FTIR Microscopic Imaging of Carious and Normal Dentin Substrates

The complexity and heterogeneity of clinically relevant substrate such as caries-altered dentin confounds analyses using conventional characterization techniques. As an example, authors have reported a dramatic drop in bond strength with caries-affected dentin, but a clear prescription of the factors that explain bonding differences between normal and caries-affected dentin has remained elusive. Objective: Using FTIR Chemical Imaging (FTIRI), we characterized the chemistry including inhomogeneities, mineral/matrix ratios, crystallinity and collagen organization of caries-infected, caries-affected (CA) and normal dentin substrates. Methods: The occlusal one-third of the crown was removed from extracted human molars (n=12), the teeth were sectioned parallel to the buccal surface using low-speed diamond saw, 5-micrometer sections were cut using a Leica Polycut S microtome and placed on a BaF2 disk for FTIR imaging analysis. Vibrational spectra were collected using a Spotlight FTIRI spectrometer (Perkin Elmer), at a spectral resolution of 4-8cm-1. Spectral images were collected from areas containing normal, caries-infected and -affected dentin, at a spatial resolution of ~6.25 micrometer. Results: The spectral comparison of these substrates showed distinct differences. The relative carbonate content was decreased in caries-altered as compared to normal dentin. Differences in mineral crystallinity and collagen cross-linking were also noted. Ratio of relative integrated intensity of phosphate/amide I was 6.85 ± 0.7 and 5.01 ± 0.8 while the carbonate/amide I ratios were 0.064 ± 0.011 and 0.045 ± 0.012 for normal and CA dentin, respectively. Conclusion: Distinct differences in collagen organization, chemical composition and distribution are noted in caries-infected and caries-affected dentin as compared to normal dentin. Further studies are required to elucidate the kinetics of these structural changes during the caries process and to understand the role that these differences play in repair and replacement of these clinically relevant substrates. Supported by NIH/NIDCR DE014392, DE015281, R0315735, R13DK069504.