下颌第一磨牙根管形态：Mandibular First Molar
eparations. It will then be necessary to remove cuspal hard tissue or restoration to locate the orifice. As part of the access preparation, the unsupported cusps of posterior teeth must be reduced. Remember, this tooth, like all posterior teeth, should always receive full occlusal coverage after endodontic therapy. Therefore a wider access cavity to locate landmarks and orifices is better than ignoring one or more canals for the sake of a "conservative" preparation, which may lead to failure. Skidmore and Bjørndal stated that approximately one third of the mandibular first molars studied had four root canals. When a tooth contained two canals, "they cither remained two distinct canals with separate apical foramina, united and formed a common apical foramen, or communicated with each other partially or completely by transverse anastomoses. If the traditional triangular outline were changed to a more rectangular one, it would permit better visualization and exploration of a possible fourth canal in the distal root." Multiple accessory foramina are located in the furcation areas of mandibular molars. They are usually impossible to clean and shape directly and are rarely seen, except occasionally on postoperative radiographs if they have been filled with root canal sealer or warmed gutta-percha. It would be proper to assume that
