To appreciate proper endodontic shaping and obturation, one must have a thorough understanding of pulpal anatomy in the teeth we may be asked to treat. I am providing a link to Versiani, Pecora and Neto, three researchers who have done extensive micro-ct analysis of pulpal anatomy and the many configurations it can take. Once you hit the link, go to the videos on that page and then follow up by clicking on a list on the left of the screen to see other videos showing the anatomy of all the teeth in the mouth in rotational views as well as coronal axial views.
Please note that while the bucco-lingual widths may vary widely, the mesio-distal diameters, with the exception of the palatal root of maxillary molars remains quite thin reflecting the thin diameter of the roots in the mesio-distal dimension. Until we address the variations that occur in the bucco-lingual plane we will not predictably cleanse the canals in that plane while routinely removing excessive tooth structure in the mesio-distal plane via greater tapered rotary preparations.