Prosthodontics - Fixed and Removable
Fixed prosthodontics
Crown retention and resistance depend on taper (keep the convergence small, roughly 6–10° per wall), surface area, preparation height, and a single path of insertion. Supragingival margins are kindest to the periodontium when aesthetics allow. For a post-and-core, retain 4–5 mm of apical gutta-percha and at least 1.5–2 mm of circumferential ferrule for predictable fracture resistance. Pontic design: sanitary (hygienic) for posteriors, ovate for aesthetics, saddle only where tissue support is needed. A cantilever needs a long-span abutment of strong root form and should not carry more than one pontic anteriorly.
Removable partial dentures - Kennedy and Applegate
Kennedy I = bilateral posterior edentulous area; II = unilateral posterior; III = unilateral posterior bounded by teeth; IV = single anterior edentulous span crossing the midline. Apply Applegate's rules: classify after all extractions are complete; do not count a missing third molar (or a second molar) that will not be replaced; the most posterior edentulous area determines the class; additional edentulous areas are modifications counted by number.
Complete dentures
Retention comes from adhesion, cohesion, atmospheric pressure and a peripheral seal; stability resists horizontal force; support comes from the denture-bearing area. Balanced occlusion keeps contacts in excursions. The neutral zone is where muscular forces are balanced.
Rule of thumb
A Kennedy Class IV has no modification spaces - it is defined by the anterior span crossing the midline.