Abstract
ABSTRACTIntroduction: Orthodontic treatment for adults is currently increasing, and therefore the need to bond brackets to restorations and temporary crowns. The use of CAD/CAM PMMA provisional restorations for orthodontic purposes have not yet been described, and there is currently insufficient information regarding the strength of bracket adhesion. Objective: This study aimed at evaluating the effects of thermocycling (TC) and surface treatment on shear bond strength (SBS) of brackets to different provisional materials. Methods: Forty specimens were made from each material [PMMA (Telio Lab), bis-acryl (Telio CS C&B), and PMMA CAD/CAM (Telio CAD)], sandpapered, and divided according to surface treatment (pumiced or sandblasted) and TC (half of the samples = 1,000 cycles, 5°C/55°C water baths) (n = 10/group). Stainless-steel brackets were bonded to the specimens (using Transbond XT), and SBS testing was performed. Data were analyzed by three-way ANOVA and LSD post-hoc tests (α = 0.05). Failure types were classified with adhesive remnant index (ARI) scores. Results: SBS values ranged from 1.5 to 14.9 MPa. Sandblasted bis-acryl and sandblasted auto-curing PMMA groups presented similar values (p> 0.05), higher than the CAD/CAM material (p< 0.05), with or without TC. When thermocycled, pumiced bis-acryl showed higher SBS than pumiced acrylic (p= 0.005) and CAD/CAM materials (p= 0.000), with statistical difference (p= 0.009). TC showed negative effect (p< 0.05) for sandblasted bis-acryl and pumiced acrylic groups. ARI predominant score was mostly zero (0) for CAD/CAM, 1 and 2 for bis-acryl, and 1 for acrylic groups. Conclusion: In general, bis-acryl material showed the highest SBS values, followed by acrylic and CAD/CAM materials, which showed SBS values lower than an optimum strength for bonding brackets.
Highlights
Orthodontic treatment for adults is currently increasing, and the need to bond brackets to restorations and temporary crowns
Table 1 summarizes the mean and standard deviation of shear bond strength (SBS) determined for each material, according to surface treatment and TC
SBS values ranged from a minimum of 1.5 MPa, to a maximum of 14.9 MPa for the sandblasted bis-acryl material without thermocycling
Summary
Orthodontic treatment for adults is currently increasing, and the need to bond brackets to restorations and temporary crowns. Provisional restorations are made from auto-curing polymethylmethacrylate (PMMA) resins.[6] these are prone to discoloration and can cause chemical irritation or allergic reactions during polymerization.[10] their polymerization shrinkage can cause marginal discrepancies in the provisional crowns.[11] A new class of material, the bis-acryl resins, shows low exothermic reaction during setting, with better strength, marginal adaptation and contour.[12] Another class of provisional material involves a novel technique, the computer-aided design/computer-aided manufacturing (CAD/CAM) materials The emergence of this technology allowed for high precision materials, since restoration is milled from pre-polymerized blocks of the provisional material, any degree of polymerization shrinkage occurs during processing of the block and not intra-orally.[9] this indirect material presents higher fracture strength and lower marginal gap than direct techniques such as bis-acryl resins.[9] one disadvantage is the cost, in comparison to conventional provisional restorations.[9] The use of CAD/CAM PMMA provisionals for orthodontic purposes had not yet been described in literature
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