New portable system for dental plaque measurement using a digital single-lens reflex camera and image analysis: Study of reliability and validation

BACKGROUND: The quantification of the dental plaque (DP) by indices has limitations: They depend on the subjective operator's evaluation and are measured in an ordinal scale. The purpose of this study was to develop and evaluate a method to measure DP in a proportional scale. MATERIALS AND METHODS: A portable photographic positioning device (PPPD) was designed and added to a photographic digital single-lens reflex camera. Seventeen subjects participated in this study, after DP disclosure with the erythrosine, their incisors, and a calibration scale ware photographed by two operators in duplicate, re-positioning the PPPD among each acquisition. A third operator registered the Quigley-Hein modified by Turesky DP index (Q-H/TPI). After tooth brushing, the same operators repeated the photographs and the Q-H/TPI. The image analysis system (IAS) technique allowed the measurement in mm(2) of the vestibular total tooth area and the area with DP. RESULTS: The reliability was determined with the intra-class correlation coefficient that was 0.9936 (P < 0.05) for the intra-operator repeatability and 0.9931 (P < 0.05) for inter-operator reproducibility. The validity was assessed using the Spearman's correlation coefficient that indicated a strong positive correlation with the Q-H/TPI r(s) = 0.84 (P < 0.01). The sensitivity of the IAS was evaluated with two sample sizes, only the IAS was able to detect significant differences (P < 0.05) with the sample of smaller size (n = 8). CONCLUSIONS: Image analysis system showed to be a reliable and valid method to measure the quantity of DP in a proportional scale, allowing a more powerful statistical analysis, thus facilitating trials with a smaller sample size.