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Elastic impression materials /certified fixed orthodontic courses by Indian dental academy


The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats. …

The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

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  • 1.
  • 2. INDIAN DENTAL ACADEMY Leader in continuing dental education
  • 3. Contents •Introduction •Definition •Classification •Requirements •Elastic impression materials •Impression making with elastomers •Methods of making impressions •Comparative properties •Hydrocolloids •Review of Literature •References •Conclusion
  • 4.
  • 5. Definition •GPT-8 - Impression - A negative likeness or a copy in reverse of the surface of an object; an imprint of the teeth and adjacent structures for use in dentistry. •GPT-8 – Impression material – Any substance or Combination of substances used for making impression or negative reproduction
  • 6. classification RIGID ELASTIC Set by chemical reaction -plaster ZnOE -alginate -non aqueous elastomers Set by temperature change compound Agar hydrocolloid
  • 7. REQUIREMENTS They should be fluid enough to adapt to the oral tissues They should be viscous enough to be contained in the tray while in the mouth they should transform into rigid state within reasonable time (approximately 7min) The set impression should not distort when removed.
  • 8. Impression should be dimensionally stable till the cast is poured. Material should be biocompatible Material should be economical Should be compatible with die and cast materials Should record the teeth and tissue accurately
  • 10. Chemically there are four types of elastomers • Polysulfide • Condensation polymerizing silicone • Addition polymerizing silicone • Polyether
  • 11. Each type is further divided into four viscosity classes • Light body • Medium / regular body • Heavy body • Putty
  • 12. • The current ADA specification recognizes three types of rubber like impression materials. • The classification type is based upon selected elastic and dimensional change of the set material, accordingly
  • 13. ADA classification Max permanent deformation Max flow in compression Max dimensional change in 24 hrs Type-1 2.5 0.5 - 0.5 Type-2 2.5 0.5 - 1.0 Type-3 5.5 2 - 0.5
  • 14. GENERAL PROPERTIES • Excellent reproduction of surface details. The low viscosity is able to record find details • They are hydrophobic. So oral tissues in the area of impression should be dry. • Co-efficient of thermal expansion of elastomers is high. So thermal contraction of set material occurs when transferred to room temperature
  • 15. • Tear strength is excellent. So impressions can be removed from thin areas. • The elastomeric materials can be copper/silver plated • • Shelf life of elastomers is good Dimensional stability
  • 16. Representative linear contraction of four elastomeric impression materials
  • 17. • For visco-elastic material slow elastic recovery may control for sometime after withdrawal of the impression, producing dimensional change. In this case the dimensional change results in more accurate impression. • But many impression materials contain volatile substances either as primary components or as by products of setting reaction. Loss of such volatile materials results in shrinkage of impression material resulting in decrease in accuracy. So for majority of materials, accuracy can be maintained by powering the cast soon after the removal of impression.
  • 18. Dimensional changes occur due to: Curing shrinkage Loss of byproducts Polyether being hydrophilic absorbs water and loses soluble plasticizers causing change in dimension Thermal contraction when transferred from mouth to room temperature
  • 19. Incomplete elastic recovery after deformation during removal Amount of filler Uniform thickness of material gives more accurate impression Time of pouring of impression. Impression should be powered after elastic recovery and before dimensional change
  • 20. POLYSULFIDES Also called as mercaptan or Thiokol MODE OF SUPPLY • It is supplied in tubes as base and accelerate in paste form • Available in three viscosities • Light bodied • Medium bodied • Heavy bodied
  • 21. COMPOSITION •BASE PASTE FUNCTION Polysulfide polymer – 80-85% This is further polymerized and cross linked to form rubber Filler (Titanium dioxide zinc sulfate) – 16-18% To provide required strength Plasticizer (Dibutyl Phthalate) To provide appropriate viscosity Small quantity of sulphur – To accelerate the reaction 0.5%
  • 22. Accelerator paste Lead dioxide – 60-68% To react with thiol group causing setting and give brown colour Filler and plasticizer To provide strength and to give adequate viscosity Oleic / stearic acid Act as retarder to control rate of setting reaction
  • 23. CHEMISTRY AND SETTING REACTION • The main component of polysulfide is a multifunctional mercaptan (-SH) or polysulfide polymer. These linear polymer contains pendent –SH groups • •
  • 24. An oxidizing agent like lead dioxide is used to initiate polymerization. Polymerization occurs by a.Chain lengthening by oxidation of terminal -SH group b.Cross linking by oxidation of pendent –SH group
  • 25. Reaction yields water as by product HS SH + HS SH SH SH HS SH SH PbO2 HS HS SH S–S  S  S  SH SH + PbO + H2O
  • 26. PROPERTIES Unpleasant odour and colour It has a long setting time of 8.12minutes Mixing time is 45 seconds Excellent reproduction of surface detail Dimensional stability. The curing shrinkage is high (0.45%) Has the highest permanent deformation (3.5%) This improves with time. So pouring of model should be delayed by half an hour
  • 27. Tear strength is 4000 gms/cm2 It has good flexibility. A 2mm spacing in the tray is sufficient to make the impression. It is hydrophobic. So impression area should be dry Shelf life is good i.e. 2 years
  • 28. SILICONE RUBBER IMPRESSION MATERIALS • Types: • Two types of silicone impression materials are available based on the type of polymerization reaction occurring during setting • Condensation silicone • Addition silicone
  • 29. • MODE OF SUPPLY • Available as base and catalyst in paste form. The condensation silicone catalyst can also be supplied as a liquid. The putty is supplied in jars. Condensation silicone is available in three • viscosities. • Light bodied • Medium bodied • Putty • Addition silicone is available in four viscosities
  • 30. CONDENSATION SILICONES Composition of Base paste Hydroxyl terminated polydimethyl siloxane Undergoes cross linking to form rubber Colloidal silica Filler
  • 31. Reactor paste Tetraethyl orthosilicate Cross linking agent Stannous octate Catalyst
  • 32. CHEMISTRY AND SETTING REACTION It is a condensation reaction Polymerization occurs as a result of cross linkage between orthoethyl silicate and terminal hydroxyl group of dimethyl siloxane to form a three dimensional network Stannous octate acts as a catalyst Ethyl alcohol is by product. Its evaporation probably accounts for much of the condensation taking place in set silicone impression
  • 33.
  • 34. • PROPERTIES Pleasant colour and odour Setting time is 6-8 minutes, mixing time is 45 seconds Excellent reproduction of surface details Dimensional stability is low due to high curing shrinkage (0.4-0.6%) and shrinkage due to evaporation of ethyl alcohol. To avoid this cast should be poured immediately. Tear strength is 3000gm/cm2 It is hydrophobic. So impression field should be dry Can be electroplated with silver or copper
  • 35. ADDITION SILICONES • • • • • • • Superior to condensation silicones Also called polyvinyl silioxane impression materials. COMPOSITION •fillers Base: Polymethyl hydrogen siloxane Other siloxane prepolymers Fillers • • • • Divinylpolydimethyl siloxane Other siloxane prepolymers Fillers Platinum salt-catalyst • Accelerator
  • 36. • CHEMISTRY AND SETTING REACTION • It is an addition reaction • In this case polymer is terminated with vinyl groups and it is cross linked with silane (hydride group). The reaction is activated by platinum salt
  • 37.
  • 38. • No reaction byproduct develops as long as correct proportions of vinyl siloxane and silane siloxane are maintained • -sulfur compounds retard the setting of addition silicone.
  • 39. PROPERTIES Pleasant colour and odour Good reproduction of surface details Setting time is 4-7 minutes and mixing time is 45 seconds It has the best dimensional stability among all elastomers. It has low curing shrinkage (0.17%) and low permanent deformation (0.05-0.3%) Good tear strength (3000gm/cm2) It is hydrophobic so impression field should be dry Can be electroplated with copper/silver Shelf life ranges from 1-2 years
  • 40. POLYETHER • Mode of Supply: • Available as base and accelerate paste in tubes • Available in three viscosities •Light bodied •Medium bodied • Heavy bodied
  • 41. COMPOSITION • Base: • Polyether polymer • Colloidal silica glycol ether (or) phthalate • Accelerator Paste: • Alkyl aromatic suffonate • Colloidal silica • Phthalate Cross linked to form rubber Acts as filler Plasticizer Initiates cross linking Filler Plasticizer
  • 43. PROPERTIES Pleasant odour and taste Setting time is short 3.5minutes, mixing time is 30 seconds Good dimensional stability Curing shrinkage is 0.24% Polyether absorb water and can change in dimension. So should not be stored in contract with water or in humid climates
  • 44. It is extremely stiff Tear strength is 3000gm/cm2 Hydrophilic, has good compatibility with stone Can be electroplated Good shelf life i.e., more than 2 years.
  • 45. IMPRESSION MAKING WITH ELASTOMERS • 1. 2. 3. 4. 5. It involves five steps Preparing a tray Preparing the material Making impression Removing the impression Preparing stone casts and dies
  • 46. • Preparing a tray: • • • • • Impressions are usually made with custom trays. Perforated stock trays are used for making impression in putty. To prepare a custom tray, an alginate impression is made and stone cast is constructed Teeth are covered with modeling wax (1 or 2 sheets approximately 3-4mm) to act as spacer and stops are provided Custom tray is prepared with tray material Slightly roughened surface of tray inside improves retention.
  • 47. • Preparing the material: • • • • • Materials are provided in two paste tubes Same length of materials should be dispensed on to mixing pad Catalyst paste is first collected on to spatula and then distributed over the base Mixing should be thorough, uniform in colour with no streaks of base of catalyst If one of the components is in liquid form such as catalyst for condensation silicone, a length of base is dispensed from tube onto the mixing pad and a drop of catalyst is added for each unit length of base.
  • 48. •Putty consistence are dispensed by volume using equal number of scoops and kneaded. •Automatic mixing and dispensing devices are available used for light, medium and heavy body consistencies. •It consists of a double barrel gun with mixing tip. The tip consists of spiral inside. The mixing tips vary in diameter length and size of the tip opening for specific consistency.
  • 49.
  • 50. • It has the advantages over hand mixing • Less air bubbles • Reduced working time • More uniform mix • A recent development in the automatic mixing and dispensing device is a dynamic mechanical mixer. Materials are supplied in plastic bags housed in a cartridge. Device uses a motor to drive parallel plunger that force the materials into a mixing tip and the spiral inside the mixing tip rotates as the materials are extruded through the tip. With this uniform mix of even higher viscosity material can be achieved
  • 51.
  • 52. • Making of impression • • • • • • Initially tray is coated with adhesive that forms bond between tray and impression material. Slightly roughened surface of tray increases adhesion. METHODS OF MAKING IMPRESSION Three techniques Single mix technique Multiple mix technique Reline technique
  • 53. • Single Mix technique: • Viscosity used is regular body • Method: • The paste is mixed and part of it is loaded into tray and part into syringe. The syringe material is then injected on to the prepared area. Then tray is seated over it.
  • 54. • Multiple mix technique: • Viscosity used is heavy body and light body • Method: • The two viscosities are mixed simultaneously on separate pads. Heavy body is loaded onto the tray and light body in to syringe. The syringe material is injected into area of preparation. Tray with heavy body is seated over it.
  • 55. • Reline technique: • Viscosity used is putty and light body • Two approaches are present • Two stage procedure • Single stage procedure
  • 56. • For two stage procedure, thick putty material is placed in stock tray and a preliminary impression is made. This forms an intra oral custom tray. Space for light body or was is provided wither by cutting away some of the putty or by using thin polyethelene sheet as a spacer between putty and prepared teeth. • A mix of thin wash material is placed into putty and putty was combination tray is seated finally to make impression.
  • 57. • For single stage procedure, was material is syringed into place and then unset putty is seated over light body but the disadvantage is that putty may displace light body. • Removal of the impression: • The material is checked for set by probing with the blunt instrument. Then impression is dislodged from the mouth with a steady pressure
  • 58. • Preparation of stone casts and dies: • • • All non aqueous elastomeric impression material are compatible with all types of gypsum products. The hydrophobic nature of VPS material make them compatible with epoxy resins used for more accurate casts and dies. Surfactant can be applied to improve the ability of hydrophobic impression material surfaces to be wet by stone.
  • 59. • Disinfection: • Condensation silicones, addition silicones and polysulfides can be disinfected with all EPA registered disinfectants without major changes provided disinfection time is short. The impressions should be immersed for the specified time and after it should be removed, rinsed and cast is poured. • A satisfactory solution for most elastomers is 2% Glutaraldehide
  • 60.
  • 61. • 1. 2. 3. 4. 5. APPLICATIONS: Impressions for fixed partial dentures Impressions for removal partial dentures Impressions for complete dentures polyether is used for Border moulding To make impressions for implant procedure 6. In maxillofacial prosthesis
  • 62. COMPARATIVE PROPERTIES OF ELASTOMERS PROPERTIES POLYSULFIDES CS AS POLYETHER FLOW high low very low very low VISCOSITY low moderate high high CREEP high moderate low very low TEAR STRENGTH 2500-7000 2300-2600 1500-4300 18004800
  • 63. %CONTR 0.40-0.45 0.38-0.60 ACTION 4-9% 3-6% 3% DIMENTI 0.4% AL CHANGE 0.6% 0.15% 0.23% CONTACT 820 ANGLE 980 9853 490 excellent excellent excellent STRAIN TISSUE DETAIL 14-17% 0.14-0.17 0.19-0.24 excellent
  • 64. SHELF LIFE fair poor excellent fair ST 8-12min 6-8min 4-7min 3-5min WT 4-7min 2.5-4min 2-4min 3min medium high veryhigh STIFFNE low SS
  • 65. AGAR (REVERSIBLE HYDROCOLLOID • Sears introduced reversible hydrocolloids in 1937. • Definition:
  • 66. • MODE OF SUPPLY: • Supplied as gel in collapsible tube • or as Cylinders in a jar
  • 67. COMPOSITION:INGREDIENT WEIGHT(%) FUNCTION agar 13-17 To provide dispersed phase borate 0.2-0.5 Provides strength sulfate 1-2 Gypsum hardener wax 0.5-1 filler Thixotropic materials 0.3-0.5 thickener water balance Reaction medium
  • 68. • PROPERTIES: • The ADA specification No 11 sets standard properties required by agar hydro colloidal material. • Flow: • The material should be able to record the fine details • Gelatin temperature:• After boiling for 8 min, the material should be fluid enough to be extruded from container. After tempering the solution should be homogenous and should set between 37 and 45 when cooled.
  • 69. • • • • Flexibility: The ADA specification requirement for flexibility allows a range of 4% to 15% at a stress of 14.2 psi. Elasticity and elastic recovery:Agar hydrocolloids are highly elastic in nature and elastic recovery occurs to the extent of 98%
  • 70. • • Accuracy and dimensional stability Agar impressions are highly accurate at the time of removal from mouth but shrink when stored in air and expand when stored in water. The least dimensional change occurs when stored in 100% humidity but immediate pouring of cast is recommended.
  • 71. • • • Working and setting time:Working time ranges between 7-15 minutes and setting time is about 5 minutes. They can be controlled by regulating flow of the water through cooling tubes. Tear and Compressive strength Tear strength is 4 psi Compressive strength is 800 gm/cm2.
  • 72. • MANIPULATION: • Conditioning until is required for manipulation of agar. • The Conditioner consists of • Boiling section • Storage section • Tempering section.
  • 73.
  • 74. • In boiling section, the material is kept for 10 min for liquefaction. • Then material is stored in storage section at 650 in sol form until it is required. • Material is tempered at 45. for 3 to 10 min so as to be tolerated by the patient. • Just before the tempering process for the bray material is completed, the syringe material is directly taken from the storage compartment and applied to be teeth. The water soaked on the layer of the tray hydrocolloid is removed from the container and gauge is removed.
  • 75. • The tray is immediately brought into position and seated with tight pressure and held with a very light force. • Gelatin is accelerated by circulating cool water (18-21) through the tray for 3-5 min. After the gelatin is over, the tray is removed suddenly with a snap.
  • 76.
  • 77. • STORAGE OF AGAR IMPRESSION: • Storage should be avoided . Storage in air results in dehydrations, and storage in water results in expansion. If storage is unavoidable it can be stored in100% relative humidity for not more than 1 hour.
  • 78. • Advantages: 1. Accurate dies can be prepared if handled properly. 2. Good elastic property and reproduces undercuts properly 3. Well tolerated by patient 4. Used for duplicating models.
  • 79. • Disadvantages: 1) Flow is less Compared to recent elastic impression materials 2) Gelatin may be painful to the patient. 3) Tears relatively easily. 4) Extensive equipment is required
  • 80. ALGINATE ( IRREVERSIBLE HYDROCOLLOIDS):• It is extracted from certain brown seaweed. The substance is called anhydro-beta-d mannuronic acid or alginic acid. • TYPES:• 1) Type II – Fast setting (1-2 min) • 2) Type II- Normal setting ( 2.4.5 min)
  • 81.
  • 82. COMPOSITION INGREDIENT WEIGHT(%) FUNCTION Potassium alginate 15% Dissolves in water and reacts with calcium ions Calcium sulfate Reacts with Potassium alginate and forms insoluble calcium alginate 16%
  • 83. Zinc Oxide 4% Acts as filler Potassium titanium fluoride 3% Accelerator Diatomaceous earth 60% Filler Sodium phosphate 2% Retarder Coloring and Flowering agents TRACES
  • 84. CHEMISTRY AND SETTING REACTION • :• The chief ingredient of irreversible hydrocolloid is one of the soluble alginates. Reaction occurs by a chemical reaction. Soluble alginates reacts with Calcium sulfate to produce insoluble calcium alginate as a gel. • The production of calcium alginate is delayed by the addition of a third soluble salt to the solution with which calcium sulfate will react in preference to the soluble alginate to form an insoluble calcium salt. • Thus, the reaction between the calcium sulfate and the soluble alginate is prevented as long as any of the added salt is left. The added salt is called retarder.
  • 85. • The reactions that occur are 1. 2Na3 PO4 + 3 CaS04  Ca3 (Po4) + 3 Na2 So4 When the supply of retarder ( trisodium phosphate) is exhausted, Calcium ions begins to react with potassium alginate to produce calcium alginate. • K2n Alg + n CaSo4-nK2So4 + Can Alg
  • 86. • CONTROL OF SETTING TIME: •Setting time can be altered by altering of water. •As the temperature increases, the setting time decreases. •For 10 rise of temperature 1 min reduction in setting time occurs. •Bowl and spatula also can be cooled to increase setting time.
  • 87.
  • 88. • MANIPULATION: For manipulations a clean bowl and metal spatula. The First step in the manipulation is to prepare a proper mixture of water and powder. Water is powered in to bowl and specified weight of powder is added and powder is carefully incorporated into water with spatula.
  • 89. • A vigorous figure 8 motion is best with the mix being stopped against the sides of bowl with intermittent rotations of the spatula to press out air bubbles. The final mix should be smooth creamy mixture that does not drip off the spatula when it is raised. Mechanical devices are also available for mixing. Their advantages are speed convenience and eliminating human errors.
  • 90. • • • • • • • • Mixing time for Fast set alginate – 45 Sec For Normal set - 60 Sec Over mixing results in Reduction in final strength as gel fibrils are destroyed Reduction in working time. Under mixing Causes Lack of homogeneity and reduced strength
  • 91. • MAKING THE IMPRESSION • A perforated tray is used • The thickness of alginate impression between the tissue and the tray should be at least 3mm. • Before seating the impression, the material should have developed sufficient body so that it may not flow out of the tray and gag the patient. Once the tray is seated in the mouth, it must be held firmly without any movement. Alginate impressions should not be removed from mouth for at least 3 minute after gelation has occurred.
  • 92. • Removal of the impression: • Alginate impression develops effective seal which can be freed by running the finger around periphery. Impression should be removed suddenly with a jerk. Torquing or twisting should be avoided. After removal impression should be washed with water to remove saliva, covered with wet gauge to prevent syneresis and cast should be poured as soon as possible.
  • 93. • PROPERTIES • ADA specification No. 18 for alginate sets following standards • Working time: • Fast setting – 1.2 to 2minutes • Normal setting – 2-4.5minutes • Setting time: • Fast setting – 1.2 minutes • Normal setting – 2-4.5minutes
  • 94. • Flexibility • It is about 14% at a stress of 1000gm/cm2 • Elasticity and elastic recovery: • Elastic recovery is 97.3%
  • 95. • Strength: • • • The compressive strength of alginate ranges from 5000-8000gm/cm2. The tear strength ranges between 350700gm/cm2. Both these properties are time dependent. If removal is delayed, strength increases.
  • 96. • Time from gelation(min) Compressive strength 0 0 .33 4 0.77 8 0.81 12 0.71 16 0.74
  • 97. • The final strength depends on • W/P ratio: Too much or too little water reduces strength • Mixing time: Over and under mixing reduces strength • Dimensional stability: • Alginate impression loses water by evaporation and shrink in air. If placed in water it absorbs and swells. So cast should be poured immediately
  • 98.
  • 99. • Advantages: • Easy manipulation • Minimum equipment • Low cost • Accurate if properly handled
  • 100. • Applications: • Making impressions for diagnostic casts for partial dentures • Making impressions for orthodontic models • Making preliminary impressions for complete dentures • For duplicating models
  • 101. • LAMINATE TECHNIQUE/ALGINATE AGAR METHOD • In this technique agar in the syringe is injected on to the area to be recorded, an impression tray containing chilled alginate is placed over it. • The alginate gets by chemical reaction, where as agar gels by means of contact with cool alginate. Since agar is in contact with teeth maximum detail care be obtained.
  • 102. • MODIFIED ALGINATES: • Traditionally alginate is supplied in two component system, powder and water. But other forms are also available. •In the form of a solution containing water and a reactor of plaster of Paris •As a two paste system one containing solution and other calcium reactor. These materials contain silicone and are supplied in tray viscosity and syringe viscosity.
  • 103. • RECENT ADVANCES • High tear strength alginates: Silicone reinforced two paste system one with alginate, other with calcium reactor. It has higher tear strength • Self disinfecting alginates containing iodophor • Dust free alginates: Organic glycol is used to agglomerate the dust particles
  • 104.
  • 105. REVIEW OF LITERATURE • Andree, Alfred and Christoph evaluated the dimensional accuracy of monophase elastic impression making with addition silicone and polyether and found no significant change.
  • 106. • Josehph, Tamer and David assessed the accuracy of three putty wash impression technique using same impression material i.e. VPS. Techniques used were 1) Putty and wash used simultaneously 2) With 2mm relief using prefabricated coping 3) With polythelene space • They concluded that PVS with 2wmm relief was the most accurate
  • 107. • Steven O Hondrum assessed the shelf life of different elastomers like polyether, polysulfide, additive silicone and found all the materials were fairly efficacious. But addition silicone showed better value during 72 month period and polysulfide with a little change.
  • 108. • John Chai, Yutaka investigated modulus of elasticity, strain and tear energy of VPS, polysulfide and polyether and concluded that high strain tolerance of PVS allows their removal without distortion from undercuts. The high tear energy of polysulfides indicates their superior resistance to tear in thin sections.
  • 109. • Alvin G. Wee evaluated the accuracy of solid implant casts fabricated from different impression materials (Polyether, AS, CS, polysulfide) and concluded that polyther (medium) was recommended for direct implant impression.
  • 110. • J.A. Payne tested the bond strength of three elastomers (Hydrosil, Reprosel, impregum) to an auto polymerized resin tray and concluded that roughening of tray increased bond strength
  • 111. • Gordon, Johnson and David evaluated the evaluated the effect of tray section (acrylic resin trays, thermoplastic trays and plastic trays) on the accuracy of elastomers and concluded that custom made trays of acrylic resin and thermoplastic material produced casts with better accuracy
  • 112. • Shirley, John H Park and Daneil E. Tira compared the accuracy of one step putty wash with two step putty wash of addition silicone impression. They found different was not significant.
  • 113. • Kern and Reinhold tested the influence of disinfectants (MD/520 and impresept) on the accuracy of reversible hydrocolloid and found accuracy change was not significant.
  • 114. • Willium Heisler and Anthony evaluated for dimensional accuracy and bond strength of irreversible hydrocolloid with irreversible hydrocolloid system and found that accuracy was suitable for clinical use and bond strength was similar to tear strength of reversible hydrocolloid.
  • 115. • L.W. Carlyle evaluated compatibility of irreversible hydrocolloid with three dental stones (Die keen, Quick stone, Hemihydrate). Results showed that Die keen was most compatible.
  • 116. • Paul, Gardener and Steven conducted a study to evaluate the effect of storage time in a 100% humid environment on the accuracy of gypsum casts poured from reversible hydrocolloid impression and concluded that reversible hydrocolloid can be stored in 100% humidity for 60 minutes before pouring.
  • 117. REFERENCES Anusavice. Dental Material, 11th edition Robert G. Craig. Restorative Dental Material Smith. The clinical handling of Dental material International Journal of Prosthodontics, 2002; 15: 168-74. Journal Prosthet Dent, 2000; 83: 161-165
  • 118. Journal Prosthet Dent, 2001; 85: 73-81. International Journal of Prosthodontics, 1998; 11: 219-23 Journal Prosthet Dent, 2000; 83: 323-31. Journal Prosthet Dent, 2003; 90: 354-64. International Journal of Prosthodontics, 1992; 5: 55-8.
  • 119. Journal Prosthet Dent, 1990; 63: 12-15 J Prosthet Dent, 1993; 70: 449-53
  • 120. Thank you Leader in continuing dental education