Home use oral hygiene product trials; timing of the last brushing before scoring; an assessment of variation

Abstract

Home use studies to evaluate oral hygiene products often standardise the time lag between plaque scoring and the previous toothbrushing. Most protocols have favoured an evening before brushing regimen, but the rationale and even the validity of this approach has not been evaluated. In this study, a group of 30 adult subjects participated in a 4-period randomised single-blind crossover evaluation of within-subjects and between-subjects variation in plaque levels after two different brushing times. Thus, on 2 occasions, plaque was scored after an "evening before" brushing and on the other 2 occasions plaque was scored after a "morning before" brushing. As expected, mean plaque levels were lower after morning brushing, but only by 11%. There was little difference for lingual plaque (4%) but a greater difference for buccal plaque (18%). Comparisons for within-subjects variation, which ideally should be low, favoured morning brushing but differences were small and not significant. Comparisons for between subjects variation, which ideally should be high to permit discrimination between high and low plaque formers, also favoured morning brushing but were only significant for lingual plaque. Intraclass correlation coefficients of reliability revealed that overall repeatability was high for both morning and evening regimens; marginally favouring morning brushing. Analyses using all four scores per subject disregarding timing of brushing increased within subjects variation and decreased repeatability, particularly for buccal plaque. In conclusion, the data support the concept of standardising the time between plaque scoring and the previous tooth-brushing. There were no clear statistically significant grounds for preferring one brushing regimen to the other, however the data favoured the morning brushing.