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Conventional Definitive Impression Technique:
Disinfect Spl. Trays & rinse in water.
Check tray is:- adequately extended antero-posteriorly & bucco-lingually.
- not interfering function of peri-denture soft tissues.
- has correct overextension (using pressure-relief paste).
Correct under-extension (adding green-stick / other material).
Apply tracing compound to the posterior aspect of the upper
tray to produce a posterior seal.
The tracing compound should extend uninterrupted from oneborder of the tray to the other to create a post dam.
In the lower tray, the compound should be added to displace
the retro-molar pad sufficient to give a posterior seal.
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Load the tray with the material.
Technique is same for the primary impression.
Upon setting, remove from mouth.Check for accuracy and form.
Disinfect procedure (hypochlorite 1,000 ppm).
Indicate the extent of the peripheral roll to bepreserved on the master cast.
Creation of the peripheral seal is essential.
Peripheral seal depends upon:
- correct outline / record of PPS tissues.
- PPS tissue reproduction in master cast .
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Definitive impression with well-defined area for the placement of carding wax
prior to boxing the impression, thereby preserving the functional width and
depth of the sulci.
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Selective Pressure Impression Techniques:
Support problems overcome by relieving master cast but;
- But in specific cases, modified impression proceduresused B/C of perceived support problems including:
- displaceable upper anterior (flabby) ridge.
- fibrous (unemployed) posterior mandibular ridge.
- flat lower ridge covered with atrophic mucosa.Several variations of impression techniques exist to deal
with the above.
General Steps for Definitive / Secondary / final Imp:
Fabricate special trays.Adjust special / custom trays.
After peripheral moulding, do specific modifications to the
trays / impression techniques.
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Impression Technique for Displaceable (Flabby) Anterior
Maxillary Ridge:
Achieve seal with peripheral functional border moulding.Record impression of maxilla in ZOE or a medium-bodied
PVS) impression material.
ZOE not recommended in a patient with a dry mouth.
On setting, the impression is removed from the mouth.
Draw the extent of the displaceable tissue on the
impression surface.
This area, and the equivalent area of the tray, are thenremoved, using a scalpel and acrylic bur.
This modification renders tray no longer retentive.
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Fibrous (Unemployed) Posterior Mandibular Ridge:
Recognized by the presence of a thin, mobile thread-like
ridge which is essentially fibrous in nature.A Staged sequence impression technique is used for this
situation.
Custom tray checked for peripheral extension.
Tray loaded with tracing compound (greenstick).Impression of the denture-bearing area recorded.
Using the heated spoon-end of a Le Cron carver:
- remove greenstick relating to crestal tissues.
Perforate tray in this region.Downward finger pressure of the modified impression, in
the mouth, should elicit no discomfort.
Record definitive impression in light-bodied PVS.
Treat impression as for a conventionally made impression.
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Flat Mandibular Ridge Covered With Atrophic Mucosa:
Equate to Atwood's Ridge Clases V & VI.
Atrophic & / or non-keratinized tissue folds seen on ridge.The impression philosophy is that a viscous admix of cake
imp. compo & stick compo removes any soft tissue folds
& smoothes them over the mandibular bone.
Discomfort arising from the 'atrophic sandwich', i.e creasedmucosa b/w CD base & mandibular bone is reduced.
Prepare the impression medium as admix of 3 parts by wt.
of (red) imp. compo & 7 parts by wt. of stick compo.
Admix made in hot water by kneading using vaselinedgloved fingers.
Make lower impression (Working time of admix is 12
minutes) by moulding the peri-tray tissues to achieve
good peripheral border recording.
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On removal, impression is chilled in water & then re-
inserted.
The operator presses on the stub handles of the tray onthe premolar region & reciprocates with thumbs on the
inferior body of the mandible:
- ideally no discomfort will be felt by the patient in the
area pressed by the operator's thumbs!Any discomfort in the DBA may be treated by adjusting the
offending area of the impression with a heated wax
knife and re-inserting as required until no further
discomfort is felt.Alternatively, painful area is relieved on the master cast.
Admix technique gives a reliable guide to the load-bearing
potential of patient's DBA when making definitive imp.
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Definitive impression made with Admix Method (MC Cord & Tyson)
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Template (Replica Denture Tray) Impression Technique:
Used when replacing existing CDs by copy method.
Replication of the form of polished surfaces of CDs
help the patient's adaptation to new dentures.
Fabricate mould of CD to obtain its acrylic replica.
Final imp. recorded in acrylic replica of CD
(template).
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Functional impression Techniques
used where problems of stability exist:
- poor muscle adaptation and /or imbalance or
- because of problems of available denture space).
- also useful in patients having recently suffered from stroke.
Two variations are commonly used for functional impressions.
- Local areas of modification
CDs exhibiting looseness, not primarily from retention problemsbut because of localized areas of poor functional adaptation.
In these cases, use a thin mix of a resilient lining material (e.gVisco-Gel, or Peripheral Seal).
The mixed material is added to the fitting surface of the denture.
Patient instructed to wear the denture for one hour.
After one hour of functional moulding CD removed from mouth.
Conventional relining process completed.
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Reline and rebase techniques (including secondary
template impressions)
Conventional reline impression is taken or a:- secondary impression for the template technique.
They are both definitive impressions.
Must consider the same degree of attention as standard
impression techniques.The denture, or its replica, to be relined is modified:
Establish peripheries /peripheral seal.
Undercuts are removed from fit surface of CD:
to ensure that master cast is not damaged onremoval of the dent
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ZOE or Elastomer (PS / PVS / PE) imp used.
Before recording the definitive impression, there is merit
in placing tracing compound as spacing on the denturein the region corresponding to the ridges of the canine
areas (But no OVD Raising).
Perforate maxillary spl. Tray in in the midline of the rugae
to prevent any possibility of imperfections in theimpression, e.g air bubbles.
Also important is good communications with the
laboratory (Good rapport b/w Lab).Conventional techniques, however, do little to inform the
technician on the customizing of upper record rims.
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Problems associated with denture space/neutral zone
This technique is well documented and has been referred
to as the neutral zone technique oranthropoidal pouch
technique.
We prefer to use the term denture form impression
technique. It is designed for patients with poor track
records of lower denture stability, a large tongue or
other anatomical anomaly.
The clinical stages are standard up to and including the
registration visit. After this, the upper denture is set up
conventionally to the prescribed occlusal vertical
dimension (OVD). Opposing the upper set-up is a resin
base with three vertical stops joined by a wire bent in a
sinusoidal manner. The stops must contact the upper
teeth at the selected OVD.
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