Cone Beam Computed Tomography(CBCT) Study Of Skeletal Class ? Patient With Lower Anterior Teeth Crowding

Objective:To study the factors affecting lower anterior teeth's faciolingual movement as well as the correlation between anterior teeth root and irregularity index (total length of five contact points in the anterior teeth region) by measurement and analysis of CBCT image of the underjaw mental region basal bone morphology of patients respectively with skeletal Class I high-angle, normal-angle and low-angle lower anterior teeth crowding, so as to provide a theoretical basis and guidance for clinical treatment.Methods:A total of 93 cases of malocclusion patients at early permanent dentition and in accordance with the inclusion criteria were selected from patients treated in the Affiliated Dental Hospital of Kunming Medical University from 2014 to 2016, and the preoperative CBCT image data of them was collected. Analysis of the difference between the thickness of cortical bone and that of cancellous bone in the lower anterior teeth region of skeletal Class I high-angle, normal-angle and low-angle patients of vertical facial type was carried out. Finally, according to different crowding degrees, a total of 34 cases of skeletal Angle's Class I high-angle,normal-angle and low-angle orthodontic patients in accordance with the inclusion criteria were selected and their cone beam CT data was collected. CBCT was adopted to measure the distance between anatomy contact points of the lower anterior teeth,and the total length of the five contact points in the anterior teeth region was calculated, which is the Bolton tooth-size discrepancy II of the patients. Finally,through simple linear regression, the correlation between the Bolton tooth-size discrepancy of the lower anterior teeth and the distance from teeth root to cortical bone was investigated.Results: The following results can be gotten from the CBCT data:1. For male patients,high-angle patients have the thinnest labial side cancellous bone of the lower anterior teeth, followed by normal-angle and low-angle patients, and no statistical significance was found between normal-angle and low-angle patients;high-angle patients have the thickest lingual side cancellous bone, followed by normal-angle and low-angle patients, and no statistical significance was found between normal-angle and low-angle patients.2. For female patients, high-angle skeletal facial type patients have the thinnest labial side cortical bone, followed by low-angle and normal-angle patients, and no statistical significance was found between normal-angle and low-angle patients; low-angle skeletal facial type patients have the thickest lingual side cortical bone, followed by normal-angle and high-angle patients, and no statistical significance was found between normal-angle and high-angle patients; low-angle skeletal facial type patients have the thickest labial side cancellous bone,followed by high-angle and normal-angle patients, and no statistical significance was found between normal-angle and high-angle patients;3. The analysis results of correlation between male patients' lower anterior teeth skeletal anatomy factors and irregularity index showed that: the width of lingual side cancellous bone is positively correlated with irregularity index, r=-0.484, P=0.049,and irregularity index ? is negatively correlated with the thickness of lingual side cortical bone, r=-0.490, P=0.046; The analysis results of correlation between female patients'lower anterior teeth skeletal anatomy factors and irregularity index showed that: the labial side cancellous bone is negatively correlated with irregularity index, and the correlation coefficient r=0.826, P<0.05.Conclusions:1.For female patients, high-angle patients have the thinnest labial side cortical bone,suggesting that for patients with lower anterior teeth retraction, some root movement control and overall retraction can be carried out to avoid the occurrence of labial side bone cortex fracture.2.For male patients, the labial side mobile range of normal-angle patients is larger than that of high-angle patients, which requires us to strictly control the labial side mobile range of high-angle cases;irregularity index is positively correlated with the thickness of the lingual side cancellous bone and negatively correlated with the thickness of the labial side cortical bone, suggesting that there's no correlation between the thickness of cortical bone and that of cancellous bone, and thick cancellous bone does not necessarily point to thick cortical bone.