Experimental procedures
For the subgroup with salivary pellicle formation (P), the specimens were initially incubated with clarified whole human saliva for 30 min at 37 °C. Modification of the pellicle was carried out with the different solutions by immersing the specimens for 2 min (25 °C, 70 rpm, travel path 50 mm) in each solution, according to the group. Then, the specimens were again incubated in human saliva for a further 60 min at 37 °C. After each step, the specimens were washed in deionized water and the excess water removed with an absorbent paper, without touching the experimental area.The specimens where the solutions were applied directly onto the dentine surface (D) were treated similarly, but not exposed to saliva. They were placed in a humid chamber for 30 min at 37 °C, then they were exposed directly to the test substances, as described above (immersion for 2 min, 25 °C, 70 rpm, travel path 50 mm), and again placed in a humid chamber for a further 60 min at 37 °C. The specimens were washed as described before.Afterwards, all specimens were individually submitted to an erosive challenge (1 min, 1% citric acid, 25 °C, 70 rpm, travel path 50 mm), washed with deionized water and the excess water was removed with an absorbent paper, without touching the experimental area. The citric acid was stored for calcium analysis (CaR), and the specimens were again submitted to the same cyclic procedure. The sequence of pellicle/no pellicle formation, incubation in the test substances, further pellicle/no pellicle formation, and the erosive challenge was repeated 10 times. After 10 cycles, the specimens were submitted to dentine surface loss (DSL) measurements.