Final answer:
The correct radiograph for determining the canal length during an endodontic procedure is the Periapical radiograph. It is essential for accurately assessing the length of the root canal and ensuring proper treatment.
Step-by-step explanation:
The radiograph that helps a dentist to determine the length of the canal during an endodontic procedure is the A) Periapical radiograph. This type of radiograph provides a detailed view of the entire tooth, from the crown to the tip of the root, and is crucial for assessing the health of the tooth's structure, detecting deeper decay, and gauging the length of the root canal. Periapical radiographs are especially important in endodontic treatments, where precision in determining the canal length is necessary to ensure that the entire root canal is cleaned and filled properly to prevent infection and abscess formation.