Tensile and shear strengths of bonded and rebonded orthodontic attachments.

The objective of this study was to investigate the effect of a low-viscosity sealing resin and temperature cycling on the tensile and shear strengths of bonded and rebonded attachments. Eighty extracted noncarious human maxillary central incisors were used. The tensile bond strengths of a chemically activated bonding paste to etched enamel, with and without a low-viscosity sealing resin and with and without 500 temperature cycles between 5 degrees C. and 55 degrees C., were determined. The tensile bond strengths on rebonding were determined on the same teeth in such a way that the rebonded specimens were subjected to the same two variables as the originally bonded teeth. The shear bond and rebond strengths were determined on the remaining forty teeth. The specimens were tested to failure in an Instron machine. The bond strengths were expressed in MN.m-2. Analysis of variance was used to analyze the data. Temperature cycling adversely affected tensile bond and rebond strengths, while the sealing resin had no additional effect on tensile and shear bond and rebond strengths. Tensile versus shear and bond versus rebond strengths for similarly prepared specimens were not significantly different.