title: The influence of masseter activity on rat mandibular growth.
abstract: Many studies have shown that mandibular and condylar growth is affected by compressive forces on mandibular bone and the condyle. It has been reported that chondroblastic differentiation and proliferation in chondrocytes play important roles in condylar growth. However, the influence of reduced compressive force on chondroblastic proliferation and mandibular bone formation is not fully understood. Thirty-six 3-week-old male Wistar rats were used in this study. In the experimental group, the masseter muscles were bilaterally resected to evaluate the influence of masticatory force on mandibular and condylar bone morphology. Six weeks after the operation, while the rats were in the pubertal growth stage, lateral X-rays were taken to analyze the skeletal pattern of the mandible. The form of the condyle and the thickness of the chondroblastic layers were evaluated by toluidine blue staining. Chondroblastic proliferation was identified by insulin-like growth factor-1 receptor (IGF-1r) immunostaining and bone resorption of the condyle was assessed by measuring tartrate-resistant acid phosphatase (TRAP) activity. Lateral X-rays of the mandible showed that rats in the experimental group tended to have large mandibular plane angles. The chondroblastic layer in the condyles of the experimental group rats was thinner than in the control group. The expression of IGF-1r immunopositive cells in the experimental group was significantly lower than in the control chondrocytes, and the number of TRAP-positive cells was significantly higher in the condylar bone of the experimental group. We conclude that masseter muscle activity is closely related to mandibular morphology during growth.
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan. yoneorts@tmd.ac.jp
authors.forename: Ikuo
authors.initials: I
authors.lastname: Yonemitsu
authors.forename: Takeshi
authors.initials: T
authors.lastname: Muramoto
authors.forename: Kunimichi
authors.initials: K
authors.lastname: Soma
mesh_terms: D000135:Acid Phosphatase / Q000032:analysis; D000818:Animals; D015415:Biomarkers / Q000032:analysis; D001732:Bite Force; D001862:Bone Resorption / Q000503:physiopathology; D002358:Cartilage, Articular / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000254:growth & development; D002452:Cell Count; D049109:Cell Proliferation; D002508:Cephalometry; D019902:Chondrocytes / Q000166:cytology / Q000502:physiology; D004396:Coloring Agents; D007527:Isoenzymes / Q000032:analysis; D008297:Male; D008334:Mandible / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000254:growth & development*; D008335:Mandibular Condyle / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000254:growth & development; D008406:Masseter Muscle / Q000502:physiology* / Q000601:surgery; D023421:Models, Animal; D010010:Osteoclasts / Q000473:pathology; D011859:Radiography; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D017526:Receptor, IGF Type 1 / Q000032:analysis; D000071681:Tartrate-Resistant Acid Phosphatase; D014048:Tolonium Chloride
chemical_list: D015415:Biomarkers; D004396:Coloring Agents; D007527:Isoenzymes; D014048:Tolonium Chloride; D017526:Receptor, IGF Type 1; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase