A Study Of The Relationship Between Third Molar Agenesis And Craniofacial Morphology In Northeast Of China

Objective: Based on the research of the congenital missing of the third molar,the missing location and the missing number,summary the relationship between the congenital missing of the third molar and the craniofacial morphology,and to provide the basis for clinical doctors' treatment plan.Methods: Patients age from 13-18,whose lateral cephalograms and orthopantomograms and from Department of Orthodontics,Hospital of stomatology,China Medical University from 2007-2015 were selected.227 patients were selected as study group who had at least one congenital missing third molar,at the same time,227 patients who had four third molars were selected as control group.Mearsured the SNA,SNB,ANB,Gonial Angle,Upper Gonial Angle,Lower Gonial Angle,ANS-PNS,Po-Go,FH-MP,LFH with Winceph 8.0 software.Record the location and number of the third molar congenital missing.SPSS 21.0 statistical software was used to analyze the data.Results: The third molar congenital missing mainly occurred in the upper jaw(41.85%),followed by the double jaw(37%)and the lower jaw(21.15%),with the maximum number of missing was 2(41.53%),followed by 1,4,and 3.There was no statistical difference between the sexes(p>0.05).Between the study group and the control group,only ANS-PNS and Po-Go showed statistically significant differences between male and female,and in the male were more than in the female.Between the study group and control group,the upper Gonial Angle,lower Gonial Angle,Gonial Angle,Po-Go and FH-MP had statistically significant difference,the upper Gonial Angle,lower Gonial Angle,Gonial Angle,FH-MP in the control group was greater than the study group,however,Po-Go in the control group was less than the study group,other measures showed no statistical difference.There was no statistical difference between the different missing number of third molars.There was no statistical difference between the different locations of congenital missing third molar.According to the ANB Angle,the study subjects were divided into skeletal class I,II class and III,and the results showed that there was no statistical difference between the study group and the control group(p> 00.05).According to FH-MP,the subjects were divided into hyperdivergent,normal devergent and hypodivergent,and the results showed that there was statistical difference between the study group and the control group(p<0.05),and the hyperdivergent proportion in the control group was higher,and the hypodivergent proportion in the study group was higher.Conclusions: First,the mainly missing of the third molar occurred in the upper jaw,followed by the double jaw,and finally the lower jaw;there was no statistical difference between the sexes.Second,the number of congenital missing of the third molar was 2,followed by 1,4 and 3,and there was no statistical difference between the sexes.Third,the congenital missing of the third molar mainly affacts the vertical development of cranial structure,but there is no obvious link with sagittal development,and the patient had a short craniofacial structure.Fourth,there was no significant correlation between the congenital missing numbers and locations of the third molar and craniofacial structure.