2.4. Scoring by Examiners

Twelve dentists were recruited (8, 9, 10, 11, and 12, with less than 5 years of clinical experience; 6 and 7, with 5–10 years of clinical experience; 3, 4, and 5, with 11–20 years of clinical experience; 1 and 2, with over 21 years of clinical experience) and participated in this experiment as examiners. In order to reach a consensus on the evaluation criteria, the reference examiner (MK) discussed the radiographs and OCT images with 12 dentists in a 1 h session. For the calibration session, MK used 12 extracted teeth images that were not included in the study.

After the discussion, the examiners performed scoring of the tooth wear level of the occlusal surface independently using the following 4-rank scale:

Score 1: Slight enamel wear. Initial tooth wear was within the enamel and more than 1/2 thickness of enamel left.

Score 2: Distinct enamel wear. Tooth wear was within the enamel and less than 1/2 thickness of enamel left.

Score 3: Tooth wear with slight dentin exposure. Tooth wear reached to the dentin-enamel junction (DEJ). Dentin exposure was slight with less than 1 mm diameter.

Score 4: Tooth wear with involvement of dentin. Tooth wear was beyond the DEJ to cause dentin exposure. The diameter of dentin exposure was more than 1 mm.

A liquid crystal display monitor was used to display either digital radiographs or 3D OCT images, associated with the occlusal view of digital photographs. For the radiographs, the original image without enhancement of contrast or brightness was used. For OCT, 3D images of occlusal surface as well as the sequence of two-dimensional (2D) tomographic images extracted from the 3D dataset were dynamically displayed in video format using a custom-developed software (KakumaViewer, Yoshida Dental). Display settings such as brightness and contrast were unchanged from the default for all images and examiners.