Investigating the Validity of the ISO 6872:2015 ‘Dentistry - Ceramic Materials’ for Chemical Solubility

Most research regarding dental ceramics focuses on the mechanical, physical and optical properties. These properties are important; however, the chemical durability of dental ceramics is also significant. The oral cavity is a complex environment, ‘in vitro’ studies have not succeeded in replicating the solubility measurements of dental ceramics perfectly. The International Organization for Standardisation has published revised chemical solubility testing methods for dental ceramics ISO 6872. These methods failed to improve the reproducibility of the chemical solubility findings (Stokes et al., 2002), which led many researchers to develop alternative methods.
Nevertheless, these ISO methods have received limited criticism in the literature. Therefore, the aim of this research was to investigate the validity of the ISO 6872 (BS ISO, 2015) ‘Dentistry: Ceramic materials’ for chemical solubility, and if required design a superior method. The current standard ISO 6872 (BS ISO, 2015) specifies the total surface area of the test specimens only. Therefore, the research hypothesis is that any alteration of the specimens’ geometry will affect the chemical solubility value of the same material.
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The initial findings showed that chemical solubility can be manipulated by altering the geometry of individual test specimens whilst still complying with the current standard. Characterisation tests such as SEM, EDS, XRD, ICP and Vickers hardness were performed to investigate the effects of the test environment on the specimens. As a result, the physical handling of the specimens was assumed to affect the outcomes of the chemical solubility test. An optimised test was designed to minimise the contact of the specimens and the findings showed that there is no significant difference between different specimens’ geometries.
The study concluded that the current prescribed chemical solubility method of ISO 6872 (BS ISO, 2015) lacks some specifications in order to be reliable in measuring the chemical solubility values of dental ceramics.