Development of a Chairside Optical Coherence Tomography System for CAD/CAM-Materials

Objectives: Dental restorations undergo fatigue damage over time due to repeated subcritical loading during daily use. Conventional methods for assessing this damage are not suitable for monitoring or intraoral use and are often destructive. Optical coherence tomography (OCT) offers a non-invasive alternative. The aim of this study was therefore to find a suitable OCT system, which can then be configured for intraoral use, to enable non-invasive monitoring of internal contact damage in monolithic CAD/CAM-materials.
Methods: Four groups of CAD/CAM-materials were investigated: composite (Brilliant Crios, Coltene), hybrid ceramic (Vita Enamic, Vita Zahnfabrik), lithium disilicate (IPS e.max CAD, Ivoclar Vivadent) and 5Y-TZP zirconia (Prettau anterior, Zirkonzahn). A CAD/CAM crown was manufactured from each group and adhesively cemented to a CAD/CAM-milled human molar. The specimens were then loaded in a mouth-motion simulator (50-500 N, 2 Hz, 37°C) for 750,000 cycles. Before and after loading, the specimens were examined using two spectral domain OCT systems (GAN210, central wavelength λ=930 nm; TEL221, λ=1300 nm) and two swept source OCT systems (ATR220, λ=1060 nm; VEG210, λ=1300 nm) from Thorlabs. The images were evaluated in terms of their quality and additional system parameters such as imaging speed and size of the field of view captured.
Results: Except for 5Y-TZP zirconia, all CAD/CAM-materials showed internal contact damage that could be displayed with all OCT systems. The optical axial/lateral resolution of the spectral domain OCT systems was better (5.5-6/8-13 µm) compared to the swept source OCT systems (11-14/13-20 µm). However, the swept source OCT systems outperformed compared to the spectral domain OCT systems in terms of field of view size and imaging speed (11x9x10 mm³ in 10.9 s, respectively 24.3 s).
Conclusions: Considering all aspects, the VEG210 system was selected as the most suitable for the development of a chairside OCT system to be configured for intraoral use.