Sorry for the week-long hiatus! I just wanted to get my administration's blessings with regards to me writing the blog. Regular posts will resume, with the possibilities of seeing posts geared towards the more personal side of being a dental student. Enjoy!
Dental Materials
Our discussion today focused on the different materials that dentists use to take impressions. Impressions are used to capture all anatomical aspects of the dentition and gingiva in order to form a dental cast. The dental cast can be used for a number of reasons, such as diagnostic planning, or used by the lab to fabricate prosthodontic devices.
Some of the older impression materials used to be of the non-elastic variety; these included dental plaster (yikes!) and zinc oxide-eugenol. Current materials allow for elastic impressions, and are typically broken down into hydrocolloids (water based) and non-aqueous elastomers (non-water based).
The hydrocolloid most commonly used is alginate (search this blog to find more specific information on alginate). One propery of alginate that is important to note is that it doesn't have the ability to create great, fine detail reproduction, so it is not accurate enough to use in the fabrication of prosthodontic devices. For such delicate cases, a dentist would typically use one of the elastomers, such as polysulfides, silicones (addition and condensation types) and polyethers.
At the school, we use an addition silicone called polyvinyl siloxane for such cases. The reaction occurs through the mixing of two different pastes through the use of a silicone gun (looks similar to a caulking gun). The resulting mix is then put into a stock or custom tray, and an impression is taken. These impressions are highly accurate, have excellent recovering abilities and are very stable. The impression can be poured for up to a week after, and multiple pours are possible. However, it is important to note that the reaction can release hydrogen gas on setting, which could form bubbles in the impression. Also, sulfur found in latex gloves and rubber dams can interfere with the polymerization process.
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