A sonic electric toothbrush (Sonicare) and an oscillating/rotating electric brush (Braun Oral-B) were compared for efficacy in removing supragingival plaque, reducing gingival inflammation, reducing probing pocket depth (Pd) and improving probing attachment levels (PAL) in a 6-month, single-blind clinical trial. Sixty-six adults with early-moderate periodontitis (5-7 mm Pd in at least two quadrants) entered the study, and 54 completed the entire study. The Sonicare and Braun groups were equally matched for plaque scores, and balanced for age, race and gender. Plaque was scored using the Turesky, Gilmore and Glickman Index. Gingival inflammation was determined by the Papillary Bleeding Score (PBS) of Loesche. Probing depths and attachment levels were determined using a manual North Carolina probe. All measurements were recorded at baseline, 2, 4 and 6 months. The mean overall plaque scores improved in both the Sonicare and the Braun groups at each of the follow-up visits. Interproximal plaque scores also improved in both groups with time, and the mean differential Sonicare post-brushing score was significantly better than the Braun at the 6-month visit (t-test; p = 0.039). Gingival inflammation also decreased in both groups over the 6-month period, but the Sonicare group showed significantly superior PBS scores at 4 months (t-test; p = 0.002) and 6 months (p = 0.005). The percentage reduction in inflammation from baseline at 6 months was 31.9% for Sonicare and 18.1% for Braun. Probing depth scores followed a similar pattern, with the Sonicare showing a mean reduction of 0.84 mm (15.8%) from baseline at 6 months, and Braun showing a 0.39 mm (7.2%) reduction (p = 0.002). In the Sonicare group probing attachment levels improved by 8.6% (MANOVA; p = 0.01), but no PAL improvement was seen in the Braun group. Overall, this study demonstrates that long-term use of these two electric toothbrushes improves periodontal health in adult periodontitis patients, and that the Sonicare brush is superior to the Braun brush in reducing gingival inflammation and probing depth. Moreover, 6 months' use of Sonicare led to actual improvement in probing attachment levels of periodontal pockets.