Incremental layers bonding of silorane composite: The initial bonding properties

Objectives Lack of oxygen inhibition layer of silorane composite with cationic polymerization raises the question of the bonding of incremental layers of the composite. This study aimed to evaluate the bond strength of the silorane composite layers. Methods Fresh, 20 s, 5 min aged silorane composite (Silorane, 3M-ESPE) was used as substrate to adhere new silorane composite. For a comparison, dimethacrylate-based composite resin (Z250, 3M-ESPE) was adhered to the silorane composite with or without intermediate adhesive resin. As a control, dimethacrylate composite with oxygen inhibition layer was attached to fresh dimethacrylate composite. The bonded specimens (n = 12/group) were water stored for 24 h. The shear bond strengths (SBS) were measured with a crosshead speed of 1.0 mm/min. Failure modes were assessed. Data were analysed by ANOVA, Tukeyʹs post hoc tests and Chi-square tests (p = 0.05). Results Dimethacrylate–dimethacrylate composite resin combination showed the highest mean SBS (33.0 MPa) values with no adhesive failures. Fresh silorane–silorane SBS was slightly lower (26.7 MPa) and was further decreased by aging the substrate for 20 s (25.4 MPa) and 5 min (22.4 MPa). The percent of adhesive failures increased from 25% to 75%, respectively. The failure modes were significantly different (Chi-square, p < 0.001). Silorane–dimethacrylate composite showed the lowest (4.0 MPa) SBS among the groups, which was increased significantly by use of phosphate–methacrylate-based intermediate resin (p < 0.05). Conclusion In order to bond dimethacrylate composite to silorane composite, a phosphate–methacrylate-based intermediate resin is required. The silorane composite showed slightly lower incremental bonding properties than conventional dimethacrylate composites.