Shear bond strength of new and recycled orthodontic brackets to enamel surface: an in-vitro study

Recycling brackets is an efficient method to reduce the cost of treatment and decrease waste to the environment. However, various recycling procedures can alter the base of the bracket, thus affecting the bond strength and clinical outcomes.

This study aimed to evaluate the SBS of new and recycled stainless steel orthodontic brackets to enamel surfaces following different recycling procedures.

Fifty extracted human premolars were collected, bonded with stainless steel orthodontic brackets. The premolars were randomly divided into five groups, Group I (control, no recycling), Group II (air abrasion), Group III (silicon carbide stone), Group IV (direct flaming), and Group V (new brackets). Rebonding was performed using the same bonding procedure. All specimens were thermocycled between 5 °C and 55 °C for 3,000 cycles and tested for shear bond strength at a crosshead speed of 1 mm/min using a universal testing machine. The adhesive remnant index (ARI) was evaluated under a stereomicroscope.

Significant differences were found between groups (p < 0.001). The highest mean SBS was observed in the new brackets group followed by the air abrasion group Grinding and flaming groups showed the lowest values. Most specimens showed an ARI score of 3, indicating that a high amount of adhesive remained on the enamel surface after debonding.

Air abrasion proved to be the most effective recycling technique, producing bond strength comparable to new brackets. Grinding and flaming resulted in lower SBS values and are less suitable for bracket recycling.