Effect Of Zinc Oxide Whiskers On Mechanical And Aesthetic Properties Of Denture Base

Denture base is a major component of removable denture. The material most commonly used for the fabrication of removable denture is polymethyl methacrylate (PMMA). Since it’s simple, easy of molding, easy to repair and has good aesthetic properties and so on. Nowadays denture always occur frequent breakage, abrasion and other problems when using because of its toughness and hardness can’t fully meet the requirements. Therefore, it’s time to improve the mechanical properties of the base material.Zinc oxide whisker is a novel functional materials developed in recent years. It can achieve the three-dimensional distribution in the matrix, change the stress conduction and distribution in the material and improve isotropic physical properties of polymers because of its unique three-dimensional structure. Moreover, zinc oxide whisker also has many unique features such as abrasion resistance, anti-aging, anti-bacterial and so on. It has been widely applied in the chemical, electronics, transportation and other fields at present.Objective:This study intended to investigate the mechanical and aesthetic properties of polymethyl methyacrylate denture base in which zinc oxide whiskers was added.Methods:We conducted five groups according to the surface treated zinc oxide whiskers content which added to denture base including control,1%,3%,5%,7%. To get the two powders mix we use an electric mixer. Then add liquid for denture acrylic to the manufacturer, conventional bath treatment. Specimens (65mm×10mm×3mm) were prepared according to ISO20795-1. After polymerization, all the specimens were polished under running water with No.320,600,800,1000,1200silicon-carbide paper, finally using precision lapping polishing machine for polishing. The test specimens were stored in water at37℃for48hours before tests.Flexural properties (bending strength, bending modulus) of denture base materials were evaluated (n=10). A three-point bending test was carried out on an Instron testing machine at a5mm/min crosshead speed. The Vickers hardness test was used to compare micro hardness values (n=5), each sample tested10points. Shade Eye NCC electronic colorimeter was used to colorimetric (n=10) according to CIE1976L*a*b*standard colorimetric system. Each sample were measured three times and record L*, a*, b*values. We used Scanning electron microscopy (SEM) to observe fracture surface samples.Results:(1)The experiment result of the denture base mechanical properties when adding zinc oxide whiskers showed that, flexural strength measured were (92.15±2.22) MPa、(101.27±1.84) MPa,(104.55±1.65) MPa,(109.00±2.70) MPa,(103.00±1.56) MPa, the flexure modulus were measured at (3140.63±216.50) MPa,(3430.51±179.24) MPa,(3501.08±203.61) MPa,(3645.30±198.68) MPa,(3555.64±122.08) MPa, Vickers hardness measured value (15.83±0.49) kg/mm2,(18.72±0.54) kg/mm2,(19.49±0.59) kg/mm2,(20.57±0.85) kg/mm2,(19.56±0.64) kg/mm2, which depending on the amount of zinc oxide whisker. Flexural strength, flexural modulus and hardness of composite material increased with the increasing content of zinc oxide whiskers in a limited range. And the flexural strength of the composites was enhanced about18.29%, flexural modulus enhanced16.07%, hardness enhanced29.9%compared with the control group when the amount of zinc oxide whiskers to be5%. The flexural strength, flexural modulus and Vickers hardness of resin base were significantly improved when adding zinc oxide whiskers.(2) Denture base resin’s color difference△E increased with the increasing content of zinc oxide whiskers. And it’s showing trend to lightness, green and yellow. Color difference△E between1%group and control group was2.62and considered clinically accepted. AE values of other groups were lager than3.3and considered clinically unaccepted.(3) Scanning electron microscopy showed that by contrast the smooth fractured surface of the control group, the fractured surface of the experimental group is complex and rough. The specimens fractured surface of1%,3%,5%group become more rough and crazing-tearing gradually deepening as the increase of the zinc oxide whisker content, wherein the tear surface groups most is5%group. Besides,7%group is less complex than5%group through this study.Conclusion:Zinc oxide whiskers filler significantly enhanced mechanical properties of denture base. Color difference of denture base was clinically accepted when zinc oxide whiskers content was1%.