Traditionally, fracture toughness (KIC) analysis of dental resin composites and ceramics has been done mainly using the three-point bend test. In the last decade, the four-point bend test has received more widespread use. Correlation between the two tests is necessary in order to interpret and compare results.
Aim: This preliminary study aimed to compare the fracture toughness of three resin composites using the three-point and four-point bend tests.
Methods: Sixteen single-notched bar-shaped specimens, 30 mm x 5.2 mm x 2.2 mm, were prepared from each of three nano-filled resin composite materials: Clearfil Majesty Esthetic (CME), Kuraray, Japan; Clearfil Majesty Esthetic Posterior (CMEP), Kuraray; Estelite Σ (ES), Tokuyama, Japan. The specimens were light cured, polished with 600-grit silicon carbide paper to remove flash and to obtain smooth surfaces and stored in distilled water at 37º C for 24 h. One half of the specimens for each material was tested using a three-point bend test device and the other half using a four-point bend test with a universal testing machine (Instron, 5544 - C7208, Canton, MA) at a cross-head speed of 0.5 mm/min until fracture. Statistical analysis was carried out using one-way ANOVA and Tukey's posthoc test at α = 0.05.
Results:
| KIC in MPa m0.5, Means (SD) |
| |||
Test | CME | CMEP | ES | ||
3-point | 0.80 (0.07) | 1.41 (0.08) | 0.86 (0.09) | ||
4-point | 0.95 (0.10) | 1.36 (0.21) | 0.93 (0.06) | ||
The only significant difference was for CME, which showed a higher fracture toughness value when tested using the 4-point bend test.
Conclusions: The fracture toughness of one resin composite varied according to the test method used. Further studies are required.