Improving TMJ Regeneration
For the TMJ injury model, 4 month-old New Zealand white rabbits were subjected to unilateral TMJ disc perforation. After anesthetizing each rabbit, the pre-auricular region of the rabbit was shaved and prepped under sterile conditions. To surgically access the superior joint space, a 1-2 cm incision was made along the lateral upper border of the zygomatic arch to directly expose the TMJ disc. A punch biopsy was used to create a 2.5 mm perforation in the TMJ unilaterally. Sham surgery was performed on the contralateral side, each side sutured similarly. Radiographic examination and phlebotomy were performed both at the time of surgery and euthanization (2, 4, 8 weeks). Gross pathological, histological, and SEM evaluation were performed on the rabbit TMJ condyles. For the TMJ regeneration model, the anatomic contour of a cadaver TMJ condyle on the right side of a New Zealand White rabbit was captured from multi-slice laser and reconstructed by computer aided design (CAD). Anatomically correct TMJ scaffolds of polycaprolactone (PCL) were fabricated by 3D bioprinting. The native rabbit TMJ condyle and condylar neck were surgically excised and scaffolds were immediately implanted without cells. In a parallel study, primary TMJ cells (TMJCs) were isolated from rabbit TMJ condyles. TMJCs were characterized using RT-PCR, colony-forming assay, and examined for multipotency, using donor-matched MSCs isolated from tibia bone marrow as comparison controls.
In the injury model, gross morphological examination revealed irregular condyle surfaces and hyperplastic discs at 2 weeks compared to sham control. At 4 weeks, the injury model demonstrated an increasingly irregular surface and enlarged condyle. By 8 weeks, condyles appeared inflamed and erythematic with severely irregular surfaces relative to sham control. SEM analysis showed disarrayed collagen fibrils on condyle surfaces, while sham control showed smooth condyle surfaces. In the regeneration model, surgically-placed scaffolds in rabbits were stable 8 weeks post-operatively. RT-PCR analysis showed TMJCs had distinct gene expression profiles compared to donor-matched MSCs. As seen in chemical-defined media, TMJCs underwent osteogenesis, adipogenesis, and chondrogenesis in pellet cultures. TMJCs formed single-cell colonies by colony-forming assay similar to MSCs.
TMJ condyles harbor distinct stem/progenitor-like cells that may participate in TMJ tissue homeostasis and regeneration. The long-term inflammatory nature of our TMJ injury model mimics the human condition and may be accurate in simulating human TMJ degeneration. Our regenerative models' stability also suggests that regenerative scaffolds may be useful in exploring novel approaches for TMJ repair.
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