.poly(methyl Metacrylate) Nanocomposites For Two Piece Cadcam [614783]

http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦55♦No. 4 ♦2018 634Poly(methyl metacrylate) Nanocomposites for Two-piece CAD/CAM
Solution as an Alternative to Monolithic Removable Prosthesis
AIDA PANTAZI1, EUGENIA EFTIMIE TOTU2*, DOREL DOROBANTU1, CORINA MARILENA CRISTACHE3*, MARIUS ENACHESCU1
1University Politehnica of Bucharest, Center for Surface Science and Nanotechnology (CSSNT), 313 Splaiul Independentei,
Bucharest, Romania
2University Politehnica of Bucharest, Faculty of Applied Chemistry and Material Science, 1-5 Polizu Str., 11061, Bucharest,
Romania
3University of Medicine and Pharmacy Carol Davila, Faculty of Midwifery and Medical Assisting (FMAM),Department of Dental
Techniques,8 Eroilor Sanitari Blvd, 050474, Bucharest, Romania
The aim of the present paper was to characterize the new pink PMMA doped with 0.4% TiO2 nanoparticles
utilized for denture base manufacturing as alternative to the one-piece, single color material for removable
denture. The PMMA base material was structurally characterized through XRD, SEM, EDX, and subsequently
by FT-IR and Raman spectroscopy. An improvement in the thermal stability of the obtained material compared
with the PMMA matrix without filler was evidenced. All performed structural analyzes are recommending
the new pink PMMA with 0.4% nano-titania as an as an alternative to the one-piece, single color material for
removable dentures processing.
Keywords: CAD/CAM denture, PMMA nanocomposite, denture base.
The computer-aided design and computer-aided
manufacture (CAD/CAM) of removable dentures is lesscommon, comparing to fixed dental restoration, due to
the complexity of the technique and data to be integrated,
in order to obtain harmonious combination of denture base,artificial teeth, mouth, and face, requiring several recording,
transfer, and reevaluation steps [1]. As manufacturing
technology, rapid prototyping (RP) has the advantage toreproduce complex shapes, with high accuracy, and
reduced material waist, when compared to subtractive
technology. Among RP , stereolithography (SLA), based onthe use of a UV laser that is vector scanned to photo-
polymerize the liquid material, creating layer-by-layer the
desire shape, with a high spatial resolution (around 50µm),was successfully used to obtain poly(methyl
methacrylate)(PMMA) complete dentures [2]. The
proposed technology allowed obtaining a monolithicdenture requiring post processing and esthetic adjustments
by applying pink gingiva, light-cured material [2]. In order
to avoid increasing thickness of the cameo surface and,consequently, impede on denture fit, a two piece
manufacturing solution was envisaged. For the proposed
manufacturing technology, two type of photo-cross linkablePMMA was utilized.
The aim of the present paper was to characterize the
new pink PMMA doped with TiO
2 nanoparticles utilized for
denture base manufacturing as alternative to the one-piece,
single color material for removable denture.
Experimental part
The 3D printed prostheses manufactured in this study
have been obtained using two different types of PMMAcomposites. For the 3D printed teeth, poly(methyl-
metharcrylate)(PMMA) filled with metallic oxides,
provided by EnvisionTEC (GmbH, Gladbeck, Germany), andreinforced with titania nanoparticles, according to a
protocol presented in our previous works [2-4], was used.
The denture base was obtained from a mixture of PMMAwith methylmethacylate (MMA) and a radical reaction
promoter (from EnvisionTEC GmbH, Gladbeck, Germany)
* email: eugenia_totu@yahoo.com; corinacristache@gmail.com All authors have equally contributed to the manuscript and they should
be regarded as main authors.to which titanium oxide nanoparticles, in both, anatase
and rutile, phases (Aldrich), has been added. The completeprocedure for obtaining a homogeneous PMMA denture
base complies with the preparation method described in
detail in another paper [3]. Due to our earlier findings [2,5,6]the optimal amount of the titanium oxide nanoparticles
added to the polymeric matrix is 0.4% (w/w).
The workflow for two-piece complete denture is similar
to the one required for obtaining monolithic removable
prosthesis. The final design and the post-processing
procedures differ, as could be observed in Figure 1. Fortwo-piece denture manufacturing, two different type of
PMMA were utilized. The final prosthesis was assembled
using self-curing acrylic resin. For the monolithic Denture,Crea.lign veneering system (Bredent, GmbH & Co.KG) was
used to obtain pink gingiva on the cameo surface.
The PMMA denture base compositional, structural and
morphological properties were characterized using
Scanning Electron Microscopy (SEM) and Energy Dispersive
X-ray Spectroscopy (EDX) techniques. Thesemeasurements have been performed on a Hitachi SU 8230
SEM system, equipped with an EDX Oxford detector-
analyzer.
The structural analysis was completed with the results
provided by a Perkin Elmer Spectrum Two Fourier
Transformed Infrared (FTIR) spectrometer, equipped withan Attenuated Total Reflection (ATR) element. ATR-FTIR
spectra have been recorded in 4000–450 cm
-1 wavenumber
range, with a resolution of 2 cm-1.
The Raman investigations were carried out at room
temperature by Confocal Micro-Raman Spectroscopy,
using a LabRam HR800 system. All the Raman spectrawere generated by exposing the samples during 100s to a
532 nm wavelength green excitation laser. The emitted
Raman signal of all studied specimens was recorded in3600–100 cm
-1 range, with a spectral resolution of 0.6
cm-1.
The thermal behavior of the denture base PMMA was
studied from room temperature (25oC) up to 1000°C using
an Universal V4.5A TA Instruments equipment. The applied

http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦55♦No. 4 ♦2018 635heating rate was 10°C/min under nitrogen atmosphere
(flow rate 50 mL/min). The sample mass was 5 mg. The
experimental investigations have been performed for theuncured denture base, 0.4% TiO
2 nanoparticles – PMMA
nanocomposite, as well as for the UV polymerized material
resulted from the 3D printer.
The XRD analysis of the prepared TiO2 nanoparticles –
PMMA denture base sample was performed using a Rigaku
SmartLab X Ray Diffractometer, at 9kW (45kV and 200mA)with Cu K
α radiation: Kα1=1.540598 Å. The XRD patterns
have been recorded within [5o-100o] 2θ range. The phase
identification was made by referring to the InternationalCenter for Diffraction Data – ICDD (PDF-2) database. The
average particle size of the nanoparticles incorporated into
the polymeric matrix, the inter-planar spacing betweenatoms and the specific surface area for TiO
2 nanoparticles
(incorporated into the denture base PMMA matrix) have
been calculated according to the procedure presented inthe next section.
Results and discussions
The X-ray diffraction patterns of PMMA and titania
nanoparticles-PMMA nanocomposite denture bases are
presented in figure 2.
The X-ray diffractograms reveal the XRD
characteristic signature of the polymeric matrix – poly
(methyl methacrylate) at 2 θ = 17.5
o. The weak peak
observed in the XRD pattern recorded for the
nanocomposite denture base at 2 θ = 22.6o is
corresponding to (101) anatase plane. This maximumis slightly down shifted as it usually appears at 2 θ =
25.3
o. The main XRD characteristics observed for PMMA
denture base with 0.4% TiO2 nanoparticles are presentedin table 1. The titania nanoparticles dimension was found
to be 31Å.
The data presented in table 1, namely the average
crystallite size and the inter-planar spacing for each
crystallographic orientation have been calculated applying
the mathematical relationships based on Bragg diffraction
law.
The average nanocrystallite size has been estimated
considering Debye-Scherer equation (1):
(1)
where D stands for crystallite diameter size ( Å), λ = 1.5406
Å, θ is the diffraction angle and β is the full width at the
half maximum in radians (FWHM/rad).
The d-spacing, inter-planar distance, was calculated
using the Bragg relationship:
(2)
Fig. 1. Workflow scheme for two-piece complete denture and for
monolithic removable prosthesis
Fig. 2. The XRD pattern for PMMA denture base
(dashed line) and 0.4% TiO2 nanoparticles – PMMA
denture base (continuous line)
Fig. 3. The XRD pattern of photo-cured PMMA denture base with
TiO2 nanoparticles
Table 1
XRD DATA FOR DENTURE BASE
PMMA WITH TIO2 NANOPARTICLES

http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦55♦No. 4 ♦2018 636where λ = 1.5406 Å, θ is the diffraction angle and d
represents the d-spacing ( Å).
The diffraction peaks’ list revealed by photo-cured TiO2nanoparticles-PMMA denture base is presented in table 2.The parameters shown in table 2 have been calculatedapplying the equations (1) and (2). The presence of 2 θ
peaks at 25.3
o and 45.9o confirms the successfully
incorporation of anatase type titania nanoparticles into thepolymer matrix. The broad diffraction peaks from Figure 3
may suggest the presence of significantly small crystallites
in material’s structure (table 2).
An important physico-chemical characteristic of our
material, namely the specific surface area, could be
calculated based on the experimental data provided byXRD experiments. The value of the specific surface area
allows to determine the specific properties of a particular
material. This may be of particular importance to ourspecific applications for 3D printed denture base
fabrication, where surface adsorption is a key factor in the
denture quality. The nanocomposite denture base containstitania nanoparticles, therefore nanoparticles’ surface state
becomes important due to the fact that such nano-oxides
have a large surface area related to their volume.
The interaction between the two components of the
nanocomposite (PMMA matrix and TiO
2 nanoparticles) is
expected to be facilitated by the high surface area of thenanoparticles involved. The specific surface area for nano-
titania embedded in PMMA matrix was estimated
considering the surface area per unit mass, using thefollowing equation:
(3)
where the particle volume was calculated assuming aspherical shape particle. Therefore, the volume was V
p =
4/3-π-r3 and the surface area Sp = 4-π-r2. The density, ρ, of
TiO2 was considered 4.23 g/cm3.
The specific surface area value calculated for titania
nanoparticles (31 Å -table 1) embedded in the 4% TiO2-
PMMA nanocomposite (fig. 1), with a volume and a surface
area of 15.598 nm3 and 3.019 nm2, respectively, was found
to be 45.75 m2/g and the Sp/Vp ratio equal to 0.19. The ratio
between specific surface area and the volume will increase
significantly with the decrease of crystallite size. The TiO2crystallites’ average size for the UV cured (UV wavelength
= 340 nm) nanocomposite denture base is 20 nm and, as
consequence, the specific surface area value wascalculated to be 70.92 m
2/g and the Sp/Vp ratio 0.30.
The FT-IR analysis revealed the two specific peaks of
the -OH group around 3385 cm-1 and 1608 cm-1,
corresponding to the stretching and bending vibrations,
respectively. The presence of the -OH functional group is
most likely due to the adsorbed water molecules. As shownin Figure 4, the presence of the acrylate group within
material’s structure is confirmed by the appearance of the
vibration band around 1716 cm
-1, attributed to the C=O
stretching mode from acrylate carboxyl group. The
vibration bands from 1383 cm-1and 748 cm-1, known to be
spe-1 and 829 cm-1, confirm the presence of poly(methyl
methacrylate) in our sample. As it can be easily observedin figure 4, the 0.4% TiO2-PMMA nanocomposite denture
base exhibits a fingerprint region characterized by the
presence of several peaks. Also, when compared to theFT-IR spectrum recorded for the 0.4% TiO
2-PMMA
nanocomposite used for 3D printed teeth [2], a wider band
structure in 1200-850 cm-1 spectral range could be
observed, which probably covers the characteristic
vibrational bands for PMMA: C-O vibration band f1161 cm-
1, and typical absorption bands of PMMA at 1062 cm-1 and
940 cm-1.
In figure 5, FTIR spectra of the PMMA denture base and
PMMA with 0.4% TiO2 nanoparticles denture base were
compared to observe the vibrational pattern changes of
the nanocomposite spectrum. The band observed at 1400
cm-1 is attributed to Ti-O-Ti vibrational modes and the band
from 1645 cm-1 is corresponding to the Ti-OH bending
modes [7,8]. The FT-IR spectra clearly show that Ti binds
to the PMMA matrix by the presence of Ti-O-Ti or Ti-OH
Table 2
XRD DATA FOR 3D PRINTED PMMA
DENTURE BASE WITH TIO2
NANOPARTICLES
Fig. 4. FTIR spectrum of PMMA denture base with 0.4%TiO2
composite
Fig. 5. FTIR spectra for PMMA denture base and PMMA with 0.4%
TiO2 denture base

http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦55♦No. 4 ♦2018 637bands, resulting into a suitable material for 3D printing
technique.
The SEM micrographs of 0.4% nano-titania – PMMA
denture base are presented in figures 6 and 7. As evidencedin figure 6, due to their high surface energy the titania
nanoparticles have a tendency for agglomeration.
Titanium oxide nanoparticles exhibit good dispersion in
the PMMA matrix (fig. 7). SEM analysis has shown that the
morphology of the polymeric nanocomposite structure is
well arranged and compact. EDX analysis was performedto determine the composition of the sample in different
regions of interest.
In figure 8 the Raman spectra recorded for PMMA
denture base, PMMA with 0.4% TiO
2 denture base and TiO2nanoparticles are presented.
In figure 9 the Raman spectra for both PMMA with 0.4%
TiO2 denture base and TiO2 nanoparticles are illustrated inFig. 6. a. SEM micrographs for
PMMA -0.4%TiO2 denture base;
b. EDX elemental mapping for
PMMA -0.4%TiO2 denture base
Fig. 7. Low angle backscattered electron images of
the
PMMA -0.4% TiO2 nanocomposite denture base;
a. without Au deposition; b. with Au deposition
Fig. 8. Comparative Raman spectra for: PMMA denture base (blue
line), PMMA with 0.4% TiO2 denture base (red line), TiO2
nanoparticles (black line)

http://www.revmaterialeplastice.ro MATERIALE PLASTICE ♦55♦No. 4 ♦2018 638Fig. 9. Comparative Raman spectra for denture base
PMMA: denture base PMMA with 0.4% TiO2 (red line),
TiO2 nanoparticles (black line)
Fig. 10. Thermal analysis (TGA) for PMMA denture base
order evidence the presence of titania nanoparticles into
the polymeric matrix. The Raman frequencies exhibited
by the nanocomposite around 398 cm-1, 517 cm-1 and 636
cm-1 are assigned to anatase-type titania, while the peaks
at 392 cm-1 and 805 cm-1 are attributed to the rutile phase
of titania, proving the presence of mixed anatase-rutiletitania nanoparticles within the prepared composite.
The result of the thermal analysis is presented in figure
10. Although, the thermogravimetric curve shows a neatand clear step between 100 and 450
0C with only one
obvious decomposition stage, or at most two, actually, the
thermogravimetric curve, TGA, presents three majordegradation steps which are overlapping. The presence of
the three overlapped thermal degradation steps has been
evidenced by the first derivative of the thermogravimetriccurve (DTG). The linear chain of macromolecular poly
(methyl methacrylate) is thermally degraded in four steps
(with maximum decomposition rates recorded at: 150,250, 350 and 450 ± 50
0C) marked by huge mass losses.
For the PMMA with 0.4% TiO2 composite denture base the
first decomposition step is associated with moisture loss.As known, decomposition temperatures are partially
dependent on factors such as type of polymerization,
additive presence, type of additive, or filler presence. Theanalyzed samples are a cross-linked PMMA polymer and
PMMA polymer mixed with 0.4% TiO
2 nanoparticles, which
are degraded in three steps. The first loss is quite small,occurring at temperatures under 100
0C, and it could be
assigned to the loss of the moisture as mentioned above.
The first decomposition stage that continues up to 2000C
can be assigned to the volatilization of small molecules/
residual monomers [9]. The second and third steps are
described by important mass losses, which may beassociated with thermal degradation of various elements
of the complex dental base structure and of the polymeric
backbone. Taking into account that the thermaldecomposition occurred under nitrogen atmosphere, then
the formed residues are mainly formed by non-volatile char
and minerals.
After the complete thermal decomposition, a very small
amount of char and mineral mixture remained in the
system. The oxygen species present may interact with thepoly (methyl methacrylate) chains resulting in a hydrogen
bond or maybe a coordination bond, especially if they are
nanostructured (as titania). The direct result of suchinteraction is an increase in thermal stability of the
nanostructured compound. Even without the previously
mentioned interaction, there is a possibility that TiO
2nanoparticles will consume a certain amount of heat and
consequently increase the thermal stability of the final
composite [3].3D printing technology for complete denture
manufacturing was first proposed by Maeda end co-
workers in 1994 [10], when the authors used a 3D laser
lithography device to additively fabricate shells ofremovable complete dentures and self-curing acrylic resin
was then used to fill the shells and to finally produces the
prosthesis. Lately, the commercially available CAD/CAMcomplete dentures, such as AvaDent digital dentures
(Global Dental Science Europe BV , Tilburg, The Netherlands
), were obtained mainly by using subtractive (milling)technology or virtually designed, 3D printed try-in and
conventionally processed dentures, such as Dentca CAD-
CAM dentures (DENTCA Inc, Torrance, CA, USA), or PalaDigital Dentures (Heraeus Kulzer, GmbH) [11,12]. Several
protocols for interim RP complete dentures have been
proposed for reducing production cost [13]. However,studies on the use of CAD/CAM additive technology with
photo-cross-linkable polymers for long term removable
complete denture manufacturing are scarce. A one-yearevaluation of color changes and stainability of ten
monolithic 3D printed complete dentures with 0.4 % nano-
titania inclusions was performed by our team and the colorchanges measured over one year were below the
maximum acceptability threshold, significantly lower as
compared to the same PMMA without TiO
2 [14]. No
evaluation was performed on the veneered denture base.
Creating a multicolored prosthesis with a multi-material
printing device (using different materials with variousproperties or color in one printing task) is still a limitation
for the printers used in dental laboratories. Therefore, the
two-piece complete denture could be a viable, alternativeto the monolithic 3D printed prosthesis. Further long-term
clinical studies are strongly needed [13].
Conclusions
The XRD analysis evidenced the presence of nano-titania
particles in the PMMA denture base and allowed thecalculation of the specific surface area of the material.
Also, the morphological characterization showed a
homogeneous composite structure, while the Raman andFT-IR investigations proved the good dispersion of TiO
2nanoparticles into the polymer matrix. The 3D printedcomposite filled with 0.4 wt. % TiO
2 exhibited better
thermal stability than the PMMA denture base.
The structural analysis of the new pink PMMA doped
with TiO2 nanoparticles recommend the use of this
nanocomposite for denture base manufacturing as an
alternative to the one-piece, single color material for
removable dentures.
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.

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Manuscript received:11.09.2018