workinglength lect 3

Working Length Working Length DeterminationDetermination

Presented byPresented by::Ameer H, AL-AmeedeeAmeer H, AL-AmeedeePh.D in Operative and Esthatic Ph.D in Operative and Esthatic DentistryDentistry

Radiographic LengthRadiographic LengthThe length of the tooth as it appears on the

radiograph.Radiographs are probably the most common method used for determining working length. Although radiographs are important in endodontic treatment, primarily for assessing canal curvature and root form, they have limitations regarding length determination. This is because the radiographic apex (the end of the root on the radiograph) and canal terminus (where the canal exits the root) often do not coincide. One absolute that can be proven by a radiograph is when a file is out of the apex. At that point, there is no doubt you are patent. If the file is right at the radiographic apex, you are usually patent. If the file is short of the apex on a radiograph, you still might be patent. This is the reason that radiographs can be used to confirm patency, but are not the most accurate method for determining working length.

Electronic apex locatorsElectronic apex locatorsAside from the surgical microscope, the electronic apex locator is the most valuable piece of endodontic equipment in my office. When used correctly, an electronic apex locator is the most accurate and efficient method for determining endodontic working length. When used incorrectly, it can be an unreliable source of frustration. Obtaining a consistent, reliable apex locator reading is necessary for developing confidence in its use.

© 2006 J.Bringas, DMD, DDS, MS

Apex locators are Apex locators are less accurate at less accurate at showing showing how close the file ishow close the file is to the canal to the canal terminus.terminus.

Final Working LengthFinal Working Length

is determined to be -1 mm from the anatomical apex as measured from the

working length (WL) radiograph.

THIS IS THE LENGTH TO WHICH THE CANAL WILL BE CLEANED & SHAPED

AND OBTURATED.

Radiographic length minus 1mm.

Select a Reference PointSelect a Reference Point

Take a Preoperative RadiographTake a Preoperative Radiograph

Preoperative RadiographPreoperative Radiograph

Measure the radiographic length.

Reference pt.

Apex

Measure the radiographic Measure the radiographic lengthlength

Ex. 22mm

Compute for Estimated Compute for Estimated LengthLength

Estimated Length is radiographic length minus 1mm.

Ex. 22mm - 1mm = 21mm

Treatment RecordTreatment Record


Incisal edge

21 mm

Set #15 file to Estimated Set #15 file to Estimated LengthLength

Insert the file into the canal to stopper length and take a

radiograph at this time.

Working Length Working Length RadiographRadiograph

The best case scenario is that there is no radiographic distortion with the preoperative radiograph.

The working length radiograph should show that the file ends 1mm short of the apex.


File appears to end 1mm short of the apex.

No need to adjust the final working length.


In this case, estimated working length is equal to the final working length.

EWL = FWLRecord FWL


Incisal edge

21 mm

21 mm


Sometimes, the radiograph shows that the file extends more apical than the ideal.

This means that the EWL is long.

Deduct this discrepancy from your EWL to arrive at the Final Working Length.


Example: EWL=21mm

Since radiograph shows that file is 1mm long then…

1mm


Example:EWL – 1mm =

FWL

21mm – 1mm = 20mm

1mm


Incisal edge

21 mm

20 mm


Sometimes, the radiograph shows that the file does not reach the ideal length.

This means that the EWL is short.

Add this discrepancy to your EWL to arrive at the Final Working Length.


Example:EWL=21mm

Since radiograph shows that file is 0.5mm short then…

0.5mm


Example:EWL+0.5

mm=FWL

21mm+0.5mm=21.5mm

0.5mm


Incisal edge

21 mm

21.5 mm


If the radiograph shows that the discrepancy is more than 2mm, then a new radiograph should be taken after computing for the working length.

Unacceptable Unacceptable discrepancydiscrepancy

workinglength lect 3

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