Periodontal ligament. Coloured scanning electron micrograph (SEM) of periodontal ligament from a tooth extraction The periodontal ligament (PDL) is the dense fibrous tissue which attaches the tooth to the alveolar bone. It is continuous coronally with the gingival connective tissue. The PDL matrix consists of collagen (collagen types of similar proportion to that of gingiva above) in an amorphous proteoglycan matrix. Magnification: x2, 000 when printed at 10cm wide.