The aims of this study were to determine the effect of different surface treatment methods and provisional materials on the shear bond strength of orthodontic brackets. One hundred and sixty samples were randomly divided into 4 material groups (n=40); A: acrylic resin (Unifast™ Trad), B: bis-acryl (Protemp™ 4), C: polycarbonate crown (3M ESPE), D: denture teeth (Cosmo™ HXL). In groups A and B, 5×5×2 millimeter box-form cavities were prepared on cured resin blocks and these cavities were filled with provisional materials. After polymerization, the materials’ surfaces were polished and stored in distilled water for 7 days. In group C and group D, samples were embedded in a self-curing epoxy resin within polyvinyl chloride pipes in which the labial surfaces of C and D were above the self-curing epoxy resin and stored in distilled water for 7 days. Samples of each group were randomly divided into 4 subgroups of the following surface treatments (n=10); 1: Control, 2: 600-grit sandpaper, 3: Assure™ Plus, and 4: Sandblast. Lower incisors brackets (Gemini™, 3M) were attached with Transbond™ XT adhesive. All samples were stored in distilled water for 24 hours. A thermocycling procedure was conducted for 500 cycles between 5 °C and 55 °C. Samples were stored in distilled water for 24 hours. The shear bond strength was measured with a universal testing machine. The mode of failure was examined under a stereo microscope.
The results of the surface treatment groups showed that the mean shear bond strength of sandblasting groups was significantly higher than all other surface treatment groups of all materials, except for sandblasting on the bis-acryl group (B4) (p<0.05). Other surface treatment methods on all materials showed no statistically significantly difference except in the polycarbonate crown with Assure™ Plus (C3), which presented the lowest mean shear bond strength (p<0.05). The mean shear bond strengths of custom type materials (group A and B) were significantly higher than the prefabricated type material (group C and D) (p<0.05).
Both types of materials and surface treatment methods influenced the shear bond strength of the brackets bonded to the provisional materials. The sandblasting technique enhanced the shear bond strength effectively in all materials except for bis-acryl that originally expressed high shear bond strength even without surface treatment. The surface treatment that uses the sandblasting technique and using bis-acryl composite which exhibited higher shear bond strength to other materials and surface treatment may offer a good option in clinical practice.