The effect of nanoparticles TiO2 on the flexural strength of acrylic resin denture plate

Introduction: Acrylic resin is still the most commonly used denture base material due to its ideal properties. However, acrylic resin denture fractures are still considered a major unsolved problem thus the addition of nanoparticles as filler was performed to increase its mechanical properties. The purpose of this study was to discovered the effect of nanoparticles TiO2 on the flexural strength of acrylic resin denture plate. Methods: This study used 27 heat-cured acrylic resin specimens sized 65 x 10 x 2.5 mm. The samples were divided into three concentration groups (n = 9), the control group; 1% of nanoparticles TiO2; and 3% of nanoparticles TiO2. The flexural strength was tested using the Universal Testing Machine. All data were analysed using the one-way ANOVA test with 95% confidence level then continued with the Least Significant Difference (LSD) test. Results: There were significant flexural strength differences in different concentration of nanoparticles TiO2. The highest flexural strength value was found in the 1% of nanoparticles TiO2 group (106.99 ± 6.09 MPa), whilst the lowest flexural strength value was found in the 3% of nanoparticles TiO2 group (91.64 ± 5.38 MPa). Significant flexural strength difference was found between the control group and the 1% of nanoparticles TiO2 group, and also between the 1% of nanoparticles TiO2 group with the 3% of nanoparticles TiO2 group (p < 0.05). Conclusion: From this study can be concluded that concentration of 1% of nanoparticles TiO2 was able to increase the flexural strength of acrylic resin denture plate.


INTRODUCTION
Acrylic resin is still becoming a preferable material for denture base because of the economic cost, repairable, easy manufacturing process, simple tools, and also stable & easily polished.However, acrylic resins also have several disadvantages, some of them are having a low flexural strength compared to the metal frames, low thermal conductivity, produces residual monomers, porosity potential, permeable, and easily fractures. 1,2Previous research showed that as much as 68% of denture fracture occurred almost after 3 years of use, 28% occurred after 1 year, and 39% of the denture needs to be repaired after 3 years of use.Denture fracture is still becoming an unsolved problem until now. 3,4everal attempts were made to increase the mechanical properties of the acrylic resin such as the flexural strength.Flexural strength is a force directly related to the fracture resistance of a denture. 5Chemical industry research nowadays are focusing on the addition of nanoparticles such as titanium dioxide (TiO 2 ), silicon dioxide (SiO 2 ), aluminium oxide (Al 2 O 3 ), and zirconium dioxide (ZrO 2 ), into an acrylic resins to produce new materials which have the same mechanical properties with the nano-oxide particles, but with the flexibility of the polymer matrix. 6Nano-oxide particles are commonly used due to the small size, strong interactions with organic polymers, non-toxic, non-biochemical reactions, with antifungal and anti-bacterial properties. 7The use of titanium dioxide nanoparticles is increasing due to the advantages over other nanoparticles, which are non-toxic, inert chemical properties, economic cost, powerful antibacterial properties, corrosion resistance, and high level of hardness. 8anoparticles TiO 2 are able to fill the PMMA chain spaces thus reducing porosity by increasing the density of the acrylic resins density. 9Silanization of the TiO 2 nanoparticles serves as a coupling agent to ensure the interfacial adhesion between the TiO 2 nanoparticles and the polymer matrix of the acrylic resin thus creates strong bonding and increases the crosslink on the acrylic resin polymer chains. 10The purpose of this study was to discovered the effect of nanoparticles TiO 2 on the flexural strength of acrylic resin denture plate.

METHODS
This study was experimental laboratory research with as much as 27 study subjects consisted of acrylic resin plate with the size of 65 x 10 x 2.5 mm (ADA® Sp.No. 12) divided into 3 groups (n = 9).All samples were divided into 3 concentration groups, namely the control group, 1% of nanoparticles TiO 2 concentration group, and 3% of nanoparticles TiO 2 concentration group.The materials used in this research were acrylic resin (QC 20-Densply ® ), Silanization of the TiO2 nanoparticles was then allowed to stand for 14 days at room temperature. 9The manufacture of test plates

Concentration group TiO2 weight (gram) Polymer weight (gram) Monomer (ml)
A (0% All test plates were immersed in aquadest for 48 hours at 37ºC before a flexural strength test was performed.11Specimens were tested for flexural strength using a Universal Testing Machine.The flexural strength data is calculated using the Modulus of Rupture formula (at a threepoint bending setup). 12he data analysis used to determine the effect of TiO 2 nanoparticle concentration on flexural strength of denture plasterboard acrylic resin was the one-way ANOVA and if there was a significant difference followed by the Least Significant Difference test with 95% confidence level (p < 0.05) as shown in Figure 3.

RESULTS
Research on the effect of concentration of nanoparticles TiO 2 on the flexural strength of denture acrylic resin polish plate was performed in the Laboratory of Materials Science Department of Mechanical Engineering Faculty of Engineering, Gadjah Mada University Yogyakarta, Indonesia.The result of flexural strength can be seen in Table 2.
The highest flexural strength was found in the 1% nano TiO 2 concentration group of 106.99 MPa, and the lowest flexural strength was found in the 3% TiO 2 particle concentration group of 91.64 MPa.The results of this study were tested using the one-way ANOVA with normality test requirement using Shapiro-Wilk (p > 0.05), and homogeneity test using the Levene test (p > 0.05) must be fulfilled.
Data were tested by using one-way ANOVA with variable concentration result there was significant difference with p = 0,000 (p < 0.05).ANOVA test data can be seen in Table 3.
The concentration variables have a significant difference (p < 0.05) so that continued with the Least Significant Difference (LSD) test.

DISCUSSION
The average result of the highest flexural strength measurement in the nanoparticles group of TiO 2 concentration of 1% was 106.99 MPa.This condition was because the nanoparticle TiO 2 acts as a filler on the PMMA matrix chain which resulted in the pressure given when the flexural strength test was distributed to the nanoparticles of TiO 2 spread evenly among the PMMA matrix with the help of silane.This result was in accordance with previous research which stated that the presence of nanotube TiO 2 was able to prevent the occurrence of crack propagation on acrylic resin denture plate. 13he 3% nanoparticles TiO 2 concentration group had the lowest average of 91.64 MPa.This result was because the excessive concentration of the TiO 2 nanoparticles caused the polymerisation of the imperfect acrylic resin so that the porosity increases and the acrylic resin had become more brittle so that it easily broke during the flexural strength test.This condition was in accordance with the opinion of Ahmed et al. which states that the concentration of excessive TiO 2 nanoparticles may increase the porosity of the acrylic resin plate. 14ne-way ANOVA test results in Table 3 showed a significant difference in the concentration group of 1% and 3% of TiO 2 nanoparticles to the flexural strength of denture acrylic resin (0.05).This was because the TiO 2 nanoparticles acting as fillers can fill the empty spaces between PMMA chains without changing the basic structure of the PMMA chain.Proper filler concentration was able to increase PMMA matrix density, whereas excessive filler concentration may interfere with acrylic resin polymerisation process and dnanoecrease the mechanical strength of acrylic resin, including flexural strength.
This result was consistent with the opinion of Alwan and Alameer which stated that the addition of nanotubes TiO 2 filled the void space between PMMA matrices and did not change the basic structure of the PMMA chain. 9The study of Nazirkar et al. proofed that the excessive concentration of TiO 2 nanoparticles may interfere with the polymerisation process of acrylic resins. 15he LSD test results showed that the flexural strength of the nanoparticles group TiO 2 concentration of 1% compared with the control group significantly increased (p < 0.05).Increased flexural strength due to silane will increase the surface energy of TiO 2 to form strong bonding bonds with the interfacial attachment between the TiO 2 nanoparticles and the polymer matrix of PMMA resulting in increased van der Waals forces and increased crosslinking of the chain polymer.The increased inter-molecular attraction forces result in shear strength between the TiO 2 particles and the PMMA matrix getting larger so that the flexural strength increases.The nanoparticles TiO 2 also decreases the porosity of the acrylic resin and modifies the surface of the acrylic resin to hydrophobic thus reducing the water sorption.This result was consistent with Salman and Khalaf's suggestion that silane was able to guarantee a homogenous distribution of nanoparticles within the PMMA matrix and form strong bonds between nanoparticles and PMMA matrices. 16Acosta-Torres et al. proofed in their research that the porosity level of acrylic resin in the group receiving TiO 2 nanoparticle addition was lower when compared to the control group. 17Harini et al. stated that the TiO 2 nanoparticles has changed the properties of the acrylic resin to hydrophobic thus reducing the water sorption. 12he results showed that the flexural strength of the 3% TiO 2 particle concentration groups compared with the 1% nanoparticles group of TiO 2 concentrations decreased significantly, this was because an increase in excessive TiO 2 nanoparticles may increase the risk of uneven mixing between polymers resulting in more monomers does not react to polymer so that the residual monomer increases and reduces crosslinking between the polymer chains.The residual monomer acts as a plasticiser since it was able to enter between the polymer chains which cause the separate chains to become more tenuous and the attraction force between molecules decreases so that the acrylic resin becomes more flexible but brittle during the flexural strength test.In the opinion of Shirkavand and Moslehifard, the addition of excessive TiO 2 nanoparticles may cause the agglomeration of the TiO 2 nanoparticles, so the microporosity and the microcrack of the acrylic resins were increased and caused a decrease in the flexural strength of the acrylic resin. 8Research conducted by Nazirkar et al. proofed that the addition of excessive TiO 2 nanoparticles may interfere with the polymerisation reaction of the acrylic resin resulting in an increasing unreacted monomers being polymers. 15The results showed that there was no significant difference (p > 0.05) between the nanoparticles group TiO 2 concentration of 3% and the control group, the flexural strength of the TiO 2 nanoparticles group with 3% concentration decreased but not significant.
The decreased flexural strength due to the excessive addition of excessive TiO 2 nanoparticle filler may, therefore, be at risk of clumping during the mixing process between the TiO 2 and PMMA nanoparticles thus disrupting the polymerisation process of the acrylic resin. 7

CONCLUSION
From this study can be concluded that concentration of 1% of nanoparticles TiO 2 was able to increase the flexural strength of acrylic resin denture plate.Further research was needed regarding the effect of nanoparticles TiO 2 concentration towards the residual monomer amount on an acrylic resin plate denture p-ISSN 1979-0201, e-ISSN 2549-6212 Available from: http://jurnal.unpad.ac.id/pjd/article/view/16110DOI: http://dx.doi.org/10.24198/pjd.vol30no1.16110Submission: Dec 2017 Publishing: Mar 2018

Figure 3 .
Figure 3. a Acrylic resin samples; b Flexural strength test