In vivo comparison of the friction forces in new and used brackets.

Studies that evaluate frictional force on orthodontic brackets usually compare ligature, archwire size, bracket alloys, and systems. However, these studies do not simulate in vitro specific conditions of in vivo situations. Aiming to evaluate some conditions not created in vitro, 30 used standard edgewise brackets (30.7 months) collected from patients in the end of treatment (group 1) and 20 as-received brackets (group 2) of the same brand were compared. The brackets used in vivo were carefully removed to avoid deformation. Frictional resistance tests of both groups were performed in a universal testing machine using a system that standardizes normal force. Five brackets from each group were analyzed with scanning electron microscopy (SEM). Student t tests were used to compare the frictional force between groups 1 and 2 and showed a statistically difference (32.91 and 21.22 g, respectively). The Mann-Whitney test showed that group 1 had more organic matter attached to the slot surface compared with group 2 (P < .05). However, a comparison of topography between the groups did not show a statistically significant difference. SEM analysis showed a statistically high correlation (r = 0.73) between organic matter adhesion to the slot surface and frictional resistance. However, the results were not significant. These results indicate the clearance of brackets and wires during sliding mechanics.