Background: The pH strip method has been proposed for use in a clinical setting for the evaluation of dental plaque pH. The aim of this in-vivo study was to compare the reliability of the pH-indicator strip method to the microelectrode technique in plaque pH measurement.
Methods: 136 subjects (7-9 years) were enrolled and, for each subject, measurements of plaque pH were made at two interproximal sites; a total of 272 sites were analyzed. Plaque pH was assessed in triplicate using pH-indicator strips (pH range: 4.0-7.0) and an iridium microelectrode with a diameter of 0.1 mm. The caries status of 544 proximal surfaces between two primary molars, in proximity at the plaque pH sites, was assessed. All measurements were performed before and 2, 5, 10, 15, 20, and 30 minutes after a mouth rinse with water solution of sucrose (10%). One-way ANOVA was performed to analyze statistically significant differences between the two techniques. Instrument reliability was measured by assessing the intraclass correlation coefficient.
Results: Comparable, not statistically significant pH values (P values range from 0.98 to 1.00) were obtained by the two methods for AUC5.7, AUC6.2, maximum pH fall and minimum pH. High intraclass coefficients were recorded (Pearson's r=0.96, Yule's Q=0.99), implying an almost perfect association when the measurements were grouped as a carious lesion being present or not on the surface near the site of measurement.
Conclusions: The use of the pH strip method has high validity and may replace the traditional microtouch electrode technique for clinical use.