A Study the Effect of Addition of Silanized Zirconium Oxide Nanoparticles on Some Properties of High-Impact Heat-Cured Acrylic Resin

Background: The incorporation of rubber has not been entirely successful because it can have detrimental effects on the transverse Strength and hence the rigidity of the denture base. Materials and methods: Zirconium oxide nanoparticales were coated with a layer of trimethoxysilylpropylmethacrylate (TMSPM) before sonication in monomer (MMA) with the percentages 3% by weight then mixed with powder using conventional procedure.(100) samples were prepared and divided into five groups according to the test performed ,Each group consisted of 20 specimens and these were subdivided into 2 groupsGroup (A): control group (10 specimens of high impact acrylic resin without zirconium oxide) and Group (B):zirconium oxide group(10 specimens of high impact acrylic resin with 3% wt zirconium oxide).The tests conducted were impact strength, transverse strength, indentation hardness(shore D), surface roughness, water sorption and solubility. The results were statistically analyzed using Dunntt t-test. Results: Highly significant increase in impact strength and transverse strength occurred with the incorporation of 3% wt Zirconium oxide nanofiller. A highly significant increase in surface hardness, but the water sorption and solubility were significantly decreased with the addition of silanized (ZrO2) Nano particles compared with the control group.no significant statistical difference in surface roughness. Conclusions: The addition of silanized ZrO2 Nano particles to high impact heat cure acrylic resin material improves the impact strength, transverse strength and surface hardness of high-impact heat-cure acrylic resin at the same time this addition decreases water sorption and solubility. On the other hand there was no change in surface roughness with the addition of 3% wt of silanized ZrO2Nano particles.


INTRODUCTION
Poly(methylmethacrylate) (PMMA) is the most commonly used material in construction of denture base since 1930 (1) .However, inadequate mechanical properties make them non-ideal (2) .This occurs when the denture is accidentally dropped on a hard surface or fractures when subjected to high mastication forces (3)(4) .
In order to overcome these problems, several attempts were made to modify and improve the impact strength, flexural strength and hardness of the PMMA.One of these attempts is a Modification of chemical structure of acrylic resin by copolymerization with rubber.The incorporation of rubber phase in in the form of butadiene-styrene co-polymer has improved the impact strength but result in increased cost and lowered transverse strength (5)(6)(7) .
Recently, much attention has been directed toward the incorporation of inorganic nanoparticles into PMMA to improve its properties.The properties of polymer nanocomposites depend on the type of incorporating nanoparticles,their size and shape,as well as the concentration and interaction with the polymer matrix (8) .Nano particles might be surface treated with saline coupling agent and embedded into PMMA to improve the bond between the matrix and filler (9) .
This study was conducted to use zirconium oxide nanoparticles that were treated with3-Trimethoxypropylsilylmethacrylate (TMPSM) and were added to high impact heat cured PMMA to get high impact PMMA/Zirconium oxide nanocomposite and study the effects of this addition on some mechanical and physical properties over pure high impact heat cured PMMA.

Surface modification of Zro 2 nano fillers:
Modification of nanofillers was done by the reaction of trimethoxysilylprpoyl methacrylate TMSPM with zirconium oxide nanopowder.

Typical process as followed:
1)30g of nano filler and 200ml pure toluene were placed into a flask then sonicated at ambient temperature for 20min (figure.1).
2) The nano filler and toluene were placed into a flask equipped with a magnetic stirrer at room temperature.
4)The flask was covered by parafilm and the slurry was 5)The solvent (toluene) was removed by rotary evaporator under vacuum at 60°C at rotary 150 rpm for 30 min.6) The modified nano filler was dried in vaccum oven at 60°C for 20 hours.Then nano filler stored at room temperature before use 4)The flask was covered by parafilm and the left standing in flask for 2 days.5)The solvent (toluene) was removed by rotary evaporator under vacuum at 60°C at rotary 150 igure2). he modified nano filler was dried in vaccum oven at 60°C for 20 hours.Then nano filler stored room temperature before use (9,10 Aprobe sonication apparatus.

Rotary evaporator of proper percentage of zirconium nanofiller (ZrO 2 ):
According to the pilot study, silanized zirconium oxide had the greatest values of flexural impact strength and hardness, the decision was made to choose filler, as a percentage of modified that added to the polymer.
4)The flask was covered by parafilm and the left standing in flask for 2 days.5)The solvent (toluene) was removed by rotary evaporator under vacuum at 60°C at rotary 150 he modified nano filler was dried in vaccum oven at 60°C for 20 hours.Then nano filler stored 10) .

Rotary evaporator of proper percentage of zirconium
addition of silanized zirconium oxide values of flexural and hardness, therefore the decision was made to choose 3% of silanized filler, as a percentage of modified t added to the polymer.

Addition of nanofillers
were added to the monomer, the fillers were well dispersed in the monomer by ultra sonication, by using a probe sonication apparatus (120 W, 60 KHz) for 3 minutes to brea crystals (Mohammad et al, 2009).nano powder was immediately mixed with acrylic powder to reduce the possibility of particle aggregation and phase separation.

Pattern Preparation
constructed as shown in figure 3 by cutting plastic plate in desired shape and dimension by using laser cutting machine according to the required test.Transverse strength, Surface roughness and Shore D. hardness tests: bar shaped specimen with dimens length, width, thickness respectively, While water sorption and solubility tests: disc with dimensions of 50 mm in diameter and 0.5 mm in thickness Impact strength test: bar shaped specimen with dimensions of (80 width and thickness respectively Mould preparation: complete denture was followed Proportioning and mixing of acrylic zirconium oxide in the s electronic balance with accuracy of (0.0001g)

Addition of nanofillers:
To prepare the dough were added to the monomer, the fillers were well dispersed in the monomer by ultra sonication, by using a probe sonication apparatus (120 W, 60 KHz) for 3 minutes to brea crystals (Mohammad et al, 2009).nano powder was immediately mixed with acrylic powder to reduce the possibility of particle aggregation and phase separation.

Pattern Preparation
Three different plastic patterns constructed as shown in figure 3 by cutting plastic plate in desired shape and dimension by using laser cutting machine according to the required test.Transverse strength, Surface roughness and Shore D. hardness tests: bar shaped specimen with dimensions of (65mm x 10 mm x 2.5 ± 0.1 mm) length, width, thickness respectively, While water sorption and solubility tests: disc with dimensions of 50 mm in diameter and 0.5 mm in thickness Impact strength test: bar shaped specimen with dimensions of (80 width and thickness respectively Fig. 3:

Mould preparation:
The conventional flasking technique for complete denture was followed

Proportioning and mixing of acrylic
Amounts of polymer, monome zirconium oxide in the study where present in table (1 electronic balance with accuracy of (0.0001g)

Addition of silanized zirconium oxide
To prepare the dough, the measured ingredients were added to the monomer, the fillers were well dispersed in the monomer by ultra sonication, by using a probe sonication apparatus (120 W, 60 KHz) for 3 minutes to break them into individual nano crystals (Mohammad et al, 2009).nano powder was immediately mixed with acrylic powder to reduce the possibility of particle aggregation and phase separation.

Pattern Preparation
Three different plastic patterns constructed as shown in figure 3 by cutting plastic plate in desired shape and dimension by using laser cutting machine according to the required test.Transverse strength, Surface roughness and Shore D. hardness tests: bar shaped specimen with ions of (65mm x 10 mm x 2.5 ± 0.1 mm) length, width, thickness respectively, While water sorption and solubility tests: disc with dimensions of 50 mm in diameter and 0.5 mm in thickness Impact strength test: bar shaped specimen with dimensions of (80 mm x10 mm x 4 mm) length, width and thickness respectively

Mould preparation:
The conventional flasking technique for complete denture was followed

Proportioning and mixing of acrylic
Amounts of polymer, monome zirconium oxide nanofillers with percentages used tudy where present in table (1 electronic balance with accuracy of (0.0001g) A study silanized zirconium oxide the measured ingredients were added to the monomer, the fillers were well dispersed in the monomer by ultra sonication, by using a probe sonication apparatus (120 W, 60 KHz) k them into individual nano crystals (Mohammad et al, 2009).The monomer with nano powder was immediately mixed with acrylic powder to reduce the possibility of particle aggregation and phase separation.
Three different plastic patterns constructed as shown in figure 3 by cutting plastic plate in desired shape and dimension by using laser cutting machine according to the required test.Transverse strength, Surface roughness and Shore D. hardness tests: bar shaped specimen with ions of (65mm x 10 mm x 2.5 ± 0.1 mm) length, width, thickness respectively, While water sorption and solubility tests: disc with dimensions of 50 mm in diameter and 0.5 mm in thickness Impact strength test: bar shaped specimen with mm x10 mm x 4 mm) length, width and thickness respectively (12) .

Plastic patterns
The conventional flasking technique for complete denture was followed.

Proportioning and mixing of acrylic:
Amounts of polymer, monomer and nanofillers with percentages used tudy where present in table (1) by using an electronic balance with accuracy of (0.0001g) A study the effect silanized zirconium oxide the measured ingredients were added to the monomer, the fillers were well dispersed in the monomer by ultra sonication, by using a probe sonication apparatus (120 W, 60 KHz) k them into individual nano The monomer with nano powder was immediately mixed with acrylic powder to reduce the possibility of particle Three different plastic patterns were constructed as shown in figure 3 by cutting plastic plate in desired shape and dimension by using laser cutting machine according to the required test.Transverse strength, Surface roughness and Shore D. hardness tests: bar shaped specimen with ions of (65mm x 10 mm x 2.5 ± 0.1 mm) length, width, thickness respectively, While water sorption and solubility tests: disc with dimensions of 50 mm in diameter and 0.5 mm in thickness (11) .Impact strength test: bar shaped specimen with mm x10 mm x 4 mm) length, The conventional flasking technique for r and silanized nanofillers with percentages used ) by using an electronic balance with accuracy of (0.0001g).Mechanical and physical tests used to examine properties: 1. Impact strength: Impact strength test was conducted following the procedure given by the ISO 179, charpy type impact testing instrument.The specimen was supported horizontally at it's ends and struck by a free swinging pendulum that released from a fixed height in the middle.A pendulum of 2 joules testing capacity was used.The charpy impact strength of un notched specimen was calculated in KJ/m 2 , according to the following: E/ B.D x 10 3 (E: impact energy, B: width of the specimen, D: thickness of the specimen).

Transverse strength:
Test was performed using a universal Instron testing machine, each specimen was positioned on the bending fixture which consists of two parallel supports (50) mm apart, the full scale was 50 Kg ,and the load was applied with a cross head speed of 1mm/min by a rod placed centrally between the supports making deflection until fracture occurs, according to the following: 3PL/2bd 2 ( p: peak load, L: span length, b: sample width, d: sample thickness).

Surface roughness:
Each specimen was tested for surface roughness using a portable surface roughness tester (Profilometer) which can measure small surface variation.This device has a diamond stylus which moves in contact with surface for 11 mm.Three measurements were done at 3 positions across each specimen surface which was divided in to 3 equal thirds and the mean of the 3 readings were recorded, as a roughness measurement.
The instrument consists of a blunt pointed indenter (0.8 mm in diameter) that present in a cylinder (1.6mm in diameter) .The indenter was attached to a digital scale that is graduated from 0 to 100 unit.The usual method was to press down firmly and quickly on the indenter and to record the maximum reading as the shore D hardness, measurements were taken directly from the digital scale reading.Five readings were recorded on different areas of each specimen by dividing the specimen in to five equal parts and the measure shore D hardness and the average of the five readings was recorded.

Water sorption and
The specimens were dried in dissecator containing freshly dried silica gel.Then they were stored in an incubator at a 37°C ±2 °C for 24 hours after that the specimens were removed to room temperature for one hour then weighed with a digital balance with an accuracy of (0.000lg).This cycle was repeated every day at the same time until a constant mass "conditioned mass"(M1) was reached after 5 days which means the weight loss from each disc was not more than 0.2mg in 24 hours (ADA Specification NO.12, 2000).The specimens were then immersed in distilled water for 7 days at 37 0 C ± 2 0 C , after this period of time, each disc was removed from the water with tweezers and wiped for 30 seconds by clean dry hand towel, left in air for 15 second then weighed ,this value represent M2.In order to obtain the value of solubility, the discs were again reconditioned to a constant mass in the desiccators at 37°C ±2 °C as done in the first time for sorption test and the reconditioned mass was recorded as (M3).The whole group was reached to M3 within 5 days.The calculation of water sorption and solubility was according to the following equations: Ws= (M2 -M1) / S WSL= (M1-M3)/ S

RESULTS
FTIR test was done to samples of zirconium oxide nanofiller and trimethoxysilylprpoyl methacrylate (TMSPM)before Silanation to evaluate active groups, as seen in Figure 4 and Figure 5. Also other FTIR was done tozirconium oxide nanofiller after Silanation to evaluate the differences in active groups, as seen in Figure6.

( 1 )
M.Sc.student.Department of Prosthodontics, College of Dentistry, University of Baghdad.(2) Assist.Prof. Department of Prosthodontics, College of Dentistry, University of Baghdad.

4 )
The flask was covered by parafilm and the 5)The solvent (toluene) was removed by rotary evaporator under vacuum at 60°C at rotary 150 he modified nano filler was dried in vaccum oven at 60°C for 20 hours.Then nano filler stored of proper percentage of zirconium 3% silanized zirconium oxide values of flexural therefore % of silanized filler, as a percentage of modified Fig.4zirconium oxide nanoparticles.

Table 3 : Descriptive statistics and groups' difference for the
h