Dental caries (tooth decay) is a significant clinical and public health problem. The development of caries lesions involves a net mineral loss of dental tissue, which can lead to progressive loss of tooth structure and associated pain and disease. Detecting, assessing, diagnosis and treating such lesions are core activities in dentistry. Currently the main detection and diagnosis aids are visual inspection and the used of a probe, together with X-ray images. Determination of the activity status of a lesion (how likely it is to progress) is required to assess treatment needs. Currently methods are problematic and involve the clinicians' subjective assessment and / or monitoring of lesions progression over a number of visits.