Coronally, the maxillary second molar closely resembles the maxillary first molar, although it is not as square and massive. Access in both teeth can usually be adequately prepared without disturbing the transverse ridge. The second molar is often easier to prepare because of the straight-line access to the orifices. The distinguishing morphologic feature of the maxillary second molar is its three roots grouped close together, and sometimes fused. The parallel root canals are frequently superimposed radiographically. They are usually shorter than the roots of the first molar and not as curved. The three orifices may form a fiat triangle, sometimes almost a straight line. The floor of the chamber is markedly convex, giving a slightly funnel shape to the canal orifices. Occasionally the canals curve into the chamber at a sharp angle to the floor, making it necessary to remove a lip of dentin so the canal can be entered more in a direct line with the canal axis. Complications in access occur when the molar is tipped in distal version. Initial opening with an end-cutting fissure bur is followed by a short-shanked round bur, which is best suited to uncover the pulp chamber and shape the access cavity. Then small hand instruments are used to establish canal continuity and working length. The bulk of the cleaning and shaping may now be accomplished with engine-mounted files on reciprocating handpieces. To enhance radiographic visibility, especially when there is interference with the malar process, a more perpendicular and distal-angular radiograph may be exposed. All caries, leaking restorations, and pulpal calcifications must be removed prior to initiating endodontic treatment. Full occlusal coverage is mandatory to ensure against vertical cuspal or crown-root fracture. Internal reinforcement, when indicated, should be incorporated immediately after endodontic treatment. (Burns RC, Buchanan LS. Tooth Morphology and Access Openings. Part One: The Art of Endodontics in Pathway of Pulp, 6th Ed. p. 148).
Keywords: micro-computed tomography, micro-ct, marco versiani, micro-computer tomography, high resolution x-ray tomography, dental anatomy, root canal anatomy