Research developments in the physiopathology of arthrogenous TMD

International multi-site research based on the use of a common set of tools applicable to both research and clinical settings advanced the scientific knowledge of temporomandibular disorders and related pain conditions. The core tool is the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD), and the methods include population studies, clinical epidemiology and clinical trials, and experimental human studies. Objective of this paper is to discuss with personal contributions the recent fields of research, in particular imaging, histological and functional changes, psycho-neuro-endocrinology aspects, implicated in the physiopathology of the joint intracapsular disorders. Several studies have compared clinical TMD diagnoses and MRI findings of the TMJ. Magnetic resonance (MR) imaging has been widely used to image abnormalities of the temporomandibular joint (TMJ). Magnetic resonance imaging can depict displacement, degeneration, reduction, and shape of the disc. Moreover, MR imaging can show joint effusion, osteoarthritis, bone marrow abnormalities of the condyle, and changes in the retrodiscal tissue, among others. Precontrast T1-weighted, T2-weighted, and proton density–weighted imaging have usually been performed to depict those abnormalities. Advances have been made in diagnosis resulting from the development of new devices known as a limited cone beam dental compact-CT (3DX). Evaluation of a bony abnormality of the temporomandibular joint (TMJ) using the limited cone-beam CT (3DX) proved to be of considerable value. A three-dimensional image of the right TMJ showed erosion and flattening of the condyle. Histological and functional changes in rabbit retrodiscal tissue associated with experimentally induced anterior disk displacement have been investigated. In particular through microscopic analysis, the different types of connective tissue (loose, intermediate, dense and hyalinized); density of fibroblast (hypocellular, moderate, hypercellular); the presence of inflammatory cell infiltrate (insignificant or significant); chondrocytes; arterial lumen (no changes, narrowed, obliterated); distribution of vascular tissue (sparse, moderate, dense); distribution of elastic fibers (sparse, moderate, dense) have been studied. Considering the multifactorial etiology of TMD and the hypothesis that some joint tissues (e.g., bone, cartilage, collagen, proteins) could be a target for sexual hormones, the sexual hormone serum levels and temporomandibular disorders will be discussed. Then the role of the psychoneuroendocrine aspects in chronic pain will be focused, in particular the relationship between TMD and fibromyalgia.