We used 3D laser microscopy to conduct a quantitative analysis and to compare the changes in root resorption due to orthodontic force with or without an interval period after development of root resorption. Experimental device with closed coil spring extending from the maxillary incisor to the first molar was used. 20 rats were divided into 4 groups; 20 rats underwent 50-gf traction for 1 week and were subsequently divided into 4 groups. 50-gf traction group was sacrificed immediately after undergoing 50-gf traction. Interval group underwent 50-gf traction and was sacrificed after an interval of 2 weeks. Continuous traction group underwent 50- gf traction and was sacrificed after undergoing further 10-gf traction for 2 weeks. Post-interval traction group underwent 50-gf traction followed by an interval of 2 weeks and were sacrificed after undergoing further 10-gf traction for 2 weeks. The surface area and volume of root resorption craters and the percentage of tooth root surface area occupied by these craters were measured using 3D laser microscopy. Traction of 10 gf caused no significant differences in the degree of tooth movement between the groups. Quantitative analysis showed no significant differences between the 50 gf traction and the interval groups; however, there was a significant difference between the continuous traction and post-interval traction groups. Results indicated that when root resorption occurs, traction should be temporarily interrupted and resumed after an interval period.
Junya Nagata, Kunihiko Nojima, Yasushi Nishii, Kenji Sueishi, Takaki Yamazaki and Yasuo Miake