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GYPSUM.pptx

  1. 1. Gypsum Products Presented By : Dr. AKANKSHA 1st year PG Department of Prosthodontics and Crown & Bridge Seminar 2
  2. 2. TABLE OF CONTENTS Introduction History Applications Dental applications Calcination
  3. 3. Setting of gypsum products Classification Properties Manipulation Infection control Conclusion
  4. 4. INTRODUCTION • Dihydrate form of calcium sulfate • White to milky yellowish • Supplied as fine hemihydrate particles • Commercial importance as Plaster of Paris • Diversified use • By-product of some chemical processing operations • Auxiliary material in clinical and laboratory procedure Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  5. 5. 9000 350-40 2800 7000 Oldest traces of plaster found in Anatolia & Syria In building, within the city and roads at Sumerian and Assyria periods Coloured wall plaster by soil mixing in Pharaohs graves at Giza Pyramid Wall and wooden ceiling plaster in ancient Greece and Rome civilizations
  6. 6. 1700 Walls of wooden houses were covered with plaster as protection against fire in Paris Plaster of Paris 1786 First scientific study on plaster by French scientist Lavoisier 1820 Plaster war as plaster was regarded as miraculous fertiliser Ottawa Indian discovered a rock outcrop where Plaster creek enters the Grand River and took a sample of the soft, sugary material, which was identified gypsum 1827
  7. 7. 1827 Le chatelier studied hydration mechanisms of plaster Crystalline theory 1889 Plaster used in interior walls and ornamental work 1889 Construction of Gypsum mine below the bed of Grand river by William T. Powers 1893 Colloidal theory 1912 Use of gypsum as medicine in Japan
  8. 8. APPLICATIONS Building constructions Soil conditioning Food additives Pharmaceuticals Medical devices Dental application Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  9. 9. DENTAL APPLICATIONS Impression material Constructing cast and die Mount cast on articulator Dental investments Bite registration Orthodontic models
  10. 10. CALCINATION PRODUCTION OF CALCIUM SULFATE HEMIHYDRATE Process in which different gypsum products are obtained from heating gypsum to certain temperatures Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  11. 11. MONOCLINIC HEXAGONAL ORTHORHOMBIC Calcium sulfate dihydrate Calcium sulfate hemihydrate Soluble Anhydrite Insoluble Anhydrite Cole Wf. Lancucki CJ. A Refinement Of The Crystal Structure Of Gypsum. Acta Crystallographics B 24:1968.
  12. 12. Dry Calcination Synthetic methods Dehydration by boiling with chemicals Wet Calcination
  13. 13. DRY CALCINATION • gypsum mineral is heated in an open kettle at a temperature of about 110 to 120°C • β- calcium sulfate hemihydrate produced • Type I and type II gypsum products Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  14. 14. WET CALCINATION • Gypsum is ground and steam heated to a temperature of 110-130 °C in a closed kiln, kettle or autoclave • -calcium sulfate hemihydrate produced • Type III gypsum product (Hydrocal) Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  15. 15. DEHYDRATION BY BOILING WITH CHEMICALS • Boiling gypsum rock in 30% CaCl2solution . • The chlorides are then washed away with 0.5 % Sodium Succinate and the material is ground to the desired fineness. • Modified -hemihydrate obtained • Type IV and V high strength dental stone ( Densite ) Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  16. 16. SYNTHETIC METHODS •  and  hemihydrate formed from by-products or waste products of Phosphoric Acid • More expensive than other gypsum products Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  17. 17.  Crystal size LARGER SMALLER  Shape IRREGULAR PRISMATIC  Packing LOOSELY PACKED AMPLE SPACE B/W CRYSTALS CLOSELY PACKED LITTLE SPACE B/W CRYSTALS  W/P Ratio MORE LESS  Strength LESS MORE  Surface area/wt. MORE LESS  Example IMPRESSION PLASTER DENTAL PLASTER DENTAL STONE  HEMIHYDRATE  HEMIHYDRATE
  18. 18. Powder particles of Plaster of Paris (-hemihydrate) Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  19. 19. Powder particles of Dental Stone (-hemihydrate) Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  20. 20. Powder particles of Improved stone (modified -hemihydrate) Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  21. 21. SETTING OF GYPSUM PRODUCTS Advanced Dental Biomaterials. 2019 Elsevier Ltd. Chapter 3:Dental gypsum and investments 37-52 EXOTHERMIC
  22. 22. SETTING REACTION THEORIES OF SETTING REACTION Colloidal theory Hydration theory Crystalline theory Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  23. 23. COLLOIDAL THEORY • Mahaelis in 1893 • Mixed with water, plaster enters into the colloidal state through the sol-gel mechanism. • In the sol state, hemihydrate particles are hydrated to form dihydrate, thereby entering into an active state. As the measured amount of water is consumed, the mass converts to a solid gel. Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  24. 24. HYDRATION THEORY • Hemihydrate undergoes hydration • Rehydrated plaster particles join together through hydrogen bonding to the sulfate groups to form the set material. Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  25. 25. CRYSTALLINE THEORY • Proposed in1887 by Henry Louis Le Chatelier • In 1907, it received the full support of Jacob Henricus vant’s Hoff • Also called Dissolution-precipitation theory • The difference in the solubilities of calcium sulfate dihydrate and hemihydrate causes the setting of these materials. Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  26. 26. STAGES OF CRYSTALLIZATION Dissolution Suspension Saturation Supersaturation Nuclei Formation Growth Of Nuclei Spherulite Formation
  27. 27. Winkler MM, Monaghan P, Gilbert JL, Lautenschlager EP. Freeze-drying and scanning electron microscopy of setting dental gypsum. Dent Mater. 1995 Jul;11(4):226-30. doi: 10.1016/0109-5641(95)80053-0. PMID: 8621042
  28. 28. Dental Materials and Their Selection, William.J.O’Brein, Fourth Edition, Quintessence Publishing Co, Inc, Chapter 4:Gypsum Products 38-61
  29. 29. STAGES IN SETTING Important physical changes recognized : • Fluid • Plastic • Friable • Carvable Dental Materials and Their Selection, William.J.O’Brein, Fourth Edition, Quintessence Publishing Co, Inc, Chapter 4:Gypsum Products 38-61
  30. 30. WATER REQUIREMENTS • Result of differences in the apparent density of the powder • Higher apparent densities, require less water Dental Materials and Their Selection, William.J.O’Brein, Fourth Edition, Quintessence Publishing Co, Inc, Chapter 4:Gypsum Products 38-61
  31. 31. Excess unreacted water in set mass Water evaporation when dried Microscopic porosities Weaking of cast 100 g Calcium Sulfate Hemihydrate 18.6 g Water Calcium Sulfate Dihydrate Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  32. 32. Required and Excess Water for Gypsum Materials Gypsum Mixing Water (mL/100 g of Powder) Required Water (mL/100 g of Powder) Excess Water (mL/100 g of Powder) Model plaster 37-50 18.6 18-31 Dental stone 28-32 18.6 9-13 High strength dental stone 19-24 18.6 0-5 Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  33. 33. WATER-POWDER RATIO (W/P) • Amount of water in millilitres added to 100 g of powder • Expressed as a fraction • Determines physical and chemical properties of set gypsum product. 45/100 or 0.45 45 mL of water is added to 100 g of powder Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  34. 34. W/P RATIO EFFECT OF HIGH AND LOW W/P RATIO Slow setting Low expansion More porosity Less strength Less surface hardness Quick setting High expansion Less porosity More strength More surface hardness THIN MIX ( high w/p ratio) THICK MIX (low w/p ratio) Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  35. 35. TEMPERATURE • Water used for mixing and environment temperatures EFFECT ON SETTING REACTION change in the relative solubilities of calcium sulfate hemihydrate and calcium sulfate dihydrate which alters the reaction change in ion mobility with temperature Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  36. 36. CHANGE IN THE RELATIVE SOLUBILITIES OF CALCIUM SULFATE HEMIHYDRATE AND CALCIUM SULFATE DIHYDRATE, WHICH ALTERS THE RATE OF THE REACTION Temperature increases solubility ratio decreases Setting reaction slowed Setting time increases Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  37. 37. CHANGE IN ION MOBILITY WITH TEMPERATURE Temperature increases Mobility of calcium and sulfate ions increases Rate of reaction increases Setting time decreases Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  38. 38. EFFECT OF TEMPERATURE ON SOLUBILITY Little change in setting time occurs between 0 °C and 50 °C. Temperature of the plaster-water mixture exceeds 50 °C, a gradual retardation occurs. At 100 °C, no reaction takes place COMPLEX REACTION FOR GYPSUM PRODUCTS Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  39. 39. HUMIDITY relative humidity increases to 70% and above moisture in the air conversion of hemihydrate to dihydrate more nuclei for crystallization Setting reaction accelerated EFFECT ON SETTING REACTION Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  40. 40. Therefore all gypsum products should be kept in a closed container and well protected from moisture in the air. Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  41. 41. CLASSIFICATION OF GYPSUM PRODUCTS
  42. 42. ACCORDING TO International Organization for Standardization (ISO 6873:2013) Type 1: Dental plaster for impression Type 2: Dental Plaster Class 1 - for mounting Class 2 - for models Type 3: Dental Stone Type 4: Dental Stone, high-strength, low-expansion for dies Type 5: Dental Stone, high-strength, high-expansion for dies Dental Materials and Their Selection, William.J.O’Brein, Fourth Edition, Quintessence Publishing Co, Inc, Chapter 4:Gypsum Products 38-61
  43. 43. ACCORDING TO ADA SPECIFICATION 25 Type 1 : Impression Plaster Type 2 : Model Plaster Type 3 : Dental Stone Type 4 : Dental Stone high strength Type 5 : Dental Stone high strength ,high expansion Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  44. 44. IMPRESSION PLASTER • Composed of plaster of Paris (β-hemihydrate) • Seldom used , replaced by less rigid materials COMPOSITION • Dental plaster • K2SO4 • Borax • Coloring and flavoring agents
  45. 45. USES • For making impressions in complete denture and maxillofacial prosthetics • Bite registration material.
  46. 46. MODEL PLASTER COMPOSITION •  hemihydrate • Modifiers USES • Diagnostic cast • Mounting casts on articulator • Artistic position of study cast • Flasking procedures MODEL PLASTER, LABORATORY PLASTER, MOUNTING PLASTER
  47. 47. DENTAL STONE COMPOSITION •  hemihydrate • 2-3 % coloring agents • K2SO4 • Borax USES • Preparation of master cast • Orthodontic models • Complete and partial denture models CLASS I STONE OR HYDROCAL
  48. 48. DENTAL STONE HIGH STRENGTH USES • Model bases • Dies for fabricating inlay, crown and bridge wax pattern • CAD/CAM dies CLASS II STONE, DIE STONE, DENSITE, IMPROVED STONE
  49. 49. DENTAL STONE HIGH STRENGTH HIGH EXPANSION EXAMPLES • Hard Rock, Jade Rock, Resinrock XL5 (Whipmix), Denflo-HX, Supra stone (Kerrlab) USES • In die, to compensate for solidification shrinkage • Fabrication of cast crowns ( inadequate expansion)
  50. 50. PROPERTIES OF GYPSUM PRODUCTS MIXING TIME, WORKING TIME, SETTING TIME SETTING EXPANSION STRENGTH OF SET GYPSUM PRODUCTS SURFACE HARDNESS AND ABRASION RESISTANCE REPRODUCTION OF DETAILS
  51. 51. MIXING TIME • Time from addition of powder to water until mixing is completed • Mechanical mixing : 20-30 sec • Hand spatulation : a minute Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  52. 52. WORKING TIME • Time from start of mixing to the point where the consistency is no longer acceptable • 3 minute working time is adequate Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  53. 53. SETTING TIME • Time that elapses from the beginning of mixing until the material hardens INITIAL SETTING TIME time required for gypsum products to reach a certain arbitrary stage of firmness in their setting process FINAL SETTING TIME time at which the material can be separated from the impression without distortion or fracture Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  54. 54. LOSS OF GLOSS TEST As reaction proceeds Excess water taken up Formation of dihydrate Mix looses its gloss TEST FOR INITIAL SET Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  55. 55. GILLMORE APPARATUS
  56. 56. Initial needle 113.4 ± 0.5 g Final needle 453.6 ± 0.5 g Lower arm preferably adjustable for height Cross arms must be designed to prevent their rotation about the vertical shaft
  57. 57. PASTE PAT Base diameter 76 ± 13 mm Top diameter 50 ± 13 mm Center thickness 13 ± 3 mm PLANE NON- ABSORPTIVE PLATE 100 ± 5 mm square PAT WITH TOP SURFACE FLATTENED FOR DETERMINING TIME OF SETTING BY GILLMORE METHOD
  58. 58. Replaceable tips may be made of stock drill rod or wire tempered after shaping and held by suitable chuck or other fastener TIP DIAMETER Initial 2.12 ± 0.05 mm Final 1.06 ± 0.05 mm DETAIL OF GILLMORE APPARATUS NEEDLE TIPS
  59. 59. Mixture is spread out Smaller needle lowered on surface No longer leaves an impression Initial set INITIAL GILLMORE TEST • Mass has still no measurable compressive strength • Cannot be safely removed from the impression Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  60. 60. VICAT TEST FOR SETTING TIME Diameter 1mm
  61. 61. Vicat Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  62. 62. FINAL GILLMORE TEST Mixture is spread out Larger needle lowered on surface No longer leaves an impression Final set Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  63. 63. COMPRESSIVE STRENGTH OF A TYPE-II MODEL PLASTER DURING SETTING Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  64. 64. CONTROL OF SETTING TIME Solubility of the hemihydrate Number of nuclei of crystallization Rate of crystal growth Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  65. 65. Solubility of the hemihydrate solubility of the hemihydrate increased supersaturation of the dihydrate is achieved faster accelerates the rate of dihydrate crystal deposition Increases the setting reaction Decreases setting time Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  66. 66. Number of nuclei of crystallization greater the number of nuclei of crystallization faster the dihydrate crystals formation Increased setting reach Decreased setting time Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  67. 67. Rate of crystal growth • Increasing or decreasing the rate of crystal growth will accelerate or retard the setting time. Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  68. 68. FINENESS finer particle size More no. of nuclei rate of the hemihydrate dissolution increased rapid rate of crystallization faster mix hardens Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  69. 69. IMPURITIES calcination incomplete/ manufactures addition gypsum particles remain increase nuclei of crystallization Faster setting reaction setting time decreased Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  70. 70. WATER-TO-POWDER RATIO more water used for mixing fewer nuclei per unit volume Slower reaction Setting time prolonged Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  71. 71. SPATULATION ( MIXING ) mixing begins formation of crystals increases Rate of spatulation increases breaks down to smaller crystals new centers of nucleation calcium sulfate dihydrate precipitated Setting time prolonged Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  72. 72. MODIFIERS FOR CONTROLLING SETTING TIME Organic material : Glue, Gelatine and gums Salts : Borax, potassium citrate, NaCl (20%) Organic material : Blood, Saliva Salts : Potassium sulfate (>2%), NaCl (2%), Sodium sulfate (3- 4%), Slurry water (gypsum <20%), Tera alba SETTING TIME SETTING TIME RETARDERS ACCERELATORS Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  73. 73. SETTING EXPANSION • Theoretically, calcium sulfate hemihydrate should contract volumetrically during the setting process. • However, experiments have determined that all gypsum products expand linearly during setting • linear expansion may be as low as 0.06% or as high as 0.5% Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  74. 74. Mahler and Bruce Ady, 1960; Lyon et al., 1955 Hemihydrate surrounded by water molecules Water around particles reduced due to hydration and particles drawn closer Crystals become entangled and intermeshed Water around particles exhausted and crystals tend to shrink which is opposed by outward thrust of crystal growth NORMAL SETTING EXPANSION Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  75. 75. Mahler and Bruce Ady, 1960; Lyon et al., 1955 HYGROSCOPIC SETTING EXPANSION Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93. Hemihydrate surrounded by water molecule Since water of hydration replace by other water molecule, particles remains at same place Lost water molecule replaced by new molecules, growth not opposed by shrinkage and crystals grow freely Intermeshing of crystals tales long time, expansion goes undisturbed Crystal expansion continues
  76. 76. Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93. Graphic representation
  77. 77. Initial mix Initial crystal growth Solid phase contact Expansion Termination
  78. 78. CONTROL OF SETTING EXPANSION Spatulation Water powder ratio Modifiers ( accelerators and retarders ) Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  79. 79. STRENGTH OF SET GYPSUM PRODUCTS • expressed - compressive strength • free-water content of set product affects its strength DRY STRENGTH excess water has been driven off by drying WET STRENGTH when water in excess of that required for hydration of hemihydrate is left Annusavice KJ. Phillip’s Science Of Dental Materials. Eleventh Edition, Elsevier Pub. Chapter 10 Gypsum Products. 255-83.
  80. 80. FACTORS AFFECTING STRENGTH Loss of excess water Water-to-powder ratio Manipulation Additives Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  81. 81. Effect of loss of excess water on compressive strength of dental stone. Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  82. 82. Compressive strength as a function of W/P ratio for five types of gypsum products Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  83. 83. SURFACE HARDNESS AND ABRASION RESISTANCE • related to compressive strength • increases at a faster rate than compressive strength as surface of the hardened mass reaches a dry state earlier than the inner portion of the mass Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  84. 84. • Mixing high-strength dental stone with a commercial hardening solution containing colloidal silica (about 30%) improves the surface hardness of the set gypsum • Abrasion resistance of 15% to 41% were observed for a high- strength dental stone impregnated with epoxy resins or a light cured dimethacrylate resin Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  85. 85. Onizuka T, Kamimura N, Kajiwara H, Nakashima A, Suenaga K, Jimi T. Influence of boiling water treatment on surface roughness and surface microstructure of set gypsum (dental stone). Dent Mater J. 1995 Dec;14(2):245-55. doi: 10.4012/dmj.14.245. PMID: 8940563.
  86. 86. Tripathi A, Gupta A, Bagchi S, Mishra L, Gautam A, Madhok R. Comparison of the Effect of Addition of Cyanoacrylate, Epoxy Resin, and Gum Arabic on Surface Hardness of Die Stone. J Prosthodont. 2016 Apr;25(3):235-40. doi: 10.1111/jopr.12314. Epub 2015 Dec 29. PMID: 26713763.
  87. 87. REPRODUCTION OF DETAILS TYPES 1 AND 2 reproduce a groove 75 μm in width TYPES 3, 4, AND 5 reproduce a groove 50 μm in width ANSI/ADA SPECIFICATION NO. 25 Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  88. 88. Gypsum dies do not reproduce surface detail as well as electroformed or epoxy dies because the surface of the set gypsum is porous on a microscopic level SCANNING ELECTRON PHOTOMICROGRAPH OF THE SURFACE OF A SET HIGH-STRENGTH STONE DIE Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  89. 89. Type W/P Ratio Setting Time ( min ) Two hour setting expansion (%) 0ne hour Compressive Strength (Mpa) Min Max I. Plaster, impression 0.50-0.75 4 ± 1 0.00 0.15 4.0 II. Plaster, Model 0.45-0.50 12 ± 4 0.00 0.30 9.0 III. Dental stone 0.28-0.30 12 ± 4 0.00 0.20 20.7 IV. Dental stone, high strength 0.22-0.24 12 ± 4 0.00 0.10 34.5 V. Dental stone, high strength, high expansion 0.18-0.22 12 ± 4 0.10 0.30 48.3 PROPERTIES OF 5 TYPES OF GYPSUM PRODUCTS Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  90. 90. MANIPULATION OF GYPSUM PRODUCTS PROPORTIONING MIXING POURING
  91. 91. PROPORTIONING Recommended W/P ratio should be used Weighing balance for weight of powder Powder should not be measured by volume (as by using a scoop) Accurate graduated cylinder for the water volume Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  92. 92. ADD POWDER TO WATER water should be added first Powder sprinkled slowly over a period of about 20-30 seconds This technique allows any air entrapped in the powder to escape, which reduces the number of bubbles in the final mix. Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  93. 93. MIXING Flexible rubber mixing bowl Metal spatula with a stiff blade Bowl should be parabolic in shape, smooth, and resistant to abrasion Handle that is convenient to hold Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  94. 94. designed to promote release of bubbles in gypsum mix and to facilitate pouring of the impression VIBRATOR Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  95. 95. smooth mix obtained Spatulation : 1 minute at 2 revolutions per second wiping inside surfaces of the bowl with spatula stirring the mixture vigorously V I B R A T O R Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  96. 96. POWER-DRIVEN MECHANICAL SPATULATOR WITH A VACUUM ATTACHMENT Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  97. 97. Smooth mix placed on vibrator mix spatulated for 20 seconds on low-speed drive of mixer powder initially wet by water as with hand mixing Vacuuming during mixing reduces the air entrapped in the mix Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  98. 98. POURING Impression tray is held in one hand against the vibrator Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  99. 99. Surface of the impression should be free of excess water Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  100. 100. With metal spatula, a small amount of dental stone is added to one open end of the impression Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  101. 101. The impression may be tilted to control the movement of the stone into the tooth depression Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  102. 102. Once the tooth depressions are completely filled, larger amounts of dental stone can be added under light vibration to fill the remaining impression Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  103. 103. The impression is then briefly placed on the vibrator for a few seconds to distribute the stone evenly across the impression Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  104. 104. The dental stone model should be left undisturbed for 45 to 60 min until the material has set completely Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  105. 105. Dental stone model is now separated from the impression Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  106. 106. INFECTION CONTROL
  107. 107. • Cross-contamination to dental office personnel via dental impressions. • Dental casts come into direct contact with impression materials and other items that are contaminated by saliva and blood from a patient's mouth, leaving the casts susceptible to cross- contamination. Annusavice KJ. Phillip’s Science Of Dental Materials. Twelfth Edition, Elsevier Pub. Chapter 9 Gypsum Products. 182-93.
  108. 108. • If an impression not disinfected, it is necessary to disinfect the stone cast. Models disinfected by immersion in 1:10 dilution of sodium hypochlorite for 30 minutes or with a spray of iodophor following manufacturer’s instructions. Craig’s Restorative Dental Materials. 14th Edition. Elsevier Pub. Chapter 12. Replicating Materials: Impression and Casting, Gypsum Products 252-60
  109. 109. Abdelaziz KM, Combe EC, Hodges JS. The effect of disinfectants on the properties of dental gypsum: 1. Mechanical properties. J Prosthodont. 2002 Sep;11(3):161-7. PMID: 12237796.
  110. 110. Abdelaziz KM, Combe EC, Hodges JS. The effect of disinfectants on the properties of dental gypsum, part 2: surface properties. J Prosthodont. 2002 Dec;11(4):234-40. doi: 10.1053/jpro.2002.129049. PMID: 12501136.
  111. 111. Robati Anaraki M, Lotfipour F, Moslehifard E, Momtaheni A, Sigari P. Effect of different energy levels of microwave on disinfection of dental stone casts. J Dent Res Dent Clin Dent Prospects. 2013;7(3):140-146. doi:10.5681/joddd.2013.022
  112. 112. CONCLUSION A wide choice of gypsum product is available One should choose the one or the combination which is most suitable for our desired requirements
  113. 113. THANK YOU FOR YOUR ATTENTION !

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