whats a 90 degree exit angle?

[Stephie3]

Advertisement - Members don't see this ad

what in the world is a 90 degree exit angle for a class II amalgam prep. someone please explain this to me. pictures would be helpful as well.

 

[ddstothecor]

If you look at the buccal wall of the molar preparation at the cavosurface, you can see two 90 degree angles - not only at the cavosurface, but the proximal wall is parallel to the long axis of the premolar next to it, and the contact is broken (an explorer tip's worth) at 90 degrees where you see the exit of the tooth/preparation junction. That wall is straight and 90 degrees to the pulpal floor of the proximal box as well.

 

[Vicviper]

Yeah, it makes it so that you have an even balance of tradeoffs - enough amalgam and enough tooth structure to not be fractured. The acceptable angle actually goes from 90-100.