Validation of a Combined RMS-MOCT Optical Probe for Periodontal Assessment

Objectives: Our objective was to develop and validate an optical probe using Raman microspectroscopy (RMS) and micro–Optical Coherence Tomography (mOCT) for chairside quantification of gingival collagen, DNA, epithelium (OE) and connective tissue (CT). We hypothesize that a high-resolution RMS-mOCT probe can discriminate between healthy and diseased sites non-invasively with accuracy comparable to histology.
Methods: The primary outcome measures were oral epithelium to CT thickness (OE/CT) and DNA to collagen type I (DNA/Col) ratios, and sulcular epithelium thickness (SE). For in vivo testing, OE/CT, DNA/Col and SE were assessed at healthy, gingivitis and periodontitis sites (n=15/group). Principal component analysis was carried. Measurement accuracy was tested ex vivo in 8 subjects with healthy gingiva undergoing crown-lengthening or with moderate-severe periodontitis undergoing pocket reduction surgery. Gingival biopsies were scanned by RMS-mOCT and histology performed. Axial sections and stained by immunofluorescence and Masson’s Trichrome were analyzed by histomorphometry. Correlation analyses between RMS-mOCT and histology were carried.
Results: A probe prototype was developed, fabricated, tested ex vivo on gingival specimens and optimized for in vivo intraoral use. The probe has 5 µm axial/lateral resolution in OCT mode and ~ 10 cm^-1 spectral resolution in RMS mode with an imaging speed of 0.5 frames/sec. The spatially co-registered RMS spectra revealed significant changes in the DNA and collagen peaks among groups. Combined RMS-mOCT analysis revealed that OE/CT, DNA/Col, and SE are significantly different among healthy, gingivitis and periodontitis sites, the latter two being more similar to each other than to health. A high correlation between histology and RMS-mOCT was observed. Qualitative analysis of DNA and Col among groups indicated Col content as the main distinguishing feature for health and DNA content for gingivitis and periodontitis.
Conclusions: Our results suggest that combined RMS-mOCT imaging accurately distinguishes between healthy and diseased sites by measuring periodontal tissue integrity.