Correlation and examiner agreement between a new method of plaque scoring and a popular established plaque index, modelled in vitro

Background, aims: Scoring of supragingival plaque is common to epidemiological studies, oral hygiene assessments and clinical trials of oral hygiene products. These clinical practices utilize indices such as the Turesky et al. (1970, Journal of Periodontology 41, pp. 41-43) modification [Turesky Plaque Index (TPI)] of the Quigley & Hein (1962, Journal of the American Dental Association 65, pp. 26-29) plaque index for evaluating plaque extension. Whilst this index is in common use by clinicians, there is potential for ambiguity in the interpretation of scores by different examiners. The aims of this study were to compare examiner agreement between a new method of plaque scoring (NMPS) and TPI, and to determine if there was a correlation between the two indices. Methods: Simulated plaque was scored from eight study casts, each consisting of 14 teeth. The two indices were both scored twice from the study casts by eight examiners experienced in plaque scoring. The first readings obtained were analysed for a correlation between the indices and between-examiner variability. Within-examiner variability was assessed using both first and second readings of each index. Results: A positive correlation was found between the two indices (r = 0.717). The NMPS was found to have better inter- and intra-examiner agreement than TPI. Conclusion: The NMPS was found to have less variability within and between examiners than TPI: evaluation of NMPS in a clinical setting would now appear warranted.