Method:CAD/CAM technology (Cerec inLab, Sirona) was used to mill orthodontic brackets with 0.018 x 0.025 inch-slot of Yttria stabilized Zirconia (In-Ceram YZ, Vita Zahnfabrik) in both low (0.05 inch) and standard (0.08 inch) profile. Moreover, the inciso-gingival height of low profile YZ brackets was reduced to half of the standard ones. 10 brackets of each size were subjected to torque by a 0.018 x 0.025-inch stainless steel arch wire (G&H) using a specially designed apparatus attached to an Instron Universal Testing Machine. The loads (gf) at failure were recorded. The average moments and degrees of torsion necessary to fracture the brackets were determined and compared to those of commercially available alumina brackets that have a profile of more than 0.075 inch: Mystique and Resolve (Dentsply GAC) tested in the same manner with equivalent sample sizes.
Results:
Group |
Torque at Failure (gm.mm) |
Significant Difference |
Torsion Angle at Failure (°) |
YZ (Zirconia, Upper Central Incisor) |
11902.4 ± 1976 |
A |
40.9 ± 6 |
Mystique (Alumina, Lower Incisor) |
9352.4 ± 2478 |
B |
33.1 ± 13 |
Mystique (Alumina, Upper Central Incisor) |
8433.1 ± 1346 |
B |
30.8 ± 6 |
Low profile YZ (Zirconia) |
8137.6 ± 1534 |
B |
31.3 ± 7 |
Resolve (Alumina, Lower Incisor) |
5405.9 ± 579 |
C |
18.7 ± 5 |
ANOVA and Tukey at p=0.05, groups with different letters are significantly different.
Conclusion: Low profile zirconia brackets showed comparable or even statistically significant higher resistance to arch wire torsion than the larger commercial alumina brackets.