How should margins be finished at the cavosurface to prevent microleakage?

• A. Margins should be rough to ensure bonding.
• B. Margins should be smooth, well-adapted, and ideally on enamel with crisp cavosurface margins.
• C. Margins should end in the middle of dentin with a heavy bevel.
• D. Margins should be extended beyond enamel into cementum.

Answer: (B)

Finishing cavosurface margins to be smooth and well-adapted is crucial for minimizing microleakage. When the margin is crisp and lies predominantly on enamel, the interface between tooth and restoration is tight and uniform, creating a barrier that resists fluid movement and bacterial ingress after placement and function. Enamel provides the most stable, least permeable border, so a margin that terminate on enamel with a clean cavosurface edge helps seal the restoration effectively.

Rough, irregular margins or margins that end in dentin or extend into cementum increase pathways for leakage because dentin has tubules and is more permeable, and cementum offers less predictable sealing. Beveling can expose more dentin and disrupt the smooth seal, further favoring microleakage. Therefore, the best practice is a smooth, well-adapted margin on enamel with crisp cavosurface margins to reduce microleakage.