Fracture Toughness Of Resin Composites Research Articles

Quantitative fractography as a novel approach to measure fracture toughness of direct resin composites

Dental resin composites generally fail from small cracks. Large crack techniques are not representative of in vivo failures. Quantitative fractography relies on the observation of small “natural flaws”. This study investigates the effect of flaws that occur from fabrication and handling on the measurement of fracture toughness for four different direct resin composites. Microtensile dog-bone shaped specimens for each of four composites were fractured to measure the strength. In addition, we measured crack sizes of the fracture initiating cracks and determined the fracture toughness from these measurements using quantitative fractographic analysis on selected specimens. The characteristic strengths (28–51 MPa) and Weibull moduli (4.9–7.8) were also determined and related to the toughness values (0.5–0.9 MPa m1/2) obtained. The elastic moduli (5–10 GPa) were measured using an indentation technique that has not been used before for direct resin composites. The indentation technique offers an alternative method for small specimens. Quantitative fractographic analysis offers a useful technique to assess fracture toughness of resin composites from cracks of the same size as observed in practice. The toughness of the direct resin composites results from a balance between the size, number and shape of filler particles and the viscosity of the resin matrix.

The effects of different liquid medias on dental composite fatigue and mechanical properties

The purpose of this study was to investigate the effect of various pH solutions on the surface mechanical properties and fracture toughness of resin composites with different micro-structure. Thirty specimens including 3M Filtek Z350 XT (nanofiller), Superlux (microhybrid), and TPH3 (nanohybrid) composites were selected and prepared for tests. Sorption, solubility, flexural strength, and flexural elastic modulus were measured according to an international standard after immersing the specimens into fruit juice, soda water, and milk solutions. Fracture toughness was evaluated after cyclic loading and analyzed under SEM. Filtek Z350 XT, TPH3, Superlux showed significantly different sorption and solubility values. In all materials, the flexural strength and flexural elastic modulus values were influenced to a greater extent by the fruit juice than the soda water. However, neither flexural strength nor flexural elastic modulus was significantly influenced by milk.

Effect of Bleaching on Fracture Toughness of Resin Composites

This study determined the effect of bleaching agents on the fracture toughness of composite materials. Four nanofilled resin composites were evaluated: Filtek Supreme Plus, Tetric EvoCeram, Premise and Esthet-X. Four concentrations of bleaching agents were tested: Opalescence PF 10%, 20%, 35% and 45%. Fifty specimens of each composite conforming to ASTM guidelines for the single edge notch bar-shaped specimen were fabricated in a metal mold. The specimens were stored in artificial saliva at 37 degrees C for a minimum of 24 hours prior to exposing them to the bleaching agents. Ten specimens of each material were used as controls. Forty specimens of each brand were evenly divided into four groups for bleaching agent application (n = 10). The resin composites were bleached on both sides for 14 days. The specimens were then subjected to a three-point bending test with a crosshead speed of 0.2 mm per second. The fracture toughness (K(Ic)) was calculated. The control group K(Ic) value of Esthet-X was significantly higher than that of the other composites in the controlled groups. Bleaching agents significantly improved the fracture toughness values of Filtek Supreme Plus. The application of bleaching agents did not significantly change the fracture toughness values of the other nanofilled resin composites tested.

Microf racture Mechanisms of Dental Resin Composites Containing Spherically-shaped Filler Particles

The effects of spherically-shaped filler particles on bending strength, bending elastic modulus, and fracture toughness of resin composites were studied. The filler content was changed by 0, 20, 40, 60, and 70 wt%. Bending properties and fracture toughnesses were determined on three-point bending specimens. Acoustic Emission (AE), i.e., the elastic wave released from a localized source in the material, was detected by sensors of a high-sensitivity and low-noise resonance type during the fracture toughness test. Detected acoustic emission signals were analyzed for parameters such as amplitude, events, and locations. The fractured surface was examined by a scanning electron microscope. The bending strength and the fracture toughness showed almost the same trend in their increasing rates by filler content, but the elastic modulus showed a much higher increasing rate. A microfracture mechanism of the dental resin composites containing spherically-shaped filler particles is proposed based on the results obtained from the AE-releasing pattern, two-dimensional AE location, and fracture surface findings. In addition to the toughening effects of crack pinning and crack branching, which are observed in the usual commercial resin composites, crack-deflecting effects are confirmed in this new type of dental resin composites.