A NEW METHOD FOR IN-VIVO QUANTIFICATION OF CHANGES IN INITIAL ENAMEL CARIES WITH LASER FLUORESCENCE

A new method for the in vivo assessment of changes in initial enamel caries lesions was developed and tested. A CCD camera equipped with a high-pass filter (lambda > 520 nm) collects the fluorescence image of carious teeth, illuminated intraorally with diffuse laser light (lambda = 488 nm). Incipient lesions show a loss in fluorescence to be expressed as a percentage of fluorescence radiance of sound tissue. A PC program (Inspektor, model QLF 1.0) is used for display, storage, and subsequent analysis of images. To enable the calculation of fluorescence loss, the fluorescence of sound tissue at the lesion site is reconstructed from the radiances of sound tissue bordering the lesion. This method was tested on 19 visually sound buccal surfaces in vivo. The differences between actual and reconstructed radiance was -1.6 +/- (SD) 1.1%, over areas varying between 8 and 14 mm(2). The repeatability of the caries quantification was tested by measuring one arrested initial caries lesion 25 times in vivo. The lesion area was 0.56 +/- 0.20 mm(2), and the loss of fluorescence was 17.6 +/- 0.7%, corresponding to a lesion depth of 17 +/- 2 mu m The new quantitative method was applied for the testing of an in vivo caries model using plaque-accumulating brackets on premolars scheduled for extraction. Videoimages were recorded in vivo before bracketing and 0, 2, 3, and 5 weeks after debracketing. Clear changes between the different time points were recorded for both lesion size and mineral content. Thus, the method seems suitable for in vivo measurement of mineral changes in natural enamel lesions on smooth surfaces and might be useful for clinical trials and evaluation of preventive measures.