Fracture resistance and failure patterns of open apex root teeth with different posts after endodontic treatment

The aim of this study is to investigate the influence of different posts on the fracture mechanics of endodontically-treated teeth with open apex. Forty-eight human maxillary anterior teeth were collected, and the root was transversely sectioned 12 mm under the cementoenamal junction (CEJ). These samples were then randomly divided into two groups, i.e., minor diameter open apex root (group A) and major diameter open apex root (group B), with mineral trioxide aggregate (MTA) placed into the apical 4 mm in the root canals. Subsequently, both groups were respectively further divided into three subgroups as follows: fiber-post (subgroup 1), metal post (subgroup 2) and non-post (subgroup 3) group. Teeth were restored with a composite resin crown and tested by using a universal testing machine at the rate of 1 mm/min cross-head. Values of the maximum fracture resistance and failure patterns were recorded and compared among all subgroups. In addition, the changes of MTA properties were carefully examined via X-ray photography. Our results indicate that (1) In group A, the mean value of fracture resistance for teeth restored with fiber posts were statistically higher than that with either metal post or non-post; (2) In group B, there was no statistically significant difference in the mean value of fracture resistance among three subgroups; (3) No statistical significance in the mean value of fracture resistance was found between group A and group B; (4) The failure modes of most samples (58%) were irreparable; (5) MTA in two teeth developed cracks after loading tests. In conclusion, endodontically-treated teeth restored with fiber posts are more resistant to fracture than those restored with either metal posts or non-post, and most of the fracture modes are catastrophic in nature.