In-vitro trabecular bone damage following mono- and bicortical mini implants anchorage in mini-implant assisted rapid palatal expansion (MARPE)

Objectives > To assess in-vitro trabecular bone damage following mono- and bicortical mini-implant (MI) anchorage in mini-implant assisted rapid palatal expansion (MARPE). Material and methods > Sixteen self-drilling MI (four MARPE appliances) were distributed in two groups according to bone insertion (monocortical and bicortical) in bovine rib. The device was activated five times (0.5 mm each). Trabecular bone damage was assessed using micro-CT scans made at baseline and after each activation by trabecular spacing parameter (Tb.Sp) (distance [mm] between the trabecular bone structure). These measurements were made in five different regions of interest (ROI) surrounding the screw (whole, superior, inferior, anterior and posterior). Two-way ANOVA with Tukey post-hoc analysis (alpha = 0.05) was used to evaluate the effect of insertion type (monocortical vs. bicortical) and activation cycle (0-5) on trabecular damage. The time effect was evaluated using ANOVA-MR test effect with Bonferroni correction (alpha = 0.003). The micro-CT images were also examined qualitatively. Results > When analysing the individual ROIs, only the superior ROI had a significant difference (P < 0.003) beginning at the fourth activation cycle. For the monocortical group, trabecular spacing was affected when the whole ROI was analysed beginning at the fourth activation cycle, while for the superior ROI, this difference became apparent beginning with the third activation cycle (P < 0.003). For the qualitative analysis, it seems that only monocortical anchorage influences the trabecular bone in the superior area. Conclusions > Monocortical anchorage is more susceptible to bone damage around the MIs, with the superior (cervical) region most strongly affected.