Regional cell density distribution and oxygen consumption rates in porcine TMJ discs: an explant study.

OBJECTIVE

To determine the regional cell density distribution and basal oxygen consumption rates (based on tissue volume and cell number) of temporomandibular joint (TMJ) discs and further examine the impact of oxygen tension on these rates.

DESIGN

TMJ discs from pigs aged 6-8 months were divided into five regions: anterior, intermediate, posterior, lateral and medial. The cell density was determined using confocal laser scanning microscopy. The change in oxygen tension was recorded while TMJ disc explants were cultured in sealed metabolism chambers. The volume based oxygen consumption rate of explants was determined by theoretical curve-fitting of the recorded oxygen tension data with the Michaelis-Menten equation. The rate on a per-cell basis was calculated based on the cell density measurements and volume based rate measured in another group of discs.

RESULTS

The overall cell density [mean, 95% confidence interval (CI)] was 51.3 (21.3-81.3) × 10(6) cells/mL wet tissue. Along the anteroposterior axis, the anterior band had 25.5% higher cell density than the intermediate zone (P<0.02) and 29.1% higher than the posterior band (P<0.008). Along the mediolateral axes, the medial region had 26.2% higher cell density than the intermediate zone (P<0.04) and 25.4% higher than the lateral region (P<0.045). The overall volume and cell based maximum oxygen consumption rates were 1.44 (0.44-2.44) μmol/mL wet tissue/h and 28.7 (12.2-45.2)nmol/10(6)cells/h, respectively. The central regions (intermediate, lateral, and medial) had significantly higher volume based (P<0.02) and cell based (P<0.005) oxygen consumption rates than the anterior and posterior bands. At high oxygen tension, the oxygen consumption rate remained constant, but dropped as oxygen tension fell below 5%.

CONCLUSIONS

The TMJ disc had higher cell density and oxygen consumption rates than articular cartilage reported in the literature. These results suggest that a steeper oxygen gradient may exist in the TMJ disc and may be vulnerable to pathological events that impede nutrient supply.