| Skeletal ClassⅡ malocclusion is a very common disease, the characteristics of whichare maxilla protrusion, retrusion of the mandible, or both of them. Because of the effectsof the appearance of the patients, so we use orthodontics to modify the appearance of them.However, for the severe skeletal class Ⅱ patients, only surgical-orthodontic treatmentcould we use to solve the problem. Because of the abnormal of the alveolar bone insagittal and vertical, the inclination of anterior teeth have been changed to fit it. During thetreatment, if the anterior teeth were moved too much to out of the range of the alveolarphysiological range, which may lead to accelerate iatrogenic sequelae, even to dehiscenceor fenestration. Although some scholars have applied X-ray radiograph to study thealveolar bone of skeletal Class Ⅱ or to evaluate part of incisors, the accuracy andcomprehensive of it is under discussion. In this study, we use CBCT to investigate thealveolar bone structure and the position of anterior teeth of the skeletal Class Ⅱmalocclusion and to compare it with normal occlusion, the change after presurgicalorthodontic treatment，and the dehiscence and fenestration of the anterior teeth.Objective We evaluate the alveolar bone morphology of the anterior teeth between the skeletalClass Ⅱ malocclusion and the normal occlusion, research the alveolar bone change afterthe preexisting dental compensation were eliminated and to study the dehiscence andfenestration of the anterior teeth.MethodsExperiment1:The skeletal Class Ⅱ group included64subjects (23men,41women,average age:26.6) and15Chinese normal occlusion subjects (6men,9women, averageage:24.7). The group were divided into3groups according to the different verticalskeletal types: high-angle subgroup(34), average-angle subgroup(19), low-anglesubgroup(11); the upper incisors are labial inclination(29), the upper incisors areupright(22), the upper incisors are lingual inclination(13) according to the upper incisorinclination. The alveolar bone structures of the anterior teeth were evaluated through usingCBCT to measure the alveolar bone thickness and the alveolar bone height of the anteriorteeth, and the anterior teeth inclination. All statistical analyses were performed with theStatistical Package for the Social Sciences version16.0.Experiment2:25patients(9men,16women, average age:25.7) who carried outsurgical-orthodontic treatment were obtained as experimental subjects, we use CBCT tocompare the thickness and height of the alveolar bone, the root length both beforeorthodontic treatment (T0) and1month before surgery (T1). All data were performed bythe t-test.Experiment3:64skeletal Class Ⅱ patients, including23men and41women wereobtained as subjects to assess the rate of the dehiscence and fenestration and to analysisthe difference between male and female.Result1.We compared the alveolar bone structure between skeletal Class Ⅱ and the normalocclusion:1）The labial and lingual alveolar bone height of skeletal Class Ⅱ, especiallythe labial height, were lower than the normal control and the alveolar bone thickness of theincisors were much lower than the normal control.2) The height of labial and lingualalveolar bone and the alveolar bone thickness of anterior teeth in low-angle subgroup were higher than high-angle subgroup.3) The difference among the different incisor inclinationsubgroups was considered statistically significant in some indicators, in which, thethickness of alveolar bone and the height of the anterior teeth alveolar bone were muchlower in the labial inclination subgroup.4)The correlations between the inclination ofupper incisors and the thickness of the alveolar bone,the apex to lingual side,the labialalveolar bone height were statistically significant. Also, the correlations between lowerincisors inclination and the apex to labial side、the alveolar bone level at the labial sidewere significant.2.The variables of pretreatment and1month before surgical were compared:1) Theapex to labial side of anterior teeth was reduced after presurgical orthodontic(P<0.05).2)Although the alveolar bone thickness of incisors reduced significantly(P<0.05), thethickness of alveolar bone of the canine was not changed statistically.3) The root lengthof the anterior teeth were reduced, especially the upper central incisors.3.Among skeletal Class Ⅱ malocclusion, fenestration were seen in the maxilla withgreater frequency, while more dehiscence were found in the mandible. There weresignificantly difference between men and women for the rate of dehiscence andfenestration in some individual teeth.ConclusionAccording to the results of this study, skeletal Class Ⅱ malocclusion patients havethe high-angle trends. The vertical alveolar bone level at the labial and lingual sides andthe alveolar bone thickness of anterior teeth in low-angle subgroup were higher than thatof high-angle subgroup in the aspect of the vertical skeletal types, while the anterioralveolar bone thickness and the anterior alveolar bone height of the labial inclination weremuch lower in the aspect of the upper incisor inclination. The impact of the verticalskeletal types is greater than the upper incisor inclination. So, the high-angle skeletal ClassⅡ malocclusion patients were needed to be paid high attention in the clinical treatment.When move the teeth, we should control the torque and select the appropriate torquebrackets to reduce the incidence of bone loss and root resorption.As the thickness of the anterior teeth alveolar bone of skeletal Class Ⅱ malocclusion are narrow, especially in the incisors. So the movement of anterior teeth would cause theroot apex closing to the labial side and the alveolar bone thickness were continuallyreduced during treatment. The right plan should be designed according to the alveolarbone situation before treatment to avoid the excessive labial-lingual movement of theanterior teeth and the attention should be paid to the periodontal health during thetreatment. |
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