Method: TMJ discs were extracted from the left joint of 24 human cadavers (12 male and 12 female). Cylindrical (5mm diameter) samples from five regions were placed into a custom built conductivity chamber. Measurements were taken at 0%, 10% and 20% mechanical strain. Volume water content (porosity) of the specimen was determined based on Archimedes' principle.
Results: Average conductivity for male TMJ disc tissue was 5.14 mS/cm at 0% strain, this value decreased to 4.51 mS/cm for 10% strain (-12.3%), and 3.93 mS/cm for 20% strain (-23.5%). Female conductivity was 5.79 mS/cm at 0% strain, 4.97 mS/cm for 10% strain (-14.2%), and 4.30 mS/cm for 20% strain (-25.7%). Volume water content (porosity) for male tissue was 76% while for female tissue it was 78%. The difference between male and female porosity was found to be significant (Students' T-test). No significant difference was found between regional conductivities or regional porosities (one-way ANOVA).
Conclusion: Our results show a significant correlation between electrical conductivity and porosity in human TMJ disc. Compressive strain induced by mechanical loading can significantly decrease electrical conductivity of TMJ disc tissue due to decreased porosity. The results also indicated that female porosity was higher than male porosity. This finding is in concurrence with female conductivity being higher and impacted more by mechanical strain than male conductivity. The measured electrical conductivity is proportional to the diffusivities of ions through the pores of the tissue. This study further confirmed that the compressive strain induced by mechanical loading impedes solute transport within TMJ discs, which supports our central hypothesis that mechanical strain may impact nutritional supply. (Supported by NIH T32DE017551)