7+ +Impressions

of 57

  • date post

    14-Apr-2018
  • Category

    Documents

  • view

    218
  • download

    0

Embed Size (px)

Transcript of 7+ +Impressions

  • 7/30/2019 7+ +Impressions

    1/57

    Impressions in FixedProsthodontics

  • 7/30/2019 7+ +Impressions

    2/57

    Impressions

    Imprint or negative reproduction, made byplacing soft, semi-fluid material in the mouth tillthe complete setting.

    positive reproduction or cast

  • 7/30/2019 7+ +Impressions

    3/57

    ImpressionsRequirements:

    Accurate reproduction of the prepared tooth(prepared and uncut surface).

    Accurate reproduction of other teeth and tissueadjacent to the prepared tooth.

    Absence of bubbles.

  • 7/30/2019 7+ +Impressions

    4/57

  • 7/30/2019 7+ +Impressions

    5/57

    Successful Impression

    Choice of Impression Material

    Technique of Impression

  • 7/30/2019 7+ +Impressions

    6/57

    Impression materials

    Impression materials are commonly classified byconsidering their elastic properties once set.

    non-elastic materials elastic materials

  • 7/30/2019 7+ +Impressions

    7/57

    Properties of Impression materials

    Wettability

    Viscosity Dimensional stability

    Cost

  • 7/30/2019 7+ +Impressions

    8/57

    Wettability

    Ease of pouring with gypsum products

    Defect free impression no air bubbles

    hydrophilic, ex.: polyether, hydrocolloids,

    hydrophobic, ex.: polysulfide, silicones

  • 7/30/2019 7+ +Impressions

    9/57

    Viscosity

    Viscosity fluidity

    consistency: light, medium, heavy, putty

  • 7/30/2019 7+ +Impressions

    10/57

    Viscosity

  • 7/30/2019 7+ +Impressions

    11/57

    Viscosity

    Thixotropy: property that allows a material to stay in atray without dripping and have low viscosity to beused in a syringe.

    viscosity of the material is reduced by increasing the

    shear rate

  • 7/30/2019 7+ +Impressions

    12/57

    Elastic impression materials

    Hydrocolloids Elastomeres

    Reversible Irreversible PolysulfidePolyether

    Silicone

  • 7/30/2019 7+ +Impressions

    13/57

    Elastic impression materials

    Hydrocolloids Elastomers

    Reversible Irreversible

    (Agar agar) (alginate)

  • 7/30/2019 7+ +Impressions

    14/57

    Reversible hydrocolloid (Agar)

    Passes repeatedly between highly viscous gel and lowviscosity sol simply through heating and cooling

  • 7/30/2019 7+ +Impressions

    15/57

  • 7/30/2019 7+ +Impressions

    16/57

    Reversible hydrocolloid

    need expensive conditioning baths and water cooled

    trays

    poor dimensional stability

    low tear resistance

  • 7/30/2019 7+ +Impressions

    17/57

    Irreversible hydrocolloid

  • 7/30/2019 7+ +Impressions

    18/57

    Irreversible hydrocolloid

    alginatevery poor dimensional stability

    Temp. affects the setting time

    low tear resistance

  • 7/30/2019 7+ +Impressions

    19/57

    Elastic impression materials

    Hydrocolloids Elastomers

    Reversible Irreversible Polysulfide

    Polyether

    Silicone

  • 7/30/2019 7+ +Impressions

    20/57

    Polysulfides light body (low viscosity), medium or regular body

    and heavy body (high viscosity).

  • 7/30/2019 7+ +Impressions

    21/57

    PolysulfidesAdvantages:

    long working time (decreased by raising temperature or

    moisture) excellent tear resistance

    cheap

  • 7/30/2019 7+ +Impressions

    22/57

    Polysulfides

    Disadvantages:

    setting reaction long

    messy to handle

    objectionable odor

    Shrinkage as a result of a continued settingreaction + evaporation of water produced as aby-product of the setting reaction

  • 7/30/2019 7+ +Impressions

    23/57

    Polyethers single regular viscosity

    heavy light bodied system

  • 7/30/2019 7+ +Impressions

    24/57

    PolyethersAdvantages:

    no reaction by-product dimensional stability

    adequate tear resistance very good elastic properties

    hydrophilic

    Disadvantages:

    high elastic modulus ,rigid when set

    absorption of water on storage in conditions of highhumidity

  • 7/30/2019 7+ +Impressions

    25/57

    Silicones Classified according to their method of

    polymerisation on setting

    condensation curing (or Type I) silicones and addition curing (or Type II) silicones.

    Available in: light, medium, heavy and puttyviscosities

  • 7/30/2019 7+ +Impressions

    26/57

    Silicones (condensation-cured) good elastic properties

    adequate tear resistance

    non-toxic and absolutely neutral in both colorand taste.

  • 7/30/2019 7+ +Impressions

    27/57

    Silicones (condensation-cured) setting reaction produces a volatile by-product (ethyl

    alcohol)

    shrinkage

    Highly hydrophobic

  • 7/30/2019 7+ +Impressions

    28/57

    Silicones (condensation-cured)

  • 7/30/2019 7+ +Impressions

    29/57

    Silicones (addition-cured) Highly dimensionally stable (pouring can be delayed

    7-10 days)

    Adequate tear resistance

    Excellent elastic recovery

  • 7/30/2019 7+ +Impressions

    30/57

    Silicones (addition-cured) release of H2 that produces bubbles in models

    prepared within the 1st hour

    hydrophobic

  • 7/30/2019 7+ +Impressions

    31/57

    Silicones (addition-cured) Setting inhibition caused by some brands of latex

    gloves.

  • 7/30/2019 7+ +Impressions

    32/57

    Silicones (addition-cured)

  • 7/30/2019 7+ +Impressions

    33/57

  • 7/30/2019 7+ +Impressions

    34/57

    Trays

    Tray selection depends on impression material used

    and viscosity Irreversible hydrocholloid and most elastomeric

    impressions can be made using prefabricatedimpression trays

    A custom tray improves the accuracy of elastomericimpression by limiting the volume of material

    The opposite is true regarding hydrocholloids

  • 7/30/2019 7+ +Impressions

    35/57

    Mixing

  • 7/30/2019 7+ +Impressions

    36/57

    Impression Technique

    Usually we use two viscosities

    1- high (heavy body or putty): make the bulk of theimpression

    2- low (light body or wash): gives details

  • 7/30/2019 7+ +Impressions

    37/57

    Two step putty/wash

    One step double mix

    Monophase ,single mix

    Impression Techniques

  • 7/30/2019 7+ +Impressions

    38/57

    Two-step technique

    (high pressure) putty is recorded first and after setting relined with a

    thin layer of wash

    Used with condensation silicon and additional silicone

  • 7/30/2019 7+ +Impressions

    39/57

    Two-step technique

    (high pressure)

  • 7/30/2019 7+ +Impressions

    40/57

    Two-step technique

    (high pressure)

  • 7/30/2019 7+ +Impressions

    41/57

    Two-step technique

    (high pressure)

  • 7/30/2019 7+ +Impressions

    42/57

    Two-step technique

    (high pressure)

  • 7/30/2019 7+ +Impressions

    43/57

    Two-step technique

    (high pressure) Suitable for subgingival margins

  • 7/30/2019 7+ +Impressions

    44/57

    One step, double mix technique

    (low pressure) putty and wash are recorded simultaneously (also

    called twin mix or laminate technique)

    Tray: putty or heavy viscosity

    Syringe: low viscosity

  • 7/30/2019 7+ +Impressions

    45/57

  • 7/30/2019 7+ +Impressions

    46/57

  • 7/30/2019 7+ +Impressions

    47/57

  • 7/30/2019 7+ +Impressions

    48/57

  • 7/30/2019 7+ +Impressions

    49/57

  • 7/30/2019 7+ +Impressions

    50/57

  • 7/30/2019 7+ +Impressions

    51/57

  • 7/30/2019 7+ +Impressions

    52/57

  • 7/30/2019 7+ +Impressions

    53/57

    Monophase , single mix technique

    One viscosity:

    In the custom tray and syringe

  • 7/30/2019 7+ +Impressions

    54/57

    Evaluation Proper mix: no visible streaks of base or catalyst

    Accurate seating of the tray: custom tray should notshow through

    Absence of voids, folds or creases especially in criticalarea around finish line

    Even un-interrupted extension of impression material

    beyond the margins of the preparation No seperation between impression material and the

    tray

  • 7/30/2019 7+ +Impressions

    55/57

  • 7/30/2019 7+ +Impressions

    56/57

    Disinfection

  • 7/30/2019 7+ +Impressions

    57/57

    ThanQ