Fixed Prosthodontics
Fixed Prosthodontics tests preparation design, retention and resistance, margin placement, provisionalization, luting, and occlusal adjustment. The exam rewards biomechanical reasoning, not memorized reduction numbers alone.
Core rules
- For metal-ceramic crowns, axial reduction is typically 1.0-1.5 mm and occlusal reduction 1.5-2.0 mm; chamfer is a common margin.
- Total occlusal convergence of 6-10 degrees improves retention; overtapered preparations require auxiliary features.
- Preserve a 1.5-2 mm ferrule on endodontically treated teeth whenever possible.
- Verify path of insertion, margin finish, and interocclusal clearance before impression.
- Use a stable provisional that maintains pulp health, occlusion, and esthetics.
Worked example
A maxillary central incisor needs a crown and has only 2 mm of clinical crown above the gingiva after caries removal. Reasoning: a ferrule is desirable but insufficient sound dentin remains; simply adding a post does not replace missing ferrule. Options are crown lengthening, orthodontic extrusion, or extraction with implant planning. If crown lengthening is chosen, re-evaluate biologic width, esthetics, and final margin position before preparation.
Traps that cost marks
- Excessive taper that destroys retention.
- Insufficient occlusal reduction causing porcelain fracture.
- Placing a margin on a questionable endodontic tooth without prognosis review.
- Ignoring provisional occlusion and cleanability.
- Adjusting final occlusion without checking excursive contacts.