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

62
Simulated clinical polishability of nanofilled resin-based composites
K. Hirata, J. Yamagawa, F. Qian, S.R. Armstrong
The University of Iowa, USA
Objectives: To evaluate baseline simulated clinical polishability
of five resin-based composites (RBC) in preparation for
polish retention and color stability evaluation.
Materials and methods: 80 Disk-shaped specimens
(D = 10.0 mm, 2-mm thick, all A2 shade, n = 16 per RBC) were
formed in a PTFE mold against mylar tape and light polymerized
for 10–20 s using an Optilux 500 (Kerr) based on the
manufacturer’s recommended curing times. Following 1 day
of 37 ◦ C dark storage, light irradiated side of each specimen
was ground with P800 grit size (21.8 �m) SiC paper on a
grinding/polishing machine (Rotopol V) under continuously
water cooling at 150 rpm with a 120 g load for 2 min to
remove resin rich layer and roughen the surface. Then, each
specimen was polished dry at 30,000 rpm with a Sof-Lex disc
Fine and Super-fine grit each for 20 s. Gloss was measured
(average of 3 measurements for each specimen was used for
data analysis) after each polishing step using a small-area
glossmeter (Novo-Curve, Rhopoint Instrumentation, East
Sussex, UK) with a square measurement area of 2 mm × 2mm
and 60 ◦ geometry. A one-way ANOVA with post hoc Tukey’s
HSD test was conducted to assess the effect of RBCs on the
polishability within each polishing time.
Results: Mean gloss units after each polishing step.
RBC Mylar P800 Sof-Lex
fine
dental materials 26S (2010) e1–e84 e29
Sof-Lex
super fine
Premise 89.85 (a) 8.35 (a) 55.99 (a) 67.08 (b)
Durafill VS 85.19 (c) 6.96 (ab) 55.20 (a) 73.53 (a)
Supreme Plus 87.79 (b) 5.81 (b) 50.97 (a) 61.89 (c)
Venus Diamond 84.91 (c) 5.77 (b) 41.29 (b) 63.89 (bc)
Esthet-X HD 89.50 (ab) 5.26 (b) 34.09 (c) 61.34 (c)
Within columns groups with same letter are not significantly different
(p > 0.05).
Conclusions: Polishability is RBC material dependent. This
may be due to differences in filler size, type and coupling to
resin matrix.
Future studies: Polish retention and color stability will
be measured after 3k, 10k, 20k, 30k and 50k thermocycles
between 5 and 55 ◦ C and compare to laboratory-grade polishing
methods.
# at time of participation in the research at The University
of Iowa, was an employee of Tokuyama Dental Corporation.
Study sponsored by Tokuyama.
doi:10.1016/j.dental.2010.08.070
63
Nanometer deformations of wet and dry composites determined
by Speckle interferometry
N. Kachrimanis 1 , P. Zaslansky 2 , W.-D. Müller 1
1 “Charité” Universitaetsmedizin Berlin, Germany
2 Max-Planck Institute for Colloids and Interfaces, Potsdam, Germany
Objectives: Dental composites placed intraorally undergo
dimensional changes due to thermal fluctuations, postpolymerisation
processes and hygroscopic water-uptake
effects. Concerning bonded restorations, these changes result
in the formation of strain and therefore, the purpose of this
study was to develop and adapt a non-destructive standardised
method for the assessment of composite dimensional
changes under dry and wet conditions at 37 ◦ C.
Materials and methods: Standardized Grandio (VOCO, Cuxhaven)
disks, (1 mm thick, 15 mm diameter) light cured (80 s)
were stored in water or in air for 1 h and 3 days at room temperature
(n = 12). Each sample was mounted on a precision heating
stage warmed to 37 ◦ C, where surface deformations over time
were monitored by electronic Speckle pattern interferometry.
Surface displacement maps were used to determine strains
every 4 s for 30 min or more, during which expansion or
contraction was monitored. The cumulative effects of loss
of water and/or post curing polymerisation shrinkage were
quantified (ImageJ).
Results: Fig. 1 depicts typical integrated dimensional
changes over time for samples in each group, placed at
37 ◦ C: Fresh samples (stored for 1 h) revealed strains of up
to 6 × 10 −5 , while dry samples undergo half the shrinkage
of wet samples. Samples stored for 3 days revealed the
curious finding that wet samples undergo half the shrinkage,
compared to dry-stored samples.
Conclusions: Non-contact deformation measurements of
mm sized samples revealed deformations produced by very
different mechanisms: water sorption or post-polymerisation
shrinkage. The Speckle interferometry method allows us to
determine nanometer deformations and small strains, relevant
to the clinical conditions where such composites are
used. Further investigation is needed to compare variations
in composition between different materials.
doi:10.1016/j.dental.2010.08.071