Abstract
The temporomandibular joint disc is a fibrocartilaginous structure, composed of collagen fibers, elastin fibers, and proteoglycans. Despite the crucial role of elastin fibers in load‐bearing properties of connective tissues, its contribution in temporomandibular joint disc biomechanics has been disregarded. This study attempts to characterize the structural–functional contribution of elastin in the temporomandibular joint disc. Using elastase, we selectively perturbed the elastin fiber network in porcine temporomandibular joint discs and investigated the structural, compositional, and mechanical regional changes through: (a) analysis of collagen and elastin fibers by immunolabeling and transmission electron microscopy; (b) quantitative analysis of collagen tortuosity, cell shape, and disc volume; (c) biochemical quantification of collagen, glycosaminoglycan and elastin content; and (d) cyclic compression test. Following elastase treatment, microscopic examination revealed fragmentation of elastin fibers across the temporomandibular joint disc, with a more pronounced effect in the intermediate regions. Also, biochemical analyses of the intermediate regions showed significant depletion of elastin (50%), and substantial decrease in collagen (20%) and glycosaminoglycan (49%) content, likely due to non‐specific activity of elastase. Degradation of elastin fibers affected the homeostatic configuration of the disc, reflected in its significant volume enlargement accompanied by remarkable reduction of collagen tortuosity and cell elongation. Mechanically, elastase treatment nearly doubled the maximal energy dissipation across the intermediate regions while the instantaneous modulus was not significantly affected. We conclude that elastin fibers contribute to the restoration and maintenance of the disc resting shape and actively interact with collagen fibers to provide mechanical resilience to the temporomandibular joint disc.
Highlights
The temporomandibular joint (TMJ) disc is a fibrocartilaginous tissue that overlies the articulating surfaces of the mandibular condyle and temporal fossa
We investigated five different regions known to possess a different quantity and organization of extracellular matrix (ECM) constituents (Scapino, Obrez, & Greising, 2006): posterior band (PB), anterior band (AB), intermediate zone central (IZC), intermediate zone medial (IZM), and intermediate zone lateral (IZL)
Our study indicates a structural–functional role of elastin fibers in the disc
Summary
The temporomandibular joint (TMJ) disc is a fibrocartilaginous tissue that overlies the articulating surfaces of the mandibular condyle and temporal fossa. The regiondependent distribution and interaction of these elements yield to a heterogeneous and anisotropic mechanical behavior of the disc under various loading conditions during jaw movement (Tanaka et al, 2003). The structural–functional characteristics of the disc can be compromised under pathological conditions (Farrar & McCarty, 1979; Schiffman et al, 2014). The etiology of disc pathology remains unknown, it has been suggested that the internal derangement may alter the ECM composition, subjecting it to abnormal loading conditions, which could lead to its degeneration (Tanaka, Detamore, & Mercuri, 2008). Structural–functional characterization of the individual structural elements of the TMJ disc can help to achieve a better understanding of the pathophysiology of the disc derangement, to establish design criteria for construction of a tissueengineered replica, and to develop more accurate computational prediction models
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