Prosthodontics and Crown & Bridge
Prosthodontics and Crown & Bridge tests complete and partial denture design, fixed prosthodontics, occlusion, and materials. Questions often ask why a prosthesis fails or which design feature is correct.
Core rules
- Complete denture retention depends on border seal, saliva, adaptation, and neuromuscular control; mandibular dentures are harder to retain because of reduced ridge area.
- Neutral zone is the area where forces from tongue, lips, and cheeks balance; teeth should be placed there.
- Kennedy Class I is bilateral posterior edentulous space; Class II is unilateral posterior; Class III is unilateral bounded; Class IV is anterior.
- A crown needs adequate ferrule and marginal fit; subgingival margins are not automatically superior.
- Balanced occlusion in complete dentures reduces tipping forces.
Worked example
A patient with a severely resorbed mandible reports that the lower complete denture dislodges when speaking. The likely cause is loss of retention from reduced ridge support and border seal. The correct reasoning is not to simply increase occlusal height; instead assess border extension, neutral zone, and consider implant overdenture. Increasing vertical dimension may worsen discomfort and accelerate resorption.
Traps
- Do not extend denture borders onto movable tissue; that breaks the seal.
- A removable partial denture should not rely on soft tissue alone for support; teeth and mucosa share support.
- Ceramic fracture may result from inadequate occlusal adjustment, not only material choice.
- Overcontoured crowns can cause plaque retention and gingival inflammation.