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. 2016 Jul 7;17:14. doi: 10.1186/s12903-016-0231-y

Fig. 5.

Fig. 5

Schematic diagram of the optical principle of the reflectometer. Arrows show the incident and reflected light beams. The top diagram (Principle) represents the highest reflection intensity. The light shines at a ~23° angle onto the enamel/tooth surface and it reflects back also at a ~23° angle (specular reflection) for the highest surface reflection intensity (SRI). The other diagrams represent originally sound teeth (S) and teeth that originally presented ETW (E). Before acid challenges, Sinitial has clear undulations of the perikymata that scatter some of the light, while Einitial has a flat smoother surface that reflects most of the light. So, in Sinitial a smaller proportion of the reflected beams will be captured by the detector (lower SRI), while in Einitial a greater proportion of the light will be reflected back to the detector (higher SRI). After the erosive challenges (S24min and E24min), the enamel surface is rougher, leading to more light scattering and, thus, lower SRI on both types of enamel (S and E)