Key Engineering Materials Vols. 361-363

Abstract: A modular ceramic femoral head was selected for use as the bearing on a novel carbon fibre reinforced plastic (CFRP) total hip replacement femoral stem. Mechanical testing was required to validate this novel combination of materials for load bearing implant application. The Ceramic Head-CFRP Stem Taper interface was tested under axial fatigue loads according to BS/ISO 7206-5, followed by static loading to failure. The assembly survived the fatigue loads and exceeded the required FDA post-fatigue strength by 50%. In parallel, the test was simulated in a Finite Element Analysis study, resulting in recommendations for the adhesive bonding technique used to attach the modular head to the CFRP stem to further improve its strength.

Abstract: Mineral trioxide aggregate (MTA) is a slow setting Portland cement (PC) based dental material for endodontic applications. The present study investigated the effect of adding either CaCl2 or Plaster of Paris (PoP) as setting accelerators on the development of the material properties and microstructure with reaction time for a PC based model system. Mechanical strength, density and relative porosity were measured after 1, 10 and 30days and the microstructure was assessed using scanning electron microscopy (SEM). The strength of all cements increased with time whereas material density and relative porosity decreased due to the progress of the hydration reaction. Cements with 5-10% CaCl2 in the liquid phase had a higher final strength and lower porosity than cements modified with 20wt% PoP in the cement powder, whilst PoP modified cement had a shorter setting time of 15min compared with 60min for 10% CaCl2 addition. The microstructure of the two modifications were noticeably different, with the CaCl2 modified cement having more interconnected needle-like crystals than seen in PoP modified cements, which may explain the higher strength of this cement.

Abstract: Recent studies showed that the particle size of fillers, using for the reinforcement of dental resin composites, should be as small as possible to provide the maximum surface area for bonding to resin monomer, and should be kept well dispersed so as to be functionalized by a silane. In the present study, porous alumina monoliths with high specific surface area, measured by the Brunauer-Emmett-Teller (B.E.T.) method, were obtained using a novel preparation method. Structure and surface reactivity have been investigated as functions of temperature and chemical treatments. The impregnation of the as-prepared material by Triméthyletoxysilane (TMES) stabilized alumina with high specific surface area at higher temperature. A FTIR study has described the effect of TMES treatment and temperature on the structure of the material. The use of allyldimethoxysilane (ADMS) as a probe molecule for measuring the surface reactivity, has allowed us to show that the treatment of samples with TMES and their reheating at 1300°C results in adsorption sites which give stronger chemical bonds. This preliminary study has, therefore, allowed us to optimize the structural and surface treatment of experimental fillers before their use in the reinforcement of resin composites or resin-modified glass-ionomer cements.

Abstract: With elongation of average human life, problem such as bone embrittlement and osteoporosis call for quick solution and the expectation for artificial biomaterials heightens. Many ceramics widely used as artificial biomaterials are limited by their poor reliability characteristics. A CeO2 stabilized tetragonal zirconia polycrystalline (Ce-TZP) matrix incorporating nanometer sized Al2O3 particles within the zirconia grains (Ce-TZP/Al2O3) was recently developed. This material experienced significant improvements in both fracture toughness and strength above the standard mechanical performance of monolithic zirconia. In this paper, we performed a macro/microscopic fracture mechanics assessment of this developed Ce-TZP/Al2O3 nanocomposite, in comparison with a 3 mol% Y-TZP according to advanced in situ confocal Raman spectroscopy techniques.

Abstract: The effects of dental grinding and sandblasting on ageing and fatigue behaviour of pressure less sintered biomedical grade Y-TZP ceramics were investigated. Disc-shaped specimens were sintered to high density for subsequent surface treatment and testing. Accelerated aging experiments by autoclaving in artificial saliva were performed under isothermal conditions at 1340C. The amount of monoclinic zirconia in the ground and sandblasted specimens was < 5% and about 15 %, respectively and the corresponding strength values were 920 MPa and 1290 MPa. After autoclaving for 24 hours, the amount of transformed monoclinic zirconia in as-sintered material was increased to 15 %, resulting in about 10% strength reduction. In contrast, no strength reduction was observed with the ground and sandblasted specimens subjected to prolonged ageing. At any ageing condition, the highest survival rate during mechanical fatigue testing was observed with the sandblasted samples and the lowest with the ground samples. The strength of the surviving specimens tested in air corresponded well to the mean flexural strength of the particular group before fatigue testing, whereas lower survival strength values and a larger variability in strength were obtained with specimens that were subjected to prolonged accelerated ageing prior to mechanical fatigue testing in artificial saliva.

Abstract: In the area of dental treatment for crown and dental implants, ceramics restoration is becoming popular due to both aesthetic needs and release of metallic allergy. However, for the restoration of defected tooth, ceramics materials with higher reliability than that of conventional glass or alumina have been required, thus raising expectations for zirconia ceramics. Since residual stress play a significant role in the reliability of dental implants, in this paper, a non-destructive assessment of residual stress is presented for a zirconia-substrate/VINTAGE ZR T-Glass system using confocal fluorescence microprobe spectroscopy.

Abstract: The glass based on a 1.5SiO2-Al2O3-0.5P2O5-CaO-0.67CaF2 composition was produced and substituted gradually by barium. The structure of the glasses was studied by multinuclear Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and Fourier Transform Infrared Spectroscopy (FTIR). It was indicated by 29Si and 31P MAS-NMR spectra that silicon was present as Q4 (4Al) and Q3 (3Al) species and phosphorus was in a Q1 pyrophosphate environment. 29Al MAS-NMR spectra showed that four fold coordinated aluminum Al (IV) was the dominant species with a second peak assigned to octahedral aluminum Al (VI). The 19F spectra suggested that the barium addition caused the formation of Al-F-Ba(n) and F-Ba(n) species. Furthermore, a distribution of silicate network including Si-O-Si stretching (Q4 and Q3) and Si-O-[NBO] (Q3) per SiO4 was reflected by the FTIR study.

Abstract: The aim of this study was to investigate the effect of surface treatments on bonding strength of two kinds of zirconia to three kinds of resin cements. After thermal cycling, the shear bonding strength of both zirconia decreased in all the resin cements. The bonding strengths of two resin cements in which primer contains silane dramatically decreased after the thermal-cycling (p<0.01). Although the surface roughness of both zirconia sandblasted by 125-%m SiC was quite larger than that by 70-%m alumina (p<0.05), there were no significant differences in the bonding strength of the resin cement to both zirconia sandblasted by 70-%m Al2O3 and 125-%m SiC (p>0.05).

Abstract: The surface crystal chemistry of enamel treated with peroxide-based (the commercial product Opalescence Xtra Boost as well as aqueous solutions of H2O2) and citric-acid-containing bleaching agents (the commercial product Rapid White as well as aqueous solutions of C6H8O7) were studied by Attenuated Total Reflectance Infrared Spectroscopy and electron-probe microanalysis. The results show that the treatment with H2O2-based reagents leads to no side effects on the enamel superficial layer, whereas C6H8O7-based agents deteriorate the enamel mineral component. Hence, bleaching with citric-acid-containing products cannot be recommended.

Abstract: In the present investigation, four titanium (Ti) surfaces of dental implants were compared through in vitro systems. The surface roughness of Ti was measured by TR240 mobile surface roughmeter. The Ti implants were seeded with human periodontal ligament cells (hPLDCs) and maintained for a period of 0-7 days. The adhesion, proliferation, and differentiation of hPLDCs were observed by using Cell morphology, cell counting and Osteocalcin (OC) immunofluorescent staining. Results suggest that surface roughness of titanium favors hPDLCs behavior and improves cell adhesion, proliferation, and differentiation.