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Special Impression Procedures
DR MAHMOOD ABU RUJAI
BDS, M.Sc ProsthodonticsFull- Time Lecturer Dep. Prosthodontics
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Requirement
record the tissues under uniform loading
distribute load over as large an area
delineate the peripheral extent of the denture
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Factors Influencing Support of the
Distal Extension Base
1. Quality of soft tissue covering edentulous ridge
A firm , tightly attached mucosa displaying moderate
thickness (2 to 3 mm) will offer the greatest support
2. Type of bone in the denture-bearing area
Cancellous bone, as compared with cortical bone, is less
able to resist vertical forces
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3. Design of the prosthesis
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4. Amount of tissue coverage of denture base
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5. Anatomy of the denture-bearing area
Each denture base must be made to fit the areas
that can serve as primary stress-bearing regions
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Indications
1. mandibular distal extension application
2. a long-span anterior edentulous base
(normally including at least the six anterior
teeth)
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Impression Methods
1. McLean physiologic impression
2. Functional reline method
3. Corrected cast procedure(selected pressure techniques)
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McLean physiologic impression
a dual impression technique
constructed a custom tray on a diagnostic cast
A functional impression was made using thistray and a suitable impression material
hydrocolloid "over-impression
could not produce same
functional displacement
generated by occlusal forces
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McLean physiologic impression
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McLean Dis Advantage
clasps is sufficient :may result i n
compromised blood flow with adverse soft
tissue reaction and resorption of the
underlying bone
clasps is not sufficient: the denture base will
be occlusally positioned (premature contact)
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Functional reline method
Done after the partial denture has been
completed (done at a later date)
adding a new surface to the intaglio of the
denture base
The partial denture is constructed on a cast
made from a single impression with a soft
metal spacer under neath to ensure a uniform
space for the impression material
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The patient must keep the mouth partially
open to permit appropriate tissue control andvisual assessment
modeling plastic is applied to the intaglio of
the denture base
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Functional reline method
1mm of modeling plastic is removed from the
intaglio surface and an impression is made
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Disadvantage
failure to maintain the correct relationship
between the framework and the abutment
teeth during the impression
failure to achieve accurate occlusal contact
following the reline procedure
occlusal discrepancies must be corrected:
slight: accomplished in the mouth
majority of cases: remount on an articulator
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Corrected cast procedure
(selected pressure techniques)
Adding an impression tray after the framework
has been fitted using a chemically activated or
light-activated resin
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Corrected cast procedure
(selected pressure techniques)
Undercuts that would interfere with removal
of the tray are blocked out
separating medium is then placed
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Tray is adapted to the cast
Boarders trimmed using a laboratory knifeand
gently rounded
the edge of the tray should be 2 to 3 mm from
the depth of the buccal vestibule
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Border molding for a corrected cast is basically
the same as that for a complete denture covers
the buccal flange to the most posterior extent
the lingual and
distolingual flanges
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THANK YOU