Fig. (2) SEM images after the seven-day remineralization Phase A period at 30,000x for enamel initially eroded for 30 minutes with 1% citric acid (a, c) or 120 minutes with 0.3% citric acid (b, d) and treated with either SS 1 (a, b) or SS 2 (c, d). The white scale bars correspond to 100 nm.