Fracture strength of different core build-up designs

Purpose: To investigate the resistance to fracture of three crown and core combinations, made with different core build-up systems on human teeth, usi ng a standardized test method. Materials and Methods: The anatomic crowns w ere removed from six groups (n = 8) of endodontically treated, human premol ars in conformity with a brass master dye, using the Celay duplicating devi ce. Three of these groups were provided with a core build-up with-out an en dodontic post (Ti-Core, Photo-Core and Ketac-Molar); two other groups were provided with a core build-up with an endodontic post (a cast post and core , and a composite with a silica post), and one group was not provided with a core. All groups were then prepared in conformity with a master dye. This preparation ended in axial dentin, 2 mm apical from the core build-up. Thu s in the sixth group (premolars without a core build-up), this preparation only affected the 2 mm axial dentin (ferrule), which resulted in a small re tention area (2 nim axial dentine) for the crown. Finally, a standard crown was cemented and 24. hrs afterwards loaded until fracture in an Instron te sting machine at an angle of 45 degrees. For comparison with the standardiz ed procedures, a seventh group (Photo-core without post) was prepared manua lly, with dimensions similar to the standardized groups. Results: Within th e standardized test set-up no significant difference in strength between th e 6 groups could be demonstrated. Only in the case of the hand-made Photo-C ore and the cast core was the fracture, load significantly different (P= 0. 01). In addition, this hand-made group displayed a larger standard deviatio n than the standardized groups. Taking into consideration the fact that the maximum bite force in the bicuspid region is about 580 N, these tests show ed that within the limitations of the stan-dardized test set-up, where the samples had no history of fatiguing, a core build-up without a post is an a lternative for the conventional cast core. In this study, the fabrication o f the standardized samples proved to be accurate, fast and economical. This method also enables the evaluation of the performance of core and crown de sign combinations in relationship to the amount of remaining tooth structur e by using different master dies and, moreover, to reduce the high standard deviation in this kind of research.