Objective: To clarify the mechanism of root resorption during orthodontic treatment, we examined cementocyte cell death and root resorption in the cellular cementum on the pressure side during experimental tooth movement. Materials and Methods: Using 8-week-old male Wistar rats, the right first molar was pushed mesiobuccally with a force of 40 g by a Ni-Ti alloy wire while the contralateral first molar was used as a control. Localization and number of cleaved caspase-3-positive and single-stranded DNA (ssDNA) -positive cells were evaluated using dual-label immunohistochemistry with anticleaved caspase-3 and anti-ssDNA antibodies. In addition, tartrate-resistant acid phosphatase (TRAP)-positive cells in the cellular cementum were evaluated using TRAP histochemical staining. Results: Caspase-3-and ssDNA-positive cells appeared at 12 hours, but were restricted to the compressed periodontal ligament (PDL) and not the cellular cementum. Cleaved caspase-3-positive cementocytes were observed in the cellular cementum adjacent to the compressed PDL on day 1. From days 2 to 4, the number of caspase-3-and ssDNA-positive cementocytes increased. TRAP-positive cells appeared on the cellular cementum at the periphery of the hyalinized tissue on day 7, and resorption progressed into the broad surface of the cementum by day 14. Conclusion: Cementocytes adjacent to the hyalinized tissue underwent apoptotic cell death during orthodontic tooth movement, which might have been associated with subsequent root resorption. (Angle Orthod. 2017;87:416-422)

Introduction: In cases with gummy smile or asymmetry of the maxilla, superior repositioning of the maxilla is required. If superior repositioning by a Le Fort I osteotomy alone is difficult, a horseshoe Le Fort I osteotomy can be used. Presentation of cases: Case 1: A 24-year-old Japanese woman patient presented with a gummy smile and an open bite. After we performed a horseshoe Le Fort I osteotomy, the maxillary segment was repositioned superiorly 3.0 mm at upper tooth number 1 (U1) and 5.0 mm at upper tooth number 6 (U6). Case 2: A 21-year-old Japanese man presented with severe facial asymmetry. After we performed a unilateral modified horseshoe Le Fort I osteotomy, the maxillary segment was superiorly repositioned 6.0 mm at the right U6. Discussion: This procedure eliminated the risk of intraoperative bleeding because it was unnecessary to remove bones around the descending palatine artery, and it was possible to maintain the chamber size of the nasal cavities. Conclusion: The horseshoe Le Fort I osteotomy is a reliable technique for cases with severe gummy smile or asymmetry of the maxilla.