Investigation of the effects of fluoride varnish, silver diamine fluoride and peptide P11-4 on dentin nanostructure in an in-vitro dentin caries model via SEM, FTIR spectroscopy and SAXS methods

Background: To evaluate and compare the structural effects of fluoride varnish, silver diamine fluoride (SDF), and peptide P11-4 on dentin nanostructure in an in vitro dentin caries model. Methods: Forty dentin discs were demineralized and treated with either SDF, fluoride varnish or P11-4. Structural changes were assessed using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and small-angle X-ray scattering (SAXS) to evaluate topographical, molecular and nanoscale modifications. Results: SEM revealed morphological differences across groups: the P11-4 group showed fibrillar structures and narrowed dentinal tubules; the SDF group exhibited blocked tubules with a granular appearance; and the fluoride varnish group presented partially occluded tubules. FTIR analysis showed a reduction in Amide A and Amide I bands in the P11-4 group, suggesting enhanced interaction with dentin collagen and early-stage remineralization. In contrast, the SDF group showed higher Amide A values, indicating limited interaction with the organic matrix. These spectral shifts imply differential impacts on the preservation and reorganization of the dentin matrix. SAXS analysis confirmed that the P11-4 group exhibited the closest nanostructural resemblance to healthy dentin, whereas the SDF group showed the least similarity. Both the P11-4 and fluoride varnish groups demonstrated organized fibrillar alignment and improved mineral patterning. Conclusions: The findings suggest that P11-4, through its biomimetic action, facilitates favorable nanostructural and molecular changes in demineralized dentin. These effects may contribute to enhanced mechanical stability and long-term clinical outcomes. Broader in vivo studies are warranted to validate these results before clinical application.