Repair of root resorption 4 and 8 weeks after application of continuous light and heavy forces on premolars for 4 weeks: A histology study

Introduction: Repair of root resorption cavities has been studied under light microscopy, scanning electron microscopy, and transmission electron microscopy. The aim of this investigation was to demonstrate the use of microcomputed tomography (micro-CT) to assist in the identification of the region of interest for light microscopy preparation. This study also qualitatively illustrated the root resorption craters with 4 or 8 weeks of retention after 4 weeks of continuous light or heavy orthodontic force application. Methods: Four patients who required bilateral extractions of maxillary first premolars as part of their orthodontic treatment were divided into 2 groups (groups I and II) of 2. The maxillary left and right first premolars were loaded with light (25 g) or heavy (225 g) orthodontic force for 4 weeks. After 4 or 8 weeks of retention, the maxillary first premolars were extracted. The extracted teeth were investigated with micro-CT. By using 3-dimensional images created by the micro-CT, the largest resorption craters on the buccal and lingual sides were identified. Parasagittal sections of these resorption craters were studied histologically under hematoxylin and eosin staining. Results: The use of micro-CT improved the efficiency and accuracy of histologic techniques. Comparatively, less root resorption was repaired by new cementum after heavy orthodontic force application and short retention time. The reparative processes seemed to depend on time, with longer retention time yielding the most amount of repair. Reparative cementum was a mixture of acellular and cellular cementum. Reparative processes seemed to commence at the central part of the resorption cavity and expand to the periphery. Conclusions: Root resorption cavities have the potential to repair regardless of the orthodontic force magnitude. Correlative microscopy with micro-CT and conventional light microscopy adds a new dimension to current root resorption investigation techniques. (Am J Orthod Dentofacial Orthop 2010;138:727-34)