Methods: Coronal dentin disks prepared from human third molars were sanded, polished and etched with 6% citric acid to produce open dentin tubules. Baseline energy-dispersive x-ray analysis (EDX) and scanning electron microscopy (SEM) images were collected. For parallel image & chemical comparison purpose, the disks (N=4) were cut into 4 small fragments, which were then random allocated to 4 treatment groups of dentifrice: NaF/nil-abrasive (Experimental gel product for non-sensitive control, NEG), SnCl2/NaF/nil-abrasive (Experimental gel product, SNG), NaF/Silica (Crest® Cavity Protection, CCP), and SnCl2/NaF/Silica dentifrice (Crest® Pro-Health Clinical – China, CPHC). Specimens were brushed for 5 cycles comprised of 1 minute Oral-B power bush application followed by 1 hour of saliva washing under agitation. Post-brushing specimens were gently agitated for 16 hours in saliva and further challenged with acidic cola for 1 minute. Treated disks were analyzed post-brushing and after acid challenge with SEM and EDX, including analysis of freeze-fractures to determine depth and chemical identity of smear layer and occlusion plugs.
Results: SEM analysis revealed nearly 100% tubule occlusion for CPHC treatment. The freeze-fracture SEM images showed sub-surface CPHC occlusion plugs 6~30 microns deep. Elemental mapping by EDX of CPHC treatment indicated Sn accumulation inside occluded tubules and surface smear layer. In contrast, no tubule occlusion was found for NEG treatment; a thin fragile Sn-containing layer was observed on surface of specimens treated by SNG. Obvious tubule occlusion was also found for CCP treatment; however, this smear layer was not as durable as CPHC against physical and chemical challenge, suggesting Sn cross-links silica particles and forms a more acid-resistant smear layer.
Conclusions: Microscopy and chemical analysis confirmed that a novel SnCl2/NaF/Silica dentifrice provides complete and deep dentin tubule occlusion by stannous and silica deposition.
Keywords: Dental materials, Dentifrices, Dentin, Occlusion and Sensitivity
See more of: Dental Materials 9: Other Materials - Chemistry, Properties and Performance