Apical root resorption in orthodontically treated subjects: analysis of edgewise and light wire mechanics.

Of the several modes of tooth movement, pressure from intrusive forces seems the most likely to cause external apical root resorption (EARR). This has been demonstrated for incisors in human beings and molars in laboratory animals. The present study examined full-banded adolescent patients and scored the degrees of in-treatment root resorption throughout the dentition. Just Class I cases with four first premolar extractions were used. Equal samples of conventional Begg and Tweed treated cases were examined with 1:1 sex ratios (total n = 83). No difference between the Begg and Tweed techniques and no sex difference was found in any of the 30 univariate tests, even though power analysis indicated a strong likelihood of finding a difference if one existed. By using multiple linear regression, significant decreases in length (EARR) were found for those roots systematically intruded in this Class I malocclusion, notably the mesial root of the maxillary first molar and the distal root of the mandibular first molar. Even though some of the present cases had been in "active" treatment up to 6 years, we found no significant association between duration of treatment and degree or amount of EARR.