Evaluation of the biomechanical properties of in vivo used orthodontic mini-implants

Aim of the study Orthodontic mini-implants, are devices that are temporarily attached to the jaws bones in order to improve orthodontic anchorage and to facilitate tooth movements. The aim of this study is to evaluate the biomechanical properties, namely, the insertion torque of 2 types of orthodontic mini-implants used intraorally for different periods of time. The secondary objective is to compare their properties with the new, unused mini-implants of same type and to correlate the intraoral use time with changing parameters. Material and methods The present study included a total of 51 orthodontic mini-implants, from two different manufacturers, Yesanchor OrlusTM (conical) and Link MIS TM (cylindrical), both having the same dimension 1.6 x 8 mm. These two types of mini-implants were divided into GC-control group: GCY (n=5), GCM (n=5) and GI-group used intraorally, the latter was divided according to the period of intraoral use in: GIY1 ≤ 12 months (n=10), GIY2≥ 12 months (n=15), GIM1 ≤ 12 months (n=7), GIM2 ≥ 12 months (n=9). In order to test the insertion torque, all the samples from the GI groups (n=41) were inserted in high-density artificial bone. Results The maximum insertion torque values for Yesanchor mini-implants varied from 35.58 Ncm to 42.34 Ncm and for MIS mini-implants from 19.44 Ncm to 25.36 Ncm. Significant decrease of the intraorally used mini-implants maximum insertion torque was demonstrated both for the Yesanchor group (p<0.05) and MIS group (p<0.05). Regarding the intraorally usage time, the differences were not significant. Conclusions Our study showed that there exist differences in maximum insertion torque between the mini-implants from two different manufacturers. We observed a decrease of the maximum insertion torque for the group of mini-implants used intraorally compared to the Control Group.