[An in-vitro study on improving the bonding strength of steel bands with the use of glass ionomer cements].

An in-vitro investigation was carried out with the aim of improving bond strength at the glass-ionomer cement/stainless steel interface, thus reducing loosening rates. In bovine incisors it had previously been shown that the week point is the glass-ionomer cement/stainless steel, rather than the enamel/glass-ionomer cement interface. In a simple, standardized experimental set-up permitting reproducible measurements, the semi-flexible and irregularly shaped orthodontic bands were replaced by solid stainless steel cylinders made of the same alloy, and both shear and tensile bond strength were measured. Using this set-up, five different types of surface preparation were compared in terms of their bond strength. The highest bond strength was found to be associated with a steel surface sandblasted with coarse aluminium oxide. In further experiments, the devices provided by the manufacturer for dosing powder and liquid were found to be quite inaccurate. This is particularly unfortunate, since the bonding properties of the glass-ionomer cement investigated proved to vary significantly with small variations in the powder:liquid ratio. To reduce the rate of loosening of orthodontic bands, the cement should be mixed at refrigerator temperature, using capsules filled by the manufacturer with the optimal dosages, and then used with bands previously sandblasted with coarse aluminium oxide powder.