Root resorption in human mandibular first premolars after rotation as detected by scanning electron microscopy

The aims of this study were to investigate the presence, location, and severity of root resorption after orthodontic rotation for different lengths of time. Eighteen mandibular first premolars due to be extracted from 9 patients were intraindividually divided into 2 groups. Eight teeth were not moved (control group), and 10 teeth were rotated (experimental group) with a force of 50 g delivered by elastomeric modules through symmetrical brackets bonded on the buccal and lingual surfaces (25 g buccally and 25 g lingually) for periods of 2, 3, 4, and 6 weeks. The teeth were extracted, fixed, and treated with 2% sodium hypochlorite to remove the organic tissue components and then dehydrated in ethanol, air-dried, coated with gold, and analyzed in a scanning electron microscope. Examination by scanning electron microscopy revealed many concavities (resorption lacunae) on the root surfaces of all rotated teeth. The resorption areas were located mainly at the medial root third, in regions that corresponded to the prominent zones of the roots. The resorption lacunae in the teeth moved for longer time periods were deeper, often affecting the underlying root dentin, and were mainly at the medial root third. Both the apical and cervical thirds were clearly less affected at all the studied intervals. The root surfaces at the nonprominent root zones did not show signs of resorption.