An anatomical study of the subpulpal wall of abnormal multirooted teeth in the narrow-ridged finless porpoise (Neophocaena asiaeorientalis)

Studies have shown that there are two mineralization patterns of roots in multirooted teeth: one forms dentin islands (subpulpal lobes) independent of the crown, and the other does not form any subpulpal lobes. In this study, we found abnormal multirooted teeth in porpoise specimens and focused on the developmental process of its root furcation. To examine the features of the tooth in detail, we used scanning electron microscopy for the morphology of the surface and micro-computed tomography (micro-CT) for the structure of the pulp cavity. The micro-CT scanning showed that a triple-rooted tooth had only one pulp chamber and one horn. In addition, we observed the intermediate bifurcational ridge-like structure and dentinal bulges on the subpulpal wall, both of which suggest the formation of the subpulpal lobes. To our knowledge, this study is the first report about teeth with supernumerary roots in Phocoenidae and also the first study to focus on the process of furcation of tooth roots in modern cetaceans. We concluded that the cause of the triple-rooted tooth was not secondary adhesion of several teeth but rather the furcation of the root at the developmental stage. Additionally, the tooth could have formed lobes during the root furcation.