| Skeletal Class II malocclusion is a kind of abnormality with high prevalence, high treatment difficulty, and severe influence on the dento-maxilla-facail structure. Therefore, the therapy for this kind of malocclusion has been the focus for the orthodontists. In this study, the mechanism of the malocclusion was investigated, then the therapies for the malocclusion in different growth stage were discussed.Objective1. To analyze the influence of mandible retrusion on the form of skeletal Class II malocclusion.2. The treatment effects of Forsus were evaluated when it was used as functional appliance for the early treatment of mandible retrusion.3. To investigate whether the single maxillary extraction or the bimaxillary extraction is suitable for the adult mandible retrusion patients. Methods1. With ANB> 5°for chosing criteria, 56 cases of the skeletal class II malocclusion patients were sampled randomly. The convexity or concavity of maxilla and mandible were analyzed, which were standed by SNA, SNB respectively. Then etiology of skeletal class II malocclusion was analyzed.2. 15 skeletal mandibular retrusion patients in the early growth and development stage were chosed randomly. All the patients were undergone the mandible advance treatment via Forsus (USA 3M). The range of treatment period was 6 to 10 months (average of 8 months). The changes of upper and lower jaws after treatment were analyzed by Ricketts cephalometric analysis. Then the treatment effects of Forsus were evaluated.3. 30 skeletal mandibular retrusion adult patients were chosed randomly. Among the patients, 15 cases were treated with two maxillary first premolars extracted (which were divided into single maxillary extraction group), whereas another 15 cases were with four first premolars extracted (which were divided into bimaxillary extraction group). The effects of two extraction treatment ways were compared in order to investigate which kind of extraction was more suitable for such malocclusion.Results1. The results of the study on the dominating etiologic factors of skeletal classⅡmalocclusionAmong the samples, the most part of patients(53.57%)were the kind with maxillary normal and mandibular retrusion. The second more part of patients (14.29%) was the patients with both the mandibular and maxillary retrusion. So the patients with mandibular retrusion accounted for nearly 70% of the sample, which were the dominating proportion. Therefore, it suggested that the etiologic factors for the skeletal classⅡmalocclusion were the mandible retrusion instead of the maxilla protrusion. And the key point for the treatment of such malocclusion is the correction of mandible tetrusion.2. The results of the study on the effect of early treatment for the mandible retrusion by ForsusIn this study, the conventional application of Forsus was modified. It was used as the appliance for the early treatment of mandible retrusion with some intraoral appliances were designed for such application. The results of the treatment way were favourable with significant correction of mandible retrusion and significant improvement of profile. The craniomaxillary changes after treatment were as following.(1) Skeletal changes: significant mandible advancement was suggested by 3.18°decrease of ANB and 4.31°increase of SNB. And the skeletal classⅡrelation was corrected.(2) Dental changes: The classⅡmolar relation and deep overjet, which were resulted by the mandible retrusion, were corrected since the molar-relation linear and the overjet decreased 5.79mm and 4.56mm respectively, and the molar relation was changed into neutroclusion from distoclusion.(3) the changes of cranio-facial relation: the facial depth angle increased 4.75°, which suggested the mandible was advanced. The facial axis angle increased 3.98°, which suggested the promotion effect of the Forsus on the growth of mandible. There was no significant change at the facial taper angle, mandibular plane angle, maxillary depth angle and palatal plane angle after treatment, which suggested that there was no rotation at both jaws.(4) the changes of deep structure: the corpus length and the mandibular arc increased 5.16mm and 4.08°respectively, which suggested that the treatment for the mandible advancement was effective. It was shown that the lower facial growth could be promoted by the Fousus since the posterior facial height increased 2.83mm.3. The results of the comparison of the treatment effects between the two kinds of extraction protocol(1) treatment time: the treatment time of the single maxillary extraction was significantly shorter than the bimaxillary extraction. (2) the cephalometric changes after single maxillary extraction treatment: the interincisal angle increased significantly (from 113.72±8.73°to 129.77±8.48°). The MAX incisor protrusion and inclination decreased significantly (from 8.02±2.18mm to 3.08±2.37mm and from 36.59±5.67°to 23.56±6.99°respectively). And they were still in the clinical normal range, which suggested that the over lingual inclination of MAX incisors did not occur. At the lower dentition, the MAND incisor inclination increased (from 29.73±3.64°to 33.75±5.73°) and was little larger than normal, which suggested that it was a kind of compensation for the mandible retrusion. Because of the changes above, the incisor overjet decreased significantly (from 6.46±1.85mm to 2.15±1.09mm), and the upper and lower lip protrusion decreased significantly (from 2.61±2.54mm to 1.22±2.99mm, and from 2.97±3.42mm to 1.31±3.11mm respectively). Z angle increased significantly (from 66.54±7.34°to 72.97±7.83°). There was no significant change at the SNA, SNB and ANB. It was suggested by the results that, for such treatment, the good occlusion and improvement of profile could be achieved by compensation at the lower anterior teeth. But the skeletal pattern could not be improved.(4) the cephalometric changes after bimaxillary extraction treatment: at the skeletal structure, the maxillary protrusion (standed by SNA) and the horizontal maxilo-mandibular relation (standed by ANB)were improved, which meant that the maxillary protrusion decreased and classⅡsleletal relation were corrected. At the occlusal relation, there were some changes as following: the interincisal angle increased significantly (from 114.09±9.56°to 137.11±8.87°). The MAX incisor protrusion and inclination decreased significantly (from 7.01±2.83mm to 2.53±1.65mm and from 31.08±7.12°to 19.88±7.28°respectively). And the MAX incisors were over lingual inclined. At the lower dentition, the MAND incisor inclination increased (from 29.65±4.93°to 22.78±5.33°) and was smaller than normal, which suggested the anterior occlusion was poor. It was shown by the results that, for such treatment at adult patients, the maxillary protrusion could be decreased and the classⅡskeletal relation could be improved. But the upper incisors were potentially over lingual inclined.Conlusions1. Maxillary protrusion in normal range and mandibular retrusion are the main mechanism of Class II skeleton malocclusion in Chinese population.2. Forsus appliance (USA 3M Corporation) can be used as functional appliance in early treatment against skeleton mandibular retrusion. Forsus appliance played significant role in promoting the mandibular growth, correcting skeletal mandibular retrusion mechanisms, and improving the facial soft tissue morphology. It suggests that Forsus appliance against the children mandibular retrusion is effective.3. Treatment with single maxillary extraction or bimaxillary extraction methods can not significantly change mandibular retrusion mechanism and correct Class II skeleton relation. But single maxillary extraction treatment is more appropriate for this kind of patients than bimaxillary extraction treatment because single maxillary extraction treatment results in the lower anterior teeth appropriate labial inclination mechanisms, which compensates the mandibular retrusion mechanisms. And good anterior occlusion could be achieved in such treatment. Meanwhile, blocking bite problems are not potentially resulted in such treatment. Therefore, we think that the single maxillary extraction protocol is more applicable to adult skeleton mandibular retrusion patients. In addition, patients are easily accepted such treatment because the treatment time is relatively short and the number of tooth needing extraction is not more. |
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