Gingival tissues showed no difference in the levels of interleukin‐18 when comparing chronic periodontitis (n = 18), aggressive periodontitis (n = 12) and healthy (n = 9) individuals.134 Saliva samples from nonsmoking individuals with chronic periodontitis showed significantly higher levels of interleukin‐18 (275.05 ± 289.46 pg/mL; mean ± SD) when compared with healthy controls (143.71 ± 103.68 pg/mL; mean ± SD).135 Candidate gene studies evaluating polymorphisms have not identified single nucleotide polymorphisms in the IL18 region correlated with periodontal disease.136. This evidence concerns the gene IL18 and chronic periodontitis.