Impression Materials BDS III

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Impression Materials BDS III Powered By Docstoc
					Dr M Slabbert
Dept Prosthodontics
Wits
First Impressions count
Classification of Impressions
 Preliminary impressions
    Taken either by the dentist or an expanded-function
     dental assistant.
    Used to make a reproduction of the teeth and
     surrounding tissues.
    Used to make (1) diagnostic models, (2) custom
     trays, (3) provisional coverage, (4) orthodontic
     appliances, and
     (5) pretreatment and post-treatment records.
Classification of Impressions- cont’d
 Final impressions
    Taken by the dentist.
    Used to make the most accurate reproduction of
     the teeth and surrounding tissues.
    Used to make indirect restorations, partial or full
     dentures, and implants.
Classification of Impressions- cont’d
 Bite registrations
   Taken by the dentist or dental assistant.
   Make a reproduction of the occlusal relationship
    between the maxillary and mandibular teeth.
   Provide an accurate registration of the patient’s centric
    relationship between the maxillary and mandibular
    arches.
                                          Study model (cast)
Oral Examination

                   Primary Impression



Final Impression                              Treatment Planning
                                                  • duplicate model

                   Mouth and tooth
                     preparation



  Master model

                                                       Denture

                       Laboratory procedure
                          • investment cast           Delivery
                          • refractory cast
                                Definition

 An impression is a negative record of the tissues of the
oral cavity which constitutes the basal seat of the denture.
 An impression is made in a material which has plasticity
and which hardens or sets while in contact with the tissue.




  Prof Owen Fundamentals of Removable partial dentures 2nd Ed pg. 124 -131
  Wits Pros Book Vol 2 Pg. 14
  Study pages 14- 31 Vol 2
  www.health.wits.ac.za/Prosthodontics Primary impressions in alginate…
The Ideal Impression Material
 Easy to mix and handle.

 Suitable working time.

 Suitable setting time.

 Compatible with die and stone

 Not toxic or allergenic to the patient.

 Dimensionally stable on setting.

 Accurate to record the fine details of the prepared tooth

 Has acceptable odor and taste.

 Adequate strength.

 Adequate shelf life.
The Ideal Impression Material
cont.
 Economical

 Ready to disinfected without loss of accuracy.

 Fluid or plastic when inserted into the mouth.

 It must be an exact record of all the aspects of the prepared tooth
  and sufficient unprepared tooth structure immediately adjacent to
  margins, to allow the dentist and the technician to be certain of the
  location and configuration of the finish line.

 Other teeth and tissue surrounding the abutment tooth must be
  accurately reproduced to permit proper articulation of the cast and
  contouring of the restoration.

 It must be free from air bubbles especially in the finish line area.
• High accuracy                      Biocompatibility
    (very small contraction <0.5%)
• High dimensional stability         Compatibility to stone
• High elastic recovery              High tear strength
• Ease of use                        Long shelf life
• Hydrophilic                        Pleasant color &taste
  and Hydrophobic
• Proper setting time                Cost
Elastic recovery
The amount of rebound after a cylinder of material is
strained 10% for 30 seconds.




                                               98%
Hydrophilic VS Hydrophobic
Which one of the impression
materials we choose?
    •What’s the job you do?
         primary impression
         final impression
    •How accurate do you want?
         removable denture
         fixed prostheses
    •What technique do you use?
IMPRESSION MATERIALS
                      Key Properties

a. Accuracy = ability to replicate the intraoral surface details.

b. Dimensional Stability = ability to retain its absolute
   dimensional size over time.
c. Tear Resistance = ability to resist tearing in thin sections
   (such as through the feather-edged material within the
   gingival sulcus.
                    Impression Tray

                      Impression



                                       Accuracy


                                      Dimensional
                                      Stability
                                        Tear
                                        Resistance
        PROBLEM ANALYSIS
What are tolerable limits for “error” in indirect procedures?


          a.   Impressions                =   +/- 0
          b.   Casts, Dies                =   +/- 0
          c.   Waxing                     =   +/- 0
          d.   Investing                  =   + 1.5%
          e.   Casting                    =   - 1.5%
          f.   Finishing, Polishing       =   +/- 0
          g.   Cementation                =   +/- 0

          Prepped
           Tooth          8 mm (=8,000 m)
           Width
                          8,000 m x 0.5% = 40 m = 20 m/side
                          Typical clinical error = >100 m/side
      CLASSIFICATION SYSTEM
               Based on Properties of Set Materials


                                            Properties:   Reaction:   Set:
Rigid:
1.   Impression Plaster                     Rigid         Irrev       (Chem)
2.   Impression Compound                    Rigid         Rev         (Phys)
3.   Zinc Oxide/ Eugenol                    Rigid         Irrev       (Chem)
Water-Based Gel:
4. Alginate (Irreversible Hydrocolloid)     Flexible      Irrev       (Chem)
5. Agar-Agar (Reversible Hydrocolloid)      Flexible      Rev         (Phys)

Elastomers:
6. Polysulfide (Rubber Base, Thiokol)       Flexible      Irrev       (Chem)
7. Silicone (Conventional, Condensation)    Flexible      Irrev       (Chem)
8. Polyether                                Flexible      Irrev       (Chem)
9. Polyvinyl Siloxane (Addition Silicone)   Flexible      Irrev       (Chem)
                  Impression materials
                                                Plaster
            Nonelastic
                                               Impression Compound

                                               Zinc oxide Eugenol

                                             Impression waxes
Impression material
                                           Agar
                         Hydrocolloids
                                         Reversible       Polysulfides
                                            Alginate
             Elastic                                      Polyethers
                                         Irreversible
                                                          Condensation
                         Non-aqueous
                                                            silicone
                          elastomers
                                                            Addition
                                                            silicone
Nonelastic

       Gypsum (Plaster)



       Impression Compound




        Zinc oxide eugenol



       Impression wax
                         Dental Plaster
Dental Plaster
• Type I – impression plaster
• Type II – model (laboratory) plaster (used for mounting casts)
plaster is composed of the β form of calcium sulfate hemihydrate Crystals
• plaster is weaker than dental stone due to:

1.) porosity of the particles, requiring more water for a plaster mix
2.) irregular shapes of particles prevent them from fitting together tightly

Dental Stone
• Type III - dental stone
(diagnostic casts)
• Type IV - high strength
dental stone (working
models)
• Type V - high-strength, high-expansion dental stone

Stone is the α hemihydrate form Types of Gypsum Products
                              Calcination
 Calcination
               H or other means
 Mineral gypsum ---------------- > Model plaster + Water
(CaSO4 . 2H2O) Dental stone      High-strength dental stone (CaSO4 . 1/2H2O)



Reverse Reaction
When calcium sulphate hemihydrate (dental plaster, stone, etc.)
is mixed with water, the reverse reaction takes place, and the
hemihydrate is converted back to the dihydrate:

     CaSO4 . 1/2H2O + 11/2H2O ---> CaSO4 . 2H2O + 3900 cal/g mol
Elastomeric Impression
Materials


 A material that is used when an extremely
 accurate impression is essential. The term
 elastomeric means having elastic or rubberlike
 qualities.
Elastic

                     Agar


    Hydrocolloids


                    Alginate
                    Hydrocolloids

     Reversible and Irreversible
 Introduced by Sears 1939
 First elastic
 Sears AW. Hydrocolloid impression technique for inlays and fixed
  bridges. Dent Digest 1937; 43: 230-234.
 Lin C, Zeiber G J. Accuracy of impression materials for complete
  arch fixed partial dentures. J Prosthet Dent 1988; 59: 288-291
 Philips Science of Dental Materials 11th Ed. Part 2 Pg. 231
Irreversible Hydrocolloid
 Material that cannot return to a solution state after
  it becomes a gel.
 Alginate is the irreversible hydrocolloid most
  widely used for preliminary impressions.
Makeup of Alginate
 Potassium alginate (Alginic Acid) (12-15%)
    Comes from seaweed; is also used in foods such
     as ice cream as a thickening agent.
 Calcium sulfate (8-12%)
    Reacts with the potassium alginate to form the gel.
 Trisodium phosphate
    Added to slow down the reaction time for mixing.
Makeup of Alginate- cont’d
 Diatomaceous earth (70%)
    A filler that adds bulk to the material.
    Controls the stiffness of the set gel
 Zinc oxide
    Adds bulk to the material.
 Potassium titanium fluoride (~10%)
    Added so as not to interfere with the setting and surface
     strength.
 Sodium Phosphate (retarder) (2%)

 Coloring and flavouring agents (traces)
Physical Phases of Alginate
 The first phase is a sol (as in solution). In the sol
  phase, the material is in a liquid or semiliquid form.
  (sol: resembles a solution, but is made up of
  colloidal particles dispersed in a liquid)
 The second phase is a gel. In the gel phase, the
     material is semisolid, similar to a gelatin dessert.
“gel” entangled framework of solid colloidal particles
in which liquid is trapped in the interstices and held
by capillary forces (Jello)
Packaging and Storing of
Alginate
 Containers about the size of a coffee can are the
  most commonly used form of packaging.
 Premeasured packages are more expensive, but
  save time by eliminating the need for
  measurement of the powder.
 Shelf life of alginate is approximately 1 year.
Fig. 46-7 Examples of packaging for alginate.
         Causes for Distortion and
      Dimensional Change of Alginate

 If an alginate impression is stored in water or in a
  very wet paper towel, the alginate will absorb
  additional water and expand. This condition is called
  imbibition.
 If an alginate impression remains in the open air,
  moisture will evaporate from the material, causing it
  to shrink and distort. This condition is called
  syneresis.
ADA Specifications
 <3% deformation with a 10% strain
Altering the Setting Times of Alginate
 Cooler water can increase the setting time if
  additional time is needed for the procedure.
 Warmer water can reduce or shorten the setting
  time of the procedure.
Water-to-Powder Ratio
 An adult mandibular impression generally
  requires two scoops of powder and two measures
  of water.
 An adult maxillary impression generally requires
  three scoops of powder and three measures of
  water.
Fig. 46-8 Scoop and water measure for alginate.
Taking an Alginate Impression
 Explain the procedure to the patient:
    The material will feel cold, there is no unpleasant taste,
     and the material will set quickly.
    Breathe deeply through your nose to help you relax and be
     more comfortable.
    Use hand signals to communicate any discomfort.

 Mouth Preparation

 Rinse and dry the patient's teeth
    If teeth are too dry, alginate will stick
An Acceptable Alginate
Impression
 The impression tray is centered over the central and
    lateral incisors.
   There is a complete "peripheral roll," which includes all of
    the vestibular areas.
   The tray is not "overseated," which would result in
    exposure of areas of the impression tray.
   The impression is free from tears or voids.
   There is sharp anatomic detail of all teeth and soft
    tissues.
   The retromolar area, lingual frenum, tongue space, and
    mylohyoid ridge are reproduced in the mandibular
    impression.
   The hard palate and tuberosities are recorded in the
    maxillary impression.
                     Trouble Shooting
 Inadequate working or setting time:

     temperature of the water, incomplete spatulation
     W/P too low
     improper storage of alginate powder

 Distortion:
    Tray movement during gelation or removed from mouth prematurely
    weight of tray compressing or distorting alginate
 impression not poured up immediately

 Tearing:
    removing impression from mouth before adequately set
    thin mixes (high W/P ratio)
    presence of undercuts (blocking out these areas before an impression may help)
    inadequate amount of impression material in tray (avoided by minimum 3 mm of impression
     material between tray and oral tissues)

 • Loss of detail:
     removed from mouth prematurely
 Consistency:
    preset mix is too thin or thick
    The W/P ratio is incorrect (avoid by fluffing powder before measuring;
     do not overfill powder dispenser)
    inadequate mixing (avoided by vigorous spatulation and mixing for
     recommended time)
    using hot water: grainy and prematurely thick mix

 • Dimensional change:
    delay in pouring
    alginate impression stored in air: results in distorted, undersized cast
     due to alginate impressions losing water when stored in air

 Porosity:
    whipping air into the mix during spatulation (proper mixing: after initial
    wetting of powder by the water, mix alginate so as to squeeze the
     material between the spatula blade and the side of the rubber bowl)

 • Poor stone surface (of cast)
    set gypsum remaining in contact with the alginate for too long a period
     of time
Reversible Hydrocolloid
 An impression material that changes its physical
 state from a sol to a gel and then back to a sol.
Chemical Makeup of Reversible
Hydrocolloid

 85% water
 13% agar
    Agar is an organic substance derived from seaweed.
 Additional chemical modifiers are added to aid in the
  handling characteristics.
  Conditioning Bath for Reversible
            Hydrocolloid
 Three Compartments

       The first bath is for liquefying the semisolid
        material. A special water bath called a
        “hydrocolloid conditioner” at 212° F liquefies the
        material. After liquefying, the preset thermostat
        cools the temperature to 150° F automatically.
       The second bath becomes a storage bath that
        cools the material, readying it for the impression.
        At this temperature, the tubes are waiting for use.
       A third bath is kept at 110° F/44° C for tempering
        the material after it has been placed in the tray.
Types of Reversible Hydrocolloid
 Tray material
    Packaged in plastic tubes. Each tube has enough
     material to fill a full arch, water-cooled tray.
 Syringe material
    Packaged in plastic or glass cartridges that fit a
     syringe or in preloaded syringe or preformed sticks
     that refill special hydrocolloid inlay syringes.
Application of Reversible Hydrocolloid
Impression Material
1.   A stock water-cooled tray is selected, making sure
     that the tray does not impinge on any of the teeth
     or soft tissue.
2.   Plastic stops are placed in the tray.
3.   Tubing is connected to the tray and to the water
     outlet for drainage.
4.   The material is liquefied and moved to the storage
     bath.
5.   The light-bodied material is placed in the syringe,
     and heavy-bodied material is placed in the tray.
6.   The light-bodied material is expressed around the
     prepared tooth, and the dentist seats the tray.
Elastic




                   Polysulfides


                   Polyethers

     Non-aqueous
      elastomers   Condensation
                     silicone


                     Addition
                     silicone
GENERAL FORMULATION
          For Elastic Impression Materials


1.   Flexible Matrix (Continuous Phase):
     a. Multifunctional Pre-Polymer or Polymer
     b. Crosslinking Agent
     c. Curing Agent (Catalyst or Initiator)
     d. Modifiers (Accelerators, Retarders,
         Plasticizers, Flavoring Agents, Colorants)

2.   Filler or Extender (Dispersed Phase):


                               Polymer (high shrinkage)
                             Filled Polymer (low shrinkage)
ELASTOMERIC IMPRESSIONS
                     Management of Shrinkage

Use 2-step techniques:          Impression Tray

                                  Impression
(a) Light-Heavy Body, OR
(b) Wash-Putty
                                                     Load tray with
                                                     heavy-bodied IM

    Cover prep with
     light-bodied IM
        from syringe


During setting shrinkage, distortion of impression is toward tray.


               Impression

                            Dies tend to be oversize and
                            so the casting is oversize.
ELASTOMERIC MATERIALS
                     Mixing and Delivery Systems


    Polyether,
 Polyvinylsiloxane




                                             2x2x2x2x2x2x2x2 = 256 folds
               Polysulfide Rubber,
                Silicone Rubber




Mixing Options:
 2 Pastes on Mixing Pad
 2 Pastes in Mixing Gun
 2 Pastes in Mixing Machine
IMPRESSION MATERIALS
 Management of Distortion During Tray Removal


                           Strain rate sensitive elastomers !


Impression Tray

  Impression                          Fast removal


                   VERY
                   FAST
                  (SNAP)
                                                  Slow removal
IMPRESSION MATERIALS
         Distortion Time Related to Setting Reaction



                       VPS Pe         PS, Silicone
                 100
CONVERSION (%)
  REACTION




                        log TIME (minutes)
Polysulfide Impression
Material
 Chemical makeup
   Base: Mercaptan polysulfide.
   Cross-linking agent: Sulfur and/or lead peroxide.
   Catalysts: Copper hydroxides, zinc peroxide, organic
    hydroperoxide.
   Fillers: Zinc sulfate, lithopone, or calcium sulfate
    dihydrate.
Manipulation and Technique
Considerations for Polysulfide Material
 Dispense pastes at the top of the mixing pad.
 Mix pastes with the tip of a spatula to incorporate the
    material first.
   Transfer the material to the fresh surface of the mixing pad.
   Water, saliva, and blood affect polysulfide material.
   Impression should be removed quickly after setting-do not
    rock the tray.
   Adhesive must be thin and dry before adding the
    impression material.
   Wait 20 to 30 minutes before pouring the impression for the
    stress relaxation to occur in the material.
   Be careful of glove powder contamination of the
    impression.
Polyether Impression Material

 Chemical makeup
   Base: Polyether
   Cross-linking agent: Sulfate
   Catalysts: Glycol-based plasticizers
   Filler: Silica
Manipulation and Technique
Considerations for Polyether Material
 Material is very stiff, which makes it difficult to
    remove without rocking.
   When removing the impression, break the seal and
    rock slightly to prevent tearing.
   Water, saliva, and blood affect polyether material.
   Added moisture will increase the impression’s
    marginal discrepancy.
   Increased water absorption occurs if a thinning
    agent is used.
Silicone Impression Material
 Chemical makeup
   Base: Poly dimethyl siloxane
   Cross-linking agent: Alkyl ortho silicate or organo
    hydrogen siloxane
   Catalyst: Organo tin compounds
   Filler: Silica
Manipulation and Technique
Considerations for Silicone Material
 The material has a limited shelf life.
 The tray requires a special tray adhesive.
 No syneresis or imbibition but does respond with
  shrinkage over time.
 The material is more flexible, so there is more
  chance for distortion during removal.
 Wait 20 to 30 minutes before pouring of models for
  stress relaxation to occur.
Polyvinyl Siloxane Impression Material
 Chemical makeup
   Base: Silicone polym
   Catalyst: Chloroplatinic acid
   Filler: Silica
     Manipulation and Technique
 Considerations for Polyvinyl Siloxane
               Material
 For dimensional stability, this is the best impression
  material.
 Pouring of the model can be delayed up to 7 to 10
  days.
 Stiffness of the material makes removal of the tray
  difficult.
 Material dispensed using auto-mixing unit and
  mixing tips.
  POLYSULFIDE RUBBER
             Chemistry and Setting Reaction

CONTINUOUS PHASE:
   Polymer                        = Mercaptan Functional Polysulfide
   Crosslinking Agent             = Sulfur and/or Lead Peroxide
   Catalysts                      = PbO2 or Copper Hydroxides (Type I)
                                    Zinc Peroxide or
                                    Organic Hydroperoxide (Type II)
DISPERSED PHASE:
    Fillers                       = TiO2 or Zinc Sulfate or
                                    Lithopone or Calcium Sulfate Dihydrate




SETTING REACTION:
    Stepwise (relatively slow), Exothermic, Affected by temperature
        POLYSULFIDE RUBBER
          Manipulation and Technique Considerations

a.    Two-step techniques recommended: Reduces air entrapment and
      surface tension effects.
b.    Material adversely affected by H2O, saliva, and blood.
c.*   Set impression should be removed quickly - do not rock tray.
d.    No syneresis or imbibition, but distortion due to continued reaction.
e.    Ideally need uniform thickness and at least 2 mm thick for accuracy.
      (1) Adhesive must be thin
      (2) Adhesive must be dry
f.    Paste-Paste Mixing Recommendations:
      (1) Dispense pastes at the top of the mixing pad
      (2) Mix pastes with tip of spatula only for 5 seconds
      (3) Transfer mass to fresh surface at center of mixing pad
      (4) Wipe spatula off with paper towel; Strop mass for 15s to constant color
      (5) Load syringe or tray
      (6) Use pad excess to monitor setting time
g.    Pouring of models:
      (1) Wait 20-30 minutes before pour for stress relaxation to occur
      (2) RB is non-reactive with model and die materials
      (3) Be careful of glove powder contamination of impression
      (4) RB can be electroplated
        SILICONE RUBBER
             Chemistry and Setting Reaction

CONTINUOUS PHASE:
   Polymer                        = Polydimethyl Siloxane
   Crosslinking Agent             = Alkyl Orthosilicate or Organo H-Silane
   Catalysts                      = Organo Tin Compounds (e.g., tin octoate)
                                    (but not dibutyl tin dilaurate)
    Modifiers                     = Colorants, Flavorants

DISPERSED PHASE:
    Fillers                       = Silica




SETTING REACTION:
    Stepwise (relatively slow), Exothermic, Affected by temperature
    H2O by-products
            SILICONE RUBBER
        Manipulation and Technique Considerations


a.   Limited shelf-life: Unstable in tubes.
b.   Requires mechanical retention or special tray adhesives
c.   No syneresis or imbibition, but continued polymerization shrinkage.
d.   Better dimensional stability than RHC but more expensive
e.   Pouring of models:
     (1) More flexible so more chance for distortion during removal
     (2) Wait 20-30 minutes before pour for stress relaxation to occur
    POLYETHER RUBBER
            Chemistry and Setting Reactions

CONTINUOUS PHASE:
   Polymer                        = Amine-terminated Polyether
   Crosslinking Agent             = Aromatic Sulfonate
   Catalysts                      =
   Modifiers                      = Colorants, Glycol Plasticizers, Flavorants

DISPERSED PHASE:
    Fillers                       = Silica




SETTING REACTION:
    Stepwise (relatively slow), Exothermic, Affected by temperature
       POLYETHER RUBBER
       Manipulation and Technique Considerations


a.   Excellent impression accuracy and dimensional stability.
b.   Stiff and therefore difficult to remove without rocking.
c.   Break seal and rock slightly to prevent tearing: Low tear resistance.
d.   Negatively affected by H2O, saliva, and blood.
     (1) Since hydrophobic, moisture increases marginal discrepancy
     (2) Increased water absorption occurs if use thinning agents
e.   Can be dispensed from automated extruder and mixer (ESPE PentaMix)
   POLYVINYL SILOXANE
            Chemistry and Setting Reactions

CONTINUOUS PHASE:
   Polymer                       = Double-bond-functional Silicone Polymer
   Crosslinking Agent            = Chloroplatinic Acid
   Catalysts                     =
   Modifiers                     = Colorants, Flavorants, Plasticizers

DISPERSED PHASE:
    Fillers                      = Silica




SETTING REACTION:
    Chain (very fast), Exothermic, Affected by temperature
    Hydrogen gas released by decomposition of crosslinking agent.
        POLVINYLSILOXANE
      Manipulation and Technique Considerations


a.   BEST impression material for dimensional stability:
           Pouring should be delayed at least 4 hours for H2 out-gassing.
           Pouring can be delayed up to 7-to-10 days (or indefinitely).
b.   Stiffness makes removal difficult.
c.   Most material dispensed using auto-mixing gun and mixing tips
COMMERCIAL PRODUCTS
       1980-1995




                   Predominantly
                   POLYSULFIDE and
                   SILICONE elastomers
                   before 1995.
COMMERCIAL PRODUCTS
            1996-2004




     Predominantly POLYETHER and
     PVS elastomers after 1996.
     IMPRESSION MATERIALS
                    Comparison of Key Properties


                                          Poor >---------------------------------> Good
1.   Accuracy (Reproduction of Detail):
     a. Wetting of Tissues:               ALG < SIL, PS < PE <= RHC, PVS
     b. Wetting by Dental Stone:          SIL, PVS < PS < PE <= ALG, RHC

2.   Dimensional Stability:               ALG <= RHC < PS, SIL < PE, PVS
     (Resistance to Distortion):
     a. Polymerization Shrinkage
     b. Thermal Shrinkage
     c. Loss of Components
     d. Stress Relaxation

3.   Tear Resistance (Elasticity):        ALG, RHC, PE < PVS , SIL < PS
     a. Elastic Deformation
     b. Strain Rate Sensitivity
IMPRESSION IMPRESSIONS
              Dimensional Stabilty




      CHANGE (%)
       PERCENT




                   PRODUCT EXAMPLES
Stock tray




  Rim lock tray   Perforated tray
                Stock tray
Special tray
(Custom tray)
Nonelastic

        Plaster



       Impression Compound




        Zinc oxide eugenol



       Impression wax
Elastic

                     Agar


    Hydrocolloids


                    Alginate



     Non-aqueous      Polysulfides
      elastomers
                      Polyethers
                       Condensation
                         silicone
                         Addition
                         silicone
Elastic
                     Agar
    Hydrocolloids

                    Alginate

                     Polysulfides


                      Polyethers

     Non-aqueous
      elastomers      Condensation
                        silicone


                        Addition
                        silicone
    (Ideal Properties)



• High accuracy                      Biocompatibility
    (very small contraction <0.5%)
• High dimensional stability         Compatibility to stone
• High elastic recovery              High tear strength
• Ease of use                        Long shelf life
• Hydrophilic                        Pleasant color &taste
  and Hydrophobic
• Proper setting time                Cost
Impression plaster
ADA type I gypsum product
Impression plaster
For   edentulous impression

Contraindication   for undercut
Composition
Calcium sulfate hemihydrate    (CaSO4)2.H20


Potassium sulfate             Reduce expansion


Borax            Reduce the rate of setting time
Starch                   Help disintegration of
           the impression from plaster model
Reaction

Calcium sulfate hemihydrate + water

       calcium sulfate dihydrate
Mechanical properties
Very low viscosity (mucostatic)
Hydrophilic
Good dimension stability 0.06%
Great accuracy
Manipulation
 Easy to mix, trapping air bubbles
 W/P ratio must be measured out carefully
 Use in special tray, thickness of 1.0-1.5 mm.
 Setting time 2-3 minutes
 Must apply separating medium before pouring
  the impression
 Powder must be stored in air tight
Advantage
Accuracy to soft tissue impression
Good accuracy
Short setting time
Disadvantage
Can not be used in undercut ridge
Able to flow to pharynges
Heat due to reaction
Sensation of dryness
Impression compound




       Type I                Type II

 Impression compound   Green stick compound
Impression with compound



                     Type I




                      Type II
Composition
Natural resin              40%
Waxes                      7%
Stearic acid               3%
Filler&inorganic pigment   50%
RESINS
 Amorphous organic substance which
  are insoluble in water
 Make Thermoplastic
 Shellac, dammar, rosin or sandarac
WAXES
 Straight chain hydrocarbon
  CH3(CH2)nCH3
 Tasteless, Odorless, Colorless
 Make Thermoplastic
 beeswax and colophany
Stearic acid
•Lubricant and Plasticizer

Fillers
Controldegree of flow
Minimize shrinkage
Improve rigidity
Diatomaceous earth, Soapstone, talc
Mechanical properties
 Thermoplastic                     37-45 C๐
 Reversible   physical process
 Very   low thermal conductivity
 High   thermal expansion
 High   contraction coefficients     0.3%
 High   viscosity
Manipulation
   Soften by heating over the flame or water bath
   Do not heat too much          volatile
   Take impression
   Room temperature water cooling
   Pour impression as soon as possible
   Warm the impression before take the cast
             Alcohol lamp
Water bath   Alcohol torch
Advantage
   Can take impression again

 Compatible with model material
Disadvantage
    Very   technique sensitive

    High coefficient of thermal expansion
    => dimensional change

   Mucocompressive

   Must be poured within one hour

   Low detail reproduction
Troubleshooting
 Distortion
 -Material is not completely cooled
 -Flexible tray
 -Delay in pouring
Troubleshooting
 Compound is too brittle or grainy


 -Prolong immersion in the water bath
Zinc oxide-eugenol
Impression paste
Zinc oxide-eugenol
 Impression paste
Zinc oxide-eugenol
 For full arch edentulous impression without or minor
    undercut

   Wash impression

   Bite registration
 Temporary cementation
 Temporary filling
Composition (base)
 Zinc oxide (ZnO)
 Oil
 Hydrogenated rosin
 Zinc acetate                 Accelerator
 Trace of water       Initiator
Composition (reactor)
 Eugenol                12~15%
 Oil
 Rosin
 Filler (kaolin)



Non eugenol paste   Carboxylic acids
Reaction
ZnO + eugenol         Zn eugenolate + ZnO(unreacted)

(powder)   (liquid)




                                   (Solid)
Mechanical properties
@ Very low viscosity



@ Irreversible chemical change

@ Low dimensional change         0.1%
Manipulation
Manipulation
 Equal length of the two paste is extruded

 Mixed with stainless steel spatula in paper
  pad or glass slab
 Mixing time                       45-60 s
   Working time                     3-5 min
            shorten by increase

          Temperature&Humidity
Advantage
 Accuracy of soft tissue impression (mucostatic)


   Good dimensional stability
   Good surface detail reproduction
 Inexpensive
 Adhere well to dental compound
Disadvantage
 Messiness
Non elastic Time
Unstable setting
 May irritating to soft tissue
Troubleshooting
 Inadequate working or setting time
 -excessive humidity and/or temperature

 Distortion
 -unstable tray
Impression wax
KORECTA WAX , IOWA WAX
Manipulation
 Functional Impression
            Disinfection of Impression
                    Materials
 Irreversible Hydrocolloids (Alginate)
     Diagnostic Casts:
          Soak 10 min in Gluteraldehyde

     Final Impressions:
        Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under damp gauze 10 min
        Spray with Sodium Hypochlorite rinse, spray again & let stand under damp gauze 10 min

 Reversible Hydrocolloid
          Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under damp gauze 10 min
          Spray with Sodium Hypochlorite rinse, spray again & let stand under damp gauze 10 min

   Addition –reaction Silicones
          In Gluteraldehyde 1 hr.,
          Rinse sterile water
          Soak in fresh solution Gluteraldehyde 10 min

 Zinc oxide eugenol
          Soak in Gluteraldehyde 10 min

 Silicone Impressions
          Soak for 10 min Gluteraldehyde

 Polyether Impressions
          Dip in Gluteraldehyde ,rinse in sterile water, dip again let stand under damp gauze 10 min


    Fundamentals of Removable Partial Dentures 2nd Ed. CP Owen
REFERENCES
•Skinner’s Science of Dental Materials
•Dental Materials and Their Selection (William J. O’Brien)
•Introduction to dental materials (Richard Van Noort)
•Dr Sukontip Arwatchanakan
•Science of Dental Materials Phillips 11th Ed.
•Stephen C. Bayne Department of Operative Dentistry School of Dentistry
University of North Carolina

• Mr. Robert Seghi Alginate Impression Materials (alginate lecture 2006.ppt)
Tray Selection Criteria
 Feel comfortable to the patient.
 Extends slightly beyond the facial surfaces of the
  teeth.
 Extends approximately 2 to 3 mm beyond the third
  molar, retromolar, or tuberosity area of the arch.
 Is sufficiently deep to allow 2 to 3 mm of material
  between the tray and incisal or occlusal edges of the
  teeth.
Characteristics of Impression Trays
 Quadrant tray
    Covers one half of the arch.
 Section tray
    Covers the anterior portion of the arch.
 Full arch tray
    Covers the entire arch.
 Perforated tray
    Holes in the tray create a mechanical lock to hold the
     material in place.
 Smooth tray
    Interior of the tray is painted or sprayed with an
     adhesive to hold the impression material.
Impression Trays
 Must be sufficiently rigid to:
   Carry the impression material into the oral cavity.
   Hold the material in close proximity to the teeth.
   Avoid breaking during removal.
   Prevent warping of the completed impression.
Table 46-1 Types of Stock Trays
Fig. 46-3 Examples of quadrant, section, and
full-arch impression trays.
Tray Adhesives
 VPS adhesives (blue)
    For polyvinyl siloxane and polyether impression
     materials.
 Rubber Base Adhesive (brown)
    Used with rubber base impression materials.
 Silicone Adhesive (orangish-pink)
    Used with silicone impression materials.
Characteristics or Elastomeric
Impression Materials
 Base
   Packaged as a paste in a tube, as a cartridge, or
    as putty in a jar.
 Catalyst
   Also known as the accelerator, is packaged as a
    paste in a tube, as a cartridge, or as a liquid in a
    bottle with a dropper top.
Forms of Elastomeric Materials
 Light-bodied
    Also referred to as syringe type, or wash type. This
     material is used because of its ability to flow in and
     about the details of the prepared tooth. A special
     syringe, or extruder, is used to place the light-bodied
     material on and immediately around the prepared
     teeth.
Forms of Elastomeric Materials- cont’d
  Regular and heavy-bodied
    Often referred to as tray-type materials, they are
     much thicker. As the names imply, they are used to fill
     the tray. Their stiffness helps to force the light-bodied
     material into close contact with the prepared teeth
     and surrounding tissues to ensure a more accurate
     impression of the details of a preparation.
Basic Impression Technique
1.   The material selected depends upon the dentist’s preference
     and the type of impression required for the procedure.
2.   The dentist prepares the tooth or teeth for the impression.
3.   The light-bodied material is prepared and loaded into the
     syringe and transferred to the dentist.
4.   The dentist places the light-bodied material over and around
     the prepared teeth and onto the surrounding tissues.
5.   The heavy-bodied material is prepared and loaded into the
     tray and transferred to the dentist.
6.   When the impression material has reached final set, the
     impression is removed and inspected for accuracy.
7.   The impression is disinfected, placed in a biohazard bag,
     labeled, and readied for the laboratory technician.
Curing Stages of Elastomeric Materials
  Initial set
     The first stage results in stiffening of the paste
      without the appearance of elastic properties. The
      material may be manipulated only during this first
      stage.
  Final set
     The second stage begins with the appearance of
      elasticity and proceeds through a gradual change to
      a solid rubberlike mass. The material must be in
      place in the mouth before the elastic properties of
      the final set begin to develop.
  Final cure
     The last stage occurs from 1 to 24 hours.
Types of Elastomeric
Materials
  Polysulfide
  Polyether
  Silicone
  Polyvinyl siloxane
Occlusal Registration
 An accurate registration of the normal centric
 relationship of the maxillary and mandibular
 arches. Also commonly referred to as the bite
 registration.
Types of Occlusal Registration

  Wax bite
    Useful when the diagnostic casts are trimmed.
    The most common technique is to use a softened
     baseplate wax.
Fig. 46-27 Wax bite registration.
Types of Occlusal Registration- cont’d
  Polysiloxane bite registration paste: Supplied
  both as a paste system and also as cartridges.
    The material is fast setting.
    There is no resistance to biting forces.
    There is no odor or taste for the patient.
    It gains dimensional stability over time.
    It is convenient to use.
Types of Occlusal Registration- cont’d
  Zinc oxide-eugenol (ZOE) bite registration paste
     ZOE paste has little to no resistance to bite closure
      and is a fast-setting material.
     Material is supplied in a paste system and
      dispensed onto a paper pad, mixed, and placed
      onto a gauze tray for the patient to bite into.

				
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