Micro-computed tomography analysis of root and canal morphology in maxillary primary molars

Effective pulpectomy of maxillary primary molars depends on a clear understanding of their complex internal root canal anatomy, yet high-resolution data on the second mesiobuccal (MB2) canal in the primary dentition remain scarce. Using micro-computed tomography (micro-CT; SkyScan 1172; 13.61 μm isotropic voxel size), the three-dimensional root and canal morphology of 60 extracted maxillary primary molars were charaterized, focusing on the prevalence, location, and morphometry of the MB2 canal, along with inter-orifice distances, canal diameters, and dentin wall thickness. Three-rooted molars predominated (83.3%). An MB2 canal was present in 43.3% of mesiobuccal roots and, when present, was consistently located palatal to the main mesiobuccal (MB1) canal, originating predominantly in the coronal third. Long-oval and oval cross-sections together accounted for almost all canals. The MB1–MB2 inter-orifice distance was the shortest of any canal pair (mean 1.12 mm), and buccolingual diameters exceeded mesiodistal diameters in the mesiobuccal, MB2, and distobuccal roots but not the palatal root. Apical dentin was thinnest in the palatal roots (0.10 mm). Maxillary primary molars therefore combine a frequently overlooked MB2 canal with thin apical walls. These findings may help clinicians plan access cavities, select instruments, and perform conservative apical preparation during pulpectomy procedures.