Introduction
Prosthetic restorations differ in material, size, shape, function and technology, which makes them hard to classify by a single rule. Several indices are used side by side, each answering a different question.
Morphologic index: what is missing?
The most widely used grouping, by the type of defect:
Fixation
- Fixed: cemented to natural teeth or implants (crowns, bridges); only the dentist can remove them.
- Removable: the patient takes them out (partial and complete dentures).
- Removable by the clinician only: usually screw-retained to teeth or implants.
Functional index: how is chewing force carried?
The basic job of a prosthesis is to pass chewing forces to the supporting tissues. How it does this is a major way to classify it.
Prophylactic index: does it prevent harm?
A good restoration doesn't only replace tissue, it protects what is left: it stops neighbours tipping and antagonists over-erupting, splints loose teeth, spreads load correctly and keeps the gingiva healthy through good margins and contours. A restoration that traps plaque or overloads abutments fails this test however well it looks.