Comparative Evaluation of Shear Bond Strength of Recycled Metal and Ceramic Orthodontic Brackets Following Different...

Fixed orthodontic treatment relies on adequate bond strength between brackets and enamel to withstand functional forces during therapy. The recycling of debonded brackets is a common practice to reduce treatment costs; however, it may compromise the shear bond strength (SBS) depending on the reconditioning method and bracket material. This in vitro study aimed to evaluate and compare the SBSs of recycled metal and ceramic orthodontic brackets after different surface treatment methods.

A total of 96 extracted human premolars were randomly divided into two main groups: metal brackets and ceramic brackets (n = 48 each). Each group was further subdivided into four subgroups (n = 12): control (new brackets), sandblasting with 50 µm aluminum oxide, burnout followed by ultrasonic cleaning, and finishing bur. All brackets were bonded using a standard protocol with a light-cured orthodontic adhesive. After debonding, the recycled brackets were treated with the respective surface-conditioning methods and rebonded to fresh teeth. The SBS was tested using a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed using the Shapiro-Wilk test for normality, two-way analysis of variance (ANOVA), and Tukey's post-hoc test. Statistical significance was set at p < 0.05.

The new brackets exhibited the highest SBS in both the metal (20.57 ± 1.16 MPa) and ceramic (26.01 ± 1.42 MPa) groups. All recycling methods significantly reduced bond strength compared to the control group. Sandblasting demonstrated superior performance among the recycling techniques, yielding 13.07 ± 2.26 MPa for metal and 20.37 ± 3.41 MPa for ceramic brackets, followed by burnout with ultrasonic cleaning (12.12 ± 0.81 MPa for metal and 14.38 ± 1.64 MPa for ceramic brackets). The finishing bur method resulted in the lowest bond strength values (7.09 ± 1.13 MPa for metal and 14.08 ± 1.49 MPa for ceramics). Two-way ANOVA revealed significant main effects of bracket type and surface treatment, along with a significant interaction between them, indicating that the effect of recycling methods differed between metal and ceramic brackets (p < 0.05).

Recycling orthodontic brackets reduces the SBS, with the magnitude of reduction varying according to the surface treatment method and bracket material. Sandblasting was the most effective in-office recycling technique. Although recycled brackets, especially those treated with sandblasting, may achieve clinically acceptable bond strengths, new brackets are recommended for optimal performance, particularly with ceramic systems. Further in vivo studies are warranted to confirm these findings under clinical conditions.