EFFECTS OF LATERAL PTERYGOID MUSCLE HYPERACTIVITY ON DIFFERENTIATION OF MANDIBULAR CONDYLES IN RATS

Background: The effects of biomechanical stress on the growth and deve lopment of the mandibular condyle have been studied by many investigat ors. However, the role of the lateral pterygoid muscle in this develop ment is not clear. Methods: Hyperfunction of the lateral pterygoid mus cles of male 3-week-old Sprague-Dawley rats was induced by electrical stimulation, and the responses of the mandibular condyles were compare d to control tissues by a double-fluorescent staining technique using polyclonal antibodies against type I and type II collagen. Electrical stimulation consisted of repeated application (5 seconds on/5 seconds off) of a 5 Hz current for up to 7 days. Results: In the first 2 days, cartilaginous tissues rich in type II collagen disappeared in the ant erior and posterior areas, which were loaded by tensional force due to direct and indirect attachment of the lateral pterygoid muscles. Tiss ues in these areas were replaced by intramembranous bone that was reac tive for type I collagen at 7 days. By the end of the experiment, the trabecula of the condyle was remodeled more perpendicularly, thus resi sting the compressive force due to hyperfunction of the lateral pteryg oid muscles. Conclusions: These results suggest that the activity of t he lateral pterygoid muscle might play a significant role in the diffe rentiation of progenitor cells and in the maturation and calcification of chondrocytes in mandibular condyles. (C) 1995 Wiley-Liss, Inc.