“…From a total of 12 studies, 10 were observational studies (6 cross-sectional [ 30 , 31 , 32 , 33 , 34 , 35 ] and four case-control [ 36 , 37 , 38 , 39 ]), 1 was an animal study [ 40 ], and 1 was an in vitro study [ 41 ]. Different fluids/tissues were used for the HDPs’ analysis, including GCF [ 30 , 31 , 34 , 36 , 37 , 38 ], saliva [ 33 , 35 , 39 ], GT [ 32 ], and human oral epithelial cells [ 41 ]. However, one study [ 40 ] used both blood and GT for the analysis.…”