Effectiveness of Simplified Dentin Bonding Systems
Original Paper: Dent Mater J 17(1): 1-10, 1998
The effectiveness of newly developed commercial dentin bonding
systems (SB, MB II and KB) was evaluated by measuring the contraction
gap width of a resin composite restored into a cylindrical dentin
cavity prepared in an extracted human molar and by measuring the
tensile bond strength to the flat dentin surface. In addition,
calcium loss during dentin conditioning was analyzed using electron
microanalyses. An experimental dentin bonding system composed of EDTA
conditioning, GM solution priming and a bonding agent containing
10-MDP was employed as a control in which it was presumed that
contraction gap formation was prevented completely. However, gap
formation was observed using the three commercial simplified dentin
bonding systems. SEM observation showed that the gap was formed
between the resin composite and the top surface of the dentin cavity
wall indicating that the fracture occurred at the adhesive interface,
but never inside the dentin nor inside the resin composite.
Key words : Dentin bonding, Contraction gap, Remaining calcium content
Original Paper: Dent Mater J 17(1): 11-20, 1998
To develop a suitable heating program for the investments which
affect the casting accuracy/defects of prostheses, a probable
microstructural change of the gypsum-bonded investments related to
the transition of refractory particles during thermal processing was
inspected by the measurement of acoustic emission (AE) signals.
Gypsum-bonded cristobalite and quartz investment molds were used. AE
measurements were carried out for the specimens in an electric
furnace that was heated/cooled at a constant rate. For the heating
process of the cristobalite investment, high AE activities were
detected in the temperature range where the cristobalite was
transformed. However, the AE signals detected were low for the second
run of the heating and cooling processes. Even in the heating
process, significant AE signals were not detected for the quartz
investment. For cristobalite investment molds, micro-cracks are
initiated and developed in relation to the transition of cristobalite
particles in the mold. This leads to deterioration of the mechanical
properties of the cristobalite investment at high temperatures
(melt-pouring), and may affect the fitness of cast prostheses.
Key words: Investment, Acoustic emission, Cristobalite
Original Paper: Dent Mater J 17(1): 21-30, 1998
The efficacy of a commercial total-etch wet-bonding dentin bonding
system and the effect of conditioning using 10% phosphoric acid both
on the Ca-content in the substrate dentin and on the efficacy of the
experimental contraction gap-free dentin bonding system were
evaluated by measuring the wall-to-wall polymerization contraction
gap width of a commercial light-activated resin composite filled into
a cyIindrical cavity prepared in extracted human dentin. The
Ca-content in the dentin was measured with an EDS. Complete marginal
adaptation was obtained only in the experimental contraction gap-free
dentin bonding system group. The Ca-content in the dentin was rapidly
reduced by the 10% phosphoric acid conditioning. It was concluded
that the dentist should not decalcify the dentin cavity wall possibly
by using a dentin conditioner such as 10% phosphoric acid because the
resin composite paste is apt to separate easily from the decalcified
dentin cavity wall during polymerization.
Key words: Phosphoric acid, Contraction gap, Glyceryl mono-methacrylate
Original Paper: Dent Mater J 17(1): 31-40, 1998
The corrosion behavior of three Ni-Ti alloys with compositions as
commercial super-elastic orthodontic wires was investigated using
polished plate specimens. Corrosion resistance was estimated by
potentiodynamic polarization measurement in 0.9 % NaCl and 1 % lactic
acid solutions and analysis of released metals by atomic absorption
spectrophotometry. The influence of Cr and Cu addition on the
structure of the surface oxide film was examined by X-ray
photoelectron spectroscopy (XPS). Addition of 0.19 at% Cr had little
effect on the structure of the oxide films and the corrosion
resistance of the Ni-Ti alloys. For Ni-Ti-5Cu-0.3Cr alloy, the
metallic Cu was enriched at the alloy/oxide film interface, resulting
in increased susceptibility to pitting corrosion above +1000 mV.
However, the passive current density and the amount of released Ni
were not significantly increased by the addition of Cu. The study
showed that small amounts of Cr and Cu added to change the
super-elastic characteristics do not change the corrosion resistance
of the Ni-Ti alloy freely immersed in simulated physiological
environments.
Key words: Ni-Ti alloy, Corrosion resistance, XPS
Original Paper: Dent Mater J 17(1): 41-50, 1998
Residual stress in the surface of dental porcelain was estimated
using laser Raman spectroscopy. Sixteen different magnitudes of
residual stress were generated in commercial porcelain disks by
tempering, ion exchange, and slow cooling. The specimens were
analyzed using a laser-Raman spectrometer with an Ar+
laser. The Raman shift of the largest peak near 500 cm-1
originating from silica was used as an indicator of the level of
residual stress. For comparison, the residual stress in the specimen
was estimated by the indentation micro-fracture method. The Raman
shift of the porcelain increased with increasing residual stress at
3.7 x 10-2 cm-1/MPa (R2=0.89). The
increase in the Raman shift corresponded to the increase in
compressive stress. In addition, the value of full width at half
maximum on the peak corresponded to the residual stress (-l.57 x 10
-1 cm-1/MPa: R2=0.82). These results
revealed that the increase of residual stress in porcelain clearly
appears on the Raman spectrum as an increase in the Raman shift. It
is thus feasible to estimate residual stress in porcelain by
laser-Raman spectroscopy.
Key words: Dental porcelain, Residual stress, Laser-Raman spectroscopy
Original Paper: Dent Mater J 17(1): 51-58, 1998
The purpose of this study was to evaluate the operator variability of
two dentin bonding systems. Fourteen undergraduate students and ten
dentists of different levels of clinical experience were selected.
Tensile bond strengths between resin composite and bovine dentin
using dentin adhesive systems (Clearfil Liner Bond II: LB II;
Scotchbond Multi-Purpose: MP) bonding systems showed a large scatter
among students and dentists. The dentists group demonstrated no
statistically significant differences for mean bond strengths between
LB II and MP. The student group recorded a statistically greater bond
strength using LB II. The mean coefficient of variation of the
dentists group showed no statistically significant difference between
LB II and MP, however that of the students group was lower with LB
II. When using MP, the dentist group demonstrated a lower coefficient
of variation than that of the student group. In order to obtain
optimal bonding performance, or when beginning the use of a new
system, the operator should be aware of the technique sensitivity of
some adhesive systems and sensitivity to operator variability.
Key words: Dentin bonding, Tensile bond strength, Operator variability
Original Paper: Dent Mater J 17(1): 59-67, 1998
This study was carried out to determine the design and thickness of
the cervical margin of a castable ceramic restoration from the point
of view of its castability. Castability of castable ceramics was
lower compared to Ag-Pd-Au and Co-Cr alloy with the use of the mesh
pattern and rod patten test (p < 0.05). It was more dependent on
the pattern thickness than alloys (p < 0.05), and perfect
reproducibility with non-measurable variability could be estimated to
reach 1.0 mm thickness of the original pattern (p < 0.001).
Marginal shape was certainly more reproducible in a right angle
shoulder than in 30, or 45 degree bevels (p < 0.05). From these
results, it is suggested that a right angle shoulder margin with 1.0
mm thickness is more suitable to castable glass ceramic restoration
than any other design.
Key words: Castability, Glass ceramics, Marginal shape
Technical Note: Dent Mater J 17(1): 68-76, 1998
The physical properties and shear bond strength of two resin-modified
glass-ionomers: RMGIs (FJL and VT) and as a control, a conventional
glass-ionomer: CGI (FJ), were evaluated. Ninety percent of the
setting shrinkage under dry conditions and nominal hygroscopic
expansion in water during 360 h occurred within the first 24 h. The
nominal hygroscopic expansion of CGI was 0.38 % while the RMGIs
demonstrated over l %, but considering the setting shrinkage the
total hygroscopic expansion of CGI and the RMGIs were over 7 times
and about 2.5 times, respectively. The thermal expansion of the RMGIs
after water immersion was greater than that under dry condition. In
contrast, FJ demonstrated expansion less than under dry condition.
There was no significant difference between FJL and VT (P < 0.05)
as regard water absorption. The shear bond strength of the RMGIs to
enamel and dentin were superior to FJ, except for VT to dentin.
Key words: Glass-ionomer, Hygroscopic expansion, Setting shrinkage
Technical Note: Dent Mater J 17(1): 77-82, 1998
The flexural properties, flexural strength, flexural modulus and
modulus of resilience, of four commercially available compomers, and
one resin-modified glass ionomer cement and one microfilled resin
comosite (as controls) immediately after light-activation and after 1
week of water storage were tested to assess the mechanical
properties. The water swelling after storage in water was also tested
to assess the characteristics in water of compomers. The flexural
test showed compomers to be statistically stronger and more resilient
than the resin-modified glass ionomer cement or the microfilled
composite, when tested immediately after light-activation and after 1
week of water storage. Water swelling of compomers was statistically
less than the resin-modified glass ionomer cement after 1 week of
water storage.
Key words: Polyacid-modified composite resin, Flexural property, Water swelling
Technical Note: Dent Mater J 17(1): 83-88, 1998
The effects of 2-hydroxyethyl methacrylate (2-HEMA) both in the
primer and in the commercial dentin bonding agent on the efficacy of
the dentin bonding system was evaluated by measuring the
polymerization contraction gap width of a commercial resin composite
restored in a cylindrical dentin cavity prepared in an extracted
human molar. Contraction gap formation was prevented in the group of
the EDTA-conditioning followed by glyceryl mono-methacrytate,
ethylene glycol and 1,6-hexanediol priming regardless of the 2-HEMA
content in the dentin bonding agent containing 10-methacryloxydecyl
dihydrogen phosphate. However, gap formation could not be prevented
completely by the 2-HEMA priming. Therefore, it was possible to
conclude that 2-HEMA was neither essential in the primer nor in the
dentin bonding agent because of its low bonding efficacy and the
resulting side effects on skin tissue as a delayed allergic
reaction.
Key words: 2-HEMA, Contraction gap, Dentin bonding