Comparison of different measurements of development of plaque and gingivitis in man.

The purpose of the present study was to compare efficiency of measurements commonly used to study the development of plaque and gingivitis in short-term clinical trials. Data from a recent experiment on the effect of mutanase on accumulation of plaque and development of gingivitis were used. Efficiency was compared using 1) level of significance and 2) minimum number of individuals necessary to obtain a statistically significant result at a given level of significance and with a given power of the test. Of all the measurements used, the gingival exudate measurement was the most efficient. Among the nonparametric indices, Plaque Index was the most efficient, especially on proximal surfaces in the mandible. Reduction of the scales for the nonparametric indices from a four-point scale to a two-point (dichotomous) scale slightly reduced experimental efficiency.