Laboratory investigation of micro-shear bond strength of the former and new composite restorations using bonding and composite systems

Methacrylate composite resins are widely used in restorative dentistry. The greatest disadvantage of these materials is polymerization shrinkage. The recent innovations include making silorane-based composites with the least amount of shrinkage. Herein, we sought to investigate micro-shear bond strength between the former and new composites using both bonding and composite systems.
Seventy-eight cylindrical methacrylate- and silorane-based composites with the height and diameter of 2 mm and 5 mm, respectively, were prepared and thermocycled for 1000 cycles for aging.Then, the blocks were divided into six subgroups: 1) Z250, after freshening and P90bonding, the new silorane layer was placed on them; 2) Z250, after freshening, acid etching, and P90bonding, the new silorane layer was attached; 3) Z250, after freshening, acid etching, and single bonding, the new Z250 layer was attached; 4) P90 composite, after freshening and P90bonding, the new silorane layer was attached; 5) P90, after freshening, acid etching, and P90bonding, the new silorane layer was attached; and 6) P90, after freshening, acid etching, and single bonding, the new Z250composite was attached. Then, all the bonded samples were tested for micro-shear bond strength by Instron machine at the speed of 1 mm/min; the samples were loaded until reaching the breaking point. To analyze the data, Kolmogorov–Smirnov test, one-way analysis of variance, and Tukey’s post hoc test were run in SPSS, version 17.
There was a significant difference in micro-shear bond strength between the groups (P=0.0001). The mean of micro-shear bond strength in the silorane-based composite group was significantly higher than that of the methacrylate-based composites (36.62±5.97 vs. 26.12±5.97; P=0.0001).
Acid etching does not significantly affect shear bond strength, but applying P90 bonding in silorane composites increases the shear bond strength. The greatest bond strength was observed in restoring the P90 silorane composite with a similar silorane composite and the least strength was found in restoring the Z250 methacrylate composite with a similar methacrylate composite. In general, the micro-shear bond strength of silorane-based composites was greater than that of the metacrylate-based composites.