A double blind, controlled, parallel group trial utilizing the experimental gingivitis model was performed on thirty young adults to evaluate the clinical effects of a 0.45% stannous fluoride dentifrice used as a slurry on dental biofilm formation and the development of gingivitis. Following a thorough examination and oral prophylaxis procedures, subjects were randomly assigned to apply one of the following dentifrices twice daily over a three-week period: A) dentifrice slurry without active ingredients; B) 0.45% stannous fluoride gel; and C) Colgate® Total dentifrice slurry (0.30% triclosan, 0.24% sodium fluoride, 2% copolymer). After three weeks, the stannous fluoride dentifrice significantly (p 0.05) reduced gingivitis compared with the Colgate® Total group by 39.7%. Gingival bleeding was also reduced relative to the Colgate® Total group. This difference was statistically significant (P 0.05). During the experimental period, the mean PlI scores increased almost linearly in all three groups without yielding any statistically significant differences. The results of this clinical trial demonstrated that, over a three-week period, the application of a 0.45% SnF2 gel significantly inhibited the onset of gingivitis compared to Triclosan/sodium fluoride/copolymer (Colgate® Total). However, neither stannous fluoride nor Triclosan/sodium fluoride/copolymer (Colgate® Total) possessed sufficient antimicrobial activity to suppress biofilm formation in the absence of regular oral hygiene practices. Keywords: prevention, gingivitis, stannous fluoride, dentifrice, plaque, discolorations