Comparison of Film Thickness of Restorative Composites Considered for Thermo-Modified Cementation.

Objective: This study proposes an updated method for the film thickness of 21 resin composites used as cements.

Materials and methods: A load of 30 N was subjected to two glass plates stacked on a heated base to simulate clinically relevant pressure and temperature during the seating of inlays/onlays/veneers. The axial position of the actuator was recorded before and after placing 22.15 mm³ of resin composite between the glass slides. The difference between the two measurements was calculated for each specimen. A total of 18 condensable restoratives, 1 injectable restorative, and 2 resin cements were tested, 5 specimens each (n = 5, N = 105). One-way ANOVA was performed for both variables and Games-Howell post hoc test was used for pairwise comparisons.

Results: The film thickness range was 6-200 μm, with the lowest values for restorative composites (AP-X, Z250, and Herculite XRV Incisal LT with 6-8 μm), followed by Gradia Direct (25 μm) and flowable/injectable composite resins, including designated cements (15-27 μm). Inspiro, Ultradent Transcend Universal, and ENA Hri dentin stood below 50 μm (range 28-49 μm). The other materials (range 81-200 μm) cannot be recommended for thermo-modified cementation.

Conclusions: The initial viscosity of restorative composites is not an indication of the film thickness when used for thermo-modified cementation. There is a wide choice of appropriate materials available on the market.

Clinical significance: Some restorative composites are able to generate very thin films and can be used as cement with numerous advantages when compared to designated flowable or dual-cure cements.