Methods: The oral enamel of the 192 extracted cariesfree third molars molars was ground flat. Then the teeth were randomly divided in 12 groups. Half of the specimens were etched for 20s, half for 40s with 37% phosphoric acid gel. The gel was rinsed with an air/water spray for varying amounts of time (5s, 20s and 40s) and dried. Then a composite cylinder was polymerized to the flattened surface: in half of the specimens with Prime & Bond NT and Esthet-X (PB-E, Dentsply, Germany) and in the other half with Excite and Tetric Ceram (E-TC, Vivadent, Germany). Specimens were thermocycled (5000x, 5°-55°C), and adaptation was evaluated quantitatively measuring microleakage along the composite/enamel interface and lengths of the resin tags into enamel microporosities.
Results: SEM analysis showed lengths of the resin tags into the flattened enamel surface between 5.1µm and 10.27µm. PB-E penetrated deeper into micoporosities of enamel than E-TC (p<0.001). Higher etching time (median 6.7µm: 20sec, median: 7.2 40sec, p<0.001) and rinsing time (median 6.9µm: 5sec, median 7µm: 20 sec, median 7.1µm: 40 sec, p<0.05) increased lengths of the tags. Concerning gap formation there was no significant difference between the two composite materials, and etching times. Increased rinsing time reduced gap formation. However, only difference between 5 sec and 40 sec rinsing was significant (p<0.05).
Conclusion: Resin tag formation of composite into enamel microporosities and gap fomation is positively influenced by increased etching and rinsing times during adhesive restoration.