Effect of air humidity on brackets bond strength to enamel

Objective: to evaluate the effect of air humidity on the bond strength of brackets to enamel treated with hydrophilic or hydrophobic agents. Methods: Sixty human sound bicuspids were selected, and ascribed to 4 groups (n=15): Group A: a hydrophobic bonding agent (Transbond XT Light Cured Adhesive, 3M UNITEK) [XT - Control], Group B: a hydrophilic bonding agent (Transbond MIP - Moisture Insensitive Primer, 3M UNITEK) [MIP - Control], both groups tested under controlled room conditions (20 to 21°C, 40 - 45% air humidity); Group C: Transbond XT Light Cured Adhesive [XT- Test], and Group D: Transbond MIP [MIP - Test], both groups tested under 34-35°C and 90-95% air humidity, as measured by a thermo hygrometer. The shear bond testing was performed in a universal test machine (Instron) at a cross-head speed of 1 mm/min, and the data were analyzed statistically by One-Way ANOVA (SPSS 10.0). After the shear bond test, the bicuspids and the respective brackets were analyzed under stereoscopic glasses (64X) for analysis and categorization of the fracture type. Results: the results of the shear bond strength in MPa (Mean ± SD) were: Group A=27.4 (7.4), Group B=31.9 (7.6), Group C=27.7 (6.5), Group D=27.2 (6.6). There were no statistically significant differences between the groups. Conclusion: the air humidity did not reduce the shear bond strength of the hydrophobic and hydrophilic bonding agents tested.