A study was conducted on the effect of an oral antiplaque rinse on plaque buildup on teeth.Eighteenpeople whose teeth were thoroughly cleaned and polished were randomly assigned to two groups ofninesubjects each. Both groups were assigned to use oral rinses (no brushing) for a 2-week period. Group 1, the control group, received a rinse that, unknown to the subjects, contained no antiplaque agent. Group 2 used a rinse that contained an antiplaque agent. A plaque indexx, a measure of plaque buildup, was recorded at 14 days with means and standard deviations for the two groups shown in the table.

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