Plaque regrowth studies: discriminatory power of plaque index compared to plaque area.

A large number of plaque-scoring methods exist for the evaluation of plaque inhibition by oral hygiene agents, products or devices. The ability of such methods to discriminate between high and low plaque scores has not been compared. In this retrospective analysis, the F-ratios for differences between treatments for plaque index and area were compared from 15, 4-day plaque regrowth studies. F-ratios favoured plaque index as having greater a discriminatory power compared to plaque area in 2/3 of the studies considered. It is concluded that, when appropriate, 2 scoring methods for plaque should be used, but if a choice is necessary, plaque index is likely to provide the greater discriminatory power over plaque area.