Long-term treatment outcomes for ectopic maxillary canine

teeth,

to evaluate incisor root resorption.

Chanelle Houmet Guitirokh

Institutionen för OdontologiOdontologi, magisteruppsats D, 30 poängVårterminen 2007

Supervisor: Associate professor Krister Bjerklin, Department of Orthodontics, Institute for Postgraduate Dental Education in Jönköping, Sweden

Examiner: Professor Sigvard Kopp, Department of Oral rehabilitation, Karolinska Institute, Stockholm, SwedenNr (ej klart ännu)

Institutionen för OdontologiOdontologi, magisteruppsats D, 30 poängVårterminen 2007

Long-term treatment outcomes for ectopic maxillary canine teeth,

to evaluate incisor root resorption.

Abstract

Background: Before the advent of CT as a diagnostic aid, many resorptive

lesions were previously undetected. Little is known of the long-term viability of

these resorbed incisors.

Aim: To monitor the fate of the maxillary incisors with root resorptions in

patients treated in Jönköping,Sweden, up to 28 years ago, for severely ectopic

maxillary canines.

Subjects and Method: The records of 39 patients were found: 35 could be

contacted and 25 agreed to participate in the study. Thus the material comprised a

total of 37 incisors in the 25 subjects. The post-treatment follow-up times ranged

from 13 to 28 years. Clinical examination was followed by intraoral radiographs

and CT. The degree of resorption was

2

collated with the clinical characteristics of the incisor. Resorptive lesions were

described and the intraoral radiographs were compared with those taken

immediately post-treatment.

Results: In all, 22 incisors with root resorption were identified. In 17, the lesions

were unchanged. Resorption had decreased in 2 cases and increased slightly in

two. In one case, the resorption had progressed to the pulp, necessitating

endodontic treatment. Two subjects had lost 3 incisors post treatment. Most of the

resorptive sites showed enhanced definition of the periodontal ligament and

improved trabeculation of the lamina dura, indicating inactive sites. Incisors with

resorption exhibited no clinically distinguishable characteristics.

Conclusions: The results suggest that incisor root resorption induced by an

ectopic maxillary canine does not tend to progress post-treatment and should not

threaten the long-term viability of the affected incisors. Teeth with root resorption

show no clinically relevant symptoms at follow-up.

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Långtidsuppföljning på incisiver med rotresorptionsskador

orsakade av ektopiskt erupterande överkäkshörntänder

Sammanfattning:

Bakgrund: Många resorptionsskador kunde tidigare inte detekteras på periapikala

röntgen innan CT användes som en diagnostisk metod. Det finns lite information

om prognosen för tänder med resorptionsskador.

Syfte: Att göra en långtidsuppföljning på incisiver med rotresorptionsskador

orsakade av ektopiskt erupterande överkäkshörntänder på patienter som har

behandlats i Jönköping, under 70 och 80 talet.

Metod: Journaler för 39 patienter kunde hittas: 35 kunde kontaktas och 25

accepterade att deltaga i undersökningen. Sammanlagt undersöktes 37 incisiver på

25 patienter. Uppföljningstiden varierade mellan 13 till 28 år. Patienterna fick

genomgå en klinisk undersökning, en intraoral röntgenundersökning och en CT-

undersökning. En bedömning gjordes om skadans omfattning utifrån intraorala

röntgen och CT. Resorptionsskadan sattes i relation till kliniska karakteristika och

skadorna jämfördes med skadorna vid avslutad behandling.

Resultat: 22 av 37 undersökta incisiver visade olika grad av resorption. 17

incisiver visade oförändrade resorptionsskador. På 2 incisiver hade rotresoptionen

läkt ut till viss del och i 2 tänder hade rotreorptionsskadan ökat något. En incisiv

visade fortsatt rotresorption som hade nått pulpan vilket hade nödvändiggjort en

rotbehandling. Två patienter hade förlorat 3 incisiver efter avslutad behandling.

4

De flesta tänder visade god parodontal läkning. Vi fann ingen skillnad mellan

kliniska karakteristika hos incisiver som hade resorberats och incisiver utan

resorptioner.

Konklusion: Resorptionsskador orsakade av ektopiska hörntänder verkar inte

försämras efter avslutad behandling. Tänder med rotresorptionsskador visar inga

relevanta kliniska symptom.

Keywords

Canine Impacted, Root Resorption, Incisors, Long-term follow-up

5

Introduction

Ectopic eruption of maxillary permanent canines is relatively common and often

requires lengthy and expensive treatment, including surgical exposure and repositioning

of the canine, followed by orthodontic realignment of the maxillary anterior teeth

(Becker 1998b).

A serious complication associated with this condition is resorption of the roots of

neighboring permanent teeth, usually the lateral incisors.

Early detection of canine impaction is therefore of fundamental importance to treatment

outcome. Careful assessment of the site and severity of any associated resorption of the

roots of adjacent teeth is essential. Concern has been expressed that general dental

practitioners may underestimate the importance of early intervention in avoiding

complications.

Treatment planning today is based on detailed examination to determine the precise

location of the impacted canine and to diagnose the location and extent of any

resorption induced on the roots of adjacent teeth.

Pre-treatment conventional intraoral and panoramic radiographs provide limited

information because of superimposition of structures on the films. Resorptive lesions

may be undetected on pre-treatment radiographs because the canine is often

superimposed on the lateral incisors.

In recent years the advent of computerized tomography (CT) as a diagnostic aid has

allowed more detailed documentation of resorptive lesions. Before the introduction of

CT many such teeth were extracted on the assumption of severe resorption, but many

resorptive lesions also remained undetected and the teeth were retained.

With respect to the response of incisors with resorbed roots following treatment of

impacted canines, short-term follow-up studies suggest that once the impacted canine

has been treated there is minimal risk for further resorption (Becker 2005). However,

lateral incisors with suspected resorption are often extracted because it is believed that

the resorption threatens the long-term viability of these teeth.

There is little information available about whether in the long-term the resorptive

lesions on retained lateral incisors undergo progression, arrest or repair. Data from long-

term follow-up studies of patients treated for ectopic canines would provide evidence-

based guidelines to support the orthodontist in therapy planning.

Incidence of impacted maxillary canines

The maxillary permanent canines are, after the third molars, the teeth most frequently

impacted. Dachi and Howell (1961) reported an incidence of 0.9%, whereas Thilander

and Myrberg (1973) estimated the cumulative prevalence in 7-13 year olds to be 2.2%.

An incidence of 1.7% was reported by Ericson and Kurol (1986b). The condition is

twice as common in females (1.17%) as in males (0.51%) and bilateral in an estimated

8% of cases. The left side is slightly more often affected than the right (Dachi and

Howell 1961).

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Diagnosis

Diagnosis, usually made by the general practitioner, is based on clinical and

radiographic examination. In most children, clinical examination, including digital

palpation at the age of 9-11, suffices. In 7-10 % of children, supplementary

radiographic examination is required (Ericson and Kurol 1986a, Ericson and Kurol

1987a).

A study of 107 children with 156 ectopic maxillary canines disclosed that in relation to

the roots of the adjacent incisors, 50% of the canines were in lingual or distolingual

position, 18% were distobuccal and 21% buccal (Ericson and Kurol 2000b).

Jacoby (1983) claimed that it is difficult to establish an accurate rate for palatal versus

labial impaction. He attributed this to the difficulty in determining whether a labially

impacted tooth might eventually erupt on its own, often further superiorly and labially

than its normal position.

Etiology

The most common reason proposed for palatal displacement of the permanent maxillary

canine is the fact that it has a long and tortuous eruption path, beginning close to the

floor of the orbit. At the age of three, the canine is high in the maxilla, with the crown

directed mesially and somewhat palatally. On its way toward the occlusal plane it seems

to strike the distal aspect of the lateral incisor and then assumes a more vertical position.

The permanent canine takes almost twice as long as the first permanent molar to erupt

(Moyers 1988).

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The etiology is still obscure, but several theories apart from the eruption path have been

proposed. Lack of space was suggested as a causative factor by Hitchin (1951),

although he offered no evidence to support this contention. Others have reported dental

crowding to be more often associated with labial impactions than with palatal

impactions. One study showed that 85% of the palatally impacted canines had sufficient

space for eruption, compared with only 17% of labial impactions (Jacoby 1983).

Enlarged canine follicles have been proposed as factors contributing to deviations in

adjacent permanent roots or inducing root resorption of adjacent incisors. However

Ericson et al. (2002) found no confirming evidence and concluded that root resorption is

probably a result of physical contact between the erupting canine and the adjacent root.

The dental follicles of ectopically positioned canines are, on average, wider than those

of normally erupting canines and asymmetry of the dental follicle is also more common.

However the main reason for an enlarging dental follicle seems to be availability of

space (Ericson and Bjerklin 2001).

In general, retarded eruption of teeth may be multifactorial and either systemic or local

or a combination of both (Moyers 1988). Systemic causes may include endocrine

deficiencies, febrile diseases and irritation. The most common causes of canine

impactions are believed to be local and are the result of any one factor, or combinations

of different factors.

Congenital absence of the maxillary lateral incisor and variation in the root size of the

canine, as well as variation in the timing of its root formation, have been implicated as

important etiologic factors associated

with canine impaction (Jacoby 1983, Bishara 1992).

9

A genetic origin for the palatally displaced canine has also been proposed. This is

supported by the fact that other anomalies are associated with the palatally displaced

canine such as anomalies of tooth form, size or position, congenital absence of various

teeth (particularly maxillary lateral incisors), delayed patterns of development and

eruption and transposition with the first premolar (Becker et al. 1981, Bjerklin et al.

1992, Peck et al. 1994, Camilleri 2005).

An association has also been shown between ectopic eruption of the maxillary first

permanent molar and that of the maxillary canine (Bjerklin et al. 1992) .

Further evidence supporting a genetic origin is:

The risk of palatal canine displacement is significantly higher in patients with

hypoplasia, peg-shaped or congenital dysplasia of upper lateral incisors, further

impacted and congenitally missing teeth (Pirinen et al. 1996, Leifert and Jonas 2003).

There is a four to fivefold greater risk for palatally impacted canines in patients

who have family members with the same anomaly (Svinhufvud et al. 1988, Peck et al.

1994).

The prevalence of the condition seems to vary in different ethnic groups:

compared to African-Americans and Chinese, Caucasians have more palatally displaced

canines (Kramer and Williams 1970, Oliver et al. 1989, Peck et al. 1994).

Impaction is twice as common in females as in males (Dachi and Howell 1961).

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Effects on neighboring permanent teeth

Various types of pressures on teeth can lead to root resorption. Examples include

orthodontic forces, excessive occlusal forces, pressure from impacted or supernumerary

teeth, and pressure from tumors and cysts. Without early intervention, an ectopic canine

in close proximity to the lateral incisor root will induce complex physiological and

chemical processes, and the root of the lateral incisor may undergo resorption (Arens

1995, Ericson and Kurol 2000b). This biological resorption process is still not well

understood, although there is anecdotal evidence that it can lead to the loss of

permanent teeth (Saldarriaga and Patino 2003).

In a recent study on 19 patients with 27 impacted teeth, con-beam computed

tomography disclosed resorption in 67% of the adjacent lateral incisors, 11% of the

central incisors and 4% of the premolars (Walker et al. 2005), confirming that the most

common site of resorption associated with an ectopically erupting canine is the root of

the maxillary lateral incisor.

Two major contributing factors are proposed: the location of the root apex of the lateral

incisor deep in the palate, where palatally impacted canines often present and secondly

the susceptibility of the incisor root to resorption (Ericson and Kurol 1987a, Ericson and

Kurol 1988b, Ericson and Kurol 2000a).

In a study of 107 children with 156 ectopic maxillary canines, resorption was reported

on 38% of adjacent lateral incisor roots and on 9% of adjacent central incisors. Of the

58 lateral incisors affected, resorption was severe in 60% (pulpal involvement),

moderate in 9% and slight in 31% (Ericson and Kurol 2000b).

A review of the associated factors indicates that it is not possible to

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predict when resorption will occur (Ryan 1997). Ericson and Kurol (1988b) showed that

resorption was three times more likely to be associated with impacted canines in

females than in males and that a more medial position and horizontal inclination of the

canine increased the risk. Despite the association between an impacted canine and a

reduction in size of the adjacent lateral incisor, resorption is more likely to occur in

cases of canine impaction where the lateral incisor is of normal size (Brin et al. 1993).

Clinical considerations

A review by Bishara (1992) concluded that canine impaction may be indicated by the

following clinical signs:

Delayed eruption of the permanent canine or prolonged retention of the

deciduous canine

Absence of a normal labial canine bulge: the canine position cannot be

ascertained by intraoral palpation of the alveolar process, or palpation discloses

asymmetry of the canine bulge

Presence of a palatal bulge

Delayed eruption, distal tipping, or migration of the lateral incisor

In this context, Ericson and Kurol (1986a) suggested that the absence of the “canine

bulge” should be considered in relation to the age of the child. In a material of 505

children aged 10 to 12 years, they found nonpalpable canines in 29% at age 10 years,

but in only 5% at 11 years and 3% after age 11. Thus in cases where eruption of the

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maxillary permanent canines is late in relation to the age of the patient, clinical

examination should be supplemented by radiographs.

Except in rare cases of pathology, root development proceeds in a constant manner,

regardless of tooth eruption or the fate of the deciduous predecessor. Thus dental age

may be accurately assessed in terms of tooth development, determined by examination

of periapical or panoramic radiographs (Becker 1998a).

Periapical radiographs

A study by Ericsson and Kurol (1987b) disclosed that in 92% of cases, periapical

radiographs enable the clinician to evaluate the position of the canine with sufficient

accuracy. In cases of tipped or proclined lateral incisors, it is difficult to determine the

position of the canine. Only in 37% of the cases was it possible to project the lateral

incisor image away from that of the canine.

Axial films and panoramic radiographs show the relationship to the lateral incisor less

clearly. Fox et al. (1995) studied 100 pairs of radiographs showing 139 ectopic canines.

Panoramic radiographs allowed accurate depiction of the position of a palatally

displaced canine crown in only about 80% of cases. Panoramic radiographs result in

relative magnification of objects located palatal to the image layer and relative

diminution of objects to the buccal. In radiographic examination to confirm clinical

suspicion of ectopic eruption of a maxillary canine, a panoramic radiograph is not

enough and should be complemented by intraoral radiographs.

Intraoral radiographs are unreliable for detection of lingual or buccal root resorption.

This was demonstrated in an experimental study by Folin and Linvall (2005),

13

undertaken to evaluate the potential of intraoral radiographs to disclose root resorption

on the palatal aspect of the roots of maxillary incisors. Although radiologists were better

than orthodontists and pedodontists at detecting areas of resorption, lesions located on

the middle third of the roots were not readily detected until a considerable area was

affected, of the order of 3.5mm

Computed Tomography

Computed Tomography (CT) is an imaging method that has proved to be superior to

other radiographic methods in visualizing hard tissue (Traxler et al. 1989, Preda et al.

1997).

Originally known as computed axial tomography (CAT or CT scan) and body section

roentgenography, computed tomography is a medical imaging method employing tomography

where digital geometric processing is used to generate a three-dimensional image of the interior of an

object from a large series of two-dimensional X-ray images taken around a single axis of

rotation. The word "tomography" is derived from the Greek tomos (slice) and graphia

(describing). The spiral CT used today produces a volume of data which can be

manipulated, through a process known as windowing, in order to demonstrate various

structures, based on their ability to block the x-ray beam. Although historically the

images generated were in the axial or transverse plane, modern scanners allow this

volume of data to be reformatted in various planes or even as volumetric (3D)

representations of structures.

Ericsson and Kurol (1987b) demonstrated that compared to intraoral radiographs,

polytomography disclosed 50% more resorptive lesions. In this material, half the teeth

14

with resorption had lesions involving the pulp. In 50 per cent of cases there were

resorptive lesions on the labial or palatal aspects of the roots: such lesions would not be

detectable on conventional periapical radiographs.

A CT-study by Ericsson and Kurol (2000b) disclosed that 48% of subjects with

ectopically positioned maxillary canines had root resorption on the adjacent incisors.

The major advantages of CT are that blurring and overlapping of the teeth are

eliminated and tissue contrast is excellent. Thus the potential to detect root resorption is

substantially enhanced. Investigation by Ericson and Kurol (2000a) confirmed that CT

scanning performed with good technique is a reliable method of accurately disclosing

tooth root resorption.

In cases of ectopic eruption of maxillary canines, the prognosis for the lateral incisor is

a major determinant in clinical decision-making and treatment planning. Bjerklin and

Ericson (2006) analysed treatment outcome and treatment planning before and after a

CT investigation of 80 children with 113 impacted maxillary canines. Supplementary

information from CT led to modification of treatment plans for 35

(43.7%) of the children. Without the CT investigation, severe resorption (pulpal

involvement) of the incisor root would have been undetected in 11 children and 13 who

had no root resorption would have had one or both lateral incisors extracted.

In recent years digital volume tomography such as Accu- I- Tomo has been proposed as

an alternative to routine CT for diagnosis and treatment planning of impacted teeth

(Chaushu et al. 2004): this method provides the same information as conventional CT,

but at less cost and a lower radiation dose.

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Treatment of impacted maxillary canines

In principle, treatment comprises surgical exposure of the canine and fixed orthodontic

appliance therapy, applying elastic traction to reposition the canine in the dental arch.

This orthodontic–surgical treatment is sometimes followed by extraction therapy

because of space deficiency.

Other approaches are presented in the literature (Jacoby 1979; Caprioglio et al. 2007).

Removable appliances can also be used (Fournier et al. 1982, McDonald and Yap

1986).

A study by Ericsson and Kurol (1988a) confirmed that when palatally

displaced maxillary canines are detected early, by 10-11 years of age, the

prognosis for normalization of the eruption path is good: after extraction of the

deciduous canine, the permanent successor can erupt into the correct position in the

dental arch. Of the 46 palatally displaced canines in this study, 36 (78%) changed from

palatal to normal eruption paths after intervention: the positions of 23 had improved

after 6 months and 13 after 12 months. The remaining canines showed no improvement

12 months after intervention. Cases in which there was more severe overlap of the

canine over the lateral incisor were less likely to respond well to this intervention.

Leonardi et al. (2004) showed only a 50% success rate for extraction of the deciduous

canine as an isolated measure to intercept palatal displacement of maxillary canines: not

significantly greater than for unerupted controls. Use of headgear in conjunction with

extraction of the deciduous canine induced successful eruption in 80% of the cases.

A study by Bruks and Lennartsson (1999) comparing interceptive and corrective

treatment groups showed the major determinant for the final outcome to be age at the

16

time of recognition and referral, while the position of the canine can be a compromising

factor.

Ericsson and Kurol (2000b) emphasized the importance of early supervision of the

maxillary canine germ and the eruption path of the canine to allow early, less invasive

intervention in cases of disturbed eruption.

Associated root resorption of adjacent teeth

In routine orthodontic treatment of uncomplicated malocclusions, shortening of the

roots of the teeth by resorption is not uncommon. It is generally acknowledged that

resorption seldom progresses after orthodontic forces are discontinued (Copeland and

Green 1986, Levander and Malmgren 2000). Whether the same applies to resorptive

lesions induced on the roots of adjacent teeth by ectopic canines has yet to be

confirmed.

A search of the literature discloses few investigations into the response of resorptive

lesions on the roots of maxillary incisors and the long-term survival of these teeth

following treatment of ectopic canines.

Severely resorbed incisors have been extracted on the assumption that the teeth have a

poor long-term prognosis (Rabie et al.1996, Rimes et al.1997, Savage and Kokich

2002).

Of the few available reports, Parker (1997) indicated that extraction or orthodontic

distancing of the impacted canine seems to arrest the resorptive process without the

need for root canal therapy if the vitality of the tooth has been maintained. Other reports

17

have disclosed progressive root resorption although minimal, in follow-up radiographs

(Shellhart et al. 1998, Saldarriaga and Patino 2003).

Before the advent of CT investigation, ectopic maxillary canines were treated without

ascertaining the presence of root resorption on the adjacent incisor roots. As it is now

known that there is associated resorption in almost half such cases, it follows that many

patients who underwent treatment for ectopic maxillary canines some years ago would

have retained incisors with undiagnosed root resorption.

The literature suggests that after intervention to correct the ectopically positioned

maxillary canine, the resorption process is arrested and the affected tooth is not

susceptible to further damage. Hence these teeth should not exhibit increased mobility

or discoloration.

The condition of the incisor root is an important determinant of the outcome of

treatment for ectopically positioned canines. More needs to be known about the effect of

root resorption on the long term prognosis for these incisors. Such information would

provide valuable guidance for the clinician in deciding whether to recommend treatment

based on extraction or retention of these incisors, or which tooth to extract.

The present retrospective study is based on long-term clinical and radiographic follow

up-of patients with ectopic maxillary canines, treated in Jönköping, Sweden up to 28

years ago i.e. before the adoption of CT as a diagnostic aid in evaluating impacted teeth.

The aim of the study was to document the condition of the maxillary incisor teeth

adjacent to the treated canines, with special reference to

resorptive lesions on the roots.

18

Hypothesis: We believe that after intervention to correct the ectopically positioned

maxillary canine, the resorption process is arrested and the affected tooth is not

susceptible to further damage and these teeth should not exhibit increased mobility or

discoloration.

19

Subjects and Methods

Subjects

The Orthodontic Department of the Institute for Postgraduate Dental Education in

Jönköping, Sweden, is the regional referral centre for cases of severe ectopically

erupting canines. The study sample comprised children referred for consultation and

treatment of ectopically positioned maxillary canines, during the late 1970’s and 1980’s.

Inclusion criteria were resorption discernible on radiographs or a high probability of an

existing resorption due to the ectopic position of the maxillary canine.

Treatment with fixed appliances had started between 1974 and 1990. All treatment had

been completed over 10 years ago. Post-treatment radiographs were available.

A search of the records disclosed 39 former patients who met the criteria. Four had

moved abroad and could not be contacted. The remaining 35 were contacted and offered

follow-up examination. Ten of them did not participate in the study: eight had relocated,

one was pregnant and one patient expressed concerns about the CT-examination. Thus

the final material comprised twenty-five participants.

Treatment start was defined as start of the fixed appliance therapy. Most of the patients

had previously undergone extraction of the deciduous canine.

The mean age at the start of treatment was 13.9 years (SD 3.65). All subjects had

severely ectopically positioned canines with suspected root resorption on the adjacent

incisors. In two cases in which the lateral incisors had been extracted due to resorptive

damage, the central incisors were examined. The mean duration of treatment was 2.6

years (SD 1.20). Treatment comprised surgical exposure of the canine and elastic

20

traction in combination with fixed appliances. One patient went abroad for 1 year and 4

months and continued treatment after her return. The mean age at the end of treatment

was 17.1 years (SD 4.45).

Treatment was completed between 1978 and 1994 (mean 1983). The mean age of the

subjects at follow-up was 37.1 years (SD 9.48).

The study was approved by the Research Ethics Committee, Faculty of Health Science,

Linköping University, Linköping, Sweden.

Method

The author (C.H. Guitirokh) conducted a clinical examination of the maxillary anterior

teeth of 24 of the subjects, recording the following variables: vitality, pocket depth,

palpation, percussion, apical tenderness, mobility, discoloration and position of the

incisors. One subject was not examined by the author and was excluded from the

clinical part of the study.

To compare vitality responses, vitality tests were conducted on the maxillary anterior

teeth, from the maxillary right canine to the maxillary left canine. An Analytic

Technology model 2006 vitality scanner (Redmond, Washington, USA) was used

throughout.

Periodontal condition was recorded by probing at eight sites on each anterior tooth:

mesial, mesiopalatal, palatal, distopalatal, distal, distobuccal, buccal and mesiobuccal.

All four maxillary incisors were palpated buccally for apical tenderness.

A percussion test was conducted on each tooth from the maxillary right canine to the

maxillary left canine to record normal or ankylotic sounds.

21

Mobility of the incisors was registered as present or not.

The incisors were evaluated with respect to aesthetics, in terms of tooth colour, position

in the dental arch and inclination. Tooth shape and tooth colour were recorded as

normal or otherwise. Tooth position, inclination and rotation were documented. The

examiner’s assessment of treatment outcome was recorded, as was patient satisfaction.

Two patients who had lost their lateral incisors post-treatment were excluded from this

evaluation. Another two patients with resorption attributable to the orthodontic

treatment itself were also excluded from the clinical evaluation.

The patients were interviewed, study models were made, digital intraoral photographs

and intraoral radiographs were taken.

The radiographs were taken with a digital Focus 2004 apparatus (Imaging

Instrumentarium), using the parallel technique, in which the x-ray beam is different

projections. All radiographs were compared with the post-treatment radiographs.

Twenty-one patients with in all thirty-three incisors “of concern” were referred for more

detailed examination by contiguous transverse CT. Four patients were not referred for

further CT examination. One patient became pregnant during the study and could not

undergo CT and one patient had such obvious and extensive resorption that CT was

considered unnecessary. Two patients had lost the incisor in question post-treatment.

The CT examinations were conducted in the city where the patient was resident. In

Jönköping a Siemens Somatome Plus CT scanner (Siemens AG, Germany) was used for

contiguous transverse CT scans with a slice thickness of 1- 2mm. Two patients were

scanned in another hospital with a General Electric Light Speed X-steam with slice

thicknesses of 0.625mm and 1mm. One patient attended a third hospital where CT scans

22

with slice thicknesses of 1mm were taken by 3D Accu- I- Tomo (J Morita MFG.Corp.,

Kyoto, Japan).

The radiographs were analysed by two oral radiologists and the author. Resorption was

described in terms of position: buccal/distobucccal, palatal, distopalatal, distal or

apical. The site of the resorptive lesion on the root was also recorded as: cervical,

middle or apical third or on the apex.

Taking into account both radiographs and CT results, the author graded the resorptive

lesions as slight, moderate or severe, based on whether the location was apical or lateral.

The location of resorbed areas was determined in three planes. Signs of apical root

resorption were registered with index scores from 0 to 4 (Figure 1a) as described by

Levander and Malmgren (1988, 2000). Figure 1b shows three different patients with

incisors that show apical root resorption in various degrees.

Figure 1a. Root resorption index for quantitative assessment of root resorption. 1. Irregular root contour; No resorption 2. Root resorption apically, amounting to less than 2 mm; Slight resorption. 3. Root resorption apically, from 2mm to one third of the original root length; Moderate resorption. 4. Root resorption exceeding one third of the original root length; Severe resorption (Levander and Malmgren 1998; Levander and Malmgren 2000).

23

Figure1b. Slight apical root resorption (left). Moderate apical root resorption (centre). Severe apical root resorption (right).

The severity of mesial, distal, buccal or lingual resorption was scored on a 4 point scale

according to Ericson and Kurol (2000):

1. No resorption- intact root surfaces, except for loss of cementum.

2. Slight resorption- up to half of the dentine thickness.

3. Moderate resorption- half way to the pulp or more; the pulp is covered with dentine.

4. Severe resorption- the pulp is exposed.

Statistical analyses

24

The results were analysed by a statistician. Different findings within the sample were

too small to give an accurate statistical significance. There are also dependent variables

such as one patient having 2 teeth with resorption within the sample which makes the

statistic very uncertain.

Ethical considerations

The study was approved by the Research Ethics committee, Faculty of

health science, Linköping University, Linköping, Sweden.

Special Significance

The evaluation of the incisor root adjacent to ectopically positioned maxillary canine

teeth is of great importance to both the patient and orthodontist in treatment planning.

We need to know more about how root resorption affects the long term prognosis of

these incisors. This ought to be taken into account when deciding on

extraction/nonextraction or which tooth to extract.

25

ResultsIn all, a total of 37 incisors was examined in 25 subjects.

However, different subgroups within the sample were too small to allow statistical

analysis.

The results of the intraoral radiographs at follow-up are shown in Table 1. Seven

subjects exhibited resorption on two or more incisors, while no resorption was

discernible in eight subjects, despite the severely ectopic canine and grave suspicion of

damage to the adjacent roots.

Table 1. Number of subjects and incisors with root resorption visible on intra oral radiographs at follow-up.

Without Uncertain Resorption Extracted

Resorption Resorption Post-treatment

Subjects(n=25) 8 2 13 2

Incisors(n=37) 9 3 22 3

Resorption was detected on intraoral radiographs in 22 incisor roots and could not be

ruled out in 3 incisors. Only one of the incisors with resorption was adjacent to a

buccally impacted canine.

Three incisors showed signs of resorption that were difficult to differentiate from

orthodontically induced resorption.

In two subjects, three incisors had been extracted post treatment. One subject had lost

two lateral incisors due to trauma. His pre-extraction radiographs were retrieved from

26

the clinic where he had undergone treatment. These did not show any extensive root

resorption at the time of extraction. One subject with a unilateral ectopic canine and

missing lateral incisor had lost a central incisor due to advanced periodontitis

approximately 10 years after treatment. Unfortunately her records at the time of

extraction had been destroyed.

The results of the intraoral radiographs and CT examination were then compared and

compiled. Although the CT examination was superior in detecting buccal and lingual

resorptions, intraoral radiographs were found to be more useful in disclosing and

comparing apical resorption. The two subjects who had undergone extractions were

excluded from the comparison as it was uncertain why the incisors were lost.

Figure 2 shows an intraoral radiograph and CT of the maxillary left central incisors. The

root resorption on the palatal aspect of the cervical third of the root, disclosed by CT

examination, is impossible to see in intraoral radiographs.

Figure 2.Distopalatal root resorption on the cervical third of the root of the maxillary left central incisor. Comparison of intraoral radiograph (left) and CT-examination (right).

Examination of the 22 incisors with root resorption disclosed 27 affected root surfaces

in 13 patients. One patient had 4 resorbed incisor roots, 6 patients had 2 resorbed incisor

27

roots and the remaining 6 patients had each only one tooth resorbed. In 11 of these

teeth the resorptive lesion was located on the palatal or distopalatal aspects of the root

and 14 incisors showed signs of apical resorption (Table 2).

Table 2. Number of resorbed surfaces disclosed by intraoral radiographs and CT examination. Some incisors were resorbed on more than one surface. Thus of 22 affected incisors, resorption was recorded on 27 surfaces.

Buccal, Palatal, Distal Apical Total

Distobuccal Distopalatal

Lateral

incisors - 5 - 5 10

Central

incisors 1 6 1 9 17

Total 1 11 1 14 27

Comparison of the location of the resorptive lesions along the roots in a vertically

divided scheme revealed 9 of the total 22 incisors with resorption of the apex, 2 with

resorption in the apical third of the root, 9 with resorption in the middle third of the

roots and 2 in the cervical third (Table 3).

Table 3.Number of diagnosed resorbed root surfaces in a combined intraoral and CT investigation. Only one surface from each tooth is registered.

Teeth Cervical Middle Apical Apex Total

third third third

Lateral

incisors 1 6 - 2 9

Central

incisors 1 3 2 7 13

Total 2 9 2 9 22

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Severity was graded as slight, moderate or severe, as described earlier. Of eight incisors

with severe resorption, six were central incisors. Five lateral incisors and two central

incisors showed moderate resorption. Slight resorption was noted in the remaining 7

teeth (Table 4).

Table 4. Severity of incisor root resorption induced by ectopic canines in 22 patients

Teeth Slight Moderate Severe Total

Lateral incisors 5 5 2 12

Central incisors 2 2 6 10

Total 7 7 8 22

All radiographs taken at the follow-up were compared to radiographs taken at

completion of treatment (Table 5).

Table 5. Resorption on the incisor roots: comparison of radiographs at follow-up and those taken on completion of treatment

Incisors Improved Unchanged Increased Total

Laterals 1 8 3 12

Centrals 1 9 0 10

Total 2 17 3 22

In two cases the follow-up radiographs showed slight improvement. The condition was

unchanged in seventeen teeth (Figure 3): in fifteen of these the periodontal ligament and

lamina dura were more distinct, with much improved trabeculation of the periapical area

with further maturation and smooth edges (Figures 3, 4 and 5). One patient with two

central incisors and a resin-bonded bridge showed obliterated pulps and

29

indistinguishable lamina dura (Figure 6). In one case the lamina dura was well-defined

but the edges were still rough (Figures 7). Resorption was more pronounced in three

teeth (Figure 8). In one of these cases the resorption had progressed and the lamina

dura was still poorly defined at the resorption site. This tooth had undergone endodontic

treatment(Figure 9).

Figure 3. Patient with severe resorption on the lateral incisors due to ectopically erupting canines (left). The lateral incisors were extracted and replaced with a resin bonded bridge. The centre radiograph was taken on completion of treatment and the radiograph to the right is 22 years post treatment. The follow-up radiograph shows slightly better definition of the PDL and the lamina dura.

Figure 4.Patient with slight apical resorption of maxillary left incisor at completion of treatment (left and centre) and 16 years post treatment (right). Note that the root shape is even and lamina dura is well-defined.

30

Figure 5. Radiographs on completion of treatment (left) and 19 years post treatment (right). Patient with moderate apical root resorption on maxillary right lateral incisor. At follow-up the resorbed area shows a better-defined PDL and lamina dura.

Figure 6.A patient with severe root resorption on both maxillary central incisors. The maxillary lateral incisors were extracted due to severe resorption. 11 and 21 were orthodontically aligned at the midline. The crowns of the maxillary lateral incisors were replaced by a resin bonded bridge. Radiograph on completion of treatment (left) and at 17 years post retention (right). The pulps of the central incisors are obliterated. The surface of the roots appears smoother and rounder. Lamina dura is indistinguishable.

Figure 7. Patient with slight resorption on the maxillary left lateral incisor at completion of treatment (left), and 16 years post treatment (right). There are no signs of the progression of the resorption on the

31

root. Lamina dura is well-defined. At follow-up the resorbed area shows a better-defined PDL and lamina dura but the edges are still rough.

Figure 8. Radiographs at treatment end (left) and 16 years post treatment (center and right ). Right lateral incisor was extracted during treatment and both central incisors show resorption due to ectopic eruption of the maxillary canines. Right maxillary incisor with severe distopalatal resorption and left maxillary central incisor show apical and distal resorption. The area of resorption shows slight progression .

Figure 9. Patient with severe distopalatal root resorption at completion of treatment (left). Endodontic treatment was undertaken many years later. Radiograph to the right is 19 years post treatment. The resorption has progressed slightly towards the pulp and the lamina dura at the resorption site still lacks definition.

Clinical results

32

The results of the clinical findings are summarized in Table 6.

All subjects were satisfied with the overall aesthetic outcome, although some

commented on the rotation or inclination of the laterals and two were dissatisfied with

the colour of the maxillary incisors. The author and subjects were in agreement with

respect to the aesthetic results in all cases.

During the study, it was observed that some of the incisors examined responded more

slowly to the electric vitality test than contralateral teeth within the same subject. For

this reason it was decided to document whether a tooth reacted at minimum 10 levels

higher than adjacent maxillary incisors.

Delayed response to the vitality test was recorded in 42% of teeth with resorption: the

corresponding result in incisors without detectable resorption was 25%.

One subject without signs of resorption was very sensitive to the electrical vitality test

and found it very painful. No other symptoms were registered for this subject.

One incisor with root resorption and one incisor without root resorption showed crown

discoloration.

Table 6. Summary of clinical findings at follow-up registration in 20 patients with 29 lateral and/or central incisors with suspected resorptive damage attributable to an ectopic canine. Two incisors were excluded because of orthodontically induced resorption

33

Resorption Without Total

resorption

(n=19) (n=10) (n=29)

Discoloration 1(5%) 1(10%) 2(7%)

Sensitive tooth - 1(10%) 1(3%)

Pockets 2(11%) 1(10%) 3(10%)

Ankylotic sound 2(11%) - 2(7%)

Palpation

tenderness 1(5%) 1(10%) 2(7%)

Vitality test

reacting more

than ten levels

later than other

maxillary incisors 5 (26%) 2 (20%) 7 (24%)

Root treatment

post-treatment 1 (5%) - 1(3%)

Deviant inclination,

rotation, position 8 (42%) 6 (60%) 12 (41%)

Increased mobility - - -

In the resorption group two subjects had pockets > 4mm: 6mm and 4.5mm,

respectively. In the group of subjects without resorption only one had a 4mm pocket.

Two subjects exhibited tenderness to buccal palpation of the apical area. Only one

showed resorption on the incisor root. These subjects were double checked, as the apical

tenderness was an unexpected finding. The incisor with resorption also had a delayed

reaction to the vitality test whereas the other incisor had no other symptoms.

34

In two subjects, ankylotic percussion sounds were recorded on central incisors with

resorption. One of these subjects had a history of trauma in the maxillary anterior region

and the other had a resin-bonded bridge on the maxillary central incisors, following

extraction of 12 and 22 due to severe root resorption.

An apical periodontitis had developed on one severely resorbed lateral incisor,

necessitating endodontic treatment a few years post-treatment. The precise date for the

endodontic treatment could not be determined.

At follow-up many of the patients had proclined, retroclined, or mesially or distally

rotated incisors, irrespective of the presence or absence of resorption.

None of the incisors showed signs of increased mobility.

35

Discussion

The present study was undertaken to investigate the long-term fate of teeth with

resorptive lesions induced by ectopic canines. Current clinical and radiographic status

was compared with the data recorded on completion of treatment some 20 years earlier.

Analysis of such long-term treatment outcomes provides evidence-based information to

support orthodontic treatment decisions.

A study with such a long follow-up period offers a challenge with respect to gathering

the sample and also ensuring that the data retrieved from treatment records can be

compared. It offers valuable information, but it is difficult to draw conclusions from

some of the findings.

Although the departmental records were searched for all patients treated for ectopic

maxillary canines over a 20 year period, only 39 cases were found with complete

radiographic records from start of treatment and post-treatment. Many records had been

destroyed. Three patients had moved abroad and could not be contacted. Thirty-six

patients were contacted: eleven could not participate, mostly because of relocation,

which is a limitation in long-term clinical follow-up studies. A further limitation is

pregnancy as many pregnant women would be reluctant to undergo radiographic

examination.

While the sample was limited to subjects with severely ectopic canines,

the incidence of resorption was still quite low (65%), confirming previous reports that it

is difficult to predict which cases will develop resorption (Ericson and Kurol 1988b).

36

Treatment of the ectopic canines had been undertaken during the 1970’s and 80’s. At

this time computed tomography had not been established as a diagnostic aid for dental

impactions. In many cases of suspected root resorption of adjacent teeth, these teeth

were extracted.

The follow-up study disclosed eight incisors with severe resorption, seven with

moderate resorption and seven with slight resorption. As many teeth with severe

resorption are extracted during treatment, it is difficult to gather a sample of subjects

with severe resorption at follow-up. In this sample, the treatment plans of two patients

had included extraction of two severely resorbed lateral incisors due to their poor

prognosis.

In all patients, the resorption had occurred before the fixed appliance treatment and the

patients then underwent significant orthodontic movement, after distancing the impacted

canine.

The mean treatment time for the impacted canine with elastic traction in combination

with fixed appliances was 2.6 years (SD 1.20). This was in line with the appropriate

radiographic monitoring for further root shortening. In no patient had it been necessary

to discontinue treatment for this reason.

There are very few follow-up studies of root resorption induced by impacted canines.

There are some similarities with root resorption induced by orthodontic forces: both

lesions comprise an area of sterile inflammation causing loss of hard tissue (Brezniak

and Wasserstein 2002). It is generally acknowledged that orthodontically induced

resorption is arrested when the force is removed. In analogy, resorption induced by an

37

impacted canine should not progress once the canine is distanced from the root

(Copeland and Green 1986, Becker 2005).

A literature review by Brezniak and Wasserstein (1993) led to the conclusion that even

extensive orthodontically induced resorption does not affect the functional capacity or

the effective life of the tooth. However, Levander and Malmgren (2000) showed

increased mobility in

maxillary incisors that undergo severe root resorption during orthodontic treatment.

It can be difficult to distinguish apical resorption induced by an ectopically positioned

canine from orthodontically induced resorption. However, orthodontically induced

resorption is usually more generalized, affecting all four anterior incisors.

When the impacted canine is very close to the incisor root, the clinician must distance

the canine from the incisor root as early in the treatment as possible, in order to

minimize the risk of resorptive damage.

Many incisors with severe root resorption are extracted on the assumption the long-term

prognosis is poor (Ryan 1997, Rimes 1997, Ericson and Kurol, 2000a). Some case

reports have indicated that retaining severely resorbed incisors can be an alternative

(Shellhart et al.1998, Saldarriaga and Patino 2003).

Resorptive damage is assessed primarily on radiographic evidence.

On intraoral radiographs it is difficult to detect resorptive damage on the buccal or

palatal aspects of the roots. It may also be difficult to differentiate between damage

attributable to orthodontic treatment and that induced by the ectopically positioned

canines, particularly because orthodontic treatment frequently involves movement of the

lateral and central incisors.

38

Computed Tomography (CT) can provide more reliable information than conventional

radiography and is useful for discerning the contour of the root and the resorbed area.

CT examination discloses sites of resorption not detectable in intraoral radiographs.

In this study intraoral radiographs proved more useful for determining apical resorption

and root shortening, particularly because it was possible to compare the follow-up

radiographs with those taken on completion of

treatment.

Because of the low radiation dose, limited 3- dimensional cone-beam computed

tomography is recommended in management of impacted canines. Examples are Tom

QR-DVT 9000 or Accu-I-Tomo ( Walker et al. 2005, Chaushu et al. 2004, Nakajima et

al. 2005). This method provides information about the size of the follicle, relative

buccal and palatal positions, the amount of bone covering the tooth and 3D proximity

and resorption of roots of adjacent teeth. The radiation dose is only one-sixth of

conventional computer tomography and its cost is considerably less (Lofthag-Hansen et

al. 2007).

The present study is unique because of the very long follow-up time (13-28 years post

retention). Most of the resorptive lesions (15 of 22) were

unchanged in area, but with a better defined lamina dura and improved

trabeculation of the periapical area, with further maturation and smooth edges. Areas of

active resorption are characterised by a poorly defined lamina dura and PDL (Ericson

and Kurol 1987b): in a few cases the lamina dura was not distinct, or the edges of the

teeth were sharp and spiky at follow-up. In two cases the lesions showed minor

improvement. In three cases the resorptions were more pronounced. In two of these

39

cases it was in the author’s opinion a result of the contouring the root and had to do with

the shape of the initial damage. One patient had developed apical periodontitis on the

lateral incisor several years post-treatment and had undergone endodontic treatment. In

this case the resorption had progressed to pulpal involvement post-treatment.

The results of the present study were in agreement with those of Becker et al. (2005)

which also showed a minimal risk of further resorption when these teeth were subjected

to orthodontic forces. Becker et al. (2005) studied 11 subjects with 20 severely resorbed

incisors and reported that none of the incisors was lost during follow-up. However, the

follow-up period was much shorter than in the present study.

In the present study, two subjects had lost their incisors post-treatment. One had lost

two lateral incisors due to trauma and one with a unilateral ectopic canine and missing

lateral incisor had lost a central incisor due to advanced periodontitis approximately 10

years after treatment. Today she has severe contralateral periodontal involvement, but

the incisors are still

in function. No records of her periodontal treatment were available.

Clinically no increased mobility or discoloration was observed. This is also in

agreement with Becker (2005).

In the group with resorption, a metallic percussion sound indicating ankylosis was

recorded in two subjects and 5 had a delayed reaction to the electrical vitality test,

compared to the 2 subjects in the group without resorption.

40

Although such a limited material allows no extrapolation of the findings, the results

show that in this sample of subjects who presented with severely ectopic canines, long-

term follow-up of the fate of the retained lateral incisors confirmed that the resorption

did not tend to progress following intervention to correct the canine impaction. Despite

the resorptive damage, these incisors had tolerated the orthodontic forces applied during

realignment of the anterior teeth. In the majority of cases there had been no progression

of resorptive lesions and few post-treatment complications. Most of the teeth with

resorption induced by the ectopic canines were in function some 20 years after

completion of the orthodontic treatment. In general the subjects were satisfied with the

treatment outcomes.

It is very difficult to find a large sample of incisors with severe resorption, partly

because improved screening of children at appropriate stages facilitates early detection

of the ectopic canine and intervention before resorptive damage occurs on the adjacent

teeth, but also because many such teeth are extracted as part of the orthodontic

treatment, to avoid future complications. A multi-center long-term follow-up of

severely resorbed incisors is warranted, in order to study clinical and radiographic

changes in a sample large enough to allow statistical analysis.

41

Conclusions

Root resorption induced by an ectopically positioned canine does not

progress post-treatment in the majority of cases.

Apical and periodontal health around a resorbed root often normalizes and

the lamina dura is more well-defined at follow-up.

Teeth affected by root resorption induced by an ectopic canine exhibit no

clinically abnormal signs or symptoms at follow-up.

42

Acknowledgements

I express my sincere thanks to Assoc. Prof. Krister Bjerklin, Institute for Postgraduate

Dental Education, Jönköping, my mentor, for sharing his knowledge, for his objective

approach, excellent supervision, and for his positive generous attitude. This work was

supported by grants from Futurum research committee in Jönköping.

Many thanks to the radiology departments in Jönköping, Halmstad and Gothenburg for

the help with the CT examinations and interpretation.

43

References

44