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Working Length Determination, Endodontic Radiology

Today we will talk about working length determination , radiology in endodontic

, why we need to have working length and why its important.

We will know all of these things in todays lecture.

We will not be able to do any proper work in endodontic if you dont know

1- where you are working 2- how long you need to go deep into the canal

S0 at first we need to have a reference point to measure the distance , the

reference point should be stable.

Stable reference pointmeans that it doesnt have undermined caries which

may affect this point so it will be lost in the next visit [ so you will lose it and you

have to start again ] .

USUALLY , the reference point for : anterior teeth is the incisal edge

Posterior teeth is tip of the cusp

*You should record your reference point location and mark the working length on

the file.

Optimal length

Usually , the opening or apical foramen of the canal doesnt locate exactly at the

tip of the root , so if you have a radiograph you measure the length of the tooth

from the incisal edge to the radiographic apex [ anatomical apex ] this will be

the length of the tooth .

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If we calculate the location of the apical foramen where it locates , usually it is up

to 2mm from the anatomical apex.

SO >> if we find out that our working length is 22mm when measure it on the

radiograph , we should subtract 2mm and we will work on 20mm.

The length that you should work on = the working length [which is the length you

have measured for the whole tooth] - 2mm

There are some terms that you will get in contact while you are working in root

canal .

FIRST The apical foramen : as we said before it isnt always on the tip of the

root so it could be on the side.

THENAnatomical apex : which is the final end of the root or the tip of the

root.

Apical constriction : you will see what do we mean by apical construction

As you see in fallowing picture :

Anatomical apex

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If we said that our working length will start from the anatomical apex thiswill be mistaken ; because when we insert our files into the canal we will

be pushing infected materials and necrotic tissues beyond the the apex, sowe should confined our instrumentation into the canal space only.

Theoretically we said that we need to end our preparation to the apicalconstriction but it is not always present , however we need to finish our

obturation at this point to get safety distance not to push infected material

beyond the apex.

First of all as we said before , we should have a pre-operative

radiograph which one of its uses to estimate the working length and as we

said we should subtract 2mm ( 1mmfor apical constriction and the other

1mmfor magnification error )

Once you measure the length of this tooth , you take a file which can goeasily into the canal passively and you mark the length that you measured

using the ruler.

( ex : if you measure the length of central incisor and it was 22mm ,so youneed to :

mark the file using a rubber stopper which comes with the file [ yellow in

color ].

slide the rubber stopper down to 20mm length.

insert the file into the canal.

let the rubber stopper seat physically on your reference point [ to be in

touch physically with your reference point ].

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This is film hogar [sry Im not sure of the spelling ] which especially used in

endodontic , it has empty pops inside.

Rubber stopper

To obtain accurate measurements of your working length , we need to take

radio graph after inserting the file into the tooth to make sure of our

measurements.

for our measurements on the x-ray film to be reliable we should use the

minimum file size .

the minimum size of the file for working length determination should be 20

( because the tip of the file beyond or smaller than this will not appear in the

radio graph specially in anterior teeth ) .

We said before that we have to place the rubber dam on the tooth beforeinserting any file.

It is imperative that the rubber dam be left in place during working lengthdetermination to ensure an aseptic environment and to protect the

patient from swallowing or aspirating instruments.

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There is something called paralleling technique in taking radio graphs we

use it in endodontic to make the length of the tooth near accurate on the film and

to make everything on the tooth clear.

According to the bookthis idea is specific to maxillary teeth which is toput the film on the opposite side of the median raphe of the palate.

Ex: if you want to take a radio graph for upper right molar , so you have toput the film beyond the median raphe of the palate on the left side.

After we took the estimated working length , inserted the file into the

canal & took a radio graph we need to look and measure and see where

does the tip locate.

If its longer than apical constriction we need to estimate or calculate how much

its longer and correct it.

[ we need to calculate and measure how much the difference from theanatomical apex , If its 1mm for example we add or subtract according to

the condition )

If the difference more than 3mm , we need to take another radio graph.

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This picture shows the variations in the calculations of corrected working

length according to the condition of the apical area

So , if we have any kind of bone resorption but there is no apical resotption=> we subtract 1.5 instead of 1

But if there is bone resorption as well as apical resorption=>we subtract 2

sometimes we have some causes that prevent us from taking a radio graph and

we cant proceed doing RCT without knowing the working length , So what we

have to do ?

There is something called apex locator this is a new technology that wasfound to tell us where is the apex of that canal and most of the time it is

really accurate , but we cant rely on this device only.

So , however you took the reading by the apex locator , you need toconfirm it with radio graph.

They say that there are some contraindications of using the apex locatorbecause it uses electrical signals that may affect patients with cardiac

pacemakers. [ its not true all the time ]

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IMPORTANCE OF RADIOGRAPHY IN ENDODONTI

endodontic radiology needs kind of modification or manipulation of

instruments or the beam .

Radiographs perform essential functions in three areas. However, they have

limitations that require special approaches.

A single radiograph is a 2-dimensional shadow of a 3-dimensional object.

For maximum information, the third dimension must be visualized andinterpreted.

The three general areas of application are :

- diagnosis

( Root and pulp anatomy , Identifying Pathosis & Characterizing normal

structures. )

-treatment

( Determinig working length , Moving superimposed structure

Locating canals & Evaluating obturation )

- recall

( Identifying new pathosis & Evaluating Healing )

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In the two pictures above :

Pic (A)this radio graph was taken in 90 degrees , so you will see two canals but

there is a shadow for another root .

Pic (B)this is when we took another radio graph with mesial angulations 20

degrees , we saw the small second MB canal which is arrowed by red.

A

this is a premolar where you can see a large radiolucency in the center whichrefers to ( pulp tissue ) and then suddenly this radiolucency will break and

become narrow which means a bifurcation area at that part (another root canal)

So >> you need to take another radio graph with an angulations in order to

separate these two objects from each other and to measure them.

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Bthe same tooth but the x-ray was taken from the mesial side but in the

patients mouth we cant take it mesial because there is another tooth.

So this radio graph to show the deference between radio graph according to

the side the it was taken from it.

when two objects and the film are in a fixed position and the radiation source

(cone) is moved, images of both objects move in the opposite direction.

So , they discover a rule which is calledSLOB Rule

(Same Lingual Opposite Buccal)

* same and opposite in comparison with the direction of angulations or movemen

of the cone.

SLOB Rulemeans when you see the two canals in the film [ assuming that the

tooth is upper and the radio graph was taken mesially ]

The mesial canal on the film is the lingual canal on the tooth

The opposite one will be buccal

In the above picture :Central (x-ray) beam passing directly through a root containing two canals

will superimpose the canals on the film.

When the cone is shifted to the mesial or distal aspect, the lingual objectwill move in the same direction as the cone; the buccal object will move in

the opposite direction (SLOB rule).

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(*actually they both move opposite to the direction of moving the cone

but the final result will be the SLOB

* The buccal shifts furthest away.

Ahere we cant see separated apex , but when we shift it mesially it

appears as two different tips

In the lower we always do distal shift

*but anterior of the lower we domesial shift

In the upper we always domesial shift

Canine right angle

Premolarsmesial shift (20 degrees)

Molars distal shift (20 degrees)

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PLEASE GO BACK TO THE SLIDES.

forgive me for any mistake

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