Detecting Incipient Caries Using Front-illuminated Infrared Light Scattering Imaging

A new method for early caries diagnosis was proposed and tested through a home-made optical examination systemthat used quantitative light fluorescence (QLF) and digital imaging fiber optic transillumination (FOTI) (DIFOTI),with light sources across a wide spectral range, from 350 nm to 1,000 nm. The front-illuminated infrared lightscattering image (FIR) showed similar diagnostic abilities to that of DIFOTI. The FIR method was invented based onthe observation that caries lesions lose the high transmittance and low scattering properties of benign enamel tissue.There are various methods for the early diagnosis of caries, such as visual examination, exploration, X-ray radiography,QLF, FOTI, and infrared fluorescence (diagnodent). Among them, methods based on optical properties are regarded ashaving the most potential. A comparative study was performed between the FOTI, QLF, diagnodent, optical coherencetomography, and FIR scattering image methods, using 20 extracted teeth samples with early caries. A scale of lesionmeasurement based on optical image contrast was proposed. The statistical analysis showed a significant correlationbetween the DIFOTI and FIR methods (r = 0.35, p < 0.05). However, the QLF and diagnodent methods showed littleassociation with FIR images, as they have different detection principles as compared with FIR. Tomographic imagesobtained by OCT, using 1,330 nm super luminescent LED as a gold standard of tooth structure, verified that the FOTIand FIR results correctly represented the lack of homogeneity in dental tissue. The newly proposed FIR methodattained similar diagnostic results to those of FOTI, but with an easier approach.