Fracture toughness of various core build-up materials

PURPOSE: The purpose of this investigation was to compare the fracture toughness of several core materials. MATERIALS AND METHODS: Five core build-up materials were tested: (1) glass ionomer, (2) resin-modified glass ionomer, (3) titanium-reinforced composite, (4) composite resin with fluoride, and (5) amalgam. Fracture toughness determinations were made using 3-point flexure of beams with a central single-edge notch. The notch was standardized by the use of a special mold into which each of the materials was condensed. Ten beams of each material were tested on an Instron test machine (Instron Corp, Canton, MA) at a crosshead speed of 1.25 mm/min. The maximum loads were determined from which the fracture toughness values (KIC) were calculated. The data were analyzed statistically using analysis of variance and t tests. RESULTS: The mean fracture toughness value in MN.m-3/2 for each of them is as follows: (1) glass ionomer, 0.717 +/- 0.071; (2) resin-modified glass ionomer, 0.747 +/- 0.061; (3) titanium-reinforced composite, 1.409 +/- 0.051; (4) composite resin with fluoride, 1.660 +/- 0.086; and (5) amalgam, 1.521 +/- 0.081. There was no significant difference in the KIC values for the glass ionomer-based materials, and both of these were significantly lower than amalgam, titanium-reinforced composite resin, and composite resin with fluoride (p < .001). CONCLUSION: The titanium-reinforced composite resin, the composite resin with fluoride, and amalgam materials showed fracture toughness most likely to withstand the stresses generated during mastication.