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A small mound of the original mix of alginate can be placed ... Weigh powder Powder added to water rubber bowl vacuum mixer Mixed for 45 sec to 1 min Place tray ... – PowerPoint PPT presentation

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  • Presented by
  • Dr. Kamleshwar Singh
  • BDS, MDS, ICMR-IF(Japan)
  • Assistant Professor
  • Department of Prosthodontics
  • King Georges Medical University, Lucknow

  • Impression
  • A negative likeness or copy in reverse of the
    surface of an object imprint of teeth and
    adjacent structures for use in dentistry. GPT 8
  • Partial denture impression
  • A negative likeness of a part or all of a
    partially edentulous arch - GPT 8

  • An impression of partially edentulous arch must
    record accurately the anatomic form of teeth and
    surrounding tissues.
  • Unless the cast upon which the prosthesis is to
    be constructed is an exact replica of mouth, the
    prosthesis cant be expected to fit properly and
    accurate cast can be obtained only from an
    accurate impression.

  • Impression trays
  • A receptacle in to which suitable impression
    material is placed to make negative likeness
  • OR
  • A device that is used to carry, confine and
    control impression material while making an

(No Transcript)
  • Impression trays can be classified broadly into
  • stock trays
  • and
  • custom trays
  • Stock trays for partially edentulous patients
    may be perforated to retain the impression
    material or they may be constructed with a
    rimlock for this purpose.
  • Another type of stock tray designed for the
    reversible type of hydrocolloid is water cooled
    trays. It contains tubes through which water can
    be circulated for purpose of cooling the tray.

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  • Modified stock tray (individual tray)
  • Robert R Renners technique
  • The stock tray can be modified with modeling
    composition and with wax to create an accurately
    fitting tray.
  • This technique can be employed in class I and
    class II cases.
  • Technique
  • Softened modeling compound is placed in the
    stock impression tray in such a way that it may
    capture the edentulous areas of mouth and include
    one or two teeth adjacent to the space.

  • Modified stock tray (individual tray)
  • Robert R Renners technique
  • The stock tray can be modified with modeling
    composition and with wax to create an accurately
    fitting tray.
  • This technique can be employed in class I and
    class II cases.
  • Technique
  • Softened modeling compound is placed in the
    stock impression tray in such a way that it may
    capture the edentulous areas of mouth and include
    one or two teeth adjacent to the space.

  • The tray is positioned in the mouth and
    compound is allowed to cool but it not permitted
    to harden completely, so that it is prevented
    from becoming hard when in contact with the
    adjacent teeth.
  • When it is hardened sufficiently to contour it
    is removed from the mouth and thoroughly chilled.

  • The compound is trimmed so that it does not
    contact the adjacent teeth and surface of
    compound in the edentulous areas is scraped to a
    depth of 2 - 4 mm to provide space for a uniform
    layer of impression material.
  • In maxillary impression the compound should
    cover the edentulous ridges and the palate and
    should accurately fit to post dam area.

  • Modification of the tray to make it adhesive
  • If Impression material to be used is either
    alginate or agar, we can heat surface of compound
    with a flame.
  • An alternate method Is to paint the surface
    of compound with a solvent such an chloroform to
    make it tacky and then to embed cotton fibers in
    it, the impression material will become enmeshed
    in cotton fiber. And if rubber base material is
    to be employed rubber adhesive is painted on the

  • Advantages over custom tray
  • 1. Impression can be accomplished in one
  • 2. Can be used inpatient with tendency to gag.
  • Advantages over conventional use of stock stray
  • Especially useful for mouth that is either
    exceptionally large or small or the one with
    anomalous contour which cannot be accurately
    fitted with conventional stock tray.

  • Disadvantages STOCK TRAY
  • a. The peripheral borders cannot be accurately
  • b. Considerably more bulkier than a custom tray.

  • Custom impression trays
  • a. Peripheral borders can be precisely recorded
    in the impression
  • b. Thickness of impression material can be
    controlled. This is important consideration when
    using rubber base type material, which should not
    exceed thickness of 2-4 mm because a section
    thicker than this is subject to distortion.

  • C. Well fitted tray will better support the
    impression in the palate, then avoiding even
    present danger of material slumping in vital
  • Custom trays are sometimes needed for mouths
    that are abnormally or of unusual configuration.

Impression Materials
  • Factors that influence the selection of
    impression materials are
  • Convenience of use
  • Time of manipulation and set
  • Cost
  • Need for special trays
  • Operator training and preference

Impression Materials
Impression Materials
Agar (reversible)
Aqueous Hydrocolloids
Alginate (irreversible)
Non-aqueous Elastomers
OBrien Dental Materials their Selection 1997
Reversible Hydrocolloid (Agar)
  • Indications
  • crown and bridge
  • high accuracy
  • Example
  • Slate Hydrocolloid (Van R)

  • Agar
  • complex polysaccharide
  • seaweed
  • gelling agent
  • Borax
  • strength
  • Potassium sulfate
  • improves gypsum surface
  • Water (85)

OBrien Dental Materials their Selection 1997
  • Gel in tubes
  • syringe and tray material

  • 3 chamber conditioning unit
  • (1) liquefy at 100C for 10 minutes
  • converts gel to sol
  • (2) store at 65C
  • place in tray
  • (3) temper at 46C for 3 minutes
  • seat tray
  • cool with water at 13C for 3 minutes
  • converts sol to gel

OBrien Dental Materials their Selection 1997
  • Dimensionally accurate
  • Hydrophilic
  • displace moisture, blood, fluids
  • Inexpensive
  • after initial equipment
  • No custom tray or adhesives
  • Pleasant
  • No mixing required

Phillips Science of Dental Materials 1996
  • Initial expense
  • special equipment
  • Material prepared in advance
  • Tears easily
  • Dimensionally unstable
  • immediate pour
  • single cast
  • Difficult to disinfect

Phillips Science of Dental Materials 1996
Irreversible Hydrocolloid (Alginate)
  • Most widely used impression material
  • Indications
  • study models
  • removable fixed partial dentures
  • framework
  • Examples
  • Jeltrate (Dentsply/Caulk)
  • Coe Alginate (GC America)

Phillips Science of Dental Materials 1996
  • Sodium phosphate
  • retarder
  • Filler
  • Potassium fluoride
  • improves gypsum surface
  • Sodium alginate
  • salt of alginic acid
  • mucous extraction of seaweed (algae)
  • Calcium sulfate
  • reactor

OBrien Dental Materials their Selection 1997
  • Weigh powder
  • Powder added to water
  • rubber bowl
  • vacuum mixer
  • Mixed for 45 sec to 1 min
  • Place tray
  • Remove 2 to 3 minutes
  • after gelation (loss of tackiness)

Caswell JADA 1986
  • Inexpensive
  • Easy to use
  • Hydrophilic
  • displace moisture, blood, fluids
  • Stock trays

Phillips Science of Dental Materials 1996
  • Tears easily
  • Dimensionally unstable
  • immediate pour
  • single cast
  • Lower detail reproduction
  • unacceptable for fixed prosthodontics
  • High permanent deformation
  • Difficult to disinfect

Phillips Science of Dental Materials 1996
  • The complete denture impression records the
    edentulous mucosa with underlying bone only,
    whereas partial denture impression records not
    only relative soft yielding tissues (the oral
    mucosa) as well as a hard unyielding substance
    (the remaining teeth).

  • Removable partial denture impression need to
    record the teeth that are irregular in contour as
    well as varying in their vertical relations to
    occlusal plane. The chosen impression material
    must be capable of recording the tissue contours
    as accurately as possible without distortion,
    which occurs as impression is withdrawn.

  • Objectives
  • To obtain an impression of all the standing
    teeth and denture - supporting tissues of each
    jaw from which study casts may be prepared.
  • The purpose of the study casts are

  • To enable special trays and occlusion rims to be
    constructed if necessary.
  • To examine the occlusion in detail on an
  • By use of a surveyor, to plan the path of
    insertion of the proposed denture, arrive at a
    tentative design and plan any mouth preparation.

  • Checking Maxillary Tray For Correct Size
  • Checking Mandibular Tray for Correct Size

  • Mixing Impression Material
  • Alginate may be mixed by hand spatulation,
    mechanical spatulation, or mechanical spatulation
    under vacuum.
  • The objective is to obtain a smooth, bubble-
    free mix of alginate. In hand spatulation a
    measured amount of distilled water at
    approximately 22 C is placed in a rubber mixing
    bowl The pre-weighed alginate powder is sifted
    from its container into the water.

  • The mixing should begin slowly using a stiff,
    broad - bladed spatula.When the powder is
    thoroughly wet, the speed of the spatulation
    should be increased The spatula should crush the
    material against the sides of the bowl to ensure
    that the material is completely mixed. The
    spatulation should continue for a minimum of 45

  • The strength of the gel can be reduced to 50
    if the mixing is not complete. Insufficient
    spatulation can result in failure of the
    ingredients to dissolve sufficiently. Then the
    chemical reaction of changing from sol to gel
    will not proceed uniformly throughout the mass of
    alginate. An incompletely spatulated mix will
    appear lumpy and granular and will have numerous
    areas of trapped air.

  • Complete spatulation will result in a smooth,
    creamy mixture. The mixing should be completed by
    wiping the alginate against the side of the bowl
    with the spatula to remove any trapped air. The
    most consistent method of making a smooth,
    bubble- free mix is mechanical spatulation under

  • The pre-weighed powder is added to the
    pre-measured water in the mechanical mixing bowl
    .The powder is thoroughly incorporated into water
    by hand spatulation. The mix is then mechanically
    spatulated under 20 pounds of vacuum for 15

  • Longer spatulation will result in a greatly
    reduced setting time of the alginate and could
    affect the strength of the gel.

  • Loading the Impression Tray
  • Small increments of the impression material
    should be placed in the tray and forced under the
    rim lock. Placing too large a portion of alginate
    at one time increases the possibility of trapping
    air The tray should be filled to the level with
    the flanges of the tray.
  • Overfilling should be avoided.

Making the Impression
  • The mandibular impression is made first because
    it usually entails less patient discomfort
    patient confidence is increased when an
    impression has been successfully completed while
    holding the tray with the left hand the dentist
    uses the right hand to remove the gauze pads from
    the patients mouth.

  • The syringe is used to inject the impression
    material over the occlusal surface of the teeth
    and into the vestibular and alveolingual sulcus
    areas. The impression material will remain in
    place if the tissues are fairly dry. A tendency
    for the alginate to form a ball and not remain
    where placed indicates that the tissues are too
    moist and that voids are likely to be present in
    the impression.

  • There is not enough time to repack the mouth
    before gelation begins, so the impression
    procedure should be completed. The impression
    should be carefully inspected and if voids are
    present in critical areas, the impression
    procedure should be repeated. Packing the mouth
    with more or larger gauze pads and avoiding
    removal of the gauze until ready to apply the
    alginate will usually prevent this problem.

The layer of alginate applied with the syringe
should be 3 to 4 mm thick If it is too thin, the
heat of the tissues of the oral cavity may cause
the material to set before the tray is seated,
resulting in a layered impression.
  • The fingers of the left hand that are retracting
    the right cheeks should depress the lower lip to
    provide good visibility. When the tray is
    correctly lined up over the teeth, the patient is
    asked to protrude the tongue. The tray is
    carefully seated so that its flanges are below
    the gingival margins of the teeth.

  • The tray should not be over seated because this
    could result in the cusps of the teeth contacting
    the tray, causing an inaccurate impression. Great
    care must be exercised in seating the tray if the
    patient has mandibular tori or other exostoses,
    or the making of this impression can be a very
    painful experience for the patient.

  • As the tray is being seated, the cheeks are
    pulled out to prevent the trapping of buccal
    tissues under the tray. The patient is asked to
    keep the tip of the tongue in contact with the
    upper surface of the tray during the gelation of
    the impression material.

  • The dentist must maintain the position of the
    tray during the entire gelation period. This can
    be accomplished most conveniently and effectively
    by placing the forefinger of each hand on the top
    of the tray in the premolar area and by placing
    the thumbs under the patient s chin.

  • The dentist through tactile sense can maintain
    an even amount of pressure on the tray even if
    the patient swallows or opens or closes the
    mouth. Any movement of the tray during the
    gelation period will result in an inaccurate
  • Allowing the patient or the assistant to hold
    the tray or leaving the patient unattended must
    be avoided.
  • Within 3 to 4 minutes the alginate should be

  • For maxillary impression, the patients is
    prepared by using the rinses and placing the
    gauzes pads described for making the mandibular
    impression. While holding the loaded tray with
    the left hand the dentist uses the right hand to
    remove the gauze pads.

  • Alginate is injected onto the occlusal surfaces
    and in all vestibular areas as for the mandibular
    arch. In addition, a fairly large amount should
    be wiped onto the palate. Failure to accomplish
    this step will usually result in an impression
    with a large void in the palatal area.

  • The loaded maxillary tray is grasped by the
    thumb and forefinger of the right hand. As the
    right posterior flange of the impression tray
    stretches the right corner of the mouth, the
    dentist s left arm should be behind the
    patients head and headrest so that the thumb and
    index finger may grasp the left corner of the
    mouth and distend it slightly to allow the
    impression tray to enter the mouth in a straight

  • No attempt should be made to seat the tray until
    the tray is in its correct anteroposterior
    position. Once the tray is in the mouth, the
    thumb and forefinger of the left hand should
    raise the upper lip to allow the dentist to see
    the relationship between the labial flange of the
    tray and the anterior teeth or the residual

  • The tray must be centered and properly aligned.
    This position can best be verified by looking at
    the patient s face from above and observing the
    position of the handle of the tray.

  • It should protrude straight from the center of
    the mouth. After the proper position has been
    verified the tray is seated by using the fingers
    of both hands over the premolar areas. As the
    tray is being seated the cheeks must be lifted
    outward and upward to prevent the buccal tissues
    from being trapped under the flanges of the tray.

  • The lip must also be lifted up and out to allow
    good visibility and to avoid trapping the lip
    between the flanges of the tray and the anterior
    teeth. Care must be taken not to over seat the
    tray to avoid. contact between the tray and cusp
    tips of incisal edge of the teeth.

  • The tray should be stabilized throughout the set
    of the impression material by keeping light
    pressure over the premolar areas on both sides of
    the arch The alginate should set in 3 to 4

  • Effect of movement of tray
  • Gelation of alginate occurs by a chemical
    reaction. When mixed with water, the sodium
    alginate and calcium sulfate in the powder react
    to form a lattice work of fibrils of insoluble
    calcium alginate. The heat of the oral tissues
    accelerates the chemical reaction, causing the
    alginate next to the tissues to gel first .

  • If the dentist exerts pressure or allows the
    tray to move during gelation of the remainder of
    the alginate, internal stresses are created that
    can distort the impression as it is removed from
    the mouth.

  • Removal of Impression from Mouth
  • Clinically, the initial set of alginates is
    determined by a loss of surface tackiness. The
    impression should be left in the mouth for an
    additional 2 to 3 minutes to allow the
    development of additional strength. Early removal
    of the weak alginate may lead to unnecessary
    tearing of the impression.

  • The gel strength doubles during the first 4-
    minutes after initial gelation. No further
    strengthening is found after that time. In fact,
    Impression is left in the mouth for 5 minutes
    rather than the recommended 2 to 3 minutes after
    initial gelation exhibits definite distortion.

  • Most alginates improve their elasticity with
    time, providing a better opportunity for accurate
    reproduction of undercuts. Impressions removed
    too early after initial gelation produce a rough
    surface of the poured cast. These data indicate
    the alginate impressions should not be removed
    from the mouth for at least 2 to 3 minutes after
    initial gelation.

  • There are two reliable methods of determining the
  • correct time for removal of the impression
  • 1. A timer can be used to measure the 2 to 3
    minute period after initial gelation or
  • 2. A small mound of the original mix of alginate
    can be placed on a glass or metal surface when
    this alginate will fracture cleanly with finger
    pressure, the impression is ready to be removed
    from the mouth.

  • Impression Methods
  • There are basically two dual impression
    techniques. The physiologic, or functional,
    impression technique records the ridge portion by
    placing an occlusal load on the impression tray
    as the impression is being made.

  • For this dual impression a custom impression
    tray was constructed over a preliminary cast of
    the arch, a function impression of the distal
    extension ridge was made, and then hydrocolloid
    impression was made with the first impression
    held in its functional position with finger

  • The underlying s tissues will be displaced
    because displacement will normally occur under
  • The physiologic impression techniques that
    discussed are as follows Mc Leans and Hindels
    methods, the functional relining method, and the
    fluid wax method.

  • The selected pressure impression technique not
    only equalizes the support between the abutment
    teeth and the soft tissue, but has the added
    advantage of directing the force to the portions
    of the ridge that are most capable of
    withstanding the force.
  • This is accomplished by providing relief in
    the impression tray in selected areas and
    permitting the impression to be recorded.

  • The need for physiologic impressions was first
    recognized by McLean and others
  • They realized the need of recording the tissues
    of the residual ridge that would eventually
    support a distal extension denture base in the
    functional or supporting form and then relating
    this functional impression to the remainder of
    the arch by means of a second impression.

  • For the production of accurate master cast the
    impression technique far out weights the
    selection of the impression material.
  • No available knowledge of the person making the
    impression material will produce results greater
    than the skill and knowledge of the person making
    the impression.

  • Which is true regarding maxillary residual ridge
  • Crest is cortical bone
  • Crest is cancellous bone with firm mucosa
  • Crest is cancellous bone without firm mucosa
  • Preesure placed on the crest result in irritation
    of these tissues

  • 2. In a maxillary denture, relief must be
  • Crestal region
  • Buccal slopes
  • Palatal slopes
  • Median palatal raphe

  • 3. Which is correct?
  • A
  • B
  • Depends upon the residual ridge
  • none

  • 4. For a distal extension base, which should be
  • Make a functional impression
  • Make an anatomic impression
  • Make an anatomic impression with stress breakers
  • Both a and c

  • 5. Functional form of the residual ridge is not
    recorded by which of the following means?
  • Under some loading, occlusal or finger
  • By specially designed trays
  • By soft impression material, such as ZnO, if the
    entire impressionn tray is uniformly relieved
  • Maintaining the consistency of the recording

  • 6.In order to increase the amount of vertically
    directed forces on the residual ridge
  • Move the rest posteriorly
  • Move the rest anteriorly
  • Reduce the number of rests
  • None is correct

  • 7. Which is not outcome of reducing the occlusal
  • Reduces vertical and horizontal forces
  • Increases vertical and horizontal forces
  • Reduces stress on the abutment teeth
  • Lessens stress on the residual ridge

  • 8. Which is true about anatomic impression
  • It is a one-stage impression method using elastic
    impression material
  • Places more masticatory load on the abutment
  • Places more masticatory loads on the residual
  • All of the above

  • 9. To evaluate complete seating of the framework
    several types of disclosing media are used. Which
    one is wrongly written?
  • Rouge
  • Chloroform
  • Pencil correction fluid
  • Waxes

  • 10. Altered cast impression technique is used in
  • Kennedy Class I maxillary residual ridge
  • Kennedy Class II mandibular residual ridge
  • Kennedy Class IV maxillary residual ridge
  • Kennedy Class III mandibular residual ridge

  • 1. b
  • 2. d
  • 3. a
  • 4. d
  • 5. c
  • 6. b
  • 7. b
  • 8. d
  • 9. c
  • 10. b