Interestingly, these two studies found levels for some of these markers were altered by smoking; sRANKL and TNF concentrations were significantly greater (P = 0.011, P = 0.001; respectively), and OPG concentration was significantly lower (P = 0.001) in smokers with periodontitis; however, such trend was not seen for salivary OC [101, 102]. Here, TNF is linked to periodontitis.