THE JOURNAL OF - Dentsply

Blunk/Zaslansky
many of the products, change the rank between the initial
water storage period, as compared with the rank after the
first year . We are aware that such ranking might be of limited
use for predicting clinical performance; therefore, clinicians
and manufacturers might need to define criteria for
“adequate performance”, not “better performance”. Clearly
such long-term effects need to be considered in addition to
operation skill and experience, 15,21 both of which are difficult
to account for, therefore consequences of these findings
necessitate further investigations.
The marginal analysis centered on the quantitative evaluation
of MQ1 (“excellent” or “continuous” margin) as a
measure for marginal integrity. It has recently been shown
that such an evaluation provides a good indicator for the
ability of an adhesive system to compensate for the shrinkage
of composite resins during polymerization, as compared
to bond strength tests. 17 The extent to which the present in
vitro results correspond to in vivo data of quantitative marginal
analysis of Class V fillings is not obvious, especially as
there are reports showing that such data are unable to predict
clinical outcome. 17 Nevertheless, results of this study
and trend analysis provide an additional means of determining
objective and standard measures of the physical attributes
of any combination of adhesive system and composites.
It therefore remains to be seen just how such details
match the outcomes of clinical investigations. It is worthwhile
to note that other studies have evaluated the marginal
quality using stress induced by mechanical loading. 12,13
The method employed in this study has the advantage that
TC induces precise and repeatable stress (assuming the coefficient
of thermal expansion of the composites stays constant),
and this concept was used to provide more information
about the effects of water storage at short and long intervals.
The present results are based on SEM evaluation of the
percentage of the different marginal qualities, calculated in
relation to the entire margin length in dentin or enamel independently.
It has been shown that when the same operator
evaluates the same specimens twice, the difference between
the results is in the range of 4%, 26 whereas when two
trained operators evaluate the same specimens, the differences
can reach 10% to 20%. 18 Therefore, all specimens in
this study were prepared and evaluated by the same operator.
It is interesting to note that for most of the products not
displaying a large discrepancy between the initial and intermediate
MQ1 values, the first-year data provide only a moderate
predictor for the longer term trend of deterioration.
Therefore, initial predictors of restorative success have limited
applicability, and more data over long periods of time
are needed. This is unavoidable even in an in vivo setting,
and is important especially when both manufacturers and
clinicians want to know as early as possible which is the best
product. It is, of course, conceivable that storage at higher
temperatures might allow faster answers to these questions.
All-in-one adhesives are rather user friendly; however, certain
indicators have suggested reduced performance that
might be associated with their usage. Compared with twostep
self-etching or etch-and-rinse adhesive systems, lower
bond strength values were reported. 5,14,19,20 It has also
been shown that permeable membranes develop after curing
due to a high hydrophilicity, which allows water movements
through the all-in-one adhesive layer. 30 Sites of incomplete
water removal and subsequent suboptimally polymerized
resins 31 have been described and termed “water
trees”. All these might contribute to extensive degradation
of the adhesive layer, 7,32 but conclusive findings have not
been confirmed. The most recent (to date) one-bottle all-inone
adhesives appear to be susceptible to phase separation
after dispensing the complex mixture of hydrophobic and hydrophilic
components, 34 and this also is assumed to contribute
to bond degradation. 33
This study has presented preliminary results of short- and
long-term water storage effects combined with thermocycling
for control and 14 all-in-one adhesive/composite treatments.
The results show that overall, few if any differences
are found in vitro between the tested products and the reference
materials. Furthermore, based on a quality estimate
associated with the marginal integrity, it has been shown
that early deterioration rates (up to 1 year) can only sometimes
be used as estimates for the rate of bond degradation
over a period of 3 years. Indeed, it seems that deterioration
rates due to storage in water are not dependent on the class
(or generation) of the adhesive: large differences in deterioration
rates seem to exist between different products, and
these are probably associated with the details of the specific
chemistry. Additional studies are still needed in order to
elucidate to what extent – and in which product – deterioration
is critical. These should then be correlated with clinical
studies so that decisive conclusions can be drawn .
It appears that the effects of long-term water storage may
not be as detrimental as usually assumed, if indeed the marginal
integrity estimates are appropriate measures of the
quality and effectiveness of recent generations of dental adhesives.
A statistically significant decrease in the amount of
MQ1 was only found in 3 out of 14 tested all-in-one adhesives
after 1 year water storage. However, in enamel, the
marginal analysis revealed fewer “continuous margins” than
the control groups for G-Bond, AQ Bond, Hybrid Bond, and
One-up Bond F Plus, and this was already observed after 1
year of water storage.
As new results of clinical evaluations emerge, and with a
growing body of data from in vitro measurements, it is hoped
that a clearer understanding of the long-term effects of the
use of these systems will emerge, thus providing an improved
guide for clinical judgement.
REFERENCES
1. Anusavice KJ. Criteria for selection of restorative materials: properties versus
technique sensitivity. In: Anusavice KJ (ed). Quality evaluation of dental
restorations. Chicago: Quintessence, 1989:15-56.
2. Armstrong SR, Vargas MA, Fang Q, Laffoon JE. Microtensile bond strength
of a total-etch 3-step, total-etch 2-etch, self-etch 2-step, and a self-etch 1-
step dentin bonding system through 15-month water storage. J Adhes Dent
2003;5:47-56.
3. Armstrong SR, Vargas MA, Chung I, Pashley DH, Campbell JA, Laffoon JE,
Qian F. Resin-dentin interfacial ultrastructure and microtensile dentin bond
strength after five-year water storage. Oper Dent 2004;29-26:705-712.
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