Fig. 16.

Cross-sectional depiction of a tooth (a) prior to acid challenge and (b) after acid challenge. After acid exposure, the amorphous surface layer is weakened, creating a porous and roughened outer surface. The pores allow acid to attack the underlying enamel, leading to demineralized enamel prism cores. Therefore, both scattering from the surface (from the roughened amorphous layer) and subsurface volume scattering (from the porous demineralized enamel) is present. However, after the application of a viscoelastic pressure-sensitive adhesive to the surface of the tooth, the adhesive fills the majority of the roughened surface, thus minimizing surface scattering without affecting volume scattering.