Ah yes… impression materials. They can be a cruel mistress. I’ve learned (the hard way) that not all impression materials are created equal and that they require different techniques to use properly.
Let’s look at the two most popular types on the market for definitive impressions, polyvinyl siloxane and polyether.
Polyether is the clear winner. It’s more hydrophilic than PVS, so it can flow around your crown margins without fear of saliva, gingival crevicular fuild, or blood. It’s also more rigid than PVS with better dimensional stability. The only downside to all that improved accuracy is that it can be a little challenging to remove the tray after setting. It’s always important to block out any undercuts, such as open gingival embrasures on other teeth in the arch, but it’s extra critical with polyether.
The margins look good but there was clearly an issue with compatibility between the heavy and light body PVS. I would not trust this impression.
A polyether impression of the same teeth reveals the strength of using a single material for both tray and wash.
Polyether wins again. PVS is mostly used with two different consistencies, e.g heavy and light body. That means we need two slightly different materials to mix and set correctly at the same time. That doesn’t happen sometimes owing to such issues as operator error and air temperature/humidity. Polyether can be effectively used as one viscosity for the tray and the wash, so we don’t have to worry about compatibility headaches.
PVS takes this round. Polyether is notorious for having an odor and taste that is compared to everything from gasoline and spoiled eggs. I’ve had a few patients express their sincere disgust with the taste of polyether to the point that they would be angry if I had to retake the impression.
Odds and Ends
Both PVS and polyether have their little quirks that can foul them up. When using PVS you should avoid using latex gloves as it can disturb the setting reaction. When using polyether be sure to store the finished impression dry, not wet. Additioanl moisture bathing the set material can alter the accuracy. PVS can be stored wet or dry.
In the end, the best material is whatever works predictably in your hands. Personally I like to use polyether for implant impressions (here and here), large crown and bridge cases with lots of prepared teeth, and tricky single unit crowns. By “tricky’ I mean areas where I’m having difficulty achieving hemostasis. I like to use PVS for simple and moderate crown and bridge cases and for denture impressions.
A final impression for an immediate denture. The PVS has captured everything we need. There are small pulls around the anterior teeth, but who cares? Those teeth will be extracted anyway.