Apex locators Flashcards
Why do we determine WL?
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
Why is WL important
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
Anatomical apex
End of the root as visualised
Radiographic apex
Inaccurate why?
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
Major apical constriction
Widest point of foramen where it exits the root - entirely within cementum
Does not produce natural stop for filling material
Minor apical constrictions
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
CDJ
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
Methods of determining WL
Tactile feedback
Paper point technique
Radiographic determination of working length
Electronic apex locators
Tactile feed back
Essential
Made complicated by sclerosis, resorption and anatomical differences
PP system
Point where moisture is present is where apex is - from periodontium
paper points placed at incrementally shorter lengths until no moisture detected
Radiographic determination of WL
Paralleling technique
Apical constriction on average 0.5-1mm short of apex
Electronic apex locators
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
Mechanism of EAL
Electrical circuit forms and is completed when file contacts PDL
First generation apex locators
Resistance based
2nd gen
impedance based
3rd gen
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
4th gen
Two frequencies to detect the apical constriction
Problems with apex locators
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
Radiographs
Pre-op essential to obtain info about shape and anatomy
Access cavity
Ideally remove any metallic restorations prior to tx
No fluid
Moist canal
Irrigating media
Not really CHX
Apex/0 reading
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
At 0 reading file should be
At the apical constriction
Rechecking the WL
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
Locating the apex
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.
