An optical device in development at the University of Washington (UW) could help prevent tooth decay by identifying at-risk teeth before cavities have had a chance to start to develop. The prototype, called O-pH, uses a low-power light system and an FDA-approved fluorescent dye solution, sodium fluorescein, to noninvasively measure oral biofilm acidity on tooth enamel and provide quantitative feedback. “Plaque has a lot of bacteria that produce acid when they interact with the sugar in our food,” researcher Manuja Sharma said. “This acid is what causes the corrosion of the tooth surface and eventually cavities. So, if we can capture information about the acidic activity, we can get an idea of how bacteria are growing in the dental biofilm, or plaque.” A new UW dental tool prototype uses a low-power light system to monitor reactions with a fluorescent dye solution to identify where tooth enamel is most at risk from the acidity of plaque. Courtesy of the University of Washington and IEEE Xplore/Creative Commons. O-pH is an optical pH-sensor that uses light in the 420-nm range to excite the fluorescein dye. It collects fluorescent light using fiber-coupled, filtered photodiodes. The system emits light from an LED that is shined on the teeth while the fluorescent dye is being applied. A probe transmits the light and collects it, while hovering over the surface of a tooth. The collected light travels back to a central measurement system, and using the information in the light, the system provides a reading of the pH on each tooth. O-pH uses a ratiometric pH sensing method to produce a numerical reading of the pH level of the dental plaque. It measures pH in the range of 4 to 7.5, the typical pH range of the dental biofilm. The UW team calibrated the system to a lab pH meter using a buffer fluorescein solution with a correlation coefficient of 0.97. The researchers verified the calibration in vitro using a different buffer solution and artificial and extracted teeth. The team tested the system on 30 pediatric subjects by measuring pH on the surface of the teeth before and after sugar rinses, in two different groups of subjects (pre-cleaning and post-cleaning). Students from the UW School of Dentistry performed the measurements under the supervision of a faculty member. O-pH revealed significant differences in biofilm pH between the pre- and post-cleaning groups. The clinical study demonstrated O-pH’s capability to differentiate between low and high biofilm load using pH measurements. The UW optical O-pH prototype can noninvasively measure the acidity of oral biofilm. Courtesy of the University of Washington and IEEE Xplore/Creative Commons. The researchers said that one drawback of the study was the inability to consistently measure the same location on each tooth during each phase of testing. To address this constraint, they will enhance O-pH to include the capability to produce images that will instantly show the dentist the precise location(s) of high acidity, where a new cavity could occur. The team converted O-pH from a point-based to an image-based device using a multimode-scanning fiber endoscope and tested this prototype on one subject. Sharma said that not all bacteria in plaque leads to cavities. Measuring the acidity of the biofilm environment can tell dentists what they need to know about potential problem areas, without needing to test for specific types of harmful bacteria. Professor Eric Seibel envisions performing the O-pH acidity test before a patient’s teeth are cleaned. “A dentist would rinse them with the tasteless fluorescent dye solution and then get their teeth optically scanned to look for high acid production areas where the enamel is getting demineralized,” he said. “We do need more results to show how effective it is for diagnosis, but it can definitely help us understand some of your oral health quantitatively,” Sharma said. “It can also help educate patients about the effects of sugar on the chemistry of plaque.” The research was published in IEEE Transactions on Biomedical Engineering (www.ieeexplore.ieee.org/abstract/document/9720240).