Evaluation of the Mechanical and Radiopacity Properties of Poly(methyl methacrylate)/Barium Titanate-denture Base Composites
Evaluation of the Mechanical and Radiopacity Properties of
Poly(methyl methacrylate)/Barium Titanate-denture Base Composites
Nidal W. Elshereksi1,2,*, Saied H. Mohamed3, Azlan Arifin1 and Zainal A.M. Ishak1
School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300
Nibong Tebal, Pulau Pinang, Malaysia
2
Department of dental technology, College of medical technology, P.O. Box: 1458, Misurata-Libya
3
Prosthodontics Department, Faculty of Dentistry, Benghazi University, P.O. Box: 9504, Benghazi-Libya
1
Received: 9 August 2014, Accepted: 21 August 2015
SUMMARY
This study aimed to evaluate the flexural and hardness properties of poly(methyl methacrylate) (PMMA)
denture base filled with barium titanate (BaTiO3). The BaTiO3 filler was treated with 3-trimethoxysilylpropyl
methacrylate, which is a silane coupling agent. Curing was performed in a water bath at 78 °C for 1.5 h. The
samples were tested for tensile and flexural strength and surface hardness. The samples were also radiographed,
and their optical densities were determined. Radiopacity values were compared with that of an aluminium (Al)
plate with equivalent thickness. A reduction in the tensile and flexural strength of the PMMA composite was
observed at high filler loadings. However, the surface hardness of the denture base composites was enhanced
as a function of filler loading. The radiopacity of the PMMA/BaTiO3 composites was also improved. Adding
10 wt.% of BaTiO3 to PMMA resulted in a higher optical density (OD) (p< 0.07) compared with that of Al.
Keywords: Dental composite, radiopaque denture base, flexural strength, surface hardness, barium
titanate
1. INTRODUCTION
Acrylic polymers were introduced
as denture-base materials in 1937.
These polymers have been wellreceived by the dental profession
such that by 1946, almost all
denture bases were constructed from
poly(methyl methacrylate) (PMMA)1.
Nevertheless, this material cannot
meet the mechanical requirements of
prostheses. Around 57% to 64% of all
removable denture failures are caused
by acrylic fractures2 because of the
fatigue and chemical degradation of
the base material3. Numerous attempts
have been made to reinforce dental
composites by impregnating them
with ceramic fillers4–7. Most fillers
used to reinforce dental composites are
silicate glasses7–12. However, they are
not sufficiently strong or they produce
stress-concentration points because of
their irregular shapes throughout the
matrix, which results in composites that
produce cracks either cutting through
fillers or propagating around filler
particles12–15. Researchers have also
shown that the use of quartz and silica
fillers results in reduced radiopacity
either before or after immersing
these fillers in artificial saliva12,16,17.
Fractures in acrylic resin dentures are
common clinical occurrences; thus,
measures should be taken to resolve
this problem2,8.
Denture bases constructed from
pure PMMA are not radiopaque
materials. Thus, this material cannot
be detected by radiographs when a
*Corresponding author: [email protected]
Smithers Information Ltd., 2016
©
Polymers & Polymer Composites, Vol. 24, No. 5, 2016
denture fractures and is ingested or
swallowed. Any delay in localizing
or removing the foreign body may
be life threatening. Radiopacity is a
prerequisite property of all intra-oral
materials, including denture-base
materials, denture liners, direct
filling restorative materials and resin
cement luting agents17. Agrawal et
al.18 concluded that partial acrylic
denture prostheses with no clasps are
radiolucent. Partial dentures, which are
small, can be accidentally swallowed.
The location of a swallowed denture
is difficult to determine radiologically.
These dentures are dangerous because
of their configuration, dimension, and
overall rotation in the oesophagus.
Several attempts have been made to
incorporate a degree of radiopacity
in acrylic denture-base materials.
barium sulfate (BaSO4) is used to
increase the radiopacity of denture
bases. However, the mechanical
properties of a denture-base material
such as transverse and impact
365
Nidal W. Elshereksi, Saied H. Mohamed, Azlan Arifin and Zainal A.M. Ishak
strengths are affected when BaSO4
is incorporated19. Other commercial
radiopaque PMMA-bone cements
contain 10.5 wt.% ZrO2, an amount
that insufficiently provides the
required radiopacity for PMMA20 and
is incompatible with the resin matrix21.
Therefore, alternative reinforcing
and radiopacifying elements are
necessary to improve the properties of
PMMA composites. Although barium,
strontium, zirconium and titanium
have been used as radiopaque materials
for dental composite resins12,22, the
most effective radiopaque material
for composite resins remains to be
determined.
T h e i n o rg a n i c f i l l e r b a r i u m
titanate (BaTiO 3) has favourable
mechanical properties23 and excellent
biocompatibility 24,25 . Although
composites containing BaTiO3 are
biocompatible, their biological
applications are limited20,26. BaTiO3
fillers have been incorporated as
a radiopacifier in PMMA matrix
because of the filler components’ high
atomic number4. A previous study20 has
inferred that acrylic bone cement filled
with 20 wt.% to 50 wt.% of untreated
or silanated BaTiO3 or SrTiO3 has
setting properties, compressive yield
strength and radiopacity that are
adequate for surgical procedures. The
radiopacity of dental materials should
be greater than or equal to the thickness
of an aluminium wedge and should not
be <0.5 mm. However, no definitive
maximum limit has been identified22.
Thus, the incorporation of BaTiO3 as
a radiopacifier into dental polymers
may be a solution to overcoming the
radiolucency shortcoming. To date, no
study has been conducted on the dental
applications of BaTiO 3 particles.
Accordingly, this study aimed to
prepare a new radiopaque denturebase material by impregnating PMMA
matrix with BaTiO3 and to evaluate the
tensile strength, flexural properties,
surface hardness and radiopacity
behaviour of the material.
366
2. MATERIALS AND
METHODS
The solid components consisted
of high-molecular-weight PMMA
(996 000 GPC; Aldrich, USA) and
0.5% benzoyl peroxide (BPO; Merck
Chemical, Germany). BaTiO3 powder
(Acros, USA) with particle size
ranging from 0.4 µm to ˂1 µm
constituted the filler. The liquid part
was composed of methyl methacrylate
(MMA; Fluka, UK) stabilized with
0.0025% hydroquinone, and 10%
of ethylene glycol dimethacrylate
(EGDMA; Aldrich, USA) as
a crosslinking agent. The silane
coupling agent 3-(trimethoxysilyl)
propyl methacrylate (γ-MPS), also
known as 3-(methacryloxy)propyl
trimethoxysilane, was supplied by
Sigma–Aldrich. γ-MPS has boiling
and flash points of 190 and 92.22 °C,
respectively. γ-MPS was used to
enhance the interaction between the
filler BaTiO3 filler and the organicmatrix PMMA.
2.1 Filler Treatment and
Sample Preparation
BaTiO3 filler initially treated with
200 mL of toluene and 10 g of BaTiO3
powder was prepared according to the
method described by Carrodeguas et
al.20. BaTiO3 powder was dissolved in
toluene. About 10 wt.% of silane was
added to the resulting solution, which
was refluxed for 15 h and then filtered
to collect the modified powder. This
powder was washed with 200 mL of
fresh toluene in a Soxhlet apparatus for
24 h, and the final product was dried at
110 °C for 3 h in a vacuum.
Five different ratios (i.e., 0, 5, 10, 15
and 20 wt.%) of the treated fillers were
used. With the exception of the 0 wt.%
filler, the other four were added to the
matrix (PMMA and 0.5% BPO). The
solid phase (PMMA, BPO, and filler)
was mixed in a planetary ball mill
for 30 min. Milling was discontinued
every 3 min during the run time and
continued after a pause of 4 min to
prevent overheating and premature
polymerization. The ceramic jars and
balls used were cleaned using sand
several times for 30 min to reduce
contamination in the powder mixture.
The mixing of powder to liquid
(P/L) was performed according to a
standard dental laboratory method.
When the mixture achieved dough-like
consistency, it was placed in a mould
onto which a pressure of 14 MPa was
applied for 30 min at room temperature.
Final polymerization (curing process)
was performed in a water bath at 78 °C
for 1.5 h4–6. The mould was left to cool
slowly at room temperature, and then
the samples were removed and polished
with fine sandpaper. The procedures
adopted in this study were consistent
with those of the prescribed standard
method for preparing a conventional
denture base in a dental laboratory27.
2.2 Tensile Testing
Tensile tests were performed
according to ASTM D–638 type IV
by using an INSTRON 5582 10 kNelectromechanical tensile testing
machine. The gauge length was set to
50 mm, and the crosshead speed was
5 mm/min. At least five samples for
each formulation were tested. Tensile
strength, Young’s modulus, energy at
break, and tensile strain were measured
and recorded.
2.3 Flexural Testing
Three-point flexural tests were
performed in accordance with the
ASTM D790–86 standard. The support
span was set at 50 mm, and the diameters
of the loading nose and supports were
20 and 10 mm, respectively. The tests
were conducted at a crosshead speed
of 2 mm/min on an INSTRON 5582
10 kN-tensile testing machine. At least
five samples for each formulation were
tested. Flexural strength and flexural
modulus were measured and recorded.
These parameters were calculated
using the following equations:
Flexural modulus =
(1)
Polymers & Polymer Composites, Vol. 24, No. 5, 2016
Evaluation of the Mechanical and Radiopacity Properties of Poly(methyl methacrylate)/Barium Titanate-denture Base Composites
Flexural strength =
(2)
where L is the span length, P is the
maximum load, b is the specimen
width, d is the specimen thickness,
and m is the tangent gradient of the
initial straight line of the load versus
deflection curve.
(3)
where P1 is the load (gf) and d 1 is
the mean diagonal of indentation
(µm). As described by Abouelmagd28,
the improvements in hardness were
calculated using Eq. (4):
HV improvement (%) =
2.4 surface Hardness (Vickers
Hardness, VHN) Testing
The hardness test was performed
according to the ASTM E 384–89
standard. A calibrated VHN tester
FV (Future-Tech) was used to force
a 0.3 kgf diamond indenter into the
sample’s polished surface. This method
was performed to optically measure
diagonal length. The hardness test
was performed on several samples of
all composite formulations, and the
average of five readings was taken for
each composite-sample formulation.
The samples were mounted by epoxy
and then polished with very fine alumina
powder. Mounted samples were used
because small-sized samples can be
easily handled during polishing. The
castable resin (epoxy resin)-mounting
materials used at room temperature
consisted of two components that were
mixed prior to use. The moulds were
simple cups that held the resin for 4 h
to 6 h until it was cured.
Grinding was initiated with a coarse
paper capable of flattening the
specimen and removing the effects of
prior operations, such as sectioning.
The next paper removed the effects
of the prior paper within a short time.
At the end of grinding, the specimen
surface was flat with one set of
unidirectional grinding scratches. A
sequence of papers (240, 340, 400,
600 and 800) was used for grinding.
Polishing was conducted manually,
i.e., the specimens were held by hand
against an abrasive charged-rotating
wheel. The specimens were moved
against the direction of rotation in an
elliptical path around the wheel. the
Vickers hardness number equation is
expressed as:
(4)
where c and m refer to the composite
and the matrix, respectively.
2.5 Radiopacity Testing
The radiopacity testing was performed
according to ISO 4049–1988 (E)
specifications. The specimens, Al plate
and film were irradiated with X-rays
at 60 kV by using an X-ray machine
(Philips-Optimus, Japan). The target
film was set at a distance of 35 cm, and
the exposure time was 1 mAs. The film
was developed and fixed using a Kodak
X-OMAT 5000 RA Processor machine.
The film density of the specimen’s
image was compared with that of
the Al plate by using a densitometer
(Radiation Measurements Inc., USA).
The variance between the density of the
tested materials and the control sample
was compared using one-way ANOVA.
3. RESULTS AND
DISCUSSION
3.1. Confirmation of Silane
Treatment by Energydispersive X-ray (EDX)
Spectroscopy
Interfacial adhesion between fillers and
polymers is important. This parameter
is especially true in polymers that
are reinforced to produce polymer
composites because the surface
treatments of the filler and its matrix
modification affect the mechanical
properties of the composite. interfacial
adhesion is improved by establishing
a chemical bond between reacting
materials (i.e., inorganic filler, BaTiO3,
and PMMA matrix). Interfacial
Polymers & Polymer Composites, Vol. 24, No. 5, 2016
adhesion can be achieved through
a preliminary treatment of the filler
surface by using a silane coupling
agent8. Silane coupling agents were
used because they contain two different
reactive groups in their molecules,
one of which can be hydrolysed.
These groups allow silane agents to
establish a strong connection between
polymer matrices and filler particles10.
The effectiveness of a silane coupling
agent to improve the bonds between
inorganic fillers and organic polymer
matrices is well documented29-31. Silane
treatment of a filler helps introduce
chemically active sites onto a ceramicfiller surface, thereby establishing a
chemical bridge between the filler
and the PMMA matrix. The present
study aimed to establish the chemical
structure of the filler after silanation.
The presence of silane in BaTiO3 filler
and PMMA matrix composites was
confirmed by EDX. Figures 1a and
1b show the EDX graphs of BaTiO3
powder before and after treatment with
silane coupling agent, respectively.
Analysis of the graph of treated BaTiO3
confirmed the presence of Si group,
which indicated the presence of silane
on the filler surface, as described by
Carrodeguas et al.20.
3.2 Tensile Properties
Table 1 shows the effects of filler
content on the tensile properties of
the BaTiO3-filled PMMA matrix. The
tensile modulus values of the filled
PMMA increased compared with that
of neat PMMA matrix. The tensile
strength of filled PMMA decreased
with increased filler content. In the
case of 15 wt.% filler content, the
tensile modulus was unaffected by
filler incorporation. Modulus was
measured before plastic deformation,
which resulted in the behaviour cited.
These measurements implied that
the interactions between fillers and
polymer matrices were not considered.
The filled PMMA (5, 10, 15 and
20 wt.%) exhibited lower tensile
strengths than PMMA matrix.
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Nidal W. Elshereksi, Saied H. Mohamed, Azlan Arifin and Zainal A.M. Ishak
Figure 1. EDX graph of BaTiO3 powder: (a) before silane treatment and (b) after
silane treatment
Table 1. Comparison of the effect of filler loading on the tensile properties of the
BaTiO3-filled PMMA matrix and the PMMA matrix
Specimen
Tensile strength Tensile modulus Tensile strain
(MPa)
(GPa)
(%)
PMMA
58.6 ± 1.4
2.2 ± 0.1
PMMA+5%
56.37 ± 0.9
PMMA+10%
55.84 ± 2.5
PMMA+15%
PMMA+20%
368
Energy at
break
(N/m2)
4.78 ± 0.4
1.15 ± 0.2
2.25 ± 0.08
3.67 ± 0.2
1.22 ± 0.2
2.31 ± 0.07
3.85 ± 0.15
1.11 ± 0.1
55.14 ± 1.2
2.36 ± 0.1
3.67 ± 0.3
1.01 ± 0.1
52.69 ± 1.8
2.42 ± 0.1
3.12 ± 0.3
0.78 ± 0.1
However, within the filled PMMA
itself, tensile strength values decreased
with increased filler content. This
finding was attributed to homogenously
dispersed filler particles because
well-dispersed particles enhanced the
crack-propagation path and plastic
deformation while absorbing a portion
of the energy. Surface energy increased
with increased filler content, which
in turn increased composite strength.
However, the filler particles were
detached from the PMMA matrix
with increased filler content. This
behaviour caused voids that increased
in size to form cracks. In addition, the
filler particles aggregated, thereby
causing inefficient stress distribution
and decreased mechanical strength
because of the agglomerates’ low
strength. A similar result has been
previously reported32, i.e., increased
filler loading causes weak adhesion
between filler particles and resin
matrix. Filler-particle agglomeration
increased with increased filler
loading. Thus, the applied stress
was non-uniformly distributed in the
composites, thereby producing local
stress concentrations. Consequently,
cracks formed particularly near the
defective, stressed areas of filler–
matrix and filler–filler interfaces.
The filled samples exhibited lower
tensile strain and energy at break
values than the unfilled samples
because of the large amount of plastic
in the latter. The plastic reduced the
high stresses at the crack tip through
plastic deformation, which resulted in
greater energy absorption. Conversely,
the lower tensile strain and energy at
break values of samples with higher
filler content may be attributed to
extensive filler agglomeration, which
led to insufficient homogeneity of local
stress distribution and subsequently
initiated deformations at particular
locations in the composites. Adding
ceramic fillers limited the mobility of
the amorphous phase in the polymer;
thus, damping of the composite was
reduced. This occurrence was expected
because increasing the filler content
Polymers & Polymer Composites, Vol. 24, No. 5, 2016
Evaluation of the Mechanical and Radiopacity Properties of Poly(methyl methacrylate)/Barium Titanate-denture Base Composites
decreased the polymer matrix and the
overall damping of the composite33.
Fibre-type fillers improve the tensile
strength of a composite because
these fibres support stresses that are
transferred from a polymer matrix
through the interfacial region. For
irregular fillers, composite strength
decreases because of the inability of
the filler to support stress transfer
from a polymer matrix; thus, decreased
tensile strength is expected. The tensile
strength of PMMA composite (σc) was
calculated in relation to the matrix
tensile strength (σp) using Eq. (5):
σc = σp (1–1.21 Vf2/3) (5)
where the constants 1.21 and 2/3 are
related to the stress concentration and
geometry of filler, respectively. For a
spherical filler that does not adhere to
a polymer matrix, the first constant is
equal to 1.21. The second constant is
equal to 1 if a material fails by planar
fracture and 2/3 if the failure is caused
by random fracture34. The tensile
modulus was calculated using Eq. (6),
as stated by Ochigbo and Luyt35:
Ec = Em (1 + 2.5 Vf) was due to the assumption that BaTiO3
particles were spherical and that they
existed as discrete particles. In reality,
BaTiO3 particles have irregular shapes
and exist as agglomerates. Moreover,
unbound particles did not function as
holes because they prevented matrix
collapse. In this case, the modulus of
the filled system should increase with
increased filler content, which is the
expected general behaviour. A change
in matrix–filler adhesion had a smaller
effect on modulus than on strength
because the latter depended more on
surface pretreatment. In fact, adhesion
degree was not an important factor as
long as frictional forces between phases
were not exceeded by the applied stress.
3.3 Flexural Properties
Figure 4 shows the analysis results of
the flexural properties of BaTiO3-filled
PMMA matrix. The flexural modulus of
the PMMA composite increased with
increased filler loading because of the
composite’s enhanced brittleness and
stiffness attributed to the rigid nature
of the filler and its poor dispersion.
The filler withstood most of the
stresses it received without undergoing
deformation because its modulus was
Figure 2. Comparison of the experimental and theoretical data of tensile strength
of PMMA composites
(6)
where E is the elastic modulus, m is
the matrix, and c is the composite.
For calculation purposes, the filler
particles were assumed to be spherical,
and composite failure was assumed to
be caused by random fractures. With
these assumptions, the variations in the
tensile strength and tensile modulus of
PMMA with filler content are shown in
figures 2 and 3. The theoretical tensilestrength values of PMMA composites
were calculated and plotted using Eq.
(5). Results showed that tensile strength
decreased with increased filler content,
whereas experimental tensile strength
values decreased with increased filler
content.
Figure 3. Comparison of the experimental and theoretical data of tensile modulus
of PMMA composites
In the case of PMMA composites, the
theoretical values of tensile modulus
were higher than the experimental
values (Figure 3). The discrepancy
Polymers & Polymer Composites, Vol. 24, No. 5, 2016
369
Nidal W. Elshereksi, Saied H. Mohamed, Azlan Arifin and Zainal A.M. Ishak
Figure 4. Comparison of the effects of filler content on the flexural properties of
the PMMA matrix containing BaTiO3 and unfilled PMMA matrix
extremely high36. Researchers have
found increased composite modulus
with increased filler content in fillers
exhibiting higher rigidity than the
matrix37,38.
Compared with unfilled samples, the
filled composite’s flexural strength
increased until the maximum filler
loading (Vf = 0.1), after which a
decrease in flexural strength was
observed. The increased strength of
the composite at low filler content
was attributed to the homogenously
dispersed filler particles. However,
the increase in filler content led to
extensive filler agglomeration and
lack of filler–matrix bonding, which
caused the formation of voids that
increased in size to form cracks. The
agglomerations represented stressconcentration points, and applying
an external load on the composite
caused more stress to concentrate on
neighbouring particles from advancing
cracks. The consequence was rapid and
successive crack propagation, which
led to brittle failure. These results
agreed with previous ones39,40, which
show that a decrease in the fracture
strength of PMMA composites is
possibly due to a decrease in the number
of siloxane linkages that produces poor
370
contact between silanised inorganic
substrate and polymeric organic matrix.
The behaviour was also attributed to
the tendency of silane coupling agents
to form aggregates on the filler surface,
which resulted in an unstable bond
between fillers and resin13.
The flexural strength of a material is a
combination of its compressive tensile
and shear strengths. With increased
tensile and compressive strengths,
the force required to fracture the
material also increases34. Although a
reduction in the flexural strength of
PMMA composites was observed at
high filler loadings, flexural strength
was higher than the standard minimum
limit established. According to ISO
20795–1:200841, the ultimate flexural
strength of any polymerized material
should not be ˂50 MPa. Thus, the
BaTiO3 filler-reinforced PMMA matrix
is a reliable material because it has high
specific modulus and strength.
3.4 Effect of Filler on Surface
Hardness (VHN)
Hardness, an important property
for comparing restorative materials,
refers to a material’s resistance to
undergo permanent surface indentation
or penetration. Indentation is the
pressing of a hard round object or
point with force against a material
sample, which produces a depression.
Depression or indentation is caused
by plastic deformation beneath an
indenter. Specific characteristics
of indentation such as shape or
depth are used as a measure of
hardness 42 . vhn is the number
obtained using the aforementioned
formulae. Improvements in hardness
were calculated using Eq. (4).
Surface finish is one of the variables
influencing the interpretation of
indentation results, especially
at low penetration depths. With
increased surface roughness, hardness
measured at depths comparable with
the roughness scale significantly
deviates from the actual hardness. This
phenomenon is due to the fact that at
low penetration depths, an indenter is
in contact with only a number of peaks,
and the apparent stiffness of a material
is low. Regardless of polishing degree,
actual contact surfaces are rough to a
particular extent. Surface undulations
range from a few nanometres to
several micrometres in the peak
heights. Therefore, penetration must
be sufficiently deep in an indentation
test for the materials to respond in
accordance with their true bulk material
properties43.
Table 2 shows the VHN values of filled
samples compared with those of PMMA
matrix. Improvements in hardness
values of the composites were calculated
using Eq. (4). The filled samples
exhibited higher surface hardness than
the pure PMMA matrix. Nevertheless,
PMMA composites exhibited increased
hardness with increased filler content.
This finding was attributed to the high
hardness value of the dispersed phase
and the imposed restriction on matrix
deformation caused by the uniform
distribution of the dispersed phase. Such
properties were achieved through the
incorporation of hard dispersed particles
into the ductile matrix. Likewise,
Ahmed and Ebrahim44 reported that
Polymers & Polymer Composites, Vol. 24, No. 5, 2016
Evaluation of the Mechanical and Radiopacity Properties of Poly(methyl methacrylate)/Barium Titanate-denture Base Composites
increasing the filler content in a polymer
matrix results in increased composite
hardness. The result of this study
agreed with those of previous ones30,45,46
showing that dental composites have
high hardness because of their high
filler content. Conversely, the lowest
filler content was combined with the
smallest filler size, which resulted in
the lowest hardness value. Under isostress conditions, composite hardness
approached that of a soft matrix,
especially at low volume fractions of
hard particles when the relative hardness
ratio (Hh:Hs) was high47.
Table 2. Comparison of the Vickers hardness of the PMMA/BaTiO3 composites
and that of the PMMA matrix
Formulations
Vickers Hardness
( kg/mm2)
Hardness Improvement
(%)
PMMA matrix
17.85 ± 0.9
0
PMMA matrix + BaTiO3 (5 wt.%)
PMMA matrix + BaTiO3 (15 wt.%)
18.32 ± 1.3
2.6
PMMA matrix + BaTiO3 (10 wt.%)
20.94 ± 1.4
17.3
21.26 ± 0.7
19.1
PMMA matrix + BaTiO3 (20 wt.%)
22.84 ± 0.5
27.9
Figure 5. Comparison of the X-ray images of the flexural samples and the
aluminium plate: (a) PMMA+ 20 wt.% BaTiO3, (b) PMMA + 15 wt.% BaTiO3, (c)
PMMA + 10 wt.% BaTiO3, (d) PMMA + 5 wt.% BaTiO3, (e) PMMA matrix, and
(f) Al plate
3.5 Radiopacity Evaluation
An X-ray image of the internal structure
of an object is called a radiograph.
Radiographic interpretation is
based on opacity visualisation and
radiograph analysis. Specimens
can be differentiated based on
their radiopacity, as shown in their
radiographs. The radiopacity of
a material depends on the atomic
numbers of the atoms present; higher
atomic numbers tend to indicate a more
radiopaque material21,27. Furthermore,
specimen thickness affects radiopacity;
a thick specimen indicates a high
degree of X-ray attenuation. As such,
the obtained image has white areas.
Radiographs show a range of densities
that include white, various shades
of grey, and black. Radiopaque
specimens appear whiter, whereas
radiolucent specimens appear blacker.
The resulting pattern of opacities
forms an image on a radiograph that
is recognisable in form and can be
interpreted.
In medical X-radiography, the
recording medium is a special
photographic film sensitive to X-rays.
An X-ray film becomes exposed when
X-rays strike a target. The presence of
several X-rays at a target causes greater
film exposure and vice versa. When a
specimen blocks X-rays by absorbing
them, a target does not get exposed.
Conversely, when a specimen does
not absorb X-rays, they pass through
a specimen and a target becomes
extremely exposed. In most cases, the
amount of exposure of a target may vary
from fully exposed to not exposed at all
depending on the internal structure and
composition of the specimen.
Denture-base materials should be
radiopaque because this property
is vital for radiological detection.
However, the radiopacity of dental
composites is limited because the
density of a polymeric material is
low. A polymeric material consists
of molecular structures containing
light elements, such as H, O, and C.
Radiopacity has been achieved by
adding X-ray contrast materials, such
as BaTiO3.
Radiopacity test results are shown
in Figure 5. PMMA composite was
more visible than PMMA matrix.
Nevertheless, a significant difference
Polymers & Polymer Composites, Vol. 24, No. 5, 2016
(p < 0.000) was observed between
0% and all formulations containing
Al and 5, 10, 15 and 20 wt.%
BaTiO 3. Statistically, the sample
with 10 wt.% BaTiO3 showed (p <
0.07) a significantly higher optical
density than Al. Improved radiopacity
was evident in cases of high filler
content, and no significant difference
was observed among 15 wt.% and
20 wt.% BaTiO3 content and Al (P <
0.611). Thus, adding BaTiO3 filler to
the denture-base material resulted in
significantly improved radiopacity.
The radiopacity of the denture-base
material increased with increased filler
ratio, but mechanical properties of the
composites were negatively affected
by brittleness of the filler.
4. CONCLUSIONS
The inclusion of BaTiO3 particles
as potential new dental fillers was
successfully performed. Incorporating
371
Nidal W. Elshereksi, Saied H. Mohamed, Azlan Arifin and Zainal A.M. Ishak
treated BaTiO3 fillers into PMMA
matrix improved the stiffness and
strength of the composite materials.
Tensile and flexural modulus increased,
whereas tensile and flexural strengths
decreased. Although the strength of
PMMA composites was lower than
that of neat PMMA, the ISO standard
was still met. The filled samples had
higher microhardness values than the
PMMA matrix. This behaviour was
attributed to the higher hardness value
of the dispersed phase and the imposed
restriction on matrix deformation
caused by the uniform dispersed phase
distribution. BaTiO3 also endowed the
denture-base polymer with radiopacity,
and a remarkable improvement in the
radiopacity of PMMA composites
was achieved. Therefore, BaTiO3/
PMMA composite could be a reliable
denture-base material because of its
high specific modulus and strength and
potential to enhance radiopacity, which
enables rapid radiographic detection to
avoid any possible health concern or
life-threatening event.
incorporation of PMMA-modified
hydroxyapatite, Progress in Natural
Science: Materials International, 23
(2013) 89-93.
4.
Elshereksi, N.W., Mohamed, S.H.,
Arifin, A. and Mohd Ishak, Z.A.,
Effect of filler incorporation on
the fracture toughness properties
of denture base poly (methyl
methacrylate), Journal of Physical
Science, 20 (2009) 1–12.
5.
Tham, W.L., Chow, W.S. and Mohd
Ishak, Z.A., Effects of titanate
coupling agent on the mechanical,
thermal, and morphological
properties of poly (methyl
methacrylate)/hydroxyapatite
denture base composites, Journal
of Composite Materials, 45 (2011)
2335–2345.
6.
7.
Atai, M., Pahlavan, A. and Moin,
N., Nano-porous thermally sintered
nano silica as novel fillers for dental
composites, Dental Materials, 28
(2012) 133-145.
8.
Perez, L.E.C., Machado, A.L.,
Vergani, C.E., Zamperini, C.A.,
Pavarina, A.C. and Canevarolo Jr,
S.V., Resistance to impact of crosslinked denture base biopolymer
materials: Effect of relining, glass
flakes reinforcement and cyclic
loading, Journal of The Mechanical
Behavior of Biomedical Materials,
37 (2014) 33-41.
Acknowledgement
The authors would like to thank the
School of Materials and Mineral
Resources Engineering, Universiti
Sains Malaysia (USM) for supporting
this work.
REFERENCES
1.
Alla, R.K., Sajjan, S., Alluri, V.R.,
Ginjupalli, K. and Upadhya, N.,
Influence of fiber reinforcement
on the properties of denture base
resins. Journal of Biomaterials and
Nanobiotechnology, 4 (2013) 91-97.
2.
Murakami, N., Wakabayashi, N.,
Matsushima, R., Kishida, A. and
Igarashi, Y., Effect of high-pressure
polymerization on mechanical
properties of PMMA denture base
resin. Journal of the Mechanical
Behavior of Biomedical Materials,
20 (2013) 98-104.
3.
372
Pan, Y., Liu, F., Xu, D., Jiang, X.,
Yu, H. and Zhu, M., Novel acrylic
resin denture base with enhanced
mechanical properties by the
Tham, W.L., Chow, W.S. and
Mohd Ishak, Z.A., Simulated body
fluid and water absorption effects
on poly (methyl methacrylate)/
hydroxyapatite denture base
composites, eXPRESS Polymer
Letters, 4 (2010) 517–528.
9.
Guo, G., Fan, Y., Zhang, J.–F.,
Hagan, J.L. and Xu, X., Novel
dental composites reinforced with
zirconia–silica ceramic nanofibers,
Dental Materials, 28 (2012) 360368.
10. Hooshmand, T., Matinlinna, J.P.,
Keshvad, A., Eskandarion, S. and
Zamani, F., Bond strength of a
dental leucite-based glass ceramic
to a resin cement using different
silane coupling agents, Journal
of The Mechanical Behavior of
Biomedical Materials, 17 (2013)
327–332.
11. Schmidt, C. and Ilie, N., The
mechanical stability of nano-hybrid
composites with new methacrylate
monomers for matrix compositions,
Dental Materials, 28 (2012) 152159.
12. Mirsasaani, S.S., Manjili, M.H. and
Baheiraei, N., Dental nanomaterials.
In: B. Reddy editor. advances in
diverse industrial applications of
nanocomposites, InTech, Croatia,
(2011) 441-474.
13. Lin, S., Cai, Q., Ji, J., Sui, G.,
Yu, Y., Yang, X., Ma, Q., Wei,
Y. and Deng, X., Electrospun
nanofiber reinforced and toughened
composites through in situ nanointerface formation, Composites
Science and Technology, 68 (2008)
3322–3329.
14. Jun, S.K., Kim, D.A., Goo, H.J.
and Lee, H.H., Investigation of the
correlation between the different
mechanical properties of resin
composites, Dental Materials
Journal, 32 (2013) 48–57.
15. Elshereksi, N.W., Ghazali, M.J.,
Muchtar, A. and Azhari, C.H.,
Perspectives for titanium-derived
fillers usage on denture base
composite construction: A review
article, Advances in Materials
Science and Engineering, (2014)
1-13.
16. Cruvinel, D.R., Garcia, L.F.R.,
Luciana, A.C., Pardini, L.C. and
Pires-de-Souza, F.C.P., Evaluation
of radiopacity and microhardness
of composites submitted to artificial
aging, Materials Research, 10
(2007) 325-329.
17. He, J., Söderling, E., Lassila, L.V.J.
and Vallittu, P.K., Preparation of
antibacterial and radio-opaque
dental resin with new polymerizable
quaternary ammonium monomer,
Dental Materials, 31 (2015)
575–582.
18. Agrawal, D., Lahiri, T.K., Parmar,
A. and Sharma, S., Swallowed
partial dentures, Indian Journal of
Dental Sciences, 4 (2012) 7-12.
19. Young, B.C., A comparison of
polymeric denture base materials,
[M.Sc. Thesis], University of
Glasgow, UK, (2010).
20. Carrodeguas, R.G., Lasa, B.V. and
Barrio, J.S.R., Injectable acrylic
bone cements for vertebroplasty
with improved properties, Journal
of Biomedical Materials Research
Polymers & Polymer Composites, Vol. 24, No. 5, 2016
Evaluation of the Mechanical and Radiopacity Properties of Poly(methyl methacrylate)/Barium Titanate-denture Base Composites
Part B: Applied Biomaterials, 68B
(2004) 94-104.
21. Kitayama, S., Nikaido, T., Maruoka,
R., Zhu, L., Ikeda, M., Watanabe,
A., Foxton, R.M., Miura, H. and
Tagami, J., Effect of an internal
coating technique on tensile bond
strengths of resin cements to
zirconia ceramics, Dental Materials
Journal, 28 (2009) 446–453.
22. Dafar, M., Reinforcement of
flowable dental composites with
titanium dioxide nanotubes, [M.Sc.
Thesis], The University of Western
Ontario, Canada, (2014).
23. Yu, J. and Chu, J., Nanocrystalline
barium titanate. Encyclopedia of
Nanoscience and Nanotechnology,
6 (2004) 389–416.
24. Baxter, F.R., Bowen, C.R., Turner,
I.G., and Dent, A.C.E., Electrically
active bioceramics: A review of
interfacial responses, Annals of
Biomedical Engineering, 38 (2010)
2079-2092.
25. Ciofani, G., Ricotti, L., Canale,
C., D’Alessandro, D., Berrettini,
S., Mazzolai, B. and Mattoli,
V., Effects of barium titanate
nanoparticles on proliferation and
differentiation of rat mesenchymal
stem cells, Colloids and Surfaces B:
Biointerfaces, 102 (2013) 312– 320.
26. Elshereksi, N.W., Mohamed,
S.H., Arifin, A. and Mohd Ishak,
Z.A., Thermal characterisation of
poly(methyl methacrylate) filled
with barium titanate as denture
base material, Journal of Physical
Science, 25 (2014) 15–27.
27. McCabe, J.F. and Walls, A.W.G.
Applied Dental Materials, 9th ed.,
Blackwell Publishing Ltd, UK,
(2008).
28. Abouelmagd, G. Hot deformation
and wear resistance of P/M
aluminium metal matrix
composites, Journal of Materials
Processing Technology, 155 (2004)
1395–1401.
29. Chaijareenont, P., Takahashi, H.,
Nishiyama, N. and Arksornnukit,
M. Effects of silane coupling agents
and solutions of different polarity
on PMMA bonding to alumina,
Dental Materials Journal, 31
(2012) 610–616.
30. Alnamel, H.A. and Mudhaffer,
M., The effect of silicon dioxide
nano-fillers reinforcement on some
properties of heat cure poly methyl
methacrylate denture base material,
Journal of Baghdad College
Dentistry, 26 (2014) 32-36.
31. Bahramiana, N., Ataib, M. and
Naimi-Jamal, M.R., Ultra-highmolecular-weight polyethylene
fiber reinforced dental composites:
Effect of fiber surface treatment
on mechanical properties of the
composites, Dental Materials,
(2015), in press.
32. Alsharif, S.O., Akil, H.M., El-Aziz,
N.A.A. and Ahmad, Z.A., Effect
of alumina particles loading on the
mechanical properties of light-cured
dental resin composites, Materials
& Design, 54 (2014) 430–435.
33. Huang, R., Xu, X., Lee, S., Zhang,
Y., Kim, B.-J. and Wu, Q., High
density polyethylene composites
reinforced with hybrid inorganic
fillers: morphology, mechanical and
thermal expansion performance,
Materials, 6 (2013) 4122-4138.
34. Elshereksi, N.W., Mechanical and
environmental properties of denture
base poly (methyl methacrylate)
filled by barium titanate, [M.Sc
thesis], Universiti Sains Malaysia
(USM), Penang, (2006).
35. Ochigbo, S.S. and Luyt, A.S.,
Mechanical and morphological
properties of films based on
ultrasound treated titanium dioxide
dispersion/natural rubber latex,
International Journal of Composite
Materials, 1 (2011) 7-13.
36. Masouras, K., Silikas, N. and Watt,
D.C., Correlation of filler content
and elastic properties of resincomposites, Dental Materials, 24
(2008) 932-939.
37. Blond, D., Barron, V., Ruether, M.,
Ryan, K.P., Nicolosi, V., Blau, W.J.
and Coleman, J.N., Enhancement of
modulus, strength, and toughness
in poly(methyl methacrylate)-based
composites by the incorporation
of poly(methyl methacrylate)functionalized nanotubes, Advanced
Functional Materials, 16 (2006)
1608–1614.
39. Lee, K.-H. and Rhee, S.-H.,
The mechanical properties and
bioactivity of poly (methyl
methacrylate)/SiO2–CaO
nanocomposite, Biomaterials, 30
(2009) 3444–3449.
40. Matinlinna, J.P. and Vallittu, P.K.,
Silane based concepts on bonding
resin composite to metals, The
Journal of Contemporary Dental
Practice, 8 (2007) 1-13.
41. ISO 20795-1. Dentistry-base
polymers-part 1: denture
base polymers, International
Organization for Standardization,
(2008).
42. Dowling, N.E. Mechanical
Behavior of Materials. 4th ed.,
Prentice Hall Inc., New Jersey,
(2012).
43. Chung, S.M. and Yap, A.U.J.,
Effects of surface finish on
indentation modulus and hardness
of dental composite restoratives,
Dental Materials, 21 (2005) 10081016.
44. Ahmed, M.A. and Ebrahim, M.I.,
Effect of zirconium oxide nanofillers addition on the flexural
strength, fracture toughness, and
hardness of heat-polymerized
acrylic resin, World Journal of
Nano Science and Engineering, 4
(2014) 50-57.
45. Balos, S., Branka Pilic, B.,
Markovic, D. Pavlicevic, J.,
and Luzanin, O., Poly (methyl
methacrylate) nanocomposites
with low silica addition, Journal
of Prosthetic Dentistry, 111 (2014)
327-334.
46. Zhang, X., Zhang, X., Zhu, B.,
Lin, K. and Chang, J., Mechanical
and thermal properties of denture
PMMA reinforced with silanized
aluminum borate whiskers, Dental
Materials Journal, 31 (2012)
903–908.
47. Kim, H.S. On the rule of mixtures
for the hardness of particle
reinforced composites, Journal of
Materials Science and Engineering,
A289 (2000) 30–33.
38. Hambire, U.V. and Tripathi, V.K.,
Experimental evaluation of different
fillers in dental composites in terms
of mechanical properties, ARPN
Journal of Engineering and Applied
Sciences, 7 (2012) 147-151.
Polymers & Polymer Composites, Vol. 24, No. 5, 2016
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Nidal W. Elshereksi, Saied H. Mohamed, Azlan Arifin and Zainal A.M. Ishak
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