CBCT Study On The Mandibular Molars Posterior Region Of Skeletal Class Ⅲ Malocclusion In Adult

Objective:Three dimensional imaging techniques of cone beam computer tomographic were used to study the three-dimensional morphological characteristics of the distal posterior region of the mandibular second molar in the mandibular mandible with skeletal III malocclusion.To investigate the morphological difference and its influencing factors in the posterior region of mandibular molar of skeletal class III malocclusion in adult.To provide reference for diagnosis and individualized treatment of skeletal class III malocclusion in adult.Materials and Methods:30 adult patients who are among the newly diagnosed patients at the first affiliated Hospital of Zhengzhou University in the Department of Orthodontics of Henan Stomatology Hospital from May 2015 to May 2017.these patients with skeletal class III malocclusion according to the data inclusion criteria already have cbct in radiology department before orthodontic treatment.According to the size of mandibular plane angle on lateral cranial radiographs produced by large field cbct,30 cases of skeletal III malocclusion in adult were selected,including 10 cases of high angle,10 cases of average angle,10 cases of low angle,15 cases of male and female,aged from 18 to34(24.67 ±4.72)years old.Using cs3 D imaging software to reconstruct the image and adjust the datum point,line,plane,etc.The length of posterior space of second molar(SRL)and the width of alveolar bone at 4mm from the top of alveolar crest(ABW4)were measured,and the width of alveolar bone at 8mm from the top of alveolar crest(ABW8)was measured.All the measured data were analyzed statistically.Results:1.There was no statistical difference between the left and right sides of the same body and between men and women(p > 0.05).2.The measurements in the low angle group were higher than those in the high angle group,and the difference was statistically significant(p < 0.05).The SRL and ABW4 in average angle was higher than those in high angle group,and the difference was statistically significant(p < 0.05).There was no significant difference in ABW8 between the average angle group and high angle group(p > 0.05).3.The measurements in the existence group of the third molar were higher than those in the group of the absence of the third molar,and the difference was statistically significant(p < 0.05).Conclusion:1.The length of the posterior space of the second molar and the width of the alveolar bone in the posterior region of the molar were different among different vertical bone face types,and were negatively correlated with the size of the mandibular plane angle.2.Cbct should be used to guide the clinical design for the treatment of mandibular dentition in the patients with mild and moderate type III malocclusion,especially in the patients with high angle and mean angle.3.The existence of the third molar has a certain effect on the size of the posterior region of the mandibular molar.