Growth of the mandible and biological characteristics of the mandibular condylar cartilage

Mandibular condylar cartilage is the center of greatest growth in the craniofacial complex, and is associated with maxillofacial skeleton morphogenesis and temporomandibular joint function. The condylar process grows in a wide range of directions from anterosuperior to posterior, resulting in highly diverse mandibular growth and morphology. Condylar growth direction is closely related to mandibular displacement direction and vertical jaw deviations (i.e., high or low angle). Condylar cartilage, which is ontogenetically designated secondary cartilage, differs from other primary cartilage (e.g., articular cartilage and growth plate of a long bone cranial base cartilage, nasal septal cartilage) in the following ways. (1) Condylar cartilage is a heterogeneous tissue containing fibroblasts, osteochondral progenitor cells, and chondrocytes. (2) Type I collagen, which is derived from progenitor cells, and cartilage-characteristic type II collagen are colocalized in the cartilaginous cell layer. Colocalization of both collagen types may be an adaptation to the complex biomechanical environments of condylar cartilage. (3) Peripheral condylar cartilage contains chondroid bone, a specialized calcified tissue with morphological properties intermediate between those of bone and cartilage. This hybrid tissue may play an important role in regulating different rates of bone formation in intramembranous and endochondral ossification, allowing for highly diverse growth directions and condylar and maxillofacial morphology.