Dental impressions. Materials.
Most prosthetic work is made of materials that require processing at elevated temperatures (metal casting, sintering of ceramics, polymerization of resins) so they cannot be made directly in the patient’s oral cavity.
This is why we use impression materials.
These are used to record the situation found in the arches and transfer it to the dental laboratory in order to create the final prosthetic piece.
In order to be able to carry out all the technical stages of prosthetic fabrication, impression materials must meet a series of requirements:
To be rigid: in order to transfer the exact situation found in the patient’s oral cavity to the laboratory, impression materials must be rigid and stable over time, in order to avoid deformations that may affect the subsequent adaptation of the prosthetic part. They must also resist forces that tend to break them.
To faithfully reproduce the details of the prepared surfaces: for a good fit and respect of the surrounding tissues, the impression materials must record the situation of the oral cavity in the smallest detail. For this purpose, there is a wide range of products on the market with different consistencies designed to faithfully record the prosthetic field.
To be flawless after removal: any substance losses, air bubbles or inclusions present after removal of the impressions will compromise subsequent treatment. If defects are found that may interfere with the success of the treatment, the impressions must be restored.
A wide variety of impression materials and techniques are currently available to the dentist and the most popular ones are presented below.
An alkaline salt powder. The impression material is obtained by mixing alginate powder with water in proportions specified by the manufacturer.
It is a material that faithfully reproduces prosthetic surfaces and is well tolerated by the patient.
However, its low dimensional stability means that alginate is only used to produce study models or to imprint antagonist arches.
Silicone addition and condensation
In recent decades, silicones have been considered the material of choice for prosthetic field impressions.
They are found in the form of two pastes, base and accelerator. They are available in different consistencies, ensuring a reliable impression that accurately records dental surfaces.
They can be used in all prosthetic impressions.
Between condensing and additive silicones, the latter have superior strength and dimensional stability.
It comes in the form of sticks or foils and is used to record inter-arch relationships, to impression areas with difficult preparations or root canals.
These are high-performance elastic materials available in several viscosities: low, medium, high.
Their increased stiffness and reduced working time have long limited their use to a small number of prepared teeth but new products offer changes in working time to the practitioner’s advantage.
The choice of impression materials is a key determinant of the quality of prosthetic treatment.
Knowing the properties and limitations of the materials helps the practitioner to adapt his work to the particularities of each patient.
Good communication between patient, practitioner and dental laboratory leads to therapeutic success.