Elastic impressions (hydrocolloids)


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hydrocolloids impression materials agar and alginate

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  • Agar- 25 microns
    Alginate-75 microns
  • Elastic impressions (hydrocolloids)

    1. 1. Elastic Impression Materials Hydrocolloids Vinay Pavan Kumar .K 1st year MDS Dept of Prosthodontics AECS Maaruti College of Dental Sciences
    2. 2. Hydrocolloids Definition Classification Composition Properties Manipulation Advantages and disadvantages
    3. 3. Impression Negative record of tissues of mouth used to reproduce the form of teeth and the surrounding tissues (GPT 8) Impression material Any substance or combination of substances used for making an impression or negative reproduction (GPT 8)
    4. 4. Colloid “Kola” means “glue” “oid” means “like” First described by Thomas Graham (1861) Colloidal state State of subdivision such that the molecules or polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm
    5. 5. Solution - a homogeneous mixture consisting of a single phase Colloid - a heterogeneous mixture of not readily differentiated two phases Suspension - a mixture of two distinct phases
    6. 6. Dispersed phase Dispersion phase Type Solid Liquid Sol Solid Gas Solid Aerosol Liquid Liquid Emulsion Liquid Gas Aerosol Gas Liquid Foam Gas Solid Solid Foam •Dispersed phase •Dispersion phase
    7. 7. Gelation There is a phase change from SOL GEL • Gel state - the dispersed phase agglomerates to form a chain of fibrils called “micelles” • Fibrils form a “brush heap structure” • The dispersion medium is held in the interstices between the fibrils by capillary attraction
    8. 8. Elastic impression material Hydrodocolloids Agar Alginate Non-aqueous elastomers Polysulfide Polyether Condensation siliconeAddition silicone
    9. 9. What is hydrocolloid? Colloid that contains water as the dispersion phase Hydrocolloid impression material are based on colloidal suspensions of polysaccharides in water. Exists in two forms • Sol form - fluid with low viscosity • Gel form - a jelly like elastic semisolid
    10. 10. Types of hydrocolloid impression material Based on the mode of gelation: Reversible – Agar • Secondary bonds hold the fibrils together • Bonds break at slightly elevated temperatures and become re-established Irreversible – Alginate • Fibrils are formed by chemical action
    11. 11. Imbibition Process of water sorption i.e. the gel swells when placed in water Syneresis Expression of fluid on to the surface of gel structure
    12. 12. A. Shrinkage phenomena occur if syneresis forces (F syneresis) are higher than osmotic forces (F osmotic). B. Osmotic active ingredients within color- changing irreversible hydrocolloid shift force balance towards F osmotic, resulting in overall expansion of material. Schematic drawing illustrating presumed processes within irreversible hydrocolloid on molecular level. Erbe C, Ruf S, Wöstmann B, Balkenhol M Dimensional stability of contemporaryirreversible hydrocolloids: Humidor versus wet tissue storage J Prosthet Dent 2012;108:114-122
    13. 13. Liquifaction Temperature Temperature at which gel changes to sol (70 -100°C) Gelation Temperature Temperature at which sol changes to gel (37-50°C) Hysteresis – Temperature lag
    14. 14. REVERSIBLE HYDROCOLLOID - AGAR • Agar is an organic hydrophillic colloid (polysaccharrides) extracted from certain types of seaweed. • 1937 – Agar was introduced by Sears. Component Function Composition Agar Brush heap structure 13 – 17% Water Reaction medium >80% Borax Strength 0.2-0.5% Sulfate Accelerator 2%-5% Wax Filler 0.5%-1% Thymol and glycerine Bactericidal and plasticiser
    15. 15. 1,3- linked â-D-galactopyranose and 1,4-linked 3,6-anhydro-á-L-galactopyranose  Agarose, is a strongly gelling, non-ionic polysaccharide  Agaropectin, is more complex polysaccharide having sulfate groups • Sol: random coils • Gelation I : Double helices • Gelation II :aggregation of helices
    16. 16. Manipulation
    17. 17. Agar hydrocolloid requires special equipment: Hydrocolloid Conditioning unit “Conditioning unit” is a thermostatically controlled unit having 3 compartments: •Boiling compartment --- water at 1000 C. •Storing compartment --- water at 650 C •Tempering or conditioning compartment --- water at 450 C. •Water cooled rim lock trays
    18. 18. Conditioning unit Liquefying Store Tempering 1000 C 650 C 460 C
    19. 19. Steps in impression preparation 1.Liquefaction - at 1000 C 2.Store in 650 C 3.Load agar in tray 4.Temper at 460C 5.Seat in patient’s mouth 6.Cool with water of 180 C – 210 C for 5mins 7.Remove by snap action 8.Pour the mold material
    20. 20. Strength The tear strength of agar - 0.8 to 0.9 N/mm ANSI/ADA Specification - 0.75 N/mm Compatibility with Gypsum More compatible than alginates Dimensional stability •Less stable due to imbibition and syneresis •Cast to be poured immediately •Agar is best stored in 100% humidity for maximum of 1hr
    21. 21. Advantages: •Dimensionally accurate •Hydrophilic - displace moisture, blood, fluids •No custom tray or adhesives required •Pleasant •No mixing required •Stone casts easily removed •Cheap compared to synthetic elastic materials •Can be reused when used as duplicating material
    22. 22. Disadvantages: •Initial expense –special equipment •Material prepared in advance •Tears easily •Dimensionally unstable •Cannot be electroplated •Difficult to disinfect •Only one model can be poured
    23. 23. Irreversible hydrocolloid – Alginate • Developed by S. William Wilding in 1941 • As a substitute to agar during World War II • Alginic acid prepared from marine brown sea weed Examples ◦ Jeltrate (Dentsply/Caulk) ◦ Coe Alginate (GC America)
    24. 24. (a) β-D-mannuronic acid. (b) α-L-guluronic acid. (c) Structural formula of sodium alginate molecule Alginate composition
    25. 25. Composition Component Function Weight percentage Sodium or potassium triethanolamine alginate Dissolves in water and reacts with calcium ions 15% Calcium sulphate dehydrate Reactor 16% Zinc oxide Filler particles 4% Potassium titanium fluoride Accelerator 3% Diatomaceous earth Filler particles 60% Sodium phosphate Retarder 2% Coloring and flavoring agent Give coloring change when setting is complete Traces
    26. 26. FORMS OF ALGINATE • Powder • Sol – Plaster of Paris acts as reactor • 2 paste system - alginate sol calcium reactor
    27. 27. Setting reaction: A reaction of soluble alginate with calcium sulphate and the formation of an insoluble calcium alginate gel Na alginate + CaSO4 Ca alginate + Na2SO4 (Powder) (Gel) Irreversible chemical reaction Working and setting times are determined by the rate of release of calcium ions (CaSO4).2H2O 2Ca2+ + 2SO4 2- + H20
    28. 28. Gelation of homopolymeric blocks of α-L-guluronic acid junction with calcium ions. Binding of divalent cations by alginate: the “Egg-box” model
    29. 29. Retarder •Calcium ions will react preferentially with the phosphate ions to form an insoluble calcium phosphate 2Na3PO4 + 3CaSO4 Ca3(PO4)2+3Na2SO4 Water powder ratio •16g of powder is mixed with 38ml of water- gelation in 3 to 4 minutes
    30. 30. Controlling setting time •Type-I : Fast setting (1- 2 minutes) •Type-II : Normal setting (4 - 5 minutes) Comparison Of Regular And Fast Set Alginate Regular set Fast Set Mixing Time 1 min 45 sec Working Time 3 min 1.25 to 2 min Setting Time 4 to 5 min 1.5 to 3 min
    31. 31. • Manufacturers adjust the concentration of sodium phosphate to produce regular and fast-set alginates • Setting time can be altered by change in temperature of the water • Higher the temperature, faster the setting • 1-minute reduction in setting time occurs for each 100 C temperature increase
    32. 32. Manipulation • Weigh powder- W/P ratio (16 g powder, 38 ml water) • Powder added to water • rubber bowl • vacuum mixer • Mixed for 45 sec to 1 min • Place tray • Remove after 2 to 3 minutes or after gelation (loss of tackiness)
    33. 33. Alternatives to Hand Mixing • Two alternatives exist for mixing alginates other than manual manipulation of the impression material. • The Alginator and the Vac-U-Mix automatically mix the alginate through the use of motorized electrical equipment
    34. 34. Stock trays-perforated – 20 holes per Sq Inch, distance between holes – 2mm Customization of trays : Modifications-wax/tracing stick impression compound/heavy-bodied silicone IMPRESSION TRAYS
    35. 35. TRAY ADHESIVES FOR ALGINATE Liquid • Diethylenetriamine polymer • Xylene • Erythrosine Spray Solvents - used to remove this adhesive
    36. 36. Properties Flexibility • ANSI/ADA Specification permits a range of 5% to 20% at a stress of 0.1MPa and most alginates have a value of 14%. •Strength • ANSI/ADA Specification :compressive strength of 0.35 MPa • Compressive strength - 0.5 to 0.9 MPa • Tear strength range from 0.37 to 0.69 MPa Sketch of tear strength specimen with load applied in the directions of the arrows; the specimen tears at the V-notch.
    37. 37. Elastic recovery Recovery >95% when the material is compressed 20% for 5 seconds. Alginate – 98.2% Variation of compression set with time of an alginate impression material at strains of 10%, 20%, and 30% applied for 5 and 10 seconds.
    38. 38. Shelf Life • One year • It deteriorates rapidly at high temperature Dimensional Stability • It has poor dimensional stability because of either syneresis or imbibition • Impressions should be stored in 100% relative humidity Reproduction of tissue details • low when compared with agar
    39. 39. Representative photographs of alginate impressions after each storage time. JeltratePlus after (a) 30 minutes, (b) 48 hours, and (c)100 hours; Alginmax after (d) 30 minutes, (e) 48 hours, and (f) 100 hours; and Kromopan 100 after (g) 30 minutes, (h) 48 hours, and (i) 100 hours.
    40. 40. WORKING TIME The working time of alginate is determined by the help of the penetrometer (from the start of mixing to the start of gelation) Fast set : 1.25 – 2mins Regular set : 2 – 4.5mins SETTING TIME The initial setting time of alginate is determined by placing a flat Polymeric cylindrical rod in contact The cylinder is withdrawn and is repeated till no alginate is sticking to its surface
    41. 41. TESTS FOR COMPRESSIVE STRENGTH • The compressive strength should exceed 0.35Mpa Tear Strength and Compressive Strength for CA37 (0,95 N/mm – 1,06 MPa) and Orthotrace (0,83 N/mm – 1,06 MPa) were significantly higher than for Hydrogum (0,54 N/mm – 0,69 MPa), Aroma Fine(0,51 N/mm – 0,57 MPa) and Blueprint(0,49 N/mm – 0,61 MPa) WOORTMAN.R, KLEVERLAAN.C.J, IPPEL.D, FEILZER.A.J Tear strength as indicator for the stability of Alginates
    42. 42. Taste and Odor • Pleasant taste and odor Compatibility of agar and alginate with gypsum • Agar and alginate cause retardation of gypsum • Overcome by immersing the impression in a solution of gypsum accelerator (2% potassium sulphate) • Incorporating a plaster hardener
    43. 43. Model plaster poured against alginate Dental stone poured against the same alginate
    44. 44. Disinfection  Immersion in 1% Sodium Hypochlorite or 2% Gluteraldehyde < 10 min immersion or sprayed with disinfectant  Current protocol (by centre for disease control and prevention) : Use of household bleach (1-10 dilution) Iodophor Synthetic phenol
    45. 45. Storage • Storage at 100% relative humidity (RH) reportedly results in minor dimensional changes Placed on pane of clear acrylic resin on top of wet sponge inside air-tight humidor Wrapped in wet tissues in contact with entire specimen surface and placed in zipper plastic storage bag If humidor storage is used, IH impressions should be poured within 4 hours. If bag/tissue storage is used, non-color change IH impressions should, preferably, be poured within 2 hours Erbe C, Ruf S, Wöstmann B, Balkenhol M Dimensional stability of contemporaryirreversible hydrocolloids: Humidor versus wet tissue storage J Prosthet Dent 2012;108:114-122
    46. 46.  There is a greater chance for distortion the longer the impression is stored  New alginates have improved long-term storage ranging from 48 to 120 hours when stored in a plastic bag
    47. 47. Advantages  Easy to mix and manipulate  Minimum requirement of equipment  Hydrophilic ,gives good surface detail even in saliva  Low cost  Comfortable to the patient  Hygienic ,as fresh material must be used  It records fine details in patients with undercuts  Good surface details are recorded even in patients with excessive salivation
    48. 48. Disadvantages  Poor tear strength  Dimensionally unstable  Lower detail production  Difficult to disinfect  High permanent distortion  Cannot be electroplated  It cannot be corrected
    49. 49. Dustless alginate • Inhaling fine airborne particles from alginate impression material can cause silicosis and pulmonary hypersensitivity • Dustless alginates were introduced which give off or no dust particles so avoiding dust inhalation • This can be achieved by coating the material with glycerine or glycol. This causes the powder to become more denser than in uncoated state
    50. 50. • Introduced by Schunichi, Nobutakwatanate in 1997 • This of comprises sepiolite and a tetraflouroethylene resin having a true specific gravity of from 2-3 • The material generates less dust, has a mean particle size of 1-40microns Low dust alginate :
    51. 51. Antiseptic alginate : • Introduced by Tameyuki Yamamoto, Maso Abinu patented in 1990. • An antiseptic containing alginate impression material contains 0.01 to 7 parts by weight of an antiseptic such as glutaraldehyde and chlohexidine gluconate per 100 parts by weight of a cured product of an alginate impression material. • The antiseptic may be encapsulated in a microcapsule or clathrated in a cyclodextrin.
    52. 52. Chromatic alginate • The alginate impression material with color indications avoiding confusion about setting time. • Color changes are visualizing the major decision points in impression making  pH of fluid mass changes during setting  Acid /base indicator in their formulation. Ex : KromaFaze (Dux Dental), Integra (Dux Dental)
    53. 53. Agar Alginate Preparation Boil, temper, store Powder, water Ease of Use Technique sensitive Good Patient Reaction Thermal Shock Pleasant, clean Ease of removal Very easy Very easy Disinfection Poor Poor Handling Properties
    54. 54. Agar Alginate Working Time (min) 7 – 15 2.5 Setting Time (min) 5 3.5 Stability 1 hour 100% RH Immediate pour Wettability and castability Excellent Excellent Cost Low Very low
    55. 55. Laminate (Agar-Alginate) technique: Inject syringe material around the prepared tooth Seat the tray loaded with alginate & allow it to set Cool alginate gels the agar
    56. 56. Advantages: Equipment cost is lower Less preparation time is required Disadvantages: Bond between agar and alginate is not always sound Alginate materials displaces the agar during seating
    57. 57. Wet field technique:  Wet the tooth surface with warm water  Syringe materials applied over the occlusal and incisal portion  Seat the tray with material  Hydraulic pressure forces the fluid material down the tooth displacing the blood & debris
    58. 58. TRIPLE TRAY TECHNIQUE • In this technique one impression records both the mandibular, maxillary arches and the occlusal relationship
    59. 59. Effect Causes Agar Alginate Grainy material Inadequate boiling Storage temperature too low Storage time too long Improper mixing Prolonged mixing Excessive gelation W/P ratio too low Separation of tray and syringe material Water soaked tray material surface not removed Premature gelation of either material Not applicable Tearing Inadequate bulk Premature removal from mouth Syringe material partially gelled when tray was seated Inadequate bulk Premature removal from mouth Moisture contamination Prolong mixing Effects of mishandling:
    60. 60. Effect Causes Agar Alginate Irregularly shaped voids Material too cold Moisture or debris on tissue Rough or chalky stone model Inadequate cleansing of impression Premature removal of die Improper manipulation of stone Excess water or hardening solution left in the impression Air drying the impression before pouring Inadequate cleaning of impression Premature removal of impression Improper manipulation of stone Excess water left in impression Model left in impression too long
    61. 61. Effect Causes Agar Alginate External bubbles Gelation of syringe material prevents flow Undue gelation preventing flow Air incorporated during mixing Distortion Impression not poured immediately Movement of tray during gelation Premature removal of impression Improper removal from mouth Use of ice water during initial stages of gelation Impression not poured immediately Movement of tray during gelation Premature removal of impression Improper removal from mouth
    62. 62. Duplicating Materials  Both types of hydrocolloids are used for duplication of casts and models in dental laboratory for fabrication of prosthetic appliances and orthodontics models  The composition of hydrocolloid type for duplicating materials are same  Agar hydrocolloid is more popular in labs because it can be used many times
    63. 63. Errors during impression making •Mix too thick •Continuous pressure •Movement during setting •Separation of alginate from tray •Inadequate working time limiting flow •Teasing the impression while removal •Too much air blown to dry the impression •Moist towel or cotton over impression for storage Rudd RW and Rudd KD. A review of 243 errors possible during the fabrication of a removable partial denture: Part I. J Prosthet Dent 2001;86:251-61.
    64. 64. ALGINATE IMPRESSION TECHNIQUE IN HIGH PALATE VAULT Nandini VV, Venkatesh K V, Nair K C Alginate impressions: A practical perspective, J Conserv Dent 2008;11: 37-41.
    65. 65. SINGLE STEP APPROACH TO MAKE DIAGNOSTIC IMPRESSIONS OF BOTH THE ARCHES & FACE BOW TRANSFER Komuravelli AK, Suresh Sajjan MC ,Single step approach to make diagnostic impressions of both the arches and face bow transfer: a novel technique. Indian J Dent Res. 2012 Jan-Feb; 23(1):2-6
    66. 66. CONCLUSION Hey…… What are you doing??? I’m trying to make a really good first “IMPRESSION”
    67. 67. REFERENCES •Craig G R, Powers J M, Sakaguchi R L Restorative Dental Materials,13th edition, USA, Elsevier publications, 2012, pg 277- 86. •Ferracane J L, Materials in Dentistry, 2nd edition, USA, Susan Katz publishers, 2001, pg 173 - 99. •Anusavice, Sheen, Rawls, Philips Science of dental materials, 12th edition, Florida, Elsevier Health Sciences, oct 2012, pg 168 - 77.
    68. 68. •Rudd R W and Rudd KD, A review of 243 errors possible during fabrication of a removable partial denture: part 1. J Prosthet Dent 2001;86:251- 61. •Walker.M.P,Burckhard.J,Mitts.D.A,Williams.K.B Dimensional change over time of extended-storage alginate impression materials. AngleOrthod. 2010;80:1110 – 1115. •O’Brien W J, Dental materials and their selection, 2nd edition, Canada, Quintessence publications, 1997,pg 127 - 32.
    69. 69. • Nandini V V, Venkatesh K V, Nair K C Alginate impressions: A practical perspective, J Conserv Dent 2008;11: pg 37 - 41. • Keita Kashima and Masanao Imai. Advanced Membrane Material from Marine Biological Polymer and Sensitive Molecular-Size Recognition for Promising Separation Technology, Advancing Desalination,2012.
    70. 70. Erbe C, Ruf S, Wöstmann B, Balkenhol M, Dimensional stability of contemporary irreversible hydrocolloids: Humidor versus wet tissue storage, J Prosthet Dent 2012;108: pg 114 - 122 Hiraguchi H et al, Effects of Disinfection of Combined Agar/Alginate Impressions on the Dimensional Accuracy of Stone Casts, Dent Mater Journal 26 (3): 457- 462, 2007 Komuravelli A K, Suresh Sajjan M C ,Single step approach to make diagnostic impressions of both the arches and face bow transfer: a novel technique. Indian J Dent Res. 2012 Jan-Feb; 23(1):2-6