Methods: Enamel specimens were randomly assigned into 6 groups (n=8), according to the combination between rinse treatments: 1min deionized water (DIW), 1min 12mM NaF (NaF) or 1min 150mM calcium lactate followed by 1min NaF (Ca+NaF); and salivary flow rates: 0.5 or 0.05ml/min, simulating normal and low salivary flows, respectively. The specimens were placed in custom-made devices, creating a sealed chamber on the enamel surface connected to a peristaltic pump. Citric acid (0.3%, pH 3.8) was injected into the chamber for 2min, followed by artificial saliva at 0.5 or 0.05ml/min for 60min. This cycle was repeated 4x/day. Thirty minutes after the 1st and 4th erosive challenges, specimens were treated with the rinse solutions (DIW, NaF or Ca+NaF). The erosion-remineralization cycles and rinse treatments were performed for 3 consecutive days. Surface loss was determined by optical profilometry. KOH-soluble fluoride and enamel fluoride uptake were determined at the end of the experiment. Data were analyzed by two-way ANOVA and Tukey test (α=0.05).
Results: Significant interaction (p<0.001) was observed for rinse treatment and salivary flow rate. Means (standard-deviation) of surface loss (μm) are presented below:
Flow rate (ml/min) |
DIW |
NaF |
Ca+NaF |
0.5 |
5.22(0.79)a,A |
3.72(1.08)a,B |
3.41(0.64)a,B |
0.05 |
8.67(0.78)b,A |
4.56(0.47)b,B |
3.93(0.46)a,B |
Different lowercase letters represent significant differences in columns, uppercase in rows. Higher KOH-soluble fluoride and enamel fluoride uptake levels were observed for Ca+NaF, followed by NaF and DIW (all significantly different, p<0.05), especially at 0.05ml/min (p<0.05).
Conclusions: The sodium fluoride rinse was able to reduce the erosion progression, which was significantly higher under low salivary flow rate conditions. The calcium lactate pre-rinse increased fluoride availability, showing some potential to increase the fluoride protection against erosion in low-salivary flow rate conditions.