Objective Based on the research of the missing of the third molar,the missing numbers and the missing positions,to analyze the relationship between the missing of the third molar and the craniofacial saggital development. Methods This study included the patients who vesited Stomalogoy Hospital of China Medical University from 2007 to 2015：select 227 patients who had at least one of the third molars missing as the study group;select 227 patients who had four third molar present as control group. Use winceph 8.0 software to measure all the lateral cephalograms of the research objects. Use correlation statistical method to perform statistical analysis. Results There was significant difference in the congenital missing number of third molar and the missing sequence was 2,1,4,3;there was statistical difference in the positions of congenital missing of third molars;the most common position was in the maxilla,followed by double jaws,then the mandible. Both in the study group and the control group,the length of ANS-PNS and Go-Po in male was greater than that of female,and there was statistical difference between the two groups;however,other measurments were not statistically different. The Go-Po length in the study group was greater than that in the control group,and there was a significant difference. There was no statistical difference between the third molar congenital agenesis or the agenesis position and the craniofacial skeletal classification. Conclusion There is no obvious relationship between the congenital missing of the third molar or the missing position and craniofacial saggital development. Both in the study group and the control group,the length of maxlli and mandible in male is greater than that of female. Agenesis of third molar does not depend on anteroposterior dimensions of the maxilla but depends on anteroposterior dimensions of the mandible.
congenital agenesis of the third molar