Objective To investigate the changes of crown to root ratio of upper anterior teeth during straight wire appliance treatment, and the correlation with age. Methods 23 juvenile patients and 23 adult patients were selected. The 46 patients were divided into two groups according to age:adolescent group and adult group. External apical root resorption and alveolar crest loss of upper anterior teeth were measured on the pre-treatment and post-treatment panoramic-radiographs. The crown to root ratios of the teeth were calculated before and after treatment. Results Before the treatment, the crown to root ratios of the central incisor group, the lateral incisor group and the cuspid group of adolescent group were 0.62 ± 0.04,0.63 ± 0.04, 0.54 ± 0. 05, respectively. After the treatment, they changed into 0.70 ± 0.06, 0.70 ± 0.06, 0.60 ±0.06, respectively. Before the treatment, the crown to root ratios of central incisor group,lateral incisor group and the cuspid group of adult group were 0.67 ± 0.04, 0. 66 ± 0. 05, 0. 57 ± 0. 05, respectively. After the treatment, they changed into 0.78 ± 0.06,0.77 ± 0. 05 ,0.70 ± 0.06, respectively. Changes of crown to root ratio of upper anterior teeth occured to every patient. There was significant difference between adult group and adolescent group( P ＜0.01 ). Conclusions The crown to root ratio of upper anterior teeth was found significantly increased after straight wire appliance treatment, and the adult group was of higher level than adolescent group,but it was still acceptable clinically.%目的 探讨直丝弓矫治器矫治前后牙齿冠根比的变化规律,及年龄因素在其中所起的作用.方法 选取青少年患者23例和成人患者23例共46例,分为青少年组和成年组,根据正畸治疗前后全口曲面断层片,以托槽为参照系,测量计算出治疗前后中切牙、侧切牙及尖牙的根尖吸收量、牙槽嵴吸收量及冠根比变化量,进行配对t检验,分析年龄因素与矫治前后冠根比变化的相关性.结果 青少年组治疗前后中切牙平均冠根比分别为0.62±0.04,0.70±0.06;侧切牙平均冠根比分别为0.63±0.04,0.70±0.06;尖牙平均冠根比分别为0.54±0.05,0.60±0.06.成年组治疗前后中切牙平均冠根比分别为0.67±0.04,0.78±0.06;侧切牙平均冠根比分别为0.66±0.05,0.77±0.05;尖牙平均冠根比分别为0.57±0.05,0.70±0.06.各组治疗前后冠根比有显著性差异,成年组上前牙冠根比变化量较青少年组显著(P＜0.01).结论 直丝弓矫治后,上前牙冠根比均明显增大,其中成年组较青少年组显著,但都仍在临床可接受的正常范围内.
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