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We describe a rare case of osteochondroma of the coronoid process of mandible accompanied by severe trismus in a 14-year-old Japanese boy. The patient had initially been diagnosed as having internal derangement of the temporomandibular joint (TMJ), and conservative treatment had failed to improve the symptoms. Despite extremely limited TMJ movement, panoramic radiography revealed no abnormality, but magnetic resonance imaging suggested internal derangement of the left TMJ. Five months later, the trismus worsened and computed tomography revealed a bone-like mass confluent with the coronoid process, which was finally diagnosed as osteochondroma. The patient then underwent intraoral coronoidectomy. (J Oral Sci 57, 389-392, 2015)

Brain and muscle Arnt-like protein-1 (BMAL1) knockout mice exhibit accelerated aging, abnormal glucose metabolism, and impaired adipocyte differentiation, among other phenotypes, which are effects associated with the BMAL1 gene. No study has investigated temporal changes in the deformation of the mandibular condyle and the presence of calcification in areas surrounding the mandibular condyle. In a study of 12 C57/BL strain mice under inhalation anesthesia, we collected images of the mandibular condyle at 6 weeks after birth and then every 5 weeks from 10 to 25 weeks after birth. At 25 weeks, deformation of the mandibular condyle was seen in 8 of 12 joints in BMAL1 knockout mice and in 2 of 12 joints in wild-type mice. At 20 and 25 weeks, deformation in areas surrounding the mandibular condyle, which are known to undergo calcification, was seen in 2 of 12 joints in BMAL1 knockout mice and in 0 of 12 joints in wild-type mice. BMAL1 knockout mice exhibited premature aging of the mandibular condyle, which suggests that circadian rhythms affect mandibular condyle morphology.

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