Film thickness of resin cements used with adhesive systems

The final film thickness of a resin adhesive and a resin cement could be affected by previous polymerization of the adhesive systems on dentin surfaces. The aim of this work was to evaluate changes in the film thickness of dual resin based cements with their adhesives as a function of polymerization of the latter on dentin surfaces. The materials used were: RelyX ARC (R) + Single Bond (SB) and Variolink base (VB) and high (HV) or low (LV) viscosity catalyst + Syntac Classic (S) or Excite DSC (E); 56 human dentin discs and 56 composite resin discs (Z250). Dentin disc surfaces were treated with 35% phosphoric acid (except for S) and the adhesive system was either polymerized or not polymerized. A 0.05 ml increment of cement mixture was placed on the dentin disc and covered with the resin disc. A 25 N load was applied for ten minutes and then, the combined thickness was measured with a digital micrometer. Sample size (n) was 4 for each cement or condition. A two-way analysis of variance was performed with a level of significance of p < 0.05. The mean film thickness (and standard deviations) in microm, with and without previous polymerization of the adhesive layer, were: R+SB: 16.50 (2.64) and 17.00 (1.41); VB+S: 21.75 (5.37) and 62.25 (0.95); VB LV+S: 24.50 (3.87) and 72.75 (1.89); VB HV+S: 28.75 (8.46) and 93.00 (53.63); VB+E: 31.75 (8.38) and 42.75 (4.34); VB LV+E: 47.75 (2.50) and 45.75 (3.20); VB HV+E: 49.25 (25.50) and 45.75 (2.75). Significant differences (p < 0.01) were found for the cements and polymerization condition as well as for the interaction between them. Instructions regarding polymerization of the adhesive layer must be followed when adhesive systems are used in combination with dual polymerized resin based cements. Otherwise, final film thickness of the adhesive and the resin cement could be affected.