Prosthodontics (Fixed and Removable)
What this domain tests
Fixed and removable prosthodontics tests treatment planning, retention, stability, support, occlusion and material choice. Questions often ask why a design fails.
Core rules
- Crown retention depends on taper, surface area, roughness, cement and ferrule. Ideal taper is about 6-10 degrees. A 2-mm ferrule improves fracture resistance in endodontically treated teeth.
- Bridge design requires appropriate abutment selection. Ante's law, that abutment root surface area should equal or exceed the pontic, is a guide, not an absolute; span, curvature and periodontal support matter.
- Occlusion should provide stable contacts in centric relation or maximum intercuspation, with no interferences in excursions. Anterior guidance should disclude posterior teeth.
- Removable partial denture support comes from rests, retention from clasps, and stability from a rigid major connector and bracing. Avoid tissue impingement.
- Complete dentures require border moulding to record sulcular extent, a posterior palatal seal and balanced occlusion in excursions.
- Implant overdentures gain retention from attachments and support from implants and tissue; avoid excessive torque.
Worked example
A mandibular Kennedy Class II removable partial denture is planned with a lingual bar and two clasps on the terminal abutments. The design lacks rests on the distal extension side, so the denture will sink and torque the abutment. Correct design adds occlusal rests and a rigid major connector, with the distal extension base properly extended.
Traps
- A short clinical crown may need core build-up or crown lengthening; excessive taper does not improve retention.
- Do not use a cantilever bridge on a weak abutment.
- Clasps are not the only retention factor; rests and connectors matter.
- Complete denture retention is not the same as stability.