Vinay Final Working Length Determination

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` Following the completion of adequate coronal

access preparation, the most critical act inassuring the success of endo dontic therapy is the

accurate determination of working length prior to

the radicular preparation.



DEFINITION

` WL defined as ³the distance from a coronal

reference point to the point at which canal

preparation and obturation should

terminate´(Ingle)





` Should not change

b/w appointments

` undermined cusps &

fillings, they should

be reduced considerably

before access preparation



` Anatomic apex- is ³tip or end of root determinedmorphologically´

` Radiographic apex - is ³tip or end of rootdetermined radiographically´

` It is an artificial measurement which is

reproducible.



Apical constriction ± [minor diameter = CDJ]

` Apical portion of root canal which has narrowestdiameter [simon 1993]

` coincides with CDJ [Kuttler 1955]

Apical foramen - is main apical opening of the rootcanal which may be located away from anatomic or radiographic apex







` CDJ- is the region where cementum and dentin areunited

` Varies from tooth to tooth, root ± root, wall ± wall

` The point at which cemental surface terminates at or near the apex of tooth.

` It is not always coincide with apical constriction

` Location of CDJ ranges from 0.5-3mm short of anatomicapex





` WL determines how far into canal ,

` It effects degree of pain & discomfort which pt willexperience

` If placed in correct limits, it plays an important role indetermining the su ccess of treatment

` Before determining a definite WL, there should bestraight line access for the canal orifice for unobstructed penetration of instrument into apicalconstriction



` Apical perforation.

` Over instrumentation& over filling.

` Increased incidence of post operative pain.

` Prolonged healing time.

` Reduced success rate.



` Incomplete instrumentation& under filling

` Ledge formation.

` Apical percolation into the unfilled ³dead space´ at theapex.



R ADIOGR APHIC :

Ingle¶s method

Wein¶s method

Grossman's method

Radiovisiography

Xeroradiography

Tactile / apical periodontal sensitivity

Absorbent Paper point evaluation



Electronic Methods ( Apex locators) : Resistance Type

Impedance Type

Frequency Type



` 1) must be accurate

` 2)easily & readily performed

` 3) easily confirmed.

` Working knowledge of the average length of all

the teeth is foremost in order to prevent errors.



maxillary mandibular ` Central 21.8 20.8

` Lateral 23.1 22.6

` Canine 26 25

` 1st premolar 21.5 21.9` 2nd premolar 21.6 22.3

` 1st molar 21.3 21.9

` 2nd molar 21.7 22.4

` 3rd molar 17.1 18.5





Stop attachment

Endo-M-block



` Clinician should develop the mental image of the position of the rubber stop on the instrument shaft ,

` Any movement from that position should be

immediately detected & corrected

` where it meets the reference point on the tooth

` Essential to record the reference point & WL of each instrument in the pt¶s chart



Disadvantages of using rubber stops

`Not only is it time consuming, butrubber stops may move up or down the

shaft,

which may lead to preparations short or past the A. constriction



` Instruments have been developed with millimeter marking rings etched or grooved into the shaft of theinstrument

` These act as a built-in a ruler with the markings placed

at 18,19,20,22 & 24 mm

` Marking rings ±best coronal reference point on thetooth is at the cavo-incisal or cavo-occlusal angle

` The marking rings are necessary when rotary Ni-Tiinstruments are used



` Radiographic method of length determination

involves measurement of radiographic apex and

then subtracting a specific value from that length



` Measure the tooth on the

preoperative radiograph

` Subtract at least 1.0mm ³safetyallowance´ for possible imagedistortion or magnification

Set the endodontic ruler & adjust the

stop on the instrument at that level

INGLE¶S METHOD





` On radiograph,

measure thedifference b/w the

end of the instrument

& end of the root



` From the adjusted length

of tooth, subtract 1.0 mm

³safety factor ́ ± to confirm

with the apical terminationof the root at apical constriction

` New corrected length

&readjust the stop on theexploring instrument



` Because possibility of radiographic distortion, sharplycurving roots, & operator measuring error , aconfirmatory radiograph of the adjusted length is highlydesirable

` When the length of the tooth has been accuratelyconfirmed, reset the endodontic r u ler at this

measurement

` Record final WL and the coronal point of reference onthe pt¶s record

` Length of the tooth in a c u rved canal be reconfirmed after instrumentation is completed

` curved canal is straightened out by instrumentation



` The magnification effect of the radiograph.` Magnification of 2 mm (d u e to divergence of

the central beam) is allowed for all teeth.

` Thus: 26mm=length measured on radiograph.

` -1mm=difference between radiographic

apex and actual foramen.

` -2mm=magnification factor

23mm=estimated WL (acc to WALTON)



A periradicular lesion will resorb bone

and apical root structure.

Bone resorption is apparent, probably there isalso root resorption, Even though it may notapparent radio graphically

If there is root resorption, the apical constriction isprobably destroyed ± hence the shorter moveback up the canal





WL distance from the apex is determined

when radio graphically there is:

No bone or root resorption: 1 mm from apex

Bone but no root resorption: 1.5 mm from

apex

` Bone and root resorption: 2 mm from



` After working to estimated WL with size

15 or 20 file a radiograph is taken.

Corrected

WLis determined bymeasuring the discrepancy between the

tip of the file and the radiographic apex.

` The file is then adjusted to 1 to 2 mmshort of the radiographic apex.





` Buccal object rule basic concept is vertical or horizontalangulation of X-ray tube changes, the object buccal or

closest to tube head moves to opposite side of radiograph compared to the lingual object

` To separate the buccal & lingual roots to visualize the WL

tube head should be moved from a20

degreem

esialangulation

` Buccal root to the opposite or distal side of radiogrph & lingual root on mesial side (SLOB)

` Misinterpretation still possible

` This can be reduced by using different types of files (K,H)or different file sizes in different canals



Actual lengthof the tooth =

GROSSMAN·S Method

Actual length of the instrument xapparent length of tooth in radiograph

apparent length of instrument in

radiograph



` If the coronal portion of the canal is not constricted, an experiencedclinician may detect an increase in resistance as the file approachesthe apical 2-3mm

` Accuracy is 64%` Inexact` Ineffective with immature apex` Highly inaccurate if the canal i s constricted throughout its entire

length/ if the canal has excessive curvature` Considered as supplementary to high quality, carefully aligned,

parallel,WL radiographs or an apex locator ` Survey few general dentist & no endodontists trust` Even most experienced specialist would be prudent to use 2 or

more methods



Limitations of tactile methods :-

When coronal portion is constricted ( i.e coronal 2/3rd )the clinician cannot discern the apical anatomy with

accuracy ,since contacts in the cervical regions that

interfere with and often mask contacts in the apical area.

This may be over come by coronal 2/3rd preparation (radicular access /step down ) to improve the quality of

tactile information .



` When the entire length of canal is constricted.

` When the canal has excessive /unusual curvature

.` Ineffective in root canals with an immature apex

,root resorption .

` By itself this method is often inexact , hence canbe used as a supplementary to more precise

methods .



` Based on pt response to pain, doesn¶t meet the idealmethod

` Therapy has gained a notorious reputation for being

painful,&

it is incumbent on dentists to avoidperpetuating the fear of endodontists by inserting anendodontic instrument & using the pt pain reaction todetermine WL

` Inflamed tissue, HP developed inside the canal may

cause moderate to severe, instantaneous pain

` Little useful information but considerable damage isdone to the pt¶s trust



Supplementary method useful in

I mmat u re apex ( wide open ) ± reliable means of

working length estimation ,by gently passing the

blunt end of a paper point into the canal after profound anesthesia has been achieved

` Moisture or blood on the apical portion that

passes Beyond the apex may be an estimation

of WL or the junction between the root apex andthe bone.



R esorption /perforation ±

` Cases where apical constriction has been lost (without free bleeding or suppuration ) the

moisture/ blood is estimate of amount of

overextended preparation .

Type : -

` Sterilized paper points (Pre-Sterile ),Color

coded ( IS

O size).` Newer Calibrated (mm markings

18,19,20,22and 26).





All apex locators function by

using human body to complete

electric circuit.

One side of apex locators

circuits connected to an

endodontic instrument and other

connected to patients body

How does it work ?



` Designed to determine canal length by

³reading´ when vital tissue has been

reached by the file tip at the apical

foramen.





` Resistance apex locators, measure apposition tothe flow of direct current or resistance

` Sono-explorer was imported from Japan by

Amadent

` Today most of the 1st gen. Apex Location devicesare off the market



RESISTANCE TYPE

` Measured the differencein resistance between thepulp and periodontalligament (6k)

` Uses direct current

` Requires dry field for accurate measurements



` Advantages:

` Easy to operate

` Digital read out` Audible indication.

` Disadvantages:

` Requires dry field.

` can not be estimated beyond 2mm.` Requires calibration.

` Pt sensitivity.

` Requires lip clip with good contact.





IMPEDANCE TYPE

` Based on impedance

measurements at same or different frequencies

` Uses alternating current

` Can be used in wet field.` Uses insulated probes.



` Based on principle of impedance

` Impedance systems are based on the theory

that the root canal, a long hollow tube, develops

an electrical impedance, caused by transparentdentin deposition which exhibits a sharp

decrease at the cementodentinal junction which

can be measured electrically



` Advantages:

` Operates in fluid environment

` Analoge meter ` No pt sensitivity

` No lip clip required.

` Disadvantages:

Difficult to operate.

No digital read out.

Requires coated probes.



` Impedence Apex Locators, measure apposition to theflow of alternating current

` Sono explorer - developed by Inoue` Apex finder ` Endo analyzer ` Digipex` Digipex ± ll` Exact- A-Pex` Foramatron iv +` Dio



` Flashing LED light and

a digital LED display

Small,Lightweight,

Inexpensive





FREQUENCYDEPENDENT M u ltiple freq u ency type

` Uses multiple frequencies to determine theposition of the file in the canal

` Uses alternating current

` Difference method/ratio method

` Can be used in wet/dry fields

` Most accurate among the three



` Measures the impedance difference between two

frequencies or the ratio of two electrical impedance to

define position of file.

Difference method : -

Works by comparing the difference in impedance using the

relative

value of two alternating currents at frequency of 1 and 5kHz .

As file moves towards the apex , the difference becomes

greater and

shows the greatest value at the apical constricture allowing for measurement of that location

For example - Endex



` Ratio method : -

` Measures the impedance of 0.4 kHz and 8 khz at thesame time .

` Calculates the quotient of impedance and expressesthe quotient in terms of position of the file inside the

canalThis quotient values are not affected by the electrical

condition inside the canal

In addition it is unnecessary to calibrate this device each

time because the microprocessor automatically controls the

calculated quotient to the a relationship with the file

position and the digital read out .

For example- Root ZX



` Frequency dependent, impedence of a given circuitmay be substantially influenced by the frequency of thecurrent flow

` Endex` Neosono ultimo Ez apex locator ` Mark v plus` JUSTWO orJUSTY II` APEX FINDER A.F. A.` Endo Analyzer 8005 ( AL& PT)` ROOT ZX` Tri Auto ZX



` Advantages:

` Easy to operate.

` Operates in fluid environment.

` Analoge read-out, audible indication

` Rechargeable.

`

Disadvantages:

` Can be short circuted.

` Requires a lip clip with good lip contact.



` Uses dual- frequency &comparative impedence

principlesMeasures 2-impedences

at 2- frequencies (8 and 0.4 kHz)



FREQUENCY DEPENDENT

T wo frequency type

Eg:Elements diagnostic system

(sybron endo )

P ropex -iv



MULTI FREQUENCY

DEPENDENT

A pex locator with built

in pulp tester

Eg:

Mini apex loator

Neosono Co- pilot

.

i - pex

Root - pi



`

Tri A

uto ZX` Endy ZX

` Sofy ZX



` Combination of Apex Locator & Endodontic Handpiece

` Cordless, automatic endodontichandpiece with a built in root ZXapex locator



SOLF Y ZX` Combination of an Ultrasonic

hand piece and a Root ZX

` Designed to preventoverinstrumentation bystopping the ultrasonicvibration when files reachesthe required location.

APEX LOCATOR WITHULTRA SONIC HANDPIECE



APEX LOC ATOR WITH

BUILT IN PULP TESTER



` Provide objective infor mation with high degree of accuracy

` Useful in conditions where apical portion i s obsr u cted by anatomicstructures such as zygomatic arch, tori, exostoses etc.

` Useful in patients with gag reflex

` Pregnant patients

` Root perforations, resorptions, root fracture

` RCT of teeth with incomplete root formation



` Accurate

` Objective measurements

` Easy & fast

` Reduction of exposure to radiation

` Perforations can be detected

` Can measure pulp space exactly to the constriction

` Can detect resorption & root fracture





RADIO VISIO

GRAPHY





` A rigid chargedcoupled device (CCD)connected by a cableto computer, monitor & printer.



` The ³Radio´ component x ray unit: Consists of a

hypersensitive intra oral sensor and a

conventional x-ray unit



` The ³³ VISIO VISIO´́ portion: Consists of a video monitor

and display processing unit



` Is a high resolution video printer that instantly

provides a hard copy of the screen image using

the same video signal.

The ³³GRAPHY GRAPHY ́́ component:

DIRECT DIGITAL RADIOGRAPHY



Advantages :

q time between exposure andinterpretation.

q radiation dose

Digital image enhancement

Patients can more easily, view andappreciate

Patients acceptance

Disadvantages :

Cost

Small sensor cant capture

Image storage

Faded image

DIR ECT DIGIT AL RADIOGRAPHY



` Determination of working length

U SES IN ENDODONTICS



` Amethod of obtaining a digital image in which an

existing radiograph is scanned & converted in to a

digital form using a CCD.



1. Improved disease detection

2. Quantification of disease change over time

3. 2D/3D reconstruction of the following.

4. Improved patient education.5. Remote electronic consultation

(tele dentistry)



` Xerographic copying process

` Both soft and hard tissues

` Equipment :

electrostatically charged aluminium plate

Selective discharge on selenium

Latent image pattern

Spraying toner Hard copyHard copy

X ray photons



XeroradiographyXeroradiography

Advantages :Advantages :

Fine detail

Pronounced edge enhancement

High image contrast

Low exposure

Disadvantages :Disadvantages :

Electro current ± discomfort

Process of development ± 15 min



` There is no statistically significant difference in WL

estimation accuracy



` Straight line access, modifications required to permit the

instrument to penetrate, unimpeded, to the apicalconstriction

` Loss of working length during cleaning & shaping can befrustating procedural error

` Monitor the working length periodically, working length maychange as a curved canal is straightened

` Loss may also related to be the accumulation of dentinal &pulpal dedris in the apical 2-3mm of the canal or

` Failing to maintain foramen patency, skipping instrumentsizes, or f ailing to irrigate the apical 1/3rd adequately



` Occationally, WL is lost owing to ledge formation or to

instrument separation and blockage of the canal

` Apical constriction:- not only narrowest part of the canal buta morphologic landmark that can help to improve the apical seal when the canal is obturated

` Failure to accurately determine & maintain WL- length beingtoo long & may lead to perforation through the A. constriction

` Destruction of constriction may lead to overf illing / overextension & an increased incident of post operative pain

` Prolonged healing period & lower success rate owing toincomplete regeneration of cementum, PDL & A.bone



` Failure to determine & maintain WL accurately cleaning &

shaping short of the apical constriction

` Incomplete cleaning & underfilling may cause persistentdiscomfort, often associated with an incomplete apical seal

` A. leakage may occur into the uncleaned & unfilled spaceshort of A. constriction leakage supports the continued existence of viable bacteria- contributes to a continuedperiradicular lesion & lowered rate of success

` Measurement should be made from a secure ref erence pointon the crown, in close proximity to the straight-line path of the instrument, a point that can be identif ied & monitoredaccurately





Definition of the working width

`

MinlWW(N)- M

inimal initial horizontal dimension Nmm short of working length.

` MinlWW0 - Minimal initial horizontal dimension at

working length.` MinlWW1 - Minimal initial horizontal dimension 1

mm short of working length

` MinlWW2 - Minimal initial horizontal dimension 2mm short of working length.

` MinFWW(N) - Minimal final horizontal dimension N

h f ki l h



mm short of working length.

` MinFWW0 - Minimal final horizontal dimension atworking length.

` MinFWW1 - Minimal final horizontal dimension 1


` MinFWW2 - Minimal final horizontal dimension 2


` MaxFWW(N) Maximal final horizontal dimension N



` MaxFWW(N) - Maximal final horizontal dimension N


` MaxFWW0 - Maximal final horizontal dimension at

working length.

` MaxFWW1 - Maximal final horizontal dimension1mm short of working length

` MaxFWW2 - Maximal final horizontal dimension

2mm short of working length



` Round (circular) : max I WW equals min IWW .

` Oval : maxiww is greater than miniww (upto 2 timesmore).

` Long oval : max i ww is two or more times greater thanmin I WW ( up to 4 times more).

` Flattened (flat , ribbon ) : Max I WW is four or moretimes greater than Min IWW.

` Irregular : cannot be defined by 1- 4.

Determination of initial working width at working length



Determination of initial working width at working length(initial apical file determination ± estimation of initialcanal diameter):-

` Three critical parameters should be taken intoconsideration in the course of cleaning and shaping theroot canal system.

1) length of the canal.

2) taper of the preparation.

3) horizontal dimension of the preparation

l l th



` canal length :

when using an instrument to gauge working length, the longer

the canal, greater the frictional resistance which may affectthe clinician¶s tactile sense.

If the coronal flare is too conservative then the shaft of theinstrument may engage the canal wall giving premature or false conclusion as to the WW.

` canal taper

Any tapering discrepancy between the gauging instrument andcanal may lead to an early instrument engagement causing afalse sensation of apical binding .

The last 3- 5 mm of the canal can have parallel walls makingcorrect determination of IWW difficult.

` canal curvature :

Th t f th t l b



The curvature of the root canal can becategorized into two dimensional, three dimensional,small radius . large radius and double curvature (s-

shaped , bayonet shaped ).

Each of these curvatures or their combination can causedeflection of gauging instrument.

` canal content:

The content of the root canal may be fibrousor calcified in the nature. The mixed canal contents cancreate different degrees of functional resistance against thegauging instrument affecting tactile sense.

` Canal wall irregularities:



g

Like attached pulp stones ,denticles reparative

dentin , resorption can create convexities or concavities

on the canal wall surface.

` instrument for determining initial working width:

The rigidity, flexibility and tapering of the

instrument used for determining IWW can affect theaccuracy.

` Eliminating or minimizing the influence of affecting



factors.

By being aware of the existence of the affecting factors

in IWW determination.

Early coronal flaring and additional canal flaring to

ensure effective irrigation and to minimize anyinterference with tactile sensation.

Careful selection of the adequate instrument having

maximal flexibility and minimal taper may avoid

interference.

Root canal preparation should follow the exact outline of



the horizontal dimension of root canal especially for long

oval and flattened root canal.

`Reaming action may result in key hole or dumb bell

demonstrating unprepared parts of root canal.

Circumferential instrumentation can confirm to outline of

horizontal dimension of the root canal at different level of canal



` Accurate determination of working length is

essential to endodontic & restorative success.` Depends on proper knowledge of root canal

anatomy, direct visualization and access to theroot canal system, accurate radiographic

technique, interpretation, exact measuringtechniques.

` Effectively using various combinations of thesetechniques will lead to significant mastery of

even most difficult root canal system.

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Vinay Final Working Length Determination