Methods: Porcine TMJ discs from young adult pigs aged 10 months were used (n=14). Each disc was divided into five regions: anterior, intermediate, posterior, lateral and medial. These specimens were then sectioned (100μm) into three layers along the superior-inferior axis. The nuclei of samples were stained (DRAQ5, Biostatus Limited) and scanned with a Leica Confocal Microscope. The volume-based cell density measurements were accomplished by counting cell numbers in specific volumes from reconstructed 3D images. This technique was validated by using biochemical assays to measure the DNA content of the same tissue samples. All data were statistically analyzed to determine significance (Student's t-test and ANOVA, Tukey's, p<0.05).
Results: Our study showed that the overall porcine TMJ disc cell density was 51,300cells/mm3, which is higher than the cell density (20,000cells/mm3) of bovine TMJ disc. No significant surface and regional variations were detected, which might be due to the young age of the animals used in this study. The cell densities measured by DNA assay was comparable to the measurements of the confocal technique.
Conclusion: We determined volume-based cell densities in porcine TMJ discs using laser confocal microscopy. The measured cell density of the TMJ disc is higher than the cell density of other cartilage tissues, such as human femoral condylar cartilage (15,000cells/mm3) and human intervertebral discs (9,000cells/mm3). This study demonstrated the unique cell density distribution which is fundamental information for in-situ cellular characterization of the TMJ disc. (Supported by NIH R03DE018741 and P20RR-017696)