ORE Part 2 · Dental Manikin (DM) guide
Class I Occluso-Palatal Cavity Preparation
A Class I (Class 1) occluso-palatal cavity in an upper molar that follows the fissure from the distal pit onto the palatal surface and finishes in a palatal step, prepared for an amalgam restoration. The test is keeping the outline within its landmarks while holding the bur upright so the step walls stay straight.
Our video demonstrates this on an upper first molar (26). In the exam, the tooth and exercise are set on the day.
What examiners look for
- An outline that follows the fissure between the oblique ridge and the distopalatal cusp
- Oblique ridge, distopalatal and distobuccal cusps and distal marginal ridge all preserved
- A lock that extends only as far as the distal pit
- Consistent depth, a smooth flat floor, and straight or slightly convergent walls
- A palatal step with straight walls, a smooth floor and a width that fits the condenser
Common mistakes
- Tilting the bur or bending the wrist when cutting the palatal step, slanting its walls
- Extending the lock past the distal pit and weakening the marginal ridge
- Widening towards the distobuccal cusp and undermining it
- Leaving ledges or irregularities on the floor of the step
- Calling it finished when the condenser enters but doesn't move freely
Candidate questions
Which landmarks must be preserved?
The oblique ridge, the distopalatal and distobuccal cusps, and the distal marginal ridge. Widen between these landmarks, never into them.
Why does an amalgam cavity need convergent walls and a lock?
Amalgam doesn't bond to the tooth, so the cavity shape has to hold it in place. Slightly convergent walls and a lock provide that mechanical retention.
Why must the bur stay upright for the palatal step?
Both step walls should be straight. Tilting the bur or bending the wrist slants them mesially or distally.