Apex locators

Question 1

Why do we determine WL?

Answer 1

To effectively undertake a root canal treatment, the clinician must accurately determine the apical limit of the root canal system as well as the position of the canal terminus

Question 2

Why is WL important

Answer 2

Studies have shown that root fillings which extend beyond the apex or are more then 2mm short of the apex are associated with a higher chance of failure

Question 3

Anatomical apex

Answer 3

End of the root as visualised

Question 4

Radiographic apex

Inaccurate why?

Answer 4

Similar to anatomical but determined by radiograph
Foramen often located to one side of apex
Varies from 0.3-0.6mm up to 3mm away from RA
Deposition of cementum can cause further discrepancies
Pathology can also change position

Question 5

Major apical constriction

Answer 5

Widest point of foramen where it exits the root - entirely within cementum
Does not produce natural stop for filling material

Question 6

Minor apical constrictions

Answer 6

Narrowest point of foramen AKA APICAL CONSTRICTION
Cementum narrows from major to minor
Variable location
usually 0.5-1mm short of the RA
At or close to point where cementum fuses with the dentine
reference point

Question 7

CDJ

Answer 7

Point where cementum fuses with radicular dentine
Considered to be point where the RC system FINISHES and periodontium begins
Ideal limit of root canal treatment
Can only be detected histologically

Question 8

Methods of determining WL

Answer 8

Tactile feedback
Paper point technique
Radiographic determination of working length
Electronic apex locators

Question 9

Tactile feed back

Answer 9

Essential

Made complicated by sclerosis, resorption and anatomical differences

Question 10

PP system

Answer 10

Point where moisture is present is where apex is - from periodontium
paper points placed at incrementally shorter lengths until no moisture detected

Question 11

Radiographic determination of WL

Answer 11

Paralleling technique

Apical constriction on average 0.5-1mm short of apex

Question 12

Electronic apex locators

Answer 12

Modern locators very reliable
Utilises resistance of root canal and PDL
Will show redline when it’s indicating file has popped through AC - deduct 0.5mm from this reading

Question 13

Mechanism of EAL

Answer 13

Electrical circuit forms and is completed when file contacts PDL

Question 14

First generation apex locators

Answer 14

Resistance based

Question 15

2nd gen

Answer 15

impedance based

Question 16

3rd gen

Answer 16

multiple frequencies to determine distance to end of canal
improved in accuracy by the presence of electrolytes and accuracy is decreased if canal is dry
83-100% accuracy

Question 17

4th gen

Answer 17

Two frequencies to detect the apical constriction

Question 18

Problems with apex locators

Answer 18

Metallic restorations will short circuit AL
Place fillings and ensure no contact with metal and chamber is not flooded with irrigating solution
Perforations will trigger an apex response when file touches perforation
Prevents an accurate apex locator reading from a perforated canal until repaired

Question 19

Radiographs

Answer 19

Pre-op essential to obtain info about shape and anatomy

Question 20

Access cavity

Answer 20

Ideally remove any metallic restorations prior to tx
No fluid
Moist canal

Question 21

Irrigating media

Answer 21

Not really CHX

Question 22

Apex/0 reading

Answer 22

Advance the file until the visual display reads ‘apex’ or ‘0’
 The apex locator is most accurate when it is giving an ‘apex’ or ‘0’ reading and contacting the PDL
 Earlier readings (such as ‘0.5’ or ‘1’) do not indicate the distance in mm from the apex
 Therefore, the best approach is to advance the file until it gives an ‘apex’ or ‘0’ reading, then manually subtract 0.5mm from the length
 This will ensure the file is within the root canal, but still close to the PDL

Question 23

At 0 reading file should be

Answer 23

At the apical constriction

Question 24

Rechecking the WL

Answer 24

Recheck with AL AFTER coronal 2/3 have been shaped
WL will decrease from the initial reading due to a decrease in canal curvature
Must be checked prior to shaping apical terminus

Question 25

Locating the apex

Answer 25

Careful study of high quality radiographs.
 Magnification of radiographs and blocking out of
extraneous light.
 Keeping apical anatomy foremost in your mind.
 Use tactile sense to locate apical constriction.
 Observe blood/fluids on instrument tip or anywhere on a paper point.
 Use and understand your apex locator.