Definition
The tooth impression is a process in which the rows of teeth are reproduced in detail separately from each other using an impression compound. There are different impression materials for this purpose, depending on the intended use of the impression. These are applied to a carrier, called an impression tray, and then placed over the tooth row.
Curing takes up to 5 minutes. Afterwards the tooth impression can be removed from the mouth. The impression is then sent to a dental laboratory for further use.
Reasons for a tooth impression
The dentist needs a dental impression for different reasons, e.g. to document the situation before prosthetic works and before the beginning of an orthodontic treatment to plan dental prosthesis for the diagnosis of tooth and jaw malpositions (orthodontic appliances) after a longer therapy for the fabrication of dental prosthesis and orthodontic appliances for the fabrication of temporaries
- To document the situation before prosthetic work and before the start of orthodontic treatment
- For the planning of dentures
- For the diagnosis of tooth and jaw misalignment (KFO)
- After completion of a longer therapy
- For the manufacture of dental prostheses and orthodontic devices
- For the fabrication of temporaries
Procedure of a tooth impression
Depending on the required accuracy, different methods and materials are used for taking impressions. While a fast alginate impression is sufficient for documentation, treatment planning and representation of the opposing jaw in case of dental prostheses, a multi-step procedure is required for taking an impression of the situation after preparation for the acquisition of a crown or bridge. With the classic alginate impression, a suitable impression tray is selected first, which can then be adapted to the patient’s situation using silicone walls if necessary.
A bonding agent (alginate adhesive) is applied to the tray while the impression material is mixed and then placed in the tray. The tray filled with alginate is pressed into the denture until the impression has set and is then carefully removed. After disinfecting the impression, a plaster model can be fabricated.
Precision impressions are somewhat more complex. To ensure that the crown margin or the implant prosthetics fit exactly to the situation in the patient’s mouth, absolute dryness and a more accurate impression material is used as alginate. For drying, the gum around the tooth or implant is first numbed, then a thread is inserted to hold the gum in place, which should remain in place for at least 10 minutes.
Beforehand, a suitable impression tray was selected or the laboratory made an individual tray from plastic. After application of the bonding agent, the tray is filled halfway with e.g. ImpregumTM or AquasilTM and one syringe. Before the tray is pressed into the denture, the dentist injects the filled syringe around the marginal areas that need to be shown particularly accurately.
These impressions take much longer to harden than an alginate impression and they become very hard, making removal more unpleasant and difficult. Another specialty is the impression of the edentulous jaw for the fabrication of a complete denture: After taking a situation impression with alginate for the fabrication of models for the production of individual trays, the actual impression of the edentulous jaw will be taken. The first step is to take a complete impression of the marginal area, then the impression of the complete jaw will be taken.
In contrast to the impression forms mentioned above, where the patient should not move, this impression requires movement of the jaw and facial muscles. As long as the impression sets, the dentist will ask the patient to make various movements, e.g. sticking out his tongue, grinning, pursing his lips, saying Ah, swallowing. This is repeated until the soft tissue is completely imaged, as this is the only way to create a well-fitting denture.
- Dentures of the upper jaw
- Dental prosthesis of the lower jaw
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