Hardness measured with traditional Vickers and Martens hardness methods.
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.


METHODS
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.


CONCLUSIONS
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.
Shahdad
Shakeel A
SA
Department of Restorative Dentistry, School of Dental Sciences, University of Newcastle upon Tyne, UK. shakeel.shahdad@bartsandthelondon.nhs.uk
McCabe
John F
JF
Bull
Steven
S
Rusby
Sandra
S
Wassell
Robert W
RW
D000180:Acrylic Resins / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D004548:Elasticity; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D019904:Polymethyl Methacrylate / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014093:Tooth, Artificial; D014783:Viscosity
D000180:Acrylic Resins; D003188:Composite Resins; D003764:Dental Materials; D008689:Methacrylates; D011140:Polyurethanes; D003776:Dental Porcelain; C029824:urethane dimethacrylate luting resin; D012822:Silicon Dioxide; D019904:Polymethyl Methacrylate