Mechanical influence of thread pitch on orthodontic mini-implant stability

The aim of this study was to evaluate the effect of pitch distance on the primary stability (PS) of orthodontic mini-implants (MIs) in artificial bone. Twenty experimental MIs were allocated to two groups, according to their geometric design: G(1) (30 degrees X 0.6 mm) and G(2) (45 degrees X 0.8 mm), and inserted into artificial bone of different densities: D-1 (0.32 g/cm(3)) and D-2 (0.64 g/cm(3)). The maximum insertion torque (IT) and removal torque (RT) values were recorded in N. cm. Loss of torque (LT) values were obtained by calculating the difference between the IT and RT. MI mobility was measured by means of a Periotest assessment. Normality and homogeneity were determined by means of the Kolmogorov-Smirnov and Shapiro-Wilk tests, respectively. A two-way ANOVA was used to detect differences between the mini-implant design and density factors. The ANOVA/Tukey tests were used to determine the intergroup difference. Higher IT values were observed for G(2) (p = 0.05) in D-2. No statistical difference for RT was observed between the groups, whereas G(2) presented higher values only for LT (p = 0.05). The Periotest values (PTV) were higher for G(1), in comparison with G(2), in D-1. G(1) presented better PS in D-2 (IT, RT and LT), whereas G(2) was found to be more stable in D-1, after evaluation with Periotest.