A pathological deepening of the gingival sulcus (crevice) produced by the destruction of the supporting tissues and the apical migration of the epithelial attachment. The junctional epithelium is located apical to the cemento-enamel junction. The base of the pocket is limited by the epithelial attachment to the cementum of the root surface. It provides an ideal protected environment for the continued growth of subgingival bacteria which release toxins that can damage the surrounding tissue and cementum. The pocket may be supra-bony, with the base of the pocket above the crest of the alveolar bone, or infra-bony, with the base apical to the crest of the alveolar bone.