.structural Investigations On Poly(methyl Methacrylate) Various [614784]

http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦55♦No. 4 ♦2018 616Structural Investigations on Poly(methyl methacrylate) Various
Composites Used for Stereolithographyc Complete Dentures
EUGENIA EFTIMIE TOTU1, CORINA MARILENA CRISTACHE2*, SELIM ISILDAK3, OZLEM TAVUKCUOGLU3, AIDA PANTAZI4,
MARIUS ENACHESCU4, ROXANA BUGA5, MIHAI BURLIBASA2, TIBERIU TOTU5
1University Politehnica of Bucharest, Faculty of Applied Chemistry and Material Science, 1-5 Polizu Str, 11061 Bucharest,
Romania.
2University of Medicine and Pharmacy Carol Davila, Faculty of Midwifery and Medical Assisting (FMAM), Department of Dental
Techniques, 8, Eroilor Sanitari Blvd, 050474, Bucharest, Romania
3Department of Bioengineering, F aculty of Chemical and Metallurgical Engineering,Yildiz Technical University, 34210 Esenler-
Istanbul, Turkey
4University Politehnica of Bucharest, Center for Surface Science and Nanotechnology (CSSNT), 313 Splaiul Independentei,
060042, Bucharest, Romania
5 University Politehnica of Bucharest,Faculty of Electronics and Telecommunications,313 Spl. Independentei, 060042, Bucharest,
Romania
The present paper is focused on analyzing if appropriate adhesion between the polymeric matrix and titania
filler nanoparticles is obtained for the PMMA-TiO2 photo-curable dental material, suitable for application in
RP – stereolithography (SLA) for complete denture manufacturing. It was found that different amounts,
between 0.2% and 2.5 % (w/w%), of added titanium oxide nanoparticles slightly modify the structural
behavior of the PMMA polymeric matrix. The material characterization was carried out using FT-IR and
microscopy techniques.
Keywords: PMMA – TiO2 functionalized nanocomposite, structural analysis, stereolithography, complete
denture
The advancements in computer-aided design and
computer aided manufacturing (CAD/CAM) encouraged
its applications in fixed and removable prosthodontics,
leading to the development of new technologies and newmaterials with improved biomechanical characteristics
and high biocompatibility. To date, subtractive technology
(milling from gingiva-colored pre-polymerized acrylicblank) for denture base and prefabricated teeth are mostly
used, in clinical environment, to manufacture CAD/CAM
dentures. Despite of the important advantages of thistechnique, such as reduced number of appointments, rapid
fabrication, improved fit and electronic archiving of
prosthetic design, computer engineered complete dentureshave some important drawbacks, mainly regarding the
expensive materials and increased laboratory costs [1,2].
Additive manufacturing or rapid prototyping (RP) and theuse of improved polymers has been foreseen as a viable
and less costly solution for complete denture
manufacturing. Furthermore, if a monolithic denture/overdenture [3,4] is envisaged, the functionalization of the
polymeric teeth during the design may also be performed
[5]. Poly (methyl methacrylate) (PMMA), the material ofchoice for removable dentures, has been lately investigated
and there are studies highlighting the effect of adding
nanofillers such as titanium dioxide (TiO
2) to improve their
specific properties [6]. PMMA-nano TiO2 composite have
shown better thermal behavior [7] in connection with a
lower water sorption and solubility [8]. From themechanical point of view, such composites are
characterized by an improved hardness, fracture resistance
and/or flexural strength [9]. However, some studies haveshown lower flexural strength when titania nanoparticles
were added into a poly (methyl methacrylate) matrix [10].
Such noted behavior could be the result of a poorhomogeneity of the final material.The present study was focused on obtaining an
appropriate adhesion between the polymeric matrix andtitania filler nanoparticles for the PMMA-TiO
2 photo-
polymerizing material for dental use, important for
enhancing the nanocomposite’s characteristics. Thestructural properties of the PMMA-nanocomposites suitable
for application in RP – stereolithography (SLA) dentistry
have been characterized by FT-IR analysis and microscopyinvestigations.
Experimental part
Reagents and apparatus
The reagents used in this work are similar to those
presented in our previously published paper [7]. Thepolymer matrix, denoted as PMMA-D, consisting in a
mixture of poly(methyl metharcrylate)(PMMA) -methyl
methacylate (MMA) and reinforcing additives solution (from
EnvisionTEC GmbH, Gladbeck, Germany ) has been used
throughout experiments, as provided. The nanofiller added
to the polymeric matrix was the titanium oxide (anatasetype) – from Aldrich. The obtained material has been used
for complete dentures manufacturing employing STL
technology. The applied workflow, described elsewhere[11, 12], was run on Envison TEC equipment.
In order to avoid the inhomogeneity and local
agglomeration of the nanofiller within the PMMA matrix,the titania nanoparticles have been functionalized with
methacrylic acid (Aldrich) according to the procedure
described in detail in [7]. After functionalization, thenanofiller was carefully mixed with the PMMA-D matrix.
The necessary amounts of the two components of the
nanocomposite were precisely weighed with an analyticalbalance in order to obtain a concentration between 0.2
and 2.5 (w/w) for TiO
2 nanoparticles in polymer.
* email: corinacristache@gmail.com All authors have equally contributed to the manuscript and they should be regarded as m ain authors

http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦55♦No. 4 ♦2018 617The SEM morphologies of the prepared nanocomposites
have been studied using a scanning electron microscopy
(SEM) system, from Oxford Instruments. In addition, theelemental mapping was obtained through EDX analysis
performed on the same equipment. O ther microscopy
investigations carried on a bright field microscope wereperformed using Leica DM 3000 LED device, equipped with
an MC 190 HD camera based on s-CMOS sensor with
reduced noise factor.
The subsequent structural analysis was investigated by
Attenuated Total Reflectance Fourier-Transformed Infrared
spectroscopy (ATR-FTIR). The FTIR spectra of all sampleswere recorded in the 4000–500 cm
-1 range, with a resolution
of 4 cm-1 at room temperature using a Bruker Tensor 27
equipment (diamond ATR). A polymeric matrix withouttitanium oxide nanoparticles was used as a reference
sample. Raman studies, which are complementary with
FT-IR measurements, were performed by Confocal Micro -Raman Spectroscopy using a LabRam HR800 system
equipped with a green He-Ne laser (532 nm) as the
excitation source. All the Raman spectra were collectedby exposing the specimens during 100 s, in the 3600–100
cm
-1 region with a spectral resolution of 0.6 cm-1. All the
experiments were performed at room temperature.
Results and discussions
An important aspect for the good functioning of
composite materials, such as PMMA – TiO2, is the filler’s
dispersion in the polymeric matrix. Therefore, the resulted
morphology is further influencing the materialcharacteristics. Taking advantage of microscopy
techniques, it is possible to investigate, at microscopic level,
the PMMA – TiO
2 nanocomposites’ structure.
The microscopy analysis confirmed a satisfactory
dispersion of TiO2 particles in PMMA polymer matrix. The
degree of nanoparticles dispersion is conditioned by the
amount of filler added into the polymer (fig. 1).significantly modified with the increasing of TiO2nanoparticles ratio. The increase of the surface roughness
is most likely caused by the aggregation TiO2 nanoparticles
into the polymeric host.
The image presented in figure 4, obtained with the bright
field microscope, is showing the dispersion of the metallic
nanofiller in the PMMA matrix, revealing the existence of acontinuous media without considerable particle
conglomerates.
The influence of the added amount of TiO
2 nanoparticles
into the PMMA polymer is also evidenced by the FT-IR
spectra illustrated in figures 5 and 6.
Fig. 1. SEM images with corresponding EDX elemental maps
acquired for different PMMA -TiO2 nanocomposites:
a. PMMA -0.4%TiO2; b. PMMA – 1%TiO2.
The nanocomposite with lower concentration of titania
nanoparticles is more homogeneous. Therefore, it could
be concluded that PMMA polymer and TiO2 nanoparticles
are compatible, as no exudation process has been
observed. For the composite with only 0.2% added TiO2 no
phase separation has been observed (fig. 2).
A higher amount of the added nanofiller added lead to
the formation of randomly distributed clusters [1] , shown
in Figure 3. As it can be observed, the surface roughness is
Fig. 2. SEM Images for: a. PMMA and b. PMMA – 0.2% TiO2
nanocomposite
Fig. 3. SEM image
showing cluster
formation for PMMA –
2.5% TiO2
nanocomposite
Fig. 4. Bright field
microscopy images for
PMMA- 0.4% TiO2
nanocomposite
From these spectra, it should be noted that as a result of
the incorporation of different titania quantities into the
matrix three important effects are observed: the intensity
of the absorption band due to the filler presence increases;the maxima positions of the main absorption bands are
shifted towards higher wavenumbers; the profile of the
absorption band has changed. The shift of the absorptionband is illustrated through inserts on figure 7.
Figure 5 presents the FT-IR spectrum of PMMA matrix
without any titania nanoparticles. The specific absorption
Fig. 5. FT-IR spectra
for PMMA matrix
without TiO2
nanoparticles

http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦55♦No. 4 ♦2018 618bands from 1384 cm-1, 1031 cm-1, 828 cm-1 and 747 cm-1,
are characteristic for the polymeric matrix to be used for
stereolithographic technique [6]. The initial spectral curves
were recorded before exposing the samples to UV radiationspecific for the employed AM technology. The FT-IR spectra
presented for samples with different amounts of titania
nanofiller put in evidence that curve recorded for the samplewith 0.2% nanofiller concentration is not significantly
modified compared to the reference spectrum – PMMA
without any nanoparticles added.For instance, there were no important differences found
between FTIR spectrum of PMMA with %0.4 TiO
2 and
PMMA with %0.6 TiO2. However, the intensities of almost
all the peaks exhibited by the nanocomposite with %0.4TiO
2 are lower.
The results shown in the inset of figure 7 put in evidence
that the shift of the absorption band depends on the amountof the added nanofiller in the case of UV exposed
specimens, as well. Specifically, for the 0.4% TiO
2 -PMMA
composite it was about 20 cm-1. The shift increased
afterwards, reaching about 50 cm-1 for 2.5 % TiO2 added.
Figure 7 presents the FT-IR spectrum of PMMA – TiO2nanocomposite after UV exposure. It could be easily
noticed that, in this case, the FT-IR spectrum of the sample
is different from those obtained for the un-irradiated
samples.
The specific absorption band for TiO2 in connection with
the stretching vibrations of bridging oxygen atoms is present
within the wavenumber range 550-900 cm-1, and the
position of the peak depends on the structural arrangement
of the oxygen atoms [13].
It is well known that TiO2 have specific Raman
fingerprints for both, anatase or rutile, structures. The
anatase-type titania is characterized by the tetragonal
space group D4h (I41/amd, with Z = 4 for anatase), while
the rutile structure belongs to the D4h (P42/mnm, with Z =
2 for rutile) tetragonal space group [14,15]. Anatase is
characterized by six Raman active modes (1A1g + 2B1g +
3Eg), while rutile possesses four Raman active modes (B1g,
Eg, A1g, and B2g). The Raman spectra illustrated in Figure 8
confirm the successful incorporation of titaniananoparticles in the PMMA-TiO
2 nanocomposite. Also, it
could be observed that the TiO2 nanoparticles are present
in both phases, anatase and rutile.
The Raman frequencies for the PMMA sample with 0.4%
TiO2 are 141 cm-1, 196 cm-1, 398 cm-1, 514 cm-1, 517 cm-1
and 636 cm-1 for anatase, while 392 cm-1 and 805 cm-1 for
the TiO2 rutile phase.
The Raman spectra recorded for the initial matrix
without titania nanofiller and for the PMMA matrix with0.4% TiO
2 nanoparticles after their exposure to UV radiation
Fig. 6. FT-IR spectra for: a. PMMA- 0.4% TiO2 nanocomposite; b. PMMA- 1% TiO2 nanocomposite;
c. PMMA- 2.5% TiO2 nanocomposite
Fig. 7. FT-IR spectrum for UV exposed PMMA – 0.4% TiO2
nanocomposite
It could be observed that there are two weak peaks at
3384 cm-1 and 609 cm-1 specific for -OH group stretching
and bending vibrations, respectively. The -OH groups most
probably come from the adsorbed water molecules. TheC-H bond (from -CH
3 and -CH2 groups) stretching vibrations
bands are placed at about 2960 cm-1. The specific vibration
band for C=O stretching of acrylate carboxyl group ispresent at 1719 cm
-1, while at 1453 cm-1 there is a vibration
band that could be attributed to the bending vibration of
the C–H bonds from -CH3 group. The bands at 1384 and
747 cm-1 can be attributed to the α-methyl group vibrations.
The bands known as the characteristic absorption
vibrations of PMMA are present at 1031 cm-1 and 828 cm-1.
Fig. 8. Raman spectra. a. TiO2
nanoparticles; b. composite PMMA +
0.4% TiO2 nanoparticles

http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦55♦No. 4 ♦2018 619are shown in figure 9. In addition, the specific Raman shifts
for titania nanoparticles have been recorded and presented
on the same graph.
The polymeric materials selected for complete dental
prostheses need to have similar physical, mechanical, and
aesthetic characteristics to natural teeth. It is well known
that f or edentulous patients, removable PMMA dentures
and overdentures are used to overcome the loss of all teeth
[16]. Nevertheless, the usual mechanical failure of the
PMMA denture base and the acrylic teeth, susceptible toabrasion could lead to a great number of complications.
Dealing with complications is not only an expensive matter
but is also inconvenient for the patients. Lately, severalstudies [7,17] proved that doping the PMMA with an
appropriate filler, as TiO
2 nanoparticles could modify the
specific properties of polymeric matrix resulting into acomposite material with improved functions.
The new trends in the additive dental technologies, i.e.
RP technique, will redirect the dental materials researchtowards complex nanocomposites.
Conclusions
The morphological and structural studies presented in
this work offer a valuable confirmation of our previous
findings [6,7,18] regarding the improved characteristics ofthe PMMA-TiO
2 nanocomposite.
In the light of the new emerging RP technology, the
PMMA-TiO2 nanocomposite that we are proposing could
be considered as a promising 3D printing material for
complete dentures and overdentures manufacturing.Fig. 9. Raman spectrum of: TiO2 nanoparticles (black line), UV
irradiated PMMA (red line) and UV irradiated PMMA + 0.4% TiO2
nanoparticles composite (blue line)
Acknowledgement: This work was supported by a grant of the
Romanian National Authority for Scientific Research and Innovation,
CCCDI – UEFISCDI, project number 30/2016 -PRIDENTPRO, (ERA-NET-
MANUNET II) within PNCDI III. Also, this research was partially
supported by the scýentific and technological research council of
Turkey, TUBITAK, project number 9150165, MANUNET ERA-NET.
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Manuscript received: 26.08.2018