Length Determination

Question 1

What is the error margin for length determination?

Answer 1

0.25-0.5mm

Question 2

What is the optimum working length for best chance of success?

Answer 2

0-2mm from radiographic apex

Question 3

What is the mechanism of action of apex locators?

Answer 3

• File clip is clipped onto endo file + lip clip placed in mouth
• Weak current is generated between clips and locator detects resistance between the clips
• Variable resistance while passing through canal impedes flow
• Once reach apex resistance decreases suddenly which is detected by locator

Question 4

What are some advantages of apex locators?

Answer 4

• More accurate than trying to estimate from radiograph
• Decreased radiation dose

-Perforations easily detected

• Can apex locate during instrumentation phase: better control with curved canals as early detection of decreased working length + decreased open apex
• Confident cleaning and shaping of apex
• Good control of apical constriction

Question 5

What are some disadvantages of apex locators?

Answer 5

• False conduction from wet field and metallic restorations and vertical root fractures + lateral canals
• If unable to reach apex can not make accurate measurement can not be made
• If open apex can get variable readings
• Only an additional tool, still need radiographs
• Do not use of patient has pacemaker
• If go to deep due to forgetting to check battery may cause damage to IAN on lower teeth

Question 6

How do you check the corrected working length?

Answer 6

• Set rubber stopper to estimated working length
• Place into canal such that rubber stopper at landmark
• Take image and assess if correct position