Elastomeric Impression Material
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.**
Important points
- Clean up ASAP or wait until set - Most of these impression materials are hydrophobic hydro = "water"; phobic = "hating" - They will not flow in areas of moisture so must have a dry field for the impression.
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
Polysulfides
- First non-aqueous elastomeric developed for dentistry - Often called "rubber base" materials - Supplied as two pastes in tubes - catalyst is 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 the two pastes together. - Mixed material is loaded into a tray
Putty System
- High viscosity material that is used with a low viscosity material - It enable the low viscosity material to be forces 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
Why use Elastomerics?
- More stable than hydrocolloids - More expensive than hydrocolloids - As a group, non-aqueous elastomerics are strong, flexible, dimensionally stable, and accurate.
Addition silicones
- Most popular of 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
Properties of polysulfides
- Much 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 with full denture impressions
Precautions/Properties
- Non-aqueous elastomeric materials may stain clothing. - Use manufacturer's instructions. - When dispensing of the 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.
Characteristics of Elastomerics
- Non-aqueous elastomeric materials set by a polymerization reaction
Elastomerics there 4 commonly used types
- Polysulfide - Condensation Silicone - Polyether - Addition Silicone - Have similar, but not identical, mixing and handling properties - Require adhesives to be painted on the tray, even if the tray is perforated
Curing
- Process of changing
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
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
Self- curing
Curing starts as soon as the base and catalyst are mixed together; this is termed
Techniques of mixing elastomerics
Paste system Automix system Mixing unit system Putty system
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 usually have two parts
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
◦Cartridge placed in a
dispensing syringe - Automixing tip is attached
The final set for curing
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
Non-aqueous elastomerics is also known as
elastomers
Material may be mixed by hand & placed into an
impression syringe - They have disposable Pouches - Placed in mixer - Extruded Two Separate Tubes : Base + Catalyst
Permanent deformation
material changes and will not regain its previous shape
The impression materials most commonly used are
non-aqueous elastomerics
Final cure
occurs between 1 to 24 hours. Only slight dimensional change
The initial set for curing
stiffening of the paste and can still be manipulated
Final Impression Materials
used to take impressions needed for pouring accurate working casts
