This study measured the ability of two powered toothbrushes (Crest SpinBrush and Crest SpinBrush Pro) to reduce gingivitis relative to baseline levels over a one-month period. This study made use of a randomized, controlled, examiner-blind, parallel design. Subjects were examined for Löe-Silness GI scores at baseline and at one month. The primary efficacy variable was GI score change at one month from the baseline GI score. Within-group comparisons to baseline were performed using paired t-tests. Secondarily, treatment group differences were examined using an analysis of covariance model, with baseline as the covariate. Separate analyses were performed for Löe-Silness GI scores and for the number of gingival bleeding sites. All comparisons were two-sided and used the 0.05 level of significance. A total of 87 subjects completed the study. Of these, there were 57 females and 30 males, ranging in age from 18 to 70 years with a mean age of 33.1 years. Baseline GI scores were 0.487 and 0.449 for the Crest SpinBrush and Crest SpinBrush Pro, respectively, and were not statistically significantly different. Both brushes demonstrated highly statistically significant reductions in GI vs. baseline (all p < 0.001), and delivered an approximately 60% reduction in GI. Baseline bleeding site scores were 37.6 and 34.4 for the Crest SpinBrush and Crest SpinBrush Pro, respectively, and were not statistically significantly different. Both brushes demonstrated highly statistically significant reductions in bleeding vs. baseline (all p < 0.001), and delivered an approximately 60% reduction in bleeding sites. None of the ANCOVA comparisons between brush groups were statistically significant (all p > or = 0.354). Both the Crest SpinBrush Pro and Crest SpinBrush powered toothbrushes were highly effective at reducing gingivitis when used per manufacturer's instructions.