impression procedures for removable partial dentures / academy of fixed orthodontics

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INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in continuing dental educationLeader in continuing dental education

 INTRODUCTIONINTRODUCTION
 IMPRESSIONIMPRESSION
 IMPRESSION TRAYSIMPRESSION TRAYS
 TRAYS USED IN RPD IMPRESSIONTRAYS USED IN RPD IMPRESSION
PROCEDUREPROCEDURE
 FACTORS INFLUENCING THE CHOICE OFFACTORS INFLUENCING THE CHOICE OF
IMPRESSION MATERIALIMPRESSION MATERIAL
 IMPRESSION MATERIALS USED-OVERVIEWIMPRESSION MATERIALS USED-OVERVIEW

 RPD IMPRESSION Vs COMPLETE DENTURE
IMPRESSION
 PRIMARY IMPRESSION
 OBJECTIVES
 PROCEDURE
 PATIENT MANAGEMENT
 CONTROL OF SALIVA
 PRECAUTIONS TO BE TAKEN FOR “ GAGGERS ”
 EXAMINATION OF IMPRESSION
 REASONS FOR REJECTING AN IMPRESSION

 FINAL IMPRESSION METHODS
 McLEAN’S TECHNIQUE
 HINDEL’S TECHNIQUE
 SELECTIVE PRESSURE TECHNIQUE
 FUNCTIONAL RELINING TECHNIQUE
 FLUID WAX TECHNIQUE
 ALTERED CAST TECHNIQUE
MODIFICATION
 REVIEW OF LITERATURE
 CONCLUSION
 REFERENCES www.indiandentalacademy.comwww.indiandentalacademy.com

INTRODUCTIONINTRODUCTION
Sensitive to technique and material procedures.Sensitive to technique and material procedures.
Not a passive activity.Not a passive activity.
Impression material accomplishes the taskImpression material accomplishes the task
operator is merely an observer.operator is merely an observer.

Combined effort event accomplished by:Combined effort event accomplished by:
OperatorOperator
basic fundamental knowledge of all aspects ofbasic fundamental knowledge of all aspects of
the impression proceduresthe impression procedures
Intra oral condition of the patient.Intra oral condition of the patient.
The position of the patient.The position of the patient.
The size and position of the tray.The size and position of the tray.
The selection of the material and technique.The selection of the material and technique.
Patient’s actions and facial muscle activity.Patient’s actions and facial muscle activity.

Impression
 A negative likeness or copy in reverse of the
surface of an object ; imprint of teeth and adjacent
structures for use in dentistry. GPT – 8
Partial denture impression
 A negative likeness of a part or all of a partially
edentulous arch - GPT – 8

 An impression of partially edentulous arch
must record accurately the anatomic form
of teeth and surrounding tissues. Unless
the cast upon which the prosthesis is to be
constructed is an exact replica of mouth,
the prosthesis can’t be expected to fit.
Properly made and accurate cast can be
obtained only from an accurate
impression.

Impression trays
A receptacle in to which suitable impression
material is placed to make negative likeness
OR
A device that is used to carry, confine and control
impression material while making an impression.

Impression trays can be classified broadly in to
stock trays
and
custom trays
Stock trays for partially edentulous patients may
be perforated to retain the impression material or
they may be constructed with a rimlock for this
purpose.
Another type of stock tray designed for the
reversible type of hydrocolloid is water cooled
trays. It contains tubes through which water can
be circulated for purpose of cooling the tray.www.indiandentalacademy.comwww.indiandentalacademy.com

Modified stock tray (individual tray)
Robert R Renner’s technique
The stock tray can be modified with
modeling composition and with wax to
create an accurately fitting tray.
This technique can be employed in class I
and class II cases.
Technique:
Softened modeling compound is placed in
the stock impression tray in such a way that
it may capture the edentulous areas of
mouth and include one or two teeth
adjacent to the space.www.indiandentalacademy.comwww.indiandentalacademy.com

The tray is positioned in the mouth and compound
is allowed to cool but it not permitted to harden
completely, so that it is prevented from becoming
hard when in contact with the adjacent teeth. When
it is hardened sufficiently to contour it is removed
from the mouth and thoroughly chilled.

The compound is trimmed so that it does not
contact the adjacent teeth and surface of
compound in the edentulous areas is scraped
to a depth of 2 - 4 mm to provide space for a
uniform layer of impression material.
In maxillary impression the compound should
cover the edentulous ridges and the palate and
should accurately fit to post dam area.

Modification of the tray to make it adhesive
If Impression material to be used is either
alginate or agar, we can heat surface of
compound with a flame.
An alternate method Is to paint the surface of
compound with a solvent such an chloroform to
make it tacky and then to embed cotton fibers in
it, the impression material will become enmeshed
in cotton fiber. And if rubber base material is to
be employed rubber adhesive is painted on the
compound

Advantages over custom tray:
1. Impression can be accomplished in one
appointment.
2. Can be used inpatient with tendency to gag.
Advantages over conventional use of stock stray:
Especially useful for mouth that is either
exceptionally large or small or the one with
anomalous contour which cannot be accurately fitted
with conventional stock tray.

Disadvantages: STOCK TRAY
a. The peripheral borders cannot be
accurately recorded.
b. Considerably more bulkier than a custom
tray.

Custom impression trays:
a. Peripheral borders can be precisely
recorded in the impression
b. Thickness of impression material can be
controlled. This is important consideration
when using rubber base type material,
which should not exceed thickness of 2-4
mm because a section thicker than this is
subject to distortion.

C. Well fitted tray will better support the impression
in the palate, then avoiding even present danger
of material slumping in vital areas.
Custom trays are sometimes needed for mouths
that are abnormally or of unusual configuration.

Impression MaterialsImpression Materials
www.indiandentalacademy.com

Factors that influence the selection of
impression materials are:
 Convenience of use
 Time of manipulation and set
 Cost
 Need for special trays
 Operator training and preference

Impression Materials
• Non-elastic
• Elastic
– Aqueous hydrocolloids
• Agar
• Alginate
– Non-aqueous elastomers
• Polysulfide
• Silicones
– Condensation
– Addition
• Polyether www.indiandentalacademy.com

Impression
Materials
Non-elastic
Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Plaster
Compound
ZnO - Eugenol
Waxes
O’Brien Dental Materials & their Selection 1997

Reversible Hydrocolloid
(Agar)
• Indications
– crown and bridge
• high accuracy
• Example
– Slate Hydrocolloid (Van R)

Composition
• Agar
– complex
polysaccharide
• seaweed
– gelling agent
• Borax
– strength
• Potassium sulfate
– improves gypsum
surface
• Water (85%)
agar hydrocolloid (hot) agar hydrocolloid (cold)
(sol) (gel)
cool to 43 C
heat to 100 C

Manipulation
• Gel in tubes
– syringe and tray material

Manipulation
• 3 chamber conditioning unit
– (1) liquefy at 100°C for
10 minutes
• converts gel to sol
– (2) store at 65°C
– place in tray
– (3) temper at 46°C for 3 minutes
– seat tray
– cool with water at 13°C for 3 minutes
• converts sol to gel

Advantages
• Dimensionally accurate
• Hydrophilic
– displace moisture, blood, fluids
• Inexpensive
– after initial equipment
• No custom tray or adhesives
• Pleasant
• No mixing required
Phillip’s Science of Dental Materials 1996

Disadvantages
• Initial expense
– special equipment
• Material prepared in advance
• Tears easily
• Dimensionally unstable
– immediate pour
– single cast
• Difficult to disinfect

Irreversible Hydrocolloid
(Alginate)
• Most widely used
impression material
• Indications
– study models
– removable fixed partial dentures
• framework
• Examples
– Jeltrate (Dentsply/Caulk)
– Coe Alginate (GC America)

Composition
• Sodium alginate
– salt of alginic acid
• mucous extraction of
seaweed (algae)
• Calcium sulfate
– reactor
• Sodium phosphate
– retarder
• Filler
• Potassium fluoride
– improves gypsum
surface
2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4
Na alginate + CaSO4 Ca alginate + Na2SO4
(powder) (gel)
H2O

Manipulation
• Weigh powder
• Powder added to water
– rubber bowl
– vacuum mixer
• Mixed for 45 sec to 1 min
• Place tray
• Remove 2 to 3 minutes
– after gelation (loss of tackiness)
Caswell JADA 1986

Advantages
• Inexpensive
• Easy to use
• Hydrophilic
– displace moisture, blood, fluids
• Stock trays

Disadvantages
• Tears easily
• Dimensionally unstable
– immediate pour
– single cast
• Lower detail reproduction
– unacceptable for fixed prosthodontics
• High permanent deformation
• Difficult to disinfect

RPD IMPRESSION Vs COMPLETE DENTURE
The complete denture impression records the
edentulous mucosa with underlying bone only,
whereas partial denture impression records not
only relative soft yielding tissues (the oral
mucosa) as well as a hard unyielding
substance (the remaining teeth).

Removable partial denture impression need to
record the teeth that are irregular in contour as
well as varying in their vertical relations to
occlusal plane. The chosen impression material
must be capable of recording the tissue contours
as accurately as possible without distortion,
which occurs as impression is withdrawn.

PRIMARY IMPRESSION
Objectives:
To obtain an impression of all the standing
teeth and denture - supporting tissues of
each jaw from which study casts may be
prepared.
The purpose of the study casts are:

To enable special trays and occlusion rims
to be constructed if necessary.
To examine the occlusion in detail on an
articulator.
By use of a surveyor, to plan the path of
insertion of the proposed denture, arrive at a
tentative design and plan any mouth
preparation.

Checking Maxillary Tray For Correct Size
Checking Mandibular Tray for Correct Size

Control of Gagging
It is usually a mistake to make too big an
issue over the making of impressions. The
dentist definitely should not bring up the
subject of gagging. The dentist should ask
whether the patient has had impression
made previously. If this is to be the patient‘s
first experience a brief description of the
procedure should be given.

That the material to be used has the
consistency of thick whipped cream and that is
sets up to a rubber consistency in several
minutes, is usually all the explanation that is
necessary. The dentist should proceed in
confident, efficient manner. Dentist usually
encounter more problems with gagging when
they are in initial stages of dental practice and
approach the making the impressions with
unsure and nervous demeanor.

Procedures that will help prevent Gagging
Seating the patient in an upright position with the
occlusal plane with the floor
correcting the maxillary tray with modeling plastic
and leaving sufficient unrelieved modeling plastic
at the posterior borders that positive contact can
be maintained against the posterior palate during
the setting of the alginate.
Not overfilling the tray with alginate.

Seating the posterior part of the tray first and then rotating
the tray into position thereby forcing excess alginate in an
anterior direction rather than out of the posterior border of
the tray.
Asking the patient to keep the eyes open during the
impression procedure This usually reduces the patient
tension.
Asking the patient to breath through the nose.
Asking the patient to keep eyes focused on some small
object.
Giving all instructions to the patient in a firm controlled
manner.

Having the patient use astringent mouth rinse
and cold water rinses before the impression is
made. The use of an anesthetic spray is usually
contraindicated because it will cause numbness
of the tongue and palate and may contribute to
the urge to gag.
Most gagging problems are psychologic rather
than physical, and confidence in the dentist will
help eliminate many of them.

Control of Saliva
Alginate has a tendency to stick to teeth
that are too dry. Therefore the teeth
should not be air dried before making an
impression. However, excessive amounts
of saliva, particularly of the thick mucous
type, will displace the alginate impression
material and will contribute to an
inaccurate impression.

The saliva can be controlled for most
patients by having the patient rinse cold
water and then packing the mouth with
2x2 inch gauze that has been unfolded to
form a strip of 2-inch gauze. In the
maxillary arch one gauze strip is placed in
the right buccal vestibule and another in
the left vestibule.

The patient can be asked to lightly hold a
third piece of gauze in the palate.
Because too much force by the patient
may displace the tissue to be recorded in
the impression, the dentist may prefer to
wipe the palatal area just before making
the impression.

In the mandibular arch one gauze strip is
placed in each of the buccal vestibules and
another is placed in the linguoalveolar sulcus
by having the patient raise the tongue,
placing the gauze in the sulcus, and then
having the patient relax the tongue to hold
the gauze in position. The gauze is removed
immediately before the impression is made.

A few patients secrete an excessive amount of
thick mucinous saliva from the palatal salivary
glands. This heavy saliva displaces the alginate
and results in an inaccurate and rough surface
to the impression.
These patients should be instructed to rinse with
an astringent mouth rinse. The 2x2 inch sponges
dampened in warm water should be used to
place pressure over the posterior palate in an
attempt to milk the glands.

This is followed by an ice water rinse
immediately before the impression is
made.
In rare instances the patient will secrete
such copious amounts of saliva that
impression making becomes extremely
difficult if not impossible.

The use of an antisialagogues in
combination with mouth rinse and gauze
packs effectively controls this salivation. A
15 mg propantheline bromide (pro-
banthine) tablet taken 30 minutes before
the impression appointment will also help
control the excessive salivation.

These drugs should never be prescribed
in the presence of medical
contraindications such as glaucoma,
cardiac conditions in which any increase in
the heart rate is to be avoided.

Mixing Impression Material
Alginate may be mixed by hand spatulation,
mechanical spatulation, or mechanical
spatulation under vacuum.
The objective is to obtain a smooth, bubble-
free mix of alginate. In hand spatulation a
measured amount of distilled water at
approximately 22 °C is placed in a rubber
mixing bowl The pre-weighed alginate
powder is sifted from its container into the
water. www.indiandentalacademy.comwww.indiandentalacademy.com

The mixing should begin slowly using a
stiff, broad - bladed spatula.When the
powder is thoroughly wet, the speed of the
spatulation should be increased The
spatula should crush the material against
the sides of the bowl to ensure that the
material is completely mixed. The
spatulation should continue for a minimum
of 45 seconds.

The strength of the gel can be reduced to
50 % if the mixing is not complete.
Insufficient spatulation can result in failure
of the ingredients to dissolve sufficiently.
Then the chemical reaction of changing
from sol to gel will not proceed uniformly
throughout the mass of alginate. An
incompletely spatulated mix will appear
lumpy and granular and will have
numerous areas of trapped air.

Complete spatulation will result in a
smooth, creamy mixture. The mixing
should be completed by wiping the
alginate against the side of the bowl with
the spatula to remove any trapped air. The
most consistent method of making a
smooth, bubble- free mix is mechanical
spatulation under vacuum.

The pre-weighed powder is added to the
pre-measured water in the mechanical
mixing bowl .The powder is thoroughly
incorporated into water by hand
spatulation. The mix is then mechanically
spatulated under 20 pounds of vacuum for
15 seconds.

Longer spatulation will result in a greatly
reduced setting time of the alginate and
could affect the strength of the gel.

Loading the Impression Tray
Small increments of the impression material
should be placed in the tray and forced under
the rim lock. Placing too large a portion of
alginate at one time increases the possibility of
trapping air The tray should be filled to the level
with the flanges of the tray.
Overfilling should be avoided.

Making the Impression
The mandibular impression is made first
because it usually entails less patient
discomfort Patient confidence is increased
when an impression has been
successfully completed while holding the
tray with the left hand the dentist uses the
right hand to remove the gauze pads from
the patient’s mouth.

The syringe is used to inject the
impression material over the occlusal
surface of the teeth and into the vestibular
and alveolingual sulcus areas. The
impression material will remain in place if
the tissues are fairly dry. A tendency for
the alginate to form a ball and not remain
where placed indicates that the tissues are
too moist and that voids are likely to be
present in the impression.

There is not enough time to repack the
mouth before gelation begins, so the
impression procedure should be completed.
The impression should be carefully inspected
and if voids are present in critical areas, the
impression procedure should be repeated.
Packing the mouth with more or larger gauze
pads and avoiding removal of the gauze until
ready to apply the alginate will usually
prevent this problem.

The layer of alginate applied with the syringe
should be 3 to 4 mm thick; If it is too thin, the
heat of the tissues of the oral cavity may
cause the material to set before the tray is
seated, resulting in a layered impression.

The fingers of the left hand that are
retracting the right cheeks should depress
the lower lip to provide good visibility.
When the tray is correctly lined up over
the teeth, the patient is asked to protrude
the tongue. The tray is carefully seated so
that its flanges are below the gingival
margins of the teeth.

The tray should not be over seated
because this could result in the cusps of
the teeth contacting the tray, causing an
inaccurate impression. Great care must be
exercised in seating the tray if the patient
has mandibular tori or other exostoses, or
the making of this impression can be a
very painful experience for the patient.

As the tray is being seated, the cheeks are
pulled out to prevent the trapping of buccal
tissues under the tray. The patient is
asked to keep the tip of the tongue in
contact with the upper surface of the tray
during the gelation of the impression
material.

The dentist must maintain the position of
the tray during the entire gelation period.
This can be accomplished most
conveniently and effectively by placing the
forefinger of each hand on the top of the
tray in the premolar area and by placing
the thumbs under the patient ‘s chin.

The dentist through tactile sense can maintain an
even amount of pressure on the tray even if the
patient swallows or opens or closes the mouth.
Any movement of the tray during the gelation
period will result in an inaccurate impression.
Allowing the patient or the assistant to hold the
tray or leaving the patient unattended must be
avoided.
Within 3 to 4 minutes the alginate should be set.

For maxillary impression, the patients is
prepared by using the rinses and placing
the gauzes pads described for making the
mandibular impression. While holding the
loaded tray with the left hand the dentist
uses the right hand to remove the gauze
pads.

Alginate is injected onto the occlusal
surfaces and in all vestibular areas as for
the mandibular arch. In addition, a fairly
large amount should be wiped onto the
palate. Failure to accomplish this step will
usually result in an impression with a large
void in the palatal area.

The loaded maxillary tray is grasped by
the thumb and forefinger of the right hand.
As the right posterior flange of the
impression tray stretches the right corner
of the mouth, the dentist ‘s left arm should
be behind the patient’s head and headrest
so that the thumb and index finger may
grasp the left corner of the mouth and
distend it slightly to allow the impression
tray to enter the mouth in a straight line.

No attempt should be made to seat the
tray until the tray is in its correct
anteroposterior position. Once the tray is
in the mouth, the thumb and forefinger of
the left hand should raise the upper lip to
allow the dentist to see the relationship
between the labial flange of the tray and
the anterior teeth or the residual ridge.

The tray must be centered and properly
aligned. This position can best be verified
by looking at the patient ‘s face from
above and observing the position of the
handle of the tray.

It should protrude straight from the center of
the mouth. After the proper position has
been verified the tray is seated by using the
fingers of both hands over the premolar
areas. As the tray is being seated the cheeks
must be lifted outward and upward to prevent
the buccal tissues from being trapped under
the flanges of the tray.

The lip must also be lifted up and out to allow
good visibility and to avoid trapping the lip
between the flanges of the tray and the anterior
teeth. Care must be taken not to over seat the
tray to avoid. contact between the tray and cusp
tips of incisal edge of the teeth.

The tray should be stabilized throughout
the set of the impression material by
keeping light pressure over the premolar
areas on both sides of the arch The
alginate should set in 3 to 4 minutes.

Effect of movement of tray:
Gelation of alginate occurs by a chemical
reaction. When mixed with water, the sodium
alginate and calcium sulfate in the powder react
to form a lattice work of fibrils of insoluble
calcium alginate. The heat of the oral tissues
accelerates the chemical reaction, causing the
alginate next to the tissues to gel first .

If the dentist exerts pressure or allows the
tray to move during gelation of the
remainder of the alginate, internal
stresses are created that can distort the
impression as it is removed from the
mouth.

Removal of Impression from Mouth:
Clinically, the initial set of alginates is determined
by a loss of surface tackiness. The impression
should be left in the mouth for an additional 2 to 3
minutes to allow the development of additional
strength. Early removal of the weak alginate may
lead to unnecessary tearing of the impression.

The gel strength doubles during the first 4-
minutes after initial gelation. No further
strengthening is found after that time. In
fact, Impression is left in the mouth for 5
minutes rather than the recommended 2
to 3 minutes after initial gelation exhibits
definite distortion.

Most alginates improve their elasticity with
time, providing a better opportunity for
accurate reproduction of undercuts.
Impressions removed too early after initial
gelation produce a rough surface of the
poured cast. These data indicate the
alginate impressions should not be removed
from the mouth for at least 2 to 3 minutes
after initial gelation.

There are two reliable methods of determining the
correct time for removal of the impression
1. A timer can be used to measure the 2 to 3 minute
period after initial gelation or
2. A small mound of the original mix of alginate can
be placed on a glass or metal surface; when this
alginate will fracture cleanly with finger pressure,
the impression is ready to be removed from the
mouth.

Reasons for Rejecting Impression
The following are specific reasons for rejecting and
repeating an impression:
1. Bubbles or voids in and around rest preparations.
2. Contact of cusp with the tray, especially when the
teeth are involved in the frame work design.
3. Show through between teeth and modeling plastic
or modeling plastic and hard palate (if the tray
has been modified for an alginate impression)

4. Voids or bubbles in palatal vault when palatal major4. Voids or bubbles in palatal vault when palatal major
connectors are to be constructed.connectors are to be constructed.
5. Peripheral underextension when a denture base has5. Peripheral underextension when a denture base has
been designed and a corrected cast impression isbeen designed and a corrected cast impression is
not planned.not planned.
6. Interproximal tearing of the impression material6. Interproximal tearing of the impression material
when coverage of those teeth has been designed.when coverage of those teeth has been designed.
7. Lack of detail on the impression surface.7. Lack of detail on the impression surface.
8. Any doubt as to the accuracy of the impression.8. Any doubt as to the accuracy of the impression.www.indiandentalacademy.comwww.indiandentalacademy.com

Impression Methods:
There are basically two dual impression
techniques. The physiologic, or functional,
impression technique records the ridge
portion by placing an occlusal load on the
impression tray as the impression is being
made.

The underlying s tissues will be displaced
because displacement will normally occur
under function.
The physiologic impression techniques
that discussed are as follows: Mc Lean’s
and Hindel’s methods, the functional
relining method, and the fluid wax method.

The selected pressure impression technique not
only equalizes the support between the abutment
teeth and the soft tissue, but has the added
advantage of directing the force to the portions of
the ridge that are most capable of withstanding
the force.
This is accomplished by providing relief in the
impression tray in selected areas and permitting
the impression to be recorded.

In those areas of the tray where relief was
not provided (the buccal shelf of the
mandibular ridge and the buccal slope and
crest of the maxillary ridge), greater
displacement of the underlying mucosa
will occur.

In both the fluid wax functional impression
technique and the selected pressure
technique an impression of the displaced
edentulous ridge is made by using an
impression tray attached to the frame
work, and the master cast is altered to
accommodate the new ridge impression.

For this reason the technique is often
referred to as the “Altered cast impression
technique” or the “corrected cast
impression technique”.

The advantage of the difference inThe advantage of the difference in
terminology is doubtful, and theterminology is doubtful, and the
descriptive terms minimally displaced referdescriptive terms minimally displaced refer
to the situation that has respondedto the situation that has responded
favorably and excessively “displaced” tofavorably and excessively “displaced” to
that which responds unfavorably are used.that which responds unfavorably are used.

The need for physiologic impressions was
first recognized by McLean and others
They realized the need of recording the
tissues of the residual ridge that would
eventually support a distal extension
denture base in the functional or
supporting form and then relating this
functional impression to the remainder of
the arch by means of a second impression.

For this dual impression a custom
impression tray was constructed over a
preliminary cast of the arch, a function
impression of the distal extension ridge
was made, and then hydrocolloid
impression was made with the first
impression held in its functional position
with finger pressure.

The greatest weakness of the technique was that
finger pressure could not produce the same
functional displacement of the tissue that biting
force produced. The apparent advantage of the
technique was lost with this weakness.
Many variations of this technique have been
developed and advocated, but all require some
form of finger loading pressure as the second
impression is made.

Hindels and other developed irreversibleHindels and other developed irreversible
hydrocolloid trays for the second impression thathydrocolloid trays for the second impression that
were provided with holes so that finger pressurewere provided with holes so that finger pressure
could be applied through the tray as thecould be applied through the tray as the
hydrocolloid impression was made.hydrocolloid impression was made.

The main change that Hindels introducedThe main change that Hindels introduced
to McLean ‘s original technique was thatto McLean ‘s original technique was that
the impression of the edentulous ridgethe impression of the edentulous ridge
was not made under pressure but was anwas not made under pressure but was an
anatomic impression of the ridge at restanatomic impression of the ridge at rest
made with a free flowing zinc oxidemade with a free flowing zinc oxide
eugenol paste.eugenol paste.

As the hydrocolloid second impressionAs the hydrocolloid second impression
was being made, however, finger pressurewas being made, however, finger pressure
was applied through the holes in the traywas applied through the holes in the tray
to the anatomic impression. The pressureto the anatomic impression. The pressure
had to be maintained until the alginatehad to be maintained until the alginate
was completely set. The two were relatedwas completely set. The two were related
to each other, however, as if masticatingto each other, however, as if masticating
forces were taking place on the dentureforces were taking place on the denture
base.base.

The main purpose of these techniques
was to relate an impression of the
edentulous ridge to the teeth under a form
of functional loading.

A disadvantage of these techniques was that if
the action of the retentive clasps of the partial
denture is sufficient to maintain the denture
base in relation to the soft tissues in the
displaced or functional form, interruption of
blood circulation would ensue, with possible
adverse soft tissue reaction and resorption of
the underlying bone.

If the action of the retentive clasps was not
sufficient to maintain that functional
relationship of the denture base to the soft
tissue, when the partial denture was in the
mouth at rest, the partial denture would be
slightly occlusal to the position it would
assume when occlusal force was applied.

This means that each time the patient ‘s
teeth came together, the remaining natural
teeth should contact only after the mucosa
had been displaced to the position at
which the impression was made. This
early or premature contact of the artificial
teeth is objectionable to many patients.

Most methods of obtaining a physiologicMost methods of obtaining a physiologic
impression for support of a distal extensionimpression for support of a distal extension
denture base accomplish the impressiondenture base accomplish the impression
procedure before completion of the denture,procedure before completion of the denture,
usually following the construction of theusually following the construction of the
framework.framework.
It is possible, however, to obtain the sameIt is possible, however, to obtain the same
results after the partial denture has beenresults after the partial denture has been
completed.completed.
The technique is referred to as a functionalThe technique is referred to as a functional
reline. It consists of adding a new surface to thereline. It consists of adding a new surface to the
inner, or tissue, side of the denture base.inner, or tissue, side of the denture base.

The procedure may be accomplishedThe procedure may be accomplished
before the insertion of the partial denture,before the insertion of the partial denture,
or it may be done at a later date f becauseor it may be done at a later date f because
of bone resorption, the denture base noof bone resorption, the denture base no
longer fits the ridge adequately.longer fits the ridge adequately.
Although the functional reline has manyAlthough the functional reline has many
advantages, and fir correcting the fit ofadvantages, and fir correcting the fit of
denture base that has been worn for adenture base that has been worn for a
period of time is essential, it does presentperiod of time is essential, it does present
many difficulties.many difficulties.

The main problems that arise are caused byThe main problems that arise are caused by
failure to maintain the correct relationshipfailure to maintain the correct relationship
between the framework and the abutment teethbetween the framework and the abutment teeth
during the impression procedure and failure toduring the impression procedure and failure to
maintain accurate occlusal contact following themaintain accurate occlusal contact following the
reline.reline.
The procedures for relining and rebasing anThe procedures for relining and rebasing an
existing removable partial denture are discussedexisting removable partial denture are discussed
in detail.in detail.

The functional reline discussed here is that doneThe functional reline discussed here is that done
to a completed partial denture before initialto a completed partial denture before initial
insertion for the purpose of perfecting the fit ofinsertion for the purpose of perfecting the fit of
the denture base to the residual ridge.the denture base to the residual ridge.
The partial denture is constructed on the castThe partial denture is constructed on the cast
made from a single impression, usually withmade from a single impression, usually with
irreversible hydrocolloid. This is an anatomicirreversible hydrocolloid. This is an anatomic
impression, and no attempt is made to alter it orimpression, and no attempt is made to alter it or
produce a functional impression of theproduce a functional impression of the
edentulous ridge.edentulous ridge.

To allow room for the impression material
between the denture base and the ridge,
space must be provided. One of the most
accurate methods of ensuring uniform
space for the impression is to adapt a soft
metal spacer over the ridge on the cast
before processing the denture base. After
processing, the metal is removed leaving
an even space between the base and the
edentulous ridge.

The portion of the technique that introduces theThe portion of the technique that introduces the
greatest hazard is the making of the relinegreatest hazard is the making of the reline
impression. The patient must maintain the mouth inimpression. The patient must maintain the mouth in
a partially open position while the border moldinga partially open position while the border molding
and impression are being accomplished because:and impression are being accomplished because:
1.The border tissues, cheek, and tongue are thus1.The border tissues, cheek, and tongue are thus
best controlled andbest controlled and
2.The relationship between the partial denture frame2.The relationship between the partial denture frame
work and the teeth must be observed.work and the teeth must be observed.

The functional reline method of improvingThe functional reline method of improving
the fit of the denture base to the residualthe fit of the denture base to the residual
ridge, although fraught with potentialridge, although fraught with potential
danger, has the advantage that thedanger, has the advantage that the
amount of soft tissue displacement can beamount of soft tissue displacement can be
controlled by the amount of relief given tocontrolled by the amount of relief given to
the modeling plastic before the finalthe modeling plastic before the final
impression is made. The greater the reliefimpression is made. The greater the relief
the less will be the tissue displacement.the less will be the tissue displacement.

The fluid wax impression may be used toThe fluid wax impression may be used to
make a reline impression for an existingmake a reline impression for an existing
partial denture or to correct the distalpartial denture or to correct the distal
extension edentulous ridge portion of theextension edentulous ridge portion of the
original master cast.original master cast.

OBJECTIVES
To obtain maximum extension of the peripheral
borders of the denture base while not interfering
with the function of movable border tissues.
To record the stress bearing areas of the ridges
in their functional form.
To record non pressure bearing areas in their
anatomic form.

The fluid wax impression is made with theThe fluid wax impression is made with the
open mouth technique so that there is lessopen mouth technique so that there is less
danger of over displacement of ridgedanger of over displacement of ridge
tissue by occlusal or vertical forces.tissue by occlusal or vertical forces.

The term fluid wax is used to denoteThe term fluid wax is used to denote
waxes that are firm at room temperaturewaxes that are firm at room temperature
and have the ability to flow at mouthand have the ability to flow at mouth
temperature.temperature.

The most frequently used fluid waxes are
Iowa wax, developed by Dr.Smith at the
University of Iowa, and Korrecta Wax no
4, developed by Dr. 0. C. and S. G
Applegate at the Universities of Michigan
and Detroit, respectively.
Korrecta wax no. 4 is slightly more fluid
than Iowa wax.

The key to the use of fluid wax lies in two areas:
space and time.
Space refers to the amount of relief provided
between the impression tray and the edentulous
ridge. :1 to 2 mm is desired.
Each time the tray is introduced into the mouth, it
must remain in place 5 to 7 minutes to allow the
wax to flow and to prevent buildup of pressure
under the tray with resulting distortion or
displacement of the tissue.

The clinical technique for the use of the fluidThe clinical technique for the use of the fluid
wax calls for the water bath maintained atwax calls for the water bath maintained at
51° to 54° C into which a container of the51° to 54° C into which a container of the
wax is placed. At this temperature the waxwax is placed. At this temperature the wax
becomes fluid. The wax is painted on thebecomes fluid. The wax is painted on the
tissue side of the impression tray with atissue side of the impression tray with a
brush.brush.

The peripheral extension of theThe peripheral extension of the
impression tray is critical. The bordersimpression tray is critical. The borders
must be short of all movable tissue, but notmust be short of all movable tissue, but not
more than 2 mm short because the fluidmore than 2 mm short because the fluid
wax does not have sufficient strength towax does not have sufficient strength to
support itself beyond that distance.support itself beyond that distance.

Inaccuracies will develop if the wax isInaccuracies will develop if the wax is
extended beyond that length. Originally aextended beyond that length. Originally a
harder wax, Korrecta Wax no:1 was usedharder wax, Korrecta Wax no:1 was used
to support the softer No.4 wax ifto support the softer No.4 wax if
extension beyond that length wasextension beyond that length was
needed. The no.1 wax however, is noneeded. The no.1 wax however, is no
longer available.longer available.

The wax is painted on the surface of the tray to aThe wax is painted on the surface of the tray to a
depth slightly greater than the amount of reliefdepth slightly greater than the amount of relief
provided. The tray is seated in the mouth. Theprovided. The tray is seated in the mouth. The
patients must remain with the mouthpatients must remain with the mouth
approximately half open for about 5 minutes. Theapproximately half open for about 5 minutes. The
tray is removed, and the wax examined fortray is removed, and the wax examined for
evidence of tissue contact. Where tissue contactevidence of tissue contact. Where tissue contact
is present the wax surface will be dull.is present the wax surface will be dull.

If needed additional wax is painted on those areasIf needed additional wax is painted on those areas
not in contact with the tissue. The tray must remainnot in contact with the tissue. The tray must remain
in the mouth a minimum of 5 minutes after eachin the mouth a minimum of 5 minutes after each
addition of wax. The peripheral extensions areaddition of wax. The peripheral extensions are
developed by tissue movements by the patient. Fordeveloped by tissue movements by the patient. For
the buccal and distobuccal extension in athe buccal and distobuccal extension in a
mandibular impression the patient must move to amandibular impression the patient must move to a
wide- open-mouth position. This will activate thewide- open-mouth position. This will activate the
buccinator muscle and pterygomandibular raphebuccinator muscle and pterygomandibular raphe
and produce the desired border anatomy.and produce the desired border anatomy.

For the proper lingual extension for a mandibularFor the proper lingual extension for a mandibular
impression the patient must thrust the tongueimpression the patient must thrust the tongue
into the cheek opposite the side of the archinto the cheek opposite the side of the arch
being border molded. The distolingual extensionbeing border molded. The distolingual extension
is obtained by having the patient press theis obtained by having the patient press the
tongue forward against the lingual surface of thetongue forward against the lingual surface of the
anterior teeth.anterior teeth.

These movements must be repeated aThese movements must be repeated a
number of times after the impression hasnumber of times after the impression has
been in the mouth long enough for thebeen in the mouth long enough for the
wax to have softened sufficiently to flow.wax to have softened sufficiently to flow.

When the impression evidences complete tissueWhen the impression evidences complete tissue
contact and when the anatomy of the limitingcontact and when the anatomy of the limiting
border structure is evident, the impression shouldborder structure is evident, the impression should
be replaced in the mouth for 12 minutes. This finalbe replaced in the mouth for 12 minutes. This final
time to be certain that the wax has completelytime to be certain that the wax has completely
flowed and released any pressure that may beflowed and released any pressure that may be
present.present.

The finished impression must be handledThe finished impression must be handled
carefully and the new cast poured as sooncarefully and the new cast poured as soon
as possible because the wax is fragile andas possible because the wax is fragile and
subject to distortion.subject to distortion.

The fluid wax impression technique can
produce an accurate impression if the
technique is properly executed The procedure
is time consuming, but if the time periods are
not followed accurately, an impression with
excessive tissue displacement will result.

Corrected castCorrected cast

Technique
1. Fashioning custom acrylic resin impression tray1. Fashioning custom acrylic resin impression tray
to retention lattice work of removable partialto retention lattice work of removable partial
denture.denture.
2. Developing denture base impression on these2. Developing denture base impression on these
trays.trays.
3. Removing edentulous ridge from master cast.3. Removing edentulous ridge from master cast.
4. Securing framework with developed bases to4. Securing framework with developed bases to
master cast.master cast.
5. Pouring the impression with dental stone.5. Pouring the impression with dental stone.

Modifications:
Variation of altered cast technique by Robert. P
Renner
After the fit of framework has been refined intra
orally, the border of residual ridge are outlined on
master cast. A small residual ridge are outlined
on master cast. A small segment of bone plate
wax is warmed over Bunsen burner and adapted
to penciled outline. The wax will act as shim /
space between residual ridge and custom tray.

Retention latticework of removable partial
denture framework is warmed over a frame
and framework is seated back on master
cast. It should be freed in one or two areas
so that the auto polymerizing acrylic resin
tray will be adapted to it.

Apply separating medium, allow it to dry and autodry and auto
polymerizing acrylic resin material is mixed andpolymerizing acrylic resin material is mixed and
adapted to edentulous area of master cast, anyadapted to edentulous area of master cast, any
excess material is trimmed.excess material is trimmed.
When acrylic material is polymerized, assembly isWhen acrylic material is polymerized, assembly is
placed in warm slurry water to soften and removeplaced in warm slurry water to soften and remove
wax spacer. Border molding is done. Vent holeswax spacer. Border molding is done. Vent holes
are placed in order to reduce hydrostatic pressureare placed in order to reduce hydrostatic pressure
developed between tray and tissues. Finaldeveloped between tray and tissues. Final
impression is accomplished using metallic oxideimpression is accomplished using metallic oxide
paste or rubber base impression material.paste or rubber base impression material.

Procedure
11. A metallic paste impression is received in the laboratory.
Remove impression material from the framework in areas
that contact the teeth.

2. Trim the master cast so that the functional impression
can be poured in correct relationship to the remaining
teeth.

3. Seat the framework on the cast, and inspect it for contact
between the functional impression and the cast. If contact
is present, the cast must be trimmed until clearance is
present.

4. Cut retention grooves into the areas of the cast that will
be corrected when the functional impression is poured

5. Adapt and seal beading wax 2 to 3 mm above the borders
of the functional impression

6. Seat the framework on the cast, and secure it in position
with sticky wax

7.7. Seal the leading edge of the impression to the cast to
prevent dental stone from flowing onto the teeth when
the cast is poured.

8. Use strips of base plate wax to compete the boxing of
the impression on the buccal and lingual aspects

9. A tight seal of beading and boxing wax is critical in this
pouring method and is difficult to attain. Test the
completeness of the seal by pouring clear slurry water into
the boxed impression. A difficult area to seal is the relief
area under the major connector.

10. Place the cast and impression in clear slurry water to
soak for 4 to 5 minutes in preparation for pouring the
corrected cast.

11. Measure and mix the improved dental stone. Pour the
boxed impression by adding small increments of stone and
using light vibration. Sufficient stone must be used to
support the heel of the cast.

12. Remove the boxing and luting materials from the
corrected cast. Shape the cast on a model trimmer.

13.13. Soften the impressionSoften the impression material in warm water, andmaterial in warm water, and
remove the framework and impression tray from theremove the framework and impression tray from the
corrected cast.corrected cast.

14. Burn the impression tray off the framework and place it
on the cast. Smooth the land area of the cast, and the
corrected cast procedures is complete.

AN ALTERED CAST PROCEDURE
TO IMPROVE TISSUE SUPPORT FOR
REMOVABLE PARTIAL DENTURES
- R J. LEUPOLD, F J. KRATOCHVIL : JPD 1965(15), 4, 672- 678

SINGLE- TRAY DUAL- IMPRESSION TECHNIQUE FOR
DISTAL EXTENSION PARTIAL DENTURES
JOSEPH A. R- JPD 1970(24,1,41-46)

IMPRESSION TECHNIQUE FOR MAXILLARY
- C D. LEACH & T E. DONOVAN JPD 1983 (50)2,283-285

AN ALTERED CAST IMPRESSION TECHNIQUE THAT ELIMINATES
CONVENTIONAL CAST DISSECTING & IMPRESSSION BOXING
-M S. CHEN AND et al - JPD 1987 (57) 4, 471-474

A MODIFICATION OF THE ALTERED CAST TECHNIQUE
-RICHARD BAUMAN & JAMES .D B – JPD 1982(47) 2, 212-213

AN IMPRESSION TECHNIQUE TO MAKE NEW MASTER CAST
FOR AN EXISTING REMOVABLE PARTIAL DENTURE
-PHILIP J. R - JPD 1992 (67) 4, 488-490

For the production of accurate master cast
the impression technique far out weights the
selection of the impression material.
No available knowledge of the person
making the impression material will produce
results greater than the skill and knowledge
of the person making the impression.

““ Good technique pays off ” is not merely a
motto to hang on a wall but these are
words of wisdom. Good technique will
indeed result in better treatment and
improved patient care.

1. Glossary of Prosthodontic Terms -8 th Edn, 2005.1. Glossary of Prosthodontic Terms -8 th Edn, 2005.
2.2. Stewart, Rudd, KuebkerStewart, Rudd, Kuebker : Clinical Removable Partial: Clinical Removable Partial
Prosthodontics.Prosthodontics.
3.3. McGivney GP, Alan B Carr David T BrownMcGivney GP, Alan B Carr David T Brown ::
McCracken’s Removable Partial Dentures-11 th Edn.McCracken’s Removable Partial Dentures-11 th Edn.
4.4. Joseph E. Grasso, Ernest L. MillerJoseph E. Grasso, Ernest L. Miller : Removable Partial: Removable Partial
Prosthodontics.Prosthodontics.
5.5. Alan A. Grant, Wesley JohnsonAlan A. Grant, Wesley Johnson : Removable Partial: Removable Partial
Dentures.Dentures.

6.6. F. James KratochvilF. James Kratochvil : Partial Removable Prosthodontics.: Partial Removable Prosthodontics.
8.8. Robert P. Renner, Louis J. BoucherRobert P. Renner, Louis J. Boucher : Removable Partial: Removable Partial
Dentures.Dentures.
9.9. Kenneth D Rudd, MorrowKenneth D Rudd, Morrow: Dental Lab, Procedure for: Dental Lab, Procedure for
Removable Partial Dentures.Removable Partial Dentures.
10.10. DavenportDavenport: Color Atlas of Removable Partial Dentures.: Color Atlas of Removable Partial Dentures.
11.11. BatesBates: Removable Denture Construction.: Removable Denture Construction.
12.12. OsborneOsborne: Partial Dentures.: Partial Dentures.

AN ALTERED CAST PROCEDURE
TO IMPROVE TISSUE SUPPORT FOR
- R J. LEUPOLD, F J. KRATOCHVIL : JPD 1965(15), 4, 672- 678
SINGLE- TRAY DUAL- IMPRESSION TECHNIQUE FOR
DISTAL EXTENSION PARTIAL DENTURES
JOSEPH A. R- JPD 1970(24,1,41-46)
IMPRESSION TECHNIQUE FOR MAXILLARY
- C D. LEACH & T E. DONOVAN JPD 1983 (50)2,283-285
AN ALTERED CAST IMPRESSION TECHNIQUE THAT ELIMINATES
CONVENTIONAL CAST DISSECTING & IMPRESSSION BOXING
-M S. CHEN AND et al - JPD 1987 (57) 4, 471-474
A MODIFICATION OF THE ALTERED CAST TECHNIQUE
-RICHARD BAUMAN & JAMES .D B – JPD 1982(47) 2, 212-213
AN IMPRESSION TECHNIQUE TO MAKE NEW MASTER CAST
FOR AN EXISTING REMOVABLE PARTIAL DENTURE
-PHILIP J. R - JPD 1992 (67) 4, 488-490www.indiandentalacademy.comwww.indiandentalacademy.com

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