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Measuring the activity of oral-bacteria in plaque, the sticky biofilm on enamel, can provide the presently lacking oral feedback to patients. We have developed O-pH, optical pH monitor that measures pH in the range of 4-7.5 and tested in vivo on 25 pediatric subjects (10-18 years) with high caries risk, 18 of these subjects had a dental cleaning within last two months and 7 didn’t have a cleaning in over 2 months. The average pH after a sugar rinse from regions of biofilm associated with caries was 5.8 and 0.5 units lower than the biofilm of sound enamel.

Tooth decay is one of the most common chronic infectious diseases worldwide. Bacteria from the oral biofilm create a local acidic environment that demineralizes the enamel in the caries disease process. By optically imaging plaque pH in pits and fissures and contacting surfaces of teeth, then medicinal therapies can be accurately applied to prevent or monitor the reversal of caries. To achieve this goal, the fluorescence emission from an aqueous solution of sodium fluorescein was measured using a multimodal scanning fiber endoscope (mmSFE). The 1.6-millimeter diameter mmSFE scans 424nm laser light and collects wide-field reflectance for navigational purposes in grayscale at 30 Hz. Two fluorescence channels centered at 520 and 549 nm are acquired and ratiometric analysis produces a pseudo-color overlay of pH. In vitro measurements calibrate the pH heat maps in the range 4.7 to 7.2 pH (0.2 standard deviation). In vivo measurements of a single case study provides informative images of interproximal biofilm before and after a sugar rinse. Post processing a time series of images provides a method that calculates the average pH changes of oral biofilm, replicating the Stephan Curve. These spatio-temporal records of oral biofilm pH can provide a new method of assessing the risk of tooth decay, guide the application of preventative therapies, and provide a quantitative monitor of overall oral health. The non-contact in vivo optical imaging of pH may be extended to measurements of wound healing, tumor environment, and other food processing surfaces since it relies on low power laser light and a US FDA approved dye.

We have developed a new tool to measure the acid production by plaque oral bacteria. Many species of oral bacteria metabolize sugars in food and produce organic acids that demineralize the dental enamel leading to the formation of cavities. Measuring the acidity level before and after a sugar rinse can indicate the susceptibility of an individual to tooth decay and location of active caries. In a case study on two subjects, a non-contact optics-based pH device was able to track pH before and after a sugar rinse. The fiber optic probe measures acidity level in difficult to access dental locations such as occlusal pits and fissures based on changes in the spectral fluorescence profile of fluorescein (FL) dye. Fiber coupled 420 nm LED excites 200uM aqueous FL solution in the mouth. The fluorescence spectrum in 450-650 nm range is obtained using an adjacent fiber optic cable coupled to a spectrometer. Chemometric analysis of endmember dianion and anion species using least-square fitting is performed to determine the pH of the FL absorbed into the extracellular region of the oral biofilm. Other unwanted noise, like background light and auto-fluorescence in the range of 450-650 nm is removed before calculating biofilm pH. Using this device in a darkened room on two subjects, we were able to measure resting pH (before a sugar rinse) and track time dependent change in pH (after a sugar rinse) in the range of pH 4-7 paving the way for first clinical optical pH measurement in the mouth.