Schematic diagram illustrating the activation of immune genes [human β-defensin (hBD)-2, hBD-3, Toll-like receptor (TLR)-2 and TLR-4], cytokines, and chemokines [tumour necrosis factor (TNF)-α, interleukin (IL)-1β, IL-8 and monocyte chemoattractant protein (CCL)-20] via the Sirtuin 1 (SIRT1) pathway triggered by exposure to mechanical stress (MS) in periodontal ligament (PDL) cells.