Preparation And Properties Of Dental Restoration Composites By Co-filling Diatomite And Nanosized Particles

Dental restoration composites have attracted more public attentions. They are gradually used instead of conventional dental amalgam alloys, because of their excellent properties. The application of dental resin composites has been extended from anterior restorations to posterior restorations. Recently, many researchers have attempted to study the mechanical properties, polymerization shrinkage, conversion, and so on, through changing the types, size and morphology of inorganic fillers, altering composition of resin matrix and using different silane coupling agent. However, poor mechanical properties were still problems of dental resin composites, especially using porous filler.In this text, porous diatomite first was used as fillers. Dental composites were prepared by co-filling diatomite and nanosized particles. Firstly, the purification of raw diatomite by acid-leaching was conducted in the HCl solution. Purified diatomite was characterized by UV-vis diffuse reflectance spectroscopy and an N2 adsorption-desorption isotherm. The results reveal that the raw diatomite before purification had a high absorbance in the UV-visible light region. However, after leaching, the absorbance of the products declined greatly, and the colour of diatomite has changed from yellow to white. The porous volume and pore diameter of the acid-leached diatomite were both larger than those of the raw diatomite. The specific surface area of the acid-leached diatomite was lower compared to the raw materials. ZrO2-coated silica nanoparticles(ZrO2-SiO2 nanoparticles) were prepared using precipitation method. ZrO2 nanoparticles were pure cubic phase with good crystallinity, and a mean crystallite size of about 5～6 nm. Both diatomite and nanosized particles were silanized with 3-methacryloxypropyltrimethoxysilane (γ-MPS). Fourier transforms infrared spectroscopy and a thermogravimetric analysis show that some amount ofγ-MPS has grafted on the surface of diatomite and nanoparticles.Dental composites were prepared by co-filling different sizes of modified diatomite and modified nano-SiO2 (OX-50) (or modified ZrO2-SiO2 nanoparticles). If the mass fraction of modified diatomite and modified OX-50 (or modified ZrO2-SiO2 nanoparticles) was 1:1 (wt.%), there would generate different filler contents of composites. Consequently, the smaller surface areas of diatomite, the more filler content of dental composites. The mechanical properties of composites were gradually enhanced with increasing filler content. However, when only OX-50 or ZrO2-SiO2 nanoparticles without diatomite, mass fraction of fillers were only 60wt.% and 58wt.%, respectively, and the composites have lower mechanical properties.The modified diatomite (500mesh white) and modified OX-50 were blended with dental resin composites at different mass ratios. The flexural strength, elastic modulus and compressive strength of dental composites were increased with the addition of diatomite. However, when the mass fraction of diatomite was more than 21wt.% in composites, the properties of composites began to decrease. To the Vicker's hardness of composites, the composites have the highest hardness containing 75wt.% fillers (modified diatomite/modified OX-50 as 1:1). After that, the hardness of composites increased with more OX-50.Dental composites were prepared containing treated diatomite (500mesh white) and silanized ZrO2-SiO2 nanoparticles. The mechanical properties of dental composites were enhanced with decreased diatomite content and increased ZrO2-SiO2 nanoparticles content. When the mass fraction of ZrO2-SiO2 nanoparticles was more than 42wt.%, the elastic modulus and compressive strength of composites were gradually reduced. However, when the mass ratios of the two kinds of particles were 28:42 and 21:49, respectively, the flexural strength and Vicker's hardness of the two composites were no significantly different from each other. The two kinds of properties of composites began to decrease, when the mass fraction of ZrO2-SiO2 nanoparticles is more than 49wt.%.The numerous and relatively large steps in the fracture surfaces of the co-filling composite are in contrast to the relatively flat fracture surfaces of the unfilled diatomite composite. The rough fracture surfaces constitute a high surface area, consuming energy in the creation of new surfaces. Therefore, the dental composites containing treated diatomite and modified nanoparticles have more filler content and better mechanical properties than which filling with only modified nanoparticles. And then dental resin composites have radiopacity because of ZrO2 nanoparticles. Radiopacity valus of composites are higher than that of dentine and enamel, which apt to detection of caries and detects adjacent to restorations.