Somewhat rectangular from the labial aspect and shovelshaped from the proximal, the crown of the maxillary central is more than adequate for endodontic access and is positioned ideally for direct mirror visualization. This tooth is especially suitable for a first clinical experience because more than a third of its canal is directly visible. Visualization of the canal proper may be enhanced with fiberoptic illumination. The first entry point, with the end-cutting fissure bur, is made just above the cingulum. The direction should be in the long axis of the root. A roughly triangular opening is made in anticipation of the final shape of the access cavity. Often, penetration of the shallow pulp chamber occurs during initial entry. When the sensation of "dropping through the roof" of the pulp chamber has been felt, the longshanked no. 4 or 6 round bur replaces the fissure bur. The "belly" of the round bur is utilized to sweep out toward the incisal; one must be certain to expose the entire chamber completely. It may be necessary to return to the fissure bur to extend and refine the final shape of the access cavity. All caries, grossly discolored dentin, and pulp calcifications are removed at this time. Leaking restorations or proximal caries should be removed and an adequate temporary restoration placed. Conical and rapidly tapering toward the apex, the root morphology is quite distinctive. Cross-sectionally the radicular canal is slightly triangular at the cervical aspect, gradually becoming round as it approaches the apical foramen. Multiple canals are rare, but accessory and lateral canals are common. Kasahara and others studied maxillary central incisors to determine thickness and curvature of the root canal, condition of any accessory canals, and location of the apical foramen. Data revealed that the thickness and curvature of canals showed adequate preparation at approximately a size 60 instrument at the apical constriction, that over 60% of the specimens showed accessory canals, and that the apical foramen was located apart from the apex in 45% of the teeth (Burns RC, Buchanan LS. Tooth Morphology and Access Openings. Part One: The Art of Endodontics in Pathway of Pulp, 6th Ed. p. 136).
Keywords: micro-computed tomography, micro-ct, marco versiani, micro-computer tomography, high resolution x-ray tomography, dental anatomy, root canal anatomy