The attachments of the temporomandibular joint disc: a biochemical and histological investigation

Abstract

Objective: The complex movement of the temporomandibular joint (TMJ) disc during mastication is controlled in large part by the disc's attachments to the surrounding tissues. This study seeks to address the lack of available quantitative data characterizing the extracellular matrix composition of the discal attachments and how these properties compare to the disc.

Design: Porcine TMJ disc-attachment complexes were carefully dissected into six discal attachments and five TMJ disc regions. All samples were assayed biochemically for total collagen, glycosaminoglycan (GAG), DNA, and hydration. Additionally, histology was performed on the whole joint to investigate the anatomy of the disc-attachment complex, and to verify the regional distribution of matrix components.

Results: Quantitative biochemical assays showed that overall water content was fairly constant in all disc and attachment regions. Disc regions generally showed higher sulfated GAG and collagen content than the attachments. In contrast, the attachments contained greater DNA content than the disc. Histological staining supported the quantitative results and also indicated more elastic fibres to be present in the attachments than the disc.

Conclusions: Although macroscopically the TMJ disc and its attachments form a seamless complex within the joint, a closer look at regional biochemical constituents reveals that these two components are distinct. Whilst the disc and attachments both contain the same major constituents, the relative amounts of these components vary based on the functional requirements of the tissue. These results can further understanding of both TMJ biology and pathology.

Figure 1

Anatomy and regions of the TMJ disc and its attachments. (A) Sagittal view of the TMJ showing the anterior and posterior discal attachments which both bifurcate into superior and anterior attachments. (B) Coronal view of the TMJ detailing the medial and lateral attachments which both blend into the joint capsule near its attachment to the condyle. (C) Depiction of the 5 disc regions and 6 discal attachments analyzed in this study, which span the joint in the anteroposterior and mediolateral directions.

Figure 2

Heat maps of biochemical content throughout the TMJ disc and its attachments. Mean content normalized to dry weight for each region is presented as color intensity in the scale to the right of each picture. The top and bottom of the scale represent the highest and lowest mean value for each parameter. (A) Water content was highest in anterior and medial attachments with few large variations. (B) Collagen content was highest in the disc compared to the attachments, particularly in the bands of the disc. (C) Overall, the disc contained more sulfated GAG than the attachments, although the medial attachment and the superior portion of the anterior attachment did contain a significant amount of GAG. (D) DNA per dry weight was generally higher in the attachments than the disc, except in the superior portion of the posterior band.

Figure 3

Whole joint histology of the TMJ. Sections were cut at 5 μm and stained with hematoxylin and eosin. (A) Anteriorly and posteriorly the disc (D) blends into the attachments which both bifurcate into superior and anterior boney connections. The disc has a denser matrix than the attachments. (B) In the medial portion of the TMJ, the disc blends into the medial attachment high in the joint and the attachment to the condyle is at the top of the condylar head. (C) On the medial side of the joint, the disc wraps around the side of the condylar head and the lateral discal attachment attaches to the condyle near its base.

Figure 4

Regional histological staining of the TMJ disc and its attachments. In general, all histological staining verified quantitative results. (A) Hematoxylin and eosin illustrate that cellular density is higher in the attachments, while the disc contains a denser ECM than all of the attachments expect PAS and PAI. (B) Alcian blue staining clearly shows the higher sulfated GAG content of the TMJ disc in comparison to the attachments. IZM and IZL have the most GAG overall, while MA was the attachment with the most staining. (C) Verhoeff’s Van Gieson staining clearly shows collagen (red-brown) and elastic (black) fibers throughout the TMJ. PAS and PAI appeared to have similar content to the disc, but the other attachments displayed increased elastin staining.