part of periodontal ligament BTO:0001020 BrendaTissueOBO The fibrous connective tissue that surrounds the root of a tooth, separating it from and attaching it to the alveolar bone. It extends from the base of the gingival mucosa to the fundus of the bony socket, and its main function is to hold the tooth in its socket. alveolar periosteum alveolodental ligament alveolodental membrane desmodontium odontoperiosteum paradentium peridental membrane peridontal membrane peridontium periodontium