THE JOURNAL OF - Dentsply

Blunck/Zaslansky
composites were used. The composite resin was inserted in
two increments (initially placed at the cervical margin), and
each increment was light cured (Astralis 10 light-curing unit,
Ivoclar Vivadent; Ellwangen, Germany) for 40 s. After finishing
and polishing (Sof-Lex Pop-on Nr. 1981 SF/F/M/C 3M
ESPE; St Paul, MN, USA), the teeth were returned to water
storage for 21 days, followed by 2000 cycles of thermocycling
(TC) between +5 and +55°C.
Prior to and after TC, impressions were taken with a
polyvinylsiloxane material (Silagum light body, DMG; Hamburg,
Germany) and replicas of the restoration and surrounding
tooth structures were produced. These were cast
with an epoxy resin following precise manufacturer guidelines
(Stycast 1266 Part A + B; Emerson and Cumming; Westerlo-Oevel,
Belgium). Once fully cured, each replica was sputter-gold
coated (SCD 030, Balzers Union; Balzers, Liechtenstein)
in preparation for inspection by SEM. Similar impression
and TC procedures were repeated after 1 year of water
storage, and for 11 products also after 3 years.
The effectiveness of each bonding system was assessed
by evaluating the margins of the restorations at the
dentin/composite and enamel/composite interface. Measurements
were performed using a dedicated SEM (AMRAY
1810, Amray; Bedford, MA, USA) and all replicas were viewed
at a magnification of 200X, and classified according to the
state of the margin in different areas in order to numerically
quantify the marginal qualities, as detailed in Table 2. By
using this method, each segment of the tooth/restoration interface
was imaged and ranked according to defined quality
criteria. These were then converted into percentage of the
total margin length, in dentin and enamel independently.
Statistical evaluation was performed using an SPSS statistical
software package (SPSS Software; München, Germany).
Within each sample group, significant differences
were determined using the nonparametric Wilcoxon test. For
comparison between the different treatment groups, the
nonparametric Kruskal-Wallis test was used followed by Bonferroni
adjustment. The statistics were calculated for the parameter
margin quality 1 (MQ1 = “excellent” or “continuous”
margin). Origin 7.0 SR0 (Originlab; Northampton, MA, USA)
was used for the weighted regression and Microsoft Excel
(2000) was used to determine the slopes between MQ1
rankings at different stages of the experiment.
RESULTS
The results of the 14 test groups were compared with those
of the 3 reference multi-bottle adhesives OptiBond FL, Syntac,
and Clearfil SE Bond. Figure 1 is a box-and-whiskers plot
of the marginal quality MQ1results determined for the enamel
margins, depicting the median, 25 and 75 percentiles.
The main result seen here is that after 1 year of water storage
(Fig 1a) and following a second TC, a reduction (significant
at p < 0.05) in the amounts of “continuous margins”
(MQ1) is seen for G-Bond, AQ-Bond, Hybrid Bond, and Oneup
Bond F Plus. No significant difference was found between
any other of the groups and the reference adhesives. After
3 years of water storage and a third TC, only AQ Bond had a
substantially lower MQ1 score (p < 0.05).
Table 2 Criteria for the marginal analysis in the SEM
Margin
quality
Definition
1 Margin not or hardly visible, no or slight marginal
irregularities*; no gap
2 No gap but severe marginal irregularities*
3 Gap visible (hairline crack up to 2μm, no marginal
irregularities*
4 Severe gap (more than 2μm), slight and severe
marginal irregularities*
* The term "marginal irregularities" refers to porosities, marginal
restoration fracture, or bulge in the restoration
Figure 2 shows the MQ1 results that were obtained for
each product in dentin following each of the three TC treatments.
Following the first TC (Fig 2a), no statistically significant
differences were found for any of the groups. The TC after
1 year of water storage (Fig 2b) revealed a decrease in
MQ1 for Prompt L-Pop in the 1999 version, Adper Prompt L-
Pop/Tetric Ceram, and One-up Bond F Plus (p < 0.05). After
three years of water storage and a 3rd TC both Prompt L-Pop
(1999) and Adper Prompt L-Pop/Tetric Ceram were found to
have substantially lower MQ1 scores than the reference
groups (p < 0.05). Data for One-up Bond F Plus, G-Bond, AQ-
Bond, Hybrid Bond, and tri-S Bond are missing for three
years, as these materials were not available for the full duration
of the present study.
To better understand the dynamics of the results presented
in Fig 2 and to obtain insights into the effects of TC
and water storage, plots were produced of MQ1 for each
group before and after TC at 21 days (T1 and T2), after 1 year
of water storage (T3 and T4) and after 3 years of water storage
(T5 and T6). Only the plots for the reference multi-bottle
products are shown as examples in Fig 3. Each data point
(T1-T6) represents the median MQ1 values with the corresponding
error bars that are the standard error of the mean
(SE). It must be emphasized that in these plots, the time intervals
between the data points are not equal. The trends of
the T1-T2, T2-T4, and T4-T6 segments were calculated in
each graph, because the effects of water storage alone (segment
T2-T3 after 1 year and segment T4-T5 after 2 additional
years) were too small to be directly and reliably visualized.
Thus, the purpose of TC was to challenge the bonds
of the restorations in order to test the marginal integrity. Further
analysis was then used to explore the joint effects of TC
after the different water storage periods.
The T1-T2, T2-T4, and T4-T6 slopes as well as the statistical
significance (p) of the difference between each pair of the
corresponding MQ1 values (obtained with the nonparametric
Wilcoxon rank test) are presented in Table 3, columns A to
F (shown as 1 st water storage [WS] vs 1 st TC, 1 st TC vs 2 nd TC,
2 nd TC vs 3 rd TC). We also calculated trends in the overall adhesive
effectiveness by fitting linear regression lines (error
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