Purpose: The aim of this study was to evaluate the effect of surface treatment and universal adhesive on the microshear bond strength of nanoparticle composite repairs.
Methods: One hundred and forty-four specimens were built with a nanofilled composite (Filtek Supreme Ultra, 3M ESPE). The surfaces of all the specimens were polished with SiC paper and stored in distilled water at 37°C for 14 days. Half of the specimens were then air abraded with Al2O3 particles and cleaned with phosphoric acid. Polished specimens (P) and polished and air-abraded specimens (A), respectively, were randomly divided into two sets of six groups (n=12) according to the following treatments: hydrophobic adhesive only (PH and AH, respectively), silane and hydrophobic adhesive (PCH, ACH), methacryloyloxydecyl dihydrogen phosphate (MDP)-containing silane and hydrophobic adhesive (PMH, AMH), universal adhesive only (PU, AU), silane and universal adhesive (PCU, ACU), and MDP-containing silane and universal adhesive (PMU, AMU). A cylinder with the same composite resin (1.1-mm diameter) was bonded to the treated surfaces to simulate the repair. After 48 hours, the specimens were subjected to microshear testing in a universal testing machine. The failure area was analyzed under an optical microscope at 50× magnification to identify the failure type, and the data were analyzed by three-way analysis of variance and the Games-Howell test (α=0.05).
Results: The variables "surface treatment" and "adhesive" showed statistically significant differences for p<0.05. The highest mean shear bond strength was found in the ACU group but was not statistically different from the means for the other air-abraded groups except AH. All the polished groups except PU showed statistically significant differences compared with the air-abraded groups. The PU group had the highest mean among the polished groups. Cohesive failure was the most frequent failure mode in the air-abraded specimens, while mixed failure was the most common mode in the polished specimens.
Conclusions: While air abrasion with Al2O3 particles increased the repair bond strength of the nanoparticle composite, the use of MDP-containing silane did not lead to a statistically significant increase in bond strength. Silane-containing universal adhesive on its own was as effective as any combination of silane and adhesive, particularly when applied on air-abraded surfaces.