Methods: CEREC blocks were selected (3M Lava Ultimate-LT [3M ESPE, St.Paul, USA], VITA Enamic-T and Vita Mark II [VITA Zahnfabrik, Bad Sackingen, GER]) and perpendicularly cut with a slow speed water cooled diamond saw. The specimens were finalized in a grinding-polishing machine with silica carbide paper of 600, 1200, 2400 grit until the dimension of 4,0±0,2mm in width, 1,2±0,2mm in thickness was reached for the flexural strength test (n=15) and 1,0±0,1mm in thickness for the CR measurements (n=10).
Three-point bending test (span=13mm, cross-head speed=1mm/min) were performed in a universal testing machine (Triax 50, Controls, Milano, Italy). The fracture load was recorded in N; the flexural strength (σ), Weibull characteristic strength (σ0) and Weibull modulus (m) were calculated.
A spectrophotometer, equipped with an integrating sphere (PSD1000/ISP-REF, OceanOptics, FL, USA) was used for translucency measurements (D65 illuminant, 10° standard observer). The Contrast Ratio was calculated with the formula (CR=Yb/Yw).
Data were statistically analyzed with One Way Analysis of Variance followed by the Tukey Test for post-hoc comparison.
Results: Results are summarized in the following table:
Materials |
σ |
SD |
Sign. |
m |
σ0 |
CR |
SD |
Sign. |
Lava Ultimate-LT |
173,69 |
23,84 |
a |
8,56 |
183,86 |
0,61 |
0,01 |
c |
Enamic-T |
128,63 |
12,72 |
b |
11,69 |
134,33 |
0,59 |
0,02 |
b |
Mark II |
106,39 |
7,80 |
c |
15,41 |
110,05 |
0,54 |
0,02 |
a |
Conclusion: All the tested materials fulfilled the ISO standard 6872:2008 requirements for Class II materials (adhesively cemented single unit posterior crowns) None of the materials fulfilled class III requirements (non-adhesively cemented) The flexural strength result in an inverse correlation with translucency and this factor should be taken into account by the clinicians during the material selection.