The Effect of Using Composite Primers, Silane and Surface Roughening on the Shear Bond Strength of Metal Brackets bonded to Old Composites

Background: One of the effective factors in successful orthodontic treatment is the use of appropriate bond between the orthodontic bracket and surface of the composite restoration. The aim of this study was to evaluate the effect of using composite primers, silane, and surface roughening on the shear bond strength of metal brackets bonded to old composites. Methods: In this laboratory study, 90 composite disks (Z350 3M) measuring 4 by 6 mm were kept in distilled water for 1 week and subjected to 5000°C heating rotation (rpm). These samples were divided into 6 groups based on the use of composite primer, surface roughening, and silane as follows: Group 1 (Control): old composite+37 % acid etching, Group 2: Old composite+37% acid etching+20 s cure. Group 3: Old composite+37% acid etching+5 s air-drying, Group 4: Old composite+acid etching+rubbing, Group 5: Old composite+roughing with diamond bur, Group 6: Old composite+Acid etching+roughing with diamond bur metal brackets were attached to the specimens and the specimens were immersed in water and in a thermal rotation system of 5000 rpm for 1 week. The shear bond strength of the brackets was measured. Results: The highest and the lowest shear bond strength values were found in the fourth and control groups, respectively, indicating a significant difference across all groups (P=0.001). In this regard, the results of least significant difference (LSD) test also showed that the mean shear bond strength of orthodontic brackets in the control group was significantly lower than that observed in other experimental groups, but without significant difference across the pointed groups. Conclusions: The use of surface roughness, composite primer, and silane together do not have a cumulative effect on the increase of the bond strength between old composite and orthodontic brackets. However, the use of each alone can increase the shear bond strength.