Capped silver nanoparticle penetration in primary dentition: an in vitro SEM-EDS analysis

PURPOSE: This study investigated the extent and distribution (surface coverage) of penetration of custom-synthesised silver nanoparticles functionalised with two different organic capping agents (casein capped and citrate capped silver nanoparticles). MATERIALS AND METHODS: Extracted human primary teeth were sectioned into dentine slices, etched to remove the smear layer, and treated topically with either the nanoparticles, silver fluoride (positive control) or deionised water (negative control). Following fixation, dehydration, and carbon coating, samples were examined using a scanning electron microscope (SEM) with backscattered electron detector. The presence of nanoparticles was verified with energy dispersive X-ray spectroscopy (EDS) for spot elemental analysis. Penetration depths were measured from longitudinal-view micrographs, and data were statistically analysed. RESULTS: All silver nanoparticles treated specimens exhibited evident surface precipitation and intratubular infiltration. Citrate-capped nanoparticles demonstrated greater penetration (32.5 ± 8.9 μm) than casein-capped (19.3 ± 7.1 μm); however, this difference was not statistically significant (p = 0.056). In contrast, silver fluoride exhibited significantly deeper and denser infiltration (117.7 ± 29.1 μm), forming continuous intratubular precipitates. EDS confirmed characteristic Ag peaks in all treated samples. CONCLUSION: Silver nanoparticles successfully infiltrated dentinal tubules. However, their penetration was shallower than silver fluoride, likely due to lower silver concentration. Their strong surface retention and controlled diffusion indicate potential for use as topical agents. Further optimisation of particle concentration and application protocol may enhance intratubular diffusion while maintaining biological safety.