BiomatII- Final Impressions

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    TUFTS UNIVERSITY SCHOOL OF

    DENTAL MEDICINE

    Tissue Management and

    Impression Making

    Ekaterini Antonellou D.D.S.

    Division of Prosthodontics

    Department of Prosthodontics and

    Operative Dentistry

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    After tooth preparation and temporization , we

    should make a final impression in order to fabricate

    a restoration

    Impression= Negative likeness of the teeth

    and the surrounding structures.

    It is the link between the prepared teeth and

    the cast on which we make the crown.

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    GOALS FOR A FINAL IMPRESSION

    Accurate

    Detailed No voids

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    PROPERTIES OF IMPRESSION

    MATERIALS

    Elasticity/rigidity -

    Flow-

    Tear strength-

    Hydrophilic- material to tolerate moisture in an impression site

    Accuracy/Dimensional stability- Working and setting time

    Ease of manipulation

    Cost effectiveness

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    Irreversible hydrocolloid(alginate)

    Used for diagnostic impressions andremovable dentures and partials

    Advantages : - Rapid set

    - Straightforward technique- Low cost

    Disadvantages:- Poor accuracy and surface

    detailPrecautions: - Pour immediately

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    Reversible hydrocolloid (agar)

    Used for multiple preparations or with problemswith moisture

    Advantages : - Rapid set

    - Low cost of actual materialDisadvantages: - Low tear resistance

    - Low stability

    - Equipment needed- Special trays needed

    Precautions: - Pour immediately

    - Use only with stone

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    Polysulfide Polymer

    Currently used mostly for removable dentures and partials Advantages : - High tear strength

    - Easier to pour than otherelastomers

    - Low cost

    Disadvantages: - Messy- Unpleasant odor

    - Long setting time

    - Stability only fair

    - Humidity and temperature reduce

    working time

    Precautions: - Pour within 1 hour

    - Use of a custom tray to minimizethe contraction of polysulfide polymerization

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    Condensation silicone

    Used mostly for lab procedures

    Advantages : - Relative short setting time

    Disadvantages:- Poor wetting

    - By products of polymerizationreaction are alcohol and water. Asa result , evaporation from the setmaterial causes dimensional

    stabilityPrecautions: - Caution to avoid bubbles when

    pouring

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    Polyether (Impregum)

    Used for most impressions ,except for very long and thin teeth

    Advantages : - Dimensional stability (can be poured morethan once ,even the next day)

    - Accuracy

    - Low polymerization shrinkage

    - Relatively short setting time- Automix available(pentamix machine)

    Disadvantages:- Set material very stiff

    - Absorption of water (should bestored dry)

    Precautions: - Care not to break the teeth whenseparating the cast

    - Block undercuts

    - Care for perio involved teeth

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    Addition silicone(Poly-Vinyl-siloxane)

    Used for most impressions

    Advantages : - Great dimensional stability (can be poured

    more than once ,even the next day)- Accuracy

    - Very short setting time

    - Automix available

    Disadvantages:- Hydrophobic

    - Poor wetting-Some materials release Hydrogen .

    Newer materials contain scavengers to

    prevent the release of gasPrecautions: - Care to avoid bubbles when pouring

    - Setting inhibition for some putties by latexgloves

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    Tissue Health

    Control of periodontal disease

    Proper contour, margins and surface of

    provisional restoration Oral hygiene

    Use of Chlorhexidine (Peridex or Periogard)

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    Saliva control

    Use of cotton rolls and dry-angles to cover

    the salivary ducts

    Use of saliva evacuators Use of local anesthesia

    Prescription of anticholinergics e.g. atropine

    or pilocarpine

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    Displacement of gingival tissues

    Mechanical displacement with non-impregnated

    cord.It is better if it is braided(Gingibraid, Van R)orknitted(Ultrapak ,Ultradent)

    Chemically impregnated cord in anastrigent(Hemodent) . They contain aluminum oriron salts that cause ischemia. Aluminum chlorideand ferric sulfate are suitable because they cause

    minimum tissue damage. Preimpregnated cords with epinephrine should be

    used with caution

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    Displacement of gingival tissues

    The inner epithelial lining of the gingival sulcus is

    removed

    Access for a subgingival crown margin

    Control of postsurgical hemorrhage

    Passage of a high-frequency current through the

    tissue from a large electrode to a small one. At

    the small electrode the current induces rapidlocalized polarity changes that cause cell

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    Displacement of gingival tissues

    Electrosurgery

    Profound local anesthesia is needed

    Not suitable on thin attached gingiva

    It should not be used with metal instruments The electrode should not touch any metallic

    restoration (can cause pulp damage)

    It should not be used on or near patientswith cardiac pacemaker or insulin pump

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    Disinfection

    Glutaraldehyde 2% 10 min soak (not for

    polyether)

    Iodophor (1:213 dilution)

    Chlorine compounds (1:10 dilution of

    commercial bleach)

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    Final steps

    Re-evaluation of the final impression

    Interocclusal record Shade selection

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