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

e28 dental materials 26S (2010) e1–e84
Materials and methods: 96 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 10–30 s, based on the manufacturer’s recommended
curing times, using an Optilux 500 (Kerr). Following 1 day of
37 ◦ C dark storage, specimens were ground under continuously
water cooling at 150 rpm with a 120 g load for 2 min
with P800 grit (21.8 �m), P2400 (8 �m), and P4000 (5 �m) SiC
paper on a grinding/polishing machine (Rotopol V). Followed
by diamond polishing of 1 �m, 0.25 �m, and 0.1 �m suspension
(MetaDi Supreme Polycrystalline Diamond Suspension,
Buehler) on polishing cloths (Micro Cloth, Buehler) with a
60 g load. The 1 �m diamond polishing was not performed for
Durafil VS as pilot studies showed a pitted surface that only
occurred with this step. 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 × 2 mm 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. When assumption of normality
was violated, one-way ANOVA based on rank-transformed
data with post hoc Bonferroni t-tests was performed.
Results: Mean gloss units after each polishing step
RBC Mylara P800a P2400 P4000a 1 �ma 0.25 �m 0.1 �ma Estelite �
Estelite
87.4 (a) 12.9 (ab) 68.2 (a) 76.4 (ab) 92.5 (ab) 93.9 (a) 94.6 (a)
� Quick 86.9 (a) 13.5 (a) 67.5 (a) 78.6 (a) 92.0 (ab) 93.9 (a) 94.6 (a)
Herculite Ultra 86.1 (a) 10.4 (ab) 40.4 (c) 71.9 (cd) 91.3 (ab) 92.9 (a) 94.6 (a)
Esthet-X HD 85.8 (a) 7.1 (c) 29.4 (d) 61.6 (e) 90.1 (b) 93.8 (a) 95.1 (a)
Supreme Plus 85.8 (a) 8.2 (bc) 51.2 (b) 74.3 (bc) 92.1 (a) 93.7 (a) 94.3 (a)
Durafill VS 76.5 (b) 7.9 (c) 44.3 (c) 69.5 (d) na 76.1 (b) 75.9 (b)
Within columns groups with same letter are not significantly different
(p > .05).
a One-way ANOVA on rank-transformed data.
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 surface roughness will
be measured after 3k, 10k, 20k, 30k and 50k thermocycles
between 5 and 55 ◦ C and compare to commercial polishing
methods.
doi:10.1016/j.dental.2010.08.068
61
A novel test chip for measuring in situ degradation of dental
composites using electrochemical impedance spectroscopy
S. Grego 1 , J.R. Piascik 1 ,B.Brown 2 , S.D. Wolter 2 , B.R. Stoner 1,2
1 RTI International, Durham, NC, USA
2 Duke University, Durham, NC, USA
Objectives: To demonstrate a novel array-chip technology
used to monitor physical properties of dental composites in
situ and to present a model for correlating electronic properties
to mechanistic changes in material structure and properties.
Materials and methods: The DECAY chip (Degradation via
Electrochemical Array) leverages microfabrication techniques
to construct a uniform array of recessed wells that may be
filled with dental restorative materials and analyzed electrochemically
in solution. The array enables uniform preparation
of multiple specimens and reference controls on a common
substrate, all of which may be evaluated simultaneously. The
DECAY-chip presented here consists of a 3 × 3 array of 100 �m
deep wells, and is used to monitor the degradation of a common
dental composite as a function of time. The data correlate
changes in measured dielectric properties to surface and bulk
changes as the composite is exposed to various chemical and
biological environments. In this preliminary evaluation, Aelite
All-Purpose dental composite (Bisco, Inc., Schaumburg, IL) was
packed into 5 of the 9 test-wells and light-cured for 40 s at
500 mW/cm 2 . A model for the system is presented, as are
future plans to standardize methodology for rapid materials
screening and in vitro analyses.
Results: Electrochemical impedance spectroscopy (EIS)
data show degradation in dielectric properties of the composite
when exposed to ethanol:DI (75:25) mixtures. These
data are then correlated to physical modes of degradation
confirmed ex situ via optical, atomic force, and electron microscopies.
Table: Change in composite as a function of timed exposure
to ethanol:DI (75%EtOH).
Composite property vs. time 1 h 24 h 210 h 360 h
Dielectric capacitance
(nF)
Dielectric leakage
resistance (M-ohms)
Total impedance at
1 Hz (M-ohms)
AFM surface roughness
(nm)
16.6 17.2 19.3 21.0
66.7 64.4 43.4 27.8
10.1 9.6 8.7 7.9
11.2 N/A 26.9 N/A
Conclusions: EIS-DECAY chip was used to detect changes
in composite capacitance and bulk resistance in addition to
total system impedance, all as a function of frequency, and
compared to physical changes in the dental composite. Models
were developed for more complex systems and correlated to
clinical models.
doi:10.1016/j.dental.2010.08.069