Publications by authors named "Shakeel A Shahdad"

2 Publications

  • Page 1 of 1

Developments in denture teeth to prevent softening by food solvents.

J Mater Sci Mater Med 2007 Aug 5;18(8):1599-603. Epub 2007 May 5.

Restorative Dentistry, The Royal London Dental Hospital, New Road, London, UK.

The effect of various food-simulating solvents on the hardness of denture teeth after varying storage times, using a Martens hardness test was determined. Martens hardness (HM) was assessed at baseline and during storage up to 1 month in distilled water (DW), peppermint oil (PO), heptane (HT) and 75% ethanol (ET) for four commercially-available denture teeth; Vivodent (VIV), Double-cross-linked Postaris (DCL), Orthosit (ORT), Candulor porcelain (POR) and two polymer based experimental denture teeth: Experimental 1 (EXP1); a hybrid nanocomposite with two different sized silanated filler particles and Experimental 2 (EXP2); containing an organic copolymer based upon urethanedimethacrylate and polymethyl methacrylate. Hardness [mean (sd)] at baseline was: VIV 142 (1), DCL 142 (1), ORT 209 (9), POR 2926 (101), EXP1 285 (11), and EXP2 146 (12). One-way ANOVA using Tukey's test on polymer-based materials showed that the hardness values of ORT and EXP1 were significantly higher than those of VIV, DCL and EXP2 (P < 0.05). Moreover, EXP1 had a significantly higher hardness value than ORT (P < 0.05). Except for EXP1, all polymer based materials showed a significant drop in hardness after storage in ET (P < 0.05). Specimens stored in water, heptane and peppermint oil showed minor fluctuations in hardness, which were not statistically significant.
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August 2007

Hardness measured with traditional Vickers and Martens hardness methods.

Dent Mater 2007 Sep 4;23(9):1079-85. Epub 2006 Dec 4.

Department of Restorative Dentistry, School of Dental Sciences, University of Newcastle upon Tyne, UK.

Objective: To determine the differences, if any, between hardness measured with traditional Vickers and Martens hardness test methods on denture teeth under 2, 10 and 50 N loads.

Method: Hardness of acrylic resin (VIV), composite resin (ORT) and porcelain (POR) denture tooth materials was measured using a traditional Vickers hardness (HV) method and Martens hardness (HM) method at 2, 10 and 50N test loads. Vickers hardness was also calculated from the force-indentation depth curves (HVfid) that were recorded during Martens hardness. Indentation creep of the three test materials was also determined during Martens hardness testing.

Results: HM values were the same irrespective of the test force used. However, HV values were different for the three test forces. ANOVA using Tukey's test of the HM data showed that the hardness of POR was significantly higher than VIV or ORT (P<0.001). Moreover, ORT had a significantly higher hardness than VIV (P<0.001). The statistical analysis of HVfid data showed similar results. ANOVA of the HV data showed the hardness of VIV to be significantly higher than ORT (P<0.001) under 2, 10 and 50 N test load. The HV values for POR under 2 and 10 N test load could not be calculated because of inability to measure the indentation diagonals. Under the 50 N load, the hardness of POR was significantly higher than VIV and ORT. POR had a significantly lower creep value than any other material tested while VIV showed a statistically significantly higher creep than ORT.

Significance: This study confirms that the visco-elastic recovery of the materials has a very significant effect on the outcome of the hardness tests of denture teeth and the Martens hardness test method has obvious advantages when testing dental materials.
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September 2007