Working Length and Instrumentation

Question 1

What is the working length?

Answer 1

Distance from a reference point (incisal edge, cusp tip) to the apical endpoint of your preparation (minor apical diameter)

Question 2

How far is the working length (on average) from the radiographic apex?

Answer 2

0.5-1 mm from radiographic apex

Question 3

Does the canal terminus always terminate at the root apex?

Answer 3

No

Question 4

What do we want to minimize when taking radiographs for working length?

Answer 4

angulation discrepancies (foreshortening/elongation)

Question 5

What is the provisional working length?

Answer 5

radiographic working length - 3mm

Question 6

What is the RCL?

Answer 6

Root canal length:

PWL - 3 +x = RCL -0.5 = WL

Question 7

Question 8

What is the problem with a WL that is too short?

Answer 8

remaining tissue/remaining bacterial biofilm

Question 9

What is the problem with a WL that is too long?

Answer 9

Loss of apical constriction/anatomy resulting in:

• possible extrusion of obturation material resulting in foreign body response (inflammation)
• loss of apical seal due to tear of apical anatomy