JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 1. Naturally stained incisors. A cross-polarized photomicrograph of the stain built up on a volunteer's incisors after using a non-abrasive tooth- paste for 1 month. Facing page 218

THE CLEANING POWER OF DENTIFRICES 219 400 200 Ii :/ .? 200 Total per cent stain scorer Figure 2. Scorers' concordance. 4OO tracings drawn from projected images of the transparencies. After training examiners by repeatedly comparing their estimates with planimeter measure- ments of traces, good agreement was found between examiners' scores as shown in Fig. 2. The slope of line of best fit was 1.2 (complete agreement would be indicated by a slope of 1.0). Measurement of stain removal on a single volunteer from a group A hygienist removed fresh plaque by brushing for 15 s with a non- abrasive toothpaste applied with a Touch-Tronic electric toothbrush (Teledyne, Aqua-Tec, U.S.A.). After independent assessment of stain area on the labial surfaces of the eight incisors by two examiners, the hygienist brushed the incisors for 10 s, using a test toothpaste applied with the electric