Why is finishing cavosurface margins on enamel preferred for reducing microleakage?

• A. Because margins on cementum are more durable.
• B. Because enamel margins with crisp cavosurface edges improve seal and reduce microleakage.
• C. Because dentin margins are stronger.
• D. Because microleakage is not affected by margin material.

Answer: (B)

Finishing cavosurface margins on enamel yields a more reliable seal and reduces microleakage. Enamel is highly mineralized and responds predictably to acid etching, which creates strong micromechanical bonds with resin-based restoratives. When the margin sits on enamel and the cavosurface edge is crisp, the adhesive layer can flow and cure uniformly right to the margin, producing a tight, gap-free seal. This minimizes pathways for bacteria, fluids, and dyes to penetrate the interface.

In contrast, margins that extend onto dentin or cementum behave differently. Dentin has tubules and a variable smear layer that complicates bonding, making the seal less predictable. Cementum is even less favorable for bonding because of its organic content and lower mineralization. Those margins are more prone to microgaps and leakage. Therefore, a margin finishing on enamel with crisp edges provides the most reliable marginal integrity and the least microleakage.