What are the three types of impression trays?

Many dental procedures will require an impression to be taken of the patient’s teeth and

surrounding oral tissues. Most common types of impressions obtained in a dental practice:

  • Preliminary impression- is used for making (a) diagnostic models, (b) custom trays for partial or dentures (c) provisional coverage for crown and bridge cases, (d) orthodontic appliances, etc.
  • Final impression-Shows accurate detail of the tissue and tooth structure for the laboratory

technician to make a cast restoration (inlay, onlay , veneer, crowns/ bridge ).

  • Occlusal (bite) registration- Reproduces the occlusal relationship of the maxillary and

mandibular teeth when occluded .

Impression Trays

Impression trays are supplied as quadrant trays, which cover on half of the arch:

Anterior trays, which are suited for the anterior teeth, and full-arch trays, which covers the complete arch.

Impression Materials

Impression materials are selected because of their unique qualities that allow dentists to obtain the most accurate reproduction. An impression material is classified according to specific properties.

  • Mechanical property-Indicates the flexibility of a material.

The two types of material are inelastic and elastic. Inelastic material is rigid and will fracture when deformed. This type includes impression compounds, impression plaster, and zinc oxide-

Eugenol (ZOE) impression paste. Elastic material can be deformed and returned to their natural

appearance. This type includes alginate, elastomers, and agar.

  • Setting property  Irreversible material indicated that a chemical reaction has occurred and that the material can not go back to it’s original state. This type includes alginate, elastomeric impression material,

ZOE impression paste, and impression plaster. A reversible material can be altered by temperature which includes agar and impression compounds.

  • Types of Impression Material

Alginate is an irreversible hydrocolloid, and is a material of choice when taking preliminary impressions for diagnostic purposes. Alginate consists of potassium alginate, which is derived from seaweed, calcium sulfate, trisodium phosphate, diatomaceous earth, zinc oxide, and potassium titanium fluoride.

Alginate is available in two settings: normal set, which has a working time of two minutes and a setting time of 4 ½ minutes, and fast set, which has working time of 1 ½ minutes and a setting time of 2 minutes. Most offices prefer using normal set alginate to give them more working time. Elastomeric impression material have an elastic or rubberlike quality after setting. These materials are supplied as a base and catalyst and are self-curing. Each type of material has a different properties and characteristics.  

Final impressions material are supplied in three forms or viscosity.

  1. Light body-is the easiest-flowing material to flow.
  2. Regular body-is slightly thicker than the light body form.
  3. Heavy body –is the thickest of the three forms.

At Greatwood Dental Assisting Program, students are exposed to all of the above materials and trays to get a better understanding of how to work with them after graduation. We encourage students to take impressions on each other so they can make models for bleaching trays.

Greatwood Dental Assisting Program

19875 Southwest Freeway, Suite 120 Sugar Land, TX. 77479.

Approved and Regulated by TWC Career Schools & Colleges

(281) 728-6012   Visit our website: www.GDAP.net

Denture impression trays from GC America should be your next purchase—here’s why.

How can there be “secret” dental impression trays? I began my quest of discovery when my laboratory lost my favorite COE impression tray. I called GC America, Inc., for a catalog and discovered a treasure trove that had not been part of my dental school kit and that I’d never seen in any convention display or heard any lecturer mention.

These metal denture impression trays originally were made by COE Laboratories. There are two kinds of full and partial denture trays: trays with perforations, for use with alginate impression materials, and solid, nonperforated trays for use with solid impression materials, such as red compound or fast-set impression plaster No. 2.

The trays are inserted into the mouth, and the facial muscles are manipulated for border molding. The impression is poured up with regular lab plaster. A base plate is fabricated from the resulting model, and this is used for the final denture impression. A well-fitted denture impression tray will lead to a well-fitted base plate and final denture impression.

The catalog shows all the standard trays, plus several pages of trays that were unknown to me. Here are five of them, listed with numbers for better understanding and quick reference:

  • No. 1. Depressed Anterior (perforated)
  • No. 2. Extra Long (perforated)
  • No. 3. McGowan-Winkler perforated immediate (depressed)
  • No. 4. McGowan-Winkler complete denture (perforated and solid)
  • No. 5. STO-K (perforated and solid)

Sheldon Winkler, DDS, designed a partial denture tray, which allows for a step down in the No. 3 tray for the remaining anterior teeth and the depressed posterior alveolar ridge. This is a 2-level impression No. 3 tray, so the edentulous posterior tray is closer to the ridge and extends deeper on the lingual mylohyoid region. This is brilliant and logical. These trays are the McGowan-Winkler perforated immediate trays for immediate and partial dentures.

The No. 1 Depressed Anterior perforated trays are for immediate and partial dentures, but have a buccal flange that is longer for wider ridge impressions, along with the 2-step depression for residual anterior teeth. The No. 3 McGowan-Winkler perforated immediate denture set of trays consists of upper and lower trays, which have a depression for the remaining anterior teeth to be extracted. The trays have two planes: the first is for the remaining anterior teeth, and the other is a step down for the posterior edentulous resorbed ridge area. These trays allow for an excellent impression of the depressed resorbed posterior ridge and the residual anterior teeth to be extracted.

COE also offers a regular partial denture impression tray in an extra long perforated version (No. 2) for the unique case of a longer-than-usual upper or lower jaw. These trays are not available with the depressed anterior.

The No. 5 STO-K trays are for full denture impressions. They are available as perforated and solid and come in three shapes to match a patient’s jaw: square, tapered, and ovoid. Each shape is available in many sizes, and the entire set, upper and lower, consists of 23 trays.

The STO-K perforated and metal lower full denture trays have a unique and very significant lingual extension into the mylohyoid region, essential for a good impression of the mylohyoid for mandibular denture retention. This impression permits a lingual flange, which is critical for denture retention. They do not have the unique button, or as much anatomical design as the McGowan-Winkler perforated immediate tray.

Such a varied tray selection lets you match the tray as closely to your patient’s anatomy as possible. It is necessary to have a complete set of trays in every size and mold (shape) to properly fit every mouth. These trays will solve a multitude of partial and full denture impression problems, because you can select a tray that best fits your patient.

A good denture starts with a good impression. A good impression starts with a good tray. A partial denture tray cannot serve as a substitute for a full denture tray. The use of some of these lesser known, but highly effective trays can make all the difference in a patient’s success with dentures.

What are the three types of impression trays?
Download Issue: Dental Products Report August 2020

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.

Materials Used

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.