title: The imbalance of masticatory muscle activity affects the asymmetric growth of condylar cartilage and subchondral bone in rats.
abstract: OBJECTIVE
  To examine the effects of imbalance of masticatory muscle activity of the rat mandible on the condylar cartilage and subchondral bone during the growth period.
  
  
  METHODS
  Forty 5-week-old male Wistar rats were randomly divided into experimental (n=20) and control (n=20) groups. In the experimental group, the left masseter muscles were resected. The rats were sacrificed at 7 or 9 weeks of age in both groups. Microcomputed tomography was used to determine the three-dimensional morphology and cancellous bone structure. For histological and histochemical examination, 5-μm-thick serial frontal sections of the condyle were stained with toluidine blue and immunostained with asporin and TGF-β1 to evaluate the promotion and inhibition of chondrogenesis.
  
  
  RESULTS
  In the experimental group, microcomputed tomography analysis showed asymmetric growth; the resected side condyles showed degenerative changes. Histological analysis showed that the total cartilage in the central region of the resected side was significantly thinner than in the non-resected side in the experimental group, as well as in the control group. Compared with the control group, the expression of asporin was significantly higher in the resected side, and significantly lower in the non-resected side. In contrast, the expression of TGF-β1-immunopositive cells in the non-resected side was significantly higher than in the resected side and the control group.
  
  
  CONCLUSIONS
  These findings imply that lateral imbalance of masseter muscle activity lead to inhibition of chondrogenesis and induce asymmetric formation of the condyle during the growth period.
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Miyazaki
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan. Electronic address: yoneman.orts@tmd.ac.jp.
authors.forename: Ikuo
authors.initials: I
authors.lastname: Yonemitsu
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Takei
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.
authors.forename: Ikuko
authors.initials: I
authors.lastname: Kure-Hattori
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ono
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000254:growth & development* / Q000378:metabolism*; D020219:Chondrogenesis / Q000502:physiology*; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D008297:Male; D008335:Mandibular Condyle / Q000000981:diagnostic imaging / Q000254:growth & development*; D008410:Masticatory Muscles / Q000503:physiopathology*; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D055114:X-Ray Microtomography
chemical_list: C000594598:Aspn protein, rat; D016326:Extracellular Matrix Proteins; D053773:Transforming Growth Factor beta1
keywords: Asporin; Condylar cartilage; Mandibular asymmetry; Subchondral bone; TGF-; β1