Current techniques to alter gene expression in mice allow direct analysis of the net role of a host factor in caries development. Towards this goal we first established protocols to induce and score caries in NFS/N mice and determined caries susceptibility in mice with targeted deletion of the gene encoding aquaporin-5 (Aqp5–/–), a water channel involved in the production of saliva. In the NFS/N strain of mice total sulcal caries and severity scores were consistent between experiments, whereas smooth surface caries scores were lower, more variable but distributed fairly evenly among the buccal, lingual and sulcal surfaces. In Black Swiss/129SvJ mice (genetic background of Aqp5–/– mice) caries scores were 50–75% lower compared to NFS/N mice, suggesting strain variation in caries susceptibility under our experimental conditions. In Aqp5–/– mice, in which the volume of total salivary secretion is reduced by 60–65%, there was a significant increase in caries, primarily on the buccal and sulcal surfaces. Results indicate that caries susceptibility increases with a reduced salivary flow that is associated with decreased water content of saliva.

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