Elastic impression materials - abhishek kavlekar


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  • Impression waxes
  • The first elastic dental impression material was the hydrocolloid, which was introduced to dentistry in 1925.Since then, many elastomeric impression materials have become available, as indicated on the time line
  • REVERSIBLE HYDROCOLLOIDOrganic hydrophillic colloid extracted from SEAWEED. It chiefly contains agarose and agaropectin.It was first discovered by AlphousPoller of Vienna in 1925 when he was trying to develop a material that could be sterilized and applied without pressure to the exposed surface of the dura matter for perfectly recording the bony margins of the skull.which was termed as ‘Negacol’ which became “Dentacol” when introduced into dentistry.Chemically it is a sulfuric ester of galactan complex.
  • Re-usability of agar is the biggest advantageImpression material approx 4 timesDuplicating mat approx 20 times
  • Basic Constituent is agar 13-17%Borate is added to stengten the gel structure but is a gypsum retarder to counteract the effect of which pot sulfate is addedWater is the principle ingredient by wt.Thymol as bactericidal agent and glycerine as plasticizer can be added
  • The temp lag between gelation n liguefaction temp makes it possible to use agar as a dental impression material
  • The 1st step in preperation of agar is to liqufy the gel to sol.
  • Special metal stock tray with narrow bore metal tube attached to outer surface connected to cold water supply are used.
  • Hydraulic pressure
  • Developed as a substitute for agar during World War IIE.C.C. Stanford, a Scottish chemist, discovered alginates from from brown seaweed (algae) also called alginin the 1880s40 yrs later, “S. William Wilding” received the patent for alginate as impression material.Linear polymer of anhydro --Dmannuronic acid” of high molecular weight.
  • Potassium alginate which dissolves in water and react wid ca ionsCalcium sulfate dihydrate-reacts widpottasium alginate to form insoluble ca alginate gel.Zinc oxide- acts as filler Potassium Titanium fluoride- acts as an accelerator for setting of the stone to be poured and ensure a hard dense cast surface.Diatomaceous earth – acts as filler and increases the strength and stiffness of the gel.Sodium phosphate – acts as a retarder by reacting preferentially wid ca ions to provide working time b4 gelation.
  • Lemon JCet al ( J Prosthet Dent: 2003 Sep;90(3):276-81.)reported that within the limitations of this study, predictable longer working and setting times were demonstrated for the irreversible hydrocolloid specimens with 1 to 8 drops of the sodium phosphate solution tested.The specimens with 8 drops of retarder solution exhibited variable setting times and would not be suitable for clinical use. The compressive strength of the modified irreversible hydrocolloid material tested was compromised because of the addition of sodium phosphate solution; however, recovery from deformation remained satisfactory as retarder solution was added
  • Clean armamrntariun is a must…previous set gypsum in bowl accelerates settingwoody found airborne particles and assessed the levels of airborne particles of alginate impression materials. They found that 10-15% of the particles were siliceous fibers. Based on this evidence it was recommended that inhalation of dust from Woody et al .J Am Dent Assoc 1977,94:501-504
  • The compressive strength of alginate doubles during the first 4 min post geation but not later…alginate improve in elasticity over time which minimizes distortion…hence a 3 min wait is recommended
  • AdvantagesMaximum reproduction of detailsEquipment cost is lowerLess preparation time is requiredDisadvantagesWeak bond between alginate and agarHigher viscosity alginate displaces agarDimensional inaccuracy of alginate limits its use to single units?????
  • For duplication agar is the most used,howevrpvc silicones are good wgichliq at 99-104 degreesPolyether also used
  • The Journal of Prosthetic DentistryVolume 55, Issue 3, March 1986, Pages 304–308Accuracy of a hydrophilic irreversible hydrocolloid/silicone impression materialD.R. Davis, D.D.S., *, J.S. Preble, D.D.S
  •  pH indicators selected from Cresol Red, α-naphtholphthalein, Tropaeolin 000, Thymol Blue, and phenolphthalein in general alginate impression materials, while the pH immediately after the mixing is slightly higher than 8, the pH is lowered according to the progress of the gelation, and the pH becomes lower than 8 when the gelation is completed. Thus, in the conventional alginate impression material compositions which change the color tone, by utilizing this phenomenon, a pH indicator that distinctly forms a color at the pH before the gelation is contained, and by utilizing the pH change after the gelation, the completion of the gelation is visually confirmed
  • Elastomers refer to a group of rubbery olymers which are either chemically or physically crosslinked.Polysulfides were the first elastomeric impression materials.2 For over 30 years, these remained the primary elastomeric material of choice until polyethers burst on the scene with their improved hydrophilicity.  Polyethers still had challenges due to poor taste, relatively low tear-strength, rigidity upon removal, and difficulty in mixing. This led to the development of the first condensation-reaction silicones and then VPS in the 1970s. These materials had excellent tear strength, great dimensional stable, a good or neutral taste, and were more flexible and not subject to plastic deformation upon removal. They had one glaring deficiency in that they are extremely hydrophobic.  Over the years, surfactants and scavengers have been added to this class of impression materials to reduce the contact angle, and to make them less hydrophobic, with a great deal of success.
  • T butylhydroperoxide
  • Plysulfide polymer has multifuncmercaptan group with 1 mole % of pendant –SH groupWeight percent of filler increases from low to high consistenciesDibutyl is added as placticiserLead dioxide gives the brown colorOtheroxidizn agents can be added as MgO, c
  • Siloxane is moderately low mol silicone with reactive terminal hydroxygrpFilers impart strength-with increase in consistency content increasesFiller particle size – 2 to 8µm 35% - low consistencies 75% - puttylike consistenciesReactor is the orthosilicateStannous octoate acts as catalyst
  • Condensation reaction Polymerization is accompanied by the release of ethyl alcohol which causes shrinkage The two step putty-wash technique reduces polymerization shrinkageTop : Structural formula of the molecules of dimethylsiloxane. Middle and bottom: Condens reaction between the OH terminal and tetraethyl orthosilicate in the presence of stannous octate. Thereaction results in the release of two ethanol molecules.
  • Filler particle size – 5 to 10 µm Particles are surface treated to make it more compatible with silicone
  • addition reactionNo reaction by-products develop as long as correct proportions are maintained.
  • A secondary reaction between moisture and residual hydrides of base polymer may lead to development of hydrogen gasThis results in pin-point voids in gypsum castsplatinum/palladium delay pouring for an hour or more
  • Polyethers go through a “snap set,” meaning the material's initial viscosity upon mixing remains relatively unchanged throughout the working time, and rapidly changes during the rest of the setting phase. Polyether materials have excellent flow properties from the start of the mix until the end of the stated working time. This is one of the properties that allows for the capture of fine details even when syringing multiple teet
  • Available intwo types:1. Paint on adhesives EgColtene, Kerr Universal VPS.2. Spray adhesives Eg Sili spray10 min
  • The 2-step putty/light-body impressions were made with 2-mm-thick resin-prefabricated copings. The 2-step injection impressions were made with simultaneous use of putty and light-body materials. In this injection technique, after removing the preliminary impression, a hole was made through the polymerized material at each abutment edge, to coincide with holes present in the stock trays. Extra-light-body material was then added to the preliminary impression and further injected through the hole after reinsertion of the preliminary impression on the stainless steel model.The 2-step putty/light-body and 2-step injection techniques were the most dimensionally accurate impression methods in terms of resultant casts. (J Prosthet Dent 2008;99:274-281)
  • Two stageSingle stage
  • Poured impression is immersed in clean rubber bowl filled with solution of slurry water and dishwashing soap. Impression must be submerged in this solution for at least 10 minutesProcedure to prevent cast breakage during separation from elastomeric impressions ☆ ☆☆Daniel Galindo, DDSa, Michael E. HaganbThe Journal of Prosthetic DentistryVolume 81, Issue 1, January 1999, Pages 37–38
  • The surfactants used were nonylphenoxy poly(ethyleneoxy) ethanol homologs of varying ethyleneoxy chain lengthWettability is max with polyether-less hydrophobic addition siliconeHydrophobic are condensation silicone-addition silicone-void-free die stone casts from the addition type silicone materials.
  • This material also has a better marginal accuracy
  • This is at 24 hours of low bodied consistencyDimensional stability is best with addition-polyether-polysulfide-condensation
  • This is at 24 hours of low bodied consistencyAddition silicone exhibit best while polysulfide exhibit least diamensional stability.
  • Polyulfide has lowest viscosity and is one of the least stiff hence can be used in undercut areas.
  • PICS
  • Stackhouse conducted A study of bubbles in a rubber elastomer manipulated under clinical conditions.Andrecommend that bubbles can be minimized by extruding the first part of the syringe contents onto a mixing pad or distant intraoral site before injecting around the critical tooth preparations.
  • The impression material has excellent physical, mechanical, and clinical qualities with noteworthy long working times, short setting times, dimensional stability, accuracy, high tear strength, good wettability, biocompatibility, and ease of cold disinfection without loss of quality. The impression material is also compatible with gypsum and silver or copper metallizing baths. Accurate casts can be obtained by means of either a double-impression technique or a double-mix techniqueProperties of a new polyether urethane dimethacrylatephotoinitiated elastomeric impression materiaThe Journal of Prosthetic DentistryVolume 63, Issue 1, January 1990, Pages 16–20
  • it was shown that vinyl siloxanethermonophase impressions and vinyl siloxanether dual-viscosity impressions display acceptable accuracy for clinical use with immersion disinfection, since the results for vinyl siloxanether were comparable to the results for representative polyether and vinyl polysiloxane materials. 
  • Elastic impression materials - abhishek kavlekar

    1. 1. ne may not get a chance to make a good first impression. But remember that the first impressio is not the last chance to make a good impression o GOOD MORNiNG
    3. 3. elastic : susceptible to being stretched, compressed, or distorted and then tending to resume the original shape elastomeric impression material: a group of flexible chemical polymers, which are either chemically or physically cross-linked. Generally, they can be easily stretched and rapidly recover their original dimensions when applied stresses are released.
    4. 4. Impression materials Rigid Impression plaster Zinc Oxide Eugenol Impression compound Impression waxes Elastic Hydrocolloid Elastomers Reversible hydrocolloid Irreversible hydrocolloid Polysulfid es Silicones Polyether s
    5. 5. 7 ↓ ↓ ↓ ↓ I 1920 I 1930 I 1 940 I 1950 I 1960 I 1970 I 1980 I1990 I 2000 ↑ ↑
    6. 6. A solid, liquid or gaseous substance made up of large molecules or masses of smaller molecules that remain in suspension in a surrounding continous medium of diffrent matter* A colloid that contains water as the dispersion phase is called as *Anusavice KJ: Philips’ Science of Dental Materials. 11th Edition
    7. 7. Organic hydrophillic colloid extracted from SEAWEED. It chiefly contains agarose and agaropectin. Introduced by Alphous Poller of Vienna” in 1925. Chemically it is a sulfuric ester of galactan complex.
    8. 8. The agar used in dentistry is supplied in the following forms- 1) Tray material 2) Syringe material 3) Agar for duplication
    9. 9. Component Function Composition( %) Agar Brush Heap structure 13 – 17 Borate Strength 0.2 – 0.5 Potassium Sulfate Gypsum hardener 1.0 – 2.0 Diatomeceous earth, Wax, Silica, clay etc Filler 0.5 – 1.0 Thixotropic materials Thickener 0.3 – 0.5 Water Reaction medium Balance 84% Alkylbenzoates Perservative 0.1 Thymol Bactericidal trace
    10. 10. Gel Liquefaction temperature Sol Gelation temperature Gel
    11. 11. LIQUEFACTION • 100°C • Minimum of 10 minutes. • Propylene glycol STORAGE • 65°C • Several days TEMPERING • ~45°C • 3 to 10 min • Never for syringe material
    12. 12. •Just before completion of tempering of tray material the syringe material is taken from the storage compartment and applied to the base of preparation •Water soaked outer layer of the tray hydrocolloid is removed • Tray is seated with light pressure & held with light force •Gelation is accelerated by circulating cool water (approximately 18 to 21 C) through the tray for 3 to 5 minutes.
    13. 13. Area to be recorded is flooded with warm water Syringe agar material – is quickly & liberally syringed over prepared tooth Tray agar placed over the syringed agar
    14. 14. • Greater than 96.5% (permanent deformation less than 3.5%) after the material is compressed 20% for 1 second • Tray types have elastic recovery of about 99% Elastic Recovery • The ANSI/ADA Specification 11 requirement for flexibility allows a range of 4 to 15% Flexibility
    15. 15. • Compressive strength is 0.8 MPa • Tear strength is 0.8 to 0.9 N/mm. • The ANSI/ADA Specification requirement: 0.75 N/mm Strength
    16. 16. • If the material is held rigidly in the tray, the impression material shrinks toward the center of its mass • Rapid cooling may cause a concentration of stresses near the tray where the gelation first takes place Distortion during Gelation • It must be sufficiently viscous so that it will not flow out of the tray • It must not be so great that it will not readily penetrate every detail of the teeth and the soft tissues Viscosity of the Sol
    17. 17. ADVANTAGES Good elastic properties. Good recovery from distortion. Accurate dies can be prepared. Palatable and well tolerated by the patient. Can be used for duplicating models. As it is not hydrophobic, it gives a good model surface. DISADVANTAGES Extensive and expensive equipment. Dimensional instability. Pain and thermal shock. Cannot be electroplated. Tears easily. Disinfection. 21
    18. 18. USES 1. Impressions for fixed prosthesis. 2. Duplicating material. 3. Tissue conditioning material.
    19. 19. •Developed as a substitute for agar during World War II •E.C.C. Stanford, a Scottish chemist, discovered alginates from from brown seaweed (algae) also called algin in the 1880s 40 yrs later, “S. William Wilding” received the patent for alginate as impression material. It is a linear polymer of anhydro - -D mannuronic acid” of high molecular weight.
    20. 20. Component Function Wt% Potassium alginate Soluble alginate 15 Calcium sulfate dihydrate Reactor 16 Zinc oxide Filler particles 4 Potassium Titanium fluoride Accelerator 3 Diatomaceous earth Filler Particles 60 Sodium phosphate Retarder 2
    21. 21. K2nAlg + nCaSO4 nK2SO4 + CanAlg 2Na3PO4 + 3CaSO4 Ca3(PO4)2 + 3Na2SO4 25
    22. 22. 26 *Lemon JC et al ( J Prosthet Dent: 2003 Sep;90(3):276-81. Never change the water powder ratio
    23. 23. Frey G, Lu H, Powers J (J Prost: 2005 Dec;14(4):221-5) Concluded that mechanical mixer improved elastic recovery and compressive strength of the alginate impression materials and had no effect on strain in compression and tear energy. A mechanical mixer facilitates the mixing of alginate impression materials and improves some mechanical properties. Mechanical mixer
    24. 24. Select a perforated tray Mixing and loading Making the impression Wait for 3mins Remove impression rapidly in a single jerk Cut off the excess
    25. 25. Morris et al ( J Prosthet Dent 1983,49: 328- 330) • Demonstrated that smoothing the surface of the mixed alginate with a wet finger, prior to making the impression, consistently resulted in fewer bubbles on the surface of casts.
    26. 26. Mixing time Setting time Working time 1. Fast set: 45 sec. 2. Regular set: 60 sec. 1. Fast set: 1.25 to 2 min. 2. Regular set: 3 to 4.5 min. 1. Fast set: 1.5 to 3 min. 2. Regular set: 3 to 4.5 min. 31
    27. 27. Elastic recovery  Greater than 95% when the material is compressed 20% for 5 seconds. Flexibility  Range of 10 to 20% at a stress of 1000g/cm2 Strength  Compressive strength–at least 0.35MPA  Tear strength – 0.37 to 0.69 MPa 32
    28. 28. Factors affecting strength Too much or too little water used for mixing Insufficient spatulation Over mixing Failure of ingredients to dissolve sufficiently Breaks up the calcium alginate gel network Results in weakened final gel, making it less elastic
    29. 29. Accuracy 1. Increase in concentration of alginate to make the material more accurate 2. Roughness of the impression surface is sufficient to cause distortion 3. Sufficiently accurate to be used for making impressions for removable partial denture prosthesis 1. Model should be poured as soon as possible 2. Stored in 100% relative humidity in a plastic bag or wrapped in a damp paper towel 3. Greater chance of distortion the longer the impression is stored Dimensional stability 34
    30. 30. Easy to mix and manipulate Minimum requirement of equipment Accuracy (if properly handled) Low cost Comfortable to the patient Hygienic (as fresh material is used for each impression) 35
    31. 31. Not accurate for crown and bridge impressions Cannot be electroplated Distortion occurs easily Poor dimensional stability Poor tear strength 36
    32. 32. 1. Complete and removable denture prosthesis 2. Study models and working casts 3. Duplicating models 37
    33. 33. Chilled alginate Syringe agar Gels by chemical reaction Gels by means of contact with the cool alginate 38
    34. 34. 39 ADA specification 20 - Type I (thermo reversible) Type II (nonreversible) Hydrocolloids are popular and have the same composition as the impression materials, but their water content is higher, consequently agar or alginate content is lower
    35. 35. 1. In the form of a sol, containing the water. A reactor of plaster of Paris is supplied separately. 2. Two paste system, one containing the alginate sol, and second containing the calcium reactor. These materials are said to contain silicone and have superior tear resistance. 3. Lee YK et al in this study concluded that addition of NaF in an alginate impression material may result in effective release of fluoride without deteriorating the properties of material itself* 40
    36. 36.  These alginates change color during manipulation to give a clear indication of mixing time, loading into mouth & setting of the material  They contain acid/base indicators that are responsible for change in color at different critical points due to changes in pH that occur during setting  Three phases of chromatic alginates are – RED PHASE: MIXING TIME ORANGE PHASE: WORKING TIME YELLOW PHASE: TIME IN THE MOUTH 41 Chromatic
    37. 37. Impression is rinsed Disinfectant sprayed liberally Wrapped in disinfectant soaked paper towel Placed in a sealed plastic bag for 10 minutes Wrapped impression is removed, rinsed and poured Household bleach Iodophor Synthetic phenols 42
    38. 38. •Shorter storage time of hydrocolloid impressions before pouring is desirable. •Agar Impressions can be stored up to 1 hour in 100% humidity or in storage media like 2% potassium sulfate* •If irreversible hydrocolloid impression pouring is to be delayed up to three hrs, then it should be wrapped with a wet towel and poured within 3 hrs, as this did not appear to affect their accuracy significantly.** *J Prosthet Dent 2001:86(3); 244-50. **Saudi Dental Journal 2002,:14(3).
    39. 39. C o m m o n f a i l u r e s a n d c a u s e s .
    40. 40. Agar Inadequate boiling Storage temperature too low Storage time too long Alginate Improper mixing Prolonged mixing Excessive gelation Water powder ratio too low Grainy material Agar Water- soaked tray surface material not removed Premature gelation of either Alginate Not applicable Separation of tray and syringe materials 45
    41. 41. Tearing Agar Inadequate bulk Premature removal from mouth Syringe material partially gelled when tray was seated Alginate Inadequate bulk Moisture contamination Premature removal from mouth Prolonged mixing 46
    42. 42. Agar Inadequate cleansing Excess water Improper manipulation of stone Air drying the impression before pouring Alginate Inadequate cleansing Excess water left on the impression Premature removal Model left in impression too long Improper manipulation of stone 47 Rough or chalky stone model
    43. 43. Agar Impression not poured immediately Movement of tray during gelation Premature removal from mouth Improper removal from mouth Use of ice water during initial stages of gelation Alginate Impression not poured immediately Movement of tray during gelation Premature removal from mouth Improper removal from mouth Separation of alginate from the tray 48 Distortion
    44. 44. Agar Gelation of syringe material- preventing flow Alginate Undue gelation preventing flow Air incorporated during mixing Agar Material too cold Alginate Moisture or debris on tissue 49 Irregularly shaped voids External bubbles
    45. 45. 50 Chemically, there are 3 kinds of elastomers 1)Polysulfides 2)Silicone a. Addition b. condensation 3) Polyethers
    46. 46. Current ADA specification 19 recognizes 3 types of elastomeric materials This classification is based on selected elastic properties & dimensional change Type Max permanent deformation Max flow in compression Max dimensional change in 24 hrs I 2.5 0.5 -0.5 II 2.5 0.5 -1.0 III 5.5 2.0 -0.5 51 Type Decription consistency Consistency test disc Diameter(mm) min max 0 Very high(putty) - 35 1 High(heavy bodied) - 35 2 Medium(medium bodied) 31 41 3 Low(light bodied) 36 - According to ISO 4823 the method of classification according to consistency is as following-
    47. 47. First synthetic elastomeric impression material Also known as MERCAPTAN or THIOKOL -Mode of supply Collapsible tubes One labeled Base paste and Other labeled Accelerator paste -Consistencies  Light body(syringe or wash)  Medium body (regular)  Heavy body 1950
    48. 48. Polysulfide polymer - 80 to 85% Fillers - 16 to 18% Titanium dioxide, lithopone, zinc sulfate, copper carbonate or silica Dibutyl phthalate-plasticizer Sulfur (0.5%) – accelerator Lead dioxide; 60 to 68% Oleic/stearic acid Retarder Deodorants BASE PASTE REACTOR PASTE
    49. 49. Chain lengthening by oxidation of terminal –SH groups Cross linking by oxidation of pendant –SH groups Polysulfide polymer Lead dioxide Polysulfide water ∆ 3 to 4 C 54
    50. 50. Long working time Good tear strength Radiopaque Good reproduction of surface detail High flexibility Lower cost Need to use custom made trays Bad odor Tendency to run down patient’s throat Stains clothing & messy to work with Must be poured within 1 hour Hydrophobic so impression area has to be dry DISADVANTAGES 55
    51. 51. Mode of supply  Collapsible tubes Base paste and Accelerator paste / liquid  Putty is supplied in jars Consistencies  Light body (syringe or wash)  Putty Also known as conventional silicones 19 55
    52. 52. Polydimethyl siloxane Fillers; 16 to 18% Calcium carbonate or silica Tetra-ethyl Orthosilicate- reactor Stannous octoate - catalyst BASE PASTE REACTOR PASTE
    53. 53. Tetra-ethyl orthosilicate Dimethyl siloxane Silicone rubber Ethyl alcohol Stannous octate ∆ 1°C Cross linkage between Orthoethyl silicate and the terminal hydroxyl group of Dimethylsiloxane to form a 3 Dimensional network 58
    54. 54. Clean, pleasant materials Highly elastic Putty-wash system improves accuracy Inaccuracy due to shrinkage Must be poured within 1 hour Hydrophobic so impression area has to be dry 59
    55. 55. Mode of supply  Collapsible tubes Base paste and Accelerator paste  Putty is supplied in jars Consistencies  Light body (syringe or wash)  Medium body (regular)  Heavy body  Putty Also known as polyvinyl siloxane or vinyl polysiloxane 1975 60
    56. 56. • Base paste Poly methyl hydrogen siloxane Other siloxane prepolymers Fillers- Divinyl poly siloxane • Reactor paste Platinum salt: Catalyst (chloroplatinic acid) Palladium: Scavenger
    57. 57. Vinyl siloxane Silane (hydride groups) Silicon e rubber Platinum salt The base polymer is terminated with vinyl groups and is cross linked with hydride groups 62
    58. 58. Highly accurate High dimensional stability Recovery from deformation on removal is excellent May be used with stock or custom trays Can be poured after 1 week Multiple pours are possible Expensive – twice the cost of Polysulfides More rigid than condensation & difficult to remove around undercuts Moderate tear strength, making removal from sub-gingival areas risky Sulfur in latex gloves and rubber dam inhibit polymerization Pouring of the stone should be delayed by 1-2 hrs, liberation of H2 gas DISADVANTAGES 63
    59. 59. 1960s Mode of supply  Collapsible tubes Base paste Accelerator paste  Third tube containing thinner may be supplied Consistencies  Light bodied(syringe or wash)  Medium bodied (regular)  Heavy bodied First elastomer to be developed primarily to function as an impression material 64
    60. 60. • Base paste Poly ether polymer Fillers; colloidal silica Glycoether or phthalate; plasticizer • Reactor paste Alkyl – aromatic sulfonate ester; cross linking agent Fillers and plasticizers Octyl phalate and 5% methyl cellulose-thinning agents
    61. 61. The main chain is a copolymer of ethylene oxide and tetrahydrofuran. Cross linking is brought about by the aromatic sulfonate ester via the imine end Groups. 66 Polyether Sulfonate ester Cross linked rubber
    62. 62. Pleasant mixing and ease of handling More accurate than polysulfide and condensation silicone Good surface detail reproduction Easily poured in stone If kept dry, will be dimensionally stable for up to 1 week High cost High stiffness Bitter taste Storage of impressions is critical cannot be left in disinfectants for long 67
    63. 63. 68
    64. 64. Silicones Polysulfides Butyl rubber Styrene/acrylonitrile Dissolved in volatile solvent such as chloroform or ketone Hydrated silica forms ethyl silicate – bonds with the tray Polydimethyl siloxane – bonds with the rubber 69
    65. 65. 1)Multiple mix technique 2)Single viscosity technique 3)Putty wash technique 70
    66. 66. Heavy and light body mixed simultaneously light body loaded in syringe Tray adhesive applied Light body injected into prepared teeth Heavy body loaded in the tray Final impression
    67. 67. Only one mix is made- Part of it is placed in the tray Another portion is placed in syringe for injection Medium viscosity of addition and polyether can be used.
    68. 68. All elastomers are compatible with gypsum products Excellent dimensional stability of addition silicone and polyether makes it possible to construct 2 or 3 casts Hydrophobic addition silicone – problem ???? 74
    69. 69. • Surfactants are added to reduce the contact angle; dilute solution of soap • Most commonly used – non-ionic surfactants oligoether or polyether substructure Hydrophilic part Silicone compatible Hydrophobic part PVS Diffusion – controlled transfer of surfactant molecules from PVS to aqueous phase Reduction in surface tension Greater wettability 75 water
    70. 70. Hydrophilized vinyl polysiloxane
    71. 71. properties
    72. 72. Impression material Mean working time Mean setting time Polysulfide 6.0 4.3 16.0 12.5 Condensation silicone 3.3 2.5 11.0 8.9 Addition silicone 3.1 1.8 8.9 5.9 Polyether 3.3 2.3 9.0 8.3 23°C 37°C 23°C 37°C 78
    73. 73. Temperature Humidity Viscosity Factors affecting working- setting time
    74. 74. 1)Polymerization shrinkage 2)Loss of by – product 3)Thermal contraction from oral temperature to room temperature 4)Imbibition 5)Incomplete recovery of deformation
    75. 75. Addition silicones -0.17% Polyether -0.24% Polysulfides -0.40% Condensation silicones -0.60%
    76. 76. Addition silicones Polyether PolysulfidesCondensation silicones
    77. 77. Addition silicones -0.17% Polyether -0.24% Polysulfides -0.40% Condensation silicones -0.60%
    78. 78. Addition silicones Polyether PolysulfidesCondensation silicones
    79. 79. Addition silicones 0.01-.03% Polyether 0.03% Polysulfides 0.5-2% Condensation silicones 0.05-0.1%
    80. 80. Probability of allergic reactions is low Polysulfide has the lowest cell death count Polyether has the highest cell death count ,toxicity and contact dermatitis among the class. The most likely problem is lodgment of impression material in gingival sulcus resulting in severe inflammation,
    81. 81. Clinical consideration : o Subgingival regions are very thin – material can tear o Residual segment of impression material difficult to detect radio opacity of polysulfide can help o Severe gingival inflammation. o Examine the gingival sulcus immediately after impression removal and also the 87
    82. 82. 2 years stannous octoate oxidizes Orthoethyl silicate is not stable in presence of tin ester 1 to 2 years Excellent shelf life; more than 2 years Cool, dry environment Tubes always tightly sealed Container closed 88
    83. 83. MATERIAL DISINFECTANTS Polysulfide Silicones (by immersion-not more than 30 min/spray) 2% Glutaraldehyde Chlorine compounds Iodophors Phenolics Polyether Chlorine compounds Iodophors Use disinfectant with short immersion time(less than 10 min) to avoid distortion(Polyether is hydrophilic) 89
    84. 84. • 1)Impression making • 2)Bite registration – The material is fast setting. – There is no resistance to biting forces. – There is no odor or taste for the patient. – It gains dimensional stability over time. – It is convenient to use. • 3)Duplication Polyvinyl siloxane and polyether duplicating materials are superior in accuracy than agar reversible hydrocolloid duplicating materials. * *Accuracy and reproducibility of reversible hydrocolloids versus elastomers duplicating materials Bahannan, S et al. The Saudi Dental Journal 1995:7( 1)
    85. 85. Common failures
    86. 86. ROUGH OR UNEVEN SURFACE ON IMPRESSION 1. Incomplete polymerization cause by premature removal. 2. improper ratio or mixing of components 3. presence of oil or other organisms on the teeth 4. Too rapid polymerization from high humidity or temperature 5. Excessively high accelerator/base ratio
    87. 87. BUBBLES 1. Too rapid polymerization , preventing flow 2. Air incorporated during mixing IRREGULAR SHAPED VOIDS 1. Moisture or debris on surface of teeth
    88. 88. ROUGH OR CHALKY STONE CAST 1. Inadequate cleaning of impression 2. Excess water or wetting agent left on surface of the impression 3. Premature removal of cast 4. Improper manipulation of stone 5. Failure to delay pour of addition silicone at least 20min
    89. 89. 1. Lack of adhesion of rubber to the tray caused by not applying enough coats of adhesive 2. filling tray with material too soon after applying adhesive or using wrong adhesives 3. Lack of mechanical retention for those materials where adhesive is ineffective 4. Development of elastic properties in the material before tray is seated 5. Excessive bulk of material DISTORTION 95
    90. 90. 6. Insufficient relief for the reline material 7. Continued pressure against impression material that has been developed elastic properties 8. Movement of tray during polymerization 9. Premature removal from the mouth 10.Delay pouring of the polysulfide or condensation silicone impression
    91. 91. Introduced in early 1988 by Genesis & LD Caulk 1. Polyether urethane dimethacrylate – elastomer resin 2. Chloroquinone – photoinitiator 3. Silicon dioxide – filler 0 Light body – syringe Heavy body – tubes 97
    92. 92. Manipulation 1. Loaded tray is seated in the mouth 2. 8mm or larger diameter optical probe is placed in the mouth below the tray 3. Blue light is activated for 3 minutes 4. Impressions can be poured immediately or stored up to 2 weeks 1. Long working time and short setting time. 2. Blue light is used for curing with transparent impression trays. 3. Tear strength – 6000 to 7500 gm/cm2 (Highest among elastomers) 4. Other properties are similar to addition silicones Properties
    93. 93. 1. Special transparent trays 2. Difficult to cure in remote area DisadvantagesAdvantages 1. Controlled working time 2. Excellent properties 3. Ease of cold disinfection without loss of quality. 4. The impression material is also compatible with gypsum and silver or copper metallizing baths 99
    94. 94. It combines the benefits of polyether and vinyl polysiloxane impression materials. The pleasant tasting hybrid impression material purportedly has hydrophilic properties, high tear strength, excellent dimensional accuracy and resistance to deformation. It is available in two setting times (fast and regular) and four viscosities (putty, heavy body, monophase and light body)
    95. 95.  Soft elastomers  Composed of powder that contains poly(ethyl methacryalte) and liquid that contains an aromatic ester – ethyl alcohol mixture (up to 30%)  Within few days they become stiffer as a result of loss of alcohol so need to be replaced every 3 days 1. Tissue conditioners for irritated mucosa 2. Temporary soft liners 3. Functional impression materials 101
    96. 96. 1. Hydrophilic; accurate impression in presence of saliva 2. Dimensional stability is fair 3. Low rigidity , Low tear strength 4. Adhere to themselves and are excellent for border molding and correctable impression technique 5. Do not distort from water absorption, but they distort easily when exposed to alcohol based disinfectants 6. Properties which make s the material effective are- Viscous behaviour-allow adaptation to irritated denture bearing mucosa for several days Viscoelasticity which cushions the cyclic forces of mastication and bruxism
    97. 97. •Tissue conditioners should not be cleaned by scrubbing with a hard brush in order to prevent tearing of the material. The use of soft brush under running water is recommended. •The greatest virtue of tissue conditioners is their versatility and ease of use. •The biggest flaw is that they are also misused
    98. 98. Elastomers since their introduction have revolutionised the art of impression making hence allowing the operator to provide acuurate fitting restorations Addition silicones and polyethers account for major portion of the current practice. Condensation silicones, Polysulfides and irreversible hydrocolloids – more sensitive with respect to handling considerations , mix-and-pour techniques, which may affect accuracy. 104
    99. 99. The understanding of basic knowledge of the impression materials and their behavior during handling are important for their use in the oral environment and clinical success. The selection of the material best suited for a particular clinical situation and technique rests with the operator.
    100. 100. • Anusavice KJ: Philips’ Science of Dental Materials. 11th Edition. Elsevier:S Louis;2003 • William J. O’Brien: Dental Materials Properties and Selection • Craig RG,Restorative Dental Materials.9th Edition. Mosby:St Louis;1993 • Impression materials: A comparative review of impression materials most commonly used in restorative dentistry DCNA 2007;51(3):629-642 • McCabe JF, Walls AW:Applied Dental Materials.9th Edition.Blackwell Publishing:Singapore;2008 • Kowdi MS, Patil SG.Prep manual for undergraduates: Dental materials.
    101. 101. • Schleier PE, et al The effect of storage time on the accuracy and dimensional stability of reversible hydrocolloid materials. J Prosthet Dent 2001 ;86(3):244-50. • Jamani KD The effect of pouring time and storage condition on the accuracy of irreversible hydrocolloid impression. Saudi Dental Journal 2002:14(3). • Woody et al Hydocolloids: A comparative study.J Am Dent Assoc 1977,94:501-504 • Lemon JC et al Facial moulage:The effevt of a retarder on compressive strength and working and setting times of irreversibe hydrocolliid impression material. J Prosthet Dent: 2003 ;90(3):276-81.
    102. 102. • Lee YK et al in this Effect of fluoride addition on the properties of dental alginate impression materials study J. Mater Sci Mater Med : 2004 ;15(3):219-24 • Morris et al Effect on surface detail of casts when irreversible hydrocolloid was wetted before impression making.J Prosthet Dent 1983,49: 328-330 • Bahannan, S et al Accuracy and reproducibility of reversible hydrocolloids versus elastomers duplicating materials.The Saudi Dental Journal 1995:7( 1) • Stackhouse, J.A., Jr., Harris, W.T., Mansour, R.M. and Von Hagen, S. A study of bubbles in a rubber elastomer manipulated under clinical conditions. J Prosthet Dent 57:591-596, 1987
    103. 103. Thank you