Contact Angles Amongst Impression Materials, Set and Unset

Objective: The adaptation of gypsum to an impression material (IP) is determined by surface tensions measured by a contact angle (CA) simulation with water.  The adaptation of IP to the tooth is affected by the surface tensions, viscosity of the material, setting time, and surfactant mixing rate.  A “CA” measurement can be made for IP on tooth structure that is the summation of all of these factors. Waiting 30s, as previously reported, before making these measurements is too long after mixing for such measurements. Determine the CA of water on set IPs.  Determine the “CA” of IP on tooth structure immediately after mixing.

Method: One poly vinyl ether silicone, one polyether, and 8 polyvinyl siloxane IPs were examined.  For water CA on IP, a flat slab was made of the light body version of each of these materials.   A calibrated drop of water was dropped on the slab and a video recording and CA measurement at 1s intervals was made with a goniometer.  For IP on tooth, bovine enamel and dentin was flattened to 600 grit and maintained wet.  Then the surface was wiped immediately before dropping the drop of IP.  A calibrated drop of IP was placed on the tooth surface through a mixing tip and fine delivery tip.  The CA was recorded as previously described. Data were analyzed at 5s, 30s and 60s after the drop was created. 3Way ANOVA was run.

Result: CAs decreased over the time of measurement.  CAs were similar on enamel and dentin for each material. By 60s the CA of water on the set material was lower than that of IP on tooth. 30s CA of IP on tooth ranged 55^o-100^o, and water on IP 21^o-115^o.

Conclusion: No one material was uniquely better set or unset.  This method can record an adaptation “contact angle” immediately after mixing.