Effect of surface roughness and adhesive system on repair potential of silorane-based resin composite

This study was performed to evaluate the influence of surface roughness and adhesive system on the repair strength of silorane-based resin composite. Twenty-four substrate discs from silorane-based Filtek P90 were made and stored for 24 h. Half of the discs were roughened against 320 grit SiC paper while the other half was polished against 4000 grit SiC paper. All discs were etched with phosphoric acid. Repair resin composite, Filtek P90 or Filtek Z250, was bonded to the treated surfaces using their corresponding adhesive; P90 System Adhesive (SA) or Adper Scotchbond Multipurpose (SBMP) ending up with four repair groups. The groups were as follows: G1: Smooth + SA + Filtek P90; G2: Roughened + SA + Filtek P90; G3: Smooth + SBMP + Filtek Z250; G4: Roughened + SBMP + Filtek Z250. Additional six unrepaired discs from each resin composite (G5 and G6) were prepared to test the cohesive strength. After 24 h, discs (n = 6/group) were serially sectioned to obtain sticks (n = 30/group) for microtensile bond strength (μTBS) testing. Scanning electron microscopic (SEM) evaluation of substrates that received different treatments as well as representative substrate-repair sticks from each group were performed. Modes of failure were also determined. Two-way ANOVA with Repeated-Measures revealed that surface treatment and repair material had no significant effect on repair bond strength of silorane-based composite material. Paired t-test showed that all repair strength values were significantly lower than the cohesive strength of Filtek P90. Adhesive failure was the predominant mode of failure which was confirmed by SEM. Surface treated Filtek P90 composite showed different textures under SEM whereas phosphoric acid did not produce clear changes. An interaction layer between SBMP adhesive and Filtek Z250 repairing composite was detected. Repair of the silorane composite was successful irrespective of the surface roughness and chemistry of the repair material used. However, it did not reach the cohesive strength of the material.