Operative Dentistry and Dental Materials
Scope
Tests cavity design, adhesion to enamel and dentin, and the selection and handling of direct restorative materials - the decisions that determine marginal seal and restoration longevity.
Cavity classification
- Class I occlusal pits and fissures; II proximal posteriors; III proximal anteriors sparing the incisal edge; IV involving the incisal edge; V cervical third; VI incisal tips and cusp heights.
Adhesion
- Etch-and-rinse: 37% phosphoric acid, 30 seconds on enamel and 15 seconds on dentin, rinse, then leave dentin visibly moist; apply ethanol or acetone primer, then hydrophobic resin.
- Self-etch: acidic monomers condition and prime in one step; simpler and less technique-sensitive, but with a weaker enamel bond - selective enamel etching is common.
- Over-drying collapses the collagen network; over-wetting dilutes the primer.
Materials
- Composite: 2–3% volumetric shrinkage; C-factor is the bonded-to-unbonded surface ratio, so place increments in high C-factor cavities.
- Amalgam: high compressive strength, no adhesion, requires mechanical retention.
- Glass ionomer: chemical bond to tooth and fluoride release, but poor wear resistance; resin-modified versions are stronger.
- Ceramics: lithium disilicate is adhesively bonded; zirconia needs airborne-particle abrasion and an MDP-containing primer.
Worked example
A non-carious cervical lesion has sclerotic dentin and a shallow enamel rim. Reasoning: sclerotic dentin has obliterated tubules and resists etching, so a self-etch or resin-modified glass ionomer approach with a small enamel bevel gives a more reliable seal than aggressive etch-and-rinse.
Traps
- Etching dentin for 30 seconds, causing collagen collapse and post-operative sensitivity.
- Confusing C-factor with shrinkage - C-factor predicts stress, not the amount of shrinkage.