Effect of changing a test parameter on the shear bond strength of orthodontic brackets.
The purpose of this study was to determine the effect of changing the crosshead speed of the testing machine on the shear bond strength of orthodontic brackets to enamel while standardizing all the other variables. Forty freshly extracted human molars were bonded using the Transbond XT adhesive system (3M Unitek, Monrovia, Calif). The teeth were randomly divided into two groups. In group I, the shear bond strength was measured at a crosshead speed of 5.0 mm/min, and in group II the shear bond strength was measured at a crosshead speed of 0.5 mm/ min. Within half an hour from the initial bonding of each tooth, an occlusogingival load was applied to the bracket, producing a shear force at the bracket-tooth interface. This was accomplished by using the flattened end of a steel rod attached to the crosshead of a Universal Test Machine (Zwick GmbH & Co, Ulm, Germany). The t-test results (t = 2.71) indicated that there was a significant difference (P = .014) in the shear bond strengths between the group tested at a crosshead speed of 5.0 mm/min and the group tested at a crosshead speed of 0.5 mm/min. The mean shear bond strengths for the two groups were 7.0 +/- 4.6 MPa and 12.2 +/- 4.0 MPa, respectively. These findings indicated that it is important to identify the parameters included in shear bond testing in order to enable meaningful comparisons of the performance of different materials.
Bishara
Samir E
SE
Orthodontic Department, College of Dentistry, University of Iowa, Iowa City, Iowa 52242, USA. samir-bishara@uiowa.edu
Soliman
Manal
M
Laffoon
John
J
Warren
John J
JJ
D001840:Dental Bonding / Q000592:standards*; D003799:Dental Stress Analysis / Q000592:standards*; D006801:Humans; D008422:Materials Testing / Q000592:standards*; D008963:Molar; D016910:Orthodontic Brackets; D019279:Resin Cements; D033081:Shear Strength
D019279:Resin Cements; C477790:Transbond XT