Evaluation of bacterial presence in the root canal by Raman spectroscopy: a preliminary study

The aim of this work is to present a potential diagnostic technique for bacterial presence at the entrance and inside the root canal of endodontically treated first molars based on Raman spectroscopy. A hollow core photonic crystal fiber probe was introduced inside the root canal to guide and collect the excitation and the Raman signals, respectively. Spectral features indicating differences between normal dentin and dentin with moderate and severe bacterial infection, at the entrance of the root canal, have been clearly detected as changes in the intensity ratios of the PO43 (-)/C-H (960 cm (-1) /1451 cm (-1)) Raman bands and the intensity ratios between the bending and stretching modes of carbonate CO32- (1034 cm(-1) and 1072 cm(-1)), respectively; these changes in the intensity ratios are common indicators of demineralization due to the presence of a bacterial infection. Raman signals of dentin with high bacterial presence exhibited a large shift (23 cm(-1)) for the stretching mode carbonate band together with changes in the collagen I band (1243 cm(-1)). Raman peaks assigned to specific membrane proteins of bacteria and organic elements were found inside the root canal by using a hollow core photonic crystal fiber probe. The presence of these Raman bands is found to be higher in the case of severe bacterial infection. This is the first Raman spectroscopy study that shows in parallel the bacterial presence within the root canal and the changes that occur in the dental tissue demonstrating the potential of this technique to assess decay of dentin inside the root canal.