The efficacy and safety of a new sonic toothbrush were studied in this single-blind study. The sonic toothbrush combines acoustic vibrations and dynamic fluid activity surrounding the bristles with direct mechanical scrubbing of tooth surfaces. Fifty-one subjects were randomly assigned to either the sonic or the manual toothbrush. Plaque scores were assessed before and after a 2-minute brushing at baseline and 1, 2, and 4 weeks. Gingivitis and sulcular bleeding scores were also taken at each evaluation. To assess long-term safety, 29 subjects returned after 6 months of product use. Repeated measures analysis of variance of the total mean plaque score indicated a significant difference between the devices over time (P < 0.01), with the sonic toothbrush demonstrating a greater level of plaque removal on all tooth surfaces. On average, the plaque reduction from the baseline score for the sonic toothbrush was 3 times greater than the manual brush. However, when broken down by dental region, the sonic toothbrush demonstrated an improved level of plaque removal ranging from 1.5 to 11.9 times better than the manual brush, with the greatest improvement in the interproximal and lingual areas. Both the gingivitis and sulcular bleeding scores exhibited a similar, significant reduction (P < 0.005) over time for both devices with an approximate 17% decrease in the gingivitis index and a 33% decrease in sulcular bleeding sites. Safety assessment after 6 months of use indicated no soft tissue abnormalities which could be attributed to the products.(ABSTRACT TRUNCATED AT 250 WORDS)