Accuracy of Two Variants of 3D-Printed Insertion Guides for Orthodontic Mini-Implants: An Ex Vivo Study in Human Cadavers

Insertion guides are becoming popular for orthodontic mini-implant positioning. The aim of this study was to evaluate and compare the accuracy of two different mini-implant insertion guides, with or without pre-drilling, in a human cadaveric model. Maxillary casts of six fresh frozen specimens were digitized to create insertion guides. Sixty mini-implants were randomly inserted with full-arch or skeletonized guides, either with or without predrilling. Pre- and post-treatment CBCTs were superimposed using rigid registration. Transformation matrices of the planned and real positions were obtained, and distances at the mini-implant neck and apex, as well as the angular deviation, were calculated. The Kruskal-Wallis test was performed, followed by a post hoc test when indicated. Out of 60 inserted mini-implants, 46 could be evaluated. Of these, 10 initially assigned to no pre-drilling required this procedure due to very high bone density. Therefore, 32 implants were inserted with pre-drilling (n = 15 full-arch; n = 17 skeletonized) and 14 without (n = 7 full-arch; n = 7 skeletonized). The lowest mean deviation at the neck was 1.22 +/- 0.6 mm, registered in the full-arch/pre-drilling group. The skeletonized/no pre-drilling group presented the lowest mean values at the apex, i.e., 1.72 +/- 1.22 mm, as well as the lowest mean angular deviation, i.e., 8.23 +/- 4.24 degrees. Significant differences among groups were observed only at the neck, with higher mean deviation in the skeletonized/pre-drilling group than in the full-arch/pre-drilling one (p = 0.014). In conclusion, within the limitations of the study, rather high deviations between planned and real mini-implant positions were found. Further studies are needed on how to improve the accuracy within in vivo settings.