Pc. Aknin et al., FRACTURE STRENGTH OF CERAMIC BRACKETS DURING ARCH WIRE TORSION, American journal of orthodontics and dentofacial orthopedics, 109(1), 1996, pp. 22-27
This study evaluated the fracture strengths of eight new vintage ceram
ic brackets with application of torsional forces. Palatal root torque
was applied at the distal side of right maxillary central incisor brac
kets with 0.022-inch dots by means of a 0.0215 x 0.027-inch rounded ed
ge stainless steel arch wire. A specially designed apparatus that atta
ched to an Instron machine was used to test the ceramic brackets. The
amount of torque, degress of torsion at failure, and fracture location
s were measured. The monocrystalline bracket did not break when the to
rquing test was applied; the portion of the wire outside the slot of t
he bracket twisted on itself. The mean torquing forces at failure rang
ed from 5755.2 gm-mm to 9316.5 gm-mm and could be separated into three
statistically different groups. The mean torsional rotation at fractu
re ranged from 32.7 degrees to 68.1 degrees for the polycrystalline br
ackets. The results suggested that all the brackets studied were suffi
ciently strong to withstand the commonly accepted magnitudes of arch w
ire torquing forces. The present investigation showed higher angulatio
n values for all the brackets than those reported by Holt(2) who used
the same apparatus with older style brackets.