Fig. 3

Method of measuring the crack depth of tooth no. 23 on contrast-enhanced cone beam computed tomography (contrast-enhanced CBCT). A The coronal plane of the crack shows the path of the crack. B The first location where the high-density crack started to appear on the contrast-enhanced CBCT scan is marked “1” in the horizontal plane. C A high-density crack image of a cracked tooth. D The crack completely disappeared and is marked “2”. E The distance from “1” to “2”,i.e., the length of segment “3”, was taken as the extension depth of the crack