A variety of natural waxes and resins have been used in dentistry for specific and well defined applications. Waxes are thermoplastic materials which are solids at room temperature but melt without decomposition to form mobile liquids. They consist of two or more components which may be natural or synthetic waxes, resins, oils and pigments. DEFINITION [GPT 8] One of several esters of fatty acids with higher alcohols, usually monohydric alcohols. PROPERTIES OF WAXES Melting range Co efficient of thermal expansion Transition temperature Mechanical properties Flow Residual stress MELTING RANGE 1
A variety of natural waxes and resins have been used in dentistry for specific and well defined applications.
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A variety of natural waxes and resins have been used in dentistry for
specific and well defined applications.
Waxes are thermoplastic materials which are solids at room temperature
but melt without decomposition to form mobile liquids. They consist of two or
more components which may be natural or synthetic waxes, resins, oils and
pigments.
DEFINITION [GPT 8]
One of several esters of fatty acids with higher alcohols, usually
monohydric alcohols.
PROPERTIES OF WAXES
Melting range
Co efficient of thermal expansion
Transition temperature
Mechanical properties
Flow
Residual stress
MELTING RANGE
Waxes have a melting range rather than a melting point.
Example : paraffin 44 – 620C
carnauba 50 – 900C
Significance:
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Mixing of waxes can change their melting range.
CO EFFICIENT OF THERMAL EXPANSION
Waxes expand when there is increase in temperature and contract when
there is decrease in temp.
Dental waxes have the greatest co-efficient of thermal expansion than
any other restorative materials in dentistry.
Eg: CET of type 1 wax is[ between 220C and37.50C] is 323×10 _6/0C
Significance:
The CET of inlay waxes are high enough that temperature changes in
wax pattern after the establishment of critical dimensional relationships may
serve as a major contributing factor in inaccuracy of finished restoration.
TRANSITION TEMPERATURE
On heating the thermal expansion rate increases abruptly above a certain
temperature
Orthorhombic crystal lattice Hexagonal form
This change is stable and progressive
Significance:
Waxes which need to be rigid should have a transition temp above 370C
eg: inlay wax.
FLOW
Is the slippage of wax molecules over each other. Measure of flow is the
measure of the degree of plastic deformation of material at a given temperature.
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Depends on
♣ The temperature of waxes
♣ Composition of wax
♣ Force causing deformation
♣ Length of time force is applied
Significance:
A greater flow of above 500C or above oral temp helps to record details.
Negligible flow at 370C reduces distortion due to internal stresses.
RESIDUAL STRESSES
Stress remaining in wax as a result of manipulation
May be due to
Occluded air
Processing
Carving
Removal from mold
During storage
Elastic memory of wax
MECHANICAL PROPERTIES
Compressive strength , proportional limit, elastic modulus of waxes are low.
These properties strongly depends on the temperature
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As the temp decreases mech properties improve
COMPONENTS
Dental waxes contain
Natural waxes
Synthetic waxes
Additives
NATURAL WAXES:
1. Minerals:
Microcrystalline
Paraffin
Barnsdahl
Ozokerite
Ceresin
Montan
2. Plants:
Carnauba wax
Ouricury wax
Candelia wax
Japan wax
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Cocoa butter
3. Insect:
Bee’s wax
4. Animal::
Spermaceti wax
SYNTHETIC WAXES :
Acra wax C
Epolene
Aerosol OT
Albacer
Castor wax
Dura wax
Flexo wax
ADDITIVES
Fats
Stearic acid
Glyceryl tristearate
Oils
Turpentine
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Color
Natural resins
Copal
Dammar
Sandarac
Mastic
Shellac
Kauri
Synthetic resins
Elvax
Polyethylene
Polystyrene
CHEMICAL NATURE
Two principle groups of organic compounds :
Hydrocarbons : saturated alkanes
Esters : myricyl palmitate [bees wax]
Some waxes in addition contains free alcohol and acids
CLASSIFICATION
BASED ON USE
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PATTERN WAXES :
Inlay casting wax
RPD Casting wax
Base plate wax
PROCESSING WAXES :
Boxing wax
Utility wax
Sticky wax
IMPRESSION WAXES
Corrective impression wax
Bite registration wax
PATTERN WAXES
Inlay wax
It is a type of pattern wax.
It is used to make patterns for metallic restorations.
Ideal requirements
Inlay wax should be uniformly softened. There should be no irregularities.
It should have good color contrast. This helps to identify the margin
between the die and the wax pattern at the finish line.
It should not flake or chip off during carving.
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It should be smoothly contoured, otherwise it will produce a rough surface
on the casting.
It should be completely eliminated during burnout with no residue.
It should be dimensionally stable from the time of fabrication till the burnout.
When used intraorally it should have good flow at the oral temperature, but
once removed and cooled it should become rigid.
The flow should be more than 70 % at 450C and less than 1 % at 370C
Classification
Classification I (ADA Sp. No. 4)
Type IType I: Medium wax employed in direct technique.
Type II:Type II: Soft wax used for indirect technique for inlays and crowns.
Available as: Blue, green or purple sticks of 7.5 cm length and 6 mm
diameter. Also available as small pellets and cones.
Commercial names: Harvard, Kerr, Peck.
Plastodent C, Jelenko green wax, S-U Dental blue wax, S-U dental green wax.
GC blue, Shofu color
Composition
i. Paraffin wax (40-60%)
Main ingredient.
It determines the melting point.
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Main disadvantage is-it flakes when trimmed. It does not give a smooth
surface, so to modify it other waxes are added.
ii. Ceresin (10%) is added to partially replace paraffin.
Reduces flakiness.
Makes it easy to contour.
iii. Gum Dammar (1%) or Dammar resin
It is a natural derivative from pine trees.
Increases the finish and gives a smooth surface.
Increases resistance to cracking and flaking making it harder.
iv. Carnauba wax (25%)
It has a high melting point.
It increases the hardness.
It decreases the flow at mouth temperature.
It gives glossiness to the surface.
v. Candellila wax
It can be used instead of carnauba wax.
It has a lower melting temperature than carnauba wax.
It is not as hard as carnauba wax.
Synthetic waxes
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In modern inlay waxes, carnauba wax is often replaced partly by certain
synthetic waxes. They have high melting point.
This allows greater paraffin content of the wax which improves working
characteristics.
Properties of inlay wax
1. Flow
Maximum flow
Type I waxes is 1 % at 370C
Type II waxes is 1 % at 300C
Maximum flow-type I and II 75 to 90 % at 450C
Significance:
Type I wax flows well at oral temperature and so can be used for direct
pattern technique.
Type ii is more rigid and needs higher temperature to soften and so used for
indirect technique.
The wax should be softened at 450C and placed into the prepared cavity.
Only at this temperature it has the highest flow. This allows accurate detail
recording.
2. Thermal properties
Coefficient of thermal expansion:
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Inlay wax has the largest CTE compared to any other material used in
restorative dentistry.
It has a linear expansion of 0.7%
Thermal conductivity :
The thermal conductivity of waxes is low.
It is difficult to heat wax uniformly.
There can be contraction during cooling
ii.
Significance:
The pattern can get distorted due to uneven heating and cooling.
This effect is seen during direct technique when there is a difference
between oral temperature and room temperature.
The pattern should not be cooled under pressure as this increases the
coefficient of thermal expansion. This can cause distortion.
Wax distortion:
When waxes are heated they soften but stresses are induced. On cooling
these stresses are released which causes distortion.
Distortion of the wax can occur due to the following reasons:
Improper heating of wax. The wax may not be heated uniformly.
When wax is not held under uniform pressure during cooling.
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When additional wax is added to an existing layer of wax, there is
difference in temperature between layers.
Stresses can be incorporated during carving the pattern.
Wax contracts on cooling to room temperature and this can cause distortion.
Gas bubbles can get incorporated during fabrication. The escape of these
gases can lead to distortion.
Constantly changing the manipulation temperature by reheating and cooling
(pooling of wax) the pattern can induce stresses.
Prevention
Some of the factors causing distortion are inherent to the property of waxes
and cannot be completely eliminated.
It can be minimized by the operator.
Minimal carving and avoiding reheating the layers of wax.
Uniform temperature of wax by uniform heating.
The stresses are released over a period of time, so by investing the pattern
immediately distortion can be minimized.
Heating instruments for carving uniformly.
A wax bath can be used. The wax is usually uniformly melted at the ideal
temperature and the die is dipped into the wax bath.
If necessary, it should be stored in a fridge.
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Uses: Patterns for inlays, crowns and bridges is first made in wax, and then
converted into metal or ceramic by casting.
Effect of physical properties of waxes on investments and casting shrinkage
[JPD1996].
The flow charac, bending strength, and softening temp of 6 industrial and 7
dental waxes were studied.
A direct relation between flow of wax and casting shrinkage was found.
It was found that as flow increased casting shrinkage decreased.
If a wax with a low flow and high strength is used, a larger casting ring
should be considered.
A study on heating and cooling of crown wax patterns [JPD 1994].
6 Different waxes were studied.
Conclusion: increase in flow by increase in temp was shown in the range of
370C -470C for majority of the materials
Rate of expansion varies during increase in temp ie. Transition temp
Most mat show flow by 61%-82% at 470C -520C
Manipulation of Inlay Wax
i. Direct Technique
It is called so because the prepared cavity is recorded directly. The pattern is
then invested.
The inlay wax is manipulated over an open flame.
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The stick should be rotated over the flame for uniform heating.
It is then placed into the cavity under finger pressure.
It should be allowed to cool gradually to mouth temperature.
The pattern should be handled to the minimum to prevent temperature
changes.
It is then invested.
The main advantage of this technique is that it saves time because there is
no need to prepare a die.
ii. Indirect Technique
Pulled pattern technique
A die is prepared from the impression.
The die is coated with a die spacer to provide space for luting agent.
A die lubricant is applied for easy removal of the pattern.
The die is dipped into a wax bath with melted inlay wax (dipping method).
The pattern is made by adding additional layer of waxes (incremental wax
addition technique)
Finally wax pattern is carved finished and polished with silk cloth.
Precautions
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Should not be softened with warm water as solvents leach out and splattering
can occur due to presence of water.
Invest all wax patterns as soon as possible to avoid distortion.
Prolonged heating should be avoided as it causes the wax to evaporate.
Accuracy of wax, auto polymerized, and light-polymerized resin pattern
materials.
When measured on intra- and extra coronal master dies, the light
polymerized, diacrylate resins had equal or better marginal fit, compared with
wax or auto polymerized acrylic resin, and were less affected by placement
technique and storage.
Casting wax
It is a type of pattern wax.
Classification (According to FDI Specification No. 140)
i. Class A 28 gauge, pink
Flow of about 10 % at 350C.
Easily adaptable at 40 to 450C.
ii. Class B 30 gauge, green
Minimum flow of 60 % at 380C.
Adapts well to the surface.
not brittle on cooling.
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iii. Class C readymade shapes, blue
Will burnout at 5000C leaving no carbon residue
Supplied As
Sheets 0.40 and 0.32 mm thickness.
Readymade shapes
Round (10 cm), half round and half pear shaped rods.
Mesh work.
Readymade sheets or in bulk.
Shaped like clasps.
Commercial name :metrodent casting wax, SPI wax
Composition
Paraffin wax
Ceresin
Beeswax
Resins
Other waxes
Base Plate Wax
It is a type of pattern wax used mainly in preparing wax patterns for
prosthesis.
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Classification (ADA Sp. No. 24)
Type I-Soft: For building veneers.
Type II-Medium: To use intraorally (in normal climates not in too warm
climates).
Type III-Hard: For use in tropical climates
Supplied as: Sheets of pink or red color.
Composition:
Generally consist of
hydrocarbon waxes-70 to 80%.
Paraffin or ceresin 8%
Beeswax 12.0%.
Carnauba 2.5%.
Natural or synthetic resins 3.0%
Microcrystalline 2.5 %
Other coloring agents.
Requirements
Linear expansion not greater than 0.8%
Should not flake during carving.
Softened sheets should cohere at 230C.
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Smooth finish on flaming.
Coloring should not stick to the plaster surface during flasking.
Uses: These waxes are used for the following purposes
Used in making occlusal rims. These are used to record jaw relations for
complete denture patients.
They can be used to fabricate patterns for removable partial denture.
To make patterns for prostheses which are processed in acrylic resins.
Processing Waxes
Processing waxes are those waxes used in the laboratory procedures for
the construction of restorations and appliances, e.g. boxing wax, beading wax,
utility wax and sticky wax.
Boxing Wax and Beading Wax
Use: Beading wax is adapted around the impression borders to create the
land area of the cast.
Boxing wax is used to build up vertical walls around the impression in order
to pour the gypsum product to make a cast base.
Supplied as: Boxing wax as sheets, beading wax as strips.
Composition
Boxing wax may contain.
Low melting hydrocarbon waxes.
Beeswax.
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Properties
Smooth and glossy on manipulation over a flame.
Seals easily.
Pliable at 210C.
Does not distort at 350C.
Commercial name : metro boxing in wax, cavex , kerr, metro ribbon wax
Uses
Beading and boxing procedure: It is a laboratory procedure after final
impression making for complete denture patients.
The beading wax is usually a thin rope of wax which is pliable at room
temperature.
This wax is adapted and fused to the margins of the impression.
Onto the beaded margins the boxing wax is adapted and the impression is
poured.
The final cast should have 2 to 4 mm of land area around the sulcus which
will be formed by the beading wax.
The cast should have a height of about 10 to 15 mm in the deepest portion.
This height of the cast is formed by the boxing wax.
Advantages
Preserves the anatomic contours.
Gives a definite thickness to the borders.
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It gives a definite form and thickness to the base.
Conserves laboratory material.
Utility Wax
Composition
Beeswax.
Petrolatum.
Resins.
Supplied as: It is available in the form of sticks and sheets. Orange or dark red in
color. In orthodontics, periphery wax is white in color.
Properties: Flow at 37.5 0C- min 65 % and max 80% . Pliable and tacky at 21-
240C.
Uses
It can be used to alter the stock tray extensions.
The following alterations can be made
• Height of the tray can be increased
• The posterior extensions can be increased.
• The palatal vault depth can be increased.
Sticky Wax
Composition
Yellow beeswax
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Rosin
Natural resins such as gum dammar.
Supplied as: Yellow colored sticks.
Properties
Sticky when melted, with a max 5 %flow at 300C and 90 % at 430C.
It adheres closely to the surfaces when applied to it.
If movement occurs the wax tends to fracture than distort.
The pieces can be easily joined in a proper relationship.
At room temperature the wax is brittle and breaks easily.
Uses
It is used to align fractured parts of acrylic dentures.
It is used to align fixed partial denture units before soldering.
It is used to seal a plaster splint to the stone cast during porcelain firing.
Impression waxes
Wax in combination with resins of low melting point can be used in
corrective impression technique in partial and complete denture prosthesis. The
peculiarity of impression wax is that they flow at mouth temperature.