The morphology of these two teeth is very similar. The central incisor has an average length of 20.5 mm and the lateral is a little longer with an average length of 21 mm. Over 40% of these teeth have two canals, but only just over 1% have two separate foramina. Careful reading of the pre-operative radiograph may show a change in the radiodensity of the root canal, indicating division into two separate canals, and a correctly designed access cavity will facilitate checking for a second canal. This is oval in shape, commencing above the cingulum and almost notching the lingual incisal edge.