THE JOURNAL OF - Dentsply

Raffaelli et al
Table 1 Groups of materials and techniques
Groups Adhesive Activator Adhesive Cement Ceramic disk
thickness (mm)
1 Prime & Bond NT no LC DC 3
2 XP BOND no LC DC 3
3 XP BOND yes NC DC 2
4 XP BOND yes NC DC 3
5 XP BOND yes NC DC 4
6 XP BOND yes NC CC 2
7 Syntac* - NC CC 2
NC: not cured (mix with SCA is applied, but not light cured); LC: light cured (light cured before placement); DC: dual curing (Light is applied on the mixed
cement); CC: chemically cured (no light is used at all). *According to the directions for use, application and light curing of Heliobond is mandatory when combined
with self curing materials.
MATERIALS AND METHODS
Bonding was performed on 70 noncarious human third molars
that were extracted after informed consent had been obtained.
They were stored in a 1% chloramine T solution at
4°C and used within one month following extraction. Prior to
the bonding experiments, the teeth were retrieved from the
disinfectant solution and stored in distilled water, with four
changes of the latter within 48 h to remove the disinfectant.
Tooth Preparation – Bonding to Deep Dentin
Bonding was performed on the occlusal surfaces of deep
coronal dentin. The occlusal enamel and the superficial
dentin of each tooth were removed using a slow-speed saw
(Isomet, Buehler; Lake Bluff, IL, USA) under water cooling.
The tooth surfaces were polished with wet 180-grit SiC papers.
The teeth were divided into 7 experimental groups of
10 teeth each. The experimental dentin groups are listed in
Table 1.
Coupling of Processed Ceramic
Empress 2 blocks (shade A2) were reduced with the Isomet
saw under water cooling to produce blocks with dimensions
similar to those of the teeth to be bonded. Each reduced
block was then sectioned with the Isomet saw to produce
2-, 3-, or 4-mm-thick, parallel-sided ceramic onlays. The inner
surface of each ceramic onlay was sandblasted with 50-
μm alumina, etched with a hydrofluoric acid gel for 90 s,
washed, air dried, and silanized using Calibra silane
(Dentsply).
To bond the ceramic disks to the dentin surface, the
bonding systems and the resin cement were used following
manufacturer’s instructions. As a curing device, a QTH light
(Dentsply DeTrey) was used (power output: 800 mW/cm 2 ).
The intensity of the curing light was tested before and after
curing with a radiometer. The bonded specimens were
stored in distilled water at 37°C for 24 h before further laboratory
processing.
TBS Evaluation and SEM Fractographic Analysis
Each tooth was sectioned occluso-gingivally into serial slabs
using an Isomet saw under water cooling. The two slabs from
each tooth were further sectioned into 0.9 x 0.9 mm ceramic-dentin
beams, according to the technique for the
nontrimming version of the microtensile test. 6 Each group
provided 37 to 53 beams for bond strength evaluation. Premature
failures that occurred during sectioning were recorded.
The specimens were stressed to failure under tension using
a universal testing machine (Model 4440, Instron; Canton,
MA, USA) at a crosshead speed of 1 mm/min. The data
were analyzed using one-way ANOVA and Tukey’s multiple
comparison tests at α = 0.05.
Representative fractured beams from each of the 7
groups were air dried and sputter coated with gold/palladium
for examination with a conventional SEM (Jeol; Tokyo,
Japan).
Statistical Analysis
Three different one-way ANOVAs were performed, each involving
different groups (Tables 2 to 4). The first two analyses
were performed in the groups with 3-mm and 2-mm ceramic
disks, respectively. The last analysis was performed
on groups with 3 different ceramic thicknesses (2, 3, and 4
mm) when samples were luted with XP+SCA+Calibra DC.
Premature failures were excluded from the statistical analysis.
It was also verified that the tooth of origin was not a significant
factor for bond strength.
As the bond strength data were normally distributed (Kolmogorov-Smirnov
test) and groups had homogeneous variances
(Levene test), one-way ANOVA was applied to test for
significance of differences among the tested groups, followed
by Tukey’s test for post-hoc comparisons. In all the
analyses, the level of significance was set at α = 95%.
RESULTS
The bond strength values found in this investigation are reported
in Fig 1 and Tables 2 to 4.
276 The Journal of Adhesive Dentistry