Effect of different bonding protocols on degree of monomer conversion and bond strength between orthodontic brackets and enamel

Abstract The objective of the present study was to evaluate the effect of different surface treatments and polymerization protocols on the bond strength of brackets to enamel, and the degree of conversion of the bonding agents. 120 bovine crowns were embedded in acrylic resin blocks and sanded. Next, the blocks were randomly assigned into 12 groups. Metal brackets were bonded to enamel according to the “surface treatment” factor (A: Phosphoric Acid; ATxt: Phosphoric Acid + Transbond XT Primer®; Tse: Transbond Plus Self Etching Primer®; and SBU: Scotchbond Universal®) and “polymerization” factor (R20: Radii-Cal®/20 seconds; V20: Valo Cordless®/20 seconds; and V3: Valo Cordless®/3 seconds). All samples were stored for 6 months (water, 37ºC) and then subjected to a shear bond strength test (SBS). Bond failures were classified according to the Adhesive Remnant Index (ARI) and analyzed with the Kruskal-Wallis and Mann-Whitney tests (5%). Using the same factors, 120 resin discs were made to assess the degree of conversion (DC) of the monomer. Data from the SBS (MPa) and DC (%) were analyzed by analysis of variance (2 factors) and Tukey’s test (5%). For the SBS, the factors “polymerization” (R20 = 8.1B; V20 = 13.2A; V3 = 5.2C, p = 0.0001) and “surface treatment” (A = 3.1C; ATxt = 13.6A; Tse = 12.3A; SBU = 6.3B, p = 0.0001) were statistically significant among groups. The highest adhesion value were found for the ATxt/V20 group (22.2A) and the lowest value for the A/R20 group (1.2E). Regarding ARI, score 2 was the most prevalent in groups A, ATxt, V20 and V3, while score 4 was the most prevalent in the Tse, SBU and R20 groups, with no significant difference between them (p = 1.0). Regarding DC, the factors “polymerization” (R20 = 66.6A; V20 = 58.4B; V3 = 45.1C, p = 0.0001) and “surface treatment” (A = 52B, ATxt = 59.7A, Tse = 51.4B, SBU = 63.8A, p = 0.0001) were statistically significant. Tse was more sensitive to the variations in polymerization protocols than the other surface treatments. Treatment A did not present suitable bond strength or degree of conversion.摘要 本研究旨在评估不同表面处理方式与聚合方案对托槽与牙釉质粘结强度，以及粘结剂单体转化率的影响。将120颗牛牙牙冠包埋于丙烯酸树脂块中并打磨，随后将试件随机分为12组。根据“表面处理”因素（A：磷酸酸蚀；ATxt：磷酸酸蚀+Transbond XT Primer®；Tse：Transbond Plus Self Etching Primer®；SBU：Scotchbond Universal®）与“聚合方案”因素（R20：Radii-Cal®/20秒；V20：Valo Cordless®/20秒；V3：Valo Cordless®/3秒），将金属托槽粘结于牙釉质表面。所有试件于37℃去离子水中储存6个月，随后开展剪切粘结强度试验（Shear Bond Strength Test, SBS）。粘结失效情况依据粘结残留指数（Adhesive Remnant Index, ARI）进行分类，并采用克罗斯卡尔-沃利斯检验与曼-惠特尼检验进行分析（显著性水平α=5%）。采用相同的分组因素，制备120个树脂圆盘以检测粘结剂单体的转化率（Degree of Conversion, DC）。剪切粘结强度（单位：MPa）与单体转化率（单位：%）的数据均采用双因素方差分析与图基检验进行分析（显著性水平α=5%）。剪切粘结强度结果显示，“聚合方案”因素（R20=8.1B；V20=13.2A；V3=5.2C，p=0.0001）与“表面处理”因素（A=3.1C；ATxt=13.6A；Tse=12.3A；SBU=6.3B，p=0.0001）在各组间均具有统计学显著性差异。ATxt/V20组的粘结强度最高（22.2A），A/R20组粘结强度最低（1.2E）。关于粘结残留指数，A组、ATxt组、V20组与V3组以评分2最为普遍；而Tse组、SBU组与R20组则以评分4最为普遍，组间无统计学显著性差异（p=1.0）。关于单体转化率，“聚合方案”因素（R20=66.6A；V20=58.4B；V3=45.1C，p=0.0001）与“表面处理”因素（A=52B，ATxt=59.7A，Tse=51.4B，SBU=63.8A，p=0.0001）的影响均具有统计学显著性。其中Tse组相较于其他表面处理组，对聚合方案的变化更为敏感。单纯磷酸酸蚀处理（A组）既未表现出理想的粘结强度，也未达到合适的单体转化率。