Cephalometric Changes And Stability Of Maxillary Protraction Therapy In Skeletal Class Ⅲ Patients Of Different Bone Ages

Objective The purpose of this study was to evaluate the skeletal and dental effects and post-treatment changes and stability following the application of combined rapid maxillary expansion (RME) and maxillary protraction in skeletal Class III patients in differentbone age groups, and to determine the relationship between the effect of maxillary protraction and bone age.Methods The 76 skeletal Class III patients with retruded maxilla were treated consecutively with RME for one or two weeks and maxillary protraction for four to eight months. The range of age before treatment was 8 to 15 years. Lateral cephalometric radiographs were used to quantify the skeletal and dental changes before treatment (T1) and immediately after treatment (T2) and 1.5 years after removal of appliances (T3). The bone age of individual patients was assesed according to cervical vertebrace maturation stage(CVMS) on cephalometric radiographs before treatment. Patients were divided into three groups:prepubertal group (CS 1-2), pubertal group(CS 3), and postpubertal group(CS 4-6). SPSS 20.0 statistical software was used to compare the differences among the three groups. The statistical methods used inthis study are paired t-test and One-way ANOVA.Results 1. Compared with the condition before orthodontics, the maxilla of all thethree groups moved ahead after orthodontics, at the same time,all the mandibles rotated backwards and downwards. The points of A and ANS moved aheadobviously, the points of B and Pog moved downwards, the MPA and anterior low facial height were increased. The relationship between the maxilla and mandible was improved significantly, the angle of ANB was increased obviously, the labial inclination of the maxillary anterior teeth, the lingual inclination of the mandibular anterior teeth, the mesial shift of the mandibular and maxillary molars, the abnormal molar’s relationship, and the overbite and overjet of anterior teeth were all corrected.Compared the three groups:after the treatment of maxillary protraction therapy for the patients of the three groups, the maxilla and the mandible were all changed a lot. The labial inclination of the maxillary anterior teeth of the postpubertal group was changed the most, and the prepubertal group was the least, there was prominent difference among the three groups (P<0.05). The anterior low facial height of the postpubertal group were increased the most, and the prepubertal group was the least, there was prominent difference among the three groups, too (P<0.05). There was no difference in the effects of maxillary advancement after maixllary protraction between the prepubertal and the pubertal group; In the postpubertal group, there was a decrease in maixllary skeletal advancement, whereas the dentoalveolar effect was increased; The posteroinferior rotation of mandible, the increase of lower facial height, and the eruption of maxillary molars showed no correlation with bone age.2. After the orthodontics was finished, as the time went on, the maxilla continued to grow ahead, but the rate and quantity of mandibular growth were more than maxilla, the sagittal relationship between the maxilla and mandible tended to reoccur, the points of B and Pog moved ahead obviously, the angle of SNB was increased, the angle of ANB was decreased. The inclination of mandibular and maxillary anterior teeth was increased to an extent. Compared the three groups:the maxilla or mandible’ s forward shift of the prepubertal group was bigger than the other two groups, the postpubertal group moved the least, there was prominent difference among the three groups (P<0.05), and when it came to the labial inclination of the maxillary anterior teeth and the lingual inclination of the mandibular anterior teeth, the prepubertal group "was changed the most, the postpubertal group was the least, there was prominent difference among the three groups (P<0.05)3. Compared with the condition before orthodontics,1.5 years after orthodontics, all the maxilla or mandible grew ahead and downwards. The points of A, ANS, B and Pog moved ahead obviously. The labial inclination of the maxillary anterior teeth, the lingual inclination of the mandibular anterior teeth, the relationship between the maxilla and mandible were all ameliorated distinctly. Compared the three groups:the maxilla of the postpubertal group moved ahead less distance than the other two groups, there was prominent differenc (P<0.05). But there wasn’t difference between the prepubertal group and the pubertal group. The anterior low facial height of the postpubertal group was increased the most, and the prepubertal group was the least, there was prominent difference among the three groups (P<0.05)Conclusion 1. The method of maxillary protraction therapy combined with rapid palatal expansion was effective for the treatment of three different bone age groups of skeletal Class III malocclusion patients. Sagittal correction was primarily a result of forward movement of the maxilla and clockwise rotation of the mandible. Overjet correction was contributed by both skeletal and dental changes. The anterior low facial height was increased, the relationship between the maxilla and mandible ameliorated distinctly, the abnormal molar’s relationship, the overbite and overjet of anterior teeth were all corrected.2. The bone of the prepubertal group was changed the most, the upper and lower anterior teeth’s compensated change of the postpubertal group was increased the most, and the prepubertal group was the least. According to this, the optimal period for maxillary protraction therapy is between prepubertal and pubertal,duringthe period, we can obtain the more skeletal change and the less teeth change.3. At the end of maxillary protraction therapy for the three different bone age groups, the position of the maxillas and mandibles was changed a lot, the interocclusal relation was improved, but the interocclusal sagittal relationship tended to recur, the chance of recurrence was the biggest in the the prepubertal group, and the postpubertal group was the smallest, compared with the other two groups, the stability after orthodontics of the prepubertal group was the worst.