When we identify potential cavities in our patients mouths, we verify whether your cavity is deep enough to expose dentin. In some cases we find that cavities are shallow and don't require any immediate intervention, saving you having to get any unnecessary fillings. The system works by shining a harmless fluorescent light in your mouth that typically fluoresces green on normal surfaces, but red in areas of high acidity that signify exposed dentin inside your tooth. This is illustrated below, notice how the light only reacts with deeper cavities that have exposed dentin and require filling. Surface cavities not requiring fillings do not fluoresce red.