The Effect of Four Surface Treatment Methods on the Shear Bond Strength of Metallic Brackets to the Fluorosed Enamel

Statement of the problem: some studies have reported the bond strength to be significantly lower in fluorotic enamels than the non-fluorosed.purpose: the purpose of this study was to evaluate the shear bond strength of metallic brackets to non-fluorosed and fluorosed teeth after different enamel conditioning.materials and method: a total of 176 freshly extracted human premolars (88 non-fluorosed and 88 fluorosed teeth) were used in this study for bonding the metallic brackets. teeth with moderate fluorosis were used according to thylstrup and fejereskov index (tfi). eighty non-fluorosed and 80 fluorosed teeth (tfi=4-6) were randomly divided into 8 equal groups of 20 teeth each. the remaining 16 teeth were used for scanning electron microscopy observation. the enamel surface was conditioned by 4 methods: acid etching for 30 sec, acid etching for 120 sec, air abrasion followed by acid etching, and er: yag laser etching followed by acid etching. the morphology of etching patterns in different groups was studied under scanning electron microscope. results: the shear bond strength of fluorosed teeth to the brackets was significantly lower than non-fluorosed ones (p= 0.003). the shear bond strength of laser-acid groups in both non-fluorosed and fluorosed teeth was significantly lower than other groups (p < 0.001). weibull analysis indicated that the chance of failure under the applied force was different between fluorosed and non-fluorosed group. the scanning electron microscope observations revealed that the fluorosed teeth treated with phosphoric acid had fewer irregularities compared to non-fluorosed teeth. the most irregularities were detected in the teeth conditioned with phosphoric acid for 120 seconds. conclusion: fluorotic enamel adversely affects the bond strength of orthodontic brackets. none of the conditioning methods tested in this study could significantly improve shear bond strength of metallic brackets. er: yag laser conditioning followed by acid further reduced the bond strength in non-fluorosed and fluorosed teeth.