special impression procedures

7/30/2019 Special Impression Procedures

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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

special impression procedures

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