O-pH: Optical pH Monitor to Measure Dental Biofilm Acidity and Assist in Enamel Health Monitoring

Bacteria in the dental biofilm produce acid after consumption of carbohydrates which if left unmonitored leads to caries formation. Measuring the acid activity of oral-bacteria in dental plaque, the sticky biofilm on enamel, can provide dentist and patients with leading indicator of oral health. In this work, we present O-pH, a device that can measure dental biofilm acidity and provide quantitative feedback to assist in oral health monitoring. O-pH utilizes a ratiometric pH sensing method by capturing fluorescence of Sodium Fluorescein, an FDA approved chemical dye. The device was calibrated to a lab pH meter using buffered fluorescein solution with a correlation coefficient of 0.97. The calibration was further verified in vitro on additional buffered solution, artificial, and extracted teeth. An in vivo study on 30 pediatric subjects was performed to measure pH before (rest pH) and after (drop pH) a sugar rinse, and the resultant difference in pH (diff pH) was calculated. The study enrolled subjects with low (Post- Cleaning) and heavy (Pre-Cleaning) biofilm load, having both unhealthy/healthy surfaces. Further, we modified point-based O- pH to an image-based device using a multimode-scanning fiber endoscope (mm-SFE) and tested in vivo on one subject. We found significant difference between Post- Cleaning and Pre-Cleaning group using drop pH and diff pH. Additionally, in Pre-Cleaning group, the rest and drop pH is lower at the caries surfaces compared to healthy surfaces. Similar trend was not noticed in the Post-Cleaning group. mm-SFE pH scope recorded image-based pH heatmap of a subject with an average diff pH of 1.5. This work builds an optical pH prototype and presents a pioneering study for non-invasively measuring pH of dental biofilm clinically.