For an Ellis Class I tooth fracture, the fracture line is typically located at which portion of the crown?

Ellis Class I fractures are enamel-only fractures that occur most commonly at the incisal edge or corner of anterior teeth. The enamel is thickest at the incisal edge (approximately 2.5 mm) and thinner toward the cervical area where it ends at the cementoenamel junction. Fractures confined to enamel typically occur at the incisal edge or incisal corner, where the enamel is unsupported by underlying dentin (the pulp is farthest from the incisal edge). The distinction between 'incisal third' regions reflects clinical and radiographic assessment of fracture depth rather than precise anatomical thirds.