This paper compares the experimental techniques utilized to assess the de- or remineralization of enamel or dentin in intra-oral studies. In in situ studies, it is important for one to know how much mineral has been lost or gained, and where the loss or gain occurred. The main emphasis in this paper is on techniques suitable for direct or indirect mineral quantification. The measuring techniques considered are microradiography, iodine absorptiometry, various microhardness tests, polarized light, light-scattering, iodide permeability, and wet chemical analysis. The various techniques are compared concerning suitability for the determination of mineral content in vol% (or wt%), mineral changes in vol% micron (or kg.m-2), and mineral distributions. Furthermore, sample preparation, the importance of protein penetration, nominal mineral loss range, the estimated mineral loss threshold, and the applicability to dentin are compared and considered. It is concluded that, although more than ten techniques are available for the measurement of changes after de- or remineralization in situ, transverse microradiography is the most practical technique for the direct and quantitative measurement of mineral content, mineral changes, and mineral distributions. Cross-sectional microhardness testing and light-scattering are also practical indirect techniques for quantitative mineral loss (or gain) determination in intra-oral studies.

Tooth color is determined by the paths of light inside the tooth and absorption along these paths. This paper tests the hypothesis that, since the paths are determined by scattering, a relation between color and scattering coefficients exists. One hundred and two extracted incisors were fixed in formalin, mounted in a standardized position in brass holders, and pumiced. A facet was prepared near the incisal edge on the labial plane to allow for Knoop hardness measurements with a 500-gram load. Light scattering by the enamel was measured in a 450/00 geometry; light scattering by both enamel and dentin was measured in a 00/00 geometry. The reflection spectrum of the tooth was measured from the labial plane with a spectroradiometer in a 450/O°geometry, with standard illuminant A and standard illuminant D65. To include all volume-reflected light, we used entire-tooth illumination and small-area measurement. CIELAB color coordinates were calculated from the spectra. Neither spectra nor coordinates showed evidence of a contribution of fluorescence to tooth color. Averaged values and standard deviations for L*,a*,b* were 69.9 (4.1), 1.22 (1.4), and 17.9 (2.9), respectively. Both scattering coefficients averaged to 0.6 (0.4) mm'l; Knoop hardness number was, on average, 271 (39) kg/mm2. L* correlated with a* (r = -0.51), with the enamel scattering coefficient (r = 0.60), and slightly with hardness (r = 0.17, p = 0.03). The colors of 28 teeth from which the enamel was removed correlated strongly with the colors of the complete tooth. This study quantitatively confirms that tooth color is determined mainly by dentin, with enamel playing only a minor role through scattering at wavelengths in the blue range.

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To allow the determination of scattering and absorption parameters of a turbid material from reflection measurements the relation of these parameters to the reflection has been described by two theoretical approaches. One approach is based on the diffusion theory which has been extended to include anisotropic scattering. This results in a reflection formula in which the scattering and absorption are described by one parameter each. As a second more general approach a Monte Carlo model is applied. Comparison of the results indicates the range of values of the scattering and absorption parameters where the computationally fast diffusion approach is applicable.