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
• 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.
a) Aerosol OT
b) Castor wax
c) Flexowax C
d) Dura wax
d) Japan wax
e) Cocoa butter
• Two main group of organic compounds in waxes are-
Some waxes contain free alcohols and acids as well.
• Complex organic compounds of varied chemical composition
• Use in dental formulations is limited
• More refined than natural waxes
• Polyethylene waxes
• Polyoxyethylene glycol waxes
• Halogenated hydrocarbon waxes
• Hyrogenated waxes
• Wax esters
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.
• Melting range
• Thermal expansion
• Mechanical properties
• Residual stress
Have a range as they contain several types of molecules, each having a range of molecular weight.
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.
• Elastic modulus
• Proportional limit
• Compressive strength
All are low when compared to other materials
• 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
• Modulus ratio for inlay and soft green casting wax is 7:1.
• To avoid non uniform distortion of the wax pattern during hygroscopic casting 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
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::
1. Temp of wax
2. The force applied
3. Time for which the force is applied
4. Flow is greatly increased as melting point is approached
• 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 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
• 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.
• 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
• 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
• Entire wax mass is plasticized & ductility increases
CLASSIFICATION OF DENTAL WAXES:
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