Prediction Of Mandibular Growth In Skeletal Class II Malocclusion Females During Adolescence Growth Spurt After Orthodontic Treatment

The incidence of skeletal Class II malocclusion accounts for nearly one third of the patients who received orthodontic treatment. This type of malocclusion affected the oral function and aesthetic of patients, evenly affected patients' psychological health. Both orthodontists and patients are desiring to predict the amount of the maxillary and mandible growth, especially the mandible. So, the precise prediction of the mandible growth will provide important information for planning treatment and evaluating occlusal stability after treatment. Recently, many researchers had studied the mandible growth character of the skeletal Class II patients, but few of them involved growth prediction. Although there are many kinds of method to predict the mandible growth, the research subjects were consist of patients who possessed skeletal Class I malocclusion. Until now, there is no one accurate prediction method which can be used in skeletal Class II patients. The aim of this study was to compare the longitudinal cephalograms using computerized cephalometric software, analyze the relationship of the mandible growth amount and the relative factors(such as: bone age, gender, malocclusion type, growth pattern, treatment timing, and so on), and then to find an accurate method to predict the mandibular growth of patients with skeletal Class II malocclsion. This study included three parts. Part I explored the mandible amount differences between skeletal Class I and Class II adult female malocclusion patients. The results showed that all nine linear measurements of Class I group were significantly larger than Class II group. It indicated that the skeletal pattern.of mandible plays a very important role in mandible growth, and it should be considered in mandible growth prediction. Part II compared the gender differences of skeletal Class II adult patients. With the same study method, the results showed that the total mandible length, the ramus length and the corpus length were statistically larger in males than in females. That indicated the mandible growth prediction should be divided into two groups according to gender. Part III was based on Class II malocclusion females with the angle ANB more than 5 degree. The subjects were in adolescence growth spurt before treatment and in later adolescence growth after treatment. All lateral cephalometric tracing were digitized on a computer with Winceph 7.0 Orthodontic Processing software. The samples were divided into two groups,extraction group (9 girls)and nonextraction group(9 girls). Results showed that the mandibular growth of the two groups had no statistical differences. It showed that extraction had no obvious effect on the mandibular growth. Then we put the two groups together to do the mandible growth prediction. By using SPSS 10.0 statistic software package, we analyzed the correlationship between the mandibleparameters and the relative factors(treatment timing, cervical vertebral bone age, the angle of Go, angle FMA,angle ANB, angle Y axis, the ratio of SGo/NMe). The results showed that the mandible growth magtitude correlated significantly with treatment timing, cervical vertebral bone age, angle Go and the ratio of SGo/NMe, and there was no significant correlationship with other factors. Two multiple regression formulae were obtained, which can be used to predict mandible growth.