Dentistry-Online

Dental impression

definition

The dental impression is a process in which the rows of teeth are reproduced in true detail using an impression compound. There are different impression compounds for this, depending on the intended use of the impression.

These are placed on a carrier, called an impression spoon, and then placed over the row of teeth. It takes up to 5 minutes to harden. The dental impression can then be taken out of the mouth. The impression is then sent to a dental laboratory and used there for further use.

Reasons for a dental impression

The dentist needs a dental impression for various reasons, for example

to document the situation before prosthetic work and before starting orthodontic treatment
for planning dentures
for the diagnosis of tooth and jaw misalignments (KFO)
after completing a long period of therapy
for the production of dentures and orthodontic devices
for the production of temporaries

Process of a tooth impression

Depending on the required accuracy, different methods and materials are used for taking impressions.

While a quick alginate impression is sufficient for documentation, treatment planning and representation of the opposing jaw for dentures, a multi-step process is required to take an impression of the situation after preparation for receiving a crown or bridge.

With the classic alginate impression, a suitable impression tray is first selected, which can then be adapted to the patient's situation using silicone walls. An adhesion promoter (alginate adhesive) is applied to the tray while the impression material is mixed and then introduced into the tray. The spoon filled with alginate is pressed into the row of teeth until the impression has hardened and is then carefully removed. After disinfecting the impression, a plaster model can be made.

Process of a precision impression

Precision impressions are a little more complex. In order to ensure that the crown edge or the implant prosthetics exactly fit the situation in the patient's mouth, absolute dryness and a more accurate impression material than alginate are used.

To dry out, the gums around the tooth or the implant are first anaesthetized, then a thread is inserted to keep the gums away and should lie there for at least 10 minutes.

A suitable impression tray was selected beforehand or the laboratory made an individual tray made of plastic. After the adhesion promoter has been applied, the spoon is filled halfway with Impregum ™ or Aquasil ™ and a syringe, for example.

Before the spoon is pressed into the row of teeth, the dentist injects the filled syringe around the edge areas that have to be shown particularly precisely. These impressions take much longer to harden than an alginate impression and they become very hard, making removal more uncomfortable and difficult.

Read on under:

Dental crown
Dental bridge
Veneer

Procedure in the toothless jaw

Another special feature is the impression of the toothless jaw for the production of a full denture (the technique that is taught at the University of Frankfurt am Main is described below):

After taking an impression of the situation with alginate to produce models that are used to produce individual trays, the actual impression of the toothless jaw is taken. The first step is to take a complete impression of the edge, then the entire jaw is imprinted.

In contrast to the impression forms mentioned above, in which the patient should not move, movement of the jaw and facial muscles is desirable with this impression. As long as the impression is hardening, the dentist prompts the patient to perform various movements, e.g. Stick out your tongue, grin, pursue your lips, say ah, swallow. This is repeated until the soft tissue is completely depicted, as this is the only way to create a well-fitting prosthesis.

You can also find out more at:

Denture of the upper jaw
Denture of the lower jaw

How long does a dental impression take?

The setting time of the impression materials is based on the manufacturer's instructions.

Alginate is usually set in around 2 minutes, while Impregum ™ and Aquasil ™ take around 7 minutes.
Luralite ™, which is used for full denture impressions, hardens after 6 minutes.

However, because of the different steps, you should plan around 5-10 minutes for alginate and at least 30 minutes for precision impressions. Depending on the situation and the patient's “cooperation”, however, impressions can take considerably longer.

Which material is used?

The most common is the alginate impression to represent the situation. Alginate is a powder made from components of algae and silicic acid, which sets with water and is produced in different colors. The minty taste and the rather elastic consistency are typical.

Highly viscous precision impression materials are, for example, Impregum ™ (purple polyether) or Aquasil ™ (green and yellow A-silicone), which set without water and are very hard.

For the functional impression of full dentures, e.g. GC ™ Iso functional sticks and used for the base Luralite ™. Both are pink, while the former can be deformed in a wax-like manner by heating and the latter sets on a eugenol basis.

This is how to make a dental impression with loose teeth

In the case of loosened teeth, a precision impression with Impregum ™ or Aquasil ™ can lead to further loosening up to the point of tooth loss. Therefore, you should either take a digital impression or use a softer material.

Alginate is suitable for situation impressions with loosened teeth. If increased accuracy is required, you can fall back on special impression materials such as Impregum Soft ™ or Express Penta ™ Putty, which are easier to demold.

Do you have loosened teeth? You might also be interested in: Periodontal disease

How do you take a digital dental impression?

A digital dental impression is created by a special camera that scans the teeth (hence also called “intraoral scan”).
This technique is the most modern, but it cannot be used in all situations. For implant work and crowns or bridges, the boundaries of which are not below the gum line. but they are quite suitable.

Depending on the manufacturer, the pine to be molded may or may not have to be dusted with powder after it has dried. Then the dentist moves the camera over the row of teeth. The success of the scan can be tracked on the PC screen. If necessary, both scanned jaws can then be put together on the PC. The 3D models calculated on the PC can be converted into plastic using a 3D printer. The dentures can then be manufactured conventionally in the laboratory.

Some systems allow the direct production of dentures after planning on the PC by coupling with a milling machine that produces ceramic crowns, ceramic inlays or plastic splints directly in the practice (e.g. CEREC).

Cost of the digital dental impression

The digital print is not taken over by the statutory health insurance.
Depending on whether both jaws or only individual teeth are scanned and which system is used in the practice, the costs can be between 20 and over 50 euros.

So you can suppress the gag reflex

The gag stimulus arises from the impression material that is pressed against the palate. Since digital dental impressions are used without impression materials, there is usually no gag reflex.

If an intraoral scan is not possible, there are various options. to suppress the gag reflex: