1. Dental waxes

2. DENTAL WAXES Definition of dental wax = thermoplastic molding material
that is solid at room temperature.
Dental waxes may be composed of natural and synthetic waxes,gums,fats,fatty acids,oils and pigments
Technically, the definition of a wax is a “thermoplastic molding material that is sold at room temperature.” By implication, heating a wax will convert it to a liquid phase and make it much more easily moldable. Not all waxes require melting to be used in indirect dental fabrication procedures.
[CLICK] Waxes are composed of 3 major components – a BASE wax (that is almost always paraffin), [CLICK] MODIFIER waxes (to contribute properties such as increased hardness, stickiness, or brittleness), and [CLICK] COLORANTS (which represent only about 1% of the composition in general). There are no fillers because, in almost all instances, waxes need to be pyrolyzed at some point. Materials being pyrolyzed are being burned to the point that they melt and/or decompose into water vapor and carbon dioxide.

3. COMPOSITION Natural waxes produced from: Synthetic waxes
Plants
Minerals: paraffin wax
Animals: beeswax
insects
Synthetic waxes
Additional components: gums, oils, resins, fats.

4. BASE AND MODIFIER WAXES
Name:
Origin:
Composition:
Melting
(C)
Density
(20C)
PARAFFIN
Mineral
Hydrocarbon mixture
50-57
0.90
CERESIN
Complex hydrocarbons
61-78
BEESWAX
Animal
Ester mixture
62-65
CANDELILLA
Plant
C21 hydrocarbons
68-70
CARNAUBA
Hydrocarbon, Ester, Fatty Acid
82-86
GUM DAMMAR
Aromatic resin
ca 120
ROSIN
Aromatic resin acid
1.08
PARAFFIN is the major component of almost all dental waxes. Materials that we call waxes are usually medium molecular weight organic materials (linear or aromatic) that are derived from mineral, animal, or plant sources. Paraffin is a linear hydrocarbon that is relatively low molecular weight (a couple dozen carbon atoms long). It is not pure because it is so difficult to isolate a single molecular weight. It is collected during the fractionation of oil into its components. Therefore, it is reported as a mixture of hydrocarbons. Its molecular weight is just high enough that at room temperature it is solid (Tm = 50-57°C). In general, as the molecular weight of wax increases, the melting temperature increases, and the density increases. That is obvious from the table above.
[CLICK] A variety of modifier waxes are routinely added to paraffin to control the final properties. Ceresin and carnuba tend to increase the hardness and water resistance of wax. Beeswax increases the stickiness. Rosin increases the brittleness. These are melted together carefully to make the final wax.
Notice that all of these have relatively low melting ranges (and so does each mixture). Therefore, during use it is crucial not to overheat a wax during melting while it is being manipulated or else some of the base or modifier waxes can be decomposed. That would change the overall properties of the wax.
INLAY WAX = Paraffin + Carnuba + Ceresin + Beeswax + Colorants

5. What are waxes used for?
Waxes have a variety of uses in clinics and laboratories.
In clinics
In laboratories
Bite registration
Boxing techniques
Alterations and adaptation for impression trays
Baseplate for complete and partial dentures
Direct waxing for cast restorations
Hold components before articulation
____________
Indirect pattern for casting

6. CLASSIFICATION OF WAXES
Pattern wax
Processing wax
Impression wax
Inlay wax
Boxing wax
Corrective impression wax
Casting wax
Utility wax
Bite registration wax
Baseplate wax
Sticky wax
_____________

7. CLASSIFICATION OF DENTAL WAXES
There are tremendous number of dental laboratory applications which involve waxes. Waxes are chosen over synthetic polymeric alternatives because they are much less expensive.
[CLICK] In general, dental waxes can be divided into 3 major classes based on their general use – (1) PATTERN waxes, (2) IMPRESSION waxes, and (3) PROCESSING waxes. [CLICK] Within each class, they can be subdivided by dental application. For example, pattern waxes can be subdivided as (a) inlay waxes, (b) casting waxes, and (c) baseplate waxes. [CLICK] Within each application category, waxes can be further subdivided on the basis of a defined set of properties (generally classified by ADA standards committees and called “types” like Type 1 or Type 2).
[CLICK] Waxes are supplied in geometric shapes that are convenient for their particular dental application (e.g., sticks, rods, sheets, ropes, …). [CLICK] The COLOR assigned to each form is intended to signify the general application. However, manufacturers do not consistently apply the color coding for anything but their own products. Therefore, inlays waxes could be green, or blue, or purple.

8. PROPERTIES
Melting range: a range of temperatures at which each component of the wax will start to soften and then flow. The operator can control the viscosity of wax by controlling temperature.
Flow: is the movement of the wax as molecules slip over each other. Melting range and flow of the wax are important in wax manipulation by operator. E.g. bite registration wax?

10. Physical Properties – Melting Range
WAX
Physical Properties – Melting Range
COMPOSITION (%)
TEMPERATURE (C)
Paraffin
Carnuba 40 30 20 60 50 70 80 90 25 75
100
LIQUID
LIQUID + SOLID
SOLID
Melting Onset (Solidus)
Melting Completion (Liquidus)
First, consider the melting properties of a simple binary mixture of paraffin and carnuba [CLICK] as representing the more complex mixture that was just described. One can actually develop a phase diagram for a wax (as shown above).
The liquidus line (representing the temperature at which complete melting has occurred) [CLICK] increases quickly from 62°C as carnuba is added to the composition. The solidus line (below which the composition is entirely solid) [CLICK] is not affected much by the carnuba additions. [CLICK] Importantly, the solid+liqud range in between is quite broad (almost 40°C). To develop wax flow, the temperature only needs to be heated to a point within the solid+liquid range or up to the point of the liquidus line but not much higher. Excessive heating would cause decomposition.
In most dental laboratories, wax is heated in a wax pot [CLICK] that maintains a constant but low temperature with the wax just barely melted. The alternative is to heat a wax instrument and dip it into the wax to melt it and pick up some material. However, this approach is very prone to overheating and decomposing the wax.
Image and graph source: Steve Bayne, University of Michigan, 2008

11. PROPERTIES
Excess residue: for the sake of accuracy in the object produced, if excess residue remains after melted wax is removed, inaccuracies may occur. (lost wax technique procedure)

12. PROPERTIES
Dimensional change: waxes expand when heated, contract when cooled. Thermal expansion of waxes is highest among dental materials. This property is important especially for pattern waxes (e.g. inlay wax). How:
If wax is heated well beyond melting range or unevenly, unacceptable expansion occurs.
If wax is allowed to stand for a long time, the release of residual stresses will lead to dimensional changes and inaccuracies. This is why pattern wax should be invested within 30 minutes of carving.

13. The elastic modulus ,proportional limit ,and kompressive strength of waxea are low compared wieh other materials. And these properties depend strongly on the temperature

14. Physical Properties – Thermal Expansion of Components
WAX
Physical Properties – Thermal Expansion of Components 25 30 40 45 35 50
1.2
1.0
0.8
0.6
0.4
0.2
TEMPERATURE (C)
EXPANSION (%)
KERR
HARD
WAX
Paraffin
Beeswax
250
ppm/C
During heating and cooling wax expands or contracts at very high rates. Compared to ceramics (1-15 ppm/°C) and metals (10-30 ppm/°C), polymers (and waxes) have very high coefficients of thermal expansion (and contraction) and over a broad range ( ppm/°C). [CLICK] A typical value for an inlay wax is ppm/°C. The rate of thermal expansion is the same as the slope of the line on the ‘expansion versus temperature’ graph shown above. A steep line has a high rate.
[CLICK] Paraffin has the highest coefficient of thermal expansion. Addition of modifier waxes such as beeswax [CLICK] and carnuba wax [CLICK] decrease the rate for the overall wax (see the for KERR HARD WAX). Control of the coefficient of thermal expansion helps to decrease the susceptibility of the wax to distortion on cooling.
Carnuba
Graph source: Steve Bayne, University of Michigan, 2008

16. PATTERN WAXES
Inlay waxes: are used to produce patterns for metal casting using the lost wax technique.

17. Inlay Casting Wax
Blue or green sticks, heat over open flame, petroleum hydrocarbons, natural resin and wax. ALL INDIRECT RESTorations, makes the pattern of a crown then the wax is replaced with metal

19. Continue,
Type I: placed directly in the prepared tooth in the direct waxing technique. This wax has a low melting range.
Type II: melted on a die outside the mouth in the indirect technique (more commonly used). These waxes are supplied as pellets and sticks. They are blue and green in color. Hard, medium, soft depending on melting range.

20. Continue,
Casting wax: used to construct the metal framework for partial and complete dentures. Supplied in sheets or preformed shapes.

22. Continue,
Baseplate wax: sheets of wax pink in color. These sheets are layered to produce the form on which denture teeth are set

23. Baseplate Wax
Petroleum hydrocarbons and natural wax, PINK SHEETS. Replaces length and width of teeth in denture or partial for try in. Melts with flame or HOT water.

24. Occlusal Rims in Baseplate wax

25. PROCESSING WAX
Boxing wax: used to form the base portion of a gypsum model. Easily manipulated at room temperature.

26. 1. Boxing Wax
Replaces patty base pour technique. Boxing wax goes around impression and then is filled with gypsum. No heat needed.
Petroleum hydrocarbon & natural resin
Red sheets 1 ½ in wide

27. Continue,
Utility wax: also called periphery wax, comes in ropes, and easily manipulated at room temperature. Used to adjust impression trays, used to cover sharp brackets and wires in orthodontic appliances, layered in sheets for bite registration.

28. Utility wax

30. Utility Wax
Adapt impression trays, cover rough ortho brackets, red or white ropes, petroleum hydrocarbon and paraffin, No heat.
Ortho= WHITE

31. Continue,
Sticky wax: comes in orange sticks that are hard and brittle at room temperature. When heated, become soft and sticky. Used to adhere components of metal, gypsum, resin during fabrication and repair.

32. Sticky wax

33. Sticky Wax
Hold items (acrylic) together to make repairs, heat in flame, ORANGE sticks, natural wax & resin

34. IMPRESSION WAXES
Corrective impression wax: used with other impression materials for edentulous impressions, to correct undercut areas. Flows at mouth temperature.
Bite registration: to produce wax bite registration for articulation of models. Susceptible to distortion, needs careful handling.

35. Bite Registration Wax
Aluwax, paraffin and beeswax, bite registration, no heat or warm water

36. Wax sheets used for impression and bite registration

37. Wax sheets, horseshoe shaped, rods

38. MANIPULATION Softened evenly in: Added in layers into an object
Warm hands
Dry heat
Flame
Added in layers into an object
Should be invested within 30 minutes of carving
Utility and boxing wax should remain dry to allow to stick when manipulated.
Should be stored at or slightly below room temperature

40. Lost wax technique
An impression of the preparation is taken and poured into high strength stone to form a die.
Wax pattern is carved
Wax or plastic sprue is attached to pattern
Pattern and sprue are encased in investment ring, into which investment gypsum is poured
Once investment sets, wax pattern and sprue are heated in a burnout oven, causing wax and sprue to vaporize (lost wax), leaving an impression of wax pattern in the empty case

41. Lost wax technique continue,
Molten metal is poured through the empty channel formed by sprue, into the empty wax pattern space.
Metal cools, sprue removed, casting cleaned and polished and now ready for cementation

42. Lost wax technique

43. REFERENCE
Dental materials, clinical applications for dental assistants and dental hygienists
Chapter 15