Comparison of clinical effects of three different positions of micro-implants intruding upper anterior teeth to improve the gummy smile

Objective To evaluate gummy smile reduction through anterior intrusion by micro-implants at three different sites, and to provide future clinical references. Methods Patients, from June 2015 to January 2016 in Department of Orthodontics, Remin Hospital of Wuhan University, who presented with Class Ⅰ or Class Ⅱ malocclusion and overgrowth of anterior maxillary alveolar bone were enrolled. Based on Quantitative Cervical Vertebral Maturation(QCVM)30 cases, phase Ⅲ or Ⅳ, including 3 male patients and 27 female patients with a mean age of 24.5 years old, were selected. The patients were randomly divided into three groups and received fixed appliance treatment. In group 1, the micro-implants were implanted between the maxillary central incisors; in group 2, they were inserted between maxillary central incisors and lateral incisors; and in group 3, they were located between the maxillary lateral incisors and the canines. Before the insertion of the micro-implants, the leveling and aligning treatment were performed. Then a force with the magnitude of 50 g per side was applied. The power chain was replaced every four weeks for 5-8 months, and the overbite was improved by 2.5 mm. The parameters before and after treatment were compared and analyzed. Results All the three groups showed significant reduction of gummy smile. Among them, 27 patients completely recovered from gummy smile and 3 patients showed a significant improvement. The amount of intrusion (Cr1-PP′) of the incisors showed a result of group 3> group 2>group 1, and the sagittal displacements U1-SN and U1-T showed a result of group 1> group 2>group 3. Meanwhile, the root resorption of the central incisors in group 1 and group 2 was more obvious. Conclusions Insertion of the micro-implants between the lateral incisors and the canines can distribute the intrusion force more uniformly, and can result in more bodily movement, with a less tendency of root resorption. Key words: Gummy smile; Micro-implant; Anterior teeth; Intrusion