A curved periodontal probe has been developed to measure the length of newly formed plaque along the gingival margin of a tooth and the length of the entire gingival margin of the tooth. Plaque is expressed as a percent of the tooth's gingival margin, and is defined as the Modified Gingival Margin Plaque Index (MGMPI). The purpose of this research was to evaluate the efficacy of three marketed antiplaque products using the MGMPI.A series of three clinical studies, involving five separate trials, was conducted. Three marketed antiplaque products were tested; PerioGuard mouthrinse, Colgate Total dentifrice and Colgate Total Plus Whitening dentifrice. Using a cross-over design, the efficacy of these test products on plaque formation was compared to Colgate Regular dentifrice. Plaque was evaluated before, and 24 hours after a single use of the above products using the MGMPI.In all studies conducted, plaque formation, as measured by the MGMPI, significantly increased over a 24-hour period. There were no significant differences in 24-hour scores between the test and control products evaluated. When the change from baseline to 24 hours was analyzed, the test products resulted in a consistently and significantly (p < 0.05) lower MGMPI mean score than the Colgate Regular dentifrice control.A new method has been developed that can measure plaque formation along the gingival margin.