| Objective:In order to effcttively contral the movement of maxillary incisor teeth during the orthodontic clinical treatment,the crown/root ratio and related indexes of upper incisor teeth in adolescent and adult patients with hyperdivergent skeletal ClassⅡmalocclusion are measured,while investigating the relevant influencing factors of crown/root ratio size.Methods: CBCT images of adolescents and adults with hyperdivergent skeletal ClassⅡmalocclusion were collected and divided into adolescent and adult groups before orthodontic treatment,with 33 cases in each group and 264 maxillary anteriors.DCT Viewer images were used to analyze the images,and the anatomical crown and root length,clinical crown and root length of 264 maxillary anteriors on CBCT images were measured,and the crown/root ratio was calculated.The relevant indexes that may affect the abnormal crown/root ratio were measured,including the vertical heigh of alveolar bone on the labial and palatine sides,the thickness of labial-Palatine alveolar bone at the root tip,the axial-Palatine Plane intersection Angle and the tooth crown/root Angle.Statistical analysis was carried out on the difference of the measured data of the two groups and the relevant influencing factors of crown/root ratio.Results:(1)Comparison of crown/root ratio:(1)The clinical crown/root ratio of upper incisor teeth in adolescent and adult groups was greater than the anatomical crown/root ratio(P <0.05),and the mean value of the clinical crown/root ratio in both groups was≥1.(2)The anatomical and clinical crown/root ratio of centeral incisor teeth in adolescent and adult groups was higher than lateral incisor teeth(P < 0.05).(2)Comparison of indexes that may affect crown/root ratio:(1)Anatomical crown length,clinical crown length,long axis-palatal plane intersection angle,apical labial alveolar bone thickness,and apical labial alveolar bone thickness of lateral incisor root tip were all higher than those of adults in adolescent group(P< 0.05).(2)The number of adults with alveolar bone vertical heigh >2mm was higher than that of adolescents(P<0.05).(3)The clinical and anatomical crown-root ratio,the crown-root angle of the middle incisor and alveolar bone thickness of apical palatine were larger than that of the lateral incisor(P<0.05),and the labial alveolar bone thickness of the root apex of the upper central incisor was smaller than that of the lateral incisor(P<0.05).(3)Analysis of factors related to crown/root ratio size:(1)The incidence of anatomic crown/root ratio ≥0.91 was higher in females(P<0.05);The incidence of clinical crown/root ratio≥0.91 was higher in males(P < 0.05).(2)The anatomical and clinical crown-root ratio of the u PPer central incisor was more than 0.91(P< 0.05).(3)Age was negatively correlated with anatomic crown/root ratioo(P < 0.05);(4)The labial thickness of the root tip was negatively correlated with the clinical crown/root ratio(P<0.05).(5)The vertical height of labial alveolar bone was positively correlated with clinical crown root ratio(P < 0.05).Conclusion:The crown/root ratio of adolescent and adult Patients with hyperdivergent skeletal Class Ⅱ malocclusion is generally maladjusted before orthodontic treatment,and central incisor compared with lateral incisor,the former more likely to have bnormal crown/root ratio.The upper incisor teeth of adults with hyperdivergent skeletal Class Ⅱmalocclusion are more labial and erect than those of adolescents.The alveolar bone of apical palatal side of lateral incisor root is less thick and the Angle of crown root is more obvious.The more the root is labial,the higher the alveolar bone height is,the more likely it is to lead to clinical crown/root ratio imbalance,and there is a certain correlation.In order to get better effect during the orthodontic clinical treatment,the treatment scheme of patiens with hyperdivergent skeletal ClassⅡ malocclusion should be designed according to the specific conditions of the maxillary incisor teeth. |
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