Dental Materials Ch 14

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diagnostic casts

postiive replicas of the teeth produced from impressions that create a negative representation of the teeth; commonly called study models and used for diagnostic purposes and numberous chairside and lab procedures.

bite registration

an impression of the occlusal relationship of opposing teeth in centric occlusion

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 luquid 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, then cooled to 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 chemical reaction, it can change into a gel.

gel

a semisolid state in which colloidal particles form a framework that traps liquid (like jell-o)

hysteresis

the property of a material to have two different temperatures for melting and solidifying, unlike water, which has one temperature for both.

syneresis

a characteristic of gels to contract and squeeze out some liquid that then accumulates on the surface.

alginate

a versatile irreversible hydrocolloid that is the most-used impression material in the dental office; it lacks the accuracy and fine surface detail needed for impressions for crown and bridge procedures.

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 wet; 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 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.

impression compound

an impression material composed of resin and wax with fillers added to make it stronger and more stable than wax

impression plaster

an impression material composed of a gypsum product similar to plaster of Paris.

zinc oxide eugenol (ZOE)

a hard and brittle impression material used in complete denture procedures.

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