Objectives . Adequate film thickness of resin cement is needed for long-term retention of restoration. The purpose of this study was to evaluate the effect of film thickness of various resin cements on bonding efficiency in indirect composite restoration.

Materials and methods . Experimental groups were divided according to film thickness (<50–150 μm) using 2 kinds of composite-based resin cements (Variolink II, Duo-Link) and 2 kinds of adhesive-based resin cement (Panavia F, Rely X Unicem). For microtensile bond strength test, indirect composite block (Tescera™: Bisco) was luted to flat dentin surface with each adhesive cement under pressure of 0.5 kgf. The bonded tooth-resin block was stored in distilled water at 37 °C for 24 h and sectioned into 1 × 1 mm beams. These specimens were tested with universal testing machine at a crosshead speed of 1 mm/min. Polymerization shrinkage of resin cements was determined with ACUVOL™ (Bisco) before and after polymerization. Flexural strength and modulus were measured by three-point bending test. Cement/dentin interface and debonded dentin surface were examined with FE-SEM (Zeiss). All data were analyzed using one-way ANOVA and Duncan’s multiple comparison test at α ≤ 0.05 level.

Results

• 1.

  Composite-based resin cements showed higher microtensile bond strength for all film thickness than that of adhesive-based resin cements.

• 2.

  Microtensile bond strength of composite-based resin cements was decreased significantly according to increasing film thickness, but adhesive-based resin cements did not show significant difference among the film thickness.

• 3.

  Composite-based resin cements showed significantly higher flexural strength, modulus and shrinkage than those of adhesive-based resin cements.

• 4.

  Uniform adhesive layer and well-developed resin tags were observed in composite-based resin cements and the debonded surface showed mixed-failed in FE-SEM.

Conclusions . The bonding performance and efficiency of indirect restoration can be affected by type of resin cements, adhesive system and film thickness.