Working length determination

WORKING LENGTH DETERMINATION

Dr. Liya Thomas

CONTENTS• Introduction

• History

• Definitions

• Clinical consideration

• Methods of determining working length

• Recent advances

• Working width

• Conclusion

• Bibliography

INTRODUCTION

• Seltzer et al were the first to report greater success in terminating cleaning & obturating the root canal system just short of the radiographic apex rather than overfilling or underfilling.(Seltzer S et al.Biologic aspects of endodontics.III Periapical tissue reactions to canal instrumentation.Part II.Oral Surg Oral Med Oral Pathol Endod

1968;26:694-705)

• Sjogren et al reported the best outcome was when the canal filling was between 0-2mm short of radiographic apex

• According to Cohen and Burns, 1 mm of a canal with a diameter of 0.25mm, which is the diameter of narrower foramens, provides enough space to lodge nearly 80,000 streptococci.so filling should be at the apex.

• Chugal found variations in success rates of root filled at different levels :

• Normal preoperative pulp & periapical tissues – filled over 1mm from radiographic apex

• Necrotic pulp & apical periodontitis – canal filling closer to radiographic apex

Chugal NM,Clive JM et al.A prognostic model for assessment of the outcome treatment:effect of biologic & diagnostic variables.Oral Surg Oral Med Oral Path Endod 2001;91:342-52

HISTORICAL PERSPECTIVES• End of 19th century: WL was calculated when file was placed in canal &

patient experienced pain

• 1899 : Kells introduced X-rays in dentistry

• 1929 : Collidge studied the anatomy of root apex in relation to treatment problems

• 1955 : Kuttler microscopically studied the microscopic anatomy of root tip, and decided that filling to the radiographic apex was an unwise clinical procedure, contributing to post operative pain.

• 1969 : Inove significantly contributed to evolution of electronic apex locators

DEFINITIONS• Working length : the distance from a

coronal reference point to the point at which canal preparation and obturation should terminate (seventh edition of the Glossary of Endodontic Terms)

• Reference point : It is the site on the occlusal or incisal surface from which measurements are made.

This point is used throughout canal preparation & obturation

Anatomy of the Root Apex (Kuttler’s studies)

A.Anatomic apexB.Apical constriction (minor diameter)F. Apical foramen

The study of the dimensions of the internal anatomy of teeth hasbeen a challenge since the studies of Kuttler, Kerekes and Trostand

• ANATOMIC APEX AND RADIOGRAPHIC APEX:

• CEMENTODENTINAL JUNCTION (CDJ)

CDJ does not always coincide with apical constriction.location of CDJ is 0.5-0.3 mm short of the anatomic apex.

Langeland

• Apical Foramen :

An accessory foramen is an orifice on the surface of the root communicating with a lateral or accessory canal.They may exist as a single foramen or as multiple foramina

Region where the canal leaves the root surface next to the periodontal ligament ( American Association of Endontists,1984)

The apical foramen deviates from the root tip in at least two-thirds of all teeth.this deviation occurs towards the buccal or lingual aspect TWICE

often as it does towards the mesial or distal aspect Levy and Glatt

• LATERAL CANALS• Periodontal vessels curve

around the root apex of a developing tooth and become entrapped in Hertwig’s epithelial root sheath resulting in formation of lateral canals

• APICAL DELTA• Branching patern of small

acessories canals and minor foramen seen at the tip or apex of some tooth

• APICAL CONSTRICTION :

It is the narrowest part of the root canal with the smallest diameter of blood supply and preparation to this point results in a small wound site and optimal healing conditions (Ricucci & Langeland 1998)

Topography of the apical constriction (DUMMER CLASSIFICATION)

“Traditional” single apical constriction was present more than half the time JADA 16:1456;1929

MAJOR AND MINOR DIAMETER

Distance between major diameter and minor diameter • 0.524mm (18-25yrs). • 0.659 mm (55 yrs +)

(kutlers study,JADA 1955)

MORNING GLORY APPEARANCE

• From the AC (minor apical diameter) the canal widens as it approaches the AF (major apical diameter).

• The space between the major and minor diameters has been described as funnel shaped or hyperbolic or the shape of a morning glory flower

SIGNIFICANCE OF WORKING LENGTH

1. Determines how far into the canal the instruments are placed & worked & thus how deeply the tissues, debris, metabolites are removed .

2. Limits the depth to which the canal filling may be placed.

3. Affects the degree of pain & discomfort that the patient will feel following the appointment.

4. If calculated within correct limits, it will play an important role in determining the success of the treatment & conversely, if calculated incorrectly, may cause the treatment to failure.

Failure to accurately determine & maintain working length

o Length too long can lead to :

1. Perforation through apical constriction

2. Overfilling or over extension3. Increased incidence of post

operative pain.4. Prolonged healing period.5. Lower success rate, owing to

incomplete regeneration of Cementum, Periodontal ligament and Alveolar bone

o Short working length can lead to :

1. Incomplete cleaning2. Underfilling3. Persistant discomfort4. Incomplete apical seal, apical

leakage which supports the existence of viable bacteria and contributes to a peri-radicular lesion

5. Lower success rate

APICAL ROOT ANATOMY & ITS IMPACT ON W.L

• Mandibular molar with apical root resorption due to a necrotic, infected dental pulp that destroyed the natural cemental-dentinal junction.

• Histologic evidence of apical resorption on external cementum (black arrows) and layering of cementum

Apical view of tooth with a C-shaped root formation. Note root morphology around the canal exits as cementum invaginates into the foramen. K-files (arrows) are exiting from the canal long before they reach the actual root surface. Actual foramina are much larger than canal exits, as indicated by widths of the red lines. Working length determination to the root length in these cases would be destructive to periapical tissue.

These potential anatomic variances have had a major impact on the precise region or location for determining the working length and termination of root canal instrumentation and obturation

• Prior to establishing a definitive working length, coronal access to the pulp chamber must provide a straight-line access into the canal orifice, thereby facilitating subsequent canal penetration.

• In anterior teeth, failure to remove the lingual ledge or incisal edge often impedes this straight-line access, resulting in lack of depth penetration to the CDJ, failure to locate all canals present, or instrument penetration into the canal wall with ledge formation.

• In posterior teeth, primarily molars, or multirooted premolars, failure to remove cervical ledges or bulges results in missed canals or binding of the penetrating instrument in the coronal third of the canal with ledge formation. The ability to penetrate

unimpeded to the CDJ is crucial to determining the working length of the root canal

HOW TO PREVENT LOSS IN W.L?

I II III

IV

HOW TO MEASURE W.L?

– In this era of improved illumination and magnification working length determination should be to the nearest one half millimeter,which is the maximum resolution of the naked eyein working distance .

– Measurement should be made from a secure reference point on the crown, that can be identified and monitored accurately, in close proximity to the straight line path of the instrument.

A silicon stop is a common aid for evaluating the working length measurement and returning to a secure reference point

Care must be taken to assure that the stop is placed on the file and measured at a right angle to the file. Otherwise, differences in length of a millimeter or more between files may occur, leading to either perforation and stripping of the apical foramen or inadequate cleaning and shaping of the apical seat, with corresponding loss of length

– Commercial stops, made of :i. Metalii. Silicon rubberiii. Plastic

Tear drop shaped

Round

– Advantages :1. Do not have to be removed during sterilization.2.In curved canals, to indicate the curvature - special tear -

shaped or marked rubber stops can be positioned with the direction of the curve placed in a pre-curved stainless steel instrument .

– Disadvantages :1.Time consuming.2.May move up and down the shaft which may lead to

preparations short or past the apical constriction

Metal or silicone stoppers to mark the working length. The stopper must clearly correspond to a cusp tip and rest firmly on it. For electronic determination of working length, the silicone stopper (left) is better than a metal stopper (right) because the metal stopper can cause a short circuit

– Length adjustment of the stop attachments should be made against the edge of a sterile metric ruler or a gauge made specifically for Endodontics.

– Eg - Guidener Endo - M - Bloc (Dentsply/Maillefer)

Has 32 depth guides in 2 rows. Front row indicators from 10-30 mm in 1mm increments.

• Some instruments have millimeter marking rings etched or grooved into the shaft .

• These act as a built-in ruler with the markings placed at 18, 19, 20, 21,22,23 & 24mm

METHODS OF WORKING LENGTH DETERMINATION

1. Radiographic method-

• Best’s method• Bregman’s method• Bramante’s method• Grossman formula• Ingles method• Weine’s method• Kutler’s method• Radiographic grid• Euclidean endometry• Xeroradiography• Direct digital

radiography

2. Non Radiographical methods-

•Digital tactile sense•Apical periodontal sensitivity•Electronic apex locator•Paper point method

SCHOOL OF THOUGHTS:1.Those who follow this concept say that the CDJ is impossible to locate clinically & radiographic apex is the only reproducible site available for length determination

2.Those who don’t follow this concept say the position of radiographic apex is not reproducible.its position depends on a number of factors like tooth angulation,position of film & film holder,adjacent anatomic structures,etc.

Techniques -BISECTING ANGLE TECHNIQUEPARALLELING TECHNIQUE

When two superimposed canals present, either-A.Take 2 individual radiographs with instrument placed in different canal at each time

B. Insert two different instrument- K file in one canal, H file in other canal and take radiographs at different angulations.

C. Apply SLOB rule, that is expose tooth from mesial or distal horizontal angle, canal which moves to same direction, is lingual where as canal which moves to opposite is buccal

i. BEST’S METHOD• Introduced in 1960

• A steel pin measuring 10 mm is fixed to the labial surface of root with utility wax,keeping the pin parallel to long axis of tooth & a radiograph is taken

• Then measurements were made with the help of a BW gauge

ii. BREGMAN’s METHOD• 25mm length flat probes are prepared & each has a steel

blade fixed with acrylic resin as a stop,leaving a free end of 10mm for placement into root canal

• This is placed in the tooth until the metallic end touches the incisal edge or cusp tip of the tooth. Then a radiographic is taken & following are measured –

ALT : apparent length of toothRLI : real length of instrumentALI : apparent length of instrument

RLT = RLI x ALT/ALI

III. BRAMANTE’S METHODIntroduced in 1974

Used stainless steel probes of various calibres & length

They were bent at one end at right angles & this bend is inserted partially into acrylic resin in such a manner that its internal surface is in flush with the resin surface contacting tooth surface

The probe is introduced in the canal such that the resin touches the incisal or cusp tip taking care to see that the bent segment of the probe would be parallel to mesiodistal diameter of crown thus making it possible to visualize on radiograph

• In this radiograph the reference points are as follows –

A : internal angle of intersection of incisal &radicular probe segment

B : apical end of probeC : tooth apex

Tooth length calculated in 2 ways :(I) Measure radiographic image length of

probe A-B,measuring radiographic image length of tooth from A-C & then measuring real length of probe

Now following equation is applied :CRD – real tooth lengthCRS – real probe lengthCAD – tooth length in radiographCAS – instrument length in radiograph

(II)Measure distance bet apical end of probe & radiographic apex.add or subtract to obtain correct WL

CRD = CRS x CAD/CAS

IV. GROSSMAN’S METHOD

CLT = KLI × ALT / ALI

• CLT= correct length of the tooth

•KLI= known length of the instrument in the tooth

•ALT= apparent length of the tooth on radiograph

•ALI= apparent length of the instrument on radiograph

DISADVANTAGES :

Wrong reading can occur because of :

1)Variations in angles of radiograph 2)Curved roots3)s-shaped , double curvature canals4)A small error will be multiplied

V. INGLE’S METHOD

This method recommended by Ingle and reviewed by Bramante and Berbert, and reported that this method is superior to other methods

VII. WEINE’S MODIFICATION

MODIFICATION IN LENGTH SUBTRACTION :

1)No resorption – subtract 1mm2)Periapical bone loss – subtract 1.5mm

3)Periapical bone loss+root apex resorption – subtract 2mm

VIII. KUTTLER’S METHOD• In young patients, average distance between minor and

major diameter is 0.524 mm where as in older patients its 0.66 mm

Advantages

•Minimal errors•Has shown many successful cases

Disadvantages

•Requires radiograph of highest quality•Time consuming •Complicated

IX. X-RAY GRID SYSYTEM

• Everett & Fixott in1963• Consists of lines 1mm apart running lengthwise &

crosswise.• Every 5th millimeter is accentuated by a heavier line to

make reading easier• Enameled copper wires are place in a Plexiglas & fixed

to a regular periapical film.• The grid is taped to a film to lie in-between the tooth &

film during exposure so patterns become in cooperated in the finished film

ADVANTAGES :•Simple method•No need for calculations

DISADVANTAGES :•Cannot be used if radiograph is bent during exposure

X. EUCLIDEAN ENDOMETRY

• Uses 2 geometrically distorted radiographs in determining real length of tooth.

• The 2 radiographs are taken with a cone fitted with a “updegraves XCP”(extension cone paralleling method)device at 2 different vertical angulations

• The actual tooth length is calculated by geometric principles from the length of the tooth in the two radiographs & the known verticular angular differences

XI. Walton and Torabinejad method

• Diagnostic film taken using paralleling technique & length is measured

• From this 3mm is subtracted to obtain estimated working length• Place stops at this length to a series of files• Then radiograph is taken• Corrected working length is determined by measuring the

discrepancy between the tip of the file and the radiographic apex• File is then adjusted 1-2mm short of the radiographic apex• No.8 , No.10 files are not used

XI. XERORADIOGRAPHY

• The term Xero-radiography is derived from the Greek word XEROS which literally means dry which differentiates this from the conventional photochemical system.

• Newer technique

XII. DIRECT DIGITAL RADIOGRAPHY

• In this digital image is formed which is represented by spatially distributed set of discrete sensors & pixels

<A> RVG :

• invented by Dr. Frances Mouyens in 1984

ADVANTAGES :•Low radiation dose•Darkroom is not required as instant image is viewed•Quality of the image is consistent•Greater exposure latitude•Image distortion from bent films is eliminated

DISADVANTAGES :•Expensive•Large disk space required to store images•Bulky sensor with cable attachment can make placement in mouth difficult•Soft tissue imaging is not very accurate

<b> phosphor imaging system

Image is captured on a phosphor plate as analogue information & converted into digital format when plate is processed

ADVANTAGES :1.Low radiation dose2.Instant images are formed3.Image manipulation facilites4.Receptor is same size as film

DISADVANTAGES :1.Expensive2.Slight inconvenience due to plastic wraps around phosphor plates3.Large disk space to store images

ADVANTAGES AND DISADVANTAGES OF RADIOGRAPHIC METHOD -

ADVANTAGES :1.Can see anatomy of tooth2.Can see curvature in roots3.Can see relationship b/w adjacent teeth & anatomic structures

DISADVANTAGES :1.Varies with different observers2.Superimposition of anatomic structures3.2D view of a 3D object4.Radiation exposure5.Cannot interpret if apical foramen has buccal or lingual exit6.Limited accuracy7.Time consuming

I) DIGITAL TACTILE SENSE

ADVANTAGES :

•Time saving

•No radiation exposure

DISADVANTAGES :

•In case of narrow canals one may feel increased resistance as file approaches apical 2-3mm•In case of teeth with immature apex,instrument can go periapically•In case of anatomical variations in apical

constriction,sclerosis, resorption, tooth type and age this method becomes unreliable

• Seidberg et al. reported an accuracy of just 64% using digital tactile sense

• This method should be considered supplementary to high-quality, carefully aligned, parallel, working length radiograph or an apex locator

II) PERIODONTAL SENSITIVITY TEST

• This method does not provide accurate readings, for example in case of narrow canals, instrument may feel increased resistance in apical 2-3mm.In immature apex, file goes beyond apex.

• In case of canals with necrotic pulp, instrument can pass beyond apical constriction, and in case of vital or inflamed pulp, pain may occur several mm before periapex is crossed by instrument.

III) PAPER POINT MEASUREMENT METHOD

This method, however, may give unreliable data :1. If the pulp not completely removed2. If the tooth is pulpless but a periapical lesion rich

in blood supply is present.3. If paper point is left in canal for a long time.

IV) ELECTRONIC APEX LOCATOR

In addition to radiography,tactile sensation has been used with questionable success , plus the drawbacks cited about radiographic length determination along with increasing concern about radiation exposure ,the introduction & development of apex locators was received with enthusiasm

These devices do not assess the position of the root apex and the name “electronic apex locator” is not appropriate ;

“electronic apical foramen locator” or “electronic root canal length measurement device” as a generic name would be

more appropriate.

• The ability to distinguish between minor & major diameter of apical terminus is the most important for creation of APICAL CONTROL ZONE.

• The apical control zone is the mechanical alteration of the apical terminus of root canal space that provides resistance & retension form to the obturating material against the condensation pressure of obturation

How does it work??

PARTS OF APEX LOCATOR :

– has four parts :-the lip clipthe file clipElectronic deviceCord which connects the above

three parts

USES OF APEX LOCATORS :

1. Provide objective information with high degree of accuracy

2. Used when apical portion of canal is constricted :• Impacted teeth• Zygomatic arch• Overlapping roots

• Excessive bone density3. Used in patients with gag refles and cannot tolerate x-ray films

4. In pregnant ladies to reduce radiation exposure

5. Useful in children,disabled patients,heavily sedated patients,etc

6. Can be used in teeth with incomplete root formation ,requiring apexification & to determine WL in primary teeth

7. Valuable tool for :i.Detecting site of root perforationsii.Testing pulp vitalityiii.Determination of perforations caused during post preparationiv.Detecting horizontal or vertical root fracturesv.Detecting internal or external resorption

Basic conditions for accuracy of eals :

1. Canal should be relatively dry2. Canal should be free from debris3. No cervical leakage4. No blockage or calcification of canals5. Proper contact of file with canal walls &

periapex

CLASSIFICATION :TYPES OF APEX LOCATORS

BASED ON DIRECT CURRENT BASED ON ALTERNATING CURRENT

ORIGINAL OHM METER USED BY

SUZUKI & SUNANDA

RESISTANCE TYPE•Root canal meter•Endometric

meter

IMPEDENCE TYPE•sonoexplorer FREQUENCY TYPE

SUBTRACTION TYPE•Endex

•Neosono ultima EZ

RATIO TYPE

2 FREQUENCIES•Root ZX

5 FREQUENCIES•AFA

•Apex finder

FIRST GENERATION APEX LOCATOR

• Resistance apex locators• Measures opposition to flow of direct current (ie

resistance)

• Eg : - root canal meter (Onuki Medical co.,japan) - endometric meter - endometric meter S II (Onuki Medical Co.)

• ADVANTAGES :1. Easily operated2. Digital readout3. Audible indication4. Detect perforation5. Can be used with K-file

• DISADVANTAGES :1. Requires a dry field2. Patient sensitivity3. Requires calibration4. Requires good contact with lip clip5. Cannot estimate beyond 2mm

SECOND GENERATION APEX LOCATOR

• Inoue introduced the concept of impedance based AL

• PRINCIPLE :measures opposition to flow of alternating current or impedence

egs : -Sonoexplorer -Apex finder -endo analyzer -Digipex -Digipex II -Exact-A-Pex

• ADVANTAGES :1.Does not require lip clip2.No patient sensitvity3.Analog meter4.Detects perforations

• DISADVANTAGES :1.No digital readout2.Difficult to operate3.Requires coated probes

THIRD GENERATION APEX LOCATORS

• Based on the fact that different sites in the canal give difference in impedance b/w high (8 KHz) & low(400 Hz) frequencies

• Difference in impedance is least in the CORONAL part & greatest at the CDJ

• As impedance is influenced by frequency of current flow these are also known as frequency dependent

• They should be called comparative impedance because they measure magnitudes of impedance which is converted to length information

• Egs :• Endex (original 3rd gen AL)• Root ZX (shaping & cleaning of canals with simultaneous monitoring

of WL)• Mark V plus• Co-pilot• Endo analyser 8005

• ADVANTAGES :1. Easy to operate2. Audible indication3. Can operate in presence of fluids4. Analogue readout5. Uses K-file

• DISADVANTAGES :1. Requires lip clip2. Chances of short circuit3. Needs fully charged battery4. Must calibrate each canal

FOURTH GENERATION APEX LOCATORS

• Measures resistance & capacitance separately• There can be different combination of values of

capacitance and resistance that provides the same foraminal reading

• This is broken down into primary components and measured separately for better accuracy and thus less chances of occurrence of errors

• Eg :neosono ultima ZX sybronendo

FIFTH GENERATION APEX LOCATORS

• It uses multiple frequencies rather than the dual frequencies of the third and fourth generations of apex locators, so it works in dry or wet canals and requires no calibration. Eg :RAYPEX

SIXTH GENERATION APEX LOCATORS

• Also called adaptive apex locators• Multi-frequency Operating System• Sound operated switching device can produce

different kinds of sound to indicate the different positions of file in the root canal. Dry and wet condition are also available for accurate reading

COMBINATION OF A.L & ENDODONTIC HANDPIECES

•Tri auto ZX

•Safy ZX

•Endy 7000

TRIAUTO ZX– Is cordless electric endodontic handpiece with built in

RootZx apex locator. The handpiece uses Ni-Ti rotary instruments that rotate at 280±50 rpm.

oAuto start-stop mechanismoAuto torque reverse mechanismoAutoapical reverse mechanism

The Root ZX is not capable of detecting the '0.5 mm from the foramen' position and thus, shouldonly be used to detect the major diameter. (i.e. Contrary to manufacturer claims,Apex Locators can only reliably determine when the file is actually touching the PDL at theapex. Set your working length 1 to 1.5 mm back from this length to avoid over-instrumentation).

Ounsi HF, Naaman A. In vitro evaluation of the reliability of the Root ZX electronic apexlocator. Int Endod J 1999;32:120-23.

ENDY 7000

•Endodontic handpiece connected to an endy apex locator•Reverses the rotation of the instrument when it reaches a point in the apical region preset by the clinician

SAFY ZX

•New development of ultrasonic systems•Handpiece + apex locator•Uses Root ZX to monitor location of file during instrumentation•Minimizes danger of over instrumentation

Comparison of accuracy of two electronic apex locators in the presence of various irrigants: An in

vitro study• Aim: This study was designed to compare the accuracy of Root ZX

and SybronEndo Mini EALs, in the presence of various irrigants.• Conclusion: The measurements of Root ZX in the presence of saline

& 1% NaOCl were closer to the AL and with no significant difference between them, while significant differences were observed with 2% CHX & 17% EDTA .Sybron Mini, in the presence of saline, 1% NaOCl and 17% EDTA, gave measurements which were shorter than the AL, whereas, in the presence of 2% CHX,WL was more accurate. Although statistically significant differences existed between the irrigants the majority of the readings were within the acceptable range of ±0.5 mm for both EALs. overall accuracy of measurements by Root ZX and Sybron Mini was 88.3% and 87.5%, respectively.

J Conserv Dent 2012;15:178-82

An in vitro evaluation of theaccuracy of the Root-ZX in the presence of

various agents.• The purpose of this study was to evaluate the accuracy of the Root

ZX in vitro in the presence of a variety of endodontic irrigants: Saline, 2% Lidocaine with 1:100,000 epi., 5.25% NaOCl, RC Prep & 3% hydrogen peroxide.

RESULTS : The most deviation (raw numbers) occurred with NaOCl, but it was not statistically significant. The Root ZX was able to consistently determine the location of the apical foramen (within approximately ±0.4mm) in the presence of any of the tested irrigants (only fill the canal, not the chamber during EAL use).

J Endodon 2001;27:209-11

Evaluation of working length determination methods: an in vivo / ex vivo study.

• This comparative study was done to determine the accuracy in measuring the working length of root canal using tactile method, electronic apex locator and radiographic method, in vivo and comparing the lengths so measured to the actual working length, ex vivo, after extraction.

• The results indicated that among the three methods, the electronic apex locator showed the highest accuracy and the highest reliability for working length determination

Indian J Dent Res. 2007 Apr-Jun;18(2):60-2

An in vivo evaluation of different methods of working length determination

• The purpose of this in vivo study was to compare the ability of digital tactile, digital radiographic and electronic methods to determine reliability in locating the apical constriction.

• RESULT : The percentage accuracy indicated that EAL method (Root ZX) shows maximum accuracy, i.e. 99.85% and digital tactile and digital radiographic method (DDR) showed 98.20 and 97.90% accuracy respectively

J Contemp Dent Pract. 2013 Jul 1;14(4):644-8

Comparison of working length determination using apex locator, conventional radiography and radiovisiography: an in vitro study.

• The purpose of this study was to compare the working length determination done using three methods, namely, apex locator (Foramatron D-10, Parkell), radiovisiography (Planmeca) and conventional radiography

• Result: The results revealed that all the three methods located the apex nearly as accurately as the actual root canal length obtained by histological ground sectioning, and among three methods apex locator being the closest to the actual root canal length.

• Journal of contemporary dental practice july 201213(4)550

Precision of Endodontic Working Length Measurements: A Pilot Investigation Comparing Cone-Beam Computed Tomography Scanning with Standard Measurement Techniques

• Study was conducted to evaluate the utility and precision of already existing limited CBCT scans in measuring the endodontic working length, and to compare it with standard clinical procedures

• Result suggested that great correlation was found between the endodontic working length as measured in the CBCT images and the EAL

JOE August 2011

Recent Advancements in Radiographic Method

• Laser Optical Disk Storage

• Cone beam computed tomography(CBCT)

(A) LASER OPTIC DISK STORAGE

• Laser optical disks are a useful medium to store radiographic images.

• An 8-inch optical disk is capable of storing up to 10,000 images with a 0.5 sec retrieval & display time.

• The image is recorded by a focused laser beam heating a thin tellurium sub oxide at specific points on the optical disk.

• When compared with normal radiographs, this method has been shown to produce images of superior diagnostic merit

(B) CONE BEAM COMPUTED TOMOGRAPHY

• Has been introduced that may prove to be more efficient and economical than either conventional tomography or computed tomography

• CBCT uses a round or rectangular cone shaped x ray beam centered on a 2-dimentional x ray sensor to scan a 360 degree rotation about the patients head

• The radiation dose delivered to the patient as aresult of one CBCT may be as little as 3% to 20% that of conventional CT scan.

The radiation dose delivered to the patient as aresult of one CBCT may be as little as 3% to 20% that of conventional CT scan.

THE FORGOTTEN DIMENSION : WORKING WIDTH

Introduction -• Haga found that mechanical preparation of root

canal to two sizes larger than the original was adequate

• Walton’s histologic study showed that canals that were instrumented to three sizes larger still were not thoroughly cleaned.

Dr. Tapish Garg et al. / IJRID Volume 3 Issue 4 Jul-Aug. 2013

The horizontal dimension of the root canal system is not only more complicated

than the vertical dimension (root canal length or working length) but also more difficult to investigate because the horizontal dimension

varies greatly at each vertical level

• “The initial and post instrumentation horizontal dimensions of the root canal system at WL and other levels” Dent Clin North Am. 2004 Jan;48(1):323-35.

• Minimum initial working width (Min IWW)• maximum final working width (Max FWW)

Current descriptions of the horizontal dimensions (crosssections)of the root canal –

1. Round (circular) : Max FWW equals Min IWW2. Oval : Max FWW is greater than Min IWW (upto two times more) 3. Long Oval : Max FWW is two or more times greater than Min IWW (upto four times more)4. Flattened (flat, ribbon) : Max FWW is four or more times greater than Min IWW.5. Irregular : cannot be defined by above

Significance…

FACTORS AFFECTING WORKING WIDTH DETERMINATION :

1. Canal Shape2. Canal Length3. Canal Taper4. Canal Curvature5. Canal Content6. Canal Wall Irregularities

Without the knowledge of above factors, “key hole or dumbbell” effects can occur with reaming or

modified reaming actions . So, Circumferential instrumentation can conform to the outline of

horizontal dimensions of root canal at different levels of canal.

Apical Widening Concepts by various authors:-

MAXILLARY TEETH RECOMMENDED APICAL ENLARGEMENT

Central incisor 70-90

Later incisor 60-80

Canine 50-70

First premolar One canal : 50-70Two canals : 35-50Three canals : 35

Second premolar One canal : 40-70Two canals : 35-50Three canals : 35

molars MB root with one canal : 35-50MB root with two canals : 35-45DB root : 40-60Palatal root : 60-100

TRONSTAD CONCEPT

Dr. Tapish Garg et al. / IJRID Volume 3 Issue 4 Jul-Aug. 2013

MANDIBULAR TEETH RECOMMENDED APICAL ENLARGEMENT

Incisors One canal : 35-60Two canals : 35-50

Canines 40-70

First premolar 40-70

Second premolar One canal : 40-70Two canals :35-50

molars Mesial root :35-45

Distal root One canal : 60-80Two canals : 40-60

• Few points against it:-• Weine et al stated that bringing every canal to

similar size is incorrect as some canals will be vastly overprepared and others will be insufficiently cleaned.

• Wu et al,2008 stated that since diameters of apical canals vary greatly in all tooth groups , no standard size is advisable for apical enlargement.

• Few points against it:-• Taking successively larger files to same length in

curved canal lead to apical lacerations or ledging

• Wu et al stated that first file to bind didn't reflect the apical diameter and aim of removing infected dentin may not be achieved.

WEINE’S CONCEPT

to sum up….• Not possible to determine canal diameter from

radiographs.CT scans are needed• Clinically, canal width – series of K-files suggested

by Ruddle• Depends on-file type & preflaring• Wu et al – diameter of the “binding” instrument

was smaller than canal diameter in 90% cases• Preflaring is essential (Tan & Messer)

So keeping in mind all the above mentioned factors, canals should be enlarged until necrotic dentin is removed and

search still goes on…

CONCLUSION

BIBLIOGRAPHY• Textbook of endodontics – Kohli• Advanced endodontics – Nageswar Rao• Textbook of Endodontics – Nisha Garg• Endodontic practices & principles.11th Edition - Grossman• Endodontics 5th & 6th Edition - John Ingle• Pathways of the pulp 10th edition - Stephen Cohen• Electronic apex locators- A Millennium Perspective

Endodontology VOL 17,ISSUE 2 ,Dec 2005 Pages 37-41• Jou DCNA vol 48;2004• JOE August 2011, Jan 2001• Journal of contemporary dental practice july 2012,(13)45-

50, 2013 Jul 1;14(4)