In vivo determination of multiple indices of periodontal inflammation by optical spectroscopy

Abstract

Background and objective: Visible, near-infrared (optical) spectroscopy can be used to measure regional tissue hemodynamics and edema and therefore may represent an ideal tool with which to study periodontal inflammation in a noninvasive manner. The study objective was to evaluate the ability of optical spectroscopy to determine simultaneously multiple inflammatory indices (tissue oxygenation, total tissue hemoglobin, deoxyhemoglobin, oxygenated hemoglobin and tissue edema) in periodontal tissues in vivo.

Material and methods: Spectra were obtained, processed and evaluated from healthy, gingivitis and periodontitis sites (n = 133) using a portable optical, near-infrared spectrometer. A modified Beer-Lambert unmixing model that incorporates a nonparametric scattering loss function was used to determine the relative contribution of each inflammatory component to the overall spectrum.

Results: Optical spectroscopy was harnessed to generate complex inflammatory profiles of periodontal tissues. Tissue oxygenation at periodontitis sites was significantly decreased (p < 0.05) compared to sites with gingivitis and healthy controls. This was largely the result of an increase in deoxyhemoglobin in the periodontitis sites compared with healthy (p < 0.01) and gingivitis (p = 0.05) sites. Tissue water content per se showed no significant difference between the sites, but a water index associated with tissue electrolyte levels and temperature differed significantly between periodontitis sites and both healthy and gingivitis sites (p < 0.03).

Conclusion: This study established that optical spectroscopy can simultaneously determine multiple inflammatory indices directly in the periodontal tissues in vivo. Visible, near-infrared spectroscopy has the potential to be developed into a simple, reagent-free, user-friendly, chairside, site-specific, diagnostic and prognostic test for periodontitis.

Figure 1

Design of the intraoral probe for the acquisition of NIR spectra from periodontal tissues. The intraoral probe consists of a 180 mm long stainless steel shaft, 5 mm diameter, housing 29 fibre optic bundles (A). Amended probe shape (B).

Figure 2

Near infrared reference spectra (500–1000 nm) for water, deoxygenated hemoglobin (Hb) and oxygenated hemoglobin (HbO₂). The extinction coefficient data for water have been multiplied by a scaling factor of 10.

Figure 3

Mean near infrared spectra from healthy, gingivitis and periodontitis sites.

Figure 4

Relative concentrations of Hb (A) and HbO₂ from healthy, gingivitis and periodontitis sites (B). Relative hemoglobin concentrations were calculated using the visible region (510 – 620 nm) of the reflected light spectrum. * Represents a significant difference from healthy sites, p<0.01. Vertical bars denote 0.95 confidence intervals.

Figure 4

Relative concentrations of Hb (A) and HbO₂ from healthy, gingivitis and periodontitis sites (B). Relative hemoglobin concentrations were calculated using the visible region (510 – 620 nm) of the reflected light spectrum. * Represents a significant difference from healthy sites, p<0.01. Vertical bars denote 0.95 confidence intervals.

Figure 5

Percent tissue hemoglobin oxygen saturation (A) and THb indices (B) derived from the relative concentrations of Hb and HbO₂. Indices are compared between healthy, gingivitis and periodontitis sites. * Represents a significant difference from healthy sites, p<0.01. Vertical bars denote 0.95 confidence intervals.

Figure 5

Percent tissue hemoglobin oxygen saturation (A) and THb indices (B) derived from the relative concentrations of Hb and HbO₂. Indices are compared between healthy, gingivitis and periodontitis sites. * Represents a significant difference from healthy sites, p<0.01. Vertical bars denote 0.95 confidence intervals.