Measurement of the setting and thermal expansion of dental investments used for the superplastic forming of dental implant superstructures

Objectives: The study examined the setting and thermal expansions of seven dental casting investments intended for use in the superplastic forming (SPE) of Ti6A14V for dental implant superstructures. The total expansion is compared with the coefficient of thermal expansion of the alloy. Methods: The unrestricted setting expansion of the investment was measured at room temperature using a lined brass trough and dial gauge. The thermal expansion was measured at a heating rate of 5 degreesC/min up to 900 degreesC. The thermal expansion of Ti6A14V was measured at a heating rate of 15 degreesC/min. Results: The Selevest investment had a small shrinkage on setting. The largest setting expansions were observed with Rema Exakt and Fujivest, Selevest DM and Fujivest had the greatest thermal expansions. Rema Exakt had the greatest overall expansion. The total expansion of Rematitan most closely matched the thermal expansion of Ti6A14V when the manufacturer's recommended special liquid to water ratio for crowns and bridges was used. Significance: SPF is a novel technique which is being applied to the manufacture of dental prostheses. As dental casting investments are used to make the dies used for SPF the dimensional changes associated with these materials should be matched to the dimensional changes of the Ti6A14V alloy used in order to achieve a passive fit. This study has identified Rematitan as an investment whose total expansion may enable an accurately fitting SPF implant superstructure to be made. (C) 2001 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.