Wettability of silicone and polyether impression materials: Characterization by surface tension and contact angle measurements

We report the surface properties of unset and set polymer impression materials by performing surface tension and contact angle measurements. Three types of impression materials were investigated: polyether, addition cure and condensation cure silicones. The high surface tension of about 50 mJ/m2 for the base and of 38 mJ/m2 for the accelerator of a polyether system is caused by polar carbonyl and ether groups, respectively. The surface tension of the silicones is in the range of 20 up to 23 mJ/m2 for both the base and the accelerator regardless of internal surfactants that were incorporated to the addition cure silicone. These different surface tension values at the liquid–air interface result in hydrophilic properties of the unset and set polyether surfaces and in hydrophobic surface properties for the silicones in contact with aqueous media. However, the wettability of an hydrophilized addition cure silicone could not be predicted by these surface tension measurements. A good strategy to quantify the influence of surfactants as well as the additional effect of the bulk polymerization of the impression material during setting are contact angle measurements with water. In this way, it was shown that the wettability of the addition cure silicones could be strongly changed during setting when an internal surfactant was added to the material that migrates to the outermost solid–liquid interface. The water contact angles on the unset material and on the completely set material were lowered considerably to less than 60°. The decrease of the water contact angle was directly related to the decrease in the liquid surface tension of the water droplet during spreading as could be proved by ADSA contact angle measurements for the set silicone system. In the partly set system, the migration of the surfactant to the outermost surface was increasingly hindered with the progression of the polymerization and cross linking resulting in high water contact angles of more than 110°.