Final answer:
A horizontal line of material seen in X-rays extending from the canal to the periodontal ligament space after obturation of a central incisor indicates a midroot fracture.
Step-by-step explanation:
After obturation (filling) of a traumatized central incisor, when a horizontal line of material is observed in the midroot area extending both mesially and distally from the canal to the periodontal ligament space, it likely indicates the presence of a midroot fracture. Accessory canals would not typically appear as a horizontal line but rather as additional canals branching from the main canal. Internal resorption would show a more irregular, localized loss of dentin internally, while external resorption would affect the external aspects of the root and be visible from the outside of the tooth. In this case, the description given of the horizontal line of material suggests that the tooth's structural integrity is compromised due to a fracture within the midroot area of the tooth.