Introduction
A casting freshly removed from the investment is rough and slightly oversized. A planned sequence of contouring, grinding and polishing turns it into a restoration that fits, looks right and keeps the gingiva healthy.
Why finish and polish?
- A smooth, glossy surface collects less plaque, stain and soft deposits, and is gentler on the gingiva.
- It reflects light better and looks more natural.
- It makes hygiene easier, which helps the restoration last.
The goal is to remove excess material, smooth rough surfaces and define the anatomy and occlusion, with minimal harm to the tissues.
Three stages
Always work from coarse to fine: each abrasive removes the scratches left by the one before.
Adjusting a cast crown in order
- Fit on the die. The inside isn't polished, but it is checked for nodules with a marking paste and cleared with a small round bur. Seat the casting gently, because forcing it abrades the die and the crown will then not seat in the mouth.
- Sprue. Cut around it with a separating disc, break the last bit by twisting, and reshape the area.
- Proximal contacts. They are left slightly tight in the wax-up; adjust with fine stones and rubber wheels until 8 µm shim stock pulls out with moderate resistance. A lost contact is hard to restore, so take care.
- Occlusion. Mark with thin articulating foil; adjust with small flame-shaped burs, never large stones that hollow the surface.
- Contour, finish and polish the outer surfaces; for a metal-resin crown, thin the buccal margins and leave a 0.5 mm metal collar.