Effect of non-ionic surfactants on surface properties of hydrophilic polyvinyl siloxane impression materials

This study examines the effect of non-ionic surfactants on surface hydrophilicity and detail reproducibility of die stone for hydrophilic polyvinyl siloxane impression materials. Hydrophilic polyvinyl siloxane impression materials were prepared with a polydimethylsiloxane composition and non-ionic surfactants. The surfactants used were nonylphenoxy poly(ethyleneoxy) ethanol homologs of varying ethyleneoxy chain length. These homologs are designated NP4, NP6, and NP10 according to the mole number of ethyleneoxy group of 4, 6, and 10, respectively. The contact angle, consistency, linear dimensional accuracy, and detail reproducibility for hydrophilic polyvinyl siloxane impression materials were tested. The non-ionic surfactants used in this study contain a silicone-loving group (nonylphenoxy group) which makes the surfactant dispersible in the silicone prepolymer. The dispersion size of these surfactants in polyvinyl siloxane prepolymers was dependent on the HLB of each surfactant. The more hydrophobic (silicone-loving) a surfactant is, the smaller the dispersion size is obtained. The incorporation of non-ionic surfactant into polyvinyl siloxanes enhanced their surface hydrophilicity and consequently led to significant reduction in contact angles. Significant differences in contact angle were found among the samples (P<0.05). The contact angle was lowest when NP4 was incorporated even though NP4 is less hydrophilic than NP6 and NP10. This implies that the exposed surfactant concentration on the surface was highest when NP4 was used. The consistency and linear dimensional accuracy of surfactant-modified silicone impression materials were not affected by the type of surfactants used in this study. However, NP4-modified polyvinyl siloxane impression material showed the highest quality reproduction of the thinnest line, indicating highest wettability with gypsum slurry among the samples. We concluded that the surface concentration of surfactant on the silicone impression material was a crucial factor in determining surface hydrophilicity. The surface hydrophilicity of surfactant-modified silicone impression materials was of major relevance for the detail reproduction of die stone.