Surface Chemical Treatment of Orthodontic Brackets for Improved Tooth Adhesion

Adhesives for orthodontic brackets, such as Bis-GMA (Bisphenol A-glycidyl methacrylate) composite resin, adhere strongly to the teeth but very poorly to metallic brackets. To compensate for the lack of adhesion, metal orthodontic brackets were developed with large bases that have a negative effect on patients’ life in terms of their esthetics and hygiene. Objective: The purpose of this study was to develop a new method of creating a strong chemical bond between metallic brackets and Bis-GMA composite based on diazonium chemistry. Method: Three models of stainless steel brackets were first coated with diazonium ions to allow covalent binding on their surfaces, and then immersed in an emulsion of Bis-GMA monomer and a catalyst to build up Bis-GMA polymer chains on the diazonium coating layer. The chemical composition of the treated metal brackets was analyzed by X-ray photoelectron spectroscopy (XPS) while the tensile and shear bonding strengths between Bis-GMA composite and the three models of surface treated metal orthodontic brackets were measured. Result: XPS result confirmed the presence of a treatment coat on the metallic brackets and the bonding strength between Bis-GMA and brackets was increased after the treatment by 2 to 3.9 folds compared to untreated brackets. Conclusion: The resulting bonding method can be utilized to decrease the size of metal brackets by at least 50% and reduce many of dental problems associated with using large brackets.