CBCT Analysis Of Crown-Root Morphology In Incisors Of Different Skeletal Malocclusions In Early Permanent Dentition

Objective Using CBCT to study the crown-root morphology of different skeletal malocclusion incisor areas in the early stage of permanent teeth occlusion,and provide a theoretical basis for the orthodontic treatment of patients with early permanent teeth occlusion.Methods 80 patients with early permanent teeth occlusion without orthodontic treatment were screened out.According to ANB,Wits value and Angle malocclusion classification criteria,all the subjects were divided into four groups,named the skeletal Class Ⅰ group,the skeletal Class Ⅱ divison 1 group,the skeletal Class Ⅱdivison 2 group and the skeletal Class Ⅲ group,with 20 people in each group.All study subjects took CBCT images before treatment,and imported the obtained imaging data into the three-dimensional image processing software Invivo 5.0 for measurement.The measurement items included the extension of the long axis of the crown and the root of the right maxillary and mandibular incisors.The included angle is the Collum angle,the labial surface angle at the three levels of the clinical crown center,clinical crown center occlusal direction and gingival direction 0.5mm,and the value of the fenestration of labial alveolar in the maxillary and mandibular incisor area is recorded.SPSS18.0 statistical software was used to compare the differences between the groups in the Collum angle of the upper and lower incisor areas with different skeletal malocclusions,the labial surface angles at the clinical crown center,clinical crown center occlusal direction and gingival direction 0.5mm,and compare the torque changes at 0.5mm in the occlusal and gingival directions at the center of the clinical crown of the same teeth.At the same time,analyze and explore the correlation of each measurement index:(1)Correlation between the Collum angle of the incisors and the labial surface angle at the clinical crown center,clinical crown center occlusal direction and gingival direction 0.5mm respectively;(2)The correlation between the Collum angle of the incisor area and the fenestration value on the labial side,the test level is α=0.05.Results(1)The Collum angles of the maxillary central incisors and lateral incisors of the skeletal Class Ⅱ division 2 group and the mandibular central incisors and the lateral incisors of the skeletal Class Ⅲ group and the labial surface angles at the three levels,namely α,α1,and α2 are respectively larger than other groups(P<0.05);the Collum angle of the maxillary central incisor of skeletal Class Ⅱ division 1 group is significantly different from the maxillary central incisor of the skeletal Class Ⅰ group and the skeletal Class Ⅲ group,the difference was statistically significant(P<0.05);(2)The α,α1,and α2 of the maxillary central incisor and lateral incisor of the skeletal Class Ⅰ group were lower than those of the other three groups(P<0.05);(3)There was a statistically significant difference in the torque change value β2 of the maxillary central incisor from the clinical crown center by 0.5mm in the occlusal direction height change(P<0.05);the torque changes in the occlusal direction and the gingival height change in the other teeth had no difference(P>0.05);the torque angle change value increases from the central incisor to the lateral incisor,approximately 1.6° for the upper central incisor,1.9° for the maxillary lateral incisor,1.7° for the mandibular central incisor,and 1.8° for the mandibular lateral incisor.(4)The Collum angle of the mandibular central incisor and the lateral incisor were linearly positively correlated with α,α1,and α2,respectively(P<0.05);(5)The Collum angle of the mandibular central incisor and the corresponding labial bone fenestration value had a positive correlation(P<0.05).Conclusions(1)In adolescents with early permanent teeth occlusion,the phenomenon of crown-root angulation is widespread.Collum angle is positively correlated with the labial surface angles at the three levels of the clinical crown center.Among them,the skeletal Class Ⅱ division 2 maxillary incisor and the skeletal Class Ⅲ the Collum angle of mandibular incisors and the labial surface angles at the three levels of the clinical crown center are significantly larger than those of other groups.During treatment,attention should be paid to the influence of the crown-root angle and labial surface angle on the torque expression of the incisor and the final tooth position;(2)The torque angle of the maxillary central incisor at the early stage of permanent occlusion is different before and after the clinical crown center occlusal height changes 0.5mm,and the torque angle change value increases from the central incisor to the lateral incisor.There must be individual design considerations;(3)The more obvious the angle of the crown-root of the mandibular central incisor of patients with early permanent teeth occlusion,the greater the fenestration value of the labial alveolar bone,and special attention should be paid to the process of the tooth movement.