Original data——In Vitro: The Influence of Orthodontic Mechanical Factors on Enamel Micro-Cracks
Description
This study sequentially tested three procedures: adhesive removal, debonding shear force, and diversified orthodontic forces. Sample Collection and Observation Methods Sample size was calculated using PASS 2021 software, with a power of 80% and a significance level of 0.05, requiring at least 12 specimens per group. A total of 454 extracted premolars were collected. Before and after the experiment, a Nikon SMZ745T stereomicroscope was used for observation at magnifications of 10× and 50×. Three core indicators, namely the number, length (μm) and width (μm) of microcracks, were measured and recorded using image analysis software. Sample Grouping and Procedures Effect of Mechanical Force from Adhesive Removal on EMCs Group 1: Teeth without initial microcracks (n=20) Group 2: Teeth with initial microcracks (n=20) Effect of Debonding Shear Force from Metal Brackets on EMCs Chemical-cured group (C group, n=25) Light-cured group (L group, n=25) Further, each group was divided into a crack-increased subgroup and a non-crack-increased subgroup based on the variation in crack number, to analyze the influences of ARI and debonding force on crack number changes. Effect of Orthodontic Forces Transmitted via Brackets on EMCs Based on the presence or absence of pre-existing enamel microcracks, the samples were divided into a no pre-existing microcrack group and a pre-existing microcrack group. Each group was further randomly assigned into either a control group (D group) or an experimental group. The experimental group was subdivided according to the type of applied force: tensile force group (T group), compressive force group (P group), lateral traction force group (L group), torque group (Z group), and rotational force group (N group). The T, P, and L groups were further divided into three subgroups based on force magnitude: 350 g (high force), 200 g (moderate force), and 80 g (low force).The Z group was divided into 20°and 40°subgroups, and the N group was set at 30°. Each subgroup consisted of 14 specimens. Statistical Analysis All data were analyzed using SPSS 27.0 software (IBM, USA) and are presented as mean±standard deviation or as median (interquartile range) [M (Q3–Q1)], depending on the distribution. For intra-group comparisons of EMCs before and after intervention, the Shapiro-Wilk test was first used to assess normality. If data followed a normal distribution, Levene test was conducted to evaluate homogeneity of variances. When both assumptions were met, a paired-samples t-test was used; otherwise, the Wilcoxon signed-rank test was applied. For inter-group comparisons of EMC changes, data were also subjected to normality and variance homogeneity tests. If data were normally distributed with equal variances, an independent-samples t-test was used; if variances were unequal, approximate t-test was adopted. If the data were not normally distributed, the Mann-Whitney U test was used. A P value of <0.05 was considered statistically significant.