ORE Part 2 · Dental Manikin (DM) guide
PFM (Metal-Ceramic) Crown Preparation
A full-coverage porcelain-fused-to-metal (metal-ceramic) preparation, checked against a putty index as you go. The challenge is reducing evenly in the right planes while keeping the cusp tip and cingulum, placing continuous margins at the right level, and staying clear of the neighbouring teeth.
Our video demonstrates this on an upper canine (13). In the exam, the tooth and exercise are set on the day.
What examiners look for
- Incisal reduction on both cusp slopes, with the cusp tip preserved
- Even labial reduction that follows the planes of the tooth, with no sharp ridges or undercuts
- A labial shoulder and palatal chamfer that are continuous, free of nicks and at a consistent level
- Palatal reduction that preserves the cingulum
- Tapered axial walls and smooth, rounded edges
- No damage to the adjacent teeth or gingiva
Common mistakes
- Over-reducing because the putty index isn't checked often enough
- Reducing the labial surface in one flat plane instead of following its thirds
- Lowering the margin while widening it — a margin can't be raised once it's cut
- Tilting the bur during proximal reduction, which changes the taper
- Letting the bur slip into the adjacent tooth
Candidate questions
How is a PFM preparation checked?
Against a putty index, repeatedly, looking for an even gap on every surface. The margin level and width are checked with a probe as well.
Why place the labial margin slightly high at first?
A margin can always be lowered during finishing, but it can't be raised once it has been over-cut. Starting at the upper end of the safe range keeps your options open.
What is planar reduction?
Reducing each third of the labial surface at its own angle so the preparation follows the tooth's natural planes, rather than cutting one flat face. The course video shows the bur angle for each third.