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Wax PPT with Audio Bees wax

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					                            LABORATORY
                              WAXES
                                 Dent204, UNC School of Dentistry




                                        Stephen C. Bayne
                                        Department of Operative Dentistry
                                        School of Dentistry
                                        University of North Carolina
                                                        27599-
                                        Chapel Hill, NC 27599-7450




Use of WAXES in dentistry are almost exclusively confined to dental laboratory settings.




                                                                                           1
            OVERVIEW OF DENTAL WAXES
               1. Definition of dental wax = thermoplastic molding material
                  that is solid at room temperature.


               2. General Composition of Waxes:

                           Wax:
                  a. BASE Wax:
                                      [eg,
                     (1) Hydrocarbon [eg, PARAFFIN] or ester types;
                     (2) High or low MW
                  b. MODIFIER Waxes:
                                Waxes:
                     (1) Hydrocarbon or ester types;
                     (2) High or low MW

                  c. COLORANT:
                     COLORANT:




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.




                                                                                         2
              BASE AND MODIFIER WAXES

             Name:        Origin:   Composition:                     Melting   Density
                                                                     (°C)      (20°C)

             PARAFFIN     Mineral Hydrocarbon mixture                50-57     0.90
             CERESIN      Mineral Complex hydrocarbons               61-78     0.91-0.92
             BEESWAX      Animal    Ester mixture                    62-65     0.95-0.96
             CANDELILLA   Plant     C21 hydrocarbons                 68-70     0.95-0.99
             CARNAUBA     Plant     Hydrocarbon, Ester, Fatty Acid   82-86     0.99-0.999
             GUM DAMMAR   Plant     Aromatic resin                   ca 120    1.040-1.120
             ROSIN        Plant     Aromatic resin acid              100-150   1.08


          INLAY WAX = Paraffin + Carnuba + Ceresin + Beeswax + Colorants




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.




                                                                                             3
         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.




                                                                                      4
                               INLAY WAX
             1. Overview:

                 a. Objective: Pattern material to accurately represent
                    desired mold space for inlays, onlays, and crowns.
                 b. Requirements for Inlay Waxes:
                    (1) Good adaptation to dies
                    (2) Thermal stability at low temperatures
                    (3) Complete pyrolysis at high temperatures
             2. Inlay Wax Composition:

                 a.   60% Paraffin Wax     = BASE Wax
                 b.   25% Carnuba Wax      = MODIFIER Wax
                 c.   10% Ceresin          = MODIFIER Wax
                 d.    5% Beeswax          = MODIFIER Wax
                 e.   <1% Colorants        = COLORANT




Let’s use INLAY WAX as an example for careful examination of the composition,
structure, and properties of a dental wax. An inlay wax is used to make patterns for
inlays, onlays, and crowns. It requires good adaptation to dies to pick up the proper
size of the restorations and quality of the margins. It should have good thermal
stability at low temperatures during manipulation procedures when it is being melted
and cooled several times. Since it will be invested and ultimately burned out of the
set investment material, it must be capable of complete and clean pyrolysis.


[CLICK] A typical composition of an inlay wax is shown above. It is mostly paraffin
(60%) with carnuba (25%) and ceresin (10%) added to increase the hardness. A
small amount of beeswax (5%) is added so that it will stick to a die. The rest of the
composition is colorant (<1%).




                                                                                        5
                                               INLAY WAX
                                    Physical Properties – Melting Range


                                                            LIQUID

                  TEMPERATURE (C)   90         Melting Completion (Liquidus)
                                    80

                                    70
                                                        LIQUID + SOLID
                                    60

                                    50

                                    40
                                                     Melting Onset (Solidus)
                                    30

                                    20
                                                             SOLID

                                                25             50              75    100

                                    Paraffin         COMPOSITION (%)                Carnuba




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.




                                                                                              6
                                                 INLAY WAX
         Physical Properties – Thermal Expansion of Components

                                                                                             KERR
                                       1.2                               250                 HARD
                                                                       ppm/°C                WAX


                       EXPANSION (%)
                                       1.0




                                                                             ax
                                                             in




                                                                          esw
                                                      Paraff




                                                                        Be
                                       0.8


                                       0.6



                                       0.4
                                                                                b   a
                                                                            rnu
                                                                       Ca
                                       0.2


                                        0
                                             0   25       30      35    40      45      50
                                                      TEMPERATURE (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 (30-600 ppm/°C). [CLICK] A typical value for an inlay wax is 250-300
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.




                                                                                                    7
                                 INLAY WAX
                Mechanical Properties and Chemical Properties


                                        Properties:
                             Mechanical Properties:
                                Flow < 1%
                                Ductility = moderate
                                Residual Stress = none

                                      Properties:
                             Chemical Properties:
                                Homogeneity = good
                                Contact Angle = low
                                Oxidation = complete




There are a limited number of mechanical and chemical properties that are routinely
monitored to insure that waxes have the same general qualities from manufacturer-
to-manufacturer. These are listed above.


Wax should be dimensionally stable once it has solidified. Therefore, the flow
should be less than 1%. Wax should be capable of some plastic deformation
(ductility) so that it will deform rather than fracturing. This also allows it to be carved
or burnished. Some thermal stresses are developed whenever wax additions are
cooled. The exterior surface tends to cool first. The molten interior slowly solidifies
and contracts. This encourages distortion or flow. Hopefully the stress is relaxed
and not important distortions result.


[CLICK] Chemically, waxes should have the same properties throughout the solid
(i.e., good homogeneity). When a wax is melted, it should WET the surface of the
material to which it is being added (e.g., die) and spread easily onto it (i.e.,low
contact angle). Finally, when it is pyrolyzed, the process of oxidation should
completely transform it into water vapor and carbon dioxide so that no residue is
left.




                                                                                              8
                THANK YOU




It is critically important to recognize the limitations or potential problems of
waxes and make sure these do not create problems along the way in
laboratory fabrication of restorations.


Thank you.




                                                                                   9

				
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