OCT assessment of non-cavitated occlusal carious lesions by variation of incidence angle of probe light and refractive index matching.

OBJECTIVES: This study evaluated (1) the detection and assessment of non-cavitated occlusal carious lesions by spectral domain optical coherence tomography (SD-OCT) and (2) the impact of varying angle of incidence (AI) of probe light and refractive index matching (RIM). METHODS: Nine extracted human molars with 18 occlusal lesions (ICDAS code 2) were visually selected. 18 regions of interest (ROI) were imaged with SD-OCT under varying AI (0 degrees , +/-5 degrees , +/-10 degrees , +/-15 degrees ) and with/without application of glycerine at 0 degrees . X-ray micro computed tomography (muCT) was used as a validation standard. muCT and OCT signals were categorized according to the lesion extent: 1-sound, 2-lesion limited to half of enamel, 3-lesion limited to enamel, 4-lesion into dentin. Agreement between both methods was assessed. Intra- and inter-examiner reproducibility analyses were conducted. STATISTICS: Cohen's kappa coefficient (kappa), Spearman's rho correlation (r(s)) and Wilcoxon test (alpha=0.05). RESULTS: Slight to moderate agreement (kappa=0.153) between muCT and OCT was obtained at an AI of 0 degrees (Wilcoxon: p=0.02). With variation of Al a substantial agreement (kappa=0.607) was observed (p=0.74). Spearman's correlation between both methods was 0.428 at 0 degrees , 0.75 with varying AI and 0.573 with glycerine. Kappa values for intra-and inter-examiner analysis ranged between 0.81 and 0.88 and between 0.25 and 0.73, respectively. CONCLUSION: Variation of AI improves the detectability of non-cavitated occlusal carious lesions. RIM can enhance signal-to-noise ratio. CLINICAL RELEVANCE: OCT could provide additional diagnostic information in single and longitudinal assessments of occlusal carious lesions.