Quantitative evaluation of the mineralization level of dental tissues by Raman spectroscopy

Abstract

Current routine clinical methodologies to diagnose diseases that affect the hard tissues of teeth present a certain lack of specificity and sensitivity, especially for incipient demineralization processes where early diagnosis is essential. The aim of this study was to investigate the reliability of Raman spectroscopy as a direct quantitative diagnostic tool for the determination of specific molecular changes in mineralized tissues and the establishment of a pattern of normality. Human healthy and caries-affected dental pieces were evaluated by Raman spectroscopy using an FT-Raman Bruker RFS100 coupled to a 1064 nm-Nd:YAG laser with an incident laser radiation up to 1500 mW. Data from the spectra were treated with OPUS™ software. The influence of Raman spectrometer parameters on the spectra dependence and repeatability was first studied, showing a linear relationship between the incident laser power and the intensity/area of the Raman bands. Two quantitative Raman mineralization indices for dental tissue diagnoses were then proposed. For them, the mineral part ((bend) at 430 cm−1 and (stret) at 960 cm−1 for hydroxyapatite) was related to the organic part (C-Hx of lipids/proteins at 2941 cm−1) by calculating the ratio between these band areas as follows: MIb (Mineralization Index bending): 430 cm−1/2941 cm−1 and MIs (Mineralization Index stretching): 960 cm−1/2941 cm−1. A pattern of normality (healthy mineralization) was established with values in the range 1.35–1.75 for MIb and 4.01–5.19 for MIs. This methodology was successfully applied to two case studies where caries which could not be identified by conventional methodologies, such as radiography, were clearly diagnosed by the proposed quantitative Raman spectroscopy. Thus, its reliability as a routine clinical tool for quantitative diagnosis of dental demineralization by external inspection was demonstrated.