Bond strength of orthodontic buttons on clear aligner materials

Purpose: To evaluate the shear bond strength of orthodontic buttons bonded on various clear aligner materials using orthodontic plastic adhesive. Materials and methods: Three types of thermoplastic materials: 1) Duran (Polyethylene terephthalate glycol), 2) Essix A+ (Polyethylene terephthalate glycol), and 3) Zendura (Polyurethane) were bonded with either metal or plastic buttons using orthodontic plastic adhesive (Bond aligner (R)). Six experimental groups with 15 specimens per group were prepared. Bond strength testing was done according to the Lap Shear Test Method (ASTM D3163) using the universal testing machine. Bond failure mode (modified from ASTM D5573) was examined with a stereoscope. Kruskal-Wallis and post hoc tests were used to analyse the differences in shear bond strength among the six groups. Results: Mean bond strengths were as follows: 1) Duran-metal (DM) (7.04 MPa); 2) Duran-plastic (DP) (5.37 MPa); 3) Essix-metal (EM) (5.55 MPa); 4) Essix-plastic (EP) (4.62 MPa); 5) Zendura-metal (ZM) (1.17 MPa); and 6) Zendura-plastic (ZP) (1.40 MPa). Shear bond strength among the three thermoplastic materials were significantly different (p < .05). For the bond failure mode, regardless of button type, Duran and Essix A+ showed substrate failure of the thermoplastic sheet, while Zendura showed adhesive failure at the thermoplastic sheet interface. Conclusion: Orthodontic buttons bonded on Duran and Essix A+ using orthodontic plastic adhesive could achieve very high bond strength that the thermoplastic sheets would tear before button detachment occurred. Buttons bonded to Zendura resulted in significantly greater bond failure rates.