Transverse and Impact Strength of Poly Methyl Methacrylate-Zirconium Oxide Nanocomposite Denture Base Material

Aims: this study aims to evaluate the effect of adding two concentrations of zirconium oxide nanoparticles (1.0% and 2.0%) to "heat-cured PMMA" in order to improve its mechanical properties such as transverse strength and impact strength. Materials and Methods: The particle size of Zirconium Oxide ZrO 2 was 20nm. The ZrO 2 nanoparticles were added to the "heat-cured PMMA" resin base at 1.0% and 2.0% by weight, respectively, to create a PMMA-ZrO 2 nanocomposite with two various percentages compared to PMMA without additives. For the transverse strength and impact strength tests, the traditional heat-curing technique was cured with a water bath to polymerize the specimens. The results of the study were statistically analyzed by using one-way ANOVA and Duncan's multiple range test with a significant P-value of 0.05. Results: The results showed that there was an increase in the transversal and impact strength for the PMMA-ZrO 2 nanocomposite at concentrations of 1.0% and 2.0% respectively, after comparison of the findings at 0.05. Conclusions: The use of Zirconium Oxide nanoparticles as dental fillers at 1% and 2% by weight improved the transverse strength and impact strength of PMMA denture base material.


INTRODUCTION
PMMA ''poly methyl methacrylate'' is an excellent biocompatible organic polymeric substance that is utilized to make denture bases (1) .It was initially used in denture construction in 1937.Since then, its strong physical and mechanical qualities make it a suitable material (2) .In all denture base materials, acrylic resins have been most often used and approved and it has been estimated that (95%) of dental polymers are composed of "Poly methyl methacrylate" thermoplastic polymers (3) .However, when used alone, PMMA has inadequate mechanical properties and inadequate surface hardness.
It was readily damaged in an event involving a strong impact or when a patient applied severe chewing pressure to the tooth base (4) .
On the other hand, low mechanical characteristics against impact, bending and fatigue are major concerns that must be addressed enhancing acrylic polymers for removable dental and acrylic appliances (5) .
Recently, a great deal of attention has been paid to the integration of inorganic nanoparticles into PMMA to enhance their characteristics.The characteristics of nanoparticles depend on the type of nanoparticles that are included, their size and shape, their concentration and their interaction with the polymer matrix (6) .Metal oxide "zirconium oxide" has several benefits, including mechanical strength, toughness, rigidity, wear strength, chemical tolerance, and high thermal stability (7) .

MATERIALS AND METHODS
In this present study sixty specimens were used, which were split into two major groups.Impact and transverse mechanical tests were performed on a subdivided group of 30 specimens (n=30).

The
proposed PMMA-ZrO2 nanocomposite study was prepared according to the following measurements: "ZrO2 of 1.0% wt. was added to the heat-cued PMMA resin base at 99% wt., ZrO2 of 2.0% wt. was added to a heat-cued PMMA resin base of 98% wt.
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) .days before being analyzed (4) .

Testing Procedures
Transverse (Flextural) strength test: The specimen was made in accordance with International Standards Organization Specification No. 1567 (ISO) specifications "65 mm length × 10 mm width x 2.5 mm thickness", as illustrated in Figure (1).
Test was performed with the specimen mounted on two parallel supports 50 millimeters apart and bent using a rod at the center of the two supports at 50 kg and 1mm/min until fracture occurred.For all specimens, the transverse strength (Q) has been determined as follows (4) :

Impact strength test:
Table (3) was shown the results of a descriptive statistical analysis of impact strength for all groups were tested.
dentures.Separating media (cold mold stitch) was employed and allowed to dry for the layer of plastic before placing the lower part of metal bottles filled with dental stone and combined in vibration according to the directions of the manufacturer to remove the trapped air, and then left to set.Acrylic sheets were used to create the plastic model which was designed using computer software (AutoCAD), and then they were engraved using a computer-controlled laser cutting machine.The length, width, and thickness of the plastic models used in the fabrication of the molds were determined according to the specifications required for each test.In both groups, the specimens were washed and stored in distilled water at 37 o C for 2

mm 2 F
In room temperature (22ºC), the impact strength test was conducted & in accordance to ISO 148, the standard specimen sizes were (55 mm length × 10 mm width× 10 mm thickness) as illustrated in Figure(2).

Figure ( 4 )
Figure (4) revealed a significant difference between the (1.0% and 2.0%) ZrO2 & the control groups.There was a significant

Figure ( 4 )Figure ( 5
Figure (4) ZrO2 groups were compared using mean, standard deviation, and Duncan's multiple range test of impact strength.

Table ( 1): Descriptive statistical analysis of roughness test
Source of variance; SS: Sum of squares; df: degree of freedom; MS: Mean square

Table ( 3
): Descriptive statistical analysis of roughness test