Micro–Computed Tomographic Evaluation of the Influence of Root Canal System Landmarks on Access Outline Forms and Canal Curvatures in Mandibular Molars

• We presented 3 access outline designs based on different anatomic landmarks.
• Conservative access shapes maintain original canal curvatures.
• Orifice relocation was greater for radicular-based access designs.
• Decreasing the angle of curvature is directly related to selective dentin removal.

IntroductionThis study investigated the influence of anatomic root canal system landmarks on access outline forms of mandibular molars and correlated these to the theoretical distance of orifice relocation and changes in canal primary curvature.MethodsThirty relatively calcified human mandibular molars were selected and examined by micro–computed tomographic imaging. Three-dimensional volume reconstructions were made, root canal system landmarks identified, and plotted: canal orifices, canal position at the furcation level, and pulp horn location. Each landmark was separately projected onto the occlusal surface, and 3 access designs were respectively proposed: (1) minimally invasive, (2) straight-line furcation, and (3) straight-line radicular. For each access design, the theoretical distance of orifice relocation and canal primary curvature were determined. Data were submitted to 2-way repeated measures analysis of variance (α < 0.05).ResultsThe orifice relocation distance required to obtain each type of access outline was greater for radicular-based accesses (0.97 ± 0.32 mm) than for furcation accesses (0.52 ± 0.30 mm, P < .001) and resulted in a greater change in canal primary curvature (P < .001; 15.9° ± 4.6° and 9.4° ± 4.3°, respectively). The canal primary curvature for each access outline type was statistically different from each other (P < .0001), whereas the minimally invasive access showed the highest mean angle (40.1° ± 8.4°) followed by the straight-line furcation (30.7° ± 7.5°) and the straight-line radicular accesses (24.2° ± 8.4°).ConclusionsThe use of different landmarks to establish access outline designs affected the primary angle of curvature in relatively calcified mandibular molars.