Comparison of Shear Bond Strength of Different Orthodontic Metal Bracket-bases Bonded on Enamel Surface – an In vitro Study

Aim: To compare the shear bond strength of different metal bracket bases bonded on enamel surface and further to evaluate the Adhesive Remnant Index score to localize the sites of adhesive fracture.

Materials and Methods: Four types of premolar metal brackets were selected according to their different mesh designs: (G1, Gemini Series,3M Unitek; G2,Micro Sprint, Forestadent; G3,Equilibrium 2,Dentaurum and G4,Mini-Master Series, American Orthodontics). One hundred brackets for each type were used and bonded on enamel surfaces of extracted human premolars (Transbond XT, 3M Unitek) and were tested to evaluate shear bond strength with an Instron Universal Testing Machine (Star Testing Systems, India). All data were analysed with ANOVA, Tukey’s HSD Post hoc test, and with descriptive statistics. The adhesive fracture site was also evaluated and classified with ARI score.

Results: G2 showed greater shear bond strength when compared with other samples (P < 0.001). G2 and G3 showed statistically significant differences in comparison with other groups with respect to shear bond strength. There was no statistically significant difference between G1 and G4. The ARI index demonstrated a large variability. G2 showed 70% of the adhesive fracture at cement-enamel interface.

Conclusion: G2 showed the highest shear bond strength in comparison with other groups. ARI score showed that G2 resulted in 70% adhesive fractures at the cement-enamel interface. An increased size of the bracket-base enhances adhesion but affects the adaptability to surface morphology of the enamel, increasing the risk of fracture at the interface with the bracket.