WAXES

Waxes have various uses in dentistry, both in the clinic and

laboratory.Dental waxes are composed of natural and synthetic waxes, gum

fats, fatty acids, oils and resins, which are blended together to achieve the

desirable working properties. Basic ingredients of all the waxes are same,

the proportioning is different depending on the use.

Chemical nature of waxes:

The two principal groups of organic compounds contained in waxes

are:

1) Hydrocarbons.

2) Esters.

Some waxes in addition contain free alcohol and acids. The

hydrocarbons in mineral waxes range from 17-44 carbon atoms.

Properties

1) Melting range

Waxes contain molecules having different molecular weight. So

they have range of melting point. This is also called transition temperature.

Due to the range of melting point, they can be easily manipulated.

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2) Thermal expansion

Waxes are thermoplastic in nature showing expansion when

subjected to rise in temperature and contraction as the temperature is

decreased. They have very high thermal expansion coefficients. This can

prove to be a disadvantage because temperature changes in wax patterns

after carving and removal from the mouth, during investing procedures

contribute to dimensional inaccuracies.

3) Mechanical properties

The elastic modulus, proportional limit, and compressive strength of

waxes are low compared to other dental materials and these properties are

dependent on the temperature.

4) Flow

Waxes deform when subjected to load. This plastic deformation

depends on temperature and is found to be low when the temperature of

wax is below the transition temperature. Ideally waxes used in dentistry

should exhibit no flow at mouth temperature to minimize distortion of the

pattern when removed from the mouth.

5) Residual stress

Waxes have low thermal conductivity and therefore it is difficult to

achieve uniform heating and cooling of the wax. When the specimen is

held under compression during cooling, the atoms and molecules are

forced closer together than when they are under no external stress. After

the specimen is cooled and on removal of the load, the motion of molecules

is restricted, and this restriction results in residual stresses when the

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specimen is heated, release of residual stresses cause an added expansion

along with the normal thermal expansion. Therefore waxes should be

moulded to the required shape with adequate heating and slow cooling to

minimize distortion.

Classification of waxes

According to origin:

Mineral origin - Paraffin wax.

- Microcrystalline wax.

- Montan wax.

- Ceresin.

- Barnsdahle

Plant origin - Carnauba wax.

- Japan wax.

- Cocoa butter.

- Candelilla.

- Quricury.

Insect origin - Bees wax.

Animal origin - Spermaceti wax

Synthetic origin - Acrawx C

- Castor wax

- Dura wax

- Flexo wax C

Manufacured from elvax, polyethylene

or polystyrene

According to application in dentistry

Pattern waxes - Inlay casting wax

Sheets

Ready shapes.

Wax up

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- Base plate wax

Processing waxes - Boxing wax

- Utility wax

- Sticky wax

Impression waxes - Corrective wax

- Bite registration wax

1) Paraffin wax

They are obtained from high boiling point fractions of petroleum

products. They are mixtures of straight chain hydrocarbons. Paraffin waxes

used in dentistry are refined and have less than 0.5% oil and hence brittle

in nature. Melting range 41°C-70°C.

2) Microcrystalline wax

They are similar to paraffin waxes except that they are obtained

from heavier oil fractions. They are a mixture of branched chain

hydrocarbons. They are less brittle than paraffin being flexible and tougher.

They have a higher melting range of 60°C-90°C.

3) Montan wax

They are used to increase the hardness and melting range of paraffin

wax. They have a melting temperature of 72°C-92°C.

4) Ceresin

It is obtained from lignite. They are used to increase the melting

range of paraffin waxes. They have high molecular weight and hardness.

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5) Barnsdahle

It is a microcrystalline wax with a melting temperatuer of 70°-74°C.

It is used to increase the melting temperature and hardness of paraffin wax.

6) Carnauba wax

It occurs as fine powder on the leaves of certain tropical palms. It is

composed of straight chain esters, alcohols, acids and hydrocarbons. They

show high hardness, brittleness and a high melting range of 84°C-90°C.

They are blended with paraffin wax to decrease the flow at mouth

temperature and produce glossy surface.

7) Candelilla

It consists of 40-60% paraffin hydrocarbons having 29-33 carbon

atoms. They have a melting range of 68-75°C.

8) Japan wax and Cocoa butter

They are chiefly fats containing glyceroids of palmitic and stearic

acids. They are rough, malleable and used with paraffin to improve

tackiness and emulsifying ability.

9) Bees wax

They are obtained from honey combs. They are a complex mixture

of esters containing mainly myricyl palmitate with saturated and

unsaturated hydrocarbons. They are mixed with paraffin wax to make it

less brittle at room temperature and reduce the flow at mouth temperature.

They have a melting range of 63-70°C.

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10)Spermaceti wax

They are obtained from sperm whale and used as a coating in

manufacturing of dental floss.

DENTAL WAXES

1) Base plate wax

Composition:

Ceresin-80%, Beeswax-12%, Carnauba wax-2.5%, Microcrystalline

or synthetic wax-2.5%, Natural or synthetic resin-3%. They are supplied as

sheets of pink or red colour.

Uses:

a) For registration of jaw relations.

b) For arranging artificial teeth and developing proper contours.

c) To make patterns for orthodontic appliances.

d) As occlusal bite registration materials.

According to ADA specification No. 24 there are 3 types:

Type I : Soft wax – It is a soft wax use for building soft tissue contours as

veneers.

Type II : Medium wax – It is used for making patterns to be tried in the

mouth in temperate climate.

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Type III : Hard wax - It is used for making patterns to be tried in the

mouth in tropical climate.

Requirements:

a) Should be easy to mould when softened.

b) Should not tear, crack or flake.

c) Should be easy to carve.

d) No residue of wax should be left after applying boiling water.

e) No dimensional change.

f) Should be capable of being melted and solidified a number of times

without change of properties.

Disadvantages:

a) High thermal expansion.

b) Dimensional changes due to stress relief.

2) Casting wax

Uses

a) Patterns for metallic framework of removable partial dentures.

Mode of supply

a) Sheets of 0.40 and 0.32 mm thickness.

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b) Readymade shapes – round rods (10 cm long) half round rods, half pear

shaped rods.

c) Matte finish or smooth finish (sheets).

Properties:

They are tacky and highly ductile.

They should adapt easily to the refractory cast.

They should burn out without leaving any residue.

3) Inlay Casting Wax

All inlays, crowns, portions of partial denture frameworks are

initiated first by developing a pattern. The pattern is then invested in a

gypsum or phosphate bonded investment material.

After eliminating wax, molten alloy is cast into the evacuated

chamber. The wax normally used for such a purpose is called inlay casting

wax. It is dark blue, dark purple, dark green or ivory in colour. Dark

colours are chosen to provide contrast between die or tooth and pattern, so

that margins can be clearly developed.

Classification

ANSI/ADA Specification No. 4 divides them into 2 types:

Type I – Medium wax employed in direct techniques.

Type II – Soft wax used in indirect techniques.

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Waxes used with direct technique must not flow appreciably at

room temperature, and the ones used for indirect technique must resist flow

at room temperature.

Composition:

a) Paraffin wax – 40-60% - It improves the moulding property.

b) Carnauba wax 25% - Decreases flow at mouth temperature and

produces a glossy surface.

c) Gum dammer 10% - Enables easy moulding and prevents cracking or

flaking. It also increases the toughness of the wax and enhances the

luster of the surface.

d) Ceresin and beeswax 5% - They modify toughness and carving

characteristics. Synthetic waxes and candelilla wax may be used in

place of carnauba wax.

Uses

Wax patterns for inlays, onlays, crowns, bridges and partial

dentures.

Ideal requirements:

a) It should have suitable softening temperature which should not be too

high especially for direct techniques. When softened, the wax should be

uniform. There should be no graininess or hard spots in the material.

b) Should have high flow when softened and low flow after solidification.

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c) Should have colour contrast with die materials and oral tissues to

facilitate proper finishing of margins.

d) There should be no flakiness or roughness of the surface when the wax

is moulded after softening.

e) Must have glossy or shiny surface.

f) Good thermal conductivity essential for uniform softening.

g) Low thermal expansion.

h) The wax should not pull with the carving instrument or chip as it is

carved.

i) Wax should burn out completely at 500°C without leaving any residue

in excess of 0.10% of the original weight of the specimen.

j) Should be rigid and dimensionally stable during insertion and removal

from die or tooth.

k) Should have a flow of not less than 70% at 45°C and not more than 1%

at 37°C.

l) Should be wetted by water easily.

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Summary of Requirements of Federal Specification for Dental Casting Wax

Type of wax Flow Breaking point

Working properties

Casting wax

Class A-28 gauge pink

Class B-30 gauge green

Class C-readymade shapes blue

35°C- maximum, 10%

38°C- minimum, 60%

No fracture at 23°C±1°C

1) Pliable and readily adaptable at 40° to 45°C.

2) Copy accurately surface against which it is pressed.

3) Shall not be brittle on cooling.

4) Vaporize at 500°C, leaving no film other than carbon.

Properties of Inlay wax

1) Flow

The accuracy and ultimate usefulness of the resultant casting depend

largely on the accuracy and fine detail of the wax pattern. This requires that

when the wax is heated to a particular temperature it should exhibit

sufficient flow under compression to be able to reproduce all the fine

details.

Revised ANSI/ADA Specification No. 4 for dental inlay casting wax (1S0 1561) has

been formulated and the following table gives a summary of the flow requirements in %.

Wax temperature

30°C 37°C 40°C 45°C

Maximum Maximum Minimum Maximum Minimum Maximum

Type I - 1.0 - 20 70 90

Type II 1.0 - 50 - 70 90

As seen from these values Type I inlay wax exhibits a marked

plasticity or flow at a temperature slightly above mouth temperature.

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The maximum flow permitted for Type I waxes at 37°C is 1%. The

low flow at this temperature permits carving and removal of the pattern

from the prepared cavity at oral temperature without distortion.

In addition both Type I and Type II waxes must have a minimal

flow of 70% at 45°C and a maximum flow of 90%.

Inlay waxes do not solidify with a space lattice, as does a metal.

Instead the structure is more likely to be a combination of crystalline and

amorphous materials, displaying limited ordering of the molecules. The

waxes lack rigidity and may flow under stress even at room temperature

(flow curve).

Diagram

2) Thermal properties

a) Thermal conductivity of waxes is low, and time is required both to heat

them uniformly throughout and to cool them to body or room

temperature.

b) Coefficient of thermal expansion is high. The waxes may expand as

much as 0.7% with an increases in temperature of 20°C or contrast as

much as 0.35% when it is cooled from 37°C to 25°C. The average

linear coefficient of thermal expansion over such a temperature range is

350 x 10-6 /°C.

This property is less significant when the wax is used in the indirect

technique because the pattern is not subjected to a change from mouth to

room temperature. The amount of the thermal dimensional change may be

affected by the previous treatment of the wax. The temperature at which

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there is a change in the rate of expansion is known as the glass transition

temperature. Some constituents of the wax probably change crystalline

form at this temperature, and the wax is more plastic at higher

temperatures.

Factors affecting thermal expansion include:

i) Entrapment of gases within the wax which expand on reheating the

wax.

ii) Temperature of the die.

iii) Method used for application of pressure to the wax.

3) Distortion of wax

Distortion results from thermal changes and the release of stresses

that arise from:

a) Contraction on cooling.

b) Occluded air.

c) Change of shape during moulding.

d) Manipulative variables like carving, removal and storage.

Thus, the amount of residual stresses are dependent on:

a) The method of forming the pattern.

b) Its handling.

c) Time and temperature of storage of the wax pattern.

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Causes of Distortion also include:

a) Uneven softening of the wax when inserted into the cavity. Some parts

of the wax pattern may thermally contract more than others when

stresses are introduced.

b) Uneven application of pressure during cooling.

c) Addition of molten wax to already cooled wax.

d) Changes in intermolecular distance during carving.

e) An increased storage time.

f) An increased storage temperature.

g) An altered temperature for fabrication.

h) Technique of fabrication.

Distortion is less in indirect technique when compared to direct

technique.

i) An increased bulk.

Reduction of distortion

a) Use only those waxes as per ANSI/ADA specifications.

b) Apply uniform pressure so that the molecules have equal intermolecular

distance.

c) Invest the pattern as soon as it is finished.

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Manipulation

Dry heat is generally preferred to the use of a water bath. The latter

can result in the inclusion of droplets of water that could splatter on

flaming, smearing of wax surface during polishing and distortion of pattern

during thermal changes.

Direct technique

a) A stick of wax is softened over a flame taking care not to overheat it.

b) It should be twisted until it becomes shiny and then removed from the

flame.

c) The process is repeated until the wax is warm throughout.

d) It is then kneaded together and shaped to the prepared cavity.

e) Pressure should be applied by the finger or by the patient biting on the

wax.

f) It is cooled gradually at mouth temperature, not by cold water.

g) For removing the pattern it is hooked with an explorer point and rotated

out of the cavity.

h) The pattern should be withdrawn in a direction parallel to the axial

walls.

i) Touching with fingers should be avoided to prevent any temperature

changes.

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Indirect technique

a) First apply a die spacer.

b) Lubricate the die with a lubricant containing a cutting agent. Any

excess must be avoided as it prevents intimate adaptation to the die.

c) The melted wax is added in layers with a waxing instrument.

d) The preparation is over built and then carved to the proper contour.

e) When the margins are being carved take care not to abrade the die.

f) A silk cloth may be used for final polishing of the pattern, rubbing

toward the margins.

4) Boxing wax

Uses

a) Used by the manufacturer to attach artificial teeth to the mounts on

which they are supplied.

b) To build up vertical walls around the impression to produce the desired

size and form of the base of the cast.

Advantages:

a) It preserves the extensions of borders.

b) It controls and provides a uniform thickness of the borders.

c) It controls the form and thickness of base of the cast, minimizing cast

trimming and use of gypsum material.

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Method

The impression is placed on a bench and soft wax is used so that the

ridge portion is approximately parallel to the bench top. Beading wax is

adapted around the periphery. This wax should be approximately 4mm

wide and 3-4mm below the borders of the impression. The height is

adjusted until a boxing wax strip extends approximately 13mm above the

highest point on the impression.

Mode of supply – In the form of sheets

Properties

a) Has high flow at room temperature.

b) Easily mouldable and can be adapted without need for heating.

c) Its tackiness allows it to stick to the impression.

5) Utility wax

It is composed of beeswax, petrolatum and other soft waxes.

Uses

a) To give a more desirable contour to a perforated tray for use with

hydrocolloids.

b) To build up flanges of tray and raise palatal portions of tray posteriorly

and in deep palate situations to prevent sagging and distortion of

impression material.

c) To stabilize bridge pontic while soldering.

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Properties

Soft, adhesive, workable at room temperature (21-24°C). Supplied

in stick and sheet forms.

6) Sticky wax

Composition – Yellow beeswax, resin, gum dammar (natural resin).

Uses

a) For joining metal parts before soldering.

b) For joining of fragments of broken denture prior to repair procedure.

Properties

a) At room temperature it is firm, free from tackiness and brittle.

b) It is easily removable by boiling water.

c) Exhibits minimum shrinkage while cooling which helps in preventing

the movements of parts to be joined.

Mode of supply

Sticks of length 7.5-10cms and diameter 0.6-0.7cms.

7) Impression waxes

They are used to record edentulous portions of the oral cavity and

are generally used in combination with other impression materials such as

polysulfide rubber, ZOE or impression compound.

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Corrective impression wax

It is used as a wax veneer over an original impression to contact and

register the details of the soft tissues. Its other applications include:

a) Functional impression of distal extension partial dentures.

b) To record posterior palatal seal area.

c) Functional impression for obturators.

Composition – Paraffin, ceresin, beeswax.

Properties – Flow at 37°C is 100%. Subject to distortion during removal

from the mouth.

8) Bite Registration wax

Composition – Beeswax, paraffin wax, ceresin.

Uses

a) To record and transfer the interocclusal relationship at centric occlusion

position to the articulator.

b) To record and transfer the centric relation position in conjunction with

silicone or ZOE wash, to the articulator.

Properties

Flow at 37°C ranges from 2.5% to 22%. Ease of manipulation,

correction and verification.

Mode of supply – U-shaped rods

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