الرحيم الرحمــــــــن الله بسم

Elastomeric impression materials

Done by Dr: Hind NihadSupervisor : Dr. Ali Dr.Yasir

Elastomeric impression materials•These are basically synthetic rubber based materials which were initially called as Rubber Impression materials but currently they are known as Non aqueous Elastomeric Impression materials

•A material that is used when an extremely accurate impression is essential. The term elastomeric means having elastic or rubberlike qualities.

• 

Classification of Elastomeric impression materials:

 •Till now the Elastomeric impression materials are devided into 3types based on the material used

•1-polysulfied

•2-polyether

•3-silicone

- Addition

-condensation

• 

Polysulfide Impression MaterialThese materials are also known as thiokol rubbers as they are derived from thiolsBase: polysulfide. and an inert filler, such as titaniumdioxide-activator paste :(containing lead dioxide, which gives the distinctive brown colour, sulphur and dibutyl or dioctylphthalate). Catalysts: Copper hydroxides, zinc peroxide, organic hydroperoxide

fig (1)

• Indications • –complete denture • –removable & fixed partial denture • Advantages• Good wettability• Good surface detail• Easy to remove• High tear strength • Disadvantages• a long working and setting time (8 to 10 minutes)• High permanent deformation• Unpleasant taste and odour• Must pour within 1 hour• Take care when disinfecting 

Manipulation and Technique Considerations for Polysulfide Material

-Dispense pastes at the top

of the mixing pad.

-Mix pastes with the tip of

a spatula to incorporate the

material first.

• Transfer the material to

the fresh surface of the mixing pad

. and Thinnen polysulfide film

fig (2)

• Impression should be removed quickly after setting-do not rock the tray

• The setting process or the polysulphide impression material is highly susceptible to changes in environmental conditions, such as temperature and humidity variation

fig (3)

POLYETHER IMPRESION MATERIALComposition:

•The polyethers come as two-paste system

•Base paste : imine terminated polymer(polyether)

•Accelerator paste:Alkyl aromatic sulfonate

Indications

•–crown and bridge

•–bite registration Advantages

•1- Hydrophilic•2-Good surface detail•3-Good dimensional accuracy•4-Good resistance to deformation•5-Highly acceptable to patient

• 6-good dimensional stability fig (4)

Disadvantages:•1-stiffness requires blocking undercuts Difficult to remove and thus multiple casts can’t be poured•2-High permanent deformation•3-Swells in disinfectants or moist environments•4-low tear strength•5-Take care when disinfecting•6-slightly more expensive

Silicones•There are two important groups of silicone impression materials. One group is known as the condensation-cured silicones and the other as the addition-cured silicones. Both are based on the polydimethyl siloxane polymer but have different end groups, giving rise to different curing mechanisms.

Syringe tray special tray stock tray

fig (5)

CONDENSATION SILICONES

•Also known as conventional silicones. These materials are based on a polydimethyl siloxane polymer with hydroxyl terminal groups.

Composition:

•Base paste : Containing silicone fluid and a filler.

•Activator paste: tetra-ethyl silicate (the crosslinking agent).

•It is important that the amount of activator paste used is carefully controlled. Insufficient TES gives rise to an incomplete cure, leaving a material with poor mechanical characteristics, such as high permanent set. Conversely an excess of TES also gives an incomplete cure, leaving many unreacted ethyl end groups

• Advantages:

•.1- Good surface detail (dry surfaces)•2-Good dimensional accuracy•3-low permanent deformation•4-Wide range of viscosities•5-Easy to disinfect•6-Highly acceptable to patient Pleasant odor & no staining 

.Disadvantages:•1-Hydrophobic•2-Shrinks on storage•3-Must pour within 1 hour•4-low tear strength • 

Addition-Cured Silicones •These materials are similar to the condensation-cured silicones, in that they are also based on a polydimethyl Siloxane polymer; however, in this case the terminal groups are vinyl’s group

The addition-cured silicones present as a :• Base paste :polyvinyl siloxane, silanol and a filler•Catalyst paste: polyvinyl siloxane, platinum catalyst and a filler.

fig (6)

Advantages:•1-Good surface detail (dry surfaces)•2-Good dimensional accuracy•3-Good storage stability•4-low permanent deformation•5-Wide range of viscosities•6-Easy to disinfect•7-Highly acceptable to patient• •Disadvantages:•1-Hydrophobic (unless surfactant added)•2-low tear strength 

•Indications •–crown and bridge and implant •–denture

•–bite registration CONSISTENCIES

Putty The addition-cured silicones - wash

fig (7)

• The elastomeric impression materials are available in a range of viscosities, depending on the amount of filler that is incorporated

• Polysulphides : heavy, medium and light bodied impression ,paste forms are available, there is no putty version.

•Polyethers• These materials are available only in a single viscosity and

can be used in a special tray using a single viscosity mix.•CCS & ACS•A wide range of viscosities are available, varying from a putty, to a heavy, a medium and a light bodied material Thus, these materials can also be used in a wide range of impression techniques.

Mechanical Properties1-Stiffness•The stiffness of the impression material once it has set can be a major consideration in the case with which it is removed from undercuts.PS < CCS < ACS < PE 2-Permanent Set•Ideally, when the impression is removed from an undercut, the deformation that results should be totally and immediately recoverable. it is important that the elastomeric materials are removed from the mouth by a sharp tug.  PS > PE > CCS > ACS3-Tear Strength•The tear strength of the impression material is also important when an impression is taken of the dentate patient.PS > PE > CCS > ACS •too high a tear strength may give rise to difficulties in removing the impression from the mouth in Cases where the impression material has flowed into the interdental spaces.  

•4-Reproduction of Surface DetailAll of the elastomeric impression materials are able to reproduce the details of the surface very accurately when a low-viscosity material is employed.•the lower the viscosity, the better the reproduction•5-Dimensional Stability and AccuracyIs affected by the amount of filler present, in that the higher the filler loading, the smaller the shrinkage•The amount of light bodied material used should always be kept to a minimum.

PE =ACS < PS < CCS

MIXING SYSTEMS

hand mixing, static Automixing, dynamic mechanical mixing

• Hand mixing• hand mixing is with the two putty systems, offered both with

condensation and addition silicones. Scoops are supplied by the manufacturer for dispensing, and the putties are most often kneaded with fingers until free from streaks.

Static Automixing

The base and catalyst are in separate cylinders of the plastic cartridge. The cartridge is placed in a mixing gun containing two plungers that are advanced by a ratchet mechanism to extrude equal quantities of base and catalyst

fig (8)

• dynamic mechanical mixing• The catalyst and base are supplied in large plastic bags housed in a cartridge, which is inserted into the top of the mixing machine. A new, plastic mixing tip is placed on the front of the machine, and when the button is depressed parallel plungers push against the collapsible plastic bags, thereby opening the bags and forcing material into the dynamic mixing tip

fig (9)

Impression Technique Twin-Mix Technique Two-Stage With Spacer Technique Two-Stage Without Spacer Technique

Twin-Mix Technique

fig (10)

• 1-The potential problems with this technique are related to the removal of the addition-cured silicones

•2- Another problem that may arise is that the putty may displace the wash in areas where surface accuracy is desirable.

Two-Stage With Spacer Technique 

• 

fig (11)

•more of the wash material is required in this technique than in the twin-mix approach, and this means that there is more setting shrinkage, as the wash has a much lower filler content. This is especially the case with the condensation-cured silicones, which also show more shrinkage on storage.•Two-Stage Without Spacer Technique

The two-stage without spacer technique is inappropriate for addition-cured silicones because the primary impression would be extremely difficult to remove from undercuts, once it has set, due to the high stiffness of the putty

• DISINFECTING IMPRESSIONS

For addition silicone (hydrophobic) soak sodium hypochlorite (1:10concentration) for 3 minutes Polyether materials cannot be immersed in disinfectants due to potential for absorption and distortion only spray

Thank you