Abstract
It has been reported that the incidence of fractures is markedly high in endodontically treated immature teeth. Clinically, it has been thought that resin composites and dentin bonding agents being used for the restoration of the access cavities may provide, to some extent, resistance against fracture to the pulpless immature teeth.
The purpose of this study was to examine the effect of restorations on the physical strength of pulpless immature incisors. In the present study, we examined the effects of access cavity restorations with several resin composites and dentin bonding agents with respect to the resistance to fracture of pulpless immature bovine incisors when the breaking loads were applied slowly on them.
The materials were 220 bovine incisors, divided into 22 groups. Each group consisted of 10 incisors. The access cavities and root canals of the teeth were restored using several resin composites, and dentin bonding agents, with or without metal inlays, or stainless steel posts.
The findings observed during the fracturing processes as well as the load curves were compared among the groups of different restorative methods. The resistance to fracture of the teeth was subjected to t-test to examine statistically the diffenrence between the experimental groups. The results were as follows.
1. The access cavities of the root canals were filled with resin composites and dentin bonding agents. When the long cylinder was used for the fracture experiment and attached into the road cell of the testing machine, most of the teeth fractured according to the course from the lingual crown surface to the labial cervical line, and the fracture patterns were similar to those observed in human endodontically treated immature incisors. By this fracture method, the teeth were significantly strengthened by filling the access cavities with resin composite alone or some resin composites with dentin bonding agents, more than the empty cavity.
2. In the teeth restrated with labial metal inlays or the deeper cavity with resin composite and dentin bonding agents, cervical root fracture were more frequent. In the teeth treated with full length posts and dentin bonding agents, the mean resistance to the fracture of the teeth was higher. A statistically significant difference was seen between the mean resistance to fracture of the teeth restored with another method. Incompleted root fracture, however, was observed in most teeth.
