Finite element analysis of maxillary incisor displacement during en-masse retraction according to orthodontic mini-implant position.

OBJECTIVE: Orthodontic mini-implants (OMI) generate various horizontal and vertical force vectors and moments according to their insertion positions. This study aimed to help select ideal biomechanics during maxillary incisor retraction by varying the length in the anterior retraction hook (ARH) and OMI position. METHODS: Two extraction models were constructed to analyze the three-dimentional finite element: a first premolar extraction model (Model 1, M1) and a residual 1-mm space post-extraction model (Model 2, M2). The OMI position was set at a height of 8 mm from the arch wire between the second maxillary premolar and the first molar (low OMI traction) or at a 12-mm height in the mesial second maxillary premolar (high OMI traction). Retraction force vectors of 200 g from the ARH (-1, +1, +3, and +6 mm) at low or high OMI traction were resolved into X-, Y-, and Z-axis components. RESULTS: In M1 (low and high OMI traction) and M2 (low OMI traction), the maxillary incisor tip was extruded, but the apex was intruded, and the occlusal plane was rotated clockwise. Significant intrusion and counter-clockwise rotation in the occlusal plane were observed under high OMI traction and -1 mm ARH in M2. CONCLUSIONS: This study observed orthodontic tooth movement according to the OMI position and ARH height, and M2 under high OMI traction with short ARH showed retraction with maxillary incisor intrusion.

Influence of the length of the loading period after placement of orthodontic mini-implants on changes in bone histomorphology: microcomputed tomographic and histologic analysis.

PURPOSE: The recent use of microcomputed tomography (microCT) has made it possible to analyze qualitative bone morphology at the implant surface and in the peri-implant region. The purpose of this study was to evaluate histomorphometric changes around the implant-bone interface after placement of mini-implants using three-dimensional microCT analysis and to compare the stability of the implants after immediate and early loads were applied. MATERIALS AND METHODS: Forty-eight orthodontic mini-implants (ORLUS, Ortholution) were placed in the mandibular buccal jawbone of eight beagle dogs. Force was applied immediately (immediate loading group) and 3 weeks (early loading group) after implant placement; control implants received no loading. An orthodontic force (250 to 300 g) was applied to the experimental implants for 3, 6, or 12 weeks before sacrifice. RESULTS: The bone-implant contact in both experimental groups was not significantly different for any loading period except for after 12 weeks of loading. The immediate loading group had higher bone volume percentages compared with the early loading group after 6 weeks, but there was no significant difference between groups after 12 weeks. This was in accordance with the results of the three-dimensional microCT analysis. CONCLUSION: Histologic and microCT analysis showed that immediate loading of mini-implants in the dog model is possible for orthodontic applications with a high bone-implant contact and 100% survival rate.

Success rate and risk factors associated with mini-implants reinstalled in the maxilla.

OBJECTIVE: To determine the difference in the success rate for two types of oral installed mini-implants (OMIs): one type of initially installed OMI and a new implant of the same type that is reinstalled. MATERIALS AND METHODS: The subjects consisted of 58 patients (19 male, 39 female; mean age = 21.78 +/- 5.85 years) who had received at least one OMI (self-drilling type, conical shape with 2.0-mm upper diameter and 5-mm length) in the attached gingiva of the upper buccal posterior regions for maximum anchorage during en masse retraction. If an OMI failed, a new one was immediately installed in the same area after 4 to 6 weeks or in an adjacent area immediately. The total number of initially installed OMIs (II-OMI) was 109 and the total number of reinstalled OMIs (RI-OMI) was 34. Statistical analysis was performed using chi2 test, Kaplan-Meier method, log-rank test, and Cox proportional hazards regression model. RESULTS: The success rate and mean duration were 75.2% and 10.0 months, respectively, for II-OMI and 66.7% and 6.4 months, respectively, for RI-OMI. Age, vertical skeletal pattern, and site and side of implantation were not related to the success rates of II-OMI and RI-OMI. Log-rank test showed that II-OMI in males and Class III malocclusions were more prone to failure. The relative risk of II-OMI failure in Class III malocclusions as opposed to Class I malocclusions was 5.36 (95% confidence interval, 2.008 to 14.31, P = .001). CONCLUSION: The success rate of the II-OMI was not statistically different from that of the RI-OMI. Sex and ANB angle might be more important factors for better II-OMI results.