Impression Materials Miu

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    Material is introduced in the mouth in a plastic condition to set against the oral tissues. It is then removed from the mouth when hardened .

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    4 5 6

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    The set impression is a negative reproduction of the oral tissues.

    A positive reproduction is obtained by pouring a suitable model or die material into it.

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    Ideal Re uirements of anIdeal Re uirements of an impression materialimpression material

    1. Accuracy:. Accuracy: a restoration or an appliance fabricated in thea restoration or an appliance fabricated in the laboratory cannot be more accurate than thelaboratory cannot be more accurate than the impression from which the used model isimpression from which the used model is

    prepared.prepared. 2. Biologically acceptable:. Biologically acceptable:

    An impression material should beAn impression material should be non-toxic, non-non-toxic, non- irritant and of acceptable odour and tasteirritant and of acceptable odour and taste ..

    33 . . It shouldIt should not be affected by the oral fluidsnot be affected by the oral fluids .. 4.4. Easily manipulated Easily manipulated , with minimal equipment., with minimal equipment. 5.5. It should have aIt should have a suitable wor in! timesuitable wor in! time to allowto allow for placement of the impression material in thefor placement of the impression material in the

    tray and then insertion of the tray into the mouthtray and then insertion of the tray into the mouthbefore be!innin! of hardenin!.before be!innin! of hardenin!.

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    Accuracy of the impression materials"Accurac

    y of the impression materials" #.#. $i!h$i!h flow at the beginning flow at the beginning , i.e. the material must be, i.e. the material must be

    in a fluid or plastic state on insertion into the mouth,in a fluid or plastic state on insertion into the mouth, totorecord fine detailsrecord fine details ..

    %.%. Dimensionally accurate Dimensionally accurate "" shouldshould not expand, contractnot expand, contract or warpor warp durin! settin!durin

    ! settin! ..

    3.3. Dimensionally stable Dimensionally stable "" onon stora!estor

    a!e of the impression inof the impression inthe dental laboratory before pourin! the castthe dental laboratory before pourin! the cast

    4.4. &hould be&hould be elastic on removal from the mouthelastic on removal from the mouth so thatso that undercuts can be recordedundercuts can be recorded without distortionwithout distortion of theof the impression.impression.

    5.5. 'urin! removal from the mouth, it should be'urin! removal from the mouth, it should be adherent to the trayadherent to the tray ..

    (.(. Compatible with the gypsum productsCompatible with the gypsum products "" not need anot need a

    separatin! medium.separatin! medium.

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    Classification of Impression MaterialsClassification of Impression Materials

    I!"ccording to manner of setting#!I!"ccording to manner of setting#! 1$1$ %hemical &irreversi'le$#%hemical &irreversi'le$#

    harden through a chemical reaction(harden through a chemical reaction( e)g)e)g) plaster impression(plaster impression(

    *inc o+ide and eugenol( alginate and ru''er 'ase impression*inc o+ide and eugenol( alginate and ru''er 'ase impression

    materials)materials)

    2$2$ ,hysical &reversi'le$#, hysical &reversi'le$# they set as a result of a change of temperature withoutthey set as a result of a change of temperature without

    chemical changes(chemical changes( e)g)e)g) agar agar( impression compound andagar agar( impression compound and

    impression wa+es)impression wa+es)

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    II. )ehavior after settin!"II. )ehavior after settin !" 'ependin! on their'ependin! on their ability to re!ain theirability to re!ain their ori!inal shape after removal from theori!inal shape after removal from the undercuts.undercuts.

    #. Inelastic#. Inelastic impression materials e.!. wax,impression materials e.!. wax, *laster of *aris, +n eu!enol and impression*laster of *aris, +n eu!enol and impression compound. hey are used only when nocompound. hey are used only when no undercut exists.undercut exists.

    %. /lastic%. /lastic impression materials e.!. impression materials e.!.

    hydrocolloids and rubber impression materials.hydrocolloids and rubber impression materials.

    hey can be used whenhey can be used when undercut exists.undercut exists.

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    Impression 0aterialsIm pression 0aterials

    Inelastic Inelastic Elastic Elastic Plaster of Plaster of Impression Impression Zinc oxide Zinc oxide

    Paris Paris compoundcompound eugenol eugenol

    Hydrocolloids Elastomers Hydrocolloids Elastomers

    gar gar lginate gar gar lginate

    Polysulphide !ilicones Polyether Polysulphide !ilicones Polyether

    Condensation dditionCondensation ddition

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    According to uses According to uses

    Edetulous Patient

    Partialy edentulous patient

    Plaster, impression compound and Zinc oxide and eugenol, hydocolloids, rubbers

    Hydocolloids, rubbers

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    According to the Accuracy According to the Accuracy

    1ry Impression

    (stock tray)

    2ry Impression

    (special tray) ompound

    impression material

    !lginate impression

    material

    Plaster impression material

    Zinc oxide"eugenol impression material

    !gar !gar impression material

    #ubbers impression materials

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    *laster of *aris*laster of *aris Used for impression ofUsed for impression of edentulous patientsedentulous patients ..

    1omposition"1om position" powder 2 waterpowder 2 water "#"# ## Ca!$%."&'H'$Ca!$%."&'H'$ (( notnot and or improvedand or improved stonestone

    because"because"

    )ea*er+)ea*er+ So it will break during removal from the undercut and thus avoidsSo it will break during removal from the undercut and thus avoidsinjury to the patient and the fractured part can be reassembled accuratelinjury to the patient and the fractured part can be reassembled accuratel $i!her * ratio$i !her * ratio ,, which increases the flow at the beginning and thuswhich increases the flow at the beginning and thus

    records fine details.records fine details.

    ess exothermic heatess exothermic heat evolved during taking of the impressionevolved during taking of the impression .. '. ,odifiers+'. ,odifiers+ 66 47 8 66 47 8 %%&& 44 decreases the setting expansion and the setting timdecreases the setting expansion and the setting tim

    99 6666 #7 borax#7 borax as a retarder as a retarder

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    -. atural gums+-. atural gums+ Improve itsImprove its handlin! characteristicshandlin! characteristics . They. They increase its cohesion and facilitate border moldingincrease its cohesion and facilitate border molding of the impression.of the impression.

    %. /lavoring agent+%. /lavori ng agent+ oreore acceptable to the patientacceptable to the patient , through, through

    agreeable taste.agreeable taste.

    0. Coloring materials+0. Colori ng materials+ !istinguish the impression!istinguish the impression from the cast, whichfrom the cast, which will also be made of gypsum products.will also be made of gypsum products.

    1. Potato starch+1. Potato starch+

    To obtain theTo obtain the soluble plastersoluble plaster . "fter the impression. "fter the impression is cast and hardened, it is soaked in hot water andis cast and hardened, it is soaked in hot water and thethe starch swellsstarch swells and the impression disintegratesand the impression disintegrates and will beand will be easy to removeeasy to remove ..

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    Accuracy of plaster impression "

    a)a) -aterial is-aterial is semi!fluid when insertedsemi!fluid when inserted into the mouthinto the mouth it hasit has e+cellent recordinge+cellent recording of the fine details)of the fine details)

    ')') TheThe dimensional changes on setting in the mouthdimensional changes on setting in the mouth are negligi'leare negligi'le due to anti!e+pansion additives)due to anti!e+pansion additives)

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    c.c. A plaster impressionA plaster impression fractures on removalfractures on removal from undercutsfrom undercuts and can be reassembled.and can be reassembled.

    e.e. Elasticity+ Elasticity+ )ein! inelastic, it will)ein! inelastic, it will not recordnot record the formthe form of the under cut.of the under cut.

    f.f. hen pourin! a plaster impression in plaster orhen pourin! a plaster impression in plaster orin stone,