Clinical study on root resorption of tooth extraction and premolar during orthodontic treatment

Objective To investigate the influence of tooth extraction to the root extraction of premolar in orthodontic treatment.Methods Fifty patients with fixed orthodontic appliances were selected in our hospital and divided into two groups of extraction and non-extraction according to whether the second premolar was pulled out or not.The root-crown ratio of the first premolar on the pre-treatment and post-treatment panoramic radiograph was measured.Through the changes of root-crown ratio,the influence of orthodontic treatment to the length of the first premolar was analyzed.Results(1) The average difference of root-crown ratio of the first premolar in the non-extraction group was 0.033 9±0.023 5 in upper jaw,and 0.032 8±0.021 7 in under jaw.(2) The average difference of root-crown ratio of the first premolar in the extraction group was 0.049 7±0.019 1 in upper jaw,and 0.048 0±0.023 5 in under jaw.(3) The difference of root-crown ratio between the non-extraction group and the extraction group had statistical significance(P0.01).Conclusion Extraction will aggravate the degree of root resorption of premolar in orthodontic treatment.