The purpose of this study was to investigate the incidence and location of the second mesiobuccal (MB2) root canal of the maxillary first molar and the relationship between the presence of an MB2 canal and the distribution of canal orifices on the pulpal floor with the aid of cone-beam computed tomographic (CBCT) technology.Methods
A total of 1008 maxillary first molars (548 patients) were randomly selected and analyzed through CBCT imaging. The association between the incidence of MB2 canals and potential impacting factors including sex, side, age, and the distribution of the main root canal orifices on the pulpal floor was explored. The interorifice distances (ie, the length of a line between the center point of any 2 orifices) at the pulpal floor level were measured using Mimics 10.01 software (ImageWorks, Materialise, Belgium).Results
The majority of 3-rooted maxillary first molars showed 2 root canals (85.4%) in the mesiobuccal root. The incidence of MB2 canals had no statistically significant difference between the left and right sides (P > .05) but had a significant association with the patients' sex and age (P < .05). Receiver operating characteristic curve analysis showed a high diagnostic accuracy (the area under the receiver operating characteristic curve = 0.92) of using the distance ratio of the interorifice distance between the main mesiobuccal and the palatal root canal orifices to the interorifice distance between the distobuccal and the palatal root canal orifices to predict the presence of an MB2 canal. A larger distance ratio (>1.26) indicated a highly probable existence of an MB2 canal. In this study, no molar presented an MB2 canal with a distance ratio of less than 1.16, whereas all molars with a ratio greater than 1.37 presented an MB2 canal without exception. A Bland-Altman scatterplot showed great agreement between the distances of the main mesiobuccal and the distobuccal canal orifices and the second mesiobuccal and the distobuccal canal orifices.Conclusions
Understanding the incidence of MB2 canals and the distribution pattern of canal orifices on the pulpal floor may help clinicians to quickly identify and locate MB2 canals.