Restorative Dentistry and Endodontics
What this domain tests
Expect questions on cavity design principles, adhesion to enamel versus dentine, pulp protection decisions, working length determination, irrigant choice and obturation quality.
Core rules
- Enamel bonding relies on acid etching creating microporosity; dentine bonding must first manage the smear layer, either removing it (etch-and-rinse) or modifying it (self-etch). Dentine is wet, tubular and permeable, so moisture control and marginal seal decide long-term success.
- Polymerisation shrinkage is highest when the configuration factor (C-factor: bonded to unbonded surface ratio) is high, as in a class I box. Incremental placement, flowable liners and soft-start curing reduce stress.
- Reversible pulpitis: remove caries, protect the pulp (calcium hydroxide or MTA for indirect or direct capping), restore. Irreversible pulpitis or necrosis: root canal treatment or extraction.
- Working length is established with a periapical radiograph and confirmed with an electronic apex locator; the apical foramen is not always at the radiographic apex.
- Irrigation: sodium hypochlorite 0.5–5.25% dissolves organic tissue and disinfects; 17% EDTA removes the smear layer; chlorhexidine is a reserve agent. Irrigant must not be extruded beyond the apex.
- Obturation: cold lateral condensation or warm vertical compaction with sealer; the canal is filled three-dimensionally to the length established. Rotary nickel-titanium files need a glide path and crown-down sequence to reduce separation.
Worked example
A mandibular first molar has a deep distal cavity, lingering pain to cold and a normal periapical radiograph. Reasoning: lingering pain after the stimulus is removed indicates irreversible pulpitis, so indirect capping is inappropriate. Plan access, working length, cleaning and shaping, then obturation and a cuspal-coverage restoration because the marginal ridge is lost.
Traps
Extruding sodium hypochlorite; obturating short because the apex locator reading was not verified; ignoring the MB2 canal in maxillary molars; placing a large composite in a high-stress class II without cuspal coverage.