Gottlieb was "the major periodontal investigator of the early 20th century. He extended the histopathologic studies of Znamensky.... His major contributions were in the nature of the epithelial attachment to the tooth and its apical migration as a manifestation of inflammatory periodontal disease, the biology of cementum, and its role in periodontal disease, trauma from occlusion, and active and passive tooth eruption" (Shklar and Chernin, Sourcebook of dental medicine (2002) 678.)