Akiko Hayashi1, Hidetaka Hayashi2, Toshitsugu Kawata3. 1. a Employee practitioner, Hiroshima, Japan. 2. b Private practice, Hiroshima, Japan. 3. c Professor and Chair, Department of Orthodontics, Kanagawa Dental University, Kanagawa, Japan.
Abstract
OBJECTIVE: To clarify whether occlusal hypofunction is one of the key determinants for root resorption during tooth movement and root resorption is prevented by its recovery. MATERIALS AND METHODS: The rats were randomly divided into one control and two experimental groups: hypofunctional and recovery groups. In the hypofunctional group, an anterior metal cap and bite plate were attached to the maxillary and mandibular incisors to simulate occlusal hypofunction. In the recovery group, the appliances were removed 7 weeks after their use, and the rats were allowed to bite for 4 weeks after removal. At the age of 16 weeks, the upper first molars were moved and after 0, 7, 14, and 21 days, the maxillae were resected. The resorption area was quantified morphohistologically and tartrate-resistant acid phosphatase (TRAP)-positive cells on the root surface were counted. We also examined the expressions of receptor activator of nuclear factor-κB ligand (RANKL), macrophage-colony stimulating factor (M-CSF), and interleukin (IL)-8 immunohistochemically. RESULTS: The amount of root resorption and the number of TRAP-positive cells were significantly greater in the hypofunctional group than in the control and recovery groups. Moreover, immunoreactivity for RANKL, M-CSF, and IL-8 was detected in the periodontal ligament and on the root surface in the hypofunctional group. CONCLUSION: Occlusal hypofunction is one of the critical factors for root resorption; however, root resorption may be prevented by recovery of occlusal function.
OBJECTIVE: To clarify whether occlusal hypofunction is one of the key determinants for root resorption during tooth movement and root resorption is prevented by its recovery. MATERIALS AND METHODS: The rats were randomly divided into one control and two experimental groups: hypofunctional and recovery groups. In the hypofunctional group, an anterior metal cap and bite plate were attached to the maxillary and mandibular incisors to simulate occlusal hypofunction. In the recovery group, the appliances were removed 7 weeks after their use, and the rats were allowed to bite for 4 weeks after removal. At the age of 16 weeks, the upper first molars were moved and after 0, 7, 14, and 21 days, the maxillae were resected. The resorption area was quantified morphohistologically and tartrate-resistant acid phosphatase (TRAP)-positive cells on the root surface were counted. We also examined the expressions of receptor activator of nuclear factor-κB ligand (RANKL), macrophage-colony stimulating factor (M-CSF), and interleukin (IL)-8 immunohistochemically. RESULTS: The amount of root resorption and the number of TRAP-positive cells were significantly greater in the hypofunctional group than in the control and recovery groups. Moreover, immunoreactivity for RANKL, M-CSF, and IL-8 was detected in the periodontal ligament and on the root surface in the hypofunctional group. CONCLUSION:Occlusal hypofunction is one of the critical factors for root resorption; however, root resorption may be prevented by recovery of occlusal function.