Response of the intermaxillary suture cartilage to alterations in masticatory function.

Like the condylar cartilage of the mandible, the cartilage at the intermaxillary suture in the rat is secondary in origin and persists well into adulthood. While the condylar cartilage is generally considered to be responsive to changes in its local biomechanical environment, little is known of the response of the intermaxillary suture cartilage to similar stimuli. In order to study the effect of changes in occlusal loads on intermaxillary suture cartilage metabolism, male weanling Sprague-Dawley rats were divided into four groups: soft diet (to discourage molar mastication), incisor clipped (to discourage incision), incisor clipped/soft diet (both treatments), and control (untreated). At 39 days of age, the intermaxillary suture opposite the first molars was removed and compared to control tissue by using histological, histochemical, and biochemical analyses. Alcian blue-stained coronal sections demonstrated moderate decreases in staining intensity and decreased chondrocyte hypertrophy in the soft diet and incisor-clipped groups. However, sutures in the incisor-clipped/soft diet group showed a considerably reduced extent of cartilage and greatly diminished cartilage hypertrophy. [35S]-sulfate incorporation (dpm/micrograms DNA) into acid-insoluble proteoglycans was significantly reduced (P less than or equal to .01) in all three experimental groups compared to controls. [35S] incorporation was further reduced in the incisor-clipped/soft diet group relative to both of the other experimental groups. Staining for alkaline phosphatase activity showed decreased intensity in the experimental groups and was almost absent in the incisor-clipped/soft diet group. These data demonstrate the plasticity of the intermaxillary suture cartilage and provide circumstantial evidence that the observed changes in cartilage morphology and metabolism may be attributable to alterations in the local biomechanical environment of the suture.