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

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