BACKGROUND: The purpose of the present study was to evaluate the effectiveness of an oral hygiene regimen in subjects presenting with substantially different severity of plaque-associated gingivitis. METHODS: The study population was selected from among a large pool of subjects undergoing an experimental gingivitis trial. At completion of the 21-day plaque accumulation period, 2 sub-groups of subjects were identified on the basis of uppermost and lowest quartile for Gingival Index (GI), respectively classified as highly-inflamed (Hinf; n=17; GI: 1.07+/-0.10) and slightly-inflamed (Sinf; n=22; GI: 0.28+/-0.09) groups. An oral hygiene regimen, based on use of amine fluoride/stannous fluoride-containing toothpaste and mouthrinse, was then prescribed for 21 days. RESULTS: Plaque Index (PI), GI, gingival crevicular fluid (GCF) and Angulated Bleeding Index (AngBI) significantly decreased after treatment in both HInf and SInf groups (p<0.001). However, PI (0.77+/-0.41 vs 0.43+/-0.33, p<0.01), GI (0.23+/-0.30 vs 0.08+/-0.11, p<0.05), GCF (15.23 +/-7.11 vs 7.66+/-2.93, p<0.0000) remained significantly greater in the Hinf group compared to the Sinf group. CONCLUSIONS: These results suggest that 1) an oral hygiene regimen based on amine/stannous fluoride-containing toothpaste and mouthrinse is effective in reducing plaque-associated gingivitis, regardless of pre-existing severity of gingival inflammation; 2) the level of improvement in gingival status, however, is dependent on the pre-existing severity of the inflammatory condition.