This study was undertaken to compare the bond strength and the fracture site of new and recycled brackets according to the base design. 252 sound premolars extracted for orthodontic treatment were collected, and Type I, Type II, Type III brackets were divided into four groups by recycling method. Each bracket was then bonded to an extracted premolar. Instron Universal Testing Machine(model 4466) was used to measure the shear bond strength, and the surface of the recycled brackets were viewed in SEM. For the analysis of the results, one way ANOVA and Scheffe's multiple range test was executed using the SPSSWIN program. 1. The shear bond strength showed statistically significant difference according to the bracket base design(P<0.001). Type III bracket(round indentation base, micro-etched) showed the highest bond strength, Type I bracket(foil-mesh base) was second, and Type II bracket(grooved integral base, micro-etched) was last. 2. The effect of recycling on the bond strength was different according to bracket type. The shear bond strength of Type I, Type II brackets showed the smallist reduction when treated for 1 minute in Big Jane(p<0.05), but the shear bond strength of Type III brackets showed no statistically significant difference according to recycling method(p>0.05). 3. In Type I, Type II brackets, frequent fracture site was bracket-resin interface, but in Type III brackets, about half of the resin was retained on the tooth surface frequently. 4. The shear bond strength was highest when about half of the resin was retained on the tooth surface(p<0.05). 5. The resin remnant on the bracket base after recycling had no effect on the shear bond strength.
Bicuspid ; Recycling ; Tooth