Dental Waxes
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Transcript of Dental Waxes
DENTAL WAXES
Contents:
Ø Introduction.Ø Uses of wax in dentistry.Ø Components of dental waxes.Ø Properties of waxes.Ø Classification of waxes.Ø Description of individual waxes.Ø Impression procedures with impression waxes.Ø References
Introduction:
Originally applied to natural occurring esters of fatty acids & monohydric alcohols,
the term now is used for both naturally occurring & manufactured products resembling
esters. They have
Dull luster
Soapy or greasy texture
Soften gradually on heating before forming a liquid
Uses in Dentistry:
Inlay pattern
Boxing of impression
Base plate
Casting wax
Utility wax
Sticky wax
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Components of dental waxes:
Natural Waxes Synthetic Waxes Additives
MINERAL a) Paraffin b) Montaux c) Barnsdhal. d) Ozokerite e) Microcrystalline
a) Aerosol OT b) Castor wax c) Flexowax C d) Dura wax
FATS Stearic acid
PLANTa) Carnaubab) Ouricuryc) Candelilad) Japan waxe) Cocoa butter
NATURAL RESINSa) Copalb) Dammarc) Sandracd) Shellac
INSECT Bees wax
SYNTHETIC RESINSa) Polyethyleneb) Polysterene
ANIMAL Spermaciti
Corrective impression
Bite registration
Dental waxes are combination of various types of natural & synthetic waxes, gums, fats,
fatty acids, oils , resins & pigments compounded to provide desired physical properties.
Natural Waxes
• Two main group of organic compounds in waxes are-
• Hydrocarbons
• Esters
Some waxes contain free alcohols and acids as well.
Synthetic Waxes
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Complex organic compounds of varied chemical composition
Use in dental formulations is limited
More refined than natural waxes
Types
Polyethylene waxes
Polyoxyethylene glycol waxes
Halogenated hydrocarbon waxes
Hyrogenated waxes
Wax esters
Composition
Polyoxyethylene waxes are polymers of ethylene glycols. They have limited compatibility
with other waxes. They have melting temperature. From 37°C to 63°C. but function as
plasticizers and toughen films of wax. Others are produced by reaction with natural
waxes.
Properties
Melting range
Thermal expansion
Mechanical properties
Flow
Residual stress
Ductility
Melting Range
Have a range as they contain several types of molecules, each having a range of
molecular weight.
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Thermal Expansion
Linear co- efficient of thermal expansion – change in length per unit original length
with 1° change in temp. Waxes have the largest co- efficient of thermal expansion among
all dental materials. Weak secondary valance forces are easily overcome by thermal
energy, more so in mineral waxes than plant waxes. Many waxes exhibit at least 2 rates
of thermal expansion. Change in rate occurs at transition points. At these points the
internal structural parts becomes become freer to expand. Because the ingredient waxes
undergo transition that do not coincide with one another, inlay waxes exhibit more than
two changes in rate of expansion.
Mechanical Properties
Elastic modulus
Proportional limit
Compressive strength
All are low when compared to other materials
Elastic Modulus
Elastic moduli of carnauba wax is highest
Bees wax – lowest
Decreases with increase in temperature.
Inlay wax (simulates a mixture of 75% paraffin & 25% carnauba wax) – 760 to 48.2 MPa
between 23°C & 40°C
Application
Modulus ratio for inlay and soft green casting wax is 7:1.
To avoid non uniform distortion of the wax pattern during hygroscopic casting
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procedure use inlay wax (less expansion) for lateral walls and soft green for occlusal
surface.
Proportional Limit/ Compressive Strength
Decrease with increase in temp.
E.g. - P.L. for inlay wax decreased from 4.82 to 0.21 from 23°C to 40°C.
C.S. – 82.7 to 0.48 MPa
Flow
Result of slippage of molecules over each other. In liquid state of wax it is synonymous
with viscosity below melting temperature. It indicates the degree of plastic deformation
at a given temp. Flow depends upon::
Temp of wax
The force applied
Time for which the force is applied
Flow is greatly increased as melting point is approached
Application
A direct inlay wax should have a high flow just a few degrees above the mouth
temperature so it is not too hot in workable condition
Should have a no flow at mouth temperature so that it does not distort during removal
of pattern
Yellow beeswax does not flow extensively till it reaches 38°C
At 40°C its flow is 7%
Has been used as an impression wax
Residual Stress
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Residual stresses always exist in a prepared wax pattern
Presence of such stresses can be demonstrated by comparison of thermal expansion
curves of annealed waxes with wax cooled under compression & expansion
Extent of change in thermal expansion depends upon
1. Magnitude of residual stress
2. Time &
3. Temp of storage of specimen
COMPRESSION
When cooled under compression, the atoms & molecules are forced together as
compared to when there is no external stress
After cooling & upon load removal, motion of molecules is restricted – residual internal
stresses
On heating the residual internal stresses is added to normal thermal expansion – hence
more expansion.
TENSION
Cooling under tension results in molecules moving away from one another comparatively
On heating, release of these internal stresses work in a direction opposite to thermal
expansion
Large internal tensile stresses may result even in contraction upon heating
Ductility
Like flow, ductility increases with increase in temperature of waxes
Lower the melting temperature of a wax, more will be the ductility
Waxes made of components having wide melting ranges have more ductility
With wide range of melting point of components, the softening point of lowest is
approached first on heating
On further heating this component liquefies, the softening point of next is approached &
so on
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Pattern Wax Processing Wax Impression Wax
1. Inlay Wax 1. Boxing Wax 1. Corrective Wax
2. Casting Wax 2. Utility Wax 2. Bite registration Wax
3. Base plate Wax 3. Sticky Wax
Entire wax mass is plasticized & ductility increases
CLASSIFICATION OF DENTAL WAXES:
Pattern Waxes
Used to form general pre determined size & contour of an artificial restoration
Later it is replaced by more durable material such as cast gold, cobalt- chrome- nickel
alloys etc
They exhibit thermal change in dimension and warpage on standing
INLAY WAXES ADA 4
Inlays, crowns & bridge units are formed by a casting process that uses lost wax pattern
technique
A pattern of wax is constructed that duplicates shape and contour of casting
After investing & spruing the wax is eliminated by heating
Typical Composition
Paraffin- 60%
Carnauba- 25%
Ceresin- 10%
Bees wax- 5%
TYPES
BY FLOW
1. Hard
2. Regular
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3. Soft
Flow can be reduced by
• Adding more carnauba wax
• Using higher melting paraffin wax
BY TECHNIQUE
(Revised ANSI/ ADA Sp. No. – 4)
Type I - Direct
Type II - Indirect
Type I - Hard wax used for forming patterns directly in mouth
Type II - Softer wax used for indirect technique
TYPE I
Lower flow at 37°C to minimize any distortion on removal from mouth
Working temperature for registering cavity details is around 45°C
Should not be high so as to avoid damage to pulp
Maximum linear thermal expansion allowed –
25°C – 30°C – 0.20%
25°C – 37°C – 0.60%
Must be mentioned by the manufacturer so that compensation is made for the shrinkage
from mouth temperature to room temperature.
Insufficient flow of wax caused by insufficient heating causes
• Lack of details
• Excess stress within the pattern
• Excess flow by over heating makes compression of wax difficult (because of lack of
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body)
• From mouth temperature to room temperature (24°C) there is 0.4 % linear
contraction
TYPE II
• These waxes are commercially available for crown & bridge work and inlays in the
form of
• Sculpturing / modeling waxes
• Dipping waxes
Sculpturing Waxes
Properties
Low shrinkage due to microcrystalline structure
Quick to apply and quick to cool with its optimum melting interval
High surface tension
Excellent carving properties due to its non-elastic and hard quality
Wide assortment of colours
Available as
• Universal
• Specific purpose like
- occlusal
- cervical
- underlay
UNIVERSAL
Ideally suited for quick coverage of large areas with wax
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Low surface tension
Low melting point
Small contraction on hardening
Excellent flow properties
OCCLUSAL
High strength - no abrading of contact points
High rigidity
Can be easily drawn due to its high surface tension
Opaque appearance for defined contours and permanent control during modeling
Difference between occlusal and universal wax
Occlusal wax - greater surface tension and high rigidity
The surface tension allows ball-shaped drops to form and harden
This eases work considerably in the waxing-up phase
The increased strength guarantees precise modeling
Universal wax - excellent flooding properties, can be used in many areas
CERVICAL
Low shrinkage
Particularly stable
Can be adapted precisely and thinly to the preparation border
Excellent carving properties
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UNDERLAY
For small undercuts and cavity coverage before inlay modeling
Significantly softer than cervical wax
Gentle elasticity
Good adaptation and carving properties
Very low shrinkage
Dipping Wax
The hotty LED is a wax dipping pot which permits controlled temperature setting and
displays the set and the actual value
Advantages
High precision via low shrinkage
Optimum viscosity at 89–91°c (192–196°f)
Precise-fitting copings with an even layer thickness
High stability and elasticity
Contains no acrylic additives
Easy to cut off the preparation border
Method:
Preparation:
· Place a thin isolating layer on the die surface.
· Build-up of bubbles and streaks are thus prevented
Dipping:
Support your hand comfortably
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Do a quick dip to just beyond the preparation border
Slowly and evenly remove the die from the wax
Just before the tip comes out hold it steady in the pot for a short time so that any excess
wax can drip down
Warpage
Patterns distort when allowed to stand unrestrained. It increases with increase in
time & temp. of storage. Because of the release of stresses introduced in pattern during
formation
Minimizing Warpage
Use higher temperature at time of formation – less force to shape – less residual stresses
Soften the wax uniformly at 50°C for 15 min
Warmed carving instruments & die
Casting Wax
Used for metallic framework of RPDs
Available as sheets (28 – 30 gage; 0.4 – 0.32 mm), readymade shapes & bulk
Serve same purpose as inlay wax, differ slightly in physical properties
Ingredients similar to inlay waxes
Sheets used to establish minimum thickness in some areas of RPD framework such as
palatal & lingual bar
No ADA specification but only a federal specification for its properties
Flow
Are to be used on a cast & not in mouth
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They have a higher flow as compared to inlay waxes at around 35 – 37°C
35°C – 10% min
37°C – 60% max
Working Properties
Slightly tacky so as to maintain position on cast
Pliable & readily adaptable at 40 - 45°C
Copy accurately against the surface which it is pressed
Shall not be brittle on cooling
Must vaporize at 500°C
Be bent double on itself without fracture at 23°C
Baseplate Wax
ADA 24
The basic use is to form occlusal rim on baseplate tray to set teeth for denture
Establish VD, contour of the denture after teeth setting
Also used for MFPs, patterns for orthodontic appliances
Checking articulating relations in mouth & transferring to articulators
Supplied as sheets 7.60 x 15 x 0.13 cm, red, pink or orange in colour
Three types
Type I – soft wax for contours & veneers
Type II – medium wax for temperate climates
Type III – hard wax for tropical climates
Mainly differ in flow with type III having least
Requirements
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Linear thermal expansion from 25° to 40°C < 0.8%
Softened sheets shall cohere readily without becoming flaky or adhering to fingers
No irritation to oral tissues
Pigment not to separate on processing
No adhesion to other sheets or separating paper on storage
PROCESSING WAXES
Boxing Wax
Aids in forming a plaster or stone cast from an impression
Boxing consists of
Adapting a long narrow strip of wax around the impression below peripheral height
Followed by a wide strip of wax to form a wax box
Also called carding wax: originally used for placing porcelain teeth in packing
Federal requirements:
Smooth glossy surface on flaming
Pliable at 21°C; retains shape at 35°C
Readily adapt to impression at room temp.
Seal easily to plaster with hot spatula
Utility Wax
• An easily workable, adhesive wax for multiple use such as-
• Improving the contour of perforated tray for hydrocolloids
• To stabilize a pontic for a temporary bridge while index is being made
FEDERAL REQUIREMENTS:
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IMPRESSION WAXES
Impression waxes, though rarely used to record complete impressions, they can be effectively used to correct
small imperfections in other impressions. They are thermoplastic materials, which flow readily at mouth
temperature and are relatively soft even at room temperature.
Impression waxes are classified as:
Corrective impression wax
Bite registration wax.
There are no ADA federal specifications for impression waxes.
Composition
Impression waxes consist typically of a mixture of low melting paraffin wax and bees wax in ratio of about 3:1.
Pliable at 21° to 24°C; workable & easily adaptable at room temp.
Flow be between 65% & 80% at 37.5 °C
Tacky at 21° to 24°C; adhesion for build up
Colour- green or black
Sticky Wax
Formulated from a mixture of waxes, resins & other additives
Sticky when melted, adheres closely to the surface
At room temperature – firm, free from tackiness & brittle
Should fracture rather than flow when deformed
Uses
Used primarily on dental stones and plasters
Used in repair for holding the metal or resin parts temporarily
Federal Requirements
Have a dark or vivid colour to distinguish from gypsum products
Shrinkage - < 0.5 % from 43° to 28°C
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In addition it may contain other wax like ceresin and also metal particles e.g. aluminum or copper particles.
Properties
Melting range
Since waxes have several types of molecules i.e. Crystalline or amorphous of different molecular weights, they
have melting ranges rather then a point. Melting range of impression waxes is much lower due to additions like
resin. Impression waxes flow at mouth temperature under occlusal load. Heat of fusion is the heat in calories
required to convert 1gm of material from the solid to liquid state at the melting temperature.
Melting temperature:
© Beeswax is 62.8°C.© Paraffin wax is 52°C.
Melting range:
© Beeswax is 34-70° C.
© Paraffin wax is 44- 60°C.
Flow
The flow of corrective temperature wax and bite registration wax is measured at 37°C and is 100% and
2.5%-22% respectively, thus these waxes are susceptible to distortion on removal from the mouth. Flow as
tested by compression of cylindrical specimens is 2—85% at 37°C.
echanical Properties
The elastic modulus, proportionately limit and compressive strength is low as compared with other materials and are
dependent on temperature.
Thermal expansion
Impression waxes expand when subjected to a rise in temperature and contract as the temperature decreased.
Paraffin and beeswax, which are the chief constituents of impression waxes, have different temperature range.
Because of the coefficient of thermal expansion is so great, the impressions should be poured immediately to
avoid distortion.
If the impression cannot be poured immediately, they should be stored at or near 0°C. Coefficient of linear
thermal expansion is 350-700 x10-6/ °C.
Advantages
1. Impression wax can be used in thin layers to record the impression surface of the ridge accurately.
2. It is relatively easy to manipulate.
3. It does not need advanced equipments.
Disadvantages
1. Distortion of the impression wax can occur when the records are stored due to the release of stresses.
2. It is technique sensitive.
3. It can be used only to record edentulous surfaces,
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Applications
Corrective impression wax is used as wax veneer over an original impression to contact and register the
details of soft tissues. It is claimed that it records the mucous membrane and underlying tissues in a functional
state in which movable tissue is displaced to such a degree that functional contact with the base of the denture is
obtained.
Functional impressions materials with thermoplastic waxes for reline procedures:
Historically, wax was one of the first materials used to make impressions of the edentulous arch. The first
commercially available "mouth temperature" waxes appeared in 1930's they were composed of natural waxes in
paraffin base. In late 1950's, thermoplastic resinous materials became available; e.g. adaptol and stalite plastic
impression material. These fluid materials were designed to record tissue under an occlusal load and accomplish
the same objectives as the waxes.
Technique
When used for a distal extension mandibular removable partial denture that has been in service a long time,
provision must me made for correcting the disorientation of the framework that occurs when resorption of the
supporting tissue allows the base to settle. This can be accomplish by building up the distal third of the base with
red modeling compound and seating framework with pressure on the rests and indirect retainers with a blunt
instrument but no force should be exerted.
Pre impression procedure
Mucosa should be allowed to recover prior to starting the impression procedures. Recovery may be facilitated by
adjusting the existing prosthesis, instructing the patient to remove the prosthesis at night and consume a soft
diet, surgical intervention or use of a tissue conditioning material.
Impression procedure
The border of the prosthesis must be satisfactory before the impression material is added. The impression will
distort too easily if it is not supported 1to 2 mm beyond the border of the prosthesis. The impression material is
placed in a hot water bath or on a hot plate to allow the material to become fluid. The entire denture base is then
coated liberally with the fluid material. A No.2 or larger brush is an acceptable applicator. The prosthesis is
placed in the patient's mouth and the patient is instructed to bring the teeth into light occlusal contact. After 4 to
5 minutes, the impression material will have reached mouth temperature. The patient should then bring the teeth
into maximum occlusal contact guided by the dentist. The border areas are moulded by the manipulation of the
dentist and the patient. The prosthesis is then removed and inspected for voids, which can be filled with more
fluid impression material. The prosthesis is reinserted in the patient's mouth and again allowed to reach mouth
temperature. The patient is given a stick of chewing gum and instructed to chew the gum on both sides of the
mouth for 5 minutes. After disposing the gum the patient rinses with ice water. The prosthesis is removed and
immediately submerged in an ice water bath.
An alternative impression material for this technique could be one of the tissue conditioning material. The
advantage that the wax or fluid resin has over the tissue conditioning material is that it results in a smooth glass
like surface on the finished denture base. This is of particular importance when a great deal of denture base
movement is anticipated and when the tissue is thin, fragile and easily abraded.
A simple formula for producing & corrective impression wax from paraffin wax and bees wax is described by
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Mc Crorie i.e. mixture of yellow bees wax and thermowax or paraffin wax with flow characteristics at 37ºC
similar to those of Korecta wax Nos. 2,3 and 4.
Wax Mixture (% flow at 37ºC)
75% yellow bees wax: 25%parafiin wax (80)
50% yellow bees wax: 50% paraffin wax (85)
25% yellow bees wax: 75% paraffin wax (89)
Korecta wax is available in four grades, each with a different degree of plastic deformation at mouth
temperature. Each grade is designed for a specific purpose.
Extra hard No.1 (pink): A reinforcing material used only on the external surface to support -wax extensions
beyond tray margins.
Hard No. 2 (yellow): Used in rebasing as a hard foundation for Korecta waxes 3 and 4 when extensive
absorption (alveolar resorption) necessitates a bulk of material. Also, used to restore occlusion in a partial
denture or a removable partial denture, which has settled due to severe tissue change.
Soft No. 3 (red): Used for minor tray correction and as an initial lining to stabilize the tray.
Extra soft No. 4 (orange): Used to secure a completely adapted impression under natural masticatory pressure.
It leaves a finished surface and registers fine tissue details.
Wax %flow at 37ºC
KorectaNo.l (extrahard) 3
Korecta No. 2(hard) 80
Korecta No.3 (soft) 85
Korecta No.4 (extra soft) 90
2. These waxes can also be used to produce a muco-compressive impression of the edentulous saddles
for a lower, free-end saddle partial denture. This is called as the Applegate technique.
Korecta wax No.1 and 4 are no longer available which were originally used for making edentulous impressions.
However necessary waxes like extra soft No. 4 -orange are available again and can be used.
Technique
The wax is melted in a water bath before being applied to the area of the impression that is faulty or to the
impression tray. The impression tray is then returned to the mouth and should be reseated with firm finger
pressure. The impression is left in the mouth for sufficient time to raise the wax to oral temperature so it will
undergo plastic flow under pressure to record accurately the denture bearing area.
The results obtained are good but the procedure is difficult. It is hard to stabilize the metal framework on the
remnant cast and it becomes necessary to add special stabilizing extensions to the structure. It is also difficult to
box and pour the second stage of the techniques and obtain a good union between both parts of the casts.
Heartwell and Rahn plainly state that wax cannot be used. Henderson, McGivney and Castlebery state that
polysulphide rubber or wax can be used for final impression of an edentulous area of a complete or partial
denture. In some applications wax may have advantages over polysulphide rubber or other impression materials.
Holmes J B found that an impression of the edentulous area of a removable partial denture made with fluid wax
created the best stability when compared with other materials.
Mc Cracken stated that in some instances placement of the tissue is necessary to obtain maximum support of
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mandibular dentures. He advocated the use of fluid wax for this purpose. This is particularly important for older
patients with atrophied mandibular residual ridges who may have contra indications for implants or other
surgical procedures.
Levin, Jogleker and Sinkford used a resinous wax for border molding and Carlile used wax for correction of a
functional impression. However, in addition to Heartwell and Rahn, Phillips, Boucher, Renner and Clark do not
mention wax as an impression material.
Wrinkles do not appear when fluid wax is used as the flow properties of wax prevent the distortion. However,
wax must flow with minimum pressure and must not overly displace tissue. An advantage of wax is that it may
be used with patients in whom saliva is a problem (dementia, hypersialogenous sialorrhea pancreatica) and in
whom pharmacological intervention is contraindicated. Also wax impressions are corrected without redoing
the procedure.
Other advantages include:
© Low cost© Easy handling© No need for adhesive© Odorless© Clean material to work with
© Absence of tissue reactions
Disadvantage:
© Distortion while removing from the undercut if care is not taken.
PPS Technique
Fluid Wax Technique
The anterior and posterior in vibrating lines are marked as for the conventional techniques on the final wash
impression.
Impressions made with zinc-oxide eugenol or plaster are preferred over the elastic impression materials as they
set rigid, are slightly resilient and when reseated in the mouth under pressure, it may distort the relationship
between the wax added to the posterior border and the rest of the denture bearing surface. Also, wax will not
adhere to elastic materials. Hence, either the material in the seal area must be removed prior to the wax
application or laboratory varnish must be applied to the elastic material in the seal area before the wax is placed.
Waxes which can be used are:
• IOWA Wax (white) developed by Dr. Earl S. Smith.
Korecta Wax No. 4(orange) developed by Dr. O.C. Applegate.
H-L physiologic paste (yellow-white) developed by Dr. C.S. Harkins.
Adaptol (green) developed by Nathan G. Kaye.
These waxes are designed to flow at mouth temperature.
Technique
The melted wax is painted onto the impression surface within the outline of the seal area.
The wax is applied slightly in excess of the estimated depth and allowed to cool to below mouth temperature to
increase its consistency and make it more resistant to flow.
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The impression is carried to the mouth and held in place under gentle pressure for four to six minutes to allow
time for the material to flow.
Position of the head and tongue.
According to Nelson, the soft palate should be impressioned in its most functionally depressed position. The
maximum depression (downward and forward position) of the soft palate will be recorded when the Frankfort
plane (porion - orbitale) is 30 below the horizontal and the tongue is firmly positioned against the mandibular
anterior teeth. The patient should not protrude the tongue beyond the approximated position of the incisal edges,
as this will foreshorten the posterior border of the final impression. The head and tongue position translate the
mandible anteriorly. The soft palate will then be passively brought downward and forward due to the indirect
attachment of the soft palatal tissues to the body of the mandible and the insertion of the palatoglossus muscle
into the side of the tongue. Flexion of the head also contributes to moving excess impression material and saliva
out of the mouth, rather than progressing down the pharynx.
While maintaining the 30° flexion of the head and the anterior tongue position, the patient is asked to periodically
rotate the head so that all the functional positions of the soft palate are recorded.
After 4-6 minutes, the impression tray is removed from the mouth and the wax examined for uniform contact
throughout the PPS area.
If tissue has been contacted, the wax will have a glossy appearance and if not contacted, it will have a dull
surface.
Addition of wax can be done, if deficient and excess can be trimmed with a hot scalpel if it protrudes from the
end of the tray.
3. A technique of impression making whereby an accurate impression of the teeth and correct border
extension of the ridges are obtained with the use of a single custom tray in conjunction with one impression
material or with a combination of materials of different physical and/or chemical properties provides for seating
the tray in a firm and positive manner- in the position that has been previously determined by a spacer.
The mouth is divided into two zones that are to be registered successively and with one of them always serving
as a support for the other. A problem with successive impressions of sections of a partially edentulous mouth is
that on making the impression of the second zone, some of the material used slips under the impression of the
first zone. To avoid this, it is suggested that before making the impression of zone II, the tray with the
impression of zone I be first placed in the mouth, correctly located, and then the impression material for zone III
injected through the tray by means of built-in-tubes.
Technique
Outline the extension of the custom tray on the diagnostic cast. Determine zone I and zone II of the future
impression and mark their limits.
Block out undercuts in zone II.
Apply the spacer. If wax is being used, cover it with metallic foil to avoid its adhesion to the acrylic resin tray
material. If a firmer support is desired, the spacer can be made of acrylic resin.
Prepare the custom tray and place the tubes that will permit the injection of the impression material for zone II.
Provide adequate venting.
Try the tray in the mouth. Verify its easy placement and withdrawal and its correct extension, especially over the
distal-extension ridge or ridges.
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Remove the spacer from zone I and prepare tray with adhesives or perforations for retention of the selected
impression material.
Make the impression of zone 1.
Remove the spacer from zone II and prepare the tray to retain the impression material. With a sharp knife, exactly
delineate the impression of zone I because some of the impression material has probably spread over the spacer.
Replace the tray in the mouth, with the impression of zone I now acting as a support, and firmly keep it in
position. Prepare an elastic impression material, load it in an adequate syringe, and inject it through the tubes
embedded in the tray.
Advantages
Because a single tray is used, a stable spatial relation is assured between the impressions of the dentulous and
edentulous segments. The technique offers an unlimited choice and combination of impression materials to
obtain the best possible results.
Working with a support ensures that the tray will maintain a stable and predetermined position not only during
try-in, but while the impression itself is made.
4. Impression wax can be applied with a brush in small quantities to 'fill' in areas of impression in which
insufficient material has been used or in which an 'air blow' or crease has caused a defect.
Wax can be used as inter occlusal recording material. However, because of its properties of having a high
coefficient of thermal expansion and high resistance to closure, this material has been graded as most inaccurate
among the interocclusal record materials. Wax plus zinc oxide- eugenol paste results in an increase in a vertical
dimension, which is attributed to the distortion of the wax material.
Bite registration wax is used to articulate accurately certain models of opposing quadrants/obtaining
occlusal records e.g. Aluwax.
Technique
Aluwax is available in sheets and in arch form, or, two sheets of wax with a cloth from center. Ideally, a
maxillary cast is obtained before the wafer to be used for registration is fabricated. The model is placed on the
Aluwax sheet or wafer. A line outlining the maxillary arch form of the teeth is inscribed on the sheet, with 3-4
mm excess left projecting facially, completely around the arch. Excess that will touch the tuberosity or retro
molar area should not be touched when centric registration is recorded. When the size and shape of the wafer
desired is obtained, the wafer is reinforced first with Ash-No 7 metal. A strip of metal approximately 4 inches
long and 1½inch width is cut and placed so that center of the wafer between the two pieces of the doubled
metal. The metal is then luted to the wafer with sticky wax on the mandibular and maxillary sides. The metal
should cover as much as of the palatal and tongue areas as possible but should not extend anteriorly past the
medial of the mandibular first bicuspid. Sufficient space must also be left for occlusal surfaces of the posterior
teeth.
After the metal has been luted to the wafer, the anterior portion is reinforced. Place the wafer over the occlusal
and incisal surfaces of the mandibular cast and inscribe a mark at the distal of each cuspid. Place the wafer on a
sheet of base plate wax and inscribe the outline of the anterior portion of the wafer to the distal marks of the
cuspids on the base plate wax. The piece of base plate wax is luted to the mandibular side of the wafer with a
hot spatula. The wafer is prevented from bending by the metal, in to the palatal area by the tongue and
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mandibular anterior teeth during closure.
The maxillary study cast is moistened or lubricated with vaseline. The wafer is warmed lightly on a flame or
water bath for about 15 seconds. The maxillary side of the wafer is placed on the moistened cast. With light
finger pressure, the wafer is keyed to the cusp tips and incisal edges of the cast. It is then chilled with water/air.
The wafer is then tried in to the mouth. The keyed portion of the wafer is placed on the maxillary teeth, held
lightly and secured with thumb and finger. The mandible is manipulated to the terminal hinge position and
hinged upwards until the mandibular anterior teeth lightly touch the base plate reinforcement. Patient is
instructed to relax and not to close or bite. Wafer is checked for fit and made certain that it does not impinge on
palatal tissues, retro molar pad area and tuberosity area. Posteriorly, it should extend 1-2 mm distal to the
posterior teeth.
Strips of Tenax wax are luted to the mandibular side of the wafer with a hot spatula. It extends from the
posterior border of the wafer to the edge of the base plate wax reinforcement. The keyed wafer is again placed
and the mandible guided into closure. The mandibular teeth should touch evenly and without pressure. When
the fit is verified and perfected, centric relation position is recorded. The completed wafer is lightly warmed;
keyed side placed on maxillary teeth and wafer is supported lightly. The mandible is manipulated into most
retruded and hinged position. The mandible is guided and closed into centric relation, imprinting just the cusp
tips of posterior teeth in to Tenax wax. The mandibular teeth will slightly indent the base plate wax. As the
mandibular teeth close the wafer, it should be left loose to avoid maxillary teeth from imprinting too deeply into
the recording wafer.
The wafer is chilled and removed in a snap to avoid distortion with the wafer still on the mandibular teeth the
mandible is guided back into centric closure. The wafer is then snapped inwards the mandible, removed in one
motion and chilled.
The centric relation record is verified by rechecking. For greater accuracy, a correction wash is taken with zinc
oxide eugenol paste, mixed and placed into the cusp indentation on each side of the wafer. Centric relation
record can be easily recorded with aluwax and impression paste in cases with edentulous posterior regions that
do not have posterior stops. The wafer is then removed and placed on the cast. A small pillar or post of wax
width ¼ in diameter formed of boxing wax is placed over each Ist and 2nd molar edentulous area and luted to
aluwax wafer with hot spatula. The wax pillars are shortened with a hot spatula until approximately ¼ inch of
space is created between the ridge and end of pillar extending to the wafer.
The maxillary and mandibular casts are fitted into the Aluwax wafer, held and distance is estimated. The wafer
with wax pillars is checked in the mouth. A wash impression is taken by placing a mound of paste on each wax
pillar. The centric relation is recorded with wash and a static impression of edentulous ridge areas. The record
is chilled and with a sharp scalpel, carefully trimmed such that impression area of about 4 mm square is present.
6. Wax can be used to make functional wax patterns.
Certain problems of occlusal harmony lend themselves to solution by the use of the functional wax pattern taken in
the mouth immediately following cavity preparation. The manner of gaining this functional pattern is not unlike
the initial steps in forming the direct wax pattern. The particular situation may or may not indicate the use of a
matrix band and retainer. Should a matrix be indicated in order to confine the wax, it is trimmed and festooned
so that soft tissues are not traumatized nor the movements of functional occlusion restricted. Thoroughly
conditioned wax is placed in the matrix band, the band seated under a heavy sustained force for about ten
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seconds. Centric occlusion and lateral excursions are then initiated. Wax may be added to any occlusal area if
under contouring is suspected. Finally the matrix band and retainer, which have been slightly lubricated with
petroleum jelly, are removed and the cervical excess is trimmed. Following removal, the pattern is subsequently
refined and the margins are perfected upon the complete die. The result should be excellent harmony of this
casting with the occlusal function.
References:
Anusavice, Philipps’: Science of dental materials, 11th edition, Elsevier.
Craig RG, Powers JH: Restorative dental materials, 11th edition, Mosby.
William J. O’ brien: Dental materials and their selection, 2nd edition.
McCabe JF, Walls AWG: Applied dental materials, 8th edition, Blackwell Science.
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