Abstract
Collagen is the building component of temporomandibular joint (TMJ) discs and is often affected by inflammation in temporomandibular disorders. The macromechanical properties of collagen are deteriorated by chronic inflammation. However, the mechanism by which inflammation influences disc function remains unknown. The relationship between the ultrastructure and nanomechanical properties of collagen in inflamed discs should be clarified. Seven-week-old female Sprague–Dawley rats were randomly divided into two groups. Chronic TMJ inflammation was induced by intra-articular injection of complete Freund’s adjuvant, and samples were harvested after 5 weeks. Picrosirius staining revealed multiple colours under polarized light, which represented alternative collagen bundles in inflamed discs. Using atomic force microscopy scanning, the magnitude of Young’s modulus was reduced significantly accompanied with disordered collagen fibril arrangement with porous architecture of inflamed discs. Transmission electron microscopy scanning revealed a non-uniform distribution of collagen fibres, and oversized collagen fibrils were observed in inflamed discs. Fourier transform infrared microspectroscopy revealed a decrease in 1 338 cm−1/amide II area ratio of collagen in different regions. The peak positions of amide I and amide II bands were altered in inflamed discs, indicating collagen unfolding. Our results suggest that sustained inflammation deteriorates collagen structures, resulting in the deterioration of the ultrastructure and nanomechanical properties of rat TMJ discs.
Highlights
Temporomandibular disorders (TMDs) are a large family of diseases affecting the structure and function of the stomatognathic system.[1]
We found that the thickness, matrix content, biomechanical properties and surface structure of rat temporomandibular joint (TMJ) discs presented remarkable changes after Complete Freund’s adjuvant (CFA)-induced chronic TMJ inflammation, and these changes result in the exposure and degradation of sub-superficial collagen fibrils.[7,8]
These results suggested that chronic inflammation in the TMJ could lead to the deterioration of mechanical properties and alteration of the disc surface ultrastructure, which might contribute to TMJ disc displacement
Summary
Temporomandibular disorders (TMDs) are a large family of diseases affecting the structure and function of the stomatognathic system.[1]. Disc displacement is one of the most common subtypes of TMD; its pathologic mechanism is unclear. TMJs exhibit inflammation and disc degeneration without disc displacement.[5,6] Early studies on cadavers revealed that the deformation of the TMJ disc is associated with synovial inflammation without displacement; previous animal studies have reported that induced chronic inflammation of TMJ results in disc degeneration, including thickening and deformation.[7] In addition, chronic inflammation of the TMJ could lead to the deterioration of macroscopic mechanical properties of discs, including a decrease in the tensile and compression modulus.[8] our group proposes an innovative theory: “inflammation may be the key factor leading to TMJ disc displacement”
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