The Adaptive Remodeling of Condylar Cartilage— A Transition from Chondrogenesis to Osteogenesis

Abstract

Mandibular condylar cartilage is categorized as articular cartilage but markedly distinguishes itself in many biological aspects, such as its embryonic origin, ontogenetic development, post-natal growth mode, and histological structures. The most marked uniqueness of condylar cartilage lies in its capability of adaptive remodeling in response to external stimuli during or after natural growth. The adaptation of condylar cartilage to mandibular forward positioning constitutes the fundamental rationale for orthodontic functional therapy, which partially contributes to the correction of jaw discrepancies by achieving mandibular growth modification. The adaptive remodeling of condylar cartilage proceeds with the biomolecular pathway initiating from chondrogenesis and finalizing with osteogenesis. During condylar adaptation, chondrogenesis is activated when the external stimuli, e.g., condylar repositioning, generate the differentiation of mesenchymal cells in the articular layer of cartilage into chondrocytes, which proliferate and then progressively mature into hypertrophic cells. The expression of regulatory growth factors, which govern and control phenotypic conversions of chondrocytes during chondrogenesis, increases during adaptive remodeling to enhance the transition from chondrogenesis into osteogenesis, a process in which hypertrophic chondrocytes and matrices degrade and are replaced by bone. The transition is also sustained by increased neovascularization, which brings in osteoblasts that finally result in new bone formation beneath the degraded cartilage.

Biglycan and Fibromodulin Have Essential Roles in Regulating Chondrogenesis and Extracellular Matrix Turnover in Temporomandibular Joint Osteoarthritis

“…To understand basic cellular mechanisms underlying TMJ OA, we harvested primary MCCs. Because the mandibular condylar cartilage is distinct from knee hyaline articular cartilage, [3][4][5][6][7][8] we compared MCCs with HACs isolated from the knee joint. Our mRNA and protein profiling revealed that the two cell populations share overlaping gene/protein expression patterns.…”

“…However, the mandibular condylar cartilage is distinct from other articular cartilages and possesses unique morphological, 3 functional, 4 biomechanical, [5][6][7] and biological 8 -11 properties. For example, the articular zone is the most superficial cellular layer that uniquely distinguishes the TMJ as a fibrocartilage.…”

Spontaneously developed osteoarthritis in the temporomandibular joint in STR/ort mice

“…The articular cartilage of the temporomandibular joint (TMJ) is composed of fibrocartilage, and undergoes endochondral ossification during the active growth period (1). TMJ osteoarthritis (OA) is typically a slowly progressive, asymmetric disease resulting in the destruction of articular tissues, and presents as functional pain, crepitus or multiple joint noises.…”

Temporomandibular joint formation and condyle growth require Indian hedgehog signaling

“…The temporomandibular joint (TMJ) is a complex skeletal structure that mediates, and is essential for, normal functioning of the jaw (Shen and Darendeliler, 2005;Wadhwa et al, 2005). Much is known about TMJ organization and biomechanical properties, and much is known about common pathologies that can affect its components in individuals of different ages, including defective growth patterns or osteoarthritis (Israel et al, 1998;Zarb and Carlsson, 1999;Broussard, 2005).…”