A: With a transillumination LSI configuration, SFI images enabled visualization of a small increase in flow speed. The mean SFI value increased by 70% as the flow speed increased from 0 to 0.34 mm/second. B: With transillumination LSI (triangles), an increase in SFI values was observed as the fluid flow changed from Brownian fluid motion (0 mm/second) to forced fluid flow (≥0.34 mm/second) within the tooth. In contrast, epiillumination LSI (squares) was insensitive to any change in flow speed. For (A), the error bars represent the standard deviation of the mean. For (B), the error bars are not visible due to the low coefficient of variation (< 3.2%) in measured SFI values.