Dependence of In Vitro Fracture Strength of Adhesive Core Buildup and Crown Complexes on Preparation Design and Cementation Technique

Purpose: To evaluate the fracture resistance of teeth restored using an adhesive core material placed under artificial crowns without pins or posts and to assess the effect of different preparation designs and cementation techniques (glass ionomer compared with adhesive cementation) used for the crowns. Materials and Methods: Eighty-three intact molars were collected. Sixty-seven teeth were decoronated (test groups and one control group), a 2-mm circular ferrule design was prepared, and four different preparation designs (2-mm- or 1-mm-deep cavities and 2-mm- or 1-mm-thick walls) were used. Three control groups were also established. Cores were built up using an adhesive material. After preparation, standardized artificial crowns (cobalt-chromium alloy) were fabricated. Half of the crowns in the test group (n = 32) were cemented using Panavia (P group); glass-ionomer cement was used for the other half (KC group). All teeth were exposed to 10,000 thermal cycles and loaded until fracture. Statistical analysis was performed, including nonparametric tests (Mann-Whitney U-test) and ANOVA. Results: In the P group, the fracture strength was significantly (p = 0.004) higher (591.75 ± 177.95 N) than in the KC group (430.18 ± 193.67 N). The effect of the preparation design was more pronounced in the KC group. In all groups simulating the most moderate type of tooth decay (2-mm-deep cavity and a 2-mm-thick wall), the fracture strength was comparable with that of intact teeth. Results from ANOVA showed that the type of cementation of the crowns affected fracture strength. Conclusion: Fracture strengths of adhesive core/crown complexes are greater when an adequate cavity for retention (at least 2 mm deep) is prepared and the crown is luted. Keywords: cores, cementation technique, fracture strength, artificial crown, preparation design