Impressions “from A to Z” – Tips & Tricks

In daily practice, more or less the only relevant information that we send to the laboratory is the impression. Unfortunately, impressions are often the weakest points in the chain of producing exact fitting restorations. There are two approaches in modern dentistry. The conventional way of working starts with conventional impression followed by the conventional way of denture fabrication. Computer aided way begins with digital intra-oral or extra-oral impression and after that, we are in a virtual world. No matter which one we prefer – the conventional or virtual method the only connection is impression. Unfortunately, independent studies show that around 80% of impressions for fixed dentures aren’t good enough or simply ‘not for use’.
Whenever we are taking about an impression we have to think about a lot of parameters. We have to deal with different materials and their properties, to adjust them to soft and hard tissue condition and to select the impression tray as well as impression method.  In this lecture we are going to discuss about that issues. We should select the right impression material regarding to tissues condition but there is no universal nor ideal material. There is a long list of requirements that impression materials have to fulfill before and after setting. the most important ones are: to have capability of plastic to rigid body transformation, to be acceptable for a patient and to have  good handling properties. They have to be non-toxic, non-irritant, tasteless, easy to prepare before set, but viscous enough not to flow out of a tray (thixotropic) and to have acceptable working and setting time. After being set, impression materials must also have good accuracy, dimensional stability, good resistant to mechanical stress, compatibility with model materials, to be resistant to disinfectant solutions and of course to be cost-effective.
There are two basic principles of impression taking. One is based on high pressure techniques and the other works on low pressure principle. Impression techniques based on high pressure include applying high pressure with high viscous tray material in order to press light body into the sulcus. Impression techniques based on low pressure use flow properties and hidrophilicity of the impression material. We can have favorite impression technique but we could not overuse it.