[Effects of margin designs on fracture strength and pattern of endodontically-treated teeth with no coronal tooth...

To determine the importance of margin design on fracture strength and pattern of endodontically-treated teeth with 0 mm of coronal tooth structure.

Using the CELAY system (MIKRONA, Switzerland), 168 human maxillary central incisors, identical in size and shape, were replicated from bovine teeth. The fracture strength and pattern of 5 types of margin design, three core materials and two levels of remaining coronal tooth structure were examined after 24 hours of water immersion (37 degrees C) under 16 conditions and 83 hours under 6 conditions without cyclic loading, as well as after 83 hours of water immersion with 300,000 cyclic loading under 6 conditions.

In the case of cast metal post-and-cores with 0 mm of coronal tooth structure, both beveled and shouldered shoulder margin designs resulted in a higher fracture strength than chamfer and shoulder ones, achieving almost the same strength of chamfer margin design with 1 mm of coronal tooth structure. In addition, pinhole preparation on the root surface increased the fracture strength of chamfer margin design to the level of those of the above-mentioned two desirable margin designs. From a fracture pattern viewpoint, however, all margin designs were unsuitable for re-restoration of the tooth.

Both beveled and shouldered shoulder margin designs improve fracture strength of endodontically-treated teeth with 0mm of remaining coronal tooth structure.