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For in vitro lesions, homogeneously formed and of fixed size, fluorescence radiance loss is used to follow lesion severity in time with QLF. In vivo lesions are inhomogeneous and the lesion area varies in time. Thus, not only the fluorescence radiance but also the lesion area must be monitored to follow lesion progression or regression. This paper describes a new parameter ¢Q to describe lesion severity with QLF. ¢Q is defined as the fluorescence radiance loss integrated over the lesion area [mm2 ·%]. ¢Q is comparable to the total amount of mineral lost from the lesion as measured with LMR. Lesion development of 50 in vivo lesions was followed 1 year with QLF. The lesion area (mm2), mean change in fluorescence radiance (%) as well as ¢Q [mm2 ·%] were recorded every 4 months. ¢Q of 21 lesions increased, of which 11 lesions showed no change in fluorescence radiance and 4 showed no change in lesion area. ¢Q of 29 lesions decreased, but 12 of these lesions showed no change in fluorescence radiance and 8 showed no change in lesion area. In 4 of the regressing lesions, the fluorescence radiance loss increased initially which was overruled by a strong decrease in lesion area. Parts of these lesions were remineralized so that the fluorescence radiance differed less than 5% from the level of sound enamel and were no longer considered carious. Line histograms showed an overall decrease in fluorescence loss over the original lesion area, but due to the decreased number of pixels attributing to the average the mean fluorescence radiance loss increased. The value of ¢Q did show a decrease implying remineralization of the lesion. We conclude that ¢Q is the appropriate parameter to describe lesion progression or regression in clinical trials with QLF. |