For the purpose of improving the degree of success of plastic bracket bonding, based on the analysis of the chemical components of plastic brackets, a systematic method for the treatment of the adhesive surface of plastic brackets was introduced in this study. After sandblasting the adhesive surfaces of two commercially available plastic brackets (Spirit and Clear Bracket), a favourable surface treatment was obtained with the application of a silane coupling agent, γ-methacryloxy propyl trimethoxy silane. The findings showed that (i) the fillers added to the plastic brackets were glass fillers with Si-OH groups distributed on their surfaces; (ii) sandblasting of the bracket surface resulted in exposure of the glass fillers; (iii) combined with sandblasting, silane coupling treatment significantly increased the bond strength (P < 0.05), which was adequate to withstand the forces generated during orthodontic therapy; and (iv) treatment with sandblasting and silane coupling 24 hours before direct bonding did not cause a significant reduction in bond strength. It is concluded that sandblasting and silane coupling treatment offers the benefit of increasing the in vitro bond strength of plastic brackets for orthodontic application.
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