Prosthodontics - Fixed and Removable
Fixed prosthodontics
A crown needs 1.5–2 mm of ferrule on sound tooth structure, a margin placed as supragingivally as aesthetics allow, and a path of insertion free of undercuts. Pontic design follows the site: modified ridge lap for aesthetics, sanitary for lower posteriors, ovate for healed ridges. Connector cross-sectional area matters more than length for strength; cantilevers concentrate load on the terminal abutment and rarely suit a lone molar. Ante's law (root surface of abutments ≥ root surface of pontic) is a rule of thumb now superseded by biomechanical assessment of bone support.
Removable prosthodontics
A removable partial denture is retained, supported and stabilised by rests, clasps, major and minor connectors and the residual ridge. Rests direct occlusal load along the long axis of abutments; the RPI design (rest, proximal plate, I-bar) reduces torque. Kennedy classification: Class I bilateral free-ends, Class II unilateral free-end, Class III bounded posterior space, Class IV anterior single space, with modification areas appraised separately. A distal extension base needs an altered cast impression and indirect retention.
Complete dentures
Establish maxillomandibular relations at the correct vertical dimension and centric relation, then develop balanced occlusion. The posterior palatal seal sits at the vibrating line; relieve the mid-palate and incisive papilla.
Worked example
A Kennedy Class II modification 1 mandible: the free-end side is supported by the ridge, so a rigid circumferential clasp on the last abutment is wrong - choose a stress-releasing design and add indirect retention on the opposite side.
Traps
- Confusing support (rests, ridge), retention (clasps, seal) and stability (fit, occlusion).
- Omitting the ferrule requirement.
- Ignoring that implants do not intrude while teeth do, changing occlusal design.