Microleakage of composite resin restorations with various etching times.

Microleakage was assessed in Class V composite resin restorations, placed in extracted noncarious human premolar teeth after the enamel cavosurface margins of the preparations had been etched with phosphoric acid for 5, 15, or 30 seconds. The restored teeth were thermocycled, placed in methylene blue dye, invested, and sectioned. The extent of dye penetration along the tooth-restoration interface in the three etching groups was compared. The group etched for 5 seconds showed the greatest leakage; leakage was statistically significantly greater than that in the groups etched for 15 or 30 seconds. The tooth-restoration interface at the occlusal and gingival margins showed more leakage than did the mesial or distal margins.