Cells were plated at 1 × 104 into 96-well plates (Corning) and allowed to attach for 24 h at 37°C. The following day, the ozonized olive oil and the CHX agents namely Corsodyl Dental Gel® or Plak Gel® were diluted 1:10 for 4 times in DMEM. The cell medium was removed from the well, and 100 mL of each diluted test agent was applied to the cell monolayers. As negative control, fresh medium was used. After 2 or 24 h of incubation at 37°C, the cell medium was pipetted off from each well and HGFs viability determined using the 3-(4, 5-dimethyl thiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay. 100 mL of MTT solution (Sigma-Aldrich) in RPMI-1640 without phenol red (Sigma-Aldrich) (5 mg/mL) was added to each well, and the monolayers were incubated for 4 h at 37°C. Then, the supernatant was removed, and the resulting formazan was dissolved by adding 100 μL dimethyl sulfoxide (Sigma-Aldrich) to each well. The optical density of formazan dye was read at 545 nm against 620 nm as background by ELISA reader (Bio-Rad, Hercules, CA, USA). The percentage of viable cells in each well was calculated relative to control cells set to 100%. Cytotoxicity responses were rated as severe (30%), moderate (30%–60%), mild (60%–90%), or noncytotoxic (>90%).[16 (link)]