Impressions in fpd/ implant dentistry course


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Impressions in fpd/ implant dentistry course

  1. 1. IMPRESSIONS IN FIXED PARTIAL DENTURE INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. Table of contents: • Introduction • Definitions • History • Review of literature • Impression materials • Tray selection and custom tray fabrication • Impression techniques • Summary • Conclusion
  3. 3. Introduction
  4. 4. • An impression is an imprint or negative likeness Well-fitting indirect restorations can only be made if there are accurate models of the oral tissues available, made from high quality impressions. A good quality impression is only obtained when we have a thorough knowledge of materials, their properties, and techniques for their best manipulation.
  5. 5. Definitions: GPT - 8
  6. 6. GPT - 8 • IMPRESSION: • a negative likeness or copy in reverse of the surface of an object; • an imprint of the teeth and adjacent structures for use in dentistry
  7. 7. GPT - 8 • IMPRESSION MATERIAL : any substance or combination of substances used for making an impression or negative reproduction • IMPRESSION TECHNIQUE : a method and manner used in making a negative likeness
  8. 8. GPT - 8 IMPRESSION TRAY • 1: a receptacle into which suitable impression material is placed to make a negative likeness • 2: a device that is used to carry, confine, and control impression material while making an impression
  9. 9. GPT - 8 • SECTIONAL IMPRESSION : a negative likeness that is made in sections. • TUBE IMPRESSION : 1: a cylinder used as a tray to confine and direct impression material to make an impression of a single tooth. 2: the impression resulting from this procedure.
  10. 10. • Elastomer – lightly crosslinked impressin mateial with elastic properties • Gelation – transformation from sol to gel • Hydrocolloid – colloid that contains water as the dispersion phase. • Imbibition – absorption of water • Synersis – fluid exuded when gel structures reconfigure to achieve equilibrium through stress relaxation. Phillips`s Science of dental
  11. 11. • Thixotropic – the time-dependent pseudoplastic flow of polymers that is characterized by the gradual decrease of viscosity under a constant applied shear rate. Phillips`s Science of dental
  12. 12. History
  13. 13. • Philip Pfaff-1756 – First described taking impression with softened wax • Christophe Francois Delabarre-1820 – Introduced the metal impression tray • Chapin Haris-1853 – First used Plaster of Paris for making impressions. • Charles Stent-1857 – Introduced the first impression compound
  14. 14. • Sears-1937 – First used agar hydrocolloids for recording crown impressions. • United States-1945 – Introduced alginate during World War II. • SL Pearson-1955 – Developed synthetic rubber base impression materials
  15. 15. • Polysulfide- Late 1950’S – First developed as an industrial sealant. • Condensation Silicone- Early 1960’s • Addition Silicone-1970’s • Polyether- Late 1970’s • Polyether Urethane Dimethacrylate - Late 1980’s
  16. 16. Review of literature
  17. 17. • Hudson (1958) described the clinical use of rubber impression materials • a combination of light and heavier bodied materials may be used in a disposable stock tray or a custom made acrylic resin tray for making impressions for fixed partial dentures. • The special syringe is used to inject the light bodied material into the prepared cavities or about the crown preparation.
  18. 18. Multiple abutment impressions using vacuum adapted temporary splints. LaForgia A. J Prosthet Dent. 1965;Jan;15(1):44-50. A LaForgia (1965) described an impression technique using vacuum adapted temporary splints
  19. 19. • Irreversible hydrocolloid for fixd partial denture impressions. G. R. Zuckerman. J prosthet Dent. 1974;32;657. Zuckerman. (1974) described a dechnique of making impression.
  20. 20. Culbreath JC. (1975) described A technique for making impressions for cast restorations. It can be used for a single preparation or for multiple preparations in a single arch. The most unique feature of the technique is that the tray is formed over the prepared teeth, either directly or indirectly. An impression technique for cast restorations. Culbreath JC. J Prosthet Dent. 1975 Apr;33(4)
  21. 21. Bonding properties and dimensional stability of hydrocolloid impression systems in fixed prosthodontics. Dahl BL, Dymbe B, Valderhaug J. J Prosthet Dent. 1985 Jun;53(6):796-800. Dahl BL, Dymbe B, Valderhaug J.(1985) Four hydrocolloid impression systems for fixed prosthodontics and one conventional alginate were tested for bonding properties between the syringe and the tray materials of the systems. Their dimensional stability was tested also after the impressions were kept in a humidor for 1, 3, and 24 hours before casts were poured.
  22. 22. Findings showed that there was a true bond between the syringe and the tray materials for all combinations. The precision tests gave a mean percent difference between the master model and the cast of less than 0.15 for all material combinations at both the 1- and 3-hours observations.
  23. 23. Incidence of impression material found in the gingival sulcus after impression procedure for fixed partial dentures. Marshak BL, Cardash HS, Ben-Ur Z. J Prosthet Dent. 1987 Mar;57(3):306-8. Marshak BL, Cardash HS, Ben-Ur Z. (1987) After impression-making procedures, remnants of Xantopren impression material were found in the gingival crevices in eight of 125 patients. In three of the eight patients, remnants were only discovered subsequent to a systematic exploration with a fine curette.
  24. 24. Although eight of 125 is not a statistically significant number, it would be nonetheless prudent to consider a routine curettage of abutment sulci after impression-making. This procedure is even more strongly recommended when a defect be detected in the crevicular region of the impression. Impressions should remain in the mouth until full setting and maximum tear strength is reached. Strict adherence to the manufacturers' instructions is necessary.
  25. 25. Accuracy of impression materials for complete-arch fixed partial dentures. Lin CC, Ziebert GJ, Donegan SJ, Dhuru VB. J Prosthet Dent. 1988 Mar;59(3):288-91. Lin CC, Ziebert GJ, Donegan SJ, Dhuru VB. (1988) The accuracy of 12 impression materials of six different types were studied by using complete-arch FPD impressions. A one-piece casting was constructed by connecting the four individual castings made for the four abutment teeth. The master prosthesis was seated on the stone casts produced from the impressions. The marginal adaptation on the four abutments was then evaluated with a travelling microscope. The individual marginal adaptation of the four castings on the abutments was also examined after sectioning the four joints.
  26. 26. They concluded that 1. The polyethers produced the most accurate complete- arch replicas. The second most accurate were the vinyl polysiloxanes, followed by the polysulfides and the irreversible-reversible hydrocolloids. The least accurate were the reversible hydrocolloids and the irreversible hydrocolloids. 2. The polyether impression materials exhibited the most consistent accuracy for a master cast to fabricate a complete-arch FPD.
  27. 27. The effect of tray selection on the accuracy of elastomeric impression materials. Gordon GE, Johnson GH, Drennon DG. J Prosthet Dent. 1990 Jan;63(1):12-5 . Gordon GE, Johnson GH, Drennon DG. (1990) study evaluated the accuracy of reproduction of stone casts made from impressions using different tray and impression materials. The tray materials used were an acrylic resin, a thermoplastic, and a plastic.
  28. 28. • The impression materials used were an additional silicone, a polyether, and a polysulfide. Impressions were made of a stainless steel master die that simulated crown preparations for a fixed partial denture and an acrylic resin model with cross-arch and anteroposterior landmarks in stainless steel that typify clinical intra-arch distances. Impressions were poured at 1 hour with a type IV dental stone.
  29. 29. Results indicated that custom-made trays of acrylic resin and the thermoplastic material performed similarly regarding die accuracy and produced clinically acceptable casts. The stock plastic tray consistently produced casts with greater dimensional change than the two custom trays.
  30. 30. A comparison of impression materials for complete-arch fixed partial dentures. Dounis GS, Ziebert GJ, Dounis KS. J Prosthet Dent. 1991Feb;65(2):165-9. Dounis GS, Ziebert GJ, Dounis KS (1991) This study compared the marginal fit of complete-arch fixed prostheses under simulated clinical conditions. Prostheses were made on casts constructed from three commonly used impression materials; polyether, polyvinyl siloxane (medium- viscosity and putty-wash), and reversible hydrocolloid.
  31. 31. they concluded that, the polyether and both addition silicone impression materials were significantly more accurate than the reversible hydrocolloid in both situations. All of the single castings were clinically acceptable, but the luted restorations made from reversible hydrocolloids were not.
  32. 32. Accuracy of one-step versus two-step putty wash addition silicone impression technique. Hung SH, Purk JH, Tira DE, Eick JD. J Prosthet Dent. 1992 May;67(5):583-9. Hung SH, Purk JH, Tira DE, Eick JD (1992) study compared the accuracy of one-step putty wash with two-step putty wash impression techniques. Five addition silicone impression materials-Mirror 3 (MR), Mirror 3 Extrude (ME), Express (E), Permagum (P), and Absolute(A)--were tested. Accuracy of the materials was assessed by measuring six dimensions on stone dies poured from impressions of the master model.
  33. 33. They concluded that • Accuracy of addition silicone impression material is affected more by material than technique. • Accuracy of the putty wash one-step impression technique was not different from the putty wash two-step impression technique except at one of the six dimensions where one-step was more accurate than two-step. Mirror 3 putty wash two-step impression presented less distortion than Mirror 3 Extrude putty wash one-step or two-step impression.
  34. 34. Irreversible hydrocolloids for crown and bridge impressions: effect of different treatments on compatibility of irreversible hydrocolloid impression material with type IV gypsums.Eriksson A, Ockert-Eriksson G, Lockowandt P, Linden LA. Dent Mater. 1996 Mar;12(2):74-82. • Eriksson A, Ockert-Eriksson G, Lockowandt P, Linden LA. (1996) The aims of their research were: 1) to determine if the compatibility between irreversible hydrocolloids (alginates) and type IV gypsums (die stones) is affected by different treatments of the impressions before pouring, and
  35. 35. • The results showed that dentists and dental technicians need to know how each specific irreversible hydrocolloid should be treated and also with which type IV gypsum it is compatible. • This research also indicated that an irreversible hydrocolloid impression should not come into contact with any liquid within the first 15 min.
  36. 36. • Lepe X, Johnson GH (1997) • study evaluated the materials after simulating overnight disinfection. • They concluded that, • Accuracy of both impression materials was adversely affected with 18 hours of immersion disinfection. • Long-term (18 hours) immersion disinfection will affect the fit of fixed partial prostheses. Accuracy of polyether and addition silicone after long-term immersion disinfection. Lepe X, Johnson GH. J Prosthet Dent. 1997 Sep;78(3)
  37. 37. Accuracy of irreversible hydrocolloids (alginates) for fixed prosthodontics. A comparison between irreversible hydrocolloid, reversible hydrocolloid, and addition silicone for use in the syringe-tray technique. Eriksson A, Ockert-Eriksson G, Lockowandt P. Eur J Oral Sci. 1998 Apr;106(2 Pt 1):651-60. Eriksson A, et al (1998) The aim was to study their ability to reproduce six differently shaped abutments of a full arch stainless steel master model correctly, by measuring: 1) the accuracy of irreversible hydrocolloid impressions with different storage periods of 15 min, 2 h, 24 h and 95 h, reversible hydrocolloid stored 15 min and 2 h, and Type III addition silicones stored 24 h when the syringe-tray technique was used; and 2) whether mixing technique or tray design had any influence of the accuracy of irreversible hydrocolloid impressions
  38. 38. They concluded that, • Storage time, mixing technique and tray design were of significant importance for the irreversible hydrocolloids. • Concerning the accuracy at the gingival margin, a shorter storage time resulted in improved accuracy, and • mechanical mixing without a vacuum and a tray designed similar to a perforated stock tray gave most accurate impressions.
  39. 39. Impression materials and techniques for crown and bridgework: a survey of undergraduate teaching in the UK. Randall RC, Wilson MA, Setcos JC, Wilson NH. Eur J Prosthodont Restor Dent. 1998 Jun;6(2):75-8. Randall RC et al (1998) The aim of this study was to document the teaching of impression materials and techniques for crown and bridgework in the undergraduate curriculum in UK dental schools Addition-cured silicones were found to predominate;
  40. 40. 71% of schools taught and used clinically a one-stage, full arch impression technique involving stock trays, and 57% of schools a full-arch custom tray technique. Routine disinfection of impressions was taught and practised in 43% of schools
  41. 41. Crown and bridge impressions--a comparison between the UK and a number of other countries. Winstanley RB. Eur J Prosthodont Restor Dent. 1999 Jun-Sep;7(2):61-4. Winstanley RB. 1999 The quality of impressions for crown and bridge work in seven countries were compared with the results found in the United Kingdom in a previous study. The results showed that metal impression trays were used more frequently, and flexible plastic trays less frequently, in the countries visited than in the United Kingdom.
  42. 42. Accuracy of three polyvinyl siloxane putty-wash impression techniques. Nissan J, Laufer BZ, Brosh T, Assif D. J Prosthet Dent. 2000 Feb;83(2):161-5. Nissan J et al 2000. This study assessed the accuracy of 3 putty- wash impression techniques using the same impression material (polyvinyl siloxane) in a laboratory model. The 3 putty-wash impression techniques used were (1)1-step (putty and wash impression materials used simultaneously); (2) 2-step with 2-mm relief (putty first as a preliminary impression to create 2-mm wash space with prefabricated copings. In the second step, the wash stage was carried out); and (3) 2-step technique with a polyethylene spacer (plastic spacer used with the putty impression first and then the wash stage).
  43. 43. • CONCLUSION. • The polyvinyl siloxane 2-step, 2-mm, relief putty-wash impression technique was the most accurate for fabricating stone dies.
  44. 44. • Influence on dimensional accuracy of volume of wash material introduced into pre-spaced putty/wash impressions. Omar R, Abdullah MA, Sherfudhin H. Eur J Prosthodont Restor Dent. 2003 Dec;11(4):149-55. Omar R et al (2003), This study compared the accuracy of stone models obtained from two-stage, pre-spaced putty/wash impressions under conditions in which known volumes of wash material were introduced during the second stage of the impression: Group I, a quantity of wash material corresponding to the space provided; Group II, double the quantity of wash material as the space provided; Group III, double the quantity of wash material, but with V-shaped vents in the putty for escape of excess material.
  45. 45. • Percentage deviations of the vertical dimensions of stone dies with respect to the master model were significantly different between Groups I and II (the latter being shorter) • For horizontal dimensions, differences were less consistent, although the deviations for Groups I and II and Groups II and III, with respect to the master model, were significantly different from each other for two of the three dimensions measured (Group II inter-abutment distances were generally larger) • It was concluded that putty recoil, resulting from compression by excess wash material, plays a significant role in the undersizing of working dies, although the level of clinical relevance is less clear.
  46. 46. Alginate impressions for fixed prosthodontics. A 20 year follow up study. Eriksson A, Ockert-Eriksson G, Eriksson O, Linden LA. Swed Dent J. 2004;28(2):53-9. The aim of this study was to estimate whether the survival ratios after 20 years of fixed prosthodontics made of alginate impressions was higher, equivalent or lower, compared to the survival ratios, shown in studies, where different impression materials were used. Eriksson A, Ockert-Eriksson G, Eriksson O, Linden LA. (2004)
  47. 47. Concluded that, fixed prosthodontics made according to the syringe-tray alginate impression method may have the same success rates after 20 years compared to that of fixed prosthodontics presented in previous longitudinal clinical studies where other impression materials
  48. 48. • A clinical evaluation of fixed partial denture impressions. Samet N, Shohat M, Livny A, Weiss EI.J Prosthet Dent. 2005 Aug;94(2):112-7. Samet N, et al 2005 This study evaluated the quality of impressions sent to commercial laboratories for the fabrication of fixed partial dentures (FPD) by describing the frequency of clinically detectable errors and by analyzing correlations between the various factors involved.
  49. 49. • The impression technique and material used, tray type, and number of prepared units were recorded for each impression. • Data relating to errors and faults, including defects in material polymerization, retention to tray, tissue contact by tray, crucial areas beyond tray borders, heavy-bodied material exposure through the wash material (for double-step impressions), inadequate union of materials, retraction cords embedded in impressions, and air bubbles, voids, or tears along the margin were also documented. • And concluded that impressions made with polyethers had the most detectable errors, followed by condensation-type silicones.
  50. 50. [Full arch impression techniques utilizing addition type poly vinyl siloxane for fabrication of tooth born fixed partial dentures] Nissan J, Rosner O, Barnea E, Assif D. Refuat Hapeh Vehashinayim. 2006 Jan;23(1):42-6, 71 • Nissan J et al 2006 This article presented several impression techniques using PVS and recommends the one that provides the most accurate impression, utilizing the superior qualities of the PVS. • The one step impression technique where no control of wash bulk and thickness exists, is considered to be the least accurate impression method with measured discrepancies as large as 7 times the original inter preparation distance and 40 times the original cross arch dimensions.
  51. 51. • Furthermore, the direct contact between the less refined putty material and the tooth preparation, as well as the high prevalence of air bubble entrapment, seriously compromises restoration longevity. • The two stage impression technique has proved to produce the most accurate and reliable impressions due to complete control of the wash bulk and thickness entailed.
  52. 52. • The ideal wash bulk thickness should range between 1 to 2.5 mm all around the abutment tooth in order to minimize distortion of its subsequent die. • The easiest and most clinically applicable method to achieve the desired space around the preparations is by loading the Putty material with the temporary crowns in place, followed by their removal at the second stage and occupation of the created space by the wash.
  53. 53.
  55. 55. Table of contents: • Introduction • Definitions • History • Review of literature • Impression materials • Tray selection and custom tray fabrication • Impression techniques • Summary • Conclusion
  56. 56. Impression materials
  57. 57. Impression Materials Aqueous Hydrocolloids Non-aqueous Elastomers Polysulfide Silicones Polyether Condensation Addition Agar (reversible) Alginate (irreversible)
  58. 58. Hydrocolloids
  59. 59. Reversible Hydrocolloid (Agar)
  60. 60. History • In 1925,Alphous Poller of Vienna was granted a British patent for a totally different type of impression material. • Later Poller's 'Negacoll’ was modified and introduced to the dental profession as 'Dentacol’ in 1928. • In 1937 by Sears introduced Agar was first into dentistry for recording crown impressions • and was the first elastic impression material available.
  61. 61. • Example – Slate Hydrocolloid (Van R) – Cohere – Superbody – Super syringe
  62. 62. Component Function Composition Agar Brush – heap structure 13 – 17% Borax Strength 0.2 – 0.5% Potassium Sulfate Gypsum hardener 1.0 – 2.0% Water Reaction 80% Alkyl Benzoate Prevent growth of mold in impression material during storage. 0.1% Color and Flavors Taste & appearance Trace Composition • Fillers; diatomaceous earth, clay, silica, wax, rubber, and similar inert powders. • Thymol and glycerin act as plasticizer and
  63. 63. agar hydrocolloid (hot) agar hydrocolloid (cold) (sol) (gel) cool to 43 C heat to 100 C
  64. 64. Available as – syringe and tray material
  65. 65. • 3 chamber conditioning unit (1) liquefy at 100°C for 10 minutes • converts gel to sol (2) store at 65°C – place in tray (3) temper at 46°C for 3 minutes – seat tray – cool with water at 20°C for 3 minutes • converts sol to
  66. 66. Advantages • Accurate reproduction of surface detail • Hydrophilic – displace moisture, blood, fluids • Inexpensive – after initial equipment • No custom tray or adhesives • Pleasant • No mixing required Phillip’s Science of Dental Materials 1996
  67. 67. Disadvantages • Initial expense – special equipment • Material prepared in advance • Thermal shock to the patient. • Tears easily • Dimensionally unstable – immediate pour – single cast • Difficult to disinfect Phillip’s Science of Dental Materials 1996
  68. 68. Irreversible Hydrocolloid (Alginate)
  69. 69. Irreversible Hydrocolloid (Alginate) At the end of the last century, a chemist from Scotland noticed that certain brown seaweed (algae) yielded a peculiar mucous extraction. He named it algin. This was later identified as a linear polymer with numerous carboxyl acid groups and named anhydro-β-d-mannuronic acid (also called alginic acid).
  70. 70. • When the agar impression material became scarce because of World war II (Japan was a prime source of agar), research was accelerated to find a suitable substitute. This result was present alginate impression material. • The general use of irreversible hydrocolloid far exceeds that of other impression materials available. • Because – Easy to manipulate – Comfortable for the patient – Relatively inexpensive (no elaborate equipment)
  71. 71. • Examples – Jeltrate (Dentsply/Caulk) – Coe Alginate (GC America) – Integra – Superjel – Tropicalgin – Xantalgin
  72. 72. I. According to setting time. • Fast set 1.25 – 2min • Regular set 3 – 4.5 min II. According to concentration of filler • Soft set • Hard set Classification of alginateClassification of alginate
  73. 73. Component Function Weight percentage Na / Potassium alginate Soluble alginate 15 Calcium sulfate dihydrate Reactor 16 Potassium titanium Fluoride Accelerator 3 Zinc oxide Filler particles 4 Diatomaceous earth Filler particles 60 Sodium phosphate Retarder 2 Composition
  74. 74. 2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4 Na alginate + CaSO4 Ca alginate + Na2SO4 (powder) (gel) H2O Reaction
  75. 75. Alginate in the form of sol - containing the water but no source of calcium ions - a reactor of Plaster of Paris Modified alginatesModified alginates Two component system (paste form) - alginate sol - calcium reactor
  76. 76. – Alginates modified by the incorporation of silicone polymers (paste form) - fine detail reproduction - tear resistance - good dimension stability Modified alginatesModified alginates
  77. 77. • Dustless alginate glycerin incorporated to agglomerate the particles. • Making the powder more dense so that no dust is formed when the lid is opened after tumbling. Modified alginatesModified alginates
  78. 78. NEWER ALGINATES • Millenium algin • manufactured by LASCOD • MILLENIUM ALGIN is considered an alginate of new generation • Maximum preciseness (15 µ) • The formulation was optimized to reduce natural contraction with water loss. The impression can be stored for many hours in a Long Life Bag before casting the model without undergoing any change for over 100 hours
  79. 79. • No hand mixing. Eliminates mess and cleanup. Saves time and material. • Delivery options. Cartridge or Volume™ automix dispensing. • Impressions remain stable. You can pour immediately or when it’s convenient. Impressions retain dimensional stability for months. NEWER ALGINATES
  80. 80. Additives • flavorings
  81. 81. Tray adhesive sticky wax or methyl cellulose can be applied to the tray (adhesive sprays are also available).
  82. 82. Manipulation • Fluff or aerate the powder by inverting the can several times. This ensures uniform distribution of the filler before mixing. • Measured amounts of powder and water are taken as specified by the manufacturer.
  83. 83. Mixing is done in a clean flexible plastic bowl with a clean wide bladed, reasonably stiff metal spatula. • It is better to use separate bowls for plaster and alginate as plaster contamination can accelerate setting. Mixing technique
  84. 84. • The mixing is started with a stirring motion to wet the powder with water. • Once the powder has been moistened, rapid spatulation by swiping or stropping against the side of the bowl is done. • A vigorous figure-eight motion can also be used .
  85. 85. Mechanical mixing devices
  86. 86. MIGMA™ Alginate Mixing Machine
  87. 87.
  88. 88. Properties of alginates
  89. 89. • Reproduction of Tissue Detail • ADA Sp. requires the material to reproduce a line that is 0.075 mm in width. • Detail reproduction is lower when compared to agar hydro-colloid.
  90. 90. Dimensional Stability • Set alginates have poor dimensional stability due to evaporation, syneresis and imbibition. Therefore, cast should be poured immediately. • If storage is unavoidable, keeping in a humid atmosphere of 100% relative humidity (humidor) results in the least dimensional change. Strength Water: powder ratio Overmixing and Insufficient spatulation
  91. 91. Elasticity and Elastic Recovery • Alginate hydrocolloids are highly elastic but less when compared to agar and about 97.3% elastic recovery occurs. • Thus permanent deformation is more for Alginate (about 1.2%). • Tear strength - varies from 350-700 gm/cm2 • Increased when the impression is removed with a snap
  92. 92. • Compatibility with gypsum: – Immersion of impression in a solution containing an accelerator for the setting of the gypsum product, before pouring the impression with the gypsum – Incorporation of a plaster hardener or accelerator • Accelerator increases the hardness of cast by – Accelerating the set of gypsum to overcome the retarding action of gel. – may react with the gel to produce a surface layer that reduces or prevents syneresis and eliminates the retarding action of the gel. Hardening solutions: potassium sulfate, zinc sulfate, manganese sulfate and potash alum 2% potassium sulfate is most
  93. 93. • Pouring of stone mixture to fill the impression should start from one end of the arch. After the impression has been filled with stone, it may be placed in either a humidor or a 2% potassium sulfate solution while the stone hardens in an atmosphere of approximately 100% relative humidity. • Cast should be kept in contact with the impression, preferably for 60 min or minimum 30 min. • If the cast is allowed to remain in contact with the hydrocolloid impression overnight, a chalky stone surface may be produced.
  94. 94. • Over Mixing Results In • Reduction in final strength as the gel fibrils are broken. • Reduction in working time. • Under Mixing Results In • Inadequate wetting, lack of homogeneity and reduced strength. • The mix being grainy and poor recording of detail.
  95. 95.
  97. 97. Table of contents: • Introduction • Definitions • History • Review of literature • Impression materials • Tray selection and custom tray fabrication • Impression techniques • Summary • Conclusion
  98. 98. Preserving alginate impression
  99. 99. Diatomaceous earth • DE, diatomite, diahydro, kieselguhr, kieselgur and Celite • is a naturally occurring, soft, chalk-like sedimentary rock that is easily crumbled into a fine white to off-white powder. • This powder has an abrasive feel, similar to pumice powder and is very light, due to its high porosity. • The typical chemical composition is – 86% silicon, 5% sodium, 3% magnesium and 2% iron.
  100. 100. • Diatomaceous earth consists of fossilized remains of diatoms, a type of hard-shelled algae. • It is used as a filtration aid, as a mild abrasive, as a mechanical insecticide, as an absorbent for liquids, as cat litter, as an activator in blood clotting studies, and as a component of dynamite. • As it is also heat-resistant, it can be used as a thermal insulator.
  101. 101. Disinfection • The current protocol for disinfecting hydrocolloid impressions recommended by the • Centers for Disease Control and Prevention is to use household bleach (1-10 dilution), or synthetic phenols as disinfectants. • After the impression is thoroughly rinsed, the disinfectant is sprayed liberally on the exposed surface.
  102. 102. Advantages • Inexpensive • Easy to use • Hydrophilic – displace moisture, blood, fluids • Stock trays
  103. 103. Disadvantages • Tears easily • Dimensionally unstable – immediate pour – single cast • Lower detail reproduction – unacceptable for working cast of fixed prosthodontics • High permanent deformation • Difficult to disinfect
  104. 104. Non aqueous elastomeric impression materials
  105. 105. • Synthetic rubbers • mimic natural rubber (scarce during World War II) • Initially called rubber impression materials • Currently referred as elastomers or elastomeric impression materials. • ADA Specipication no. 19 identifies as “nonaqueous elastomeric dental impression materials” Phillip’s Science of Dental
  106. 106. Aqueous Hydrocolloids Non-aqueous Elastomers Polysulfide Silicones Polyether Condensation Addition Agar (reversible) Alginate (irreversible)Classification
  107. 107. Non-Aqueous Elastomers • Viscosity classes – low, medium, high, putty – Monophase Phillip’s Science of Dental Materials Single phase or monophase – single component material with sufficient shearing potential that it can be used as the syringe material and the tray material.
  108. 108. Polysulfide
  109. 109. Polysulfide • The first elastomer used for dental impressions • Sometime referred to – By the type of material, such as rubber base impression material – By the processing terminology, such as vulcanizing impression material – By chemistry, such as mercaptan impression material or – By the name of one of the first manufacturers, such as the Thiokol Corporation.
  110. 110. • Examples – Permlastic (Kerr) – Omni-Flex (GC America) – copper hydroxide system. – Coe-flex (GC-Amer) – Neo-plex (Miles) Supplied as : Paste in collapsible tubes as base and accelerator. Base is white and accelerator is brown or grey.
  111. 111. Composition Phillip’s Science of Dental Materials Base paste Polysulphide polymer Lithopone and titanium dioxide filler strength Di butyl phthalate plastisizer viscosity Sulphur0.5% Enhance the reaction Reactor paste Lead dioxide Gives Dark brown color filler plasticizer Oleic acid or stearic acid Retarders Control rate of setting
  112. 112. • Available in 3 viscosities, • light body and medium body heavy body. • Tray adhesive: • Butyl rubber or styrene/ acrylonitrile dissolved in a volatile solvent such as chloroform or a ketone
  113. 113. Reaction lead dioxide reacts with the polysulfide polymer causing: • Chain lengthening by oxidation of terminal – SH groups. • Cross linking by oxidation of the pendant – SH groups.
  114. 114. Modifications • Reactor – lead dioxide replaced by organic hydroperoxide e.g. t-butyl hydroperoxide. – But this has poor dimensional stability because of volatility. • Inorganic peroxides such as copper.
  115. 115. Manipulation • With the proper lengths of the two pastes squeezed onto a mixing pad or glass slab, • the catalyst paste is first collected on a stainless steel spatula and then distributed over the base, and the mixture is spread out over the mixing pad • The mass is then scraped up with the spatula blade and again smoothed out.
  116. 116. • If sufficient force is applied and spatulation is performed rapidly, the material will seem thinner and easier to handle. • This phenomenon is known as pseudoplasticity. • Most accurate impressions are made using custom acrylic trays because of uniform thickness of the material.
  117. 117. • Mean working time – 6.0 min at 23 degree – 4.3 min at 37 degree • Mean setting time – 16 min at 23 degree – 12.5 min at 37 degree
  118. 118. Accelerators of curing • An increase in temperature • A drop of water Retarders of curing • A decrease in temperature (chilled, dry glass slab)
  119. 119. • Elasticity improves with time, so longer the impression can remain in the mouth before removal, greater the accuracy. • Polysulfide ranks as one of the least stiff of the elastomeric impression materials.
  120. 120. • Unset material has high level of viscosity. This thick consistency of the uncured material helps displace an unwanted fluid present while seating the impression. • Also, the excess material extruded from the tray does not flow easily because of the high viscosity, reducing the potential discomfort to the patient during seating of a tray.
  121. 121. Advantages Disadvantages Long working time Requires a custom tray Proven accuracy Must be poured in stone immediately High tear resistance Potential for significant distortion Less hydrophobic Odor offends patients inexpensive to use Messy and stains clothes Long shelf life Second pour is less accurate Polysulfide
  122. 122. Silicones
  123. 123. silicones Condensation Addition
  124. 124. Condensation reaction – a polymerization reaction in which the polymer chains all grow simultaneously and a reaction byproduct is formed. CONDENSATION SILICONE Also known as conventional silicone
  125. 125. Available in 3 viscosities – Light body – Medium body – Putty body • Paste – two pastes in collapsible tubes • Putty – jars
  126. 126. Condensation Silicone • Examples – Speedex (Coltene/Whaledent) – Primasil (TISS Dental) – Accoe (GC-Amer) – Xantopren (Unitek) – Elasticon (Kerr) – Cuttersil (Miles)
  127. 127. Composition Phillip’s 1996 Phillip’s Science of Dental Materials Composition Components Function Base paste Hydroxyl terminated polydimethyl siloxane prepolymer undergoes cross linking to form rubber Silica Filler Reactor Orthoethyl Silicate Cross linking agent Stannous octate Catalyst
  128. 128. The polymerization occurs as a result of cross linkage between the orthoethyl silicate and the terminal hydroxy group of the dimethyl siloxane, to form a three dimensional network. The reaction is exothermic ( 1deg C. rise)
  129. 129. Properties • Setting time is 8-9 minutes • Mixing time is 45 sec
  130. 130. • Tear strength 3000gm/cm lower than polysulfide • Hydrophobic – area should be dried. Avoid air bubbles while pouring the cast • It is stiffer and harder than polysulfide. The hardness increases with time.
  131. 131. • The spacing in the tray is increased to 3mm to compensate for the stiffness. • Can plated with silver/ copper. Silver plating is preferred. • Shelf life is slightly less than polysulfides due to the unstable nature of the orthoethyl silicates.
  132. 132. Advantages • Better elastic properties • Clean, pleasant • Stock tray • putty-reline • Good working and setting time Phillip’s Science of Dental
  133. 133. Disadvantages • Permanent deformation – high – 1-3% • Poor dimensional stability – high shrinkage • polymerization • evaporation of ethanol – pour immediately • within 30 minutes • Hydrophobic – poor wettability Phillip’s Science of Dental
  134. 134. Addition Silicones
  135. 135. • Frequently called polyvinylsiloxane or viny polysiloxane impression materials. Addition silicones
  136. 136. Supplied in • 4 viscosities – Light body – Medium body – Heavy body – Putty
  137. 137. Addition Silicones • Examples – Extrude (Kerr) – Express (3M/ESPE) – Aquasil (Dentsply Caulk) – Genie (Sultan Chemists) – Virtual (Ivoclar Vivadent)
  138. 138. Composition Phillip’s Science of Dental Materials Components Function Base paste Hydroxyl terminated polymethyl siloxane prepolymer Undergoes cross linking to form rubber Colloidal silica Filler Reactor Polyvinyl silicone prepolymer Colloidal silica Filler Chloroplatinic acid Catalyst
  139. 139. Reaction
  140. 140. • Improper balance between the vinyl siloxane and silane siloxane contribute to the liberation of hydrogen gas • To overcome this manufacturer adds palladium (scavenger) or wait for an hour before pouring the impression.
  141. 141. • Setting time – 5-9 min • Mixing time – 45 sec • Best dimensional stability among elastomers. • Curing shrinkage 0.17% • Permanent deformation 0.05-0.3% • Tear strength -3000gm/cm • Extremely hydrophobic surfactant detergent
  142. 142. • Electroplated with silver or copper. • Low flexibility • Harder than polysulfide – extra spacing 3 mm should be provided in the impression tray. • Care should be taken while removing the cast from the impression to avoid any breakage. • Shelf life ranges from 1-2 years
  143. 143. Advantages • Excellent reproduction of surface details • Highly accurate • High dimensional stability – pour up to one week • Stock or custom trays • Multiple casts • Easy to mix • Pleasant odor Phillip’s Science of Dental Materials
  144. 144. Disadvantages • Expensive • Sulfur inhibits set – latex gloves – ferric and Al sulfate retraction solution • Short working time • Lower tear strength • Possible hydrogen gas release – bubbles on die – palladium added to absorb – Moisture control – impression making
  145. 145. Modifications in PVS • Adding palladium scavenger to tie up any hydrogen gas • Less hydrophobic • Smaller holding device, cartridges making easier to use.
  146. 146. Polyether • First material introduced for dental impressions. • Introduced in Germany in late 1960s.
  147. 147. Available as • base and accelerator in collapsible tubes. • The accelerator tube is usually smaller. • Earlier supplied in single viscosity. • A third tube containing a thinner was provided. • Available in 3 viscosities – Light body – Medium body – Heavy body
  148. 148. Polyether • Examples – Impregum F (3M/ESPE) – Permadyne (3M/ESPE) – Pentamix (3M/ESPE) – P2 (Heraeus Kulzer) – Polygel (Dentsply Caulk)
  149. 149. Composition Base Paste Imine terminated prepolymer Becomes cross linked to form rubber Silica Filler – to control viscosity Glycol ether or Pthalate Plasticizer Reactor paste Alkyl aromatic sulfonate ester Initiates cross linking Silica Filler Pthalate Plasticizer
  150. 150. • Polyether based polymer that is cured by the reaction between aziridie rings • The main chain is a copolymer of ethylene oxide and tetrahydrofuran. • Cross linking and thus setting, is brought about by an aromatic sulfonate ester. • Is an exothermic reaction – 4-5deg C.
  151. 151. • Elasticity – stiffest of impression materials – New formulation of medium or regular body are less stiff – When used in thinner sections decreases the stiffness. • Impressions must be kept in cool, dry environment. Properties
  152. 152. • Sulfonic ester may cause skin reaction. To avoid this, mix thoroughly before making an impression and direct skin contact should be avoided. • Setting time is around 8.3 min. • mixing time - 30 sec. • Heat increases the setting time.
  153. 153. • Is extremely stiff – flexibility 3% • Its hardness is higher than polysulfides and increases with time. Removing it from undercuts is difficult, so extra spacing 4mm should be given. • Tear strength is good 3000gm/cm • Hydrophilic – so moisture in the impression field is not so critical. It has the best compatibility with stone. • Can be electroplated with silver or copper. • Shelf life > 2 years.
  154. 154. Advantages • Highly accurate • Good dimensional stability • Least hydrophobic • Good surface detail • Pour within one week – kept dry • Multiple casts • Good wettability • Good shelf life Phillip’s Science of Dental Materials
  155. 155. Disadvantages • Expensive • Short working time • Rigid – difficult to remove from undercuts • Bitter taste • Low tear strength • Absorbs water – changes dimension – Leaches components Phillip’s Science of Dental Materials
  156. 156. Modifications • Reducing the stiffness and producing polyether in low and heavy viscosities have been the major changes.
  157. 157. Comparison of Properties • Working time – longest to shortest • agar > polysulfide > silicones > alginate = polyether • Setting time – shortest to longest • alginate < polyether < agar < silicones < polysulfide O’Brien Dental Materials & their Selection
  158. 158. Comparison of Properties • Stiffness – most to least • polyether > addition silicone > condensation silicone > polysulfide = hydrocolloids • Tear strength – greatest to least • polysulfide > addition silicone > polyether > condensation silicone >> hydrocolloids O’Brien Dental Materials & their Selection
  159. 159. Comparison of Properties • Cost – lowest to highest • alginate < agar = polysulfide <condensation silicone < addition silicone < polyether • Dimensional stability – best to worst • addition silicone > polyether > polysulfide > condensation silicone > hydrocolloid Phillip’s 1996 O’Brien Dental Materials & their Selection
  160. 160. Comparison of Properties • Wettability – best to worst • hydrocolloids > polyether > hydrophilic addition silicone > polysulfide > hydrophobic addition silicone = condensation silicone • Castability – best to worst • hydrocolloids > hydrophilic addition silicone > polyether > polysulfide > hydrophobic addition silicone = condensation silicone O’Brien Dental Materials & their Selection
  161. 161. Removal of impression • One method for determining the time of removal is – to inject some of the syringe material into an interproximal space that is not within the area of operation. – Can prodded with a blunt instrument from time to time, and when it is firm and returns completely to its original contour
  163. 163. Composition - polyether urethane dimethacrylate resin. - diketone initiator - amine accelerator - 40 – 60% silica filler (SILICON DIOXIDE)
  164. 164. • Clear tray(TRANSPARENT), photo initiated by 400 – 500 nm blue light • Advantage - unlimited working time (CONTROLLED BY OPERATOR), • TEAR STRENGTH-6000-7500 gm/cm • short setting time • Disadvantage - surface polymerization
  165. 165. Fabrication of custom tray
  166. 166. Armamentarium
  167. 167.
  168. 168.
  169. 169. Tray stops
  170. 170. 0.025 mm
  171. 171. 2-3 mm
  172. 172.
  173. 173. Thermoplastic tray
  174. 174.
  175. 175. Vacuum formed
  176. 176. Visible light polymerized
  177. 177.
  178. 178.
  179. 179.
  180. 180.
  181. 181.
  182. 182.
  183. 183.
  184. 184.
  185. 185. • The advantages of this combination system compared with agar or alginate used individually is • The minimization of equipment required to record an agar impression (no water cooled tray is needed) and • The fact that agar is more compatible with gypsum model materials than alginate. • It is also relatively cheap in comparison to many synthetic elastomers.
  186. 186. • Lin et al. demonstrated that the accuracy of this combination system is better than either the reversible or irreversible materials used separately and • is comparable to that of polysulphide impression materials.
  187. 187. Vinyl polysiloxane addition silicone Extrude xp (kerr) - putty impression material Extrude (kerr) - extra heavy body impression material Extrude (kerr) – medium body impression material Extrude (kerr) - wash light body impression material
  188. 188. Condensation silicone 1. Xantopren(kulzer) Comfort - Regular body Silicone Impression Material 2. Speedex (coltene)- light body silicone impression material 3. Speedex (coltene) - putty silicone impression material 4. Xantopren m mucosa (kulzer)- medium body impression material
  189. 189. Polyether impression material • Impregum penta (3M/ESPE)— light viscosity Polyether impression material • Impregum Penta (3M/ESPE)— - Medium viscosity Polyether Impression Material • Impregum Penta (3M/ESPE)— —Heavy body polyether impression material • P2 Standard -- Regular set Monophase polyether impression material
  190. 190. Polysulfide impression material permalastic (kerr) – heavy body permalastic (kerr)– light body permalastic (kerr)– regular body
  191. 191. Addition Silicones • Surfactants added – reduce contact angle
  192. 192. SO3 - + R+ CH3 – CH – CH2 – CO2 – CH – (CH2)n – O – CH – (CH2)n – CO2 –CH2 – CH –CH3 N H2C CH2 R R m N H2C CH2 N H2C CH2 R – N – CH2 – CH2 – + N H2C CH2 N H2C CH2 R – + + Polyether Reaction catalyst base ring opening Phillip’s Science of Dental Materials 1996
  193. 193. • These materials were developed to overcome some of the disadvantages of polysulfide materials, such as their objectionable odor, the staining of linen and uniforms by the lead dioxide, the amount of effort required to mix the base with the accelerator, the rather long setting times, the moderately high shrinkage on setting and the fairly high permanent deformation.
  194. 194. Thank you For more details please visit