Papers by Keyword: Biaxial Flexure Strength

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Authors: Drago Skrtic, S.Y. Lee, Joseph M. Antonucci, D.W. Liu
Abstract: This study explores how a) the resin grafting potential for amorphous calcium phosphate (ACP) and b) particle size of ACP affects physicochemical properties of composites. Copolymers and composites were evaluated for biaxial flexure strength (BFS), degree of vinyl conversion (DC), mineral ion release and water sorption (WS). Milled ACP composites were superior to unmilled ACP composites and exhibited 62 % and 77 % higher BFS values (dry and wet state, respectively). The average DC of copolymers 24 h after curing was 80 %. DC of composites decreased 10.3 % for unmilled Zr-ACP and 4.6 % for milled Zr-ACP when compared to the corresponding copolymers. The WS increased as follows: copolymers < milled Zr-ACP composites < unmilled Zr-ACP composites. The levels of Ca and PO4 released from both types of composites increased with the increasing EBPADMA/TEGDMA ratio in the matrix. They were significantly above the minimum necessary for the redeposition of HAP to occur. No significant consumption of released calcium by the carboxylic groups of methacryloxyethyl phtahalate (MEP) occurred at a mass fraction of 2.6 % of MEP in the resin. Improvements in ACP composite’s physicochemical properties are achieved by fine tuning of the resin and improved ACP’s dispersion within the polymer matrix after ball-milling.
Authors: Jun Cui, Yi Fan Chen, Yong Lie Chao, Chun Xia Chen, Jun Ou, Lei Sui, Wei Qun Zhang
Abstract: The purpose of this study is to determine the bi-axial flexural strength, weibull modulus and fracture mode of bilayered alumina glass-infiltrated core and the veneering porcelain. Forty disk specimens were fabricated from alumina glass-infiltrated core (HSDC-A) and veneer porcelain (Vintage AL). The specimens were equally divided into four groups as: MV, monolithic specimens of veneer material; MC, monolithic specimens of core material; BV, bilayered specimens with the veneer in tension; BC, bilayered specimens with core material in tension. Mean flexure strength, standard deviation and associated Weibull modulus were determined using bi-axial flexure (ball-on-ring) for each group. Both optical and scanning electron microscopy were employed for identification of the fracture mode and origin. The surface loaded in tension influenced the bi-axial flexural strength and reliability of the composites. The frequency of specimen delamination, Hertzian cone formation and sub-critical radial cracking in the bilayered discs are also dependent on the surface loaded in tension.
Authors: A. Díaz, Wynette Redington, Stuart Hampshire
Authors: Hideo Sato, Naoko Kubota, Seiji Ban, Youichi Yamasaki
Abstract: The aim of this study was to determine the biaxial flexure strength of a commercially available dental pulp capping or cavity liner material, mineral trioxide aggregate (MTA). MTA and a conventional pulp capping material, calcium hydroxide, were used in this study. Each material was prepared into a disk-shaped specimen. Those specimens were stored in 100% humidity atmosphere at 23 or 37°C for 3 or 24 h. Six specimens in each condition were used for the biaxial flexure test using a piston-on-three-ball according to ISO-6872. Surface pH values were determined. The biaxial flexure strengths of MTA after setting in 24h were larger than those of Dycal (p <0.01). pH value of MTA was higher than that of Dycal. These results indicated that MTA was clinically usage material.
Authors: Nam Sik Oh, S.I. Jeong, S.H. Kim, Keun Woo Lee, Myung Hyun Lee, I.K. Kim, Dae Joon Kim
Abstract: This study was designed to evaluate mechanical properties and the marginal fitness of glass infiltrated alumina core fabricated from aqueous alumina tape. Utilizing the automatic Dr. Blade model (DP-150 of Japan JinChungjungGi manufacturer) fabricated the slurry into 0.5 ㎜ thickness aqueous-based alumina tape. The coefficient of thermal expansion and biaxial flexural strength of alumina composite produced from alumina tape were investigated. Three upper central resin incisors were prepared with 90o, 110o, 135o shoulder margin for all-ceramic crown. Individual tooth model’s impressions were taken 15times each to make epoxy resin die. Cores were made of alumina tape to each and every dies. Crown setting was done on the epoxy resin dies. The specimens were evaluated for measuring for marginal gaps of glass infiltrated alumina core fabricated from aqueous alumina tapes under 180 magnifications with Kan Scope(Sometech Vision, Korea) was done. The retained measurements were analyzed with Turkey’s Studentized Range Test for marginal fitness of each specimen. Coefficient of thermal expansion of alumina tape was 7.5x10-6/°C, and biaxial flexural strength was observed to be 498±32MPa. The marginal fits of alumina cores made of alumina tapes showed the least marginal gap of 41.5 ㎛ in the 110o shoulder margin, and increasingly with 135o, 90o shoulder margin. Marginal fitness should be better in angles larger than 90o.
Authors: T. Nejatian, A. Johnson, R. Van Noort
Abstract: The fracture resistance of polymethyl methacrylate (PMMA) the most popular denture base materials, is not satisfactory. The aim of this study is to improve the mechanical properties of PMMA by adding filler particles. Different inorganic filler particles including micronised glass flakes, acryl silane micronised, glass flakes 350nm, TiO2 and ZrO2 with different ratios by weight were incorporated into heat-cure plain PMMA and processed with optimal condition [2.5:1 Powder/ monomer ratio, conventional packing method and water bath curing for 2 hours at 95°C] to produce 12mm diameter and 2mm thick discs. Plain PMMA without additives was prepared as a test control. Three types of mechanical tests, biaxial flexure, microindentation fracture toughness and Vickers hardness were carried out on the samples. It was found that incorporating the particles did not improve the biaxial flexural strength of the resin. However, TiO2, ZrO2 and micronised glass flakes increased the fracture toughness of the resin. The hardness of PMMA was improved by the incorporation of all the particles.
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