Conservative Dentistry and Endodontics
Conservative Dentistry and Endodontics
This domain tests caries management philosophy, adhesive dentistry mechanics, and the biological and technical steps of root canal treatment.
Core rules
- Critical pH is about 5.5 for enamel and 6.2–6.5 for dentin/cementum; demineralisation is reversible until cavitation, which is the basis of minimal intervention and remineralisation with fluoride, CPP-ACP or silver diamine fluoride.
- Bonding: 37% phosphoric acid removes the smear layer, exposes collagen and creates a hybrid layer; total-etch performs well on enamel, self-etch is more forgiving on dentin. C-factor is bonded surface area divided by unbonded free surface - high C-factor concentrates polymerisation shrinkage stress.
- Working length is 0.5–1 mm short of the radiographic apex, confirmed with an electronic apex locator; patency and glide path precede shaping; NiTi rotary files need torque and speed control in curved canals.
- Irrigation: sodium hypochlorite 0.5–5.25% for tissue dissolution and antimicrobial action, 17% EDTA as a final chelator to remove the smear layer. Never mix hypochlorite and chlorhexidine - a brown parachloroaniline precipitate forms.
- Extruded hypochlorite causes severe pain, swelling and ecchymosis: stop, cold compresses, analgesia, and monitor the airway.
Worked example
A class I cavity measures 4 mm × 4 mm at the surface and 2 mm deep. Bonded area = floor (16 mm²) + walls (perimeter 16 mm × 2 mm = 32 mm²) = 48 mm². Free unbonded surface = 16 mm². C-factor = 48/16 = 3. High C-factor means most shrinkage stress is transferred to the bond, risking marginal leakage and post-operative sensitivity, so place the composite in increments of no more than 2 mm and consider a flowable liner to act as a stress-absorbing layer.
Traps
- Quoting a single irrigant as sufficient: hypochlorite alone leaves the smear layer, EDTA alone does not disinfect.
- Mixing hypochlorite with chlorhexidine 'for broad coverage'.
- Confusing working length with the radiographic apex, causing over-instrumentation.
- Assuming a radiolucent periapical lesion always needs retreatment - a healing lesion can look worse before it looks better.