Molecular basis of articular disk biomechanics: Fluid flow and water content in the temporomandibular disk as related to distribution of sulfur

The temporomandibular articular disk was used to test the hypothesis that there is a positive relationship between the sulfur concentration and the amount of water held in the tissue, and an inverse relationship between sulfur concentration and the rate of fluid flow from the disk during compressive loading. Elemental concentrations were measured for sulfur, potassium, sodium, chlorine, phosphorus and calcium in each area of the disk by electron probe x-ray microanalysis. X-ray microanalysis showed high sulfur content coincident with histochemical localization of glycosaminoglycans. Further analysis of the elemental content revealed a strong correlation between sulfur and K ⁺, suggesting that the predominate counterion on fixed sulfates is a K⁺ rather than Na⁺. The resistance to fluid flow was measured by determining the cumulative grams of water forced from the tissue at multiple intervals during centrifugal loading. Values were expressed as grams water per gram dry mass and then plotted against time. Multiple regression analysis of sulfur content and water content values revealed a significant inverse, rather than a positive correlation between sulfur content and both the initial water content and the water content following centrifugal loading. Potassium content also had a strong negative correlation with water content. Curve analysis of flow rates revealed that there were two water compartments, an inner, more tightly held water compartment with a slower flow rate, and an outer compartment with a flow rate 2 to 3 times faster than that of