Abstracts of the Academy of Dental Materials Annual ... - IsiRed

sectioned, placed into 50% (w/v) ammoniacal silver nitrate
solution for 24 h, exposed to photodeveloping solution and
observed using SEM. Percentage distribution of metallic silver
particles in the resin/dentin interface was calculated using
digital image analysis software. Shrinkage stresses and stress
rates of resin composites were measured continuously from
start of light curing and up to 30 min using a Tensometer testing
machine (NIST, Gaithersburg, MD). Data were analyzed by
one-way ANOVA followed by a Tukey multiple comparisons
test. (p < 0.05).
Results: Increasing C-factor did not affect the nanoleakage
of low shrinkage composites, meanwhile silver nitrate depositions
were significantly increased in high C-factor cavities in
the control group. Mean maximum shrinkage stresses results
were 0.94 ± 0.1, 1.79 ± 0.18 and 2.14 ± 0.23 MPa for SIL, AL and
Z, respectively.
Conclusion: Using low shrinkage composites in cavities
with high C-factor may be an alternative to avoid the deteriorating
effect of increasing the C-factor on the bond of resin
composite to dentin.
doi:10.1016/j.dental.2010.08.065
58
Can filler-size affect the colour and gloss of resin-composites?
H. Elbishari, J. Satterthwaite, Nick Silikas
School of Dentistry, University of Manchester, United Kingdom
Objectives: To study the effect of filler size on the colour
change and gloss over time in three different storage media.
Materials and methods: Disc shaped specimens
(2 mm × 10 mm) prepared and polished using OptiDisc
(Kerr Dental). Samples allocated to 4 groups (n = 12) according
to their filler size. Gloss and colour measured with a
Novocurve glossmeter and Minolta colourmeter, respectively,
and then stored in three media (water, cola and red wine).
Measurements for gloss and colour were then recorded 24 h,
2 weeks and 3 months, respectively. Data was analysed with
one-way ANOVA (SPSS, 16.0).
Results: Filler distribution resulted in significant changes in
colour (�E). �E values ranged from 1.6 to 15.6 and gloss from
89.6 to 51.3. In all cases the trimodal filler distribution, that
incorporated small size nanofillers (100 nm), resulted in the
least colour change. All materials had high initial gloss values.
Storage media affected gloss and there was a gloss reduction
with all storage media. Red wine had the highest reduction in
gloss values.
Conclusions: Filler size and distribution had a significant
effect on the aesthetic properties (colour and gloss) of resincomposites.
Storage media and storage time also significantly
affected these properties. Prolonged storage time resulted in
the highest changes.
doi:10.1016/j.dental.2010.08.066
dental materials 26S (2010) e1–e84 e27
59
Choosing the allocation method for clinical trials in restorative
dentistry
H. Fron 1 , P. Durieux 2 , G. Chatellier 2 , F. Gillaizeau 2 , J.P. Attal 1
1 URB2I, Université Paris Descartes, France
2 APHP HEGP; INSERM, UMR S 872/20, France
Objectives: Treatment allocation in restorative trials is
generally defined by pre-set random tables. However, this
method does not account for prognostic factors of the restorations
and does not respect allocation concealment, so that
treatment groups are not comparable and conclusions are
biased, especially because the groups are small-sized. Comparable
groups are obtained by optimizing balance between
groups and limiting allocation predictability. Two methods
could be used in restorative dentistry to achieve comparability:
blocked randomization and minimization. Blocked randomization
consists in using a separate randomization list for each
prognostic group. Minimization is an adaptive method that
minimizes the imbalance between the number of patients in
each treatment group over a number of prognostic factors. The
purpose of this study was to choose between these two methods
for a randomized controlled trial comparing ceramic and
composite CAD-CAM inlays.
Materials and methods: A Visual Basic for applications
program was computed. 1000 sets of 350 patients were simulated
according to the proportions expected for each of
the four main predictive factors (inlay/onlay, premolar/molar,
vital/non vital tooth, operator). These patients were allocated
by minimization with a varying random element and stratification
with blocks of 2 and 4. Allocation methods were
compared in terms of predictability and balance.
Results: The balance obtained with blocked randomization
was better than expected, although minimization proved to
better account for balance and predictability at the same time.
Minimization with a random element of 30% achieved the lowest
imbalance (0.51% of the sample size) and predictability
(52.68% when operator remembered his three last allocations).
Conclusions: Minimization with a 30% random element
allowed accounting for four prognostic factors in the planned
clinical trial and achieving excellent group comparability. Simulations
help decide which allocation method is best for a
clinical trial in restorative dentistry.
doi:10.1016/j.dental.2010.08.067
60
Polishability of nanofilled resin-based composites
K. Hirata, J. Yamagawa # , S. Geraldeli ∗ , F. Qian, S.R. Armstrong
The University of Iowa, USA
Objectives: To evaluate baseline laboratory-grade polishability
of six resin-based composites (RBC) in preparation for
polish retention and surface roughness evaluation.
# at time of participation in the research at The University of
Iowa, J. Yamagawa was an employee of Tokuyama Dental
Corporation. Study sponsored by Tokuyama.