Microvasculature of normal juvenile and adult porcine TMJ discs

Angiogenesis is a factor in developing inflammatory conditions such as osteoarthritis, a common pathology of the temporomandibular joint (TMJ). TMJ discs are often referred to as avascular. However, studies have shown that microvessels exist throughout human discs. Objective: Establishing baseline microvessel density (MVD) values of normal porcine TMJ discs will support using the pig as a model for TMJ dysfunction such as osteoarthritis. Methods: Discs were harvested from 5 juvenile (1-2 months) Yucatan pigs (Sinclair Laboratories) and 5 adult (7-10 months) farm pigs (Pine-Ridge; Barlow, OH). Paraffin-embedded specimens were divided into superior/inferior surfaces then into anterior/intermediate/posterior bands creating six comparable regions. Microvessels were stained immunohistologically using a standardized peroxidase system (ImmPRESS©; Vector Laboratories) with anti-human von Willebrand factor acting as the primary antibody to bind vascular endothelial cells. Specimens were observed under a light microscope using a 10x objective (Olympus-BX51). MVD was quantified (ImageJ) in each area from captured digital images (Spot-Mac). Comparisons of MVD among regions, bands, and surfaces within and between age groups were made using ANOVAs and t-tests. Results: Microvessels were present in all areas of juvenile and adult samples; however no significant difference in density was found when bands, surfaces, and regions were compared within age groups (p>0.05). The MVD of anterior band (0.53±0.46/mm2) and inferior surface (0.49±0.40/mm2) were most dense in the adults. The posterior band (1.16±0.79/mm2) and superior surface (1.21±0.75/mm2) were most dense in juveniles. No significant differences were found when specific areas were compared between age groups (p>0.05). However, juvenile total MVD (0.86±0.76/mm2) was significantly greater (p=0.005) than adult MVD (0.40±0.35/mm2). Conclusion: Although the TMJ disc is considered avascular, this study demonstrates that microvessels are present in limited numbers throughout all regions of adult and juvenile pig discs. These normal MVD values can be used to study TMJ pathologies using the pig model.