Applied Material - Rubber Impression Materials PDF

Applied material Level 2 II. Rubber impression materials Non-aqueous materials(synthetic rubber base) long coiled mol...

Applied material Level 2 II. Rubber impression materials Non-aqueous materials(synthetic rubber base) long coiled molecules when stretched → uncoiling → easy to deform & deformation is reversible. they are essentially flowable low M.W. polymers which can be converted to non flowable rubbers at room temperature when mixed with a suitable reactor to induce polymerization reaction. Types: 1) polysulfide 2)silicones(addition & condensation) 3)polyether) the different consistencies of each type are governed by the molecular weight of the polymers and the amount of fillers present. 1.Polysulffide: o Light consistency. o Regular consistency. o Heavy consistency. 2. Silicones: Condensation& Addition: o Light consistency. o Regular consistency. o Heavy consistency. o Putty consistency. 3. Polyether. : Regular consistency.  In general: - ↑ dimensional stability than hydrocolloids. - can be electroplated (except polyether). - More tear strength - More than on viscosity is present - But it’s more expensive - Indications: 1)crown & bridge (2ry impression) 2)partial denture (2ry impression) 3)Inlay 1. Polysulfide Rubber (Mercaptan or Thiokol): (light, regular & heavy)  These materials are supplied as two pastes The base paste The reactor paste (catalyst or accelerator) Polysulfide polymer : with terminal SH groups & pendant Lead dioxide (Pb02): This causes polymerization and SH groups. cross- linking oxidation of SH groups and gives the Filler: ( 1 to 54%) (e.g. titanium dioxide) to provide the brown color of the paste. required strength. The percentage of fillers controls the Plasticizers. consistency from light regular, heavy, to putty. Oleic or stearic acid: Both retarders to control the rate Plasticizers: As dibutylphthalate to offer the appropriate of setting. viscosity to the paste.  setting mechanism: ✓ Condensation polymerization between PbO2 & polysulfide → & cross-linking. & elimination of water as a byproduct → shrinkage. o Oxidation of terminal SH group polymer chain o Oxidation of pendent SH group cross linking ✓ reaction is accelerated by: a) increase temp 12 | P a g e Dr. eslam ezzat Applied material Level 2 b) presence of moisture (one drop of water). c)increase in reaction ratio.(increase catalyst) Properties  Accuracy 1)Flow : highly accurate & can record fine details 2)Dimensional accuracy & stability: poly shrinkage 0.25 % occurs for 24 hours. Also after setting the by product(water) is lost causing shrinkage 3)Elasticity: viscoelastic with 98 % 4)Flexibility : the most flexible of all rubbers (removed from undercut with minimum stress)(the least stiffness)  N.B: the property that determine ease removal from undercut is flexibility. 5)Compatibility with die material: compatible with die material & the use of surface-active agent (surfactant) to improve wetting. (as it is hydrophobic) 6)Tear strength: Polysulfides have the highest resistance to tearing to 700 % 7)used with acrylic special tray with (2-3mm thickness) to decrease the amount of polymerization shrinkage & no need for adhesive 8) Disinfection: can be disinfected by most of the antimicrobial solutions without adverse dimensional changes e.g. 10 minutes immersion in 10% solution of hypochlorite. 9) Electroplating: Polysulfide is hydrophobic so It can be electroplated by silver plating (G.R)  Adv. : 1.need no adhesive (self-adhesive to custom tray) 2.High tear strength 3. Easy to remove from undercut (high flexibility)  Disadvantage: 1) bad odor & taste (sulfur taste ). 2)long setting time 10-12 min 3)high per. Deformation 4)must be poured within one hours as polymerization reaction continue after setting 5)sticky & difficult to mix 2. Silicone Rubber:. Composition: There are two types of silicone rubber. a) Condensation type. b) Addition type Both are based on the polydimethyl siloxane polymer but have different end groups, giving rise to different curing mechanisms 13 | P a g e Dr. eslam ezzat  Applied material Level 2 A) Condensation type: (light, regular, heavy & putty) supplied as a base paste and a liquid catalyst or paste. Base Catalyst : (Usually liquid and sometimes paste) 1) polydimethy-siloxane: With 1)alkyl silicate: For cross-linking. terminal (OH group). 2)Fillers 2) Tin compound as dibutyl tin dilaurate or tin octoate act as reaction catalyst  Setting reaction of condensation types:  Condensation polymerization with the formation of a ethyl alcohol as by¬product Polydimethyl siloxane + Orthoalkylsilicate Tin.octoate Silicone rubber + alcohol (By. Product) (Base paste) (Catalyst paste)  The formation of the elastomer (impression occurs through a cross linkage between the terminal OH groups of the polymer and the alkylsilicate to form a three dimensional network.  Properties 1)setting time are generally shorter & elasticity developed earlier The elastic recovery is 99.5%. 2)very hydrophobic 3)adequate tear strength) but low when compared to polysulfide or polyether) 4)regular body can withstand up to 300 % extension before tear. 5)elastic properties almost ideal 6)properties related to filler content 7)dimensional changes after setting, may be due to continued slow setting or loss of alcohol produced as a byproduct causing shrinkage of 0.6% in 24 hours 8)should be cast as soon as possible 9) Flexibility: Less flexible than polysulfide but more than polyether 10) Disinfection: They can be disinfected without affecting the properties. 11) Electroplating: They can be electroplated as polysulfide 3. Addition type (vinyl silicone) (4 consistency) (best type of all rubber base)  These materials are supplied as two pastes. (No liquid form). Base paste catalyst: 1)dimethyl siloxane polymer in which some of 1)dimethyl siloxane polymer in which some the methyl methyl groups are placed by vinyl groups groups are replaced by hydrogen. 2)Filler 2)Filler. 3) chloroplatinic acid as catalyst. 14 | P a g e Dr. eslam ezzat  Applied material Level 2  Setting reaction: ✓ On mixing the two pastes a platinum catalyzed addition reaction occurs, causing cross-linking between the two types of siloxane pre-polymers. ✓ The reaction does not involve the production of byproducts. ✓ Cross-linking produces an increase in viscosity coupled with the development of elastic properties.  Properties 1. no by-products so polymerization shrinkage of only 0.05%.  but there is release of hydrogen gas so they add hydrogen absorber to prevent gas accumulation as it may cause blistering 2. latex gloves should not be used with as powder inside it retards the reaction but use vinyl gloves or plastic 3. properties is very similar to condensation silicone 4. adequate setting characteristics & tear resistance coupled with near ideal elastic property(mcq) 5. The most significant difference between the addition curing and condensation curing materials is in their relative dimensional stability Application: primarily used in crown & bridge & occasionally for partial denture. 4) Polyether Rubbers: (cationic ring opening addition polymerization)  supplied as two pastes. Base Catalyst a.A polyether polymer with terminal 1)sulfonic acid ester (aromatic sulfate). Catalyst ethylene-imine group. 2)Filler: Give body& Control viscosities & Physical b.Filler: give body& control viscosity properties. 3)plasticizer: Smooth mix and physical properties c.Plasticizer Setting reaction: When the two pastes are mixed together a cationic, ring opening addition polymerization occurs. Polyether + sulfonic ester Polyether rubber (Impression rubber) (Base paste) + (Catalyst) 15 | P a g e Dr. eslam ezzat Applied material Level 2 *as reaction proceeds, viscosity increases & form relatively very stiff polymer.  Properties: 1. The reaction is of the addition type with no byproduct being produced 2. Each pre-polymer molecule has two reactive eimine groups, individual propagation reactions may produce simple chain lengthening or crosslinking. 3. As the reaction proceeds, the viscosity increases and a rigid crosslinked rubber is produced 4. adequate tear resistance and elastic properties approaching those of the silicones. 5. relatively stiff when set. 6. Flexibility: The least flexible of all rubbers, which represents difficulty in removal from the mouth. should have high thickness (4-6 mm) 7. The accuracy of polyether impressions compares favorably with other regular-bodied elastomers. 8. Dimensional stability and accuracy: very good dimensional stability. Polymerization shrinkage of 0.25% occurs in 24 hours 9. Hydrophilic and absorbs water under conditions of high humidity. 10. Elasticity: It is visco-elastic with elastic recovery of 98.9%. 11. Compatibility with die material: They are compatible with die material producing excellent surface. Does not need surfactant to improve the wettability 12. Mechanical properties: Tear resistance is better than that of silicone impression but less than polysulfide. 13. Disinfection: o It can be disinfected by various antimicrobial solutions without adverse changes, provided that the disinfectant time is brief. o Polyethers are susceptible to dimensional changes if the immersion time is longer than 10 minutes because of their hydrophilic nature 14. Electroplating: It is hydrophilic, thus it cannot be electroplated  Applications: 1. used primarily Crown and bridge 2.occasionally for partial denture work  suitable for use with either stock trays or special trays. viiiiiip *Thickness :all rubber bases used in thin sections 2- 3 mm to decrease amount of polymerization except polyether should be more than 4 mm as it is stiff * The most flexible of all elastic impression : alginate mcq * the most flexible of all rubbers : Polysulfide Rubber * the least flexible of all rubbers: Polyether * all rubber bases are hydrophobic except Polyether 16 | P a g e Dr. eslam ezzat Applied material Level 2 Elastomeric impression material 1.Polysulfide rubber base 2. Silicone rubber 3. Polyether rubbers Condensation Addition 1) Form of two pastes system two pastes system or paste &liquid two pastes system supply Light Light Light Regular Regular Regular heavy Heavy heavy Putty Application Whole edentulous jaw Whole edentulous jaw Quadrant impression Quadrant impression Quadrant impression Composition Lead oxide catalyst Tin octoate Chloroplatinic acid Sulphonic acid Manipulation. All need adhesive Equal length of the two paste-2 3mm in thickness inside the tray except for polyether due to its high stiffness Properties 1) Flow Record fine details Record fine details Record fine details 2) Elasticity 98% 99.5% (ideal) 98.9% 3)Dimensional 0.25% shrinkage 0.6% shrinkage 0.05% 0.2% shrinkag accuracy Shrinkage occurs due to shrinkage differences in temperature between the mouth & the room as well as by product 4)Dimensional All Should be cast within 1hr stability 5) Adhesion All Needs adhesive With the tray 6) Compatibility Compatible Incompatible evolution of H 2 Compatible with Cast But surfactant is needed to surfactant is needed to improve Does not need surfactant improve their wetability their wetability To improve the wetability 7) Taste Sulfur odour Pleasant Pleasant 8) Tear strength High Least less 9) Disinfection & Can be Can be Can not be because it is electroplating hydrophilic 17 | P a g e Dr. eslam ezzat