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 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 the 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 long chains but procedures 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.
A dental impression material?
allows the creation of a replica of the structures involved
Which one of the following impression materials is transformed from a sol to a gel state when set?
alginate
What are some elastic impression materials?
alginate, polyetherimpression material, & polyvinyl siloxane (PVS) impression material
The types of impression materials that are considered hydrophilic are those that?
Have good surface-wetting characteristics
Hydrophobic impression materials?
need a dry field to get the best results
Alginate impression material?
Can be immersed in an appropriate disinfectant for up to 30 minutes without distorting
An irreversible hydrocolloid
Cannot reverse from a gel to a sol because a chemical reaction prevents it.
The elastic recovery (or rebound) of alginate impression material can be increased by which one of the following?
Leaving the impression in the mouth for 1 minute beyond its set.
Preliminary impressions are useful for all of the following except?
All-ceramic inlays.
Are useful: diagnostic casts (study models)
custom trays
provision restorations
Three of the following impression materials are the most commonly used. Which one is not commonly used?
polysulfide
Which impression materials are the most commonly used?
polyether, polyvinyl siloxane, alginate
The three key properties that materials used for final impressions must possess include all of the following except one. Which one?
wettability
The 3 key properties that materials used for final impressions must possess include?
accuracy, dimensional stability, & tear resistance
Which one of the following impression materials has the lowest tear strength?
alginate
It is important for an accurate impression that the tray not be?
Too flexible
Which one of the elastomers has the highest natural (no chemicals added) wettability?
polyether
As the viscosity of the impression material increases, which one of the following properties decreases?
accuracy
Which of the following elastomers will imbibe water when stored in it and change dimensions?
polyethers
Which one of the following statements is true about the addition silicones?
They are very dimensionally stable
The least accurate of the elastic impression materials is?
alginate
After removing a PVS impression from the mouth it is found that the surface has unset material on it. What can cause this to happen?
Incomplete mixing of the material, residual ferric sulfate astringent on the teeth, contamination from latex gloves.
PVS substitutes for alginate have all of the following advantages?
Dimensionally stable for long periods.
Can be repaired several times.
Do not have to be poured right away.
At present, the most common method of creating space in the gingival sulcus of a prepared tooth for wash (syringe) material is which one of the following?
retraction cord
Which one of the following astringents has the potential to be dangerous to patients with cardiovascular disease?
racemic epinephrine
Which one of the following impression materials is least affected by soaking it in a disinfectant solution for 2 hours?
polyvinyl siloxane
Disinfecting of impressions?
must be done for all impressions
Reasons the wash material may tear when removing the set impression from the mouth include?
Narrow sulcus width (<0.2 mm)
very deep sulcus
sharp edges on the preparation
A successful double-bite impression for a crown on tooth #30 includes all of the following?
The margins and a little of the tooth beyond are captured in the impression.
No large voids are present in the walls of the preparation.
Opposing teeth are captured in the proper bite relation.
Digital impressions have several advantages over traditional impressions. Which ones?
Impression material and associated supplies are not needed.
Digital impressions can be electronically transferred to the laboratory.
Images of the preparation can be viewed from multiple angles before being sent to the laboratory.