Non-Aqueous Elastomeric Impression Materials

why use elastomerics?

- More stable than hydrocolloids - More expensive than hydrocolloids - As a group, non-aqueous elastomerics are strong, flexible, dimensionally stable, and accurate.

polymerization

a chemical reaction linking monomers together to form a polymer ongoing reaction; it is never quite complete the reaction is sensitive to moisture and temperature the more moisture and/or higher temperature, the shorter the setting time and less working time

dimensional stability

ability of material to keep its shape after it has been removed from the mouth

deformation

ability of material to resist permanent change by stresses during removal from the mouth

elastomerics require ______________ to be painted on the tray, even if it is perforated

adhesives

two separate tubes

base and catalyst

cartridge

base and catalyst are placed in separate compartments of a single cartridge - cartridge place in a dispensing syringe - automixing tip is attached

mixing

come in two pastes which are different colors all (except for putty) are mixed together like polysulfides instead of manually mixing, many are supplied in double-barreled cartridges which are placed in an "automix" gun the automix gun forces the two pastes together and out through a spiral-shaped baffle tip working times and setting times vary according to manufacturer

syringe technique

dispensing gun or cartridge and syringe

final set

elasticity appears and then the material goes through the gradual change to a solid, rubbery mass. the material should be in the patient's mouth before the final set begins

polysulfides

first non-aqueous elastomeric developed in dentistry often called "rubber base" materials suppled as two pastes in tubes - catalyst: usually dark brown; the base is usually white two pastes are dispensed in equal lengths on a paper mixing pad and a spatula is used to mix together mixed material is loaded into a tray

putty system

high viscosity material that is used with a low viscosity material it enables the low viscosity material to be forced around the teeth two colored materials are scooped and then kneaded together do not use latex gloves - only nitrile or vinyl gloves

viscosities of addition silicones

light body medium body heavy body monophase putty

permanent deformation

material changes and will not regain its previous shape

precautions/properties of nonelastomerics

may stain clothing use manufacturer's instructions when dispensing catalyst or base, place the opening of the tube on the mixing pad with a wiping motion, dispense. then clean the opening of the tube & replace the cap do not interchange caps from the base & catalyst most of these materials are hydrophobic - they will NOT flow in areas of moisture so must have a dry field for the impression

properties of polysulfides

more accurate than alginate can be used to take impressions needing finite detail such as crowns, inlays, and bridges today are sometimes used for final impressions for dentures least accurate of the non-aqueous elastomeric impression materials should be poured within several hours after mixing recommend to use with custom tray disagreeable smell and taste can stain clothing longest working time of any elastomeric impression material (4-6 minutes) longest setting time; must stay in the mouth for 10-15 minutes hydrophilic but only used for a single pour use w/ full denture impressions

addition silicones

most popular of all non-aqueous elastomeric impression materials used for crown and bridge procedures clean and do not have an unpleasant taste or smell addition silicones are the most accurate, stable, and expensive of all impression materials also called vinyl polysiloxanes, and polyvinylsiloxanes (PVS) allow for more than one pour in gypsum stone

impression materials most commonly used are

non-aqueous elastomerics (or elastomers) Type Characteristics Working Ability Polysulfide •Paste material supplied in two tubes •Strong odor and taste •Poor stiffness and stability •Hard to mix •Long mixing time (60 sec) •Very long setting time (10-15 min) Polyether •Paste material supplied in two tubes or cartridges •Acceptable odor and taste •Good stiffness and stability •Easy to mix •Short mixing time (30-45 sec) •Fast setting time (6-7 min) Condensation Silicone •Supplied as paste and liquid •Acceptable odor and taste •Average stiffness and stability •Fairly easy to mix •Average mixing time (30-60 sec) •Average setting time (6-10 min) Addition Silicone •Supplied as two paste system, putty, or in cartridges •Acceptable odor and taste •Excellent stiffness and stability •Easy to mix •Short mixing time (30-45 sec) •Average setting time (6-8 min)

bite registration

non-aqueous elastomerics may be used for bite registration mixed material is placed on the occlusals of the mandibular arch, then patient bites into the material

final cure

occurs between 1 to 24 hours. only slight dimensional change

techniques of mixing elastomerics

paste system automix system mixing unit system putty system

which of the materials is light bodied?

polyether

elastomerics are named based on

polymerization chemistry - polysulfide - condensation silicone - polyeither - addition silicone

curing

process of changing is called curing curing starts as soon as the base and catalyst are mixed together; this is termed self-curing

condensation silicones

second non-aqueous elastomeric developed for dentistry - based on silicone rubber - hydrophobic - cleaner materials to use than polysulfides, but it is hard to pour models without voids - must be poured as quickly as possible - not as popular as other similar products

characteristics of elastomerics

set by polymerization reaction usually have two parts - a base and a catalyst mixed together - base is supplied as paste - catalyst is known as the accelerator base and catalyst are packaged together and should not be used with other materials

initial set

stiffening of the paste and can still be manipulated

material may be mixed by hand & placed into an impression ?

syringe

impression techniques

syringe technique tray technique putty wash technique direct placement

final impression materials

used to take impressions needed for pouring accurate working casts

polyethers

working time and setting time are shorter than polysulfides very stiff and set quickly - usually use a disposable, plastic tray also very clean material but have unpleasant taste very accurate and easy to pour with gypsum products higher cost impregum is the most popular polyether product single viscosity