Shear Bond Strength between Metal Orthodontic Brackets and Chemically-Prepared Dental Base Alloy Surfaces: An In vitro Study
Objectives: This study was designed to measure and compare the shear strength of the bond between metal orthodontic brackets and dental base alloys when different metal primers and different adhesive bonding systems were applied without any mechanical preparation on the alloy surfaces.
Materials & Methods: Seventy-two dental base alloy discs were cast and randomly categorized into three groups (24 each) according to the different type of metal primer to be used: 1) No primer, 2) Alloy Primer, and 3) Reliance Metal Primer. Brackets were bonded to the discs of each subgroup according to the bonding system used: 12 discs of light-cured adhesive and 12 discs of self-cured adhesive. After the discs were stored in 37°C distilled water for 24 hours, thermal cycling was performed on them. Shear bond strength was tested using a universal testing machine. Descriptive and comparative statistical analyses of the bond strength were carried out. The failure mode was also investigated.
Results: The type of dental adhesive and the type of metal primer affected the shear strength of the bond (p < 0.05). Light-cured bonding adhesive without primer could not bond to the alloy surfaces while self-cured adhesive showed high bond strength. For light-cured bonding adhesives, Alloy Primer produced significantly greater bond strength than did Reliance Primer. For self-cured adhesive, Alloy Primer showed comparable bond strength to Reliance Primer. Metal primers with self-cured adhesive revealed significantly greater bond strength than self-cured adhesive alone. The failure mode after bracket debonding differed with the primer used with self-cured adhesive. No adhesive remains on alloy surface when bonded with light-cured adhesive.
Conclusions: Metal primer can significantly improve the shear strength of the bond between orthodontic adhesives and dental base alloy surfaces. In this in vitro study, combination of metal primer and self-cured adhesive is recommended
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