APICAL ROOT RESORPTION IN ORTHODONTICALLY TREATED ADULTS

This study analyzed the relationship in orthodontically treated adults between upper central incisor displacement measured on lateral cephal ograms and apical root resorption measured on anterior periapical x-ra y films, A multiple linear regression examined incisor displacements i i four directions (retraction, advancement, intrusion, and extrusion) as independent variables, attempting to account for observed differenc es in the dependent variable, resorption. Mean apical resorption was 1 .36 mm (sd +/- 1.46, n = 73). Mean horizontal displacement of the apex was -0.83 mm (sd +/- 1.74, n = 67); mean vertical displacement was 0. 19 mm (sd +/- 1.48, n = 67). The regression coefficients for the inter cept and for retraction were highly significant; those for extrusion, intrusion, and advancement were not. At the 95% confidence level, an a verage of 0.99 mm (se = +/- 0.34) of resorption was implied in the abs ence of root displacement and an average of 0.49 mm (se = +/- 0.14) of resorption was implied per millimeter of retraction. R(2) for all fou r directional displacement variables (DDVs) taken together was only 0. 20, which implied that only a relatively small portion of ft-ie observ ed apical resorption could be accounted for by tooth displacement alon e. In a secondary set of univariate analyses, the associations between apical resorption and each of 14 additional treatment-related variabl es were examined. Only Gender, Elapsed Time, and Total Apical Displace ment displayed statistically significant associations with apical reso rption. Additional multiple regressions were then performed in which t he data for each of these three statistically significant variables we re considered separately, with the data for the four directional displ acement variables. The addition of information on Elapsed Time or Tota l Apical Displacement did not explain a significant additional portion of the variability in apical resorption, On the other hand, the addit ion of information on Gender to the information on the four directiona l displacement variables yielded an R(2) value of 0.35, which indicate d that these variables taken together could account for approximately a third of the observed variability in apical resorption in this sampl e.