Effect of two erosive protocols using acidic beverages on the shear bond strength of orthodontic brackets to bovine enamel

Abstract Objective: To assess the short-term effect of two in vitro erosive challenge protocols on the bond strength of metal orthodontic brackets on bovine enamel. Methods: Sixty bovine incisors were selected and randomly divided into six groups: AS7 (artificial saliva - 7 days, Control Group); CC7 (Coca-Cola™ - 7 days); LJ7 (lime juice - 7 days); AS30 (artificial saliva - 30 days, Control Group); CC30 (Coca-Cola™ - 30 days); LJ30 (lime juice - 30 days). Microhardness testing was performed prior to the erosive challenge to verify the standardization of samples. Immersion was performed 4x/day for five minutes, for either 7 or 30 days. After immersions were concluded, the brackets were bonded and shear bond strength was assessed after 48 hours. The Adhesive Remnant Index (ARI) was also assessed. Data were analyzed by two-way ANOVA, followed by Tukey’s post-hoc and Student’s t test for paired samples, and the Kruskal-Wallis non-parametric test (α = 5%). Results: The mean and standard deviation of microhardness testing of total samples were 281.89 ± 44.51 KHN. There was no statistically significant difference in shear bond strength for the time factor (7 or 30 days; F5.54= 0.105; p = 0.901). However, there was a statistically significant difference for the solution factor (F5.54= 6.671; p = 0.003). These differences occurred among solutions of Saliva x Coca-Cola™ (p = 0.003) and Coca-Cola™ x Lime Juice (p= 0.029). The assessment of the Adhesive Remnant Index showed no significant difference between groups. Conclusions: The immersion time used in the erosion protocols did not affect the bond strength of brackets to teeth. Coca-Cola™ induced significantly higher shear bond strength values than lime juice and artificial saliva. However, the short term effects of 7/30 days in this in vitro study may not be extrapolated for in vivo ones. Clinical studies should be conducted, substantiating the laboratory results.

摘要 目的：评估两种体外侵蚀刺激方案对牛牙釉质上金属正畸托槽粘结强度的短期影响。方法：选取60颗牛切牙，随机分为6组：AS7（人工唾液-7天，对照组）、CC7（可口可乐™-7天）、LJ7（柠檬汁-7天）、AS30（人工唾液-30天，对照组）、CC30（可口可乐™-30天）、LJ30（柠檬汁-30天）。侵蚀刺激前先行显微硬度测试以验证样本标准化程度。每日浸泡4次、每次5分钟，分别持续7天或30天。浸泡结束后，粘结正畸托槽并于48小时后测定剪切粘结强度（shear bond strength），同时评估粘结残留指数（Adhesive Remnant Index, ARI）。采用双因素方差分析（two-way ANOVA）、Tukey事后检验、配对样本Student t检验及Kruskal-Wallis非参数检验进行数据分析，检验水准α=5%。结果：全部样本的显微硬度测试均值与标准差为281.89±44.51 KHN。时间因素（7天或30天）对剪切粘结强度无统计学显著差异（F5.54=0.105，p=0.901）；但溶液因素存在统计学显著差异（F5.54=6.671，p=0.003），具体差异见于人工唾液组与可口可乐™组（p=0.003）以及可口可乐™组与柠檬汁组（p=0.029）。粘结残留指数评估显示各组间无显著差异。结论：本研究所用的侵蚀刺激时长未对托槽与牙体的粘结强度产生影响。可口可乐™组的剪切粘结强度值显著高于柠檬汁组与人工唾液组。但本体外研究中7/30天的短期效应无法外推至体内环境，需开展临床研究以验证实验室所得结果。