Study On The Correlation Between The Mesiodistal Width Ratio And The Crowding In Adult Lower Incisor Based On CBCT

Objective:Cone-beam computed tomography(CBCT)images were used to measure the width ratio of adult lower incisors.The ratio was used as the numerical expression of the crown shape of lower incisors,and the correlation between the width ratio and crowding was analyzed,so as to provide some reference for clinical practice.Method:The irregularity index(IRID)of mandibular anterior tooth was measured by pre-treatment CBCT images in 18-25 years old adults with skeletal class I malocclusion who were treated in the Department of Orthodontics,Nanchang University stomatological hospital from January 2017 to June 2020,and two groups of subjects were selected:the crowded group(group A)and the non-crowded group(group B),of which 45 cases(21 males and 24 females)were in group A(IRID>3mm)and 40 cases(19 males and 21 females)were in group B(IRID≤3mm).Two groups of pre-treatment CBCT image data were imported into Materialise Mimics21.0 software for 3D reconstruction.Using the function of multiplanar reformation and measurement,the mesiodistal width of incisors were measured at the incisal and cervical(level of the cemento-enamel junction)areas.The incisor width ratio was calculated as the numerical expression of the mandibular incisor crown shape.The data were imported into SPSS 21.0 for independent sample t test and regression analysis test to analyze the correlation between the width ratio of incisors and crowding.Result:1.The mean incisal maximum mesiodistal width of the incisors in group A was0.35 mm larger than that in Group B,the mean cervical mesiodistal width in group A was 0.23 mm smaller than that in Group B,and the mean value of width ratio in Group A were 0.18 higher than that in Group B,by independent sample t test,the differences were statistically significant(p<0.01).Compared with the non-crowded group,the incisors in the crowded group had a larger incisal maximum mesiodistal width and a smaller cervical mesiodistal width,and a larger width ratio.2.The regression equation between the width ratio and the irregularity index was Y=0.345*X-47.66,r~2=0.788,and the correlation coefficient r~2=0.875.There is a high correlation between the width ratio of mandibular incisors and crowding.Conclusion:1.Compared with the adult patients with well-aligned mandibular anterior tooth,the adult patients with crowded mandibular anterior tooth had a larger incisal maximum mesiodistal width and a smaller cervical mesiodistal width,and a larger width ratio.2.There was a significant correlation between the width ratio of mandibular incisors and crowding.The larger the width ratio,the more crowded the lower anterior teeth.