This will be a single-centre, randomized, blinded, placebo-controlled, 6-treatment, 4-period crossover, incomplete block design, in situ caries study in healthy adults who wear a removable bilateral mandibular partial denture. The denture will be modified to accommodate 4 gauze-covered specimens of human dental enamel (4x3mm) that have been previously demineralized in vitro to form either S or low-R lesions (2 specimens of each lesion type will be used with each participant). After 14 days of twice daily product use off-site, the 2 S lesion specimens will be removed at the study site, with the remaining 2 low-R lesion specimens removed at the study site after a further 14 days of product use. To determine the remineralization ability of the treatments, all specimens will be analyzed by transverse microradiography (TMR) and enamel fluoride uptake (EFU), with the S lesions additionally analyzed by surface micro hardness (SMH) and the low-R lesions additionally analyzed by quantitative light fluorescence (QLF).