Movement of mini-implants subjected to directional orthodontic forces for intrusion or distal movement of the maxillary teeth: a nonrandomized clinical study

PurposeThe aim of this study was to compare the movement of mini-implants subjected to orthodontic forces in the sagittal and vertical directions.Materials and methodsTwenty-four young patients with a total of forty-six mini-implants placed between the maxillary second premolar and the maxillary first permanent molar were divided into two groups. Group 1 (G1) consisted of patients undergoing distalisation, whereas Group 2 (G2) consisted of patients undergoing intrusion. In both groups, bilateral orthodontic forces were applied from the mini-implants in the sagittal (G1) and vertical (G2) directions, respectively. Linear and angular measurements were used to evaluate mini-implant displacement in both groups using cone beam computed tomography (CBCT) scans obtained before treatment (T1) and toward the end of treatment (T2). The Wilcoxon signed-rank test and the Mann–Whitney U test were used, respectively, to compare mini-implant displacement within and between the groups, respectively. A Kaplan–Meier survival curve was plotted to estimate the duration for which the mini-implants were likely to remain in the oral cavity.ResultsIn G1, a statistically significant increase in both vertical and sagittal angulation of the mini-implants was observed, directed toward the occlusal and mesial directions, respectively (p = 0.016 and p<0.001). In G2, an increase in vertical angulation toward the occlusal direction and a mild distal angulation were observed; however, these changes were not statistically significant. In both G1 and G2, a statistically significant linear displacement of the mini-implants was detected, with movement toward the maxillary second premolar in G1 (p<0.001) and away from the maxillary second premolar in G2 (p = 0.006).ConclusionMini-implant movement was greater under sagittal orthodontic forces than under vertical forces. Minor displacement of mini-implants occurs when subjected to orthodontic forces—particularly in the sagittal direction—but this movement may not necessarily indicate implant failure.