Each subject included in the study will have their WSLs assessed and categorised clinically using the International Caries Detection and Assessment System, (ICDASii) (International Caries Detection and Assessment System Coordinating Committee, 2009a), by ICDASii calibrated examiners. Examiner reliability will be determined by scoring extracted teeth and teeth validated by histology. Reproducibility will be measured using Kappa scores. All lesions on the buccal surfaces of teeth will be included in the study. Intra-oral digital photographs will also be taken of each participant in a reproducible manner, and the photographs analysed by two different blinded ICDASii calibrated examiners, who will be recruited to the study simply to score the clinical photographs. A colour standard (CasMaTCH; Bear medic, Tokyo) will be used to allow colour matching of the images.