Study On The Differences Between GoGn-SN Angle And MP-FH Angle And The Influencing Factors

Malocclusion is an oral disease of high incidence,and it is defined as all kinds of deformities caused by uncoordinated relationship of the teeth,jaw and cranium.It has been reported that about 50% malocclusion patients suffer from vertical disorders.High-angle face and low-angle face are two main types of vertical disorders,and they are absolutely different in terms of pathogenesis,clinical characteristics and treatment.Vertical facial type not only provides clues to the growth direction of the craniofacial complex,but also plays an important role in orthodontic treatment and prognosis.Nowadays,orthodontists mainly utilize the mandibular plane angle on the diagnosis of vertical disorders,and GoGn-SN angle,MP-FH angle are the most commonly used indicators in the evaluation of mandibular plane angle and vertical facial type.The method of determining the two indicators is different,GoGn-SN angle consists of SN plane as base plane and GoGn plane as mandibular plane;while MP-FH angle consists of Frankfort horizontal plane as base plane and MP plane as mandibular plane.Both clinical case analysis and some literature studies have shown that it is always inconsistent for GoGn-SN angle and MP-FH angle to evaluate vertical facial type.Then,how much is the difference between GoGn-SN angle and MP-FH angle,where does the difference derive from,whether the difference is affected by sagittal or vertical craniofacial characteristics,how should we judge the analysis when the diagnostic results of GoGn-SN angle and MP-FH angle do not match?There is little literature about these problems.This study aims to solve these problems by the cephalometric analysis of normal occlusion individuals and malocclusion patients,so as to provide some reference for clinical diagnosis and analysis.The thesis consists of the following three parts.1 Study on the difference between GoGn-SN angle and MP-FH angle among normal occlusion individualsObjective:To explore the difference between GoGn-SN angle and MP-FH angle,its gender difference and the source where it comes from,by the cephalometric analysis of normal occlusion individuals.Methods:120 normal occlusion individuals(60 females,60 males)who study in FMMU were chosen randomly.The lateral cephalograms of these individuals were collected and measured.To analyze distribution range of GoGn-SN angle and MP-FH angle and its difference by descriptive statistics;to analyze the gender difference of GoGn-SN angle and MP-FH angle and its difference by group t-test;to analyze the correlation between the difference and SN-FH angle or MP-GoGn angle by Pearson product moment correlation.Results:Both GoGn-SN angle and MP-FH angle showed significant gender difference among normal occlusion individuals(P<0.05),which were bigger in females.GoGn-SN angle was bigger than MP-FH angle(P < 0.05),but no significant gender difference was shown for the difference between GoGn-SN angle and MP-FH angle(P>0.05),which was 5.10±2.93°and showed significant correlation with SN-FH angle(P<0.01).Conclusions: No significant gender difference was shown for the difference between GoGn-SN angle and MP-FH angle,and GoGn-SN angle is about 5°bigger than MP-FH angle in adults with normal occlusion.2 Study on effects of craniofacial factors on the difference between GoGn-SN angle and MP-FH angleObjective:To explore the effects of craniofacial factors on the difference between GoGn-SN angle and MP-FH angle among malocclusion patients.Methods:200 malocclusion patients(100 females,100 males)were chosen randomly.The lateral cephalograms of these patients before treatment were collected and measured.To screen craniofacial factors which affect the difference between Go Gn-SN angle and MP-FH angle by Pearson correlation analysis;to find out its Change characteristics on the screened out craniofacial factor by one-factor ANOVA and LSD-t test.Results: For malocclusion patients,the difference between GoGn-SN angle and MP-FH angle showed negative significant correlation with Y axis angle(P<0.01)which represents the direction of mandibular growth,while no significant correlation with ANB angle(P>0.05)which represents sagittal craniofacial characteristics.The difference between GoGn-SN angle and MP-FH angle grew smaller from horizontal growth pattern to vertical growth pattern,significant difference was shown between horizontal growth pattern and vertical growth pattern,while no significant difference between vertical growth pattern and average growth pattern.Conclusions: The difference between GoGn-SN angle and MP-FH angle was mainly affected by Y axis angle which represents the direction of mandibular growth among malocclusion patients,and it grew smaller from horizontal growth pattern to vertical growth pattern.Sagittal skeletal pattern had no significant effect on the difference between GoGn-SN angle and MP-FH angle.3 Study on the difference between GoGn-SN angle and MP-FH angle on diagnosisObjective: To explore the difference between GoGn-SN angle and MP-FH angle in the diagnosis of vertical facial type,to evaluate the credibility of GoGn-SN angle and MP-FH angle.Methods:200 malocclusion patients(100 females,100 males)were chosen randomly.The lateral cephalograms of these patients before treatment were collected and measured.The sample was classified into different vertical facial types by GoGn-SN angle and MP-FH angle respectively,then the classification results were analyzed in order to find out their difference in diagnosis.Pearson correlation analysis was used to screen a credible item on vertical diagnosis besides GoGn-SN angle and MP-FH angle,then the selected item was used to evaluate the credibility of GoGn-SN angle and MP-FH angle.Results:When the diagnosis of vertical facial type was based on GoGn-SN angle,GoGn-SN angle and MP-FH angle showed the highest inconsistency rate for patients who were defined as low-angle face,while showed the lowest inconsistency rate for patients who were defined as high-angle face.When the diagnosis of vertical facial type was based on MP-FH angle,GoGn-SN angle and MP-FH angle showed the highest inconsistency rate for patients who were defined as high-angle face,while showed the lowest inconsistency rate for patients who were defined as low-angle face.FHI showed the highest correlation with GoGn-SN angle and MP-FH angle,which can be taken as a third reliable index.Analyzing the patients defined as different vertical facial types according to FHI,GoGn-SN angle was supported by the diagnostic result of most cases.Conclusions: When the diagnosis of vertical facial type was based on GoGn-SN angle,it was of high accuracy if defined as high-angle face,while it was necessary to combine the other indicators for further analysis if defined as low-angle face.When the diagnosis of vertical facial type was based on MP-FH angle,it was of high accuracy if defined as low-angle face,while it was necessary to combine the other indicators for further analysis if defined as high-angle face.No matter it is based on GoGn-SN angle or MP-FH angle,the accuracy of the diagnosis based on GoGn-SN angle was higher than that of MP-FH angle for patients who were defined as average-angle face.It intended to support GoGn-SN angle on the diagnosis of vertical facial type when the diagnostic results of GoGn-SN angle and MP-FH angle did not match.