An electronic search of PubMed, Web of Science, and Scopus was conducted using appropriate keywords, as follows: (leptin OR leptin receptor OR LEPR OR OBR OR OB-R OR Ob-Rb) AND (dental pulp OR periapical tissues OR apical granuloma OR apical abscess OR periapical abscess OR periapical granuloma OR apical cyst OR periapical cyst OR periapical granuloma OR periradicular tissues OR pulpitis OR apical periodontitis). This evidence concerns the gene LEP and periapical periodontitis.