Root Resorption After Orthodontic Intrusion and Extrusion: An Intra-individual Study

Objectives: The aim of this investigation was to compare root resorption in the same individual after application of continuous intrusive and extrusive forces. Methods: In nine individuals, five girls and four boys (mean age 15.3 years), the upper first premolars on both sides of the maxilla were randomly selected for intrusion or extrusion with a continuous force of 100 cN for eight weeks. The control group consisted of 10 maxillary first premolars from six randomly selected orthodontic patients. Root resorption was detected by scanning electron microscopy. Quantitative assessment of the percentage of resorbed area of the total root surface was determined on composite micrographs. The severity of root resorption was also assessed by visual scoring of the roots. Results: Root resorption mainly occurred at the apical part of the roots in both experimental groups. The mean percentage of resorbed area of intruded teeth was 5.78±3.86% and that of extruded teeth (1.28±1.24%) and the difference was significant (P=0.038). A significant difference in root resorption was found between the intrusion and the control group, but not between the extrusion and the control group. In addition, a large individual variation was found. Conclusions: The quantitative results indicate that intrusive forces cause more severe root resorption than extrusive forces of the same magnitude in the same individual.