RPD Impression Modified
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Transcript of 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.
Impression Techniques
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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.
Impression Techniques
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
Factors influencing support
from distal extension bases
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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..
Factors influencing support
from distal extension bases
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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.
Factors influencing support
from distal extension bases
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.
Imp. for Dis. Ex. R.P.D.
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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.
Imp. for Dis. Ex. R.P.D.
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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
Imp. for Dis. Ex. R.P.D.