rpd impression modified

7/30/2019 RPD Impression Modified

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special Impression

procedures for removable

partial dentures


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Goals of Impression Techniques

for RPD

Record hard unyielding tissues (teeth)as well as the soft yielding tissues

(mucosa) and Surfaces that will contactthe RPD framework

Delineate accurately Critical landmarks:preipheral extention retromolar pads,

hamular notch, vestibular depths and

edentulous regions.


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1- Anatomic ridge form:

for tooth suppoted R.P.D. (Kenedysclass III, short span class IV) so the edentulous ridges dont

contribute to the support of theR.P.D.

Single, pressure-free imp. records

the teeth and soft tissues in theiranatomic form .

Impression Techniques


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2-Physiologic or functional ridgeform:

for tooth- tissue supported R.P.D.

(Kenedys class I,II,long span class IV) When the occlusal forces fall on tooth-

tissue supported R.P.D., the ridgecontribute to support as well as teeth

This imp. recordteeth in their anatomicform and the ridge in its functionalform under pressure.



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2-Physiologic or functional ridge form: for tooth tissue supported R.P.D. (Kenedys class

I,II,long span class IV)

The imp. must:

1. Record and relate the tissuesunder uniform loading.2. Distribute the load over as large

an area as possible3. Accurately delineate theperipheral extent of the denturebase.


F i fl i f di l


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Factors influencing support from distalextension bases (factors influencing theamount of tissue displacement1- Quality of soft tissues covering edentulous

ridge

2- Type of bone making up denture bearing

area3- Design of partial denture

4- Amount of tissue coverage of denture base:

5- Amount of occlusal forces6- Anatomy of denture bearing area:

7- Fit of denture base:

8. Type and accuracy of the impression

registration:


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1- Quality of soft tissues coveringedentulous ridge

It should be firm, dense fibrous C.T. of eventhickness

slightly compressible and firmly attached to thebone

Factors influencing support fromdistal extension bases (factors influencing

the amount of tissue displacement


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2- Type of bone making up denturebearing area:

The ideal ridge would consist of:

Cortical bone that covers denseCancellous bone with broad rounded

crest and high vertical slops.

Cortical bone can resist vertical forces better thancancellous bone.

Factors influencing support from distal extensionbases(factors influencing the amount of tissuedisplacement


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3- Design of partial denture:

Knowledge of basic principles of designs

guides the management of functional forces.

The use of indirect retainer will control

rotational movement of distal extensionRPD.

Factors influencing support

from distal extension bases


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4- Amount of tissue coverage of

denture base:

The broader the coverage of the

edentulous ridge, the greater thedistribution of the load & the smallerthe force per unit area




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5- Amount of occlusal forces:1-

Number of artificial teeth.2-Width of the occlusal table.

3- Efficiency of occlusal table.

4- type of the opposing dentition5-powerfull musculature of the patientIt influences the amount of support required to

stabilize the denture base..




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6- Anatomy of denture bearing area:

To distribute the forces of masticationto the ridge most efficiently, themajority of force must be directed tothe primary stress bearing areas,that are capable of withstanding thatforce.



fl f


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Factors influencing support from

distal extension bases7- Fit of denture base:Support is enhanced by intimate contact

between the mucosa and the fitting surface

of the partial denture;8. Type and accuracy of the impression

registration:

the majority of the force must be directed toportions of the ridge that are capable ofwithstanding the force


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At the imp. stage:

Mcleans and Hindels methods = dual imp. Technique= pseudo-functional imp. or

Impressions with custom trays.At the framework stage:

Altered cast method either by functional imp.method(fluid wax) or by selected pressure imp.method

At the finished denture stage:

Functional relining method using fluid wax or zincoxide euginol or rubber base relining method.

Impression for distalextension R.P.D.


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Imp. for Dis. Ex. R.P.D.1. At the imp. stage:


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1- At the imp. stage: McLeans technique (closed mouth)

The technique consists of making an impressionof the edentulous ridge in border-mouldeddenture base tray which is provided withocclusion rims.

Impression paste is used to record ridge areasunder biting stresses

After setting of ZnO eugenol it is removed,tested, reinserted; overall alginate impression ismade with the ZnO imp.seated in the mouth.

Imp. for Dis. Ex. R.P.D.


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1- At the imp. stage:

McLeans technique (closed

mouth) Since the tray used for the overall imp. is

in contact with the occlusal rims, finger

pressure is necessary to hold theoriginal imp. in its functional positionwhile the hydrocolloid material geles.



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1- At the imp. stage: Disadvantages

If the clasp action is sufficient to maintain the

denture base in its intended position, This mayresult in compromised blood flowwith adversesoft tissue reaction and bone resorption.

If clasp action is not sufficient to maintain that

functional relationship of the denture base tothe soft tissue, this will result in floatingdenturewithpremature contact and patientdissatisfaction.



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Imp. for Dis. Ex. R.P.D.2. At the framework stage:


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Altered cast method :

Steps:1- after the RPD frame work is constucted on anatomic

imp.cast.it should be evaluated

for any metal projections and sharp

edges.

2-check the RPD metal frame

work in the patients mouth


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Altered cast method

3-the impression tray is madeusing chemically activated resin, a

the frame work with the

attached impression tray is

placed in the patients mouth

and correct peripheral extension

4-border molding the impression

tray using low fusing modelingplastic < green or grey sticks >


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Altered cast method

5-the final impression is made by

using zinc-oxide euginol paste

with the mouth opened andtripod pressure is applied on

occlusal rests and indirect retainer

6-after the impression material is

set, the tray is removed and

checked for any discrepancies


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7. The metal framework with theattached imp. is positioned onthe master cast with allocclusal rests properly seated

in their prepared recesses.

8. The entire assembly is boxed

and poured in a differentcolored stone.

Altered cast method


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Imp. for Dis. Ex. R.P.D.3- At the finished denture

stage: Functionalrelining method:


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3- At the finished denture stage:Functional relining method: The finished denture is relined by

applying for example ZnO eugenol imp.paste to the acrylic fitting surface of thedistal extension saddle

the impression is made with the denturebeing seated by pressure on the occlusalrests and indirect retainers only.

No pressure is applied to the occlusalsurface of the artificial teeth


rpd impression modified

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