Objectives: New CAD-CAM blocks with different compositions have recently been developed. To characterize the fracture toughness (FT) of such materials, a chevron-notched beam FT method has widely been used, in particular as standard FT method for large specimens. This study aimed to measure FT of different CAD-CAM blocks using a new simplified and miniaturized method.
Methods: Fifteen mini-fracture toughness specimens (mini-FT; 1.5x2.0x.14mm) were prepared for each CAD-CAM material: hybrid ceramic (Cerasmart, GC), feldspar ceramic (Vitablocs Mark II, Vita Zahnfabrik) and zirconia-reinforced lithium-silicate glass ceramic (Vita Suprinity, Vita Zahnfabrik). For each mini-FT specimen, a single notch was prepared using a 150-µm diamond blade under water-cooling. The specimens were loaded until failure in a 4-point bending test setup.
Results: Significant differences in mini-FT were observed between the different CAD-CAD blocks. The hybrid ceramic material performed better at the level of the Weibull characteristic strength, followed by the zirconia-reinforced lithium-silicate glass ceramic and feldspar ceramic.
CAD-CAM block
| Mean1
| SD
| n
| β2(m)
| η3
| b104
| Characteristic strength5
|
Cerasmart
| 3.2
| 0.3
| 15
| 10.7
| 3.38
| 2.74 [2.33-3.02] (a)
| 3.38 [3.21-3.57] (a)
|
Vita Suprinity | 2.8
| 0.3
| 15
| 9.9
| 2.94
| 2.35 [1.98-2.61] (a,b) | 2.94 [2.79-3.12] (b)
|
Vitablocs Mark II
| 2.2
| 0.1
| 15
| 18.5
| 2.29
| 2.03 [1.85-2.15] (b)
| 2.29 [2.22-2.37] (c)
|
1Mini-FT in MPa√m, 2Weibull shape parameter, 3Weibull scale parameter, 4Confidence interval at 10% reliability, 5Confidence interval at 63.2% reliability (groups with the same letter are statistically not different).
Conclusion: The mini-FT test enabled to differentiate between the CAD-CAM materials regarding fracture toughness; the hybrid ceramic presented the highest mini-FT, which was also significantly higher than that of the feldspar ceramic.