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Dental Impressions: Definition, Types, And Uses | Hawaii Family Dental

Written by Danica Lacson on September 27, 2018

What are Dental Impressions?

Dental impressions are defined as the negative imprint of the teeth and other parts of the oral cavity (gums, surrounding tissues, etc.) which is used to create an exact three-dimensional model of these structures.

Where are Dental Impressions used?

These imprints are often used in oral health care for various purposes including prosthodontics, orthodontics, dental crowns and bridges, maxillofacial prosthetics, oral and maxillofacial surgery, in diagnosis, mouth guards, whitening trays, and for the permanent dental record to document before-and-after phase.

What are the Types of Dental Impressions?

There are three main types of dental impressions — preliminary, final, and bite registration.

  • Preliminary impressions are accurate reproductions of a patient’s mouth. This type of impressions is usually used to construct study models for the diagnosis, documentation of dental arches, and as a visual aid for education.
  • Final impressions have the exact details of the tooth structures and their surrounding tissues. They are used to make casts and dies with the precise details of the tooth structures and their surrounding tissues. The casts and dies are utilized by dental laboratory technicians for the construction of crowns, bridges, dentures, and other restorations.
  • Bite registrations are employed to document the occlusal relationship between arches which is essential when establishing the articulation of maxillary and mandibular casts.

What materials are used to create Dental Impressions?

The most widely used material, especially for preliminary impressions, is irreversible hydrocolloid. Hydrocolloids can exist in a sol or a gel state. The physical transformation from sol to gel called gelation can either be reversible – changed by thermal factors – or irreversible – changed by chemical factors, depending on the type of hydrocolloid used. Irreversible hydrocolloids do not change after gelation.

The most often used irreversible hydrocolloid is alginate. Alginate is a naturally-occurring polymer usually obtained from brown seaweed. This biomaterial has numerous applications in biomedical science as well as engineering due to its biocompatibility.

How are Dental Impressions created?

In creating an impression, impression trays are also used. The impression material is placed on the tray which is then placed into the mouth.

The trays are designed for different areas of the mouth and included quadrant trays which cover half an arch and fill and full trays which cover the complete maxillary or mandibular arch.

Metal, plastic, or disposable Styrofoam trays are available in various sizes suitable for children and adults. Trays may also be perforated or pierced with a hole or holes to promote a mechanical lock with the impression.

The liquid material, which varies depending on the use of the impression, is poured into the tray. Impressions may demand a rigid mold or a more elastic or pliable material. Tray selection will also depend on the purpose of the impression.

Following the pouring of the liquid into the tray, the tray is then placed onto either the upper or lower set of teeth, covering the entire dental arch. The area which the impression covers also differ depending on the kind of dental work the patient’s condition requires. For upper impressions, the roof of the mouth is included, while for lower impressions, the floor of the mouth and under the tongue are included.

The tray is removed from the mouth after a stipulated amount of time or when the liquid material has set, hardened, and has become a solid rubber mass. The result will then be sent to the laboratory for processing.

The Thing About Taking Dental Impressions Is…

It can make you gag.

Luckily, there are guidelines your dentist or dental hygienist can go along with to lessen gagging while taking dental impressions, according to Margaret Walsh and Michele Leonardi Darby in the fourth edition of their book “Dental Hygiene: Theory and Practice.”

Keep the material away from the posterior third of the tongue where the gagging reflex is located.

Seat the maxillary tray from the posterior to the anterior to direct the flow of the impression material anteriorly away from the muscular or soft palate.

Place a wax dam on the posterior border of the maxillary tray. The wax will help contain the material.

Fill the impression tray to the level just below the wax beading on the tray rim to avoid overfilling. Make sure the size of the tray can accommodate the impression material.

Seat the patient in an upright position. Bend the patient’s head forward with the chin tilting down when the tray is being inserted in the mouth.

Be calm, confident, and gentle.

Direct patients to take slow and deep breaths through the nose point their toes and pinch the skin between their index finger and thumb.

But, often, no matter how brave you are in fighting the urge to gag, your reflex takes the best of you, making your dental impression experience not as impressive as you want it to be.

Fortunately, there is a way to get impressions of your teeth structures without worrying about gagging.

How? Through a digital impression system.

What are Digital Dental Impressions?

Digital impressions utilize digital technology to create dental impressions on a computer, saying goodbye to the traditional method of impression tray and liquid material.

A dental instrument with a camera or intraoral scanner which takes multiple shots of the oral cavity is wired to the digital impression system which creates a three-dimensional model. The final image is then sent (via e-mail) to a technician who will prepare the mold and submit it to a dental laboratory for the creation of the final product.

Aside from freeing you from gagging, digital impressions also shorten dental appointments and lessen the margin of error associated with the traditional dental impressions.

Digital impression systems are also being used in creating same-day Honolulu dental restorations, allowing dentists to restore patients’ beautiful smiles in one dental visit.

Disclaimer: The oral health information published on this web page is solely intended for educational purposes. Hawaii Family Dental strongly recommends to always consult licensed dentists or other qualified health care professionals for any questions concerning your oral health.


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