Changes of crown to root ratio of upper anterior teeth during orthodontic treatment of juvenile and adult patients:a preliminary study

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(P0.01).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.