Evaluation Some of the Physical Properties of Poly Methyl Methacrylate-Zirconium Oxide Nanocomposite Denture Base Material

Aims : the current study aimed to add two concentrations of zirconium oxide nanoparticles (1.0 percent and 2.0 percent) to "heat-cured PMMA" in order to improve its characteristics such as transverse strength and impact strength. Materials and Methods : The particle size of Zirconium Oxide ZrO2 is 20nm. The ZrO2 nanoparticles were added to the "heat-cured PMMA" resin base at 1.0 percent and 2.0 percent by weight, respectively, to create a PMMA-ZrO2 nanocomposite of two various percentages to compare to PMMA without additives. For the transvers strength test and impact strength test, the traditional heat-curing technique was used with a water bath to polymerize the specimens. The data of the study were evaluated using a one-way ANOVA and a Duncan multiple range test with a significant P-value of (0.05). Results : An increase in transversal and impact strength for PMMA-ZrO2 nanocomposite of 1.0 and 2.0 percentages was noticed after comparison of the findings at (p0.05). Conclusion : By using Zirconium Oxide nanoparticles as dental filler at 1% and 2% by weight, the transverse strength and impact strength of PMMA denture base material were enhanced.

bases (1) .It was first used in the manufacture of dentures in 1937.It is strong physical and mechanical properties have made it a suitable material since then (2) .Acrylic resins have been used and approved in all denture base materials, and it is estimated that (95%) of dental polymers are made up of "Poly methyl methacrylate" thermoplastic polymers (3) .
PMMA, on the other hand, has poor mechanical properties and a low surface hardness when used alone.It was easily damaged by a strong impact or when a patient applied severe chewing pressures to the tooth's base (4) .
Low mechanical properties against impact, bending, and fatigue, on the other hand, are major concerns that must be addressed in order to improve acrylic polymers for removable dental and acrylic appliances (5).The incorporation of inorganic nanoparticles into PMMA to improve their properties has recently received a lot of attention.Nanoparticle properties are determined by the type of nanoparticles used, their size and shape, concentration, and interaction with the polymer matrix (6) .
Zirconium oxide is a metal oxide with numerous advantages, such as strong mechanical strength, toughness, rigidity, wear strength, chemical tolerance and good thermal stability, making it helpful to strengthen dental materials such as denture bases, also; zirconium oxide Nanoparticle has great strength, corrosion resistance, strong mechanical strength and abrasion resistance (7) .

MATERIALS AND METHODS
It was decided to use a study sample of 60 specimens, which were split into two major groups.Impact and transverse mechanical tests were performed on the subdivided group of 30 specimens (n=30).
The proposed PMMA-ZrO2 nanocomposite study was prepared according to the following measurements "the ZrO2 of 1.0% wt. was added to the heat-cued PMMA resin base of 99% wt., ZrO2 of 2.0% wt. was added to the heatcued PMMA resin base of 98% wt, table (1).Using sensitive balance to achieve an even ZrO2 distribution within the PMMA matrix", then; the sample preparation was done by mixing 1.0% and 2.0% by weight ZrO2 nano powder with "heat-cured PMMA" fluid monomer, then; sonicated and dispersed in the liquid monomer by an ultrasonic probe of 20W and 60 kHz for three minutes, after that; the "heat-cured PMMA" polymer powder was added and sonicated in the same way to avoid particles agglomeration (8) . .

Testing Procedures
Indentation hardness test: The test was performed using an indenter in the shape of a 1.25 mm round steel ball.Shore D hardness testers from China (SHAW) were utilized.

Surface roughness test:
The samples have been made with ISO measurements "10mm length ×10mm width ×2mm thickness" in accordance with Nevzatoģlu et al (10) , as indicated in the  with a scan length of 0.8mm (11) .The specimen surface roughness was assessed directly, 10 specimens from each group were measured.Five measurements were carried out and a mean value was measured for each sample and utilized for statistical analysis; then, the specimens of surface roughness were compared to the control group for each group.

RESULTS
Indentation hardness test:

DISCUSSION
Indentation hardness test: After addition of Zirconium oxide nanoparticle at 1.0 percent (96.5 IU) and 2.0 percent (97.5 IU), the mean values of shore D hardness were significantly higher as compared to the control group (92.6 IU).
The statistical findings were shown significant higher mean values of 1.0% ZrO2 of (96.5 IU) and 2.0% ZrO2 of (97.5 IU) when compared to the control group which was (92.6 IU).
There is also the possibility that the nanoparticles affect the elastic modulus of the PMMA, which increases the hardness of the produced nanocomposite (12,13) , since the modulus of elasticity of PMMA is proportional to the hardness property (14) .
Adding nanoparticles to PMMA may enhance its stiffness and hardness, as the nanoparticles prevent chain motion by increasing the crosslink density (15) .There is a correlation between filler loading and hardness of reinforced PMMA, according to this study.The nano zirconia dispersion uniformity inside the material was also shown to be a significant factor.In addition, the increased cross-linking density of the nanocomposite made it more stiff and resistant to penetration.
This substantial improvement in hardness may agree with the results of another study by Fatalla et al., (2020) in which ZrO2 nanoparticles were added to "heat-cured PMMA" (4) .

Surface roughness test:
The contact stylus tracing method was used in this study because it was simple, fast, and reliable for determining

CONCLUSION
The

Figure ( 3 )
Figure (3) revealed a significant difference between the (1.0% and 2.0%) ZrO2 & the control groups.There was no significant

Figure ( 3 )
Figure (3) ZrO2 groups were compared using mean, standard deviation, and Duncan's multiple range test of indentation hardness.

Figure ( 4 )
Figure (4) revealed a significant difference between the (1.0% and 2.0%) ZrO2 & the control groups.There was no significant

Figure ( 4 )
Figure (4) ZrO2 groups were compared using mean, standard deviation, and Duncan's multiple range test of surface roughness.
surface roughness.Surface roughness mean values decrease considerably after the addition of Zirconium oxide nanoparticles in the 1.0 % (0.166 m) and 2.0 % (0.150 m) groups, respectively, when compared with the control group (0.325 m) and that means the addition of zirconium nanoparticles will decrease the surface roughness the cause that make it advantageous material to be used in many situations worldwide.The current study's findings were similar with Akash and Guttal's (2015) research, which demonstrated that increasing the concentration of nanoparticles would cause a reduction in dispersion inside the polymer matrix, a conclusion was corroborated by the SEM imaging result.

Table ( 1
): Amounts of added percentages of ZrO2 with PMMA by weight leaving to set.The plastic model was made out of acrylic sheets that were designed using computer software (AutoCAD) and then engraved using a computer-controlled laser cutting machine.The length, width, and thickness of the plastic models used in

Table ( 4
) Descriptive statistical analysis of roughness test

Table ( 5
) ANOVA was used to compare the surface roughness of different ZrO2 groups