Objectives: This study investigated the surface hardness of the thin layer in two dual-cured luting agents {Nexus 2 (NX) and Variolink II (VL)} irradiated through or not through different thickness (1 through 5 mm) of CAD/CAM ceramic. Methods: A piece of adhesive tape with a circular hole was positioned on the ceramic plate surface to control the cement layer (approximately 50 µm). The ceramic plate with cement paste within the circle was placed on a clear glass to obtain a flat surface, and the material was polymerized using a visible-light-curing unit for 40 s. The surface hardness was recorded at a series of time intervals up to 5 days, starting from the end of a light-irradiation period. Data were analyzed by repeated measure analysis of variance (p<0.05). Results: The increase in hardness was more rapid over the first 0.5 h; thereafter a low rate increase continued up to maximum hardness. The rate is slower for ceramic thickness of 4 and 5 mm compared with thinner ceramic. For the VL, the differences in the KHN values at between directly and 120 h of post-irradiation were higher than that of the NX at all ceramic thickness. Conclusion: Ceramic thickness had a significant affectation on hardness development in both dual-cured luting agents, especially when ceramic thickness was more than 4 mm. The polymerization of NX seems to be more dependent on light exposure compared with VL.
|
|
Knoop hardness number (KHN) |
|||||||||||
|
Post-irradiation time (h) |
CAD/CAM ceramic thickness (mm) |
|||||||||||
|
0 |
1 |
2 |
3 |
4 |
5 |
0 |
1 |
2 |
3 |
4 |
5 |
|
|
Luting agent |
Nexus 2 |
Variolink II (high viscosity) |
||||||||||
|
0 |
23.5 (0.5) |
24.0 (0.9) |
21.8 (0.4) |
20.2 (0.6) |
13.6 (1.2) |
- |
28.0 (0.9) |
28.0 (0.4) |
25.9 (0.4) |
23.5 (0.3) |
17.4 (0.9) |
14.4 (0.9) |
|
0.5 |
28.0 (0.3) |
28.3 (0.9) |
27.2 (0.8) |
25.6 (0.4) |
18.6 (1.1) |
12.0 (1.0) |
32.6 (0.5) |
32.3 (0.4) |
31.5 (0.5) |
29.8 (0.4) |
23.5 (0.9) |
20.2 (0.8) |
|
1 |
30.0 (0.4) |
30.0 (0.3) |
28.5 (0.5) |
26.4 (0.2) |
19.7 (1.3) |
12.8 (1.2) |
34.2 (0.4) |
34.0 (0.3) |
33.1 (0.5) |
31.5 (0.8) |
25.5 (1.1) |
22.1 (0.6) |
|
4 |
31.7 (0.4) |
32.1 (0.6) |
31.0 (0.4) |
28.6 (0.5) |
21.3 (1.4) |
13.7 (1.2) |
37.8 (0.4) |
37.9 (0.8) |
36.6 (0.7) |
35.1 (0.4) |
29.6 (1.3) |
24.9 (1.0) |
|
24 |
33.4 (0.6) |
33.4 (0.8) |
31.7 (0.3) |
30.0 (0.8) |
23.9 (1.6) |
15.1 (1.4) |
40.5 (0.5) |
40.4 (0.8) |
38.8 (0.3) |
37.5 (0.5) |
35.0 (1.6) |
29.4 (0.2) |
|
120 |
33.5 (0.2) |
33.5 (1.1) |
32.4 (0.9) |
30.7 (1.0) |
24.8 (2.6) |
17.3 (2.5) |
40.3 (0.5) |
40.4 (0.5) |
38.6 (1.0) |
38.0 (0.5) |
35.2 (2.3) |
29.7 (1.5) |