ORE Part 2 · Dental Manikin (DM) guide
Class I Cavity Preparation
A Class I (Class 1) occlusal cavity running between the mesial and distal pits, leaving the marginal ridges intact. It looks simple, which is why marks are lost on it: the test is control — an even floor at a consistent depth, walls of the right shape, and a width that matches the gauge without over-cutting.
What examiners look for
- An outline that stays between the pits and doesn't undermine the marginal ridges
- A smooth, flat floor at an even depth from end to end
- Walls of the right shape for the restoration, with no divergence
- A width that matches the condenser supplied — it drops in and moves freely
- Rounded internal corners and no roughness left on the floor
Common mistakes
- Changing the bur angle partway through, giving uneven walls and floor
- Leaving the middle of the cavity shallower than the ends
- Over-widening instead of cutting a little at a time and checking the fit
- Over-flaring the mesial and distal walls
- Leaving a sharp or square corner at one end of the outline
Candidate questions
How wide should a Class I preparation be?
Wide enough for the condenser you're given to drop in and move freely along the cavity, without obvious gaps at the sides. Widen in small steps and check often.
Should the walls be parallel?
In the course video the buccal and palatal walls are made slightly convergent and the mesial and distal walls only slightly flared. Divergent walls lose retention.
How do I avoid an uneven floor?
Keep the bur at a constant angle along the long axis of the tooth and recheck the depth often. The centre tends to end up shallower than the ends, so level it before you widen.