Differentiation of enamel lesion activity by vertical reflection intensity - a methodical description

This article describes two objective, instrumental approaches for the distinction of enamel lesion activity - the in vitro measurement of surface layer porosity and surface roughness - and on this basis, the in vivo measurement of vertical reflection intensity (VRI). They are based on the subjective visual and tactile criteria of a dull and rough or a shiny and smooth surface, accepted by the known diagnostic systems, Nyvad criteria, International Caries Detection and Assessment System II, and Universal Visual Scoring System. With a scanning white-light interference microscope, the active lesion surface had a high porosity (118 pores) and a high roughness (Ra 190 nm) constituting a field of view of 280×210 μm. The inactive lesion surface had almost no porosity (one pore) and a more than 10-fold lower roughness (Ra 10 nm) for the same area. These differences result in a different light reflection of the lesion surfaces, which can be measured as VRI with a chromatic confocal sensor with spacer (mean VRI: active lesions, 7%; inactive lesions, 25%; sound enamel, 35%). In addition to monitoring, this sensor allows an in vivo handheld evaluation in a single (visit) examination.