The purpose of this study was to evaluate the influence of using the dental operating microscope (DOM) for detection of the mesiolingual (ML) canal orifice in extracted maxillary molars compared with unaided vision (no loupes or headlamps).Using a clinical simulation model system, we mounted 39 maxillary molars in a dentoform and placed them into a mannequin. After rubber dam placement and preparation of standard access, 2 attempts were made to locate the ML canal with unaided vision. Then the teeth were examined by using a DOM. Finally, all teeth were sectioned, stained, and evaluated with the DOM for actual presence of an ML canal.ML canal orifices were detected in 20 of the teeth with a sharp explorer and mirror. In the remaining teeth, 12 ML canal orifice were located by using the DOM. Qualitative nonparametric comparisons were used.The results of this study indicate that the DOM provides increased opportunity for the dentist to detect canal orifices.