ORE Part 2 · Dental Manikin (DM) guide
Class III Cavity Preparation
A Class III (Class 3) cavity: a small proximal cavity on an upper anterior tooth, prepared from the palatal side under indirect vision. The challenge is opening the incisal and gingival contacts cleanly without damaging the adjacent tooth or bringing the margin forward into the visible labial surface.
Our video demonstrates this on an upper central incisor (21). In the exam, the tooth and exercise are set on the day.
What examiners look for
- A neat, roughly rectangular outline with a straight incisal margin
- A uniform, shallow depth that follows the tooth contour
- Incisal and gingival contacts opened enough to pass a matrix strip
- A margin that can't be seen from the front, preserving the aesthetic zone
- Rounded internal angles and smooth walls
- The adjacent tooth protected and undamaged
Common mistakes
- Cutting the floor too deep while opening the contact, pushing the cavity labially
- Working near the contact without separating and protecting the adjacent tooth
- Extending the margin into the labial aesthetic zone to force a tight contact
- Using the wrong gingival margin trimmer for the surface
- A curved or ditched incisal margin, or sharp internal angles
Candidate questions
What if I can't open the contact without going too far labially?
Don't push the margin into the aesthetic zone. If your depth is correct, stop and explain to the examiner that you've avoided the visible surface.
Why place a wedge and band first?
Separating the teeth gives you room to work and protects the adjacent tooth from the bur and hand instruments.
How long should a Class III take?
Once you're familiar with the technique, aim for around half an hour.