elastomeric Impression DENTAL material

transcript

Elastomeric Impression Materials

Elastomeric = Rubber-like polymers that show an elastic behavior at the time of load

application

These polymer molecules have weak interaction in

between (Van der Wall forces), although they are tied

together in 3D network.

On stretching (on loading) chains uncoil

At rest (off loading) chains snap backC

ical N

Higher tear strength

More stable dimensionally in storage

(No Synersis, Imbibation or Evaporation)

Ability to be electroplated

But, Quite Expensive !!!!But, Quite Expensive !!!!In c

rocolloid

Elastomeric impression materials

Polysulfide(hydrophobic)

SiliconesPolyether

(hydrophilic)

Condensation Silicone

(hydrophobic)

Addition silicone

Hydrophobic type

HydrophilictypeF

iffere

rmsMaterials’

Consistency

Medium

PuttySilicone materials only

Polysulfide Rubber Polysulfide Rubber Impression MaterialImpression Material

CHEMISTRY A. Composition:

Base paste 1. LMW Polysulfide with two terminal and one pendant

SH groups 2. Fillers (Titanium dioxide) 3. Plasticizer (Dibutyl phethalate)

Catalyst paste1. Lead dioxide (Brown) or organic peroxides (Gray)

reactor2. Fillers (Titanium dioxide) 3. Plasticizer (Dibutyl phethalate)

B. Setting Reaction:

+ Pb +H2o

HS---- R ---- SH HS---- R ---- SH

SH SH+PbO2

HS---- R ---- S S---- R ---- SH

S + Pb +H2o

HS---- R ---- SH HS---- R ---- SH

SH SH+PbO2

HS---- R ---- SH HS---- R ---- SH

SH SH+PbO2

HS---- R ---- S S---- R ---- SH

Condensation polymerization (exothermic + shrinkage) with releasing of H2O as reaction by-product

It occurs as a series of simple oxidation reactions

Oxidation of terminal SH groups polymer chains

Oxidation of pendent SH groups Cross-linking

Material sets via condensation polymerization reaction

Water is the reaction by-product Evaporation of water + polymerization shrinkage

Dimensional changes in storage Water could cause air bubbles in stone cast Polysulfide is hydrophobic, and can be electroplated

Lead dioxide is toxic and has bad smell, so it has been replaced in recent products by peroxide compoundsP

OBVIOUS CHARACTERS

Condensation SiliconeCondensation SiliconeImpression MaterialImpression Material

Base paste 1. LMW silicone polymer with terminal OH groups 2. Fillers (Colloidal silica or titanium dioxide) (white)

Catalyst paste1. Alkyl silicate (Cross linking)2. Tin dilaurate or Stannous octoate (Activator)

HO Si - O - Si OH +

CH3 CH3

C2H5OC2H5O

C2H5O C2H5O

C2H5OHSi

HO Si - O - Si

CH3 CH3

HO Si - O - Si

CH3 CH3

Si - O - Si OH

CH3 CH3

Si - O - Si OH

CH3 CH3

HMW Silicon Polymer Ethyl Alcohol

Dimethyl Siloxane Alkyl Silicate

StanousOctoate

HO Si - O - Si OH +

CH3 CH3

C2H5OC2H5O

C2H5O C2H5O

C2H5OHSi

HO Si - O - Si

CH3 CH3

HO Si - O - Si

CH3 CH3

Si - O - Si OH

CH3 CH3

Si - O - Si OH

CH3 CH3

StanousOctoate

HO Si - O - Si OH +

CH3 CH3

HO Si - O - Si OH +

CH3 CH3

C2H5OC2H5O

C2H5O C2H5O

C2H5OC2H5O

C2H5O C2H5O

C2H5OHSi

HO Si - O - Si

CH3 CH3

HO Si - O - Si

CH3 CH3

Si - O - Si OH

CH3 CH3

Si - O - Si OH

CH3 CH3

StanousOctoate

Condensation poly-merization (exothermic + shrinkage) releasing C2H5OH as reaction by-product

It occurs as a series of cross-linkage of siloxane polymer to alkyl silicate in presence of the activator, to form a 3D polymer networkC

Material sets via condensation polymerization reaction

Ethyl alcohol is the reaction by-product Evaporation of alcohol + polymerization shrinkage

Dimensional changes in storage > that of polysulfide Alcohol could cause air bubbles in stone cast Cond. silicone is hydrophobic, and can be

electroplated either with silver or copper

e OBVIOUS CHARACTERS

Addition SiliconesAddition SiliconesImpression MaterialsImpression Materials

Base paste 1. Poly methyl hydrogen siloxane (Hydried or silane

terminated silicone)

2. Other Siloxane pre-polymers

3. Fillers

Catalyst paste1. Divinyl poly(dimethyl siloxane)

2. Platinum salt activator (Chloroplatinic acid)

3. Siloxane pre-polymers

4. Fillers

Addition polymerization (exothermic + shrinkage) with no release of by-product

It occurs as a series of cross-linkage between vinyl-terminated silicon and silane-terminated (hydried) silicon molecules, in presence of the catalyst (platinum salt) to form a 3D polymer network

A side reaction (Releasing hydrogen gas Air bubbles in gypsum cast) may occur if : 1. No balance between vinyl siloxane and the hydried silicone2. Moisture react with hydrides of the base polymer

Adding noble metal (platinum or palladium) to the composition will act as hydrogen absorberA

Adding surfactants (surface tension reducing agents) to the composition of add. silicone help turns the material to be hydrophilic (water lover)

Advantages:1. Better wetting of soft tissue registration of better details2. Air bubbles in gypsum cast

Disadvantages:1. Difficult to be electroplated2. Setting reaction could be retarded in presence of sulfur (in latex gloves) or sulfate compounds (in gingival retraction cords)

HYDROPHILIC SILICONEA

Material sets via Addition polymerization reaction (No by-product) More dimensionally stable than condensation-polymerized materials

Hydrogen gas may release from a side reaction in presence of moisture or imbalance of the reactants. But, adding noble metal to the composition prevents the release of hydrogen gas no air bubbles in the gypsum cast

Add.silicone is hydrophobic and can be electroplated, however adding of surfactants turns the material hydrophilic

OBVIOUS CHARACTERS

Polyether RubberPolyether RubberImpression MaterialImpression Material

Base paste 1. LMW polyether with terminal imine groups

2. Filler (colloidal silica)

2. Plasticizer (dibutyl phethalate or glycoether)

Catalyst paste1. Aromatic sulfonate reactor (Sulfonic acid ester)

2. Fillers

3. Plasticizer

CHEMISTRY

B. Reaction: (Cont.d) Material sets via ring opening addition poly-

merization reaction (No by-product) of imine- terminated polyether with the aromatic sulfonate

LIGHT-CURED POLYETHER It is based on polyether-urethane dimethacrylate,

photo-initiator, accelerator, and silicone filler (has refractive index similar to resin that helps in maximizing the depth of curing)

This material is no longer be usedPoly

Material sets via Addition polymerization reaction (No by-product) More dimensionally stable than condensation polymerized materials

Set material is so stiff (as a result of high rate of crosslinking), so tray adhesive must be used to retain the material within the tray at the time of removing an impression

Polyether is hydrophilic and can absorb water in wet condition (swelling), accordingly Can not be electroplated should be stored in dry environment to preserve its

dimensional accuracy

OBVIOUS CHARACTERSP

Comparative Properties Comparative Properties of Elastomeric Impression of Elastomeric Impression

MaterialsMaterials

Biological properties:

1. Lead dioxide (polysulfide) is toxic, but following the manufacturer’s instruction will decrease this risk

2. Alcohol by-product (cond. Silicone) is irritant to oral soft tissues

3. Aromatic sulfonate (polyether) is irritant, but proper mixing will decrease this irritability

Interfacial properties:

1. Hydrophilicity… Polysulfide, cond. Silicone, & add. Silicone are

hydrophobic Hydrophilic silicone and polyether are Hydrophilic

2. Compatibility with model and die materials... Hydrophilic materials can not be electroplated Polysulfide could be electroplated with silver, while

silicones could be electroplated either with silver or copper

hydrophobic materials may cause air bubbles in stone casts

Interfacial properties: (cont.d)

3. Separating media… There is no need (elastic materials) for separating

medium before pouring the cast

4. Detail reproduction… Although, hydrophilic materials show better

registration of details than hydrophobic ones, Polysulfide is the best detail reproducer due to its higher flow rateCom

Mechanical properties:

1. Flexibility... Polysulfide > Cond. Silicone > add. Silicone > polyether

2. Flow...Polysulfide > Cond.silicone > Polyether > Add. Silicone

3. Permanent deformation…Polysulfide > Cond.silicone > Polyether > Add. Silicone

4. Tear strength…Polyether > polysulfide > silicones

5. Recovery…Rubber materials are viscoelastic, so impressions should be poured 30 min after removal from the patient mouth in order to get the whole elastic and delayed recovery of imp.mat.

Chemical properties:

1. Dimensional changes…Cond. silicone > polysulfide > Polyether > add silicone

All materials are associated with setting (polymerization) shrinkage

All condensation polymerized materials are less stable in storage as a result of evaporation of the reaction by-product

2. Odor…Lead dioxide-containing polysulfide has bad smellCom

Practicability:

1. Mixing time... (45 sec.- 1 min.)

2. Working time... (average 5 min.)

3. Setting time... (average 8-12 min)

4. Coast... higher than hydrocolloids

5. Shelf life…storage in refrigerator elongate the shelf life

6. Disinfection… could be done either by spray or short immersion technique using NaOCl, Iodofore or Glutaraldehyde. Care should be expressed with hydrophilic materials (not immersed for long time)

Materials’ ManipulationMaterials’ Manipulation

Mixing:

1. Using paper pad (Glass slab) and SpatulaLight, medium and heavy consistencies

2. Hand KneadingHeavy or putty consistency

3. Automixer and DispenserCartridge form only (Light, medium, heavy)

4. Automatic mixingAll consistencies, special electric mixer + special material form

Trays:

1. Stock tray... Used with heavy and putty consistency Retention come through; tray perforations, rim locks, or tray

adhesive

2. Special tray… Used with light and medium consistency Retention comes from; tray perforations and tray adhesive

3. Wash impression... Some times heavy or putty impressions act as special tray for

light consistency material

1. Impression making... Copper ring impression Monophase impression Double mix single phase impression Double mix double phase impression (over-wash impression) Closed mouth-double arch impression

2. Occlusal bite registration…A specially supplied rubber material is used for this purpose (commonly cartridge form)Man

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elastomeric Impression DENTAL material

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