| The clear aligner is favored by patients for its invisible and comfort.At the same time,it is selected by many orthodontists because of its high efficiency and convenience of molar distalization.However,we found that the effect of distalization cannot be reproduced perfectly,with the increase of clinical cases,and the efficiency of expression is also affected by various factors.This article includes two cases of Class Ⅱ deep overbite and one case of Class Ⅲ malocclusion patients treated with clear aligners,and both were molar distalization in the presence of the maxillary third molar.Through three-dimensional images and models superimposition with before and after treatment,the position change of the maxillary third molar and the actual expression rate of the molar distal movement were measured,the influence of the third molar on the maxillary molar distal movement was discussed,and to guide the clinical reasonable design.Case 1: A hyperdivergent adolescent patient with skeletal Class Ⅰ and Angle Class Ⅱ with early period of permanent dentition,only the right maxillary second molar have erupted.Use the clear aligner to control the occlusal plane during the maxillary molar disatalization,cooperate with the interproximal enamel reduction of the maxillary teeth to align the upper midline,and adjust the Bolton ratio caused by the lack of a lower anterior tooth.Meanwhile,correct the deep overbite by the anterior teeth intrusion.After treatment,the occlusion and profile improved.The measurement data showed that the actual expression rate of the maxillary molars distalization is 54%(D1.5/D2.8)after the end of the first phase,and the unerupted maxillary third molar have moved backward and upward after the molar distalization.Case 2: A hypodivergent adolescent with skeletal Class Ⅱ,in the early period of permanent dentition,the maxillary second and third molars were embedded,and the mandible was retrusion significantly.Align the upper dentition by a small amount of maxillary molars distalization,open the deep overbite by the anterior teeth intrusion.After treatment,The patient’s mandible grew significantly,the occlusion and profile improved.The effeciency of the maxillary molar distalization at the end of the first stage was-8%(M0.1/D1.2),and the third molars continued to erupt.Case 3: An adolescent patient with mild skeletal Class Ⅲ,the maxillary third molars were embedded,and the upper and lower anterior teeth were slightly crowded.Correct the molar relationship and relieve crowding by upper and lower molars distalization.After the first phase,the upper and lower anterior teeth have aligned and the molar relationship was corrected,but still not completely class Ⅰ molar relationship.At the end of the first phase,the mean effeciency of the mandibular first molars was 21%(D0.3 /D1.4),while the maxillary molar was43%(D0.6/D1.4).Meanwhile,the maxillary third molars continued to erupt,and the eruption occurred to self-correct.Based on the measurement analysis and comparison of the three cases,it was found that the effeciency of the molars distalization of the clear aligners has been overestimated,there is a loss of anchorage during the treatment,the anterior teeth and molars will move back and forth.In the clinical,attention should be paid to prevention,design certain overcorrection and reasonable choice of anchorage.At the same time,the position of the unerupted third molar after the distal maxillary molars will change accordingly,which may aggravate the embedded and lead to impacted.So before the treatment,the true size of the distal space should be clearly judged,and the imaging data should be carefully checked to assess the possibility of impact and maxillary tubercle fracture or resorption risk after extraction.After comprehensive consideration,the feasibility of distal movement of maxiilary and the removal of maxillary third molars were determined,and the appropriate extraction time was selected. |
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