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INTRODUCTION: Adult patients typically require high-quality orthodontic treatment for ceramic brackets, but some clinicians remain concerned about the bond strength of these brackets. Therefore, the aim of this study was to determine the shear bond strength and de-bonding characteristics of metallic and ceramic brackets bonded with two types of bonding agents. METHODS: In an experimental study done in 2013 in Babol, Iran, 120 extracted human maxillary premolar teeth were randomly divided into four groups as follows: HM group: metallic bracket/conventional bonding agent; SM group: metallic bracket/Transbond self-etching primer; HC group: ceramic bracket/conventional bonding agent; SC group: ceramic bracket/Transbond self-etching primer. Twenty-four hours after thermocycling (1000 cycle, 5 °C-55 °C), the shear bond strength values were measured. The amount of resin remaining on the tooth surface (adhesive remnant index: ARI) was determined under a stereomicroscope. Enamel detachment index was evaluated under a scanning electron microscope. To perform statistical analysis, ANOVA, Kruskal-Wallis, and Tukey post-hoc tests were applied. The level of significance was set at p <0.05. RESULTS: The mean shear bond strength values (MPa ± SD) were group HM=12.59, group SM=11.15, group HC=7.7, and group SC=7.41. Bond strength differences between groups HM and SM (p=0.063) and between HC and SC (p=0.091) were not statistically significant. There were significant differences between HM and HC and between SM and SC groups (p < 0.05). Insignificant differences were found in ARI among all groups. CONCLUSION: Our findings indicated that the metallic brackets had higher bond strengths in comparison with ceramic brackets. In addition, self-etching primer was able to produce fewer bonds compared with the conventional technique. Many samples showed the bracket-adhesive interface failure or failure inside the adhesive.
RESUMO
PURPOSE: There is a controversial body of evidence regarding optimal insertion angulation of an orthodontic miniscrew as a mean of skeletal anchorage. MATERIALS AND METHODS: A bracket head-type 8-mm-long miniscrew (60-degree symmetrical trapezoid thread, 0.1-mm thread fillet, 0.2-mm thread height, with 0.5-mm thread pitch) was designed and monocortically inserted at 30, 45, 55, 70, 90, 110, 125, 135, and 150 degrees of inclination to the surface of bone. A bilayer cortical (1.6 mm) and cancellous (8.5 mm) bone model was constructed, adopted from a 22-year-old male patient's cone beam computed tomography (CBCT) image of his anterior hard palate area. A horizontal force of 2 N was applied parallel to the bone surface. Bone material was simulated as normal and osteoporotic bone. The maximum equivalent von Mises stress and microstrain values were separately calculated for the miniscrew, cortical bone, and cancellous bone. Deflections of the whole bone and miniscrew were also reported. RESULTS: A significant lower stress was found in the cancellous bone compared to the cortical bone. Osteoporotic bone displayed higher strain values. Overall, 30-degree models exhibited the lowest von Mises stress and strain values for the cortical layer and miniscrew in both normal and osteoporotic models. Meanwhile, 90-degree models displayed the lowest strain values in the osteoporotic and normal cancellous bones. Minimum bone and miniscrew deflection values were related to the model of 30-degree insertion angulation. CONCLUSION: These results showed that, within the limitations of the study, the 30-degree angulation of miniscrew insertion toward the direction of applied force could lower the cortical bone stress and strain.
