Dental Impressions of Teeth in Dentistry
The impression is then cast using gypsum in order to create an accurate copy of the mouth (a model). The cast is later used to create dental prosthetics. The quality of the dental prosthetic, the correct fitting correlates directly to the quality of the impression. Impressions should be carried out using full impression trays, using only partially filled impression trays is usually less accurate due to the fact that the two impression are not brought together correctly. The use of a partially filled impression plate means that the technician has only partially complete models which pivot relative to one another on a common axis and are therefore unable to be correctly positioned, the dental prosthetic cannot be accurately modeled.
A complete impression allows for complete models of the jaw with a so-called three point contact. Only when the models do not pivot can the technician create a perfectly fitted dental prosthetic. In order to produce exact impression margins, the impression material must cover the teeth completely. To make this possible, there can be no gingival tissue, blood or saliva covering the teeth; therefore, bleeding must be stopped (i.e. using a cauter) and the gingival tissue pushed away from the teeth (i.e. using special stitches). Only by following the above criteria are technicians are able to obtain exact dental impressions.
A preliminary impression, stops the teeth from making contact with the impression tray, known as “press through“. If the metallic impression tray becomes visible during this procedure then the procedure must be repeated. ”Press through” results in an inaccurate impression of the affected tooth, which means that the technician will produce a prosthetic that requires extensive sanding or has ill-fitting crown margins. After the preliminary work, the actual impression is made using a small syringe to place the impression material on the most delicate areas the material is then distributed using a pressurized air gun. The custom impression tray with impression material is then placed in the mouth.
The impression tray should be left in the mouth according to the manufacturer’s guidelines, a conscientious dentist always uses a stopwatch; the topic is discussed further in our video entitled "Setting Time". Finally, the impression is then removed from the mouth and checked using magnifying glasses, corrected, packaged, and sent to the technician. The technician must then make the cast of the impression within an allotted time period. If this time is exceeded then the impression begins to deform, another factor that may result in poorly fitting dental prosthetics!