The effect of early static loading on the in vitro shear/peel bond strength of a 'no-mix' orthodontic adhesive

This study addressed the question of whether shear and tensile loads applied 15 minutes after bonding metal brackets to enamel affected the shear/peel bond strength of the adhesive. Ninety standard 0.022-inch stainless steel edgewise premolar mesh-backed brackets were bonded using a no-mix chemical-cured adhesive to 90 teeth, which had been prepared in a standardized manner. After 15 minutes three groups of 30 teeth were subjected to the following regimes: no applied load, tensile static load of 0.77 N (78 g), and shear static load of 0.77 N. After 14 days storage in 100 per cent relative humidity at 37°C, the shear/peel strength of the adhesive bond was measured using a purpose built jig mounted on a universal testing machine. Shear/peel bond strengths were analysed using Weibull statistics. The Weibull moduli of the three groups indicated that the adhesive performed consistently despite early static loading. Characteristic strengths were 9.22, 9.27, and 9.05 MPa for the control, tensile, and shear groups, respectively. The findings indicate that static loads (such as tying in or archwires) can be placed on brackets 15 minutes after cementation, without a clinically significant reduction in bond strength of the tested adhesive.