Improved dimensional stability of polysulfide elastomers

Polysulfide elastomers are widely used dental impression materials for selected applications. Compared to other widely used elastomers, addition silicones, and polyethers, they suffer from perceived inferior dimensional stabilities.  If they could be modified to yield dimensional stabilities equivalent or superior to polyethers, they would be a more economical alternative to these materials. In an old study of surfactant additions for improved wettability, it was casually observed that improved dimensional stability could also result.  Objective: This study was designed to determine whether addition of selected polyoxyethylene-nonylphenol surfactants will increase dimensional stabilities of commercial polysulfide elastomers. Materials and Methods: Experimental materials consisted of three commercial polysulfide impression materials, Coe-Flex (CF) and Omniflex (OF), from GC-America and Permlastic (PL) from Kerr.  Materials were mixed according to manufacturer’s directions.  For the modified materials, commercial nonyl-phenol-ethoxylate surfactants were incorporated.  For seven experimental groups surfactants were incorporated at 2 weight percent:  CO-210, CO-430, CO-520, CO-530, CO-610, CO-630, and CO-710 (Rhodia, Cranberry, NJ).  Samples consisted of five specimens. Immediately after mixing, the material was transferred to the dimensional accuracy die specified in ANSI/ADA Specification 19. The dimensional accuracy was determined by measuring the distance between the impressions of the scribed lines as described in the specification.  Dimensional stability was determined by repeating measurements after 1, 2, 7, 14, 21, 28, 56, and 91 days. Results: Improved dimensional stability was seen in the following modified groups as compared to their control: PL with CO-430 and CO-710; OF with CO-210. The 0.5% specification limit change was exceeded on the following days: PL control at 14, PL CO-430 at 21, PL CO-710 at 28, OF control at 2, and OF CO-210 at 7. None of the CF modified materials improved upon the control. Conclusions: Certain selected surfactants improve dimensional stabilities of polysulfide impression materials, although probably of little clinical import.