Mechanical loading leads to osteoarthritis-like changes in the hypofunctional temporomandibular joint in rats

Objectives: Temporomandibular joint (TMJ) hypofunction secondary to feeding a liquid dietin the growing period leads to morphological hypoplasia. However, few studies haveevaluated the results ofmechanical loading onthe hypoplastic TMJ. Thisstudy investigatedwhether TMJ hypofunction in rats causes osteoarthritis (OA)-like changes when exposed tomechanical loading.Design: Male 21-day-old Wistar rats weredivided intofour groups.The first group (C)servedas the control. In the second group (W), mechanical loading was applied to the TMJ bycontinuous steady mouth opening (3 h/day for 5 days) from 63 days of age. A jaw-openingdevice was used to hold the mandible open in the maximal mouth-opening position with acobalt–chromium (Co–Cr) wire (w: 0.9 mm). Groups C and W both received a normal harddiet. The third group (L) and fourth group (LW) were fed a liquid diet and group LW weresubjected to the same loading as group W. We evaluated the TMJ using micro-CT, toluidineblue staining and immunohistochemistry of matrix metalloproteinase (MMP)-13.Results: In group LW in the superior and posterior regions of the condyle, bone volumefraction, trabecular thickness and trabecular number were significantly decreased andtrabecular spacing was significantly increased. The ratio of MMP-13 immunopositive cellswas significantly higher than in the other groups. OA-like changes were also observed,including reduced thickness of the cartilage, irregularities in the chondrocytic layer, andcell-free areas.Conclusions: TMJ hypofunction in rats is likely to lead to OA-like changes when exposed tomechanical loading.# 2014 Elsevier Ltd. All rights reserved.* Corresponding author. Tel.: +81 3 5803 5530.E-mail addresses: yoneman.orts@tmd.ac.jp, yoneorts@tmd.ac.jp (I. Yonemitsu).