Salivary Gland and Tooth Abnormalities Massively Increase Caries Susceptibility in A Mouse Model of Cleft Lip/Palate

Objectives: Individuals with cleft lip/palate (CLP) exhibit an increased incidence of dental abnormalities, including enamel defects and taurodontism. Changes in salivary function, such as prolonged clearance times, have also been described in cleft children. Anecdotally, an increase in caries incidence and severity has been seen in the CLP population, but it is not clear whether this is due to poor oral hygiene or to biological defects. IRF6 is the most prominent CLP gene and is expressed in all epithelia. To avoid the embryonic lethality associated with ablation of Irf6 in all epithelia, we developed a mouse model in which Irf6 was conditionally ablated only in the late embryonic oral epithelium (Irf6 Null-E). Previously, we found these Irf6 Null-E mice exhibited enamel mineralization and tooth morphology defects that were associated with delayed polarization of ameloblasts. We have now also noted grossly abnormal salivary gland morphology. The goal of this study was to determine whether Irf6 Null mice exhibit a higher caries outcome compared to background matched controls.
Methods: Irf6 Null-E and control mice were inoculated with S. mutans cariogenic bacteria using oral swabs, and fed a 56% sucrose diet (5BCB) with 5% sucrose water. Mice were euthanized after 8 weeks and scored for caries under a dissecting microscope and following microCT imaging. Bacterial quantity and viability were assessed to investigate the extent of oral cavity colonization. Salivary glands were assessed functionally using pilocarpine and histologically postmortem.
Results: A striking increase in caries was observed in Irf6 Null mice compared to controls (P<0.0001), and this was associated with a significant increase in total and S. mutans bacterial populations. Both saliva flow rate and buffering capacity were severely decreased in the Null mice; histology showed massive defects in salivary gland ductules.
Conclusions: In addition to altered tooth morphology and decreased enamel mineralization, abnormal salivary gland function may be significantly increasing caries susceptibility and severity in the CLP population. For children with IRF6 mutations, implementation of early oral health strategies may be warranted.