ch 15 impression material

diagnostic casts

positive replicas of teeth and surrounding oral tissues and structures produced from impressions that create a negative representation of the teeth

what type of cast is commonly called study models and used for diagnostic purposes?

diagnostic cast

preliminary impression

impression of the dentition or edentulous arch and surrounding tissues taken as a precursor to other treatment

what type of cast is often used to make casts of oral structures for planning and to construct custom trays or provisional restorations?

preliminary casts

final impression

detailed impression of oral structures used to make an accurate cast from which restorations or prostheses are made

bite registration

impression of upper and lower teeth in 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 doesn’t go into the solution but is suspended within another substance

sol

liquid phase of colloid

gel

semisolid phase of colloid

hydrocolloid

water-based colloid used as an elastic impression material

reversible hydrocolloid

agar impression material that can be heated to change a gel into a fluid sol state that can flow around teeth, then cooled to gel again to make an impression

irreversible hydrocolloid

alginate impression material that is mixed to a sol state and as it sets converts to a gel by chemical reaction

agar

powder derived from seaweed that is a major component of reversible hydrocolloid

alginate

versatile irreversible hydrocolloid that is the most used impression material in the dental office

which impression material lacks accuracy and fine surface detail needed for impressions for crown and bridge procedures?

alginate

elastomers

highly accurate elastic impression materials that have qualities similar to rubber

which impression material is used extensively in indirect restorative techniques such as crown and bridge procedures?

elastomers

imbibition

act of absorbing moisture

surfactant

chemical that lowers the surface tension of a substance so that it is more readily wetted

polysulfide

elastic impression material that has sulfur-containing functional groups

rubber base impression material

polysulfide

condensation silicone

silicone rubber impression material that sets by linking molecules in long chains but produces a liquid by-product by condensation

addition silicone

silicone rubber impression that also sets by linking molecules in long chains but produces no by-product

polyvinyl siloxane

very accurate addition silicone elastomer impression material with no taste or order

polyether

rubber impression material with ether functional groups; has high accuracy and is popular for crown and bridge procedures

astringent

chemical used in tissue management during gingival retraction to control bleeding and constrict tissues

flash

common term for the cuff of impression material that extends apical to the margin of a crown preparation and represents an impression of the root or unprepared tooth

digital impression

detailed digital images of the preparation, surrounding and opposing teeth, and tissues taken by digital scanner for purpose of making restoration

intraoral scanner

type of camera that takes digital images of oral structures for CAD/CAM procedures

types of impressions

-preliminary

-final

-bite registration (occlusal)

types of impression materials

-elastic

-inelastic

elastic impression materials include:

-hydrocolloid (agar & alginate)

-polysulfides

-silicone rubber materials

-polyethers

-hybrid of polyether and polyvinyl siloxane

key properties of impressional materials

-accuracy

-tear resistance

-dimensional stability

impression trays

used to carry the impression material to the mouth and to support it until it sets, is removed from the mouth, and is poured into dental plaster or stone

types of impression trays

-stock

-triple tray

-bite registration

-custom tray

stock trays

pre-manufactured plastic or metal full arch trays

stock sectional trays

stock trays used for sectional impressions

triple trays

stock sectional tray that is used to make an impression of the teeth being treated and the opposing teeth at same time

bite registration tray

u-shaped plastic frames with thin fiber mesh stretched between the sides of the frame

custom trays

constructed in laboratory with chemical-cured, light-cured, or thermoplastic resins that conform to patient’s mouth

working time of regular-set alginate

2-3 minutes

working time of fast-set alginate

1.25-2 minutes

setting time of regular-set alginate

2-5 minutes

setting time of fast-set alginate

1-2 minutes

what can be done for patients with sensitive teeth when prepping alginate?

use regular-set alginate with warm water

technique for mixing alginate impressions

-powder to water

-2 scoops powder to 2 units of water

-reg set mixing within 45 seconds

-fast set mixing within 30 seconds

technique for loading alginate tray

-large increments quickly as possible

-small number of large increments to reduce chance for entrapped air

-wet finger used to create smooth trough to orient the tray over teeth

-maxillary: place thumb on palate portion to avoid overfilling

technique for seating alginate tray

-mandibular: right hand clinician stands at 8:00

-maxillary: right hand clinician stands behind at 11:00

-use right side of tray to retract left corner of mouth

-posterior to anterior

ways to control gag reflex

-topical anesthetic

-utility wax on posterior extent of upper tray to contain material

-use fast-set alginate

-do not overfill tray

-seat posterior to anterior

-position patient’s head forward, chin down

-use distraction, breath through nose

criteria for acceptable impression: max & mand

-all teeth and alveolar processes recorded

-peripheral roll and frenums included

-no large voids and few small bubbles present

-good reproduction of detail

-free of debris

-no distortion

-alginate firmly attached to tray

criteria for acceptable impression : max

-palatal vault recorded

-hamular notch area included

criteria for acceptable impression: mand

-retromolar areas included

-lingual extensions recorded

infection control of alginate impressions

-rinse with cold water after unseating impression

-spray with cavicide

types of elastomers

-polyvinylsiloxane

-silicone rubber

-polyether rubber

-polysulfide rubber

silicone rubber

-putty like

-condensation reaction silicone

-rarely used

polyether rubber

-relatively rigid material

-gives good tissue detail

-unstable in presence of water

polysulfide rubber

-must be poured same day for accuracy

-messy hand mix only

-has unpleasant sulfur odor

-used for inlays, crown and bridges