Comparative assessment of different recycling methods of orthodontic brackets for clinical use

Abstract

BACKGROUND: This study aimed to assess bond strength of the resin/bracket interface, under in-vitro shear stress, of metal brackets recycled by different clinical protocols. METHODS: Sixty stainless steel orthodontic brackets were bonded on acrylic resin. The Transbond XT (TM) resin was applied at the base of the bracket aided by a matrix, obtaining 1 mm of thickness, and photoactivated with a LED device (40 s; 500 mW/cm(2)). Samples were randomly divided into four groups (N=15) according to the reconditioning/recycling protocol: aluminum oxide (AO) 90 mu m; hydrofluoric acid 60 s (HA60); hydrofluoric acid 120 s (HA120); hydrofluoric acid 60 s + silane (HA60S). After recycling, the resin was applied at the base of the bracket for shear testing in a universal testing machine (0.5 mm/min). After reconditioning/recycling, the surfaces were analyzed by Scanning Electron Microscopy. Data obtained after the shear test were subjected to ANOVA and Tukey's test (P<0.05). RESULTS: The AO group presented higher values of shear bond strength compared to the other reconditioning/recycling protocols (P<0.05). The HA120 and HA60S groups presented statistically similar results, but HA120 presented strength below the recommended limit. CONCLUSIONS: The recycling technique by aluminum oxide sandblasting was more effective for reconditioning orthodontic brackets when compared to the other protocols. The reconditioning technique with 10% hydrofluoric acid followed by the application of silane bonding agent may be used as an alternative protocol.