2018 Volume 61 Issue 6 Pages 368-377
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<0.05) than that of the other materials (-1.5). All of the materials exhibited a negative correlation between the thickness and the refractive index by simple regression analysis.
Conclusion: Refractive index measurement of the metal-free restoration materials was possible via SS-OCT, including for NA (zirconia), which cannot be measured by conventional refractometry due to its high refractive index. In this study, we confirmed that the refractive index obtained by SS-OCT is influenced by the specimen thickness. It is suggested that by measuring the refractive index of the material in advance and digitizing the refractive index data, the actual thickness of the material can easily be measured at the chair-side. We suggest that SS-OCT has wide potential in clinical applications, not limited to its value as an imaging technique.
