Estimation of the water content of human teeth using near infrared spectroscopy

Detection of tooth caries using imaging at one or two NIR wavelengths is entering clinical practice, with imaging based on an increase in O-H overtone and combination features associated with increased porosity and water content in decayed or demineralised teeth, and/or change in light scattering with change in tooth porosity. Further consideration of the spectroscopy behind this application is warranted, given details of a NIR spectroscopy-based model for tooth water content has not been previously reported. A partial least squares regression model for tooth water content was developed using a second derivative pretreatment and five factors, achieving a cross validation R 2 of 0.91 and RMSECV of 0.4 % w/w, with model weightings consistent with reliance on O-H features. This result indicates that caries detection is likely based on (water) absorption rather than scattering features.