Aim: Evaluate the prevalence of mesiolingual canal prevalence orifice in mesiobuccal roots of maxillary first molars using five methods of visualization.
Materials and methods: About 73 first permanent maxillary molars were analyzed. Visual clinical analysis of the presence of the fourth canal was performed using a straight endodontic exploratory probe (EXDG16®) and a K10 manual file (SybronEndo®). Dental elements that were not located on the fourth canal were analyzed with the aid of a magnifying glass (Zeiss®) with a 2.5-fold increase and those teeth in which the fourth canal was not found went through the examination with clinical surgical microscope (OPTO®) with magnification of 20 times with both the explorer and endodontic file. Next, a periapical radiography of the teeth was performed in the teeth in which the mesiolingual canal was not yet found to observe the presence or absence of the fourth canal. Afterward, the teeth in which the canal was not yet located were scanned using the microtomography equipment (SkyScan®), at 100 kV and 100 μA, with an isotropic resolution of 16 μm.
Results: The mesiolingual canal was located in 70 teeth (95.8%) and in only 3 teeth it was not identified.
Conclusion: The visual method in the fourth canal search has limitations, whereas the composite magnifying glass, the clinical surgical microscopy, and the computerized microtomography are efficient methods for locating the fourth canal in the upper first molars.
Clinical significance: The anatomical complexity of the first maxillary molars is one of the factors that leads to high failure rates in the endodontic treatments of this group of teeth. In most clinical situations, the mesiolingual canal goes unnoticed by professionals, since conventional radiographs do not always allow the visualization of all root canals. Determining an effective method for locating the mesiolingual canal is of paramount importance to the success of endodontic treatment.
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