Biochemical analysis of carious dentine using Raman spectroscopy

Methods: Over 3 million high-resolution Raman spectra from 8 extracted human carious teeth were recoded using a Renishaw “inVia” Raman microscope in StreamLine™ mode. Green AF signals across each carious lesion from all samples were acquired with a similar spatial resolution using confocal fluorescence microscopy. The Knoop microhardness (KHN) from a total of 233 co-localised areas were recorded from the same samples and allocated subjectively into the three zones.

Results: Cluster analysis of the Raman data, performed using in-house software, produced five independent spectral components representing mineral content, protein content, porphyrin fluorescence (PF), putative infected dentine signal (IDS) and affected dentine signal (ADS). The distributions of the 5 Raman components and the AF signal were matched across all samples and their average values were calculated for each corresponding KHN area. Sound dentine, the positive control, showed that it contains 61% mineral cluster and 33% protein cluster. The infected dentine was defined significantly by the KHN (<20.6), AF (>14.4 A.U.) and by the relative contribution of the mineral (<36.4%), PF (>25.3%) and IDS (>0.3%) clusters. Protein cluster was not statistically related to the KHN (r=0.00) or AF (r=0.04). Delineation between affected and sound dentine was observed using the KHN (at 43), AF (at 5.8 A.U.), PF (at 7.6%) and ADS (at 2.5%) parameters.

Conclusions: This study concludes that Raman spectroscopy can provide a non-invasive and objective evaluation of different carious dentine zones. Being able to detect and assess clinically the caries-affected dentine during minimally invasive operative caries management is important to control the risk of unnecessary tissue removal.