IL6 and periapical periodontitis: In addition, Gomez et al. in 2009 found hypomethylation of IL-6 gene in people with periodontal disease [168] and Küchler et al., recently, have deeply reviewed the literature to investigate how apical periodontitis pathogenesis ranges from microbial to genetic factors [137]: the most suggestive results emphasized the interindividual variation in apical periodontitis pathogenesis and severity of host response (phenotype).