Smear Layer Formation and Environmental Stability of Commercial Dentifrices

Dentifrices with proven clinical desensitization efficacy include formulations which form smear layers to block patent tubuli. Factors which may affect relative efficacy of this dentifrice class include rate of smear layer formation and resistance of formed layers to environmental challenges (Zsiska, IADR San Diego 2011, Poster 2634)  Objectives: This study examined dentinal tubule occlusion and smear layer stability of 4 commercial sensitivity dentifrices as compared to a negative control. Methods: Etched coronal dentin specimens were prepared from extracted human third molars. Specimens were randomized for average patent tubule diameter and density allocated to five dentifrice treatment groups (N=6) including: NaF/silica (Crest® Regular CR - negative control); NaF/Triclosan/SpecialSilica (Colgate® Total Sensitive CTS); HAP/MFP/Citrate (Mentadent® Sensitive Expert MSE); Novamin Bioglass/MFP (Sensodyne® Repair&Protect SRP); SnF₂/Hexametaphosphate (Crest® Pro Health CPH).  Pellicle-coated specimens were brushed with dentifrice for 5 brushing cycles comprised of 2 minute paste applications followed by 1 hour of saliva immersion. Following mechanical challenge (gentle agitation overnight) and acid challenge (cola beverage for 1 minute) to examine chemical durability (AW), surfaces were imaged by light microscopy after 60sec brushing (PB1/2), 1 full brushing cycle (PB1), 5 brushing cycles (PB5), and acid wash (AW). Specimens were graded blinded to treatment on a 6-point scale. Results: PB1/2 CR 0.66c, CTS 1.95b, CPH 2.87a, MSE 1.74b, SRP 0.55c; PB1: CR 1.30c, CTS 2.51b, CPH 3.22a, MSE 2.94ab, SRP 1.47c; PB5: CR 2.47b, CTS 3.24a CPH 3.38a, MSE 3.10a, SRP 2.21b, AW: CR 1.69b, CTS 1.97b CPH 2.72a, MSE 1.75b, SRP 1.82b (a≠b≠c p < 0.05 Students t comparison). Conclusion: CPH exhibited most rapid onset of smear layer formation.  Other sensitivity dentifrices (exception SRP) also formed extensive smear layers with multiple brushing. CPH smear layers exhibited strongest resistance to environmental challenges.  These results point to clear mechanism differences in dentin surface reactivity provided by commercial formulations.