The purpose of this study was to compare the ability of experienced and newly trained investigators to use the published Global Plaque Index and a newly developed Proximal/Marginal Index (PMI) that focuses on disclosed plaque at clearly defined proximal and marginal surfaces. Four independent clinical studies were performed, two with each index, on 11 subjects per study. In each study, examinations were conducted before and after brushing, to determine inter- and intra-examiner comparisons over a range of plaque levels. Inter-examiner reliability estimates for the PMI were at a level below Global Plaque index means. Intra-examiner agreement values were similar for both indices. Both scoring systems are considered sufficiently validated to detect product differences in clinical studies.