Date of Award

Spring 1993

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)



First Advisor

Dhuru, Virendra B.

Second Advisor

Ferguson, Donald J.

Third Advisor

Kittleson, Russell T.


With the introduction of ceramic brackets to orthodontics many clinicians have met with frustration when attempting torquing movements of the dentition treated with ceramic brackets. The occurrence of ceramic bracket fracture from archwire torsion has been deemed excessive. The purpose of this study was to determine the fracture resistance of four commercially available ceramic brackets during archwire torsion. The brackets included in the study were, Starfire TMB ("A" Company), Allure Ill (GAC International), Transcend 6000 (Unitek) and Lumina (Ormco). Of these, Starfire TMB is made of single crystal alumina while the others are made of polycrystalline alumina. Buccal root torque was applied from the distal side of upper right central incisor brackets with 0.018 inch slots by means of a 0.018 x 0.025 inch stainless steel archwire. A specially designed fixture with an analog torque meter was used to test four types of ceramic brackets in sample groups of 30. The amount of angular deflection in degrees and torsional moment to an accuracy of 0.1 oz-in. of the archwire at bracket fracture were measured and the fracture location was recorded. The following conclusions were made: 1. During buccal root torque of central incisor brackets, the ceramic rackets could be separated into three strength levels based on the mean torsional moment at fracture. In decreasing order, the first level contained Starfire TMB, which was statistically different from all other brackets at p<0.01. The second strength level included Lumina which was statistically different from Starfire TMB and Transcend 6000 at p<0.01 and from Allure Ill at p<0.05. Included in the weakest level at p<0.05 and p<0.01 was the Allure Ill and Transcend 6000. Fracture locations were statistically different at the p<0.01 level for Starfire TMB and all other groups due to almost half of the brackets resisting fracture within the range of the torquemeter used. 2. Allure Ill ceramic brackets fractured occurring through the base. Lumina and Transcend 6000 were not statistically different exhibiting fracture locations through the gingival wing. 3. The bracket exhibiting the highest mean torsional moment prior to fracture was of monocrystalline composition (Starfire TMB). The polycrystalline type bracket showing the highest mean torsional moment was Lumina. Lumina brackets also demonstrated the greatest variation in torsional strength.



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