(a) Visual assessment using dental tools - gold standard for early occlusal caries. Inset figure shows different kinds of probing instruments used by dentists (b) Bitewing X-ray with an interproximal lesion between teeth 3 and 4 - gold standard for early interproximal caries (c) Patient’s mouth after using a biofilm disclosing agent to see dental biofilm coverage (d) Biofilm micro-environment: pH level is lower moving from surface to enamel. Extracellular Polymeric Substance (EPS) composition and characteristic is shown in the inset figure. (e) Caries formation (f) O-pH in operation at a dental clinic with an inset figure showing a closer look of the device inside the mouth. The tip of the probe used to transmit and collect light is hovering over the occlusal surface of the subject.