| BackgroundWith the developing of the orthodontics as well as the increasing number of adult patients, invisible appliances have been more and more popular among orthodontic doctors and patients. In order to achieve the aesthetics beauty during orthodontic treatment, previous researchers designed a series of invisible orthodontic system: ceramic bracket, invisalign, lingual appliance, etc. The lingual appliance system is completely invisible, which benefits patients in both aesthetic beauty during treatment and excellent results eventually.Bimaxillary dentoalveolar protrusion was common in clinic, and they were the main chiefs why patients seeking for treatment as well. Ideal position of maxillary dentoalveolar and incisor are essential for function, stability, and esthetics of maxillofacial system. With the purpose of achieving perfect facial profiles as well as facial balance, orthodontic doctors usually take the treatment plan with four premolars extraction to retract the anterior teeth. The retraction of anterior teeth is the key point to treatment. Due to its special mechanical characteristics, torque control of anterior teeth is difficult during retraction in lingual orthodontic treatment. Torque control could be achieved either by appling torque on the archwire directly or using lever-arm mechanics to adjust the lines of force coming through the center of resistance. ObjectiveThis study aimed to apply a customized lingual appliance for adult patients with bimaxillary protrusion. Micro-implant and lever-arm were used to retract the anterior teeth. Panoramic pantomogram and cephalometric radiograph were taken during four periods: before treatment, before retraction, 3 months after retraction, after retraction. Changes in the teeth, bone and soft tissue were compared by collecting data. The moving tendency of incisors and methods of torque control of anterior teeth were also discussed by using micro-screw and lever-arm during the retraction of anterior teeth. Methods8 adult patients with bimaxillary protrusion were involved(3 males and 5 females), with a mean age of 23.21±4.778 years. A customized lingual appliance system was applied each of them with the treatment plans were to extract four first premolars. Micro- implant and lever-arm were used to retract the anterior teeth. The site for placement of the micro-implant was selected as the palatal side of alveolar bone between the second premolar and first molar of maxillary, 6mm above the alveolar bone crest. The lever-arm with 7mm in length was placed in the distal of the lateral incisor. Panoramic pantomogram and cephalometric radiograph were taken before treatment(phase T1), before retraction(phase T2), 3 months after retraction(phase T3), after retraction(phase T4). SPSS 17.0 was employed to process and analyze the data. A paired t–test was conducted to evaluate the variation differences among phase T1, T2, T3 and T4. Results1. Changes in hard tissue: Significant reducing of SNA occurred in each phase. Maxillary retraction was accompanied by significant redistribution of A point. SN-OP increased as well. However, took T3 and T4, T2 and T4 in analysis,ANB reduced. There were no significant difference in the remaining data.2. Changes in soft tissue: nasolabial angle increased. The distances between upper/lower lip and E line reduced.3. Changes in central incisors: U1-FHp, U1a-FHp, U1a-CFH reduced However, U1a-CFH increased only in the phase range from T2 to T3. SN-U1 reduced significant from T3 to T4. There were no significant difference in the remaining data.4. Changes in first Molar: U6-FHp, U6a-FHp, U6-CFH, reduced when compared phase T1 and T4, T3 and T4, T2 and T4, besides there were no significant difference in the remaining changes.5. Changes in overbite and overjet: overbite and overjet reduced significant. Conclusions1. For adult patient with anterior teeth lingual tipping, anterior teeth torque control during retraction could be achieved by customized lingual appliance system with lever-arm and micro-implant system(implant height: 6mm from the alveolar bone crest; hook height: 7mm).2. Better occlusion and facial profile could be achieved by retraction of anterior using customized lingual appliance with lever-arm and micro-implant system for adult. |
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