Effect of salivary contamination on shear bond strength of composite resin used between teeth and brackets

ABSTRACT

Enamel contaminations with salivary proteins or blood are the major reasons for debonding of brackets. The purpose of this study was to evaluate shear bond strengths of bonded brackets with enamel surfaces under different conditions. The Concise composite [3M, Unitek] was used for adhesion of 0.018 inch standard brackets [3M, Unitek]. Fresh human saliva was used for contamination of enamel surfaces. 90 teeth were divided into 6 groups 1- No surface contamination, 2- Contaminated after etching, 3- Contamination after application of bonding resin, 4- Contamination after etching, then re-etching, 5- Contamination after resin bond application, then re-etching and 6- Contamination after resin bond, then application of resin bond again. Surface contaminations were dried in all groups. After bracket bonding, the samples were held in distilled water in 37°C for 24 hours. Specimens were then thermo-cycled for 650 times at 5°-55°Centigrade. Shear bond strengths were measured by DARTEC machine. Data were evaluated by Duncan and variance analysis. Statistical analysis of data reveals significant differences only in groups one and four [P < 0.05]. The maximum shear bond strength was observed in the fifth group [21.61 +/- 2.6 MP] and the minimum in the third one. After salivary contamination of enamel, adequate clinical shear bond strength can be gained with drying of contaminated area and re-etching for 10 seconds. No washing is required in this case