Thermal expansion of selected parent dental alloys used for fixed partial denture

Author(s): Lionel Aranda, Pascal De March, Patrice Berthod

The dimensional variation of the differentmaterials included in the ceramicmetallic dental prostheses is of a great importance since manufacturing them involves several heating phases until rather high temperatures are reached (near 1000°C) and subsequent cooling phases down to room temperature, for heat-treating porcelain to achieve the required properties and aspects without damaging it because of too great difference of thermal expansion behaviour with the internal strengthening metallic framework. The present work consists in studying the thermal expansion and retraction behaviours of eight parent alloys the thermal dimensional variations of which are the one of the whole framework since they represent almost its whole length. Thiswas done by reproducing the temperature cycling known by real prostheses after porcelain covering. It appears that the dimensional evolution can be different among the studied alloys since the thickness of some of them decreases during the first thermal cycles while this never occurs for other parent alloys. Further the average thermal expansion and retraction coefficients vary among the different classes of nobility of the alloys as well as between the alloys of a same nobility class. An attempt was done for establishing an empiric correspondence between the thermal expansion coefficient of each parent alloy and the one of the main elements of its chemical composition.Arather good agreementwas additionally found between the measured values and the ones of the manufacturer.

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