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Adhesive fracture at cement–post interface; or (e) Cohesive fracture of post. Resin-dentin interdiffusion zones
were examined with a scanning electron microscope (SEM) (model 5800 LV, Tokyo, Japan).
Results and discussion
Two-way ANOVA revealed that the bond strength values were significantly affected by the resin-based
luting agent (
P
<0.0001) and the post space region (
P
<0.0001). There was no significant interaction (
P
=0.474)
between the resin-based luting agent and the post space region.
Table 1.
Regional push-out bond strength values (mean ±SD) in MPa
Variolink II
Panavia F 2.0
RelyX Unicem
Coronal
10.92±7.52
A
12.56±4.64
A
18.72±8.67
A
Middle
6.59±2.62
M
6.24±2.50
M
17.05±6.30
N
Apical
2.38±1.80
X
5.13±1.90
Y
15.80±8.67
Z
*Mean values with the same letter in each row indicated no significant difference at
P
<.05
*Mean values connected with a vertical line in each column indicated no significant difference at
P
<.05
The mean bond strength values and standard deviations at the coronal, middle, and apical regions for
each cement were shown in Table 1. At the coronal region, even though RelyX Unicem provided the highest
average bond strength value, statistically significant difference was not presented among the three luting agents
(
P
>0.05). High standard deviation might create similar bond strength values although the RelyX Unicem group
had nearly double the bond strength of Variolink II. Most of the bond strength tests using tooth structure as the
bonding substrate suffered from the high standard deviation values because there was a variation of individual
teeth, although the teeth collection procedure was controlled. At the middle and apical region, RelyX Unicem
showed a significantly higher bond strength than those of Panavia F 2.0 and Variolink II. The etch-and-rinse
system, Variolink II, and the self-etch system, Panavia F 2.0 seemed to provide similar bond strengths at all
regions except the apical region where the bond strength of Variolink II was the lowest at only 2.38 MPa.
The reason that higher bond strength was obtained from RelyX Unicem might be due to the moisture
tolerance behavior. Some water might remain in the canal, especially within the dentinal tubules due to poor
visibility and difficulty in moisture control. The monomer of RelyX Unicem can react with basic salts and tooth
apatite through functional groups modified by phosphoric acid. Water is formed in this neutralization. This step
increases hydrophilicity, improving adaptation of the cement to the tooth structure and moisture tolerance. In a
previous study, Bitter
et al
. (2006) reported the same result that RelyX Unicem had a significantly higher bond
strength compared with other materials, while Variolink II had a significantly lower bond strength compared with
others. SEM observation was performed to evaluate the quality of the hybrid layer and resin tag formation, but
characteristics shown in SEM micrographs might not be able to represent the quantitative bond strength values.
