TNF and periodontitis: Several cytokines are related to the regulation of RANKL expression, among which IL-1β, IL-6, and TNF-α are recognized as key factors contributing to its upregulation by studies on both root resorption and periodontitis.32,40–42 Given that the initiation of osteoclastogenesis in root resorption and in periodontitis share a similar mechanism, it is reasonable to infer that resorptive tissues might derive from periodontal tissues in ECR.33,34