FRACTURE STUDIES OF SELECTED DENTAL RESTORATIVE COMPOSITES

Objectives. The purpose of this study was to evaluate the flexure stre ngth, elastic modulus, and fracture toughness (mode I, mode II, and mi xed mode) of resin and four specially made dental restorative composit e materials. Methods. Testing was done on prismatic bars in flexure an d disk specimens in diametral compression. Fracture strengths were ana lyzed using Weibull statistics. Statistical analysis consisted of a on e-way analysis of variance followed by a Tukey multiple means analysis for each of the materials. In addition, the fracture strengths were a nalyzed using Weibull statistics due to the brittle behavior exhibited by these materials. Results. The experimental results showed that the addition of fillers resulted in a significant three-fold increase in flexure modulus and a significant 30-50% increase in fracture toughnes s from the resin. As was indicated by the different Weibull modulus va lues, strength data obtained from four-point bending were not related with strength data from three-point bending. A straight notch vs, a re latively sharp V-notch gave higher fracture toughness values. Fracture toughness was dependent on the depth of a straight notch and was prac tically independent of the V-notch depth. Mode I and II fracture tough ness in two composites (75Sr and 75Sr10) were carried out on precracke d disk specimens in diametral compression. The results of mode I tough ness were close to those obtained from the flexure testing. The mode I I toughness values were greater than the mode I values by more than 30 %. The data fit an equation of the form KIKIC + (K-II/K-IIC)(2) = 1(wh ere K-I, K-II are the mode I and II stress intensity factors and K-IC, K-IIC are the respective critical values). Significance. Notching tec hnique, testing configuration (three-point vs. four-point loading), an d method of testing (bar vs, disk) have significant effect on the frac ture properties.