Cyclophosphamide-induced temporomandibular synostosis.

The study of malformations helps toward a better understanding of normal development, which is of significance to the orthodontist. Experiments in teratology have induced an extensive variety of facial abnormalities, but temporomandibular joint (TMJ) synostosis has never been previously reported. Ten pregnant female rabbits were treated with a daily injection of 50 mg. cyclophosphamide (DNA synthesis inhibitor), from day 11 to day 14, which is the period that precedes formation of the face. The control sample comprised five female rabbits. The fetuses were obtained by cesarean section on day 28 and stained with alizarin. Six of the ten treated female animals produced offspring that had TMJ synostosis. The skull with TMJ synostosis showed a retrognathic mandibular pattern in relation to the maxilla, and the bony trabeculae in the mandibular angle showed a downward orientation instead of the horizontal orientation seen in animals without synostosis. The length of the heads was significantly smaller in the treatment group than in the control group; within the treatment group, the heads with synostosis were significantly smaller than those without synostosis. It could be hypothesized that the cyclophosphamide might have affected intrinsic factors in the temporomandibular mesenchyma; an impairment in the development and function of the mandibular musculature, which is a vital factor in joint development and maintenance, might also have contributed to the genesis of the malformation. The association of immobilization and mandibular hypodevelopment seems to be in agreement with today's theories on maxillofacial growth.