Viscosity of chitosan impacts the efficacy of F/Sn containing toothpastes against erosive/abrasive wear in enamel.

Objectives: Chitosan (Ch) in F/Sn-toothpastes can increase toothpastes' anti-erosive efficacy. Whether efficacy can be further increased by changing chitosan's viscosity was study aim.

Methods: 192 human enamel specimens were assigned to 2 × 6 groups (n = 16 each): Four F/Sn (500 ppm F, 800 ppm Sn) toothpastes with chitosan (0.5 %, viscosity 50, 500, 1000 or 2000 mPas), negative-control (no F/Sn/chitosan), positive-control (F/Sn, no chitosan). The study was conducted in two experiments (E1/E2). Specimens were cyclically demineralised (10 d, 6 × 2 min/d; 0.5 % citric acid); half of groups (E1) was exposed to toothpaste slurries (2 × 2 min/d), the other half was additionally brushed (2 × 15 s/d, E2). Tissue loss (mean ± SD, μm) was quantified profilometrically. Element analysis (EDX, wt%) on specimen surfaces and on toothpastes' particulate fraction and SEM analysis of specimen surfaces were performed.

Results: Tissue loss in negative-controls (E1/E2) was 4.96 ± 1.55/12.76 ± 2.45. Toothpastes with active agents (AA) reduced tissue loss compared to negative-control (p < 0.0001). E1: All AA caused precipitates, being the thickest after Ch500. Chitosan increased carbon retention, not tin retention. E2: Only Ch1000 increased efficacy (-0.97 ± 4.48) compared to positive-control (2.98 ± 1.32; p = 0.05). EDX showed comparable carbon values in all AA; tin content was higher in Ch1000 (6.5 ± 3.4) compared to other AA (range: 3.8 ± 0.3-4.3 ± 1.3). On abrasives, tin adsorption was decreased by all chitosans. SEM revealed minor structural differences.

Conclusions: Chitosan viscosity has impact on efficacy of F/Sn toothpastes. Under erosive/abrasive conditions Ch1000 showed the best protective effect with higher tin retention on surfaces and lower tin absorption by abrasives.

Clinical Significance: The biopolymer chitosan shows protective effect against enamel erosion and erosion/abrasion when used in an F/Sn toothpaste with specific viscosity.