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 miniimplants 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. Keywords: histomorphometry, microcomputed tomography, mini-implant