiology of root resorption appears to be remarkably multifactorial and remains

largely unknown. Many studies have investigated and attempted to isolate causative

factors related to OIIRR, and have identified numerous risk factors29, 30. These can be

broadly grouped into biological, dental, and mechanical factors. Examples of biological

factors include genetic factors such as individual susceptibility31-34 and ethnicity24, as well as

environmental factors such as allergies35, 36 and medications37-40. Previous history of

resorption and trauma15, 26, 41, 42, tooth morphology24, 43, 44, and bone density39, 45, are

examples of dental factors. Lastly, treatment duration27, 46-48, force magnitude12, 49-52, and

type of tooth movement53-57 are examples of mechanical factors implicated in OIIRR. These

mechanical factors are of particular interest to the clinician as they may be controlled and

modified in an attempt to reduce their influence upon root resorption.

In terms of clinical and practical significance, the degree of root resorption in most

cases will be inconsequential and will not affect the long term survival or functionality of the

afflicted teeth or dentition10, 48. However, in some cases the decreased crown to root ratio

resulting from severe resorption can significantly affect the prognosis, especially in the

presence of periodontal disease or trauma58. Fortunately the risk of severe root resorption



is rare occurring in less than 5% of treated patients21, 23, 59, and a number of strategies have

been suggested to help minimise the process including:

I. pre-treatment assessment of medical and family history24, 28, 31, 34,

II. radiographic assessment at 6 months into treatment (or at 3 months in high risk

individuals)46, 60,

III. reducing treatment duration13, 27, 46, 61,

IV. reducing force magnitude9, 12, 13, 62, and

V. halting treatment for periods of up to 3 months if resorption is detected33, 61, 63.

The resorption process usually ceases once the orthodontic force is removed10, 64,

with repair beginning once the force has decreased below a certain level62, 65 and tending to

increase with time66-68.

Recently, the use of mechanical vibration concurrently with orthodontic treatment

has been suggested as a possible means of reducing treatment duration as well as root

resorption; however there is limited research in this area. Mechanical modulation of bone

architecture has been found to have beneficial effects on fracture healing69, 70, disuse

atrophy71-73, and musculoskeletal degeneration74, 75 including osteoporosis76-78; as well as

enhancing mechanical signalling within bone79-81. Cyclical mechanical loading in animal

models has also been shown to increase bone remodelling82-84, and vibration of rat molars

at 60 Hz has demonstrated significantly increased tooth movement and a suggested trend

towards decreased root resorption85. Vibration produced as a result of a pulsed electro-

magnetic field has also demonstrated evidence for faster tooth movement86. Furthermore,



vibratory stimulation has been reported as a method to significantly reduce pain after

orthodontic appliance adjustment87, 88.

Previous studies have used a wide range of methods to investigate root resorption,

ranging from two dimensional (2D) radiographs17, 31, 35, 60, 89-93, and light microscopy9, 49, 66, 90,

94-100, to scanning electron microscopy (SEM)12, 32, 67, 101, and transmission electron

microscopy (TEM)102. However, three dimensional (3D) methods, including stereo SEM

imaging55, 103, and X-ray microtomography (XMT)52, 64, 104-106 have been shown to be more

accurate and more reliable for quantitative measurements of root resorption52, 107, 108.

The aim of this study was to investigate the effect of mechanical vibration, applied

over 4 weeks to maxillary first premolars, on the volume of root resorption craters

associated with application of a buccally directed controlled orthodontic force (150g), using

Micro-computed tomography for qualitative and quantitative volumetric analysis. This

study is a continuation of the root resorption research conducted by the Orthodontics

Department in the Faculty of Dentistry at the University of Sydney.



2 Review of the Literature

2.1 Cementum

The periodontium is a complex structural and functional component of the dental

apparatus. It is defined as those tissues supporting and investing the tooth, and consists of

cementum, periodontal ligament (PDL), alveolar bone, and gingiva109-112. Cementum is a

major component of the tooth root and it plays a very central role in the process of

orthodontically induce inflammatory root resorption. As a result of its significance in root

resorption, this section of the review will focus principally upon cementum and its

characteristics.

2.1.1 Definition & Role of Cementum

Human cementum was first described in 1853, and has since been described as the

thin layer of non-uniform calcified connective tissue secreted by cementoblasts onto the

root dentine111, 113. Cementum is continuous with the underlying root dentine and the

overlying PDL, forming an interface between the two111. Its slow formation throughout life

allows for continual adaptation and reattachment of the PDL fibres.

Developmentally, cementum appears to be derived from the investing layer of the

dental follicle, and it is similar in composition and physical properties to bone except it is

avascular, and lacks innervation114. It is also less readily resorbed than bone, which is

important for orthodontic tooth movement. The reason for this feature is unknown but it

may be related to111:

Physicochemical or biological differences between bone and cementum.



Inherent properties of the pre-cementum layer.

The increased density of Sharpey’s fibres (particularly in acellular cementum).

The proximity of epithelial cell rests to the root surface.

The prime and vital function of cementum is to provide an interface on the root

surface for attachment of the principle collagen fibres of the PDL109, 110, 115. It is a highly

responsive mineralised tissue that maintains the integrity of the root, helps to maintain the

tooth in its functional position via adaptation of fibre attachment, and is involved in tooth

repair, regeneration and pulp protection109, 111, 115, 116.

2.1.2 Classification & Types of Cementum

Previous studies have identified several different types of cementum, which vary

according to a number of factors including formation, location, function, structure,

composition, and degree of mineralisation109, 111, 114. Based on these characteristics,

cementum can be classified as follows111, 112, 117, 118:

1. Primary or Secondary cementum.

This classification is related to the timing of development. Primary cementum is

formed during root formation, whilst secondary cementum is formed when the

tooth is in occlusion and then on throughout life.

2. Cellular or Acellular cementum.

This classification is related to the presence or absence of cells within the matrix.

Acellular cementum covers the root adjacent to the dentine, while cellular

cementum is usually found mainly in the apical regions or overlying the acellular

cementum layer.



3. Extrinsic or Intrinsic fibre cementum.

This classification is related to the origin of the collagenous fibres in the matrix.

Intrinsic fibres originate from secretion by cementoblasts, and extrinsic fibres are

PDL fibres incorporated into the matrix.

Seven different types of cementum have been illustrated in the literature111, 112, 118;

however Bosshardt109 describes 3 fundamentally different varieties of human cementum

and these can vary from tooth to tooth and/or region to region on the same tooth. These

are:

1. Acellular extrinsic fibre cementum (AEFC).

This type of cementum corresponds with primary acellular cementum and is the first

cementum variety deposited on the developing root, and therefore is mostly found

on the cervical and middle thirds of the root, although it may extend further apically

in anterior teeth117. AEFC formation begins shortly after crown formation concludes,

and is completed prior to the tooth reaching occlusion, at which point cellular

intrinsic fibre cementum formation begins119. AEFC formation is slow and

differentiation of the cementoblasts involved occurs in close proximity to the

advancing root edge. As the name indicates, this type of cementum is cell free;

however it is densely packed with collagen fibres known as Sharpey’s fibres120 which

are derived from the principle fibres of the PDL111. This high density of fibre

insertions reflects its vital role in anchoring PDL attachment and tooth support

during function121. AEFC has the ability to adapt according to functional demands

and physiological movements, altering the orientation of the Sharpey’s fibres as

required120.



2. Cellular intrinsic fibre cementum (CIFC).

This third variety of cementum in humans generally corresponds with secondary

cellular cementum and is usually found in the apical third or furcation regions where

no AEFC has been laid down111, 118. CIFC contains intrinsic fibres which run parallel to

the root surface in a circular fashion, and cementoblasts which have become

trapped in the ECM during its rapid deposition109 Acellular intrinsic fibre cementum

(AIFC) may result when the formation occurs more slowly and cells are not

incorporated. The lack of Sharpey’s fibres means CIFC doesn’t have a direct role in

tooth attachment120, however its adaptive behaviour allows it to maintain the tooth

in its proper position112, 117, 118 and its rapid formation gives it a reparative role. As a

result, it tends to be the main type of cementum found in areas of resorption repair.

Towards the root apex, and in furcation areas, AEFC and the CIFC may commonly be

present in alternating layers described as cellular mixed stratified cementum

(CMSC)109, 111, 118. CMSC serves to reshape the root surface to compensate for

physiological drift and non-physiological shifting of teeth within their sockets110.

3. Acellular afibrillar cementum (AAC).

This type of cementum is found either at or just above the cemento-enamel junction

(CEJ) covering minor areas of cervical enamel110. AAC formation is believed to begin

at the end of enamel maturation109, and it is usually thinly distributed, acellular with

a mineralised ground structure, and is the only type of cementum containing no

collagen fibres. Due to the lack of collagen fibrils and absence of cells within the

matrix, its precise function is unknown109.



2.1.3 Development of Cementum

Although cementum formation occurs along the entire length of the root,

cementogenesis and root dentine formation are intimately related in that cementogenesis

initiation is limited to the advancing root edge during root development111, 117, 118. At this

site, Hertwig’s epithelial root sheath (HERS) is believed to send an inductive message to the

ectomesenchymal pulp cells, stimulating them to differentiate into odontoblasts and

deposit a layer of pre-dentine111, 112. Soon after odontoblast differentiation, HERS becomes

interrupted and detaches from the dentine surface allowing ectomesenchymal cells from

the dental follicle to come into contact with the pre-dentine surface109-111, 117, 118. The next

series of events leads to differentiation of cementoblasts and subsequent deposition of

cementum on the root surface, however the specific cells involved and the exact sequence

of events is still unresolved111. The classical theory suggests the cementoblasts are derived

from the mesenchymal cells of the dental follicle109, 110, 113, 114, whereas others have

suggested the cementoblasts are derived from the epithelial cells of HERS120, 122-124. The

evidence seems to favour the classical theory109.

When root development is about two thirds completed and the tooth is about to

enter its functional stage, AEFC formation gives way to CIFC formation (although CIFC may

be produced earlier, on furcation surfaces in multi-rooted teeth)109, 125-127. The conditions

and factors responsible for this transition are unknown. When root formation is complete,

the whole surface is covered by cementum, with cervical AEFC layers having attained a

thickness of -15 pm and apical CIFC layers exceeding this value. In addition, CMSC starts its

development on the apical root portion109, 110, 118.



The formation of cementum can also be divided into 2 distinct developmental

stages, the pre-functional stage, and the functional stage. The pre-functional stage consists

of cementum formation (primary cementum) prior to occlusal loading, and also determines

the distribution of the cementum varieties along the root surface. The formation during this

stage is slow, resulting in the acellular cementum varieties. The functional stage consists of

cementum formation (secondary cementum) just prior to occlusal loading, which then

continues through life. The formation during this stage is mainly rapid, resulting in cellular

cementum varieties117.

2.1.4 Composition & Components

As mentioned previously, the composition of cementum is very similar to bone128,

containing on a wet-weight basis 65% inorganic material, 23% organic material and 12%

water. By volume, the composition comprises approximately 45% inorganic material, 33%

organic material, and 22% water111, 129. These values may very however from sample to

sample, and within the different types of cementum109 as the degree of mineralisation

varies in different parts of the tissue; some acellular zones may be more highly calcified than

dentine.

The organic matrix on the other hand is primarily collagen (principally type I

collagen), in addition to concentrations of non-collagenous proteins that appear to be

similar to those found in bone109, 111, 115. Among these proteins are bone sialoprotein,

osteopontin and other cementum specific elements that are involved in periodontal

reattachment and/or remineralisation.



The principal inorganic component is found in the form of hydroxyapatite crystals,

although other forms of calcium are also present at higher levels than in enamel and

dentine109, 111. As with enamel, the concentration of trace elements including fluoride tends

to be higher at the external surface. Fluoride levels are also found to be higher in acellular

cementum130.

2.1.4.1 Organic matrix

The cemental organic matrix is primarily derived from the extrinsic fibres of the PDL

(Sharpey’s fibres), and from the intrinsic fibres produced by local cementoblasts. Type I

collagen constitutes approximately 90% of this matrix, while type III collagen constitutes 5%

and is found in high concentrations during development and repair of mineralised tissues109,

111, 115, 131. The collagen plays an important structural and morphogenic role, as well as

providing a scaffold for mineralisation111.

As mentioned, the organic matrix also comprises a number of non-collagenous

proteins including primarily bone sialoprotein and osteopontin109, 132, as well as other

examples such as fibronectin, dentine matrix protein, proteoglycans, glycosaminoglycans,

and several growth factors114, 128. Overall, the function of the non-collagenous proteins

within the organic matrix includes stimulation of cell migration, attachment, proliferation,

protein synthesis, and mineralisation during root formation123.

2.1.4.2 Mineral component

The mineral content of cementum tends to vary according to the type of cementum

present, with AEFC being more highly mineralised than CIFC and CMSC109. It is made up in

the most part by hydroxyapatite crystals which are thin and plate-like and similar to those

found in bone, as well as small concentrations of amorphous calcium phosphate133. These



hydroxyapatite crystals are on average 55 nm wide and 8 nm thick, which is much smaller

than the crystals within enamel. As a result of this, the cemental surface has a greater

capacity for absorption of other trace elements such as Fluoride, but is also more

susceptible to decalcification in the presence of acid conditions111, 128, 133.

It has been proposed in the literature that the mineral content or components of

cementum may influence its resistance to root resorption11, 134. Fluoride has been shown to

have a relatively high concentration of 0.9% in cementum, which is related to the fluoride

exposure of the individual, and also generally increases with age109, 130. Rex and co-workers

found fluoride tended to accumulate in the surface layers of the cementum where it reacted

with the hydroxyapatite, showing limited diffusion into deeper layers135.

2.2 Root Resorption & Orthodontically Induced Inflammatory

Root Resorption

The term “root resorption” is a general term that can be used to describe either the

physiological or pathological process that results in loss of tooth structure.

Physiological root resorption occurs naturally and primarily refers to the resorption

of the roots of the deciduous dentition during the process of tooth eruption. It can also be

seen in the permanent dentition to a lesser extent as a result of physiological changes

occurring over time111.

Pathological root resorption on the other-hand is not as benign. It usually results

from trauma, disease, or iatrogenic causes65, and involves either internal resorption within

the canal or external resorption of the root surface. Internal pathological resorption affects



the dentine and pulpal walls within the root canal and is initiated within the pulp. External

pathological resorption affects the outer dentine and cementum surfaces and is initiated

within the periodontium111.

2.2.1 Definition

Root resorption has had several descriptions and definitions as the process has been

studied and further understood. It was initially defined as the destruction of formed tooth

structure3 but more recently it has been described as a physiological or pathological process

that involves the active removal of tooth structure5, specifically mineralised and non-

mineralised cementum and mineralised dentine, in association with the PDL remodelling

process136.

Pathological external root resorption occurring as a result of the inflammatory

reaction within the PDL induced by orthodontic force and tooth movement, has been

defined separately by Brezniak and Wasserstein7 as Orthodontic Induced Inflammatory Root

Resorption (OIIRR). This inflammatory process is fundamental to tooth movement as well as

root resorption and as such is present to some degree in all orthodontic patients7-10.

2.2.2 History

Root resorption has been studied extensively over the last century. The occurrence

of root resorption in permanent teeth was first documented and discussed by Bates in

18562, who referred to the process as “absorption” resulting from trauma to the periodontal

membrane. The link between root resorption and orthodontic tooth movement wasn’t

made until 1914 when Ottolengui identified resorption that resulted specifically from

orthodontic treatment6.



In 1927, Ketcham radiographically investigated apical root resorption and suggested

root shortening could result from an anatomical variation, impaction, or orthodontic

treatment. He found 21% of his sample showed some degree of resorption of the anterior

teeth with the maxillary teeth being more affected than the mandibular teeth17. In a later

study, he found root resorption was present in approximately 1% of non-orthodontic

patients and concluded that hormonal or dietary factors may also play a role in the

aetiology of root resorption92.

During this period, both of the terms “absorption” and “resorption” were used inter-

changeably in the literature to describe the process of root resorption. The term

“resorption” was proposed as being the most appropriate to describe the process in 19323,

and this terminology remains in use today.

Since then, the process of root resorption has been further defined and described

culminating in its contemporary definition as stated above.

2.2.3 Incidence & Prevalence

The incidence of OIIRR in the general population is unpredictable and varies within

the literature7 as a result of the different techniques used to assess and measure the

presence and volume of resorption ‘craters’.

Previous histological studies of orthodontically treated teeth have reported a greater

than 90% occurrence of root resorption11-13, while radiographic studies14-20 have suggested

incidences ranging from 0% - 100%. More recently, the incidence of root resorption in

adults has been shown to increase from 15% pre-treatment23, to 25% - 76% after at least 12

months of treatment21-25. In adolescents the incidence has been reported between 5% -



18%16, 22, 26, 27, while Kurol used combined histological and radiographic techniques and

found an incidence of 93%90.

The incidence of root resorption in untreated teeth has also been reported in many

of the same studies, similarly suggesting incidences ranging from 0%89 - 100%15, 28. A

histological study by Henry and Weimann11 found 90.5% of non-orthodontically treated

teeth displayed evidence of resorption. The most commonly affected area was the root

apex, followed by the mesial, buccal, distal, and lingual surfaces. They also found resorption

increased with age, and concluded from their study that some degree of root resorption can

be considered normal and is associated with the remodelling of bone and tissue that

accompanies physiological tooth movement throughout life11, 28.

When assessed using panoramic or peri-apical radiographs, the average OIIRR is

usually found to be less than 2.5mm16, 22, 93, 137, 138, or varying from 6% - 13% for different

teeth58. When graded scales are used26, OIIRR is primarily found to be minor or moderate in

most patients27, 35, 139, 140. Fortunately, severe root resorption, defined as exceeding 4mm or

one third of the original root length, is rare and seen in only 1% – 5% of teeth16, 21, 23, 27, 60, 139.

Incidence of Moderate Resorption

Definition: Incidence:

> 2mm resorption 25% 24

> 3mm resorption 30% 21

> 2mm to 1/3rd of root length 10% - 20% 27, 141

12% - 17% 137

Incidence of Severe Resorption

Definition: Incidence:

> 5 mm resorption 5% 21

> ¼ of root length 3% 59

> 1/3rd of root length < 1% - 3% 16, 23



Maxillary teeth, especially the lateral incisors, tend to be at greater risk of root

resorption17, 24, 31, 137, 142, followed by mandibular incisors and first molars. This appears to

be related to the transfer and concentration of forces at the root apex143.

2.2.4 Classification

Pathological external root resorption has a variety of appearances and has been

classified accordingly by several authors within the literature including Andreasen144,

Tronstad145, and Brezniak and Wasserstein29. These classifications include:

1. Surface resorption – Tends to involve brief resorption of small areas of cementum

followed by spontaneous repair. It is a self limiting process followed by repair and

not usually detected radiographically.

2. Replacement resorption – Occurs where the PDL is absent or suffered extensive

necrosis, and bone replaces the resorbed surface. This process results in ankylosis

and is often seen after traumatic dental injuries.

3. Inflammatory resorption – Occurs where resorption reaches the dentinal tubules of

a tooth with an infected, necrotic pulp. Inflammatory mediators and phagocytic cells

colonise the resorbed and denuded cementum surface, and later invade the tubules

and pulpal tissue. Under normal circumstances, the root is protected from

resorption via cementum externally and pre-dentine internally; however,

inflammatory resorption occurs when the pre-dentine or cementum become

mineralised. Tronstad further classified inflammatory resorption into 2 categories:

I. Transient inflammatory resorption – Occurs where root damage is minimal

and the resorptive stimulation is brief, and is frequently seen in traumatised,

or orthodontically or periodontally treated teeth. It usually lasts only 2-3



weeks followed by repair with cementum-like tissue, and is usually

undetected radiographically.

II. Progressive inflammatory resorption – Occurs where the resorptive stimulus

remains for a longer duration, as in orthodontic treatment. Once the

pressure in the PDL is released, the resorption is halted. It is usually visible

radiographically.

Root resorption associated with orthodontic treatment is most commonly surface

resorption or transient inflammatory resorption29, and rarely results in replacement

resorption (ankylosis)7. In 2001, Brezniak and Wasserstein classified OIIRR into 3 types

based upon severity; which is determined by the extent to which the root surface is

involved7, 146. These types are:

1. Cemental or surface resorption with remodelling – Affects the outer cemental layers

which are resorbed and then subsequently fully regenerated or remodelled once the

etiologic factor has been removed.

2. Dentinal resorption with repair (Deep resorption) – Affects both the cementum and

outer layers of dentine which are resorbed and the defect is usually repaired with

cementum. The subsequent root shape after this resorption and repair may not be

identical to the original form.

3. Circumferential apical root resorption – Involves significant resorption of the hard

tissue components of the root apex, and results in root shortening. Repair only

occurs within the cemental layers, so resorption is irreversible once apical root tissue

loss occurs beneath the cementum. Sharp edges may remodel however.



2.2.5 Grading

Several subjective scoring systems have also been proposed for grading the severity

of the OIIRR15, 147. The grading system still commonly utilised today was proposed by

Malmgren et al26, and classifies apical root resorption into 4 categories (Appendix 6.1).

Root Resorption Index

Grade 1 Irregular root contour

Grade 2 (minor) <2mm root resorption

Grade 3 (severe) >2mm to 1/3rd of root length

Grade 4 (extreme) Resorption > 1/3rd of root length

2.2.6 Aetiology

As mentioned previously, root resorption occurs as a physiological process, primarily

in the deciduous dentition but also in the permanent dentition. It can also occur as a

pathological process, with potentially significant resorption, as a result of a number of

factors including impaction of adjacent teeth, peri-apical or periodontal inflammation,

occlusal trauma, tumours or cysts, metabolic or systemic disturbances, orthodontic

treatment, and idiopathic resorption148.

The aetiology of root resorption associated with orthodontic treatment however,

remains largely unknown, and appears to be remarkably multifactorial. Many studies have

investigated and attempted to isolate causative factors related to OIIRR, and have identified

numerous risk factors29, 30 associated with increased resorption. These can be broadly

grouped into biological, dental, and mechanical factors and it is the mechanical factors

which are of particular interest to the clinician as they may be potentially controlled and

modified in an attempt to influence and reduce root resorption.



The exact contribution of patient versus treatment factors to the aetiology of OIIRR

is still elusive in the literature, and the existence of large individual variation in responses

appears to be the only consistent finding149.

2.2.6.1 Biological Risk Factors

The biological risk factors associated with OIIRR include those factors which are

directly related to the patient and cannot be altered or controlled by the clinician. Some of

these factors may be within the control of the patient suggesting a genetic or environmental

origin.

2.2.6.1.1 Genetic factors

1. Individual susceptibility & genetics

Individual susceptibility is considered to be one of the major factors in determining

root resorption potential with or without treatment, highlighted by the fact that resorption

can occur in both cases11, 47, 150, as well as varying between individuals and within the same

individual at different times29, 62. Root resorption is related to the individual’s own tissue

response and metabolic activity so, metabolic signals such as hormones, body type and

metabolic rate may play a crucial role affecting the relationship between osteoblastic and

osteoclastic activity which modifies cell metabolism and individual response to disease and

trauma62.

The genetic influence on susceptibility to OIIRR remains somewhat controversial

mainly due to the difficulty in separating the contribution of genetic factors from

environmental factors such as orthodontic treatment34. Newman was the first to formally

propose a genetic component to OIIRR31 and a number of recent studies also support the

idea of a genetic influence34, 150, 151. Harris et al, investigated the incidence of OIIRR in



sibling pairs and reported a heritability of 70% for resorption of the maxillary incisor roots

and the mesial and distal roots of the mandibular first molars151. Ngan et al, investigated

OIIRR using a twins model and found the quantitative concordance estimate was 49.2% for

monozygotic twins and 28.3% for dizygotic twins34. Both studies confirm the presence of a

genetic component. Other studies have also reported familial clustering of OIIRR, however

the pattern of inheritance was unclear31, 152.

Interleukin-1 (IL-1) and tumour necrosis factor (TNF) are pro-inflammatory cytokines

known to induce the synthesis of a variety of proteins that in turn elicit acute or chronic

inflammation. IL-1b has been implicated in bone resorption accompanying orthodontic

tooth movement, and increased levels have been found in the gingival crevicular fluid of

patients undergoing orthodontic treatment. Tumour necrosis factor receptor super-family

11alpha (TNFRSF11A) is another candidate gene which encodes for receptor activator of

nuclear factor kappa beta (RANK)153. RANK together with its ligand (RANKL) is an essential

signalling molecule for osteoclast formation and activation. Polymorphism can influence the

activity of these molecules; Al-Qawasmi and colleagues identified the roles of gene

polymorphism of IL-1b and TNFRSF11A in OIIRR. They found patients homozygous for IL-1b

allele 1 (known to decrease production of IL-1) had a 5.6 fold increased risk of resorption154.

2. Ethnicity

Ethnicity has also been implicated in influencing susceptibility. Sameshima and

Sinclair24 investigated the prevalence of resorption in several populations, and found

Caucasians and Hispanics were more prone to OIIRR than patients of Asian descent.

However, Smale and colleagues did not report any association between race and extent of

OIIRR155.



3. Gender

The incidence of OIIRR, or its severity during treatment, does not appear to be

associated with gender. While several studies have reported a higher incidence in females14,

31, 156, and others have reported a higher incidence in males48, 157, most investigators have

concluded there is no correlation between OIIRR and gender24, 33, 58, 151, 158-160.

4. Age

Historically it was believed the incidence of resorption increased with age in

conjunction with the aging changes experienced by the periodontium such as increased

cemental thickness, increased bony density and concurrent decreased vascularity, and

decreased PDL plasticity and vascularity9, 16. As a result, tooth movement is associated with

the generation of more areas of hyalinisation30. However, almost all recent studies suggest

age at the start of treatment is poorly correlated with the incidence of OIIRR41, 48, 63, 66, 160-165.

Some investigations have found the risk of OIIRR is lower in patients treated before

the age of 11 years, reporting roots with incomplete development before treatment

reached a significantly greater length than those that were fully developed137, 166.

2.2.6.1.2 Environmental factors

1. Asthma & allergy

Several studies have implicated both asthma and allergy as aetiological risk factors in

OIIRR.

Increased incidence of resorption has been found in patients suffering from chronic

asthma regardless of whether the condition was medicated or not35, 96, 167. McNab and co-

workers described a higher incidence of root resorption, especially blunting of the maxillary

molars, in chronic asthmatic patients compared to healthy controls. Davidovitch et al found



elevated levels of alveolar bone osteoclasts in areas of PDL compression in guinea pigs with

induced allergic asthma, suggesting that chemical mediators produced in the asthmatic

state may influence cell populations and enhance the resorption process167. It has been

proposed that the incidence of resorption of posterior teeth may be related to changes in

the immune system in asthmatic patients resulting from proximity of the upper molar roots

to the inflamed maxillary sinus, and/or the presence of inflammatory mediators in these

patients. These inflammatory mediators may enter the periodontal ligament and act

synergistically to increase susceptibility to resorption35, 161. However, the increased

incidence of root resorption appeared to be confined to an increase in root blunting, and

therefore asthma may only represent a minimal risk that may not affect the function or

longevity of the posterior teeth35.

Allergies also appear to increase the likelihood of developing OIIRR. Nishioka et al,

investigated the correlation between excessive root resorption and several immune system

factors, and found the incidence of allergy, asthma, and root blunting were increased in root

resorption patients36. Other studies have also demonstrated an association between

asthma and allergies, and increased occurrence of root resorption96, 168.

2. Endocrine & hormone imbalance

The endocrine system is closely tied to bone activity and metabolism so disorders

affecting calcium metabolism such as hypothyroidism, hyperparathyroidism, Paget’s

disease, and other diseases, have been associated with altered resistance to root

resorption169-171. Linge and Linge16 suggest the hormonal imbalance doesn’t cause

resorption it only influences the process.



The risk of resorption has been shown to be higher in subjects with a decreased

bone turnover rate, such as in patients with hypothyroidism39, 171; and lower in subjects with

increased bone turnover, such as with hyperparathyroidism.

3. Nutrition

A number of authors have concluded that malnutrition or nutritional imbalance is

not a major aetiological factor in root resorption16, 45, however calcium and vitamin D

deficiency in rats has been associated with increased parathyroid hormone (PTH) and

osteoclast levels, greater and more rapid bone resorption, and more severe OIIRR3, 171.

4. Drugs & medications

The role of certain drugs and medications in the pathogenesis of root resorption has

also been investigated in the literature, including non-steroidal anti-inflammatory drugs

(NSAIDS)37, 38, 172-174, corticosteroids22, 175-179, L-thyroxine180-182, and most recently

bisphosphonates39, 40, 134, 183.

NSAIDS inhibit cyclo-oxygenase and subsequent prostaglandin production, and are

commonly taken for treatment of pain and inflammation. The effect of NSAIDS on tooth

movement and root resorption has been controversial in the literature but recent research

has shown some NSAIDS produce a reduction in root resorption37, 38, 184 without affecting

tooth movement37.

Corticosteroids are commonly used to treat allergies and asthma as well as a variety

of other conditions. A recent study reported reduced root resorption in an experimental

group receiving long term corticosteroids which they suggested may be due to faster

remodelling of bone, reduced hyalinisation, and reduced remodelling of root tissue178.



However, the effect of corticosteroids on resorption is still unclear and appears to be

dependent upon the dose and the animal model175, 177.

Potent bone resorption inhibitors like bisphosphonates have become a popular

treatment option for patients suffering from osteoporosis. They inhibit resorption by

directly or indirectly inducing apoptosis in osteoclasts, and have been found to cause a

dose-dependent inhibition of root resorption in rats as well as decreased osteoclast

numbers and tooth movement39, 40, 185, 186. On the other hand, it has also been

demonstrated that these drugs can actually increase vulnerability to the resorptive

process134, 183 by producing alterations in the cemental surface of the root via inhibition of

acellular cementum formation.

Administration of L-thyroxine in rats has been demonstrated to increase the

resistance of cementum and dentine to osteoclastic activity181 and reduce the extent of root

resorption182.

5. Alcohol consumption

Chronic alcoholics are at increased risk of developing severe root resorption during

orthodontic treatment as a result of altered calcium homeostasis which stimulates PTH

production that in turn enhances resorption of mineralised tissues167, 187.

6. Habits

Habits such as nail biting15, 31, 188, finger sucking beyond the age of seven137, and

tongue thrust31, 162 have historically been associated with the development of resorption.

Conversely, more recent reviews have suggested habits do not play any significant role16, 161.



Orthodontic elastic wear during treatment for anterior open bite (AOB), resulting

from long term tongue thrust, may promote root resorption rather than the habit itself41.

2.2.6.2 Dental Risk Factors

A number of local dental risk factors have also been proposed as potential

aetiological agents in the pathogenesis of OIIRR.

2.2.6.2.1 Pre-existing resorption

Pre-existing root resorption has been shown to be an important risk factor for the

development of severe OIIRR with treatment26, 30, 31, 41. Studies such as Massler and

Malone15 have shown there is a high correlation between the amount and the severity of

root resorption present before treatment and the root resorption discovered after

orthodontic treatment.

2.2.6.2.2 History of trauma

Teeth which have been previously traumatized may experience external root

resorption even in the absence of orthodontic treatment, the extent of which is related to

the severity of the trauma42. For example, mild to moderate injuries such as subluxations

can cause resorption in less than 1% of injured teeth while more severe injuries such as

avulsion and re-implantation can cause resorption in 74% - 96% of affected teeth42.

OTM of traumatised teeth may increase the risk of OIIRR16, 137, 189, though once again

this may be dependent upon the severity. Malmgren et al26 found that traumatized teeth

with no sign of resorption are no more resorbed than non-traumatized teeth while Kjaer156

found teeth with minor to moderate injuries are at no greater risk of OIIRR than uninjured

teeth.



A recent study found no statistically significant difference in the incidence of OIIRR

between patients with traumatized and non-traumatized teeth140, yet if a previously

traumatized tooth exhibits resorption before treatment, then there is a greater chance that

OTM will enhance the resorptive process29, 150.

2.2.6.2.3 Dental morphology, anomalies, and agenesis

A number of mostly observational studies have reported abnormal root shape, such

as pipette shaped or narrow roots and dilacerations, as well as other dental anomalies

including taurodontia, agenesis, and ectopic or transplanted teeth, are risk factors for

OIIRR24, 27, 31, 60, 155, 156, 162, 190. Oyama and colleagues43 suggested abnormal root morphology

may increase the risk of root resorption due to the greater loading of the roots during


Conversely, other investigators have found no significant correlations between

dental anomalies140, 191, peg-shaped roots or microdontia of lateral incisors142, and OIIRR.

Short roots are also commonly believed to undergo more resorption31, 158, although a

more recent study supports the opposite view that the tendency for resorption increases with

increasing tooth length44. This is possibly because longer teeth need stronger forces to be

moved meaning the actual displacement of the root apex will be greater during torquing

movements24, 44, 143.

Agenesis of multiple teeth (4 or more missing teeth) is also associated with increased

risk of root resorption22. This is probably due to orthodontic forces being distributed over fewer

teeth as well as the requirement for more extensive and longer treatment in such cases60.



2.2.6.2.4 Endodontic treatment

The effect of previous endodontic treatment on the incidence of resorption during

OTM has always been of concern however the link between endodontic treatment and

OIIRR is still not clearly established.

A higher frequency and severity of resorption in endodontically treated teeth during

orthodontic treatment has been reported192. On the other hand, recent authors have found

teeth with previous root canal treatment exhibit a lesser propensity for apical root

resorption44, 157, 161 and have suggested these teeth are more resistant to resorption because

of increased dentine hardness and density10, 65. Recent work by Esteves and colleagues

demonstrated no significant difference between endodontically treated teeth compared to

vital teeth in terms of OIIRR, suggesting endodontically treated teeth can be moved

orthodontically as readily as vital teeth193.

OTM itself creates an inflammatory response which may exacerbate an existing

resorptive process but, if the tooth has been successfully treated endodontically with

healthy periodontium, it should be no more susceptible to resorption than a normal tooth.

2.2.6.2.5 Periodontal status

Owman-Moll and Kurol concluded from their study that periodontal disease, as well

as habits like nail-biting and lip/tongue dysfunction, increases the risk of external root

resorption during orthodontic treatment96.

Hypo-functional periodontium has also been documented as an aetiological factor.

Hypo-functional periodontium exhibits progressive atrophic changes in all functional



periodontal structures, and it may accelerate resorption as a result of decreased ability to

distribute the mechanical stress of orthodontic forces194, 195.

2.2.6.2.6 Specific tooth type vulnerability

According to the literature, maxillary teeth have the highest risk and incidence of

root resorption15, 92, 138, exhibiting more resorption than mandibular teeth10, 17, 31, 58, 149.

According to severity, the most frequently affected teeth have been listed (from highest to

lowest) as the maxillary laterals, maxillary centrals, mandibular incisors, distal root of

mandibular first molars, mandibular second molars and maxillary second premolars24, 29, 30,

140, 142, 149, 158, 196.

The maxillary incisors, especially the lateral incisors, are generally the most affected

since they tend to undergo the most movement during orthodontic treatment.

Furthermore, their root form, and relationship to the surrounding periodontium, means

most of the forces tend to be transferred to the apex24.

Beck and Harris160 have explained that the use of archwire anchorage bends, mesial

to the first molars, causes compression of the distal roots within the socket and subsequent

initiation of resorption.

2.2.6.2.7 Severity & type of malocclusion

A positive association between malocclusion and OIIRR has been made within the

literature41, 93, 137, 140, 149, 151, however the relationship seems to be more related to the

amount and type of tooth movement required, and the duration of treatment, rather than

the malocclusion itself151, 160. I.e. the extent of apical resorption is associated with the



amount of tooth movement33, 44, 47, 150, 197 which in turn is a function of the severity of the

malocclusion.

Kaley and Phillips found Class I patients with acceptable overjet were significantly

less likely to show OIIRR compared to Class II or III patients59. Similarly, Taner et al198 found

Class II division 1 patients experienced significantly more resorption than Class I patients

undergoing orthodontic treatment with first premolar extraction, although no significant

differences were found between the amount of OIIRR and tooth inclination or duration of

active treatment.

Significant associations between resorption and the magnitude of overbite139 or

overjet reduction during treatment have also been found by some24, 48, 140, 150, but not all,

investigators16. Patients undergoing extractions during treatment had greater root

resorption which may be related to longer treatment duration and an increased amount of

tooth movement149.

From the literature, it can be concluded that root resorption can be associated with

all types of malocclusion when combined with orthodontic treatment7, 161.

2.2.6.2.8 Alveolar bone density & turnover rate

The density of the alveolar bone may also affect the incidence of root resorption. It

has been postulated that OTM in dense bone requires greater or longer force application,

consequently resulting in increased OIIRR9, 62, 65. Goldie and King45 hypothesised there are

more marrow spaces in less dense alveolar bone which facilitate and improve the action of

active resorptive cells resulting in reduced OIIRR45. Conversely, when the rate of bone

turnover is decreased the risk of OIIRR increases39.



In a human study, Otis and co-workers199 measured the amount of alveolar bone around

the root including the thickness of cortical bone and density of the trabecular network, and

found no significant correlation with the extent of the OIIRR.

2.2.6.2.9 Dental age & stage of root development

Several studies have suggested that teeth with open apices may be more resistant to

OIIRR than teeth with closed apices (i.e. completed root development)19, 137, 200, although

others have disagreed, suggesting instead that these teeth do not achieve normal root

length164.

Dilaceration and root stunting may be the final result of deflection of Hertwig’s

epithelial root sheath caused by orthodontic tooth movement. The incidence of

dilaceration has been shown to increase with treatment from 25% - 33%200.

2.2.6.3 Mechanical Risk Factors

Finally, there are also a number of mechanical factors which have been linked to root

resorption. These mechanical factors are directly related to the mechanics or orthodontic

therapy itself and are of particular interest to the clinician as they may be controlled or

modified in an attempt to reduce their influence upon root resorption.

2.2.6.3.1 Treatment duration

The majority of studies in the literature agree that the severity of root resorption is

directly related to treatment duration7, 9, 16, 27-30, 46, 65, 101, 137, 140, 149, 155, 158, 160, 196, 198, 201.

Considering that orthodontic force induces an inflammatory reaction that is fundamental to

both tooth movement and root resorption7, it makes sense that the longer a tooth is

exposed to the inflammatory process the more likely and more severe the resorption may

be. Sameshima and Sinclair149 described a significant correlation between duration of



treatment and root resorption on maxillary central incisors, and in their study evaluating the

extent of OIIRR following 4, 8, and 12 weeks of light (25g) and heavy (225g) buccally

directed forces on maxillary and mandibular premolars Paetyangkul et al concluded that the

extent of resorption increased significantly with treatment duration106.

Artun and co-workers concluded that the risk of one or more teeth with more than

1mm of resorption from T2 to T3 (6months to 12 months after bracket placement

respectively) was 3.8 times higher than from T1 to T246. Similarly, Levander and Malmgren

reported 34% of the teeth examined in their study showed root resorption after 6-9 months

of treatment and this number increased to 56% at the end of treatment (19 months)27.

The duration of treatment is often related to factors such as the severity of the case

and also patient co-operation. As the difficulty of the case increases often larger

movements are required resulting in increased treatment time. Similarly, poor patient

attendance will also result in prolonged treatment. Levander and colleagues investigated

the effect of a pause in active treatment, on teeth that had experienced root resorption

during the initial 6-months of treatment, and showed that the amount of resorption was

significantly more in those patients treated with continuous forces without a pause61.

2.2.6.3.2 Type & extent of tooth movement

The type, direction, and extent of tooth movement have a considerable role in OIIRR.

The greatest damage is observed with intrusion and torque as these movements produce a

higher force per unit area and thus cause more tissue necrosis and root resorption33, 52, 54, 59,

67, 102, 160, 202. Han et al, found intrusion of teeth causes 4 times more root resorption than

extrusion mainly because the root shape concentrates the pressure at the conical apex54.

Another study reported maxillary incisors are 4.5 times more likely to have severe root



resorption if they undergo root torque59. It has been proposed that a combination of

intrusion and root torque has the highest risk for OIIRR33, 63.

In contrast, bodily tooth movement has been associated with decreased risk of root

resorption compared to tipping due to the differences in stress distribution along the root

surface33, 53, 65. In their finite element model (FEM) study, Rudolph and colleagues203 found

tipping movements resulted in stress concentration at the alveolar crest and root apex,

while bodily movement resulted in a more even distribution across the root surface. Purely

intrusive, extrusive, and rotation movements resulted in stress concentration at the apex.

Extrusive tooth movement is considered to induce the least root resorption when compared

to other types of tooth movement54.

As mentioned previously, teeth that are moved further have extended exposure to

the resorptive process47, 197 and not surprisingly, the extent of tooth movement has been

linked to the degree of root resorption89, 141, 149, 196. The maxillary incisors are at the highest

risk of OIIRR since they are commonly moved the greatest distance especially in extraction

cases141, 149, 196, 204-207.

2.2.6.3.3 Force magnitude & duration

Many animal208-210 and human studies12, 50, 102, 211, 212 have demonstrated that the

severity of OIIRR is directly proportional to the magnitude of the applied orthodontic force.

As discussed previously, heavy forces exceeding the PDL capillary blood pressure9, 213

induces excessive hyalinisation161 and interferes with the repair process of resorption

craters12, 13, 62, 209. This has been confirmed by recent SEM, TEM, and Micro-CT studies on

human premolars which have found an increased amount of root resorption associated with

increased force levels12, 52, 102, 107, 214. It has been suggested that the distribution of



resorption lacunae is related to the amount of stress on the root surface, and that the rate

of lacunae development is more rapid with increasingly larger applied forces12, 50, 51, 56, 102.

In contrast, several studies have suggested there is weak9 or no correlation between

the amount of root resorption and force magnitude49, 98. From their histological studies,

Owman-Moll and co-workers found that root resorption was not particularly force-sensitive

but there was a large individual variation49, 98.

In terms of duration of applied force, the results within the literature are conflicting.

It has been proposed that a potential difference may exist between the tissue responses to

continuous or discontinuous forces32. I.e. an intermittent force prevents formation of

hyalinised zones and when inactive, allows reorganization of tissues and restoration of

blood flow in the compressed areas53, 65, while a continuous force on the other hand does

not allow adequate restoration or repair of the damaged cells and tissues. Several studies

have supported this demonstrating that a pause in force application or intermittent force

application results in lesser root resorption compared to continuous force application32, 61,

102, 215-217. Conversely, others have found no difference between teeth that were moved

with either a continuous or an interrupted force89, 97. It must be noted that intermittent

forces produce less tooth movement than continuous forces over the same period97, 216, 218

and may be a confounding factor when comparing continuous versus intermittent forces.

There is weak evidence suggesting jiggling forces have a role in increasing root

resorption and as a result removable appliances and inter-maxillary elastics should be used

sparingly16, 161.



2.2.6.3.4 Appliances & treatment techniques

A number of studies within the literature have compared the extent of resorption

following treatment with different types of orthodontic appliances in an attempt to identify

an appliance or technique that causes less OIIRR. Some authors have found one or another

technique to be more advantageous over another33, 138, 139, 204, 206, 219-221, for example McNab

et al found more external root resorption in patients treated with Begg appliances

compared to those treated with Edgewise appliances220. Conversely, others have found no

significant difference when comparing appliance or technique26, 33, 58, 160, 222, for example

Blake and co-workers58 found no statistically significant difference in resorption between

Speed appliances & Edgewise appliances. The clear advantage of one system over the

others has yet to be demonstrated within the literature and it may also be argued that the

differences between techniques is due more to their respective differences in treatment

time and mechanics employed rather than the appliances themselves.

In terms of conventional edgewise systems compared to various active and passive

self-ligating appliances no statistically significant differences in resorption has been found58,

223, 224. Similarly, Alexander225 reported the same amount of root resorption associated with

both continuous arch and sectional arch mechanics, and concluded that individual variability

has greater influence than so called “round tripping” of teeth.

With regard to fixed versus removable appliances, one group has found significantly

greater resorption associated with fixed appliances16, 137. Along the same lines, Barbagallo

and colleagues214 compared fixed appliances and removable sequential thermoplastic

appliances but found light forces produced by fixed appliances and thermoplastic aligners

affect root resorption in a similar way.



Magnets have been suggested by some to produce a more favourable physiological

tissues response thus decreasing the risk of OIIRR226, 227, although further research in this

area is required.

2.2.6.3.5 Extraction versus non-extraction

This topic is controversial in the literature and both techniques have the potential to

induce soft and hard tissue damage. McNab and co-workers stated the incidence of root

resorption after extraction treatment was 3.72 times higher than non-extraction

treatment35. Similarly, Sameshima and Sinclair also reported extractions to be a significant

factor in root resorption149. In contrast, McFadden et al158 reported no difference in the

extent of root resorption in patients treated with or without extractions.

2.2.6.3.6 Transplanted teeth

Transplantation of teeth is particularly technique sensitive and success is

predominantly determined by the care taken to avoid injury to the PDL and cemental

surfaces during the procedure. Successfully transplanted and fully assimilated teeth will

react to orthodontic force in a similar way to normal teeth228 and will be subject to the same

influencing factors.

2.2.7 Diagnosis of Root Resorption

Clinically, radiographs are the only method for diagnosing OIIRR and the most

commonly used are periapical radiographs and panoramic radiographs such as the

orthopantomogram, and to a lesser extent lateral cephalograms.

The orthopantomogram is often indicated during orthodontic treatment for a

number of reasons and has a number of advantages including providing an overall view of



the dentition, lower radiation dose for the patient than a full mouth series91, and are fairly

simple and fast to obtain. However, the quality of the image is dependent on correct

patient positioning, the closeness of the desired anatomical structures to the focal trough as

objects outside the trough will be out of focus, and the amount of magnification108 which is

relatively constant in the vertical dimension but horizontal measurements are less

reliable229. According to Sameshima and Asgarifar93, if initial and final orthopantomograms

are used for root resorption assessment, the results may be exaggerated by 20% due to

magnification. The lower incisor area is the most likely to be distorted.

In comparison, periapical radiographs are often considered superior to

orthopantomograms and are recommended instead60 as they result in less radiation

exposure, and are subject to less distortion and fewer superimposition errors93, 230.

Paralleling techniques can also be used which allow for geometrically accurate images which

can then be standardised at different time points. The lateral cephalogram has been shown

to provide an accurate and reproducible view of the length of the upper incisor, but

overlapping results in an obscured image making diagnosis difficult91.

When comparing digital and conventional radiographs, there appears to be little

difference in terms of diagnostic sensitivity231. The only advantages of a digital system are

that it can allow earlier quantification of small changes in root length60, 222, and provides

similar diagnostic sensitivity with lower radiation doses. On the other hand, computed

tomographic scanning offers a significant advantage in terms of detection and

quantification232-234, but is also more costly and associated with higher levels of radiation

which limits its clinical application93.



2.2.7.1 Location of OIIRR

The distribution of resorptive areas on the root surface varies in association with the

pressure zones generated by different types of tooth movement. Non-orthodontically

induced root resorption appears to distribute equally over the marginal and apical regions

of the root13 unlike OIIRR, which tends to occur preferentially in the apical region because

the fulcrum of most tooth movement usually lies occlusal to the apical half of the root159.

The apical region is also more susceptible to OIIRR as a result of the different orientation of

the apical PDL fibres, which increase the stresses in this region11, as well as the presence of

the more friable acellular cementum48, 159.

2.2.8 Pathogenesis & Mechanisms of Root Resorption

The development and pathogenesis of OIIRR can be summarised simply into the

following 7 steps:

As mentioned, OIIRR is associated with local compression of the periodontal

membrane during orthodontic tooth movement. Historically, Schwartz213 hypothesised

forces exceeding the capillary blood pressure would lead to over-compression of the PDL,

cutting of the blood supply, and resulting in an aseptic coagulation necrosis process, i.e.

hyalinisation. These hyalinised areas must then be removed to facilitate tooth

Development and Pathogenesis of OIIRR

1. Application of orthodontic force 2. Over compression of PDL

3. Initiation of local inflammatory reaction

4. Resorption of hyalinised tissue begins

5. Formation of resorption lacunae 6. Resorption continues until hyalinised

zone is removed, or force level decreases

7. Repair begins when PDL is de-compressed



movement235, 236. A series of studies by Brudvik and Rygh in rats and mice have confirmed

root resorption is part of the cellular activity involved in eliminating these hyalinised zones4,

100, 136, 237-239.

The pathogenesis of OIIRR occurs in two phases146:

1. Injury to the external root surface, yielding denuded mineralized tissue.

2. Extended stimulation of multinucleated cells.

Multinucleated cells colonise the denuded mineralized tissue, initiating the

resorption process. Without continued stimulation by those cells involved in the resorption

process, spontaneous repair will occur with cementum-like material within 2-3 weeks

(surface resorption). With continued stimulation, the inflammatory process in the presence

of the denuded root will persist, and may involve the underlying dentine which is usually

non-reversible and detected radiographically7, 29, 136, 240.

In orthodontic-induced resorption, the initial injury results from the pressure applied

to the root during tooth movement. The pressure subsequently produces the areas of

ischemic necrosis and hyalinisation in the PDL7, 146, which then initiate the inflammatory

response.

The initial elimination process takes place at the periphery of the hyaline zone,

where blood supply to the periodontal ligament exists or is even increased116. During

removal of the hyaline zone, the nearby root surface consisting of the cementoblast layer

covering the cementoid can be damaged241, exposing the underlying mineralized cementum

to the resorptive process136, 237. In severe cases the orthodontic pressure itself may directly

damage the outer root surface7.



The first cells to be involved in the resorption process are macrophage-like cells,

scavenger cells from the hematopoietic lineage, most probably activated by the signals

coming from the sterile necrotic tissue7.

The root surface under the main hyaline zone is resorbed several days later when

the repair process in the periphery is already taking place49, 66, 90, 94-98. The resorption

process continues until no hyaline tissue is present and/or the force level decreases7.

Resorption lacunae expand the root surfaces and indirectly decrease the pressure exerted

through force application. This decompression of the PDL allows the resorption process to

reverse and the cementum to be repaired, and as a result these resorbing areas may show

signs of concurrent active resorption and repair13, 67.

2.2.8.1 Histopathology

Brudvik and Rygh’s extensive rodent research has provided illumination of the

histological sequence of the resorption and repair process. They found that periodontal

cellular activity varies with time and location4, 100, 136; describing three sequences of events

occurring in two locations, the peripheral and main hyalinised zones.

1. Tartrate resistance acid phosphotase (TRAP)-negative macrophage-like cells from the

PDL, with no ruffled borders, initiate resorption in the peripheral zone. These cells

remove necrotic tissue as well as the surface layers of un-mineralised and

mineralised cementum.

2. TRAP-positive multinucleated or mononucleated cells initiate resorption of the main

hyalinised zone and continue resorbing the damaged and un-damaged mineralised

cementum. These cells are derived from the adjacent marrow spaces and PDL, and



have similar origins, cytological characteristics, and functional characteristics, to

osteoclasts136, 237, 242.

3. The reparative process occurs while active resorption is still taking place in the

central zone. It begins in the periphery and extends to the central zone.

2.2.8.2 Biochemistry

As mentioned, the mechanical stimulation of the PDL cells results in initiation of a

local inflammatory reaction which is characterized by synthesis of Prostaglandin E2 and

increased Cyclic adenosine monophosphate (cAMP)243. The process is regulated by hormones,

neurotransmitters, and cytokines including IL-1a, IL-1b, and TNF243-247.

Recent research has investigated the role of osteoprotegrin (OPG) and RANKL in

osteoclastogenesis248, and hence it’s possible role in resorption249. RANKL is a TNF related

ligand expressed by osteoblasts, and acts by binding to the RANK receptor on the osteoclast

lineage cells, which then stimulates rapid differentiation of osteoclast pre-cursors into

mature osteoclasts250. OPG is a decoy receptor produced by osteoblastic cells which

competes for RANKL binding. Wise and colleagues251 in rats, as well as Yasuda et al252, 253

have identified this role of cytokines as well as RANKL & OPG, demonstrating increased

RANKL and decreased OPG expression in physiological root resorption associated with tooth

eruption. Low et al induced root resorption in rats and found increased levels of RANKL in

sites adjacent to resorption zones242. Compressive forces have also been found to be

associated with increased production of RANKL & decreased production of OPG254 . More

recently, Nishimura et al investigated vibration in rats and noted enhanced RANKL

expression in PDL fibroblasts and osteoclasts on the compression side after 3 days, and

increased numbers of PDL osteoclasts after 8 days85.



2.2.8.3 Resorptive Resistance

Cementum appears to be more resistant to resorption than alveolar bone109,

however the precise mechanism of this resistance is still poorly understood. When this

resistance is compromised7, severe OIIRR although rare, can occur. A number of

explanations exist within the literature attempting to explain this resorptive resistance, and

most agree that the root’s outer layers including the cementoblasts, and pre-cementum and

cementoid layers, provide an overall protective function7, 238.

It has been hypothesised that odontoclasts are unable to resorb the mature collagen

of the un-mineralised pre-cementum and cementoid layers9, and that these layers may also

inherently synthesise potent anti-collagenases which are no longer produced when the root

surface is damaged or the PDL is compressed7, 62, 255. It has also been suggested that a

physical breach in these layers will allow mineralised tissue to come into contact with the

PDL matrix providing a chemotactic stimulus for resorbing cells145, 255.

Andreasen postulated cemental resistance was mainly due to the cells within the

PDL such as cementoblasts, fibroblasts, osteoblasts, endothelial, and peri-vascular cells,

which repair areas of resorption by generating new cementum and PDL fibre

attachments144.

A recent clinical study revealed that exposure of roots to two sequential periods of

orthodontic treatment actually decreased the extent of OIIRR22, suggesting remodelled

cementum may contribute some additional protective effect.



2.2.8.4 Repair

The process of repair of resorption craters begins when the orthodontic force is

removed or reduced below a certain level62, 65. Schwarz213 suggested this level is equivalent

to the capillary blood pressure of 20-26g/cm2, however this is still uncertain. Regardless,

the result is repair via deposition of cementum and establishment of new PDL9, 67, 68, 256, 257.

The repair process has been described as a migration of cementoblasts over the

resorbed surface, which then compete for available surface space and progressively exclude

the osteoclasts and cementoclasts258. The initial repair material is acellular cementum

which is laid down and then gradually replaced by cellular cementum as repair continues66,

95, 188, 259-261. The location and direction of the initial repair is controversial, and has been

described as beginning from the periphery, the bottom, or from all directions67, 102, 238, 239.

A number of studies have discussed the timing of onset of repair, with considerable

variation, and have found that the reparative process may occur even in the presence of

active resorption12, 67. Repair has been reported to occur as little as one week into

retention66, while other studies have found repair between 2 and 3 weeks260, and even up

to 35 to 70 days after force removal9, 12, 13.

The amount of repair is not constant and appears to increase with time66-68

especially during the first 4 weeks. By the 5th to 6th week the process slows down and

reaches a steady state98.

Vardimon and colleagues described the repair process as occurring in 4 phases261:



1. The Lag phase - which occurs between the end of resorption and the beginning of

repair. This phase is largely explained by the dissipation of residual forces, and the

differentiation of cementoblasts9, 13.

2. The Incipient phase – which occurs 14 days later, and is a transitional phase between

no apposition and active deposition.

3. The Peak phase – follows between 14 to 28 days later, and involves a spurt in matrix

formation and incorporation of extrinsic fibres into the intrinsic cementum matrix.

4. The Steady deposit phase – which occurs between 42 to 56 days, and involves a

steady deposition of mixed fibrillar cementum.

2.2.9 Prognosis, Prevention, & Management of OIIRR

As mentioned previously, the extent of root resorption in most cases is minor and is

inconsequential to the long term survival or functionality of the afflicted teeth or

dentition10, 48. However, in some cases the decreased crown to root ratio resulting from

severe resorption can significantly affect the prognosis, especially in the presence of

periodontal disease or trauma58.

Loss of apical root length due to resorption appears to be less detrimental than an

equivalent loss of periodontal attachment at the alveolar crest, especially in cases with less

than 3mm of external root resorption23. Apical root length loss of up to 3mm is equivalent

to only 1mm of crestal bone loss and clinically has a similar effect262. In an average sized

normally shaped maxillary central incisor, with no alveolar bone loss during orthodontic

treatment, a root shortened by 5mm will still have 75% of its periodontal attachment

remaining (95% of patients). No adverse physiological or pathological effects have been

reported with loss of root length of up to 20%48.



However, increased mobility has been reported when 9mm or more of the root

length has been lost to resorption263, 264, and the reduction in root length can result in an

unfavourable crown to root ratio of the affected teeth affecting their suitability for

prosthetic anchorage and abutments58.

2.2.9.1 Prevention

Fortunately the risk of severe root resorption is rare, occurring in less than 5% of

treated patients21, 23, 59. A number of prevention strategies have been proposed in the

literature28 to help minimise the risk and extent of OIIRR and many are targeted at factors

implicated as aetiological risk agents. These strategies include:

I. A thorough assessment of the patients medical and family history prior to treatment

to identify potential risk factors24, 28, 31, 34,

II. Resolution of habits such as nail biting and tongue thrusting162, 188,

III. Treatment at an earlier age as younger patients and developing teeth have been

found to have a reduced incidence of root resorption9.

IV. Reduction of treatment duration13, 27, 46, 61,

V. Reduction of force magnitude9, 12, 13, 62 and use of intermittent forces28, 32, 216,

VI. Increasing the interval between appointments to reduce the frequency of force

activation.

VII. Radiographic assessment at 6 months into treatment (or at 3 months in high risk

individuals)46, 60, and

VIII. Halting treatment for periods of up to 3 months if resorption is detected33, 61, 63.

Once the orthodontic force has been removed research has shown the resorption

process usually ceases10, 64, and repair begins. The repair process has been found to begin



once the orthodontic force has decreased below a certain level62, 65 and tends to increase

with time66-68. When post treatment root resorption does occur, it is usually associated with

factors such as traumatic occlusion and active force-delivering retainers265.

2.2.9.2 Management

The potential risk of OIIRR as a consequence of orthodontic treatment must be

discussed with the patient and parents during the initial consultation266. If root resorption is

detected during active treatment, the decision to continue, modify, or discontinue

treatment must be made. A number of management techniques or procedures have been

outlined within the literature including:

I. Halting treatment and placing passive arch wires for 2-3 months61.

II. Cease force application for 4-6 months or in extreme cases terminate treatment149.

III. Reassess treatment goals to reduce further damage. Either terminate treatment or

consider a compromise. For example, compromise options may include

prosthodontic restoration instead of closing spaces, surgery to minimise further

tooth movement, and inter-proximal reduction rather than extractions161.

IV. Continued radiographic examination until resorption has ceased161.

V. Appropriate counselling and regular review149.

As mentioned previously, active resorption usually ceases after appliance removal

but if this does not occur, subsequent root canal therapy with calcium hydroxide may be

required267. Fixed retaining appliances should be placed with caution as occlusal trauma to

the fixed teeth or segments may lead to further extreme resorption161.



2.3 Research Methodologies for Evaluation of OIIRR

Historically, OIIRR has been studied utilising histological or radiographic

methodologies however these are not always the most accurate means of assessment or

measurement, hence the variability in root resorption incidence in the existing data.

Radiographs provide only a 2D representation of a 3D process, meaning resorption in

certain areas such as the buccal and lingual root surfaces may not be detected268.

Histological examination is more accurate than radiographic assessment however this can

only be performed on extracted teeth.

More recently, 3D volumetric quantitative evaluation of resorption craters using

SEM or XMT technology has been shown to be a feasible alternative with a high level of

accuracy and repeatability107, 108, 211. A mathematical computer based reconstruction of pre-

and post treatment dental images has also been shown to be a reliable technique for

measuring root resorption222.

2.3.1 Radiography

Radiographic detection is an important tool in identifying root resorption and has

been used in a number of studies17, 31, 35, 60, 89-93; however it is less useful in quantifying the

extent of the resorption present. Due to their 2D nature, radiographs can help detect root

shortening before, during, or after treatment, but surface resorption can only be detected if

it occurs mesio-distally at direct right angles to the focal beam of the X-rays or if resorption

has progressed to an advanced stage108. Varying degrees of magnification also affect the

quantitative value of radiographs.



Panoramic radiographs are widely considered to be a valuable tool for identifying

resorption as they provide a low radiation overall view of the entire dentition269, however

they have been found to overestimate the amount of root loss by 20% or more when

compared with periapical radiographs (PA‘s)24. Furthermore, superimposition of other

anatomical structures over the teeth may show up as real or actual shadows, or the roots of

proclined teeth may appear shortened or even lie outside the focal trough, thus reducing

the quality of the final image91, 219, 270.

Periapical radiographs have been used as an alternative, and have been found to

provide less distortion and finer detail in comparison to panoramic radiographs60, 61, 93. The

quality and accuracy of PA’s may be affected by a number of factors including film

orientation and x-ray tube position91, and they also have an inherent magnification factor

however this is usually less than 5%271. The paralleling technique with PA‘s has been

described as the technique of choice for detecting root shortening although it has also been

shown to be geometrically inaccurate272.

The lateral cephalogram has been shown to yield an accurate and reproducible view,

however its use is limited to the upper incisors, and it is also affected by a magnification

factor of 5-12% as a result of the radiographic set up91. Furthermore, overlapping of the

right and left side make the individual images unclear108 and difficult to assess.

While radiography is a valuable diagnostic tool in detecting OIIRR, quantitative

measurements are relatively poor and it is limited to the clinical situation108. It may also be

argued that routine use of radiographs during orthodontic treatment may introduce a

source of bias into the assessment of incidence by facilitating detection28.



2.3.2 Serial Sectioning & Light Microscopy

Serial sectioning and light microscopy has also been used in a number of publications

investigating the extent and repair of OIIRR in various clinical scenarios9, 49, 66, 90, 94-100. This

method involves progressive sectioning of the tooth, with the resulting slices stained and

examined under light microscope. Using this technique, less detail is missed and the

measurements are more accurate than light microscopy alone.

The limitations of this method relate to the fact that craters may be missed or

overlooked, and the difficulty of the technique may introduce some bias. Root resorption

craters vary in size and shape and thus irregularly shaped or small craters could be partially

or totally overlooked as a result of the 2D nature of the sections. Additionally, tooth shape

is hardly uniform making it difficult to accurately section a tooth along its long axis,

potentially resulting in apical or some mid-root craters being missed107, 108.

2.3.3 Scanning Electron Microscopy

As mentioned, a number of studies have also utilised SEM in order to investigate

OIIRR12, 32, 67, 101, 212. The SEM technique allows enhanced visual and perspective assessment

of the root surface and resorption craters, with minimal specimen and tissue preparation.

Despite providing detailed information regarding the resorption lacunae as well as the

mineralised structure of cementum, this method is very time consuming and difficult to

perform on larger samples as the specimen must be prepared and the desired image view

chosen before an image is created273. Another limitation relates to parallax errors resulting

from the difficulty in obtaining an absolute straight on view of the curved resorption

lacunae108, which can subsequently lead to significant measurement errors.



Stereo SEM imaging was subsequently devised to overcome the inherent difficulty in

obtaining an accurate 3D quantitative measurement of irregularly shaped craters on a

curved root surface107. This method involves taking 2 images, offset by 6°, of each crater

producing a stereo pair of each crater. These stereo images are then converted into an 8-bit

greyscale depth map allowing 3D mapping and volumetric analysis of each crater. This

method has been shown to be highly accurate and reproducible107, 108, although relatively

time consuming and technique sensitive.

2.3.4 X-ray Micro-Tomography

Micro-computed tomography (Micro-CT) is a variant of a medical computed

tomography scan system that allows non-destructive high spatial-resolution imaging of the

interior micro-structure of a material274, 275. With this technique, a series of x-ray

projections are made and recorded through each 2D slice of the object at various angles

around an axis which is perpendicular to the slice plane. Each 2D x-ray ‘absorption’ map is

then combined to produce a 3D map using digital computing276. The slices can be recreated

in any plane, and the data is reproducible in all 3 dimensions. The 3D dataset makes

identification of the resorption lacunae easier273 and can be used to qualify and quantify the

resorption craters on the root surface52, 104.

In 2-dimensional digital images the unit of measurement is a pixel, which is a 2D

representation of the smallest unit of colour value or shade of grey within the image. In

computed tomography, the pixel is assigned an x and y-axis value. The number of pixels per

unit surface area is related to the resolution of the image in that increasing the number of

pixels per unit area increases the resolution of the image275. In 3-dimensional imaging, the



basic unit of measurement is a voxel. The voxel is has an added z-axis value which indicates

depth, and thus allows the voxel to be used to measure volume275.

The use of this technology for patient applications is limited by radiation dose and

duration of exposure. The radiation dosage must be kept to a minimum ‘safe’ level, and the

duration reduced to avoid unwanted distortion as a result of involuntary patient movement.

These limitations are not applicable to inanimate objects, where higher radiation dosage

and longer scan times can be used to improve image quality275.

Micro-CT relies on a density difference between the structure of interest and the

surrounding material. Porous materials such as minerals, ceramics, or polymers, are

particularly suited to this method. Other suitable materials include bone, teeth, lung tissue,

archaeological and paleontological specimens, coral and wood.

2.3.4.1 SkyScan 1172 Desktop X-ray Micro-Tomograph

The SkyScan 1172 Desktop X-ray Micro-tomograph (SkyScan, Aartselaar, Belgium,

Appendix 6.4), is a fourth generation computed tomography scanner which, as the name

suggests, is a compact desktop system utilised for microscopy and micro-tomography. Its

components include an X-ray shadow microscopic system combined with a computer with

tomographic reconstruction software.

The SkyScan 1172 unit utilises a cone beam X-ray source and is able to achieve a

maximum spatial resolution of 2 - 5 µm. The system obtains multiple x-ray shadow

transmission images of the object from different angular views, as the object rotates on a

high-precision stage. The X-ray detector consists of a high-resolution charged coupled

device, and the images received from these detectors are stored as 16 bit Tagged Image File



Format (TIFF) picture files with a resolution of 1024x1024 pixels. Once image acquisition is

complete, software utilising a modified Feldkamp cone-beam algorithm277 (NRecon, Version

1.4.2; Skyscan, Aartselaar, Belgium) produces slice-by-slice axial reconstruction. The

resultant axial 2D images are generated as 1024x1024 pixel bitmap (BMP) image stacks with

an 8-bit greyscale dynamic range.

The cross-sectional datasets can be used with a variety of image analysis and 3D

volume rendering software packages such as VG StudioMax (Version 1.2, Volume Graphics,

GmbH, Heidelberg, Germany), for 2D or 3D morphometrical analysis or to produce 3D

images and animations.

2.3.4.2 Previous Dental Research Using Micro-CT Technology

Micro-CT technology has been utilised in a number of studies investigating a variety

of subjects ranging from material science and mineral analysis, to the study of calcified

tissues including teeth and bone278. While some have attempted in-vivo studies, this

technology has been mostly limited to in-vitro or inanimate specimens279, 280.

In terms of dental research, Micro-CT has been used to investigate the mineral

content of human enamel, dentine281-283 and carious dentine284; study the internal anatomy

of teeth and root canals285-288; analyse oral implants and their stability in bone289-291; and

examine the effects of lasers and phosphoric acid etching on enamel278, 292.

Only recently has Micro CT technology been utilised to investigate and examine OIIR.

Harris and co-workers52 investigated the volume of root resorption associated with no force

versus light force (25g) and heavy force (225g), finding a significant 2-fold and 4-fold

increase in the light- and heavy-force groups respectively51, 106. In their study comparing the



effect of continuous and intermittent forces on OIIRR, Ballard et al217 found intermittent

forces induce significantly less resorption. When looking at the repair of resorption craters

after continuous light and heavy forces, Cheng and co-workers64 found no significant

difference in the amounts of repair at 4 or 8 weeks after 4 weeks of continuous force,

although the resorptive activity was more pronounced with heavy forces; furthermore

crater volume was positively correlated with tooth movement and negatively correlated

with chronologic age. In other studies, the maxillary first premolars were shown to be more

likely to suffer from OIIR than mandibular first premolars106, and certain types of tooth

movement (torque and rotation etc) were shown to induce more resorption than other

types202, 293.

Clear sequential thermoplastic appliances are a popular alternative to traditional

orthodontic appliances in some cases. Barbagallo and co-workers214 used Micro CT to

quantify the effect of these thermoplastic appliances on OIIRR craters, concluding that

sequential thermoplastic appliances produced similar effects to light orthodontic forces with

traditional fixed appliances on root cementum.

Fluoride has been reported to be beneficial in preventing root resorption in cases of

dental trauma, however Foo et al104 found that while systemic fluoride reduced the size of

resorption craters it was variable and statistically insignificant.

Finally, Deane and co-workers utilised XMT technology to investigate the incidence

of physiological root resorption associated with unerupted third molars105. They compared

physiological root resorption found in unerupted non-impacted maxillary third molars with

premolar teeth from previous studies which had undergone light and heavy orthodontic



forces. From their study, they found unerupted third molars had similar cube-root

resorption volumes to first premolars subjected to light buccal and intrusive forces, and

concluded that resorption might occur as part of hard tissue remodelling and turnover.

2.4 Vibration

Mechanical vibration can be described as a mechanical stimulus characterised by an

oscillatory motion294 and its intensity is determined by certain variables which include295:

I. Frequency: The frequency of vibration is determined by the number of cycles in 1

second and is measured in Hertz (Hz).

II. Amplitude: The amplitude is determined by the extent of the oscillatory motion and

is measured in millimeters (mm).

III. Magnitude: Vibration can also be described as having a magnitude which is

expressed as a function of Earth’s gravitational field (9.8ms2 = 1g) and is measured in

grams (g)

In the biological setting, it is undisputed that external mechanical signals or stimuli

are in general vital in maintaining the skeletal structure and integrity296, with bone

remodelling continually being influenced by the magnitude and distribution of the

functional strains within the bone296. I.e. decreases in functional loading induce elevation of

osteoclastic activity1 resulting in a net loss of bone297, whereas increases in loading (such as

exercise) stimulate osteoblastic activity298 resulting in net improvements in both bone

quantity and quality299, 300.

Associations between bone morphology and mechanical load stimuli were made as

early as Galileo301, 302 who supported the theory that bony trabeculae are arranged in



particular morphological patterns induced by function in order to optimise resistance to

loading. Wolff303 in 1892 attempted to explain this relationship between bone morphology

and function, and was the first to publish the concept of “form follows function” more

commonly known as “Wolff’s Law”, however Wolff’s law is unable to fully explain functional

bone adaptation as it fails to identify the specific parameters of the osteogenic mechanical

stimulus296.

Early human observational studies have also made the link between weight

bearing/mechanical loading activity304 and bone mineral density305, 306. Human exercise

studies show that high impact activity such as gymnastics have a higher osteogenic potential

than low impact activity such as swimming or rowing298, 307, 308. Similarly, exercises involving

unilateral activity such as tennis show greater bone mass in the loads bearing limb309, 310. In

contrast, disuse from immobilisation311 or space travel induces catabolic effects in the

bone312-315.

Following on from these initial observations, it was the investigation into possible

treatment modalities for osteoporosis that formed the impetus for further research into

dynamic mechanical stimuli in the biological and medical setting. In recent years, a number

of therapeutic uses for mechanical modulation of bone structure and density have been

identified including:

I. Improving the rate of fracture healing69, 70,

II. Reversing the decrease in bone mass and density associated with disuse atrophy71-73,

III. Enhancing muscle and bone mass in cases of musculoskeletal degeneration74, 75, and

osteoporosis76-78, and



IV. Enhancing mechanical signalling within bone79-81.

2.4.1 Whole Body Vibration

Whole body vibration (WBV) as apparent from its name, involves exposure of the

entire body to vibration, as opposed to local vibration where stimulation is applied to an

isolated region. WBV is produced with the use of a vibrating platform through which

vibrations generated by motors underneath the platform are transmitted to the person295.

WBV has been examined for its potential as a means of reducing the loss of bone

density associated with extended periods in space314, 316, or patients with disabling

conditions71, 72, 74. The fitness industry has also introduced and used WBV294, 317, while more

recently it has found applications in the areas of physical therapy and rehabilitation318, and

professional sports294. There are currently many whole body vibration devices available

commercially for use in both the fitness and health care areas294, 295, 319. These devices all

vary in terms of the frequency of vibration, which can range from a few Hz up to 50 Hz, and

the amplitude which can range from a few micrometres to several millimetres295. The

attractive advantages of vibration therapy are that it is non invasive, and can be applied in a

low impact manner which is critical in elderly or diseased individuals319.

In their review, Prisby and co workers319 noted that although the scientific

knowledge base behind the use of vibration devices is increasing steadily, an optimal

operating threshold is as yet undetermined and it is unknown whether such a threshold

would be applicable to all tissues of the body. The vibratory protocols (i.e. frequency,

duration, and amplitude) utilised in the literature to date lack standardisation and vary

considerably, making it difficult to formulate appropriate conclusions regarding the most



effective protocol(s)319, 320. They suggest that future research is required to determine and

develop an optimal vibration protocol which will most likely vary depending on the

population using the vibration (e.g. young vs. elderly) as a result of differences in bone

quality, remodelling patterns, and responsiveness319.

2.4.2 Vibration & Dentistry

In more recent times, the use of mechanical vibration concurrently with orthodontic

treatment has been suggested as a possible means of not only reducing treatment duration

but also root resorption and pain perception. To date however there is limited research in

this area.

2.4.2.1 Rate of Tooth Movement

As has been discussed previously, duration of treatment is one of the more

important mechanical risk factors involved in the aetiology of OIIRR16, 27, 28, 149, 161, 167 and has

also been associated with an increased risk of caries321 and periodontal sequelae322.

Treatment duration is directly influenced by the rate of tooth movement which is

limited by the physiological processes involved in remodelling the paradental tissues i.e.

bone and PDL remodelling1, 243, 323-326. In their study, Roberts et al described the maximum

rate of molar translation in the maxilla as approximately 2mm/month in a rapidly growing

child or 1mm/month in a non growing adult327. Numerous attempts have been made to

increase this rate of movement ranging from reducing appliance friction328 and using

adjunctive pharmacological or hormonal therapies329-331, to the more recent introduction of

surgical corticotomy and distraction techniques332-337, however these techniques are often



invasive or further complicate treatment. Several studies more recently, have investigated

the efficacy of mechanical vibration in relation to increasing the rate of OTM85, 86.

In their rat study, Darendeliler and co-workers86 explored the effect of high

frequency low magnitude vibration induced by pulsed electromagnetic fields (PEMF) on the

rate of tooth movement. They compared the effect of vibration alone; vibration versus

vibration and coil spring; PEMF alone versus PEMF and coil spring; and finally vibration and

coil spring versus PEMF and coil spring. Their results showed:

i. The coil spring with sham or active magnets moved the teeth more than the magnets

with or without vibration,

ii. The coil spring moved the teeth more than coil-magnet combination under the

PEMF,

iii. The magnets moved the teeth more than the sham magnets under the PEMF,

iv. There was no significant difference in tooth movement between the coil spring and

magnet combinations without the PEMF, and

v. There was no difference between magnets and sham magnets without the PEMF.

From these results, the authors concluded that OTM with coil and magnets may be

enhanced by vibration induced by PEMFs.

Nishimura et al85 also conducted an animal study investigating the effects of

vibratory stimulation on rate of tooth movement and root resorption in rats. As part of the

study, they also examined the cellular and molecular mechanisms underlying the

acceleration of tooth movement. A buccal force was applied to the rat molar and in the

experimental group a vibratory protocol of 60Hz, 1g was also applied for a period of 8



minutes on days 0, 7 and 14. The results obtained demonstrated tooth movement in the

experimental group was significantly greater than the control group, as seen by enhanced

RANKL expression of fibroblasts and osteoclasts in the PDL of the vibration group. No

significant difference in root resorption between the two groups was found, although a

trend towards reduced resorption was noted in the vibration group. From these results, the

authors concluded that adjunctive mechanical vibration might increase the rate of

orthodontic tooth movement via enhanced expression of RANKL in the PDL without

additional damage to the tissues, such as root resorption.

2.4.2.1.1 Acceledent Device

A new oral vibrating device, the Acceledent device (OrthoAccel technologies Inc,

USA), has recently become commercially available and is intended for adjunctive use during

orthodontic treatment. OrthoAccel technologies Inc, claims the Acceledent device enhances

conventional fixed appliances or aligners and moves teeth faster via accelerated bone

remodelling achieved using pulsing forces.

The device concept was developed by Dr Jeremy Mao, who investigated the effects

of cyclical forces on sutural growth82-84, 338. Mao and colleagues based this research upon

the experimental suture model designed by Meikle and co-workers which mimics the forces

that the PDL and other sutures of the cranium are exposed to during OTM339. From this

research, Mao and co-workers found cyclical forces between 1 Hz and 8 Hz, with forces

ranging from 0.3N to 5N, increased bone remodelling82-84, 338 commonly by an order of up to

2.5 times the non-vibration rate.

According to OrthoAccel technologies Inc, the vibratory protocol of the Acceledent

device is based upon on the whole body vibration studies conducted by Rubin and



colleagues304, 340. The device produces an operating frequency of 30Hz with amplitude of

20g, and patients are instructed to utilise the device for 20 mins per day during the course

of their orthodontic treatment. OrthoAccel technologies Inc, claims the results of a

prospective randomised control trial conducted on 45 patients at the University of Texas

Health Science Centre, San Antonio, confirms an accelerated tooth movement both during

initial alignment (2.06 times or 106% faster) and space closure (1.38 times or 38% faster)

phases of orthodontic treatment.

2.4.2.2 Pain Control

Pain is a complex experience which often accompanies orthodontic appointments88

and is one of the most cited negative effects of orthodontic treatment341. It is of concern to

patients as it is listed as one of the key reasons for avoiding orthodontic therapy342, 343, and

to clinicians as it is one of the main reasons for poor compliance344 and oral hygiene345.

The perception of orthodontic pain is part of the inflammatory reaction generated by

the application of orthodontic forces243 and is evoked by the release of pro-inflammatory

mediators such as substance P, histamine, and prostaglandins induced by the changes in

PDL blood flow243, 341. Traditionally, analgesics and NSAIDs have been used for control of

pain during orthodontic treatment88, 341 however the major concern with NSAIDs is their

anti-inflammatory action which may interfere with the process of tooth movement37, 38, 184,

341. Several other methods of pain control have been proposed ranging from anaesthetic

gels and bite wafers or chewing gum346, to using lower force levels although pain is still

experienced by most patients347. More recently, low level laser therapy347, transcutaneous

electrical nerve stimulation348, 349 have been shown to be effective in dental and orthodontic

pain control341.



Vibratory stimulation also appears to be a potential method of pain control88, 341. It

is thought that vibratory stimulation may interfere with the pain pathways350 and also act to

intercept the ischemic response by re-establishing the blood supply88. Nanitsos et al87

found local anaesthetic injections given with concurrent vibration elicited a lower pain

rating and less pain descriptors on a visual analogue scale than. They concluded that

vibration can be used to decrease the pain associated with dental local anaesthesia. In the

orthodontic setting, Marie and colleagues88 investigated the effect of a small battery

operated vibrating motor with a soft detachable mouthpiece on post orthodontic

adjustment pain. They found the appliance was effective at reducing pain but only if used

prior to the onset of pain. If applied after the onset of pain, most patients were unable to

tolerate the vibration.



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4 Manuscript

The Effect Of Mechanical Vibration (113 Hz Applied to Maxillary First

Premolars) On Root Resorption Associated With Orthodontic Force: A

Micro-CT Study.

A condensed version of this manuscript is to be submitted for publication to the American Journal of Orthodontics & Dentofacial Orthopedics



Johnathan L.E. Grove, BDSc

Post-graduate student

Discipline of Orthodontics

Faculty of Dentistry

University of Sydney

Tamer Türk, DDS, PhD

Professor

Department of Orthodontics


University of Ondokuz Mayis

Selma Elekdag-Türk

Associate Professor



University of Ondokuz Mayis

Peter Petocz, PhD

Associate Professor, Statistician

Department of Statistics

Macquarie University, Sydney

Oyku Dalci, DDS, PhD

Lecturer




Carmen Gonzales, DDS, PhD

Senior Lecturer




M. Ali Darendeliler, BDS, PhD, Dip Ortho, Certif.

Orth, Priv. Doc

Professor and Chair




Address for Correspondence:

M. Ali Darendeliler

Department of Orthodontics

Sydney Dental Hospital

Lvl 2, 2 Chalmers Street

Surry Hills, NSW 2010

Australia

Phone +61 2 93518314

Fax +61 2 9351 8336

Email: [email protected]

mailto:[email protected]



4.1 Abstract

Introduction: Recent research has suggested vibratory stimulation may enhance

bone turnover, increase rate of tooth movement, and reduce root resorption. However to

date there is little research investigating the influence of vibration on orthodontically

induced inflammatory root resorption. This study was undertaken to examine the effect of

mechanical vibration on the extent of root resorption craters associated with the application

of a controlled orthodontic force.

Method: 14 patients (11 females and 3 males) aged 12.1 to 15.5 years, requiring

premolar extraction as part of their orthodontic treatment, were used for this study. A

controlled buccal tipping force of 150 grams was applied bilaterally to the maxillary first

premolars of each patient for an experimental period of 4 weeks (28 days). Using a split-

mouth procedure, each patient was randomly assigned a “vibration” and “non-vibration”

side. Buccally directed vibration of 113Hz, using an Oral B HummingBird unit with a

modified tip, was applied to the maxillary first premolar on the “vibration” side for

10mins/day for the experimental period. At the end of the experimental period, the

maxillary first premolar teeth were extracted according to a strict protocol to avoid damage

to the cementum and root surface. Each sample was imaged using a Micro-CT scan x-ray

system (SkyScan 1172, SkyScan, Aartselaar, Belgium), and then analysed with specially

designed software to determine the volumetric measurements of the resorption craters.

Results: Overall, there was a significant difference in the total root resorption

volume between the vibration and non-vibration sides (p=0.003), with vibration reducing

the amount of resorption by 33% on average. Except for the buccal surface, all other tooth



surfaces and vertical thirds studied exhibited a reduction in root resorption volume with

vibration, however only the palatal surface was significant (p=0.006) while the mesial

surface and apical third were marginally significant (p=0.018, & p=0.019 respectively).

Regression analyses of all regions studied showed the amount of reduction in resorption

volume associated with vibration was correlated with the amount of resorption experienced

by the control teeth. This was evident especially on the mesial and palatal surfaces

(p<0.001 & p=0.006 respectively).

Conclusions: Mechanical vibration as applied in this study shows the potential of its

use in preventing or reducing orthodontic root resorption. However the clinical significance

of such application should be evaluated on a sample undergoing a complete course of


Key words: Root resorption, vibration, orthodontic force, micro-computed

tomography, 3D analysis, volumetric measurements.

4.2 Introduction & Literature Review

Root resorption is an undesirable and unavoidable consequence of orthodontic

treatment1-4. Brezniak and Wasserstein4 suggested the application of an orthodontic force

induces an inflammatory reaction within the PDL which is essential to tooth movement and

is also fundamental to root resorption. They described this orthodontic force induced root

resorption as Orthodontic Induced Inflammatory Root Resorption (OIIRR).

The aetiology of root resorption appears to be remarkably multifactorial and remains

largely unknown. Many studies have investigated and attempted to isolate causative

factors related to OIIRR, and have identified numerous risk factors5, 6. These can be broadly



grouped into biological, dental, and mechanical factors. Examples of biological factors

include genetic factors such as individual susceptibility7-10 and ethnicity11, as well as

environmental factors such as allergies12, 13 and medications14-17. Previous history of

resorption and trauma18-21, tooth morphology11, 22, 23, and bone density16, 24, are examples of

dental factors. Lastly, treatment duration25-28, force magnitude29-33, and type of tooth

movement34-38 are examples of mechanical factors implicated in OIIRR. These mechanical

factors are of particular interest to the clinician as they may be controlled and modified in

an attempt to reduce their influence upon root resorption.

In terms of clinical and practical significance, the degree of root resorption in most

cases will be inconsequential and will not affect the long term survival or functionality of the

afflicted teeth or dentition3, 28. However, in some cases the decreased crown to root ratio

resulting from severe resorption can significantly affect the prognosis, especially in the

presence of periodontal disease or trauma39. Fortunately the risk of severe root resorption

is rare, occurring in less than 5% of treated patients40-42, and a number of strategies have

been suggested to help minimise the process including 1) pre-treatment assessment of

medical and family history7, 10, 11, 43, 2) radiographic assessment at 6 months into treatment

(or at 3 months in high risk individuals)26, 44, 3) reducing treatment duration25, 26, 45, 46, 4)

reducing force magnitude2, 29, 46, 47, and 5) halting treatment for periods of up to 3 months if

resorption is detected9, 45, 48. The resorption process usually ceases once the orthodontic

force is removed3, 49, with repair beginning once the force has decreased below a certain

level47, 50 and tending to increase with time51-53.

Recently, the use of mechanical vibration concurrently with orthodontic treatment

has been suggested as a possible means of reducing treatment duration as well as root



resorption; however there is limited research in this area. Mechanical modulation of bone

architecture has been found to have beneficial effects on fracture healing54, 55, disuse

atrophy56-58, and musculoskeletal degeneration59, 60 including osteoporosis61-63; as well as

enhancing mechanical signalling within bone64-66. Cyclical mechanical loading in animal

models has also been shown to increase bone remodelling67-69, and vibration of rat molars

at 60 Hz has demonstrated significantly increased tooth movement and a suggested trend

towards decreased root resorption70. Vibration produced as a result of a pulsed electro-

magnetic field has also demonstrated evidence for faster tooth movement71. Furthermore,

vibratory stimulation has been reported as a method to significantly reduce pain after

orthodontic appliance adjustment72, 73.

The aim of this study was to investigate the effect of mechanical vibration applied

over 4 weeks to maxillary first premolars, on the volume of root resorption craters

associated with application of a buccally directed controlled orthodontic force (150g) using

Micro-computed tomography for qualitative and quantitative volumetric analysis.

4.3 Material and Methods

4.3.1 Sample

The sample consisted of 28 maxillary first premolar teeth obtained from 14 patients

(11 females and 3 males) who required extraction of these teeth as part of their orthodontic

treatment at Ondokuz Mayis University, Turkey. Written informed consent was obtained

from all subjects and parents or guardians, and ethics approval was obtained from the

University of Ondokuz Mayis Medical Research Ethics Committee (Decree No: OMU-TAEK



2010/135) and the South Western Sydney Local Health Network Ethics Review Committee

(Protocol No x11-0016 & HREC/11/RPAH/19).

All subjects were aged between 12.1 to 15.5 years, with a mean age of 13.6 years,

and were recruited according to strict selection criteria:

1. Need bilateral maxillary first premolar extractions and fixed appliance orthodontic

treatment.

2. Permanent Dentition.

3. Similar degree of minimal crowding on each side of the maxillary arch.

4. No previous orthodontic or orthopaedic treatment.

5. No previous dental treatment of the maxillary canines (reported or observed).

6. No history of trauma, bruxism or parafunction.

7. No past or present signs or symptoms of periodontal disease.

8. No craniofacial anomalies.

9. No significant medical history or medication that would adversely affect the

development or structure of the teeth and jaws and any subsequent tooth

movement.

150 grams of controlled buccally directed force was applied to the left and right first

maxillary premolar of each subject. Using a split-mouth design, each subject was randomly

assigned a “Vibration” and “Non-vibration” side. The maxillary first premolars were then

extracted after the experimental period of 4 weeks (28 days).



The experimental period, appliance design, and force level used in this study were

chosen to comply with the resorption protocols previously carried out in the Department of

Orthodontics at the University of Sydney32, 33, 37, 49, 74-78.

4.3.2 Appliance design

0.022” x 0.028” slot SPEED Orthodontic brackets (Strite Industries Cambridge,

Ontario, Canada) were bonded to the maxillary first permanent molar and first premolar

teeth. Bilateral 0.017” x 0.025” Beta-titanium molybdenum alloy (TMA) springs were used

to apply 150 grams of buccally directed force to the first premolars for the experimental 28

days. The force magnitude of the spring was measured using a strain gauge (Dentaurum,

Germany). A layer of multi-cure Glass ionomer cement (GIC) (3M Unitek, USA) was bonded

onto the occlusal surfaces of the lower first molar teeth to minimise occlusal trauma &

interferences during the experimental period.

Using a split-mouth study design, each subject was randomly assigned a “Vibration”

and “Non-vibration” side. Buccally directed vibration using a Hummingbird (Oral B, USA)

with a modified tip was applied to the maxillary first premolar on the “Vibration” side for 10

mins per day for 28 days. According to the operating specifications the HummingBird

operates at approximately 8000 RPM, which corresponds to 133 Hz. Pre-study testing using

an optical tacheometer, found the average frequency was 6800 RPM or 113Hz. The

batteries in the device were changed every 2 weeks to ensure maximal consistent output.

Each subject was monitored on a daily basis by one of the authors (SE) to ensure

compliance with the vibration protocol.



4.3.3 Specimen collection

At the end of the 4 week experimental period, the maxillary first premolars were

extracted with necessary care taken to avoid surgical trauma to the root cementum during

the extraction procedure. Upon removal, each tooth was separately stored in a container of

sterilized de-ionized water (Milli-Q®, Millipor, Bedford, Mass) which has been tested

previously as an appropriate storage media79. The teeth were then sent to the Orthodontic

Department at the University of Sydney for analysis.

Each tooth was placed in an ultrasonic bath for a period of ten minutes and then

cleaned with a damp gauze swab in a rubbing motion to remove all traces of residual PDL

and soft tissue fragments. Care was taken to avoid damage to the cementum. Each tooth

was then disinfected in 70% alcohol for 30 minutes and left to bench dry.

4.3.4 Sample Analysis

Each sample was scanned using the SkyScan 1172 desktop x-ray micro-tomograph

system (SkyScan, Aartselaar, Belgium), which allows non-destructive three-dimensional

reconstruction of an object’s inner structure from two-dimensional x-ray shadow

projections. The system obtains multiple x-ray shadow transmission images of the object

from different angular views as it rotates on a high-precision stage. From these shadow

images, cross-sectional images of the object are reconstructed by a modified Feldkamp

cone-beam algorithm creating a complete 3D representation of internal microstructure and

density over a selected range of heights in the transmission image.

Each tooth was scanned individually from just below the cemento-enamel junction

(CEJ) to just above the apex, rotating 360 degrees around the vertical axis with a rotation



step of 0.23 degrees. The x-ray tube was set at a voltage of 60kV and current of 167µA, and

each sample was scanned without filters at a resolution of 17.2µm.

Three dimensional (3D) data sets were obtained for each sample from Skyscan’s

volumetric reconstruction software NRecon (Version 1.4.2; Skyscan, Aartselaar, Belgium),

which uses a modified Feldkamp algorithm to reconstruct the acquired angular two

dimensional (2D) projections. The three dimensional data sets were then rendered as 3D

visualisations using VG StudioMax software (Version 1.2; Volume Graphics GmbH,

Heidelberg, Germany). From these 3D visualisations, the resorption craters were located,

recorded with reproducible X, Y, and Z coordinates, and then exported for volumetric

analysis. The craters were grouped 1) according to their location on the root surface e.g.

buccal, palatal, mesial or distal; and 2) according to their location in the vertical plane e.g.

apical, middle or cervical. The vertical location was determined by measuring the total

length of the root from the CEJ to the apex and dividing it into equal thirds.

Quantitative volumetric analysis was achieved using Convex Hull Software (CHull2D)

developed by the Australian Centre for Microscopy and Microanalysis at the University of

Sydney. This program applies 2D convex hull algorithms to each 2D slice of the 3D data set,

allowing the volume to be measured in each slice and then compiled to give an overall

volume per crater in Voxels.

All measurements were carried out by one operator (JG) to eliminate inter-operator

variability.



4.3.5 Statistical Analysis

Statistical analysis was performed using IBM SPSS Statistics, Version 19 (IBM

Corporation, USA). Paired t-tests were performed to determine the significance of vibration

versus non-vibration in relation to the total resorption volume per tooth, per root surface

(buccal, palatal, mesial, and distal), and per vertical third (cervical, middle, and apical).

Regression analyses were also performed to determine the relationship between the

amount of root resorption and the improvement due to vibration, in the various regions

studied. Repeat measurements were carried out to determine the error of measurement.

To allow for multiple comparisons, a “P” value of ≤ 0.01 (rather than P ≤ 0.05) was

considered significant.

4.4 Results

The compliance rate during the experimental period was 100%, with all subjects

monitored each day by one of the authors (SE) for the duration of the vibration application.

The sum of the volume of resorption craters for each tooth was calculated (Table I),

as well as the overall total volume, mean, and standard deviation, in the vibration and non-

vibration groups. The mean total volume in the vibration group was 0.261mm3 whereas the

mean total volume in the non-vibration group was 0.389mm3 (Table II). All but 2 of the

subjects experienced a decrease in the volume of root resorption in the vibrated teeth

(Figure 3), and a paired t-Test showed a statistically significant difference in the total root

resorption volume per tooth on the vibration side when compared to the non-vibration side

(p=0.003) (Table V). On average, vibration reduced the amount of resorption by 0.128mm3

(or 33%).



When the sample was analysed in terms of the different tooth surfaces, the distal,

palatal, and mesial surfaces experienced a decrease in total root resorption volume in the

vibration sample (Figure 4), however only the palatal surface showed a statistically

significant difference (p=0.006) while the mesial surface showed marginal significance

(p=0.018) (Table V). Interestingly, the buccal surface showed more resorption in the

vibration sample compared to the non-vibration sample, however this was not statistically

significant (p=0.311) (Table V). The mean volume and standard deviation for each surface is

shown in Table III.

When the sample was evaluated by vertical thirds, all three regions exhibited a

decrease in total resorption volume with vibration (Figure 5), however only the apical third

showed marginal significance (p=0.019) (Table V). The mean volume and standard deviation

for each third is shown in Table IV.

A regression analysis (Table VI) was performed comparing the amount of root

resorption experienced by the non vibration teeth and the reduction/improvement (non-

vibration volume – vibration volume) in root resorption as a result of vibration. This analysis

revealed a marginally significant relationship (p=0.082) between the amount of reduction in

resorption volume, and the amount of resorption experienced by the associated non-

vibration side. Similar regression analyses (Tables VII & VIII) performed on the various tooth

surfaces and vertical thirds found similar significant relationships associated with the mesial

and palatal surfaces (p=0.000, and p=0.006, respectively), and marginal significance

associated with the cervical and apical thirds (p=0.019 respectively). The remaining regions

did not show a significant relationship.



When analysed graphically (Figures 6b, 7, & 8), these regression analyses revealed a

consistent positive trend between the improvement (reduction in resorption volume)

associated with vibration, and the amount of resorption associated with non-vibration, in all

the aspects studied.

Repeat measurements were carried out to determine the overall standard error of

measurement (SEMeas=0.012mm3) and the coefficient of variance (CV=6.8%).

4.5 Discussion

This prospective clinical trial examined the effect of mechanical vibration on the

volume of root resorption craters to determine if the application of vibration would reduce

or exacerbate the resorption resulting from a controlled orthodontic force of 150grams.

Despite its multi-factorial nature, root resorption severity has been closely linked to a

number of mechanical factors including force magnitude and duration. These factors are

fundamentally associated with stress distribution and concentration within the PDL and

alveolar bone, development of areas of hyalinisation, and subsequent bony remodelling and

root resorption12, 13, 21, 80, 81. Recent research has shown that mechanical vibration can

enhance bone remodelling and turnover54, 57, 62, 67, 68, 82-84, and thus could potentially reduce

root resorption by reducing the stress concentration and duration within the PDL.

In this investigation a force of 150grams was chosen to represent a more clinically

relevant force, intermediate between the relatively light and heavy forces used in previous

root resorption studies32, 33, 37, 75, 76, 85-88. The study duration of 4 weeks (28 days) is

consistent with previous studies, conducted at the orthodontics department at the



University of Sydney32, 37, 49, 76, 85, 86, 88-91, and while others have employed longer

experimental duration22, 23 resorption craters were still evident.

The vibration protocol utilised in this study was 113Hz applied for only 10 minutes a

day. This protocol would have produced a force characteristic closest to intermittent forces

which have been shown to allow cementum to heal and prevent further resorption8, 92, 93, as

well as increasing RANKL expression in PDL cells with less cell damage94. This protocol is in

contrast to the Acceledent device, which is able to produce vibration of 30Hz with a force of

20 grams and is meant to be applied for 20mins per day. The Acceledent protocol is similar

to that used by the Juvent 1000 vibration plate which produces 0.2 - 0.3G (force of gravity)

at 30-45 Hz and is designed for use in strengthening the musculoskeletal system.

The frequency of 113Hz was chosen as there is little agreement in the literature

regarding an optimal vibration protocol, and it was also practical to modify a device

(Humming Bird Dental Floss Device) which is approved for intra-oral use. The majority of

studies investigating vibration to date have utilised a large range of frequencies, durations,

and applied force. Prisby and co-workers have summarised most of this data in their review

of the effect of whole body vibration in humans and animals95. They conclude that the

vibratory protocols (i.e., waveform, frequency, duration, and amplitude) reported in the

literature vary considerably, making definitive conclusions regarding the most effective

protocol extremely difficult, and in addition they suggest the most appropriate protocols

will most likely depend upon the subject population as protocols developed for young

individuals may be inappropriate for the elderly.



This study found a significant difference in resorption volume between vibration and

non-vibration, showing a decrease in resorption in all but 2 of the subjects. In their study,

Nishimura and co-workers70, applied 60 Hz, 1.0 m/s2 to the first molars of rats by using a

loading vibration system for 8 minutes on days 0, 7, and 14 during orthodontic tooth

movement. They reported no significant difference between vibration and non-vibration in

terms of root resorption after 21 days; however they did note a trend towards decreased

resorption in the vibration group. They suggested this trend may have been the result of

vibration preventing blood flow obstruction and the development of areas of hyalinization.

In their review, Prisby et al proposed that vibration has the potential to alter tissue

perfusion, however the magnitude of this effect is tissue specific and depends on the

vibration regimen95.

In our study, the resorption in the buccal-cervical & palatal-apical regions

corresponded with the areas of expected pressure within the PDL, and was consistent with

the resorption associated with a buccal tipping movement as shown in previous studies49, 75,

77, 96, 97. The presence of resorption on the mesial and distal surfaces is not consistent with a

buccal tipping movement suggesting a rotational or torquing component to the tooth

movement96, which is highly probable considering the simple design of the force delivery

appliance that was a compromise between simulating the real clinical scenario and reducing

complexity and patient discomfort. This may have affected the locations and amounts of

the resorption craters measured. Future studies ideally should attempt to completely

isolate individual tooth movements.

Interestingly, the buccal surface showed more resorption in the vibration group

compared to the non-vibration group although this was not statistically significant. This



finding could potentially indicate a concentration of vibration in this region which may be

detrimental by interfering with the vascularity or bone turnover. Studies looking into the

effect of vibration on tissue perfusion have found differing results, with one study finding

reduced tissue perfusion with 5mins vibration at 31.5Hz and 125Hz98, while another found

increased perfusion with 3 bouts of 60s vibration at 30Hz99. However, the ability of

vibration to alter tissue perfusion and modify the vascular network appears to be tissue

specific and dependent upon the vibration regimen95.

In terms of vertical thirds, the pattern of resorption in the non-vibration group was

consistent once again with the expected areas of stress concentration within the PDL. All 3

regions experienced a decrease in resorption in the vibration group however the apical

region experienced a much greater decrease compared to the cervical region. This may be

due to a greater susceptibility to resorption in the apical region100, and differing cementum

composition with apical cementum being softer with less Sharpey’s fibres49, 101.

The results of the regression analyses comparing the volume of resorption on the

non-vibration teeth with the resorption difference showed a consistent trend of increasing

resorption reduction with vibration that was associated with increasing resorption volume

with non-vibration. Individual susceptibility is considered to be one of the major factors in

determining root resorption potential with or without treatment, highlighted by the fact

that resorption can occur in both cases27, 100, 102, as well as varying between individuals and

within the same individual at different times5, 47. This trend suggests that the beneficial

effect of vibration is dependent upon the individual susceptibility of the patient to root

resorption, i.e. the more susceptible the patient, the greater the potential benefit of

vibration.



The results of this study are promising, suggesting a potentially distinct benefit from

the use of vibration in conjunction with orthodontic treatment, although the sample size of

this study is small and limits the extent and strength of the data obtained. The results

suggest vibration frequencies higher than 30Hz may very well be applicable to the dental

environment; however the most appropriate frequencies, durations, and amplitudes of

vibration necessary for a beneficial response are still unknown95. Subsequent research is

required to further elucidate the potential benefits and effects of vibration in the dental

arena.

4.6 Conclusions

Based on the results obtained in this study regarding the effect of 113Hz mechanical

vibration applied for 10mins per day for 4 weeks in conjunction with 150g buccal tipping

forces, the following conclusions can be drawn:

1. Mechanical vibration seems promising in preventing or reducing orthodontic root

resorption.

2. There is a consistent trend toward increased benefit from vibration in those patients

who experience higher amounts of root resorption.

3. Vibration in orthodontics is a new field and shows potential based on this study.

However the clinical significance of such application and potential optimal

protocol(s) should be evaluated on a sample undergoing a complete course of

orthodontic treatment to ensure efficacy and safety.



4.7 Acknowledgement

This study was supported by the Australian Society of Orthodontics Foundation for

Research and Education Inc., and the Australian Dental Research Foundation.

We wish to thank Leanne Batley, NSW Oral B representative, and Oral B for providing

the HummingBird units for use in this study.



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4.9 List of Figures

Figure 1: Intra-oral views, and schematic design, of the 0.017” x 0.025” TMA spring.

Figure 2: Oral B HummingBird unit with modified tip



Figure 3: Total resorption volume per tooth

Figure 4: Overall resorption volume per surface

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Tota

l res

orp

tio

n v

olu

me

(m

m3

)

Subject

Total resorption volume per tooth

Non-vibration

Vibration

0.000 0.500 1.000 1.500 2.000

Buccal

Mesial

Palatal

Distal

Total resorption volume (mm3)

Too

th S

urf

ace

Overall resorption volume per surface

Non-vibration

Vibration



Figure 5: Overall resorption volume per vertical thirds

Figure 6: a) Graph of resorption volume per subject (vibration versus non-

vibration), with line of best fit (dotted line = equal amounts of resorption, vib &

non-vib). b) Regression graph with line of best fit showing the relationship between

the effect of vibration and the amount of resorption experienced on the non-

vibration side per subject.

0.000 0.500 1.000 1.500 2.000 2.500

Cervical

Middle

Apical

Total resorption volume (mm3)

Ve

rtic

al T

hir

d

Overall resorption per vertical thirds

Non-vibration

Vibration



Figure 7: Regression graphs, with lines of best fit, showing the relationship per

subject between the effect of vibration (Improvement) and the amount of

resorption experienced on the a) Buccal, b) Mesial, c) Palatal, and d) Distal, aspects.



Figure 8: Regression graphs, with lines of best fit, showing the relationship per

subject between the effect of vibration (Improvement) and the amount of

resorption experienced on the a) Cervical, b) Middle, and c) Apical, aspects.



4.10 List of Tables

Table I: Total volume of root resorption per tooth

Total resorption per tooth (mm³)

Subject Vibration Non-vibration

1 0.078 0.084 2 0.569 0.674

3 0.238 0.263

4 0.271 0.555

5 0.372 0.576

6 0.678 0.622

7 0.145 0.299

8 0.121 0.219 9 0.206 0.170

10 0.280 0.453 11 0.232 0.293 12 0.121 0.196 13 0.157 0.524

14 0.186 0.521

Table II: Total volume of root resorption per experimental group

Resorption volume per group (mm³)

Group Total Mean SD

Vibration 3.654 0.261 0.173

Non-vibration 5.450 0.389 0.192

Table III: Total volume of root resorption per tooth surface

Total root resorption per tooth surface (mm³)

Tooth surface

Vibration Mean SD Non-

vibration Mean SD

Buccal 1.382 0.099 0.077 1.115 0.080 0.057 Mesial 0.593 0.042 0.054 1.547 0.110 0.103 Palatal 1.008 0.072 0.073 1.662 0.119 0.098

Distal 0.672 0.048 0.083 1.127 0.081 0.065

Total 3.654 5.450



Table IV: Total volume of root resorption per vertical third

Total root resorption per vertical thirds (mm³)

Tooth thirds Vibration Mean SD Non-

vibration Mean SD

Cervical 1.880 0.134 0.069 2.324 0.166 0.080

Middle 0.438 0.031 0.076 0.896 0.064 0.068

Apical 1.336 0.095 0.088 2.230 0.159 0.108

Total 3.654 5.450

Table V: Paired Differences

Paired Differences

t df Sig. (2-tailed) Mean

Std. Deviation

Std. Error Mean

95% Confidence Interval of the

Difference

Lower Upper

Vibration - Non-

vibration -0.128 0.132 0.035 -0.205 -0.052 -3.624 13 .003

Buccal(V) - Buccal(NV)

0.019 0.067 0.018 -0.020 0.058 1.053 13 .311

Mesial(V) - Mesial(NV)

-0.068 0.094 0.025 -0.122 -0.014 -2.705 13 .018

Palatal(V) - Palatal(NV)

-0.047 0.053 0.014 -0.077 -0.016 -3.309 13 .006

Distal(V) - Distal(NV)

-0.033 0.078 0.021 -0.077 0.012 -1.576 13 .139

Cervical(V) - Cervical(NV)

-0.032 0.075 0.020 -0.075 0.012 -1.573 13 .140

Middle(V) - Middle(NV)

-0.033 0.070 0.019 -0.073 0.008 -1.747 13 .104

Apical(V) - Apical(NV)

-0.064 0.089 0.024 -0.115 -0.013 -2.689 13 .019



Table VI: Regression analysis – Comparing overall non-vibration & overall

improvement with vibration

Coefficients

Model

Un-standardised Coefficients

Standardised Coefficients t Sig.

B Std. Error Beta

(Constant) Nonvibration

-.001 .075

-.013 .990

.332 .175 .481 1.900 .082

a. Dependent Variable: Impr

Table VII: Regression analyses per tooth surface – Comparing non-vibration & the

improvement with vibration.

Coefficients

Model


Standardized Coefficients t Sig.

B Std. Error Beta

(Constant) BuccalNV

-.042 .032

-1.316 .213

.286 .327 .245 .877 .398

a. Dependent Variable: BucImp

Model



B Std. Error Beta

(Constant) MesialNV

-.018 .020

-.902 .385

.783 .138 .854 5.692 .000

a. Dependent Variable: MesImp

Model



B Std. Error Beta

(Constant) PalatalNV

.003 .017

.154 .880

.371 .112 .692 3.323 .006

a. Dependent Variable: PalImp

Model



B Std. Error Beta

(Constant) DistalNV

.001 .033

.018 .986

.398 .327 .332 1.217 .247

a. Dependent Variable: DisImp



Table VIII: Regression analyses per vertical third – Comparing non-vibration & the

improvement with vibration

Coefficients

Model



B Std. Error Beta

(Constant) CervicalNV

-.064 .039

-1.639 .127

.579 .215 .614 2.698 .019

a. Dependent Variable: CerImp

Model



B Std. Error Beta

(Constant) MiddleNV

.006 .025

.255 .803

.413 .277 .395 1.491 .162

a. Dependent Variable: MidImp

Model



B Std. Error Beta

(Constant) ApicalNV

-.017 .036

-.468 .648

.505 .186 .616 2.710 .019

a. Dependent Variable: ApiImp



5 Future Directions

The benefits of mechanical vibration therapy have been studied increasingly in the

medical field for a wide range of uses including improving bone mass and density, improving

balance and mobility, and preventing or improving muscle strength and performance etc. In

contrast, the utilisation of vibration protocols is relatively new in the realms of dentistry,

and very little is known about the potential benefits for the orthodontist. What little

research exists, investigating the effect of vibration on orthodontic tooth movement, pain

sensation, and craniofacial structures, is mainly limited to animal studies.

This study was based upon the methodology of previous root resorption studies

conducted at the Department of Orthodontics, Faculty of Dentistry University of Sydney.

Certain limitations of this methodology include short duration and small sample size. A

number of the results obtained in this study showed a distinct trend however were not

statistically significant, which could be the result of the short duration or small sample size.

Further research should utilise longer study durations and larger sample sizes to circumvent

these limitations.

As previously discussed, little consensus exists in the literature regarding optimal

vibration protocols to enhance benefit and ensure minimal detriment. This study

demonstrated positive results utilising a frequency of 113Hz. Future studies should

investigate the effect of different vibration protocols (comparing different frequencies,

magnitudes, and durations) and different vibration devices or methods of application.

These future investigations should attempt to determine the optimal vibration protocol(s)

for the oral environment. Furthermore, the influence of age and sex need to be assessed, as



different protocols may be required depending upon age and sex to achieve maximum

beneficial results.

The Acceledent device has been advertised to work with all orthodontic appliances

including lingual fixed appliances, labial fixed appliances and removable thermoplastic

appliances. The efficacy of mechanical vibration protocols in conjunction with different

orthodontic appliances needs further investigation.

In accordance with the methodology of previous studies, the maxillary first

premolars were used in this study as these teeth were to be extracted as part of the

orthodontic treatment plan. As discussed previously however, the maxillary incisor teeth

are the most effected by root resorption and as such further investigations need to assess

the effect of vibration protocols on different teeth.

This study focused solely upon the effect of mechanical vibration on the incidence

and amount of root resorption. For mechanical vibration to become a true adjunctive

treatment in the orthodontic field, future research should examine the effect of vibration

protocols on the rate of orthodontic tooth movement, orthodontic pain perception, and

rate of repair of resorption. Furthermore, Nishimura and co-workers suggested the

application of mechanical vibration may induce alterations in blood flow in the adjacent

periodontal ligament. To examine this possibility, further biomolecular and biochemical

research is required.

Further research is required to investigate the potential correlation bwn individual

susceptibility and the benefit of vibration. Analysis of the results of this study suggested a



distinct correlation between increased benefit of vibration and those patients who

experienced more root resorption. This research may possibly involve genetic testing.

FEM analysis offers a unique opportunity to model and observe the distribution and

propagation of vibration through the dental, paradental, and craniofacial structures; as well

as the effect of vibration on areas of compression & tension within the PDL after application

of various types and magnitudes of orthodontic force. In future studies, different vibration

protocols should be modelled, as well as the effect of vibration in conjunction with different

types of orthodontic appliances including sequential thermoplastic aligners.

Adjunctive vibration protocols in orthodontics are new and their effects and benefits

are still relatively unknown. The results of initial investigations have been positive, and the

introduction of the Acceledent device has opened the door for potentially widespread

mainstream use of vibration in the orthodontic arena. Further studies both clinical and

laboratory will be needed to expand our knowledge in this burgeoning field.



6 Appendices

6.1 Appendix: Index for Qualitative Assessment of Root

Resorption

(Malmgren O, Goldson L, Hill C, Orwin A, Petrini L, Lundberg M. Root resorption after

orthodontic treatment of traumatized teeth. American Journal of Orthodontics 1982;

82(6):487-91).



6.2 Appendix: Sample distribution and split-mouth study design

6.3 Appendix: Specimen collection procedure

Extraction of 1st

PM

Stored in de-ionized water

(Milli Q)

Ultrasonic bath for 10 min.

Mechanical cleaning with a rubbing motion

Disinfection with 70% alcohol for

30 min.

Bench dry at ambient

temperature

14 Subjects

Randomly assigned “Side A”

(No-Vibration).

Application of 150g orthodontic

force.

No vibration applied.

Sample collected for analysis.

Randomly assigned “Side B”

(Vibration).

Application of 150g orthodontic

force.

Vibration protocol applied

10 mins/day.

Sample collected for analysis.



6.4 Appendix: SkyScan 1172 desktop x-ray micro-tomograph

(SkyScan, Aartselaar, Belgium)

6.5 Appendix: Images from VGStudio Max

(Volume Graphics GmbH, Heidelberg, Germany)



6.6 Appendix: Data – Total resorption per tooth

Total resorption per tooth (mm³)

Subject Vibration Non-vibration

1 0.078 0.084

2 0.569 0.674

3 0.238 0.263

4 0.271 0.555

5 0.372 0.576

6 0.678 0.622

7 0.145 0.299

8 0.121 0.219

9 0.206 0.170

10 0.280 0.453

11 0.232 0.293

12 0.121 0.196

13 0.157 0.524

14 0.186 0.521



6.7 Appendix: Data – Total resorption per tooth surface

Root resorption per tooth surface (mm³)

Subject Buccal-V Buccal-NV Mesial-V Mesial-NV Palatal-V Palatal-NV Distal-V Distal-NV

1 0.059 0.041

0.019 0.044 2 0.138 0.111

0.157 0.246 0.351 0.185 0.057

3 0.130 0.092

0.022 0.108 0.083

0.066

4 0.068 0.105 0.041 0.231 0.094 0.105 0.067 0.113

5 0.031 0.030 0.111 0.192 0.149 0.271 0.081 0.083

6 0.334 0.151 0.050 0.209 0.020 0.050 0.274 0.213

7 0.104 0.204

0.032 0.095 0.009 8 0.067 0.143 0.033 0.046

0.023 0.021 0.007

9 0.012 0.004 0.178 0.141 0.016 0.006

0.018

10 0.110 0.043 0.005 0.057 0.166 0.170

0.183

11 0.090 0.051 0.047

0.077 0.125 0.018 0.118

12 0.090 0.078 0.004

0.023 0.034 0.004 0.084

13 0.107 0.044 0.020 0.285 0.017 0.117 0.012 0.079

14 0.041 0.019 0.104 0.206 0.041 0.188

0.107

Total 1.382 1.115 0.593 1.547 1.008 1.662 0.672 1.127

Mean 0.099 0.080 0.042 0.110 0.072 0.119 0.048 0.081

SD 0.077 0.057 0.054 0.103 0.073 0.098 0.083 0.065



6.8 Appendix: Data – Total resorption per vertical third

Root resorption per vertical thirds (mm³)

Subj Cervical

Vibration

Cervical Non-

vibration

Middle Vibration

Middle Non-

vibration

Apical Vibration

Apical Non-vibration

1 0.037 0.041

0.041 0.044

2 0.138 0.256 0.289 0.184 0.142 0.235

3 0.130 0.141

0.033 0.108 0.090

4 0.110 0.205

0.006 0.161 0.344

5 0.142 0.134 0.008 0.206 0.222 0.236

6 0.348 0.292 0.039 0.068 0.291 0.262

7 0.104 0.203 0.030

0.011 0.096

8 0.103 0.194

0.002 0.018 0.023

9 0.161 0.039 0.014 0.119 0.031 0.011

10 0.114 0.196

0.072 0.166 0.185

11 0.128 0.051 0.045 0.052 0.058 0.190

12 0.092 0.126

0.036 0.029 0.034

13 0.128 0.220 0.012 0.105 0.017 0.199

14 0.145 0.226

0.014 0.041 0.281

Total 1.880 2.324 0.438 0.896 1.336 2.230

Mean 0.134 0.166 0.031 0.064 0.095 0.159

SD 0.069 0.080 0.076 0.068 0.088 0.108

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