title: Mechanical loading leads to osteoarthritis-like changes in the hypofunctional temporomandibular joint in rats.
abstract: OBJECTIVE
  Temporomandibular joint (TMJ) hypofunction secondary to feeding a liquid diet in the growing period leads to morphological hypoplasia. However, few studies have evaluated the results of mechanical loading on the hypoplastic TMJ. This study investigated whether TMJ hypofunction in rats causes osteoarthritis (OA)-like changes when exposed to mechanical loading.
  
  
  METHODS
  Male 21-day-old Wistar rats were divided into four groups. The first group (C) served as the control. In the second group (W), mechanical loading was applied to the TMJ by continuous steady mouth opening (3h/day for 5 days) from 63 days of age. A jaw-opening device was used to hold the mandible open in the maximal mouth-opening position with a cobalt-chromium (Co-Cr) wire (φ: 0.9mm). Groups C and W both received a normal hard diet. The third group (L) and fourth group (LW) were fed a liquid diet and group LW were subjected to the same loading as group W. We evaluated the TMJ using micro-CT, toluidine blue staining and immunohistochemistry of matrix metalloproteinase (MMP)-13.
  
  
  RESULTS
  In group LW in the superior and posterior regions of the condyle, bone volume fraction, trabecular thickness and trabecular number were significantly decreased and trabecular spacing was significantly increased. The ratio of MMP-13 immunopositive cells was significantly higher than in the other groups. OA-like changes were also observed, including reduced thickness of the cartilage, irregularities in the chondrocytic layer, and cell-free areas.
  
  
  CONCLUSIONS
  TMJ hypofunction in rats is likely to lead to OA-like changes when exposed to mechanical loading.
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Yuhei
authors.initials: Y
authors.lastname: Ikeda
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, 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, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Takei
authors.affiliation: Maxillofacial Anatomy, Department of Maxillofacial Biology, Division of Maxillofacial/Neck Reconstruction, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Shibata
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ono
mesh_terms: D000818:Animals; D003799:Dental Stress Analysis; D008297:Male; D008409:Mastication / Q000502:physiology; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism; D010003:Osteoarthritis / Q000000981:diagnostic imaging / Q000209:etiology* / Q000503:physiopathology*; D051381:Rats; D017208:Rats, Wistar; D013314:Stress, Mechanical; D013704:Temporomandibular Joint / Q000000981:diagnostic imaging / Q000503:physiopathology*; D055114:X-Ray Microtomography
chemical_list: D053509:Matrix Metalloproteinase 13; C507083:Mmp13 protein, rat
keywords: Growth; Matrix metalloproteinase-13; Mechanical loading; TMJ-osteoarthritis; Temporomandibular joint hypofunction