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

e32 dental materials 26S (2010) e1–e84
and the thickness (1 mm) of the composite layers used in the
experimentation.
doi:10.1016/j.dental.2010.08.075
68
Fracture toughness of GIC—A mechanistic approach on the
nanoscale
B. Brandt 1 , K. Durst 1 , R. Belli 2 , M. Goeken 1 , U. Lohbauer 2
1 Department of Materials Science and Engineering, University of
Erlangen-Nuernberg, Germany
2 Dental Clinic, University of Erlangen-Nuernberg, Germany
Objectives: To investigate the fracture toughness KIc of a
dental glassionomer (GI) cement in terms of terms of different
storage intervals and to correlate the development of macroscopic
data with findings on the nanoscale.
Materials and methods: Bars with dimensions of
25 mm × 2mm× 2 mm were produced out of a model GI
cement (Schott/Evonik, Germany) and stored for 24 h, 7 d,
and 21 d in water of 37 ◦ C. Sharp notches were cut into the
bars using a diamond wheel saw blade and a razor blade.
Fracture toughness (n = 15) was measured using the SENB
(single-edge-notched-bending) method. The actual notch
depth for each specimen was measured after fracture under a
light microscope. A Nano Indenter (G200, Agilent Tech., USA)
was used to observe the elastic modulus and local hardness
on the nanoscale. Therefore, flat specimens were produced,
surface polished using the lapping technique, and stored as
described above. Local mechanical properties were measured
on glass particles and matrix of the set cement. Load-control
(LCM) and Continuous Stiffness (CSM) measurements were
performed.
Results: An increasing fracture toughness was measured
with extended storage times. The KIc increased from
0.22 MPa m 0.5 after 24 h up to 0.24 MPa m 0.5 (7 d) and finally to
0.27 MPa m 0.5 after 21 d. The elastic modulus of the GI composite
increased from 12.2 GPa (7 d) up to 16.1 GPa after 21 d.
Hardness increased from 0.27 GPa (7 d) up to 0.43 GPa after 21 d.
The glass particles showed an elastic modulus of 65.5 GPa and
a hardness of 0.69 GPa.
Conclusions: Mechanical properties on the nanoscale
reflect the macroscopic data without any disturbing influence
from material inhomogeneities, porosity, etc. Over
time, the elastic modulus showed a higher increase compared
to the macroscopic fracture toughness measurements.
The material performance was found to be determined
by the matrix behaviour. On the nanoscale, a viscoplastic
response of the matrix component could be proved.
Nanoindentation is a very useful technique for improving
the macroscopic behaviour of a GI cement and suitable
for localizing the weakest link in the composite structure.
doi:10.1016/j.dental.2010.08.076
69
Comparison of two self-adhesive composite flowables
R. Guggenberger, T. Luchterhandt, A. Stippschild
3M ESPE, Seefeld, Germany
Objectives: Aim of this study was to compare the bond
strength of a self-adhesive composite flowable (Vertise Flow,
Kerr Corp., USA) with an experimental self-adhesive composite
flowable on dentin and enamel in two different adhesion
test methods.
Materials and methods: The adhesion test methods
used were a macro-shear bond strength test (SBS) (method
described in IADR-CED 2009, abstract # 84, C. Thalacker et al.)
with a bonding area of 21.8 mm 2 and the Ultradent microshear
bond strength test UBS with a bonding area of 4.4 mm 2 .
The substrates were bovine teeth (n = 6) ground to dentin or
enamel, using a 600 grit SiC paper. Bonded specimens were
tested after 24 h storage in tab water at 36 ◦ C, in a universal
testing machine with a crosshead speed of 2 mm/min. Following
manufacture’s instructions, for Vertise (Vts) a first layer
was rubbed on the tooth surface for 20 s and then light cured
for 20 s using an Elipar Freelight (3M EPSE). For the experimental
self-adhesive flowable (Exp-SA) the material was brought
directly on the tooth surface (without a first layer) and light
cured for 20 s.
Results: The following table shows the bond strength in
MPa. The standard deviations are given in parentheses. All
data were analyzed by ANOVA (p < 0.05). Means with the same
letters are statistically the same.
Material Test
method
Adhesion to
dentin [MPa]
Adhesion to
enamel [MPa]
Vts SBS 7.7 (2.1) a 13.3 (2.4) c
Exp-SA SBS 10.6 (1.7) b 11.9 (3.9) c
Vts UBS 7.0 (1.3) I 8.6 (3.6) III
Exp-SA UBS 11.9 (2.2) II 9.1 (4.1) III
Conclusions: In both adhesion tests Exp-SA, used without
a first layer, was found to have a higher adhesion to dentin
than Vts and an equal adhesion to enamel.
doi:10.1016/j.dental.2010.08.077
70
Temperature stress distributions in posterior composite
restorations: A 3D-FEA study
N.A. Manchorova
Medical University, Faculty of Dental Medicine, Department of Operative
Dentistry and Endodontics, Plovdiv, Bulgaria
Objectives: The purpose of this study was to investigate the
thermal stress distributions of dentin-adhesive interfaces in
a three-dimensional finite element (3D FE) model of a human
upper premolar with various Class I and Class II cavity types
and sizes after nanocomposite restorations.
Materials and methods: The human upper premolar was
digitized with a micro-CT scanner with a resolution of