Ex vivo detection and characterization of early dental caries by optical coherence tomography and Raman spectroscopy

Abstract

Early dental caries detection will facilitate implementation of nonsurgical methods for arresting caries progression and promoting tooth remineralization. We present a method that combines optical coherence tomography (OCT) and Raman spectroscopy to provide morphological information and biochemical specificity for detecting and characterizing incipient carious lesions found in extracted human teeth. OCT imaging of tooth samples demonstrated increased light backscattering intensity at sites of carious lesions as compared to the sound enamel. The observed lesion depth on an OCT image was approximately 290 microm matching those previously documented for incipient caries. Using Raman microspectroscopy and fiber-optic-based Raman spectroscopy to characterize the caries further, spectral changes were observed in PO4 (3-) vibrations arising from hydroxyapatite of mineralized tooth tissue. Examination of various ratios of PO4 (3-) nu2, nu3, nu4 vibrations against the nu1 vibration showed consistent increases in carious lesions compared to sound enamel. The changes were attributed to demineralization-induced alterations of enamel crystallite morphology and/or orientation. OCT imaging is useful for screening carious sites and determining lesion depth, with Raman spectroscopy providing biochemical confirmation of caries. The combination has potential for development into a new fiber-optic diagnostic tool enabling dentists to identify early caries lesions with greater sensitivity and specificity.

Applications of Raman Spectroscopy in Dentistry: Analysis of Tooth Structure

“…Recent studies on Raman spectroscopy have shown promising results in diagnosing early dental caries (3,6,24,(35)(36)(37). As stated previously, dental caries is characterized by demineralization of inorganic substance (hydroxyapatite crystals) and destruction of organic substance (collagen matter).…”

Background removal from polarized Raman spectra of tooth enamel using the wavelet transform

“…We have previously used this polarization ratio as a quantitative measure to assess the extent of demineralization of enamel. [5,6] Where our previous investigations showed that other subtraction methods such as linear and polynomial fitting failed to provide adequate separation of stained sound enamel and unstained carious enamel, the current studies show that the wavelet transform technique is an effective and practical tool to separate the Raman signal of tooth enamel from the background and noise. The multiresolution wavelet method described is computationally efficient and uses established functions within Matlab's Wavelet Toolbox, which is in principle accessible to all.…”

“…[2][3][4] In addition, we have recently demonstrated that polarized Raman spectroscopy (PRS) using near-infrared excitation can readily be used to differentiate between sound enamel and carious enamel using the depolarization ratio based on the integrated peak intensities of the symmetric phosphate stretching vibration at 959 cm 1 . [5][6][7] However, for tooth enamel therecan be a strong interfering background in the Raman spectrum resulting from extrinsic stains arising from food, drugs, tobacco usage or other sources and intrinsic stains, which obscure small Raman signals and affect calibration and quantitation based on spectral peak information. In order to use the depolarization ratio to distinguish sound enamel from early carious regions in stained enamel, it would seem that it is only necessary to remove the background from the small wavenumber interval in the region of 900-1000 cm 1.…”

“…Although we focus primarily on the 1 ( 959 cm 1) peak for quantitative analyses, our early studies have also shown that there are subtle changes in the 2, 3 and 4 phosphate vibrations. [5] By correcting the background of the entire Raman spectrum, we can potentially gain additional insight regarding the alterations occurring in the other phosphate vibrations. For these various reasons, we began exploring alternative methods for background removal that would involve the entire Raman spectrum in order to obtain reliable diagnostic results.…”

Early caries detection using optical coherence tomography: a review of the literature

“…Otis et al demonstrated improved imaging characteristics of a system operating at 1,310 nm vs. 850 nm. 85 Canadian groups have also devoted their studies to caries research using OCT. 8,[86][87][88] They also used PS-OCT systems; however, they creatively combined polarized Raman spectroscopy (PRS) with OCT in detecting early carious lesions. Raman spectroscopy uses laser excitation and the resulting scattering effect is observed in the target tissues.…”