Quantitative light-induced fluorescence (QLF): a method for assessment of incipient caries lesions

Objectives: To review the literature on validation and application of the q uantitative light-induced fluorescence (QLF) method for quantitative assess ment of early enamel lesions in vivo and in vitro. Methods: QLF uses light with wavelengths around 405 nm to excite yellow flu orescence at wavelengths above 520 nm. Its diagnostic capacity is based on the mechanism that the intensity of natural fluorescence of a tooth is decr eased by scattering due to a caries lesion. The equipment, the data process ing and the interaction between equipment and operator are described. Results: The method has been validated by many authors; the results are pre sented and compared. For artificial lesions, the validation line is curved. For larger mineral losses, the curve is linear with a slope of 10% fluores cence loss corresponding with a mineral loss of 0.15 kg(.)m(-2). For lesion s caused by natural caries, it is tentatively concluded that fluorescence l oss is linear to mineral loss with a slope similar to that of artificial le sions. Reliability and reproducibility have been tested in vivo and show in terexaminer values of the interclass correlation coefficient, r, of 0.93 <r <0.99. Confounding factors are inadequate reconstruction of sound fluoresc ence values and drying of the lesion before or during measurement. In vivo application showed that statistically significant changes between different preventive regimes could be proven in only 6 months of study time. Conclusion: QLF offers a potential tool to reduce the time needed for clini cal research. Its objectivity will prove useful in epidemiological surveys. QLF provides visual and quantitative feedback to patients.