Bond strength of pre-coated flash-free adhesive ceramic brackets. An in vitro comparative study on the second mandibular premolars

Abstract

Clinical studies show a mean bond failure rate of orthodontic brackets, which ranges between 6% and 8%, with a predominance for the second mandibular premolars. The pre-coated flash-free adhesive ceramic brackets allow to obtain, according to their manufacturer, a low bond failure rate, while ensuring a simplified implementation. The aim of this study was to measure the shear bond strength of ceramic brackets bonded with the direct method using a pre-coated flash-free adhesive system, and to compare it with the shear bond strength of the old generation precoated brackets and that of operator coated brackets to the buccal surface of the second mandibular premolars. 45-second mandibular premolars extracted for orthodontic purposes were randomly distributed into 3 groups of 15 teeth each. In the first group, the brackets were precoated with the APC™ Flash-Free® system (3M Unitek; in the second group, with the APC Plus® system (3M Unitek), and in the third group, the brackets were bonded manually with the Transbond XT® composite (3M Unitek). The enamel surface was prepared in the same way for the 3 groups: etching using 36% orthophosphoric acid, followed by the application of the Transbond XT® primer adhesive (3M Unitek). Each sample was submitted to shear bond strength forces using a Universal Testing Machine LRX® (Lloyd Instruments LTD., Fareham, UK) in shear mode with a crosshead speed of 1.0mm/min. The bond strength values of the brackets were recorded in megapascals (MPa) for each tooth. The mean values were then compared using the one-way ANOVA test. Although the mean shear bond strength value for the APC Flash-Free® group was lower than those of the two other groups, this difference was not statistically significant (P=0.276). Given the experimental conditions of this in vitro study, the shear bond strength of the brackets precoated with the APC Flash-Free® system is comparable to the two other conventional systems.