Waxes

Waxes
Dr. Waseem Bahjat Mushtaha
Specialized in prosthodontics

introduction:
Waxes are hydrocarbon materials, they are used in
dentistry as an integral part of many technical
procedures, e.g.:
• Wax patterns for Inlays partial denture.
• Boxing an impression.
• Making occlusion rims.
• Joining or attaching temporarily parts of broken dental
appliance.
Because they are used for different purposes we have
different types of waxes composed of different blends.

Basic Constituents Of Dental waxes
I- Wax
Natural wax:
The basic constituents of dental waxes come from three main sources:
mineral, insect, and vegetable.
1. Mineral wax: e.g.
Paraffin wax obtained during the distillation of crude petroleum. It is
brittle at ambient temperature.
Ceresin is also a mineral wax, again obtained during the distillation of
crude petroleum. It is less brittle than paraffin wax, due to its oil
content.
Microcrystalline wax differs from paraffin wax in that the crystal
structure is more branched and the carbon chain is longer. This wax is
tougher, more flexible and has a higher tensile strength and melting
point.

2.Insect wax:
e.g. Bees wax, obtained from honeycombs.
When blended with paraffin wax, at room
temperature, it is less brittle, and higher
temperature reduces its flow.

3.Vegetable wax: e g.
Carnuba wax obtained from South American palm trees.
Carnuba wax and candelila wax are hard, lustrous, and
tough waxes. When blended with paraffin wax they harden
it and raise its solid-solid transition temperature.
- Resins and gums are also vegetable wax, they are used to
add adhesive qualities to waxes.
Synthetic wax:
They are produced by combination of various chemicals in
the laboratory or by chemical action on natural waxes.
2 Additives:
Gums, fats, fatty acids, natural and synthetic resins and
pigments of various types.

General properties
Waxes have a number of important properties to their dental
use. Different uses require different properties. Waxes for
patterns probably require most carful balance. Some of the
important properties are:
1(Melting rang.
2(Thermal expansion.
3(Mechanical properties.
4(flow.
5(Residual stresses.
6(ductility.

1(Melting range
1(Waxes have melting ranges rather than
melting points.
2(Mixing of waxes may change their melting
range.
3(Melting range varies depending on its use.

2(Thermal expansion
Waxes expand when subjected to a rise in
temperature and contract as the temperature is
decreased.
Coefficient of thermal expansion and its
importance:
Dental waxes and their components have the largest
CTE among the materials used in restorative
dentistry. Temperature changes in wax patterns
after removal from the mouth, can produce
inaccuracies in the finished restoration.

3(Mechanical properties
The elastic modulus, proportional limit and
compressive strength of waxes are low
compared to other dental materials. These
properties are strongly dependent on the
temperature. As temperature decreases, the
properties improve.

4(Flow
Flow is an important property, especially in inlay
waxes. When melted the wax should flow readily
into all the parts of the die. Flow is dependent on:
1(Temperature of the wax
2(Force applied
3(The length of time the force is applied.
Flow increase as the melting point of the wax is
approached.

5(Residual stresses
Regardless of the method used to make a wax
pattern, residual stresses exist in the
complete pattern. The residual stress may
be compressive or tensile in nature.

Example A:
When a specimen is held, under compression
during cooling the atoms and molecules are
forced closer together. After the specimen is
cooled to room temperature and the load is
removed, the motion of molecules is
restricted. This restriction result in residual
stress ( hidden stresses) in the specimen.
When the specimen is heated, release of the
residual stress is added to the normal
thermal expansion, and the total expansion
is greater than normal.

Example B:
When a specimen is cooled while under
tension, the release of the residual tensile
stress result in a dimensional change that is
opposite to thermal expansion, i.e. it can
result in overall contraction of the
specimen.

6(Ductility
Like flow, the ductility increases as the
temperature of the wax is increased. In
general, waxes with low melting points
have greater ductility than those with high
melting points.

Dental application of waxes
I Pattern waxes:
All pattern waxes have two major qualities, thermal change in
dimension, and the tendency to warp or distort upon standing which
create serious problems in their use, whether an inlay pattern, a crown,
or a denture is being constructed.
Such restorations as inlays, crowns and bridge units are formed by a
metal or an alloy casting process that utilizes the lost wax pattern
technique:
- A pattern of wax is first constructed that duplicates the shape and
contour of the desired restorations.
- The pattern then is embedded in investment material to form a mold
to the pattern.
- The wax is subsequently eliminated by heating and softening to be
replaced by the restorative material.

1(Composition:
The main constituents usually present in an inlay casting
wax are:
a) Paraffin wax: 60% this is a mineral wax derived from
petroleum.
Paraffin wax is brittle at ambient temperature, therefore it
flakes when carved rather than giving a smooth surface. It
exhibits a volume contraction between 11 and 15% upon
solidification from the molten stage.
b) Therefore we use the beeswax 5% which decreases the
brittleness at room temperature, prevents flaking and
improves the carving properties.
c) Carnuba wax 2.5% and gum dammar 10%: these are added
to obtain suitable melting ranges and solid-solid transition
temperature. They also improve the adhesive qualities,
smoothness and prevent cracking. They may be replaced
partially by synthetic resins.

2(Requirements:
in case of making an inlay pattern, it is either done by the:
a) Direct technique i.e. in the mouth.
b) Indirect technique i.e. on a model or die.
In the first technique:
a) Should have as low a thermal contraction as possible, though it is
inevitably high.
b) - Have a large flow about 5°C above mouth temperature, so that
good detail of the cavity will be obtained.
- A negligible flow at 37°C, so that no distortion will occur on
removal of the pattern from the cavity.
c) It should be of contrast color to that of the mouth and tooth, in order
to distinguish it easily when used In the mouth.
In addition all Inlay wax:
d) Should be easy to carve without chipping or flaking.
e) Burn out of the mould without leaving any residue.

Direct Technique
Hold the stick of wax over the visible flame and rotate it
rapidly until it becomes plastic taking care not to volatilize
the wax. The softened wax is shaped approximately to the
form of the prepared cavity.
After the wax is inserted into the cavity, it is held under
finger pressure while it solidifies. The wax should be
allowed to cool gradually to mouth temperature. Cooling
rapidly by application of cold water results in differential
contraction and development of internal stresses.
Localized reheating of wax with warm carving instruments
has a similar effect and more distortion may occur. A cold
carving instrument should be used for direct wax pattern.
Withdraw the wax pattern carefully in the long axis of the
preparation. The pattern should be touched as little as
possible with the hands to avoid temperature changes.

Indirect technique:
Inlay pattern is prepared over a lubricated die. If molten wax
is used, very little residual stresses occur.
Dipping method :In case of full crowns, the die can be dipped
repeatedly, into
hot liquid wax. The wax is allowed to cool, carved, and
removed from the die.
Softening in warm water: This technique is not
recommended as
— Soluble constituents may leach out and the properties of
wax will change
— Water gets into the wax causing splattering on the
flame, interference with the softening of the wax surface
and distortion of the pattern on thermal changes.
Adding in layers: The wax is melted and added in layers
using a spatula or a brush.

Wax Distortion
Wax distortion is the most serious problem in inlay wax. It is due to
release of stresses in the pattern caused due to:
1) Contraction on cooling
2) Occluded gas bubbles
3) Change of shape of the wax during moulding
4) From manipulation, carving, pooling, and removal.
Thus the amount of residual stress is dependent on:
— The method of forming the pattern.
— Its handling and
— Time and temperature of storage of the wax pattern.
Causes of distortion:
Distortion is due to any method of manipulation that creates
inhomogenity of wax involving the intermolecular distance

Factors causing distortion under control of the operator
cannot be totally eliminated. Distortion of the wax can
occur:
• If wax is not at uniform temperature when inserted in the
cavity. Some parts of the wax pattern may thermally
contract more than others when stresses are introduced.
• If wax is not held under uniform pressure during cooling.
•If the wax is melted and added in an area of deficiency, the
added wax will introduce stresses during cooling.
• During carving some molecules of wax will be disturbed
and stresses will result.

To avoid
Minimal carving and change in temperature.
Minimal storage of pattern. Invest
immediately.
Use warm instruments for carving.
Store it in a fridge if necessary.
Some relaxation and distortion of pattern
occurs regardless of the method used.
It cannot be totally eliminated. It can only
be reduced to a point which is not of
clinical importance.

This is for blocking out edentulous ridge
and to fill in voids and undercuts

2Modelling wax:
This is used as a pattern material, and for the registration
of jaw rerationships, in the construction of dentures.
Properties:
a) It should be easy to mould when softened, and not tear,
flake or crack.
b) It should be easy to carve.
c) It should be capable of being melted and solidified a
number of times without change of properties.
d) No residue of wax should be left after applying the
process of wax elimination.
Manipulation:
It is important that the wax is evenly heated throughout its
whole bulk and adapted to shape before cooling, to
minimize subsequent distortion due to relief of internal
stresses.

3Sheet casting wax:
Used to build the pattern of the metallic framework of removable
partial denture.
Manipulation:
They are supplied in sheets which have been rolled to a precise thickness.
When such wax is being manipulated. Care must be taken not to make
it thinner. This can be avoided by heating the wax in hot water and
using moist cotton wool to adapt it to shape. It is important that both
clasps and connectors of cast metallic dentures should be of the correct
thickness.
Properties:
Ready-formed polymeric patterns are available to simplify the waxing-
up of a cast of partial denture.
Both casting waxes and polymeric components should burn out from
the mould without leaving any residue.

prefabrication RBD casting wax
pattern

4Carding or boxing wax:
This is a wax with a high flow value at room temperature
and is easily moldable without the need for heating.
They are used in dental laboratories to “box in” impression
prior to casting up.
5 Sticky wax:
this is an adhesive brittle wax, usually made of bees wax
(white or ye1low) to which resin and gum dammar are
added. They become sticky when melted. As they harden
they become firm, brittle and free from tackiness. They are
used to assemble metallic or resin pieces temporary for
different purposes. Also it is used to stick pieces of plaster
or stone together.

6(Utility wax:
Consists mainly of beeswax, petrolatum, and other
soft waxes in varying proportions.
Supplied:
It is available in the form of sticks and sheets. It is
used to adjust contour of perforated tray for use
with hydrocolloids (e.g. to raise flange height, to
extend the tray posteriorly, and to raise palatal
portion of the tray in cases of deep palate). It is
pliable and can be easily moulded. It is adhesive
and can stick to the tray.

7(Impression waxes, corrective waxes:
They are characterized by their high degree
of flow at mouth temperature.

Waxes

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