Methods: Sixty box-shaped cavities in 3 mm depth were prepared on occlusal surfaces of extracted human third molars. A two-step etch-and-rinse (Single Bond 2) was applied for the thirty cavities while the other half of cavities was bonded with a two-step self-etching (Clearfil SE Bond). For each adhesive, the cavities were further divided into three subgroups- no liner/base; 0.5 mm thickness of RMGIC (Vitrebond) applied as a liner; or 1.0 mm thickness of Vitrebond applied as a base, before adhesive application. All cavities were restored incrementally with a resin composite (Z250XT) and kept in 100% humidity at 37 0C for 24 h. Each restored cavity was cut in bucco-lingual direction to obtain two specimens. One specimen was detected for 2% methylene blue dye leakage at the horizontal and vertical walls, and the percentages of dye staining were calculated. The other specimen was investigated under SEM for gap formation detection.
Results: For the restorations bonded with Single Bond 2, the absence of lining/base showed the lowest dye staining at the horizontal walls, which significantly lower than the restorations with thin RMGIC lining (P= 0.019). Increase the thickness of RMGIC as a base reduced dye staining, which was not significantly different from that of the no lining/base group. For the restorations bonded with Clearfil SE Bond, the absence of lining/base also showed the lowest dye staining at the horizontal walls, but not significantly different from the restorations with the RMGIC lining or base (P>0.05). There was no significant difference in dye staining at the vertical walls among six experimental groups (P>0.05).
Conclusions: Internal adaptation of the restorations without RMGIC lining/base was superior to those with the lining/base.