Dental impressions are negative imprints of the teeth and oral cavity (gums, surrounding tissues, etc.). Dental procedures use impressions to produce three-dimensional models. Prosthodontics, orthodontics, dental crowns and bridges, and oral and maxillofacial surgery are all typical applications.
What Types of Dental Impressions are there?
There are three main types of dental impressions — preliminary, final, and bite registration.
- Preliminary impressions are accurate reproductions of a patient's mouth. They’re typically used in the diagnosis process, as well as for recording dental arches and teaching purposes. To make a preliminary impression, dentists use a putty-like material that hardens when exposed to air. Once it hardens, the dentist will remove the material from your mouth and use it to create a model of your teeth.
- As you might be able to guess from the name, final impressions are used to create an exact replica of your tooth structures and surrounding tissues. This replica is then used to make casts or dyes with the precise details of your tooth structures and surrounding tissues. To make a final impression, dentists use either alginate or silicone-based materials. Alginate is a putty-like material that hardens when exposed to water while silicone-based materials harden when exposed to air. Like with preliminary impressions, the dentist will remove the material from your mouth once it hardens and use it to create a model of your teeth.
- Bite registration impressions are used to capture how your upper and lower teeth fit together (aka your bite). To make a bite registration impression, dentists use materials like vinyl polysiloxane or polyether impression compounds. These materials have a putty-like consistency but harden when exposed to light or heat. Once the material hardens, the dentist will remove it from your mouth and use it to create a model of your bite.
The most widely used material is an irreversible hydrocolloid, especially for preliminary impressions. Hydrocolloids can exist in a sol or a gel state. Depending on the hydrocolloid type utilized, the physical process of gelation, which turns a sol into a gel, can either be reversible (changed by heat variables) or irreversible (changed by chemical components). Irreversible hydrocolloids do not change after gelation.
Alginate is the most common irreversible hydrocolloid. The most common source of the naturally occurring polymer alginate is brown seaweed. Because of its biocompatibility, this biomaterial has a wide range of applications in biomedical science and engineering. Alginate impressions are quick and easy to take, and they provide an accurate representation of the teeth and surrounding tissues. However, alginate impressions can only be used once; after taking an impression, the alginate must be disposed of.
Other materials that can be used for dental impressions include plaster, silicone elastomers, and polyethers. Plaster impressions are less accurate than alginate impressions but they are more durable and can be reused multiple times. Silicone elastomers provide good accuracy and detail but can be more expensive than other materials. Polyethers offer excellent accuracy and detail but require special handling and storage conditions.
How Dental Impressions are Created
The first step in creating a dental impression is to select the appropriate type of impression tray. There are various types of impression trays that are available, and the type of tray that is used will depend on the size and shape of the mouth, as well as the purpose of the dental impression. The most common type of impression tray is the quadrant tray, which covers half of an arch. Other types of impression trays include full and fill trays, which span the entire maxillary or mandibular arch. Once the appropriate type of tray has been selected, it is time to prepare the tray for use.
The next step is to prepare the tray for use. This involves adding the liquid Impression material to the tray according to the instructions for use. The type of impression material that is used will depend on the type of dental impression that is being made. For example, some impressions may require a more rigid mold while others may require a more elastic or pliable material. Once the Impression material has been added to the tray, it is time to place the tray into the mouth.
The final step is to place the impression tray into the mouth and bite down firmly in order to create the dental impression. It is important to bite down evenly in order to avoid distortion of the impression. Once you have bitten down evenly, hold still for a few moments until the impression has set. Once it has set, the dentist will remove the impression tray from your mouth.