Tooth Root Cross-section Variations of Significance for Endodontic Microsurgery and Predicted Risk of Concealed Canal Isthmus Based on Cross-sectional Morphology: Three-dimensional Morphological Analysis of Japanese Maxillary First Molars Using Micro-CT

Abstract

The present study aimed to classify variations in tooth root cross-sectional morphology after conventional endodontic microsurgery in the maxillary first molars and to accurately predict the risk of concealed isthmus deeper in the root based on the observed morphology. Using micro-CT data, tooth root cross-sections obtained at 3–6 mm from the apex were classified as Types I–V according to the isthmus classifications of Hsu and Kim. The rates of mismatch between isthmus classifications in the cross-sections at 3 mm from the apex and those obtained deeper in the root at 4–6 mm from the apex were calculated. High rates of match were observed between classifications in tooth root cross-sections at 3 mm from the apex and those deeper in the tooth root (4–6 mm) in the distobuccal (83%) and paratal (90%) roots, while the rate of match in the mesiobuccal root was low (36%). In mesiobuccal roots with incomplete isthmus at 3 mm from the apex, the probability of complete isthmus deeper in the root was 90% or higher. Accessory root canals and lateral branches were often found not only close to the apex, but also concealed deeper in the root more than 3 mm from the apex in the mesiobuccal roots of the maxillary first molars. Thus, as with cases of complete isthmus, treatment requires enlargement of the root canal to create a cavity that encompasses the main root canal and any smaller structures, followed by retrograde filling.