Strength ≠ Strength15. March, 2016
Data on the strength of dental materials often differs very widely, which frequently makes it difficult for users to compare materials. Sometimes the wrong data are used for evaluating a material’s properties. For example, the hardness value of a material provides no information about its strength/stability. In order to evaluate “stability”, the strength value should be used. When comparing different materials, it is essential to ensure that not only the actual figures are quoted, but also information on the unit (usually Megapascal [MPa]) and, above all, the test method employed. Different test methods produce different results for the same material (see image above). For dental ceramics the following tests are mostly used:
> 4-Point bending test
> 3-Point bending test
> Biaxial bending test
The tests for biaxial and 3-point flexural strength produce the highest values. The 4-point bending test produces lower, yet by no means less significant or even “worse”, values. Comparing the characteristic values of different materials obtained using different test procedures is not directly possible and inevitably leads to misinterpretation.