Influence of Thermal Cycles Number on Bond Strength of Metallic Brackets to Ceramic

Abstract The aim of this study was to evaluate the effect of different number of thermal cycles on the shear bond strength (SBS) of metallic orthodontic brackets bonded to feldspathic ceramic by a composite resin. Twenty-five ceramic cylinders were etched with 10% hydrofluoric acid for 60 s and received two layers of silane. Brackets were bonded to the cylinders using Transbond XT and assigned to 5 groups (n=5): Group 1 - Control group (without thermal cycling); Group 2 - 500 thermal cycles; Group 3 - 5,000 thermal cycles; Group 4 - 7,000 thermal cycles and Group 5 - 10,000 thermal cycles. Light-activation was carried out by Radii Plus LED. SBS testing was carried out after 24 h of storage in deionized water and thermal cycling (5/55 oC and 30 s dwell time). Five brackets were bonded to each cylinder, totalizing 25 brackets for each group. Data were submitted to one-way ANOVA and Tukey’s test (α=0.05). The Adhesive Remnant Index (ARI) was evaluated at 8× magnification. The SBS (MPa) of control group (9.3±0.8), 500 (9.0±0.7) and 5,000 (8.4±0.9) thermal cycles were significantly higher than those after 7,000 (6.8±0.6) and 10,000 (4.9±1.0) thermal cycles (p摘要 本研究旨在评估不同热循环次数对复合树脂粘结的金属正畸托槽与长石质陶瓷间剪切粘结强度（shear bond strength, SBS）的影响。将25个陶瓷圆柱试件用10%氢氟酸蚀刻60秒后，涂覆两层硅烷偶联剂。使用Transbond XT将托槽粘结至陶瓷圆柱，并分为5组（每组n=5）：第1组为对照组（无热循环）；第2组经500次热循环；第3组经5000次热循环；第4组经7000次热循环；第5组经10000次热循环。采用Radii Plus LED光固化机进行光固化。所有试件在去离子水中储存24小时并完成热循环处理（温度区间5/55℃，停留时间30秒）后，开展剪切粘结强度测试。每个陶瓷圆柱粘结5个托槽，每组总计25个托槽。采用单因素方差分析（one-way ANOVA）与Tukey检验（α=0.05）对数据进行统计分析。以8倍放大倍率评估粘结残留指数（Adhesive Remnant Index, ARI）。对照组（9.3±0.8）、500次热循环组（9.0±0.7）及5000次热循环组（8.4±0.9）的剪切粘结强度（MPa）均显著高于7000次热循环组（6.8±0.6）与10000次热循环组（4.9±1.0）（p