Restorative Dentistry and Endodontics
This domain tests tooth preparation principles, adhesion to enamel and dentine, pulp diagnosis, chemomechanical canal preparation, obturation, and the choice of restoration for a root-filled tooth. Expect questions that give a clinical finding and ask for the most defensible next step or the reason a restoration failed.
Adhesion and preparation
- Phosphoric acid etch (30-40%) for about 15 seconds on enamel; selective enamel etching improves the durability of self-etch adhesives on dentine.
- Polymerisation shrinkage and the configuration factor rise in deep narrow cavities; place composite in increments of about 2 mm and consider indirect restoration for large cavities.
- Typical preparation: axial taper of 6-10 degrees, occlusal reduction of 1.5-2 mm, axial reduction of 1-1.5 mm, and a defined finish line (chamfer for metal-ceramic, rounded shoulder for ceramic).
- Ferrule of 1.5-2 mm of sound dentine above the margin protects a root-filled tooth; posts are indicated only when retention cannot be achieved otherwise.
Pulp and periapical diagnosis
- Cold refrigerant is the most dependable vitality test; electric pulp testing gives false positives in multirooted and recently traumatised teeth.
- Percussion and palpation indicate apical periodontitis, not pulp status; a sinus tract should be traced with gutta-percha to its source.
- Cracked tooth: biting test, transillumination, selective wedge and direct visualisation of the fracture line.
- Vital pulp therapy with a calcium silicate cement is viable when exposure is small and haemostasis is achieved.
Canal preparation and irrigation
- Working length from an apex locator, confirmed radiographically, ending 0.5-1 mm short of the apical foramen.
- Establish a glide path, use a crown-down sequence, maintain patency and recapitulate to prevent ledge formation and transportation.
- Sodium hypochlorite (1-5.25%) dissolves tissue and is antimicrobial; EDTA 17% removes the smear layer; never mix hypochlorite and chlorhexidine because a precipitate forms.
Worked example
A 46-year-old has irreversible pulpitis in 46 with a fractured disto-occlusal wall. Cold response is prolonged, percussion is mildly tender, and the radiograph shows a deep carious lesion approaching the pulp. The plan is complete caries removal, canal treatment, verification of working length with an apex locator, copious hypochlorite, obturation with warm vertical compaction, and cuspal coverage because a marginal ridge is lost.
Traps
- Reading percussion tenderness as evidence of pulp vitality.
- Choosing a post when ferrule and core build-up would retain the tooth.
- Mixing hypochlorite with chlorhexidine.