Restorative dentistry, endodontics and prosthodontics
Linking materials science to clinical failure
Restorative questions test adhesion and stress. Understand acid-etch bonding to enamel (micromechanical, resin tags) versus dentine bonding (hybrid layer, smear-layer modification, wet dentine), and the difference between etch-and-rinse and self-etch systems. Polymerisation shrinkage stress rises with the configuration factor (C-factor), highest in a deep, narrow, unbonded class I cavity, so incremental or bulk-fill techniques and good bonding matter. Know the pulp-protection hierarchy and when indirect or direct pulp capping is defensible.
In endodontics be fluent in pulp and periapical diagnosis (reversible versus irreversible pulpitis, necrotic pulp, symptomatic apical periodontitis, acute apical abscess), in working length (apex locator confirmed radiographically, typically 0.5–1.0 mm short of the radiographic apex), in glide-path creation and NiTi rotary shaping, and in irrigants: sodium hypochlorite dissolves tissue and is antimicrobial, EDTA removes the smear layer, chlorhexidine is an alternative where hypochlorite is unsuitable. Remember a post does not strengthen a root; it only retains a core.
Prosthodontics hinges on design: path of insertion, guiding planes, rest seats, reciprocation, Kennedy classification with Applegate's rules. For crowns, aim for 6–10 degrees of axial taper, adequate occlusal reduction and a smooth, ideally supragingival, finish line.
Worked example: after crown preparation a premolar shows 2 mm of sound supragingival axial dentine all round. Rule of thumb - 1.5–2 mm of circumferential dentine coronal to the margin provides a ferrule and greatly improves fracture resistance; if absent, consider crown lengthening rather than a post.
Traps: mis-defining C-factor, assuming posts reinforce roots, and confusing irrigant actions.