Clinical Application of Micro-Implant Anchorage in Initial Orthodontic Retraction
Micro-implant is a device that is temporarily fixed to bone for the purpose of enhancing orthodontic anchorage either by supporting the teeth of the reactive unit or by obviating the need for the reactive unit altogether, and which is subsequently removed after use. The purpose of this study was to evaluate the clinical efficiency of micro-implants in reinforcing anchorage during the initial retraction of anterior teeth, check the rate of initial retraction for 8 weeks, and assess the stability of micro-implants during this period. Eighteen micro-implants were placed (10 in the maxilla and 8 in the mandible) and immediately loaded with 200–250 g of force using 9-mm closed coil Nitinol springs. The amount of space closure was measured every 2 weeks until the eighth week. Cephalometric measurements were made at the end of the study to evaluate anchor loss, if any. Micro-implant stability was also assessed. The rate of initial retraction in the maxilla at the end of 8 weeks was 1.65 mm/quadrant and 1.51 mm/quadrant in the mandible. The amount of retraction on the left side of the arches was 1.66 mm/quadrant and 1.49 mm/quadrant on the right side. The average initial retraction for both arches per month was 0.78 mm. An anchor loss of 0.1 mm (0.06%) was observed in the maxilla while no mandibular anchor loss was recorded. The rate of initial retraction observed in the maxilla was more than that achieved in the mandible. Initial retraction was also more on the left side of the arches. There was no anchor loss in the mandible. The micro-implant-reinforced anchorage was helpful in minimizing anchor loss and accepted heavy traction forces but did not bring about a faster rate of retraction.

Figure 1. AbsoAnchor micro-implants used in the study. Figure 2. Postinsertion intraoral periapical (IOPA) radiograph – Maxillary arch. Figure 3. Postinsertion IOPA radiograph – Mandibular arch. Figure 4. Immediate loading of right side upper and lower micro-implants. Figure 5. Immediate loading of left side upper and lower micro-implants. Figure 6. Upper occlusal photograph (mirror image) after immediate loading. Figure 7. Lower occlusal photograph (mirror image) after immediate loading. Figure 8. Dial gauge to measure the loading force on the micro-implant. Figure 9. Measurement of extraction space using a Vernier caliper.

Figure 10. Cephalometric parameters used for measurement of anchor loss. Figure 11. Right side at the end of 8 weeks of retraction. Figure 12. Left side at the end of 8 weeks of retraction. Figure 13. Upper occlusal photograph (mirror image) at the end of 8 weeks of retraction. Figure 14. Lower occlusal photograph (mirror image) at the end of 8 weeks of retraction.
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