Here’s a case we finished today. The mesial canals were tight apically but the ML maintained a solid block at the canal terminus. Turns out it was the mesial surface of the distal root. Nice distinct mesial roots. And no, that’s not a busted instrument at the apex of MB.

To put this topic to rest, I took the same tooth from earlier and xrayed it from two directions with 90 degrees rotation in between. The first film shows a file in the tooth just a bit past ideal working length (if your goal is the radiographic apex). The file is a little long past the root surface.

The second film shows the tooth rotated 90 degrees clockwise. No change in relative position of the file has taken place but it appears much further out the root than before.

This is a fairly simple concept, but is part of so much debate in Endodontics…

“…and I’ve never seen a canal exit short of the radiographic apex,” is what a general practitioner told me a few years ago with a smug kind of experience-teaches-me-as-much-as-an-advanced-specialty-program-does kind of look. Funny thing is, seeing how recently he had graduated he couldn’t even have been that experienced.

As a specialist, this kind of rhetoric just gets your goat. But as specialists, we know from where this kind of commentary arises.

This guy probably took a few Endo (root canal) courses where he learned some Schilder Technique¹ basics, like “fill to the radiographic apex” and the lecturer didn’t bother (or didn’t know themselves) that teeth such as the one on the right exist.

Sure, the Schilder technique mandates a fill to the radiographic apex rather than the canal terminus, but with the understanding that you’ll be filling a little long every so often. This rational was developed prior to current apex locator technology and isn’t really practical today². If we can stay out of the periodontal ligament and supporting tissues with our obturation materials, we minimize the risk of persistent sensitivity and/or foreign body reactions.

1. Schilder H. Filling root canals in three dimensions. Dent Clin North Am. 1967 Nov;:723-44. [↩]
2. Stein TJ, Corcoran JF. Radiographic “working length” revisited. Oral Surg Oral Med Oral Pathol. 1992 Dec;74(6):796-800. [↩]