Diagnostic Casts
positive replicas of the teeth and surrounding oral tissues and structures produced from impressions that create a negative representation of the teeth; commonly called study models and used for diagnostic purposes and numerous chair side and laboratory p
Preliminary Impression
an impression of the dentition and surrounding tissues taken as a precursor to other treatment; often used to make casts (models) of oral structures for planning, and to construct custom trays or provisional restorations.
Final Impression
a detailed impression of oral structures used to make an accurate cast from which restorations or prostheses are made.
Bite registration
an impression of the upper and lower teeth in the patient's normal bite relation.
Dimensional Stability
ability of a material to maintain its size and shape over a period of time.
Accuracy
ability of a material to adapt to and flow over the surfaces of the oral structures to record fine detail.
Tear Resistance
ability to avoid tearing when the material is in thin sections.
Colloid
glue-like material composed of two or more substances in which one substance does not go into solution but is suspended within another substance; it has at least two phases: a liquid phase called a sol and a semisolid phase called a gel.
Hydrocolloid
a water-based colloid used as an elastic impression material.
Reversible Hydrocolloid
an agar impression material that can be heated to change a gel into a fluid sol state that can flow around the teeth, and then cooled to a gel again to make an impression of the shapes of the oral structures.
Irreversible Hydrocolloid
an alginate impression material that is mixed to a sol state and as it sets converts to a gel by a chemical reaction that irreversibly changes its nature.
Agar
a powder derived from seaweed that is a major component of reversible hydrocolloid.
Sol
liquid state in which colloidal particles are suspended; by cooling or a chemical reaction, it can change into a gel.
Gel
a semisolid state in which colloidal particles form a framework that traps liquid.
Alginate
a versatile irreversible hydrocolloid that is the most used impression material in the dental office; it lacks accuracy and fine surface detail needed for impressions for crown and bridge procedures.
Syneresis
a characteristic of gels when left standing to contract and squeeze out some liquid that then accumulates on the surface.
Elastomers
highly accurate elastic impression materials that have qualities similar to rubber; they are used extensively in indirect restorative techniques, such as crown and bridge procedures.
Imbibition
the act of absorbing moisture.
Surfactant
a chemical that lowers the surface tension of a substance so that it is more readily wetted; for example, oil beads on the surface of water, but soap acts as a surfactant to allow the oil to spread over the surface.
Polysulfide
an elastic impression material that has sulfur containing (mercaptan) functional groups; it has also been referred to as rubber base impression material.
Condensation Silicone
a silicone rubber impression material that sets by linking molecules in a long chains but produces a liquid by-product by condensation.
Addition Silicone
a silicone rubber impression that also sets by linking molecules in long chains but produces no by-product; the most commonly used addition silicones are the polyvinyl siloxanes.
Polyvinyl Siloxane (PVS)
very accurate addition silicone elastomer impression material; it is used extensively for crown and bridge procedures because of its accuracy, dimensional stability, and ease of use.
Polyether
a rubber impression material with ether functional groups; it has high accuracy and is popular for crown and bridge procedures.
Astringent
a chemical used in tissue management during gingival retraction to control bleeding and constrict tissues.
Digital Impression
detailed digital images of the preparation, surrounding and opposing teeth, and tissues taken by a digital scanner for the purpose of making a restoration.