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Addison O.,University of Birmingham | Sodhi A.,University of Birmingham | Fleming G.J.P.,Materials Science Unit
Dental Materials | Year: 2010

Objectives: Cementation of all-ceramic restorations with resin-cements has been demonstrated to reduce the incidence of fracture in service. The aim was to investigate the influence of loading force and loading duration applied during cementation on the reinforcement conferred by a resin-cement on a leucite reinforced glass-ceramic. Methods: 210 glass-ceramic discs (12 mm diameter, 0.8 mm thickness) were allocated to seven groups (n = 30). The bi-axial flexure strength (BFS) was determined for 'as-fired' specimens (group A), following HF-acid etching (group B) and following etching and centrally loading on a semi-compliant substrate with 30 N for 300 s (group C). Further etched specimens were coated with Rely-X Unicem resin-cement under cementation loading of 5 or 30 N, for 60 or 300 s (groups D-F) prior to BFS determination using multilayered analytical solutions. BFS data was compared using factorial or one-way analyses of variance and the Weibull analysis. Results: HF-acid etching of the 'as-fired' surface resulted in a significant reduction in mean BFS (P < 0.001) whereas resin-cementation subsequently conferred significant strengthening (P < 0.001) ranging from 24 to 38% and dependent on the loading parameters employed. A factorial significance (P = 0.004) of seating load (5 or 30 N) and significant factorial interaction (P < 0.001) of seating load and load duration (60 or 300 s) on the mean BFS were identified. Significance: The magnitude of resin-reinforcement conferred was sensitive to the loading parameters investigated although the mechanisms underlying the variation appear complex. Similar patterns of variability can be expected clinically impacting on the clinical longevity of resin-cemented glass-ceramic restorations. © 2010 Academy of Dental Materials.

Sekkina M.M.A.,Materials Science Unit | Elsabawya K.M.,Taif University | El-Maghraby A.,National Research Center of Egypt | El-Maghraby A.,Taif University
Oriental Journal of Chemistry | Year: 2013

The present investigations introduce new trend of applying AFM-microscopy to visualize a real 3D-imaging of sample's surface topography. High resolution AFM-investigations indicated that crystalline asprin has regular arrays of atomic arrangement with no violation in the bulk of asprin. TM deflection AFM- gave us good approximation to the diffusion of grain throughout the surface topology of investigated asprin. The AFM-deflection centers imaging indicated that the numbers of grains distribute in circular arrangements on the surface and material bulk. 3D-visualized imaging introduce precise determination of exposure surface area interacting with dissolving agent.

Elsabawy K.M.,Materials Science Unit | Elsabawy K.M.,Taif University | Abou Sekkina M.M.,Materials Science Unit | Asker M.A.,Materials Science Unit | And 2 more authors.
Solid State Sciences | Year: 2010

The sample with in the general formula Bi2-xPbxSrV2O9, where x = 0.0, 0.05, 0.1, 0.2, 0.3, and 0.6 mol were synthesized by the high temperature solid state reaction and firing method. The X-ray diffractograms confirmed the formation of single phased layered perovskite in all samples. TGA and DTA thermal analyses on the green samples included steps of thermal analysis of strontium carbonate, bismuth carbonate, ammonium vanadate, lead oxide and finally on the high temperature solid state formation. The effect of lead dopings on the sintering, structural and micro-structure, properties of 212BiSrV-ceramics were investigated. The infrared absorption spectra show a series of vibrational modes within the range of 400-1600 cm-1. © 2010 Elsevier Masson SAS. All rights reserved.

Bhamra G.S.,Materials Science Unit | Fleming G.J.P.,Materials Science Unit | Darvell B.W.,University of Hong Kong
Dental Materials | Year: 2010

Objective: To investigate the effect of irradiance through choice of LED light-curing unit (LCU) and fiber-optic tip on the mechanical properties of methacrylate resin-based composites (RBCs). Methods: Rectangular bar-shaped specimens (25 mm × 2 mm × 2 mm) of four RBCs, irradiated from one side for the manufacturer's recommended times with one of two LED LCUs, and with either 8 or 13 mm tip diameter, were tested in three-point bend for flexural strength and modulus of elasticity; Vickers hardness was measured on top and bottom surfaces, on overlapped and non-overlapped irradiation sites. The effects and interactions of all factors were examined by analysis of variance. Results: While the materials tested differed significantly for all properties (P < 1 × 10-6), there was no significant effect for LCU, tip, or irradiance for flexural strength or modulus of elasticity. For hardness, the only significant effect overall was due to irradiance on the bottom surface. Conclusions: Both LCUs and both tips could be used to give adequate top surface hardness, but the recommended maximum increment thickness is too great for adequate cure at the bottom with the tested LCUs at the recommended times. An extended experimental design would be valuable to test behavior at much elevated irradiances. © 2009 Academy of Dental Materials.

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