Introduction

The waxes used in dentistry normally consist of two or more components

which may be natural or synthetic waxes, resins, oils, fats and pigments. Blending

is carried out to produce a material with the required properties for a specific

application. Waxes are thermoplastic materials which are normally solids at room

temperature but melt, without decomposition, to form mobile liquids. They are,

essentially, soft substances with poor mechanical properties.The use of wax in

dentistry is an established phenomenon. Whether it is formation of inlay patterns,

boxing of impressions, taking bite registrations or making bite rims all require the

waxes with specific properties.

The specific use of the dental wax determines the physical properties that

are most desirable for a successful application.

Waxes, gums, fat and resins

Dental waxes may be composed of natural and synthetic waxes, gums,

fats, fatty acids, oils, natural and synthetic resins, and pigments of various types.

The desired waxes working characteristics are achieved by a blend of appropriate

natural and synthetic waxes, resins and other additives.

Historically, waxes have been classified according to their origin: (1)

mineral, (2) plant, (3) insect, and (4) animal; however, a better classification is

based on their chemical composition. The two principal groups of organic

compounds contained in waxes are hydrocarbons and esters, although some waxes

contain free alcohols and acids as well

Natural Waxes Synthetic waxes Additives

Mineral- Paraffin

Microcrystalline

Barnsdahl

Ozokerite

Ceresin

Montan

Plant – Carnauba

Acrawax C

Aerosol OT

Castor wax

Flexo wax

Epolene N 10

Albacer

Aldo 33

Stearic acid

Glyceryl tristearate

Oils-turpentine, colour

Natural resins

Rosin – copal, dammer

Sandarac, mastic

Shellac, kauri

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Ouricury

Candelilla

Japan wax

Cocoa butter

Insect- Beeswax

Animal- Spermaceti

Durawax 1032 Synthetic resins

Polyethylene,polystyrene

NATURAL WAXES

These are classified according to their origin into

Mineral

Plant

Insect

Animal

They may also be classified based on the chemical composition

- Hydrocarbons

- Esters

- Some do contain free alcohol and acids as well.

The natural waxes are complex combinations of organic compounds of

reasonably high molecular weight. The composition varies depending on the

source and the time of collection; therefore the dental manufacturers must blend

the particular batches of wax to obtain the properties desired for a particular

application.

MINERAL WAXES

Paraffin waxes;-

- Obtained principally from high boiling point fractions of petroleum.

- Mixtures of chiefly straight chain saturated hydrocarbons containing 26 to

30 carbon atoms.

- Melting range 40 ºC to 71 °C .melting temperature increases with the

increase in molecular weight, but decreases if oil is present in the wax.

- Paraffin wax used in dentistry is refined and has less than 0.5 percentage

oil.

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- During solidification and cooling, a volumetric contraction occurs that

varies from 11% to 15%.

- Crystallization is in the form of plates predominantly.

Microcrystalline waxes;-

- Obtained from heavier oil fractions in the petroleum industry.

- Higher melting points ranging from 60 to 91 ºC

- They crystallize in small plates and are more flexible and tougher.

- They are branched chain hydrocarbons and have higher molecular weight

41 to 50 carbon atoms.

- Less Volumetric contraction compared to paraffin waxes.

Barnsdahl ;-

- Microcrystalline wax with boiling point 70°C to 74°C used for increasing

melting range and hardness and reducing flow of paraffin waxes.

Ozokerite;-

- An earth wax found near petroleum deposits.

- Melting temperature about 65°C consisting of microcrystalline structure of

needles or short plates.

- Usually added to paraffin wax to improve its physical properties.

Ceresin;-

- Obtained from natural mineral petroleum refining or lignite refining.

- Straight and branched chain hydrocarbons.

- High molecular weight and hardness.

- Used to increase melting range of paraffin wax.

Montan wax;-

- Obtained by extracting various lignites.

- Melting temperature ranges from 72°C to 92°C.

- Mixture of long chain esters of 40 to 58 C- atoms accompanied by free high

molecular weight alcohols and acids and varying amounts of resins.

- They are hard, brittle, lustrous, and blend well with other waxes.

PLANT WAXES

Carnauba and Ouricury waxes;-

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- Composed of straight chain esters, alcohols, acids and hydrocarbons.

- They have high hardness, brittleness, and high melting temperatures.

Carnauba - 84° C to 91° C

Ouricury - 79 ° C to 84° C.

- They have outstanding quality of increasing melting range and hardness of

paraffin wax.

Candelilla wax;-

- Consists of 40% to 60% hydrocarbons containing 29 to 33 carbon atoms,

accompanied by free alcohols, acids, esters and lactones.

- Melting temperature 68°C to 75.

- Hardens paraffin wax.

Japan wax and cocoa butter;-

These are not true waxes but are fats. Japan wax is mixed with paraffin

wax to improve tackiness and emulsifying ability. Cocoa butter is used in

dentistry as a protector against dehydration of soft tissues and to protect silicate

products temporarily from moisture during setting or to protect them from

dehydrating after they set.

INSECT WAX

Beeswax:

- Complex mix of esters, saturated and unsaturated hydrocarbons and high

molecular weight organic acids.

- Melting temperature 63°C to 70°C

- It is brittle at room temperature but plastic at body temperature.

- Mainly used in sticky wax.

ANIMAL WAX

Spermaceti wax:

- Used as a coating on dental floss.

SYNTHETIC WAX:

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Synthetic waxes are sparingly used in dentistry. They are highly refined

with very little contamination and have a limited compatibility with other waxes.

They function as plasticizers and tend to toughen films of wax.

FATS

They are similar to wax in that they are colourless, odourless, tasteless, in

pure form, however waxes are harder and have higher melting points. Fats are

basically esters of fatty acids. Hydrocarbon oils are used to soften wax. Silicone

oils aid in ease of polishing of the waxes.

RESINS

These are complex, amorphous mixtures of organic substances. They

exhibit specific behaviour rather than definite chemical composition. Most are

obtained from plants. Shellac however is an insect product. They are blended with

waxes for dental use. Resins Dammar and Kauri are added to harden the wax.

CHARACTERISTIC PROPERTIES OF WAXES

MELTING RANGE

THERMAL EXPANSION

MECHANICAL PROPERTIES

FLOW

RESIDUAL STRESS

DUCTILITY

Melting range

Waxes have a melting range and not a definite melting point. Different

components in the dental wax affect the melting range. The melting of a mix of

paraffin with high melting waxes results in paraffin melting near its usual

temperature, but the entire wax does not appear melted because the matrix of the

higher melting wax does not melt until a higher temperature is reached.

2.5% carnauba wax has little effect on the melting range.

> 10 % carnauba wax increases the melting range rapidly.

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Thermal Expansion

Waxes expand when temperature rises and contract on decrease of

temperature. Blending of waxes can to some extent control this property. Waxes

have the highest coefficient of thermal expansion compared to other materials

used in dentistry. Mineral waxes have greater thermal expansion than plant waxes

due to weaker secondary valence forces. Many waxes exhibit two ranges of

expansion between 22° and 55°C. These changes occur at transition points and are

attributed to internal structural parts being freer to move. Certain inlay waxes

have more than 2 changes in rate of expansion because the transition points of the

ingredients do not coincide.

Clinical significance:-

Possible distortion to patterns due to temperature changes leading to

inaccurate castings.

Mechanical properties

The moduli of elasticity, proportional limit, compressive strength, are low

for waxes and depend on temperature strongly. Modulus of inlay waxes are

important in hygroscopic casting procedures in which the wax pattern is subjected

to stresses of expansion of the investment during setting. This is controlled by

using waxes of different modulus in different areas. E.g. the lateral walls of the

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crown are prepared using inlay wax and occlusal surface using soft green casting

wax. The ratio of modulus being 7:1 Inlay: Casting wax which is approximately

the ratio needed for most patterns to obtain uniform expansion in the occlusal

compared to the margin areas.

Flow

Flow is generally associated with fluids or plastic substances and is

visualized as slippage of molecules over each other. In the case of waxes in liquid

state flow is synonymous with viscosity or internal friction. Below the melting

point it is a measure of the degree of plastic deformation at the given temperature.

Flow is dependent on temperature, force and duration of force. It greatly increases

as the melting point is approached. Depending on the application the flow may be

useful and in other cases harmful. E.g. direct inlay wax should have good flow

few degrees above room temperature but essentially no flow at room temperature.

Mineral waxes flow upto 50% at 20°C below their melting point due to weak

secondary valence forces. Plant waxes flow 50% only few degrees below their

melting point. The exception to this is Montan mineral wax which has ester

groups like plant waxes.

Residual stresses

Residual stresses are incorporated invariably in the wax pattern regardless

of the techniques. When we consider the thermal expansion curves of annealed

wax with wax that has been cooled under compression or tension, the annealed

wax follows the same curve on cooling or heating. In the case of specimens

prepared by holding under compression during cooling, the residual stresses cause

the molecules to move closer and subsequent heating results in greater expansion

than routine due to the relaxation of the stress.

Similarly when the specimen is prepared by subjecting it to tensile stress, the

curve will be lower than that of annealed specimen and may even lead to

contraction when the residual tensile stresses are released.

Ductility

Ductility increases with temperature. Waxes with lower melting point

have greater ductility than waxes with higher melting point. A blended wax with

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components having wide melting range will show greater ductility then those with

narrow melting range.

DENTAL WAXES

Classification based on use and application.

Pattern Processing Impression

Inlay Boxing Corrective

Casting

- sheet

- ready shapes

- wax-up

Utility Bite

Base plate Sticky

Pattern waxes are used to replicate the restoration. Two important concerns are

thermal change in dimension and tendency for distortion.

Processing waxes act as auxillaries in various procedures.

Impression waxes are seldom used now.

INLAY DENTAL WAX

Requirements of wax-pattern materials The major requirements of waxes used to

construct wax patterns by either the direct or indirect technique are as follows.

(1) The wax pattern must conform to the exact size, shape and contour of the

appliance which is to be constructed.

(2) No dimensional change should take place in the wax pattern once it has been

formed.

(3) After formation of the casting mould, it should be possible to remove the wax

by boiling out or burning without leaving a residue.

The ability to record detail depends on the flow of the material at the

moulding temperature, which is just above mouth temperature for direct

techniques and just above room temperature for indirect techniques. Accuracy and

dimensional stability depend on dimensional changes which occur during solidifi

cation and cooling of the wax. Distortions may also occur if thermal stresses are

introduced.

Composition:

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Paraffin 60%

Carnauba 25%

Ceresin 10%

Beeswax 5%

Inlay waxes come under ADA specification no: 4 and 3 types are recognized.

Types A, B and C. The non volatile residue should be a maximum of 0.1 % in all

the types.

Type A - Used in indirect techniques. It is hard wax and has little flow.

Type B - Medium wax used for making direct patterns in the mouth.

Type C - Soft wax used in indirect techniques and has maximum flow.

Maximum linear thermal expansion permitted between 25°& 30°C is

0.20% and between 30°& 37°C is 0.60%. They should soften without flaking and

during carving should not chip or flake. The flow of inlay wax can be decreased

by adding carnauba wax or selection of high melting paraffin wax.

Flow characteristics of inlay wax.

FLOW % WAX TEMPERATURE ° C

Minimum Maximum A B C

- 1 43 37 34

1 15 46 40 37

50 85 49 43 40

70 90 52 46 43

Thermal coefficient of expansion

The rate of thermal expansion of type B wax is greatest from just below

mouth temperature to just above 45° C. The knowledge of amount of expansion

and contraction is imperative to obtain accurate castings.

Warpage

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Inlay wax patterns tend to warp on standing and this tendency to warp

increases with temperature and prolonged storage time.

Warpage can be minimized by

Softening wax uniformly by heating at 50°C for at least 15 min before use.

Using warm instruments.

Using a warm die.

Adding wax in small increments.

Storing patterns in refrigerator if not being invested within 30 minutes.

Investing the pattern at the earliest.

Using solid wax sprue or hollow metal sprue filled with sticky wax during

spruing will reduce distortion.

Inlay waxes are generally produced in deep blue, green or purple rods or sticks

about 7.5 cm long and 0.64 cm in diameter.

CASTING WAX

Used for the designing of patterns for RPD framework. They are available

as

Sheets of 28 to 30 gauge(.4 & .32 mm)

Readymade shapes – round, half round, half pear shaped rods & wires

Bulk material

Difference between inlay and casting wax is minimal and related to the

physical properties. The composition is similar but the proportions are different.

Casting wax sheets are used to establish minimum thickness in certain areas of the

partial denture framework, such as the palatal and lingual bar. They are also used

for post damming of complete maxillary denture impressions, for checking high

points and for producing wax bites of cusp tips for articulation of stone casts.

Physical characteristics

Casting wax comes under federal specification No: u-w-140. It possesses a

slight degree of tackiness which maintains their position on the cast. According to

the federal specification they are put into 3 classes, however their properties like

flow, breaking point, and working properties are similar for all the classes. The

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wax should be capable of bending double on itself without fracture at a

temperature of 23°C i.e. it should have good ductility.

Most of the pattern waxes are being replaced by preformed plastic patterns.

Type of

casting waxFlow

Breaking

pointWorking properties

Class A

28 gauge

pink

35°C-max

10%

38°C-min 60%

No

fracture at

23°±1°C

- Pliable & readily

adaptable at 40-45°C

- Copy accurately the

surface on which it is

adapted

- Not be brittle on cooling

- Vapourize at 500°C

leaving no film other

than carbon.

Class B

30 gauge

green

Class C

Ready

shapes

blue

BASEPLATE WAX

Base plate waxes are used for

Establishing vertical dimension in complete denture construction

Establishing the plane of occlusion

Forming the initial arch form

Forming the tray

Serves to produce the desired contour after teeth setting

Designing removable orthodontic appliances.

Composition:

Ceresin 80%

Beeswax 12%

Carnauba 2.5%

Resins 3%

Microcrystalline or synthetic waxes 2.5%

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Physical properties: - This wax comes under ADA specification number 24.

Three types of waxes are recognized. These are normally supplied in sheets of 7.6

X 15 X .13 cm. normally marketed in pink or red colours.

Type I - Soft wax for building veneers.

Type II - Medium wax used for patterns to be tried in mouth in temperate

climates.

Type III - Hard wax used in tropical climates.

Type Temperature °C Flow % Practical requirements

Type I

soft

23 - 1 -Linear thermal expansion from

25-40°C <0.8%

-softened sheets should cohere

readily without flaking or

adhering to fingers.

- no tissue irritation

-trim easily with sharp

instrument at 23° C

-smooth surface after gentle

flaming

-no residue on porcelain or

plastic teeth.

-colouring should not separate

or impregnate plaster during

processing.

-no adhering to other sheets or

paper during storage.

37 4

5

85

45 - -

Type II

medium

23 - 0.6

37 - 2.5

45 5

0

90

Type III

hard

23 - 0.2

37 - 1.2

45 5 50

BOXING WAX

It comes under federal specification u-w-138. These are used to make box

around the impression into which freshly mixed plaster or stone is poured and

vibrated. In general it should be tacky and have strength and toughness sufficient

for convenient manipulation.

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UTILITY WAX

It comes under federal specification u-w-156. Utility wax is used when an

easily workable, adhesive wax is desired (e.g. contouring perforated tray prior to

alginate impressions). It is supplied in sticks and sheets. Colour ranges from dark

red to orange. Ductility and flow are the highest amongst dental waxes. It is

comprised of beeswax, petrolatum, and soft waxes.

CORRECTIVE IMPRESSION WAX

Used as a wax veneer over an original impression to contact and register

the detail of the soft tissue. It records tissue in functional state. It is not covered

under any specifications but flow is generally 100% at 37ºC.

BASE PLATE WAX

It is used for articulating accurately certain models of opposing quadrants.

It is generally made from 28 gauge casting wax sheet or from hard Base plate

wax. Certain bite waxes contain aluminium or copper particles. Flow ranges from

2.5% to 22% at 37 ºC and is susceptible to distortion on removal from the mouth.

BITE REGISTRATION WAX

It is covered by federal specification u-w- 00149a. It is formed by

mixing waxes and resins. It is sticky when melted and adheres to the surface

closely. It is firm and free from tackiness at room temperature and is brittle.

Type of wax Flow Colour Working properties

Boxing wax

UW- 138

Green

Black

Smooth glossy surface on

flaming,

Pliable at 21 °C,

Retains shape at 35º C,

Seals easily to plaster with

hot spatula.

Utility wax

UW- 156

At 37.5ºC

65-80%

Orange

Dark red

Pliable at 21-24 ºC

Tacky at 21-24 ºC

Sufficient adhesion to

build up.

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Sticky wax

UW- 00149a

30ºC – 5%

max

43ºC – 90%

min

Dark or

vivid

Sticky when melted

Adheres closely

Not more than 2% residue

on burnout.

Not more than 5%

shrinkage from 43ºC to

28ºC

References

Kenneth Anusavice: Phillips Science of Dental Materials 10th Ed. W B

Saunders & Co 1998.

Robert Craig: Restorative Dental Materials 10th Ed. Mosby Year Book Inc

1997.

Reese J A, Valega T M: Restorative Dental Materials: An Overview

Volume one. Quintessence Publishing Co 1985.

Craig R G, O’Brien W J: Dental Materials, Properties and Manipulation 6th

Ed. Mosby Inc 1996.

John F. McCabe, Applied Dental Materials, Ninth Edition, Blackwell

Publishing

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