Miniscrews For Maxillary Incisor Intrusion In Adult

Correction of a deep-bite malocclusion often confuses orthodontists. Generally, there are 3 ways to correct overbite:intrusion of the incisors, extrusion of the posterior teeth and the combination. However, almost all the conventional methods accompany extrusion of the anchorage tooth as counteracting force, diminishing their clinical effectiveness. Extrusion of the anchorage posterior teeth may increase lower facial height, in turn lead to posterior rotation of the mandible and, as a result, mandibular plane angle increases. This bite opening may be desirable in brachyfacial patients who have a low mandibular plane angle, but is not desirable in some patients with dolichofacial skeletal patterns. Furthermore, an adult patient will have a different skeletodental response to orthodontic bite opening than a growing patient. With minimal extrusion of the molars, the adults increase the original mandibular plane angle. While adolescent patients maintain a stable mandibular plane angle even with a significantly greater amount of molar extrusion attributed to the greater amount of posterior mandibular development.Besides the conventional mechanics, the increasing use of mini-implants have found their way, also in this type of tooth movement, providing maximum anchorage control and requiring minimal compliance, playing important part in several aspects of orthodontic. Several articles have focus on the mini-implants in the intrusion of maxillary incisors, however, no detailed research about the clinical evaluation and periodontal change is present.Objective:To investigate the clinical effects of miniscrews in the maxillary incisors intrusion of adults, estimate the change of the maxillary incisor in 3 dimensions, lip-mouth relationship and the periodontal supporting tissue. And then, comparing the effect between minisrews and conventional utility arch, to evaluate the difference and provide information for the clinical maxillary incisor intrusion.Methods:40 adult patients, withⅢ°deep bite, overgrowth of maxillary anterior alveolar and partly uncoordinated relationship between maxillary lip and maxillary anterior teeth after levering were chosen and divided into two groups randomly:miniscrew group and conventional utility arch group. Miniscrews were inserted into the labial alveolar bone between the roots of maxillary lateral incisors and canines in the miniscrew group, and then 50g force in each side was imposed by nickel titanium closed-coil springs,Ωbends were used 1mm before the medial of maxillary first molar brackets and connected together. In the conventional utility arch group, typical 0.016×0.016 inch stainless steel wires were used. The cephalometric films, intraoral periapical radiographies with metal guide bars, facial photos and periodontium review were taken before and after the intrusion. The major measurement items are the alteration of the maxillary first molar in vertical dimension, torque and length of maxillary central incisors, overbite, clinical crown of maxillary central incisors, probing depth (PD), gingival index (GI), plaque index (PI) and so on. PASW statistics 18.0 was used for the Statistical analysis.Results1. In the miniscrew group, there is no change of U1-SN, U6-PP distance, U6-SN or root length of the maxillary incisor was observed. Significant reductions in overbite, maxillary incisor intrusion(3.42±1.17mm), and maxillary incisor to upper lip were observed after intrusion of the incisors. Smile arc improved significantly. The maxillary central incisors' width-length ratio performed normal after the treatment. What's more, probing depth (PD), increased, and the width of keratinized gingiva(WKG) decreased.2. In the conventional utility arch group, significant increases of U1-SN, U6-PP distance were observed. Similar change in overbite, maxillary incisor intrusion(2.95±0.78mm), and root resorption presented after the intrusion. Improved lip-tooth relationships, normal maxillary central incisors'width-length ratio, slightly increase of the PD can also be seen after the treatment. WKG decreased similarly.3.There were significantly greater reductions in maxillary incisor to palatal plane and U1-Stm in the miniscrew group than in the conventional utility arch group (P<0.05). More improvement of smile arc in the miniscrew group. No significant difference of U6-PP distance, root resorption or periodontal supporting tissue between the two groups after intrusion was observed (P>0.05). Furthermore, the utility arch group took significantly more treatment time than the miniscrew group and showed increase of Ul-SN and U6-PP.Conclusion1. As relatively stable anchorage, miniscrew can intrude upper incisors significantly by simply controlling the force moment, improving the aesthetic.2. No meaningful change of U6-PP distance or madibular plane angle can be found in the miniscrew group.3. Comparing to the the minisrew group, conventional utility arch group shows the shortcoming in intruding upper incisors. More treating period is needed and increase of U6-SN and U1-SN can be observed in the utility arch group. No additional root resorption or periodontal supporting tissue was observed between the two.