The periodontal ligament is a complex connective tissue that surrounds the tooth root and attaches the tooth to the alveolar bone. It is composed of collagen fibers, ground substance, blood vessels, nerves and cells. The principal collagen fibers resist various forces on the tooth and help transmit these forces to the bone. The periodontal ligament provides nutrition to surrounding structures, allows for remodeling and repair, and has proprioceptive functions through its nerve endings.