Refractive Index Measurement of Dental Materials by Swept-source Optical Coherence Tomography

Purpose: The aim of this study was to examine the clinical efficacy of swept-source optical coherence tomography (SS-OCT) for measuring the refractive index of metal-free restoration materials, for which accurate measurements are difficult to obtain by conventional refractometry. Methods: Twenty-five specimens with dimensions of 10×10×1.0 mm (vertical×side×thickness) were used, consisting of five specimens each of five types of material: ESTELITE BLOCK (EB), IPS Empress CAD (IEP), IPS e-max CAD (IEM), VITA SUPRINITY for KaVo ARCTICA (VS), and NACERA pearl 1 (NA). Eight areas on each specimen were randomly selected as measuring points. The refractive index was calculated from the optical path length (OPL) and the actual thickness obtained by the OPL matching method. The mean refractive index was then calculated based on the data from each type of metal-free restoration material. To investigate whether the thickness of the specimen influenced the refractive index, simple regression analyses were performed. Results: The refractive index of NA, which is difficult to measure by conventional refractometry, was 2.227 (±0.023), a significantly higher value (p