A joint is the location at which two or more bones make contact. They are constructed to allow movement (except for skull bones) and provide mechanical support, and are classified structurally and functionally. Structural classification is determined by how the bones connect to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the two types of classifications. Structural classification names and divides joints according to the type of binding tissue that connects the bones to each other. There are three structural classifications of joints: fibrous joint - joined by dense irregular connective tissue that is rich in collagen fibers; cartilaginous joint - joined by cartilage; and synovial joint - not directly joined - the bones have a synovial cavity and are united by the dense irregular connective tissue that forms the articular capsule that is normally associated with accessory ligaments.
Fibrous joints are connected by dense connective tissue, consisting mainly of collagen. These joints are also called "fixed" or "immovable" joints because they do not move. These joints have no joint cavity and are connected via fibrous connective tissue. The skull bones are connected by fibrous joints called sutures. Syndesmoses of long bones and gomphoses of teeth are also types of fibrous joints. The movement of the root within a gomphosis has a threefold effect. It lessens some of the impact between the upper and lower teeth in biting; it pumps blood and lymph from the periodontal membrane into the dental veins and lymph channels; and it stimulates sensory nerve terminals in the membrane to send signals to the brain centers that control the muscles of mastication. A joint disorder is termed an arthropathy, and when involving inflammation of one or more joints the disorder is called an arthritis.