Dental restorations are often combinations of two or more materials joined together with chemical or mechanical bonding. As well, they are often bonded to teeth. The bond strength between the different materials is crucial for the longevity of a restoration. Differences in material properties will affect the binding properties.
Bonding properties are measured using different test methods depending on the intended use of the material. Some dental standards of which NIOM may perform the bond strength testing are ISO 9693-1:2012 Compatibility testing – Part 1: Metal–ceramic systems, ISO 9693-2:2016 Compatibility testing – Part 2: Ceramic–ceramic systems, ISO 10477:2004 Polymer-based crown and bridge materials, ISO 29022:2013 Adhesion – Notched-edge shear bond strength test, and the technical specification ISO/TS 11405:2015 Testing of adhesion to tooth structure.
NIOM is accredited for bond strength testing of bonding between alloys and veneering ceramics according to ISO 9693-1:2012. This test is also used for zirconia-based ceramics. For the so-called Schwickerath test, veneering ceramic is fired onto core materials at high temperature and both materials contract during cooling. Difference in coefficients of thermal expansion may cause interfacial stresses. Other properties like visco-elasticity of the glass phase of the veneering ceramic will also influence the stress relation. These circumstances are described in a research article¹.
For other types of core ceramics, there has not been any standard test procedure until ISO 9693-2:2016 was published recently. The methods of this standard will be incorporated in NIOM’s test portfolio.
NIOM is also accredited for ISO 29022, where bonding between a composite and enamel or dentine surface of human teeth is tested. More than 50 different bonding materials (adhesives) have been investigated at NIOM during the years and some results can be found at https://www.niom.no/content/dentin-adhesives.
1. Kvam K, Hero H. Stress relaxation in titanium–ceramic beams during veneering. Biomaterials. 2002; 22: 1379–1384.