WHAT ARE IMPRESSION MATERIALS?
Impression materials are used to make replicas of oral structures.
All impression materials must be in a plastic or fluid state while the replica is being made.
A model or cast material (eg, plaster of Paris or high-strength stone) is poured into the impression and, upon setting, produces a positive impression of the tissues of interest.
Usually the impression material is carried to the mouth in an unset (plastic) condition in a tray and applied to the area under treatment. When the impression material has set, it is removed from the mouth with the tray.
The cast is made by filling the impression with dental stone or other model material.
The accuracy, detail, and quality of this final replica are of greatest importance.
Sometimes impression materials are used to duplicate a cast or model that has been formed. when more than one positive reproduction is required.
Such impression materials are referred to as duplicating materials.
Types of Impressions
A) Preliminary impressions
i) Taken either by the dentist or an expanded-function dental assistant.
ii) Used to make a reproduction of the teeth and surrounding tissues.
iii) Used to make (1) diagnostic models, (2) custom trays, (3) temporary coverage, (4) orthodontic appliances, and (5) pretreatment and post‑treatment records.
B) Final impressions
i) Taken by the dentist.
ii) Used to make the most accurate reproduction of the teeth and surrounding tissues.
iii) Used to make indirect restorations, partial or full dentures, and implants.
C) Bite registrations
i) Taken by the dentist or dental assistant.
ii) Make a reproduction of the occlusal relationship between the maxillary and mandibular teeth.
The requirements of impression materials
1. Accuracy and detail reproduction
2. Dimensional stability
- Compatible with model materials
- Resistant to disinfectant solutions
3. Good handling properties – easy to prepare/mix, adequate working and setting times
4. Acceptable for a patient – non-toxic, non-irritant, tasteless, Cost effective
Classification of impression materials
Non-elastic impression materials:
- Impression Plaster
- Impression compound
- Zinc Oxide Eugenol
- Impression Waxes
These materials are rigid and therefore exhibit little or no elasticity. Any significant deformation produces a permanent deformation. They are used mainly for edentulous patient (Complete Denture) cases.
Elastic impression materials:
- Agar hydrocolloid (reversible)
- Alginate hydrocolloid (irreversible)
- Polysulfide
- Condensation silicone
- Addition silicone
- Polyether
The non-elastic and elastic impression materials will be further discussed in the coming posts.
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