Casting-Defects-Ppt.pptx

SEMINAR BY
ARIFA HASSAN
1ST MDS
PROSTHODONTICS

 Introduction
 Casting
Procedure
 Casting defects
 Classification of defects
 Distortion
Surface roughness
Surface irregularities
Discoloration
 Porosity
solidification defects
trapped gases
residual air
 Incomplete casting
 Summary

 In dentistry the lost-wax casting technique was not
popular until 1907 when W.H. Taggart introduced this
technique and casting machine. Today the lost-wax
technique is common practice and is used for a variety
of casting operations
 Any imperfections or irregularities that result in
unsuccessful casting which interferes with the fit of
final restoration or its esthetic and mechanical
properties

 In dentistry the resulting casting must be an accurate
reproduction of the wax pattern in both surface details
and overall dimension.
 Reproducing the wax up in metal with predictable
results has always been a challenge.
 Small variation in investing or casting can
significantly effect the quality of the final restoration.
 Successful castings depend on attention to detail and
consistency of technique

Definiton
 Casting is defined as something that has been
cast in a mold, an object formed by the
solidification of a fluid that has been poured or
injected into a mold.(GPT)
 “Casting is the process by which a wax pattern
of a prepared tooth is fabricated and converted
to its metallic replica”(Rosentiel)

Finishing and polishing
Quenching and Pickling
Molten metal is cast into the void created by the wax pattern and the sprue
Invested pattern is heated until all the remnants of wax are burned away
The pattern and sprue are invested
All aspects of final restoration are incorporated into the wax pattern
Wax pattern is first formed on a die or directly on the tooth.

 An unsuccessful casting result in considerable
trouble and loss of time, in almost all instances,
defects in castings can be avoided by strict
observance of procedures governed by certain
fundamental rules and principles.
 Seldom is a defect in a casting attributable to other
factors than the carelessness or ignorance of the
operator.
 With present techniques, casting failures should be
the exception, not the rule
Phillip’s science of dental materials-11th edition by Kenneth J.Anusavice
page.337

 Defects in castings can be classified under four
headings(According to Anusavice)
 (1) Distortion
 (2) Surface roughness and irregularities
 (3) Porosity
 (4) Incomplete casting or missing detail

 Roughness
 Nodules
 Fins
 Incompleteness
 Voids or porosity
 Marginal discrepancies
 Dimensional inaccuracies

General
problems
Problems
with internal
porosity
Problems
with
external
porosity
accuracy
distortion
bubbles
fins
short rounded margins
miscasting's
pits
localize shrinkage porosity
subsurface porosity
micro porosity
back
pressure
porosity
According to O’Brien

 Any marked distortion of the
casting is probably related to
the distortion of the wax
pattern.
 This type of distortion can be
minimized or prevented by
proper manipulation of the
wax and handling of the
pattern
Phillip’s science of dental materials-11th edition by Kenneth J.Anusavice.page338

 Distortion can occur during
spruing the pattern because of
the heat transferred to the
pattern

 Wax shrinks during cooling(.2%) and may distort at a later time if
cool too fast
 Can also caused by the Stresses occur in the inlay wax as a result of
the heating and manipulation of the wax during fabrication of the
pattern.
 To Minimise the distortion :
 A wax pattern should not be subjected to temperature extreme that
may cause stress relief and distortion in shape
 Patterns should never be left off the die.
 Invested as soon as possible after fabrication.
Phillip’s science of dental materials-11th edition by Kenneth
J.Anusavicepage 289
Materials in dentistry –priciples and applications by Jack L.Ferracane.page241

 Unquestionably some distortion
of the wax pattern occurs as the
investment hardens around it.
 The setting and hygroscopic
expansions of the investment may
produce a non-uniform expansion
of the walls of the pattern.
 This type of distortion occurs in
part from the non uniform
outward movement of the proximal
walls
Phillip’s science of dental materials-11th edition by Kenneth J.Anusavice page;338

 The characteristics of investments depend on
various factors such as the liquid-powder ratio,
particle size and chemical composition of the
powder, and mixing methods.
 The time between mixing and heating influences
the setting behaviour of the investment.
 Moreover, setting expansion may lead to distortion
of the wax pattern.
Restorative dental materials -8th edition by Robert G.Craig.page473

 Effect of wax melting range and investment liquid
concentration on the accuracy of a three-quarter crown
casting
 Michio Ito et al,The Journal of Prosthetic Dentistry Volume 87,
Issue 1, January 2002, Pages 57–61
 Conclusion:
1. Within the limitation of this study,casting shrinkage was affected
by the type of wax used
2. The higher the softening temperature, the larger the casting
shrinkage.

 The surface of a dental casting should be an
accurate reproduction of the surface of the wax
pattern from which it is made, excessive roughness
or irregularities on the outer surface of the casting
necessitate additional finishing and polishing,
whereas irregularities on the cavity surface prevent
a proper seating of an otherwise accurate casting
 Surface roughness should not be confused with
surface irregularities.
 A smooth surface not only prevents plaque and
calculus accumulation, but it also improves the
corrosion resistance of the alloy

 Surface roughness is defined as relatively
finely spaced surface imperfections whose
height, width, and direction establish the
predominant surface pattern.
 Surface irregularities are isolated
imperfections, such as nodules, that are not
characteristic of the entire surface area
Phillip’s science of dental materials-11th edition by Kenneth J.Anusavice.page338

CAUSES:
 Air bubbles
 Water film
 Rapid heating rates
 Under heating
 Liquid : Powder ratio
 Prolonged heating
 Casting pressure
 Composition of Molten alloy
 Foreign bodies / Carbon inclusion
 Impact of molten alloy
 Pattern position

 Air bubbles that become attached to the pattern during
or subsequent to the investing procedure cause small
nodule on a casting.
 Such nodules can sometimes be removed if they are
not in a critical area.
 However, for nodules on margins or on internal
surfaces, removal of these irregularities might alter the
fit of the casting.
Phillip’s science of dental materials-11th edition by Kenneth J.Anusavicepage.338

 Bubbles of gases trapped between the wax pattern and
the investment produce nodules on the casting surface
 Large nodule- Air trapped during investing
 Multiple nodules – Inadequate vacuum during mixing
Improper brush technique
Lack of surfactant.
 Nodules on occlusal surface – Prolonged vibration after
pouring
Contemporary fixed prosthodontics-4th edition by Rosenstiel.Land.Fujimoto.page702

Introduction to metal-ceramic technology-2nd edition by W.Patric Naylor.page94
Rough casting with multiple nodule due to failure to evacuate the
investmet’s gaseous by-products during mixing

Prevention
 The best method to avoid air bubbles is to use the vacuum
investing technique.
Advantages of vacuum mixing-----
1) Remove air bubbles
2) Produce smooth castings
3) Increase tensile strength of investment
4) 95% of castings free of nodules.
5) Removes all the gaseous by products of chemical reaction
of investment material
Introduction to metal-ceramic technology-2nd edition by W.Patric Naylor page95

 If a manual method is used various precautions has to
be taken to eliminate air from the investment mix
before the investing.
 The use of a mechanical mixer with vibration both
before and after mixing should be practiced routinely.

 The incidence of nodules on casting is more in
hand mixing than vacuum mixing.
 The best method is vacuum mix and vacuum
pour technique. But most popular method
vacuum mix and open pour(hand pour)

 A wetting agent may be helpful in preventing
the collection of air bubbles on the surface of
the pattern, but it is by no means a certain
remedy.
 It is important that the wetting agent be applied
in a thin layer. It is best to air dry the wetting
agent, because any excess liquid dilutes the
investment, possibly producing surface
irregularities on the casting.

 Wax --- water repellent
 Creates space in between wax & investment
 Appears as minute ridges or veins
 If the pattern is moved slightly, jarred or vibrated after
investing, or if the painting procedure does not result in an
intimate contact of the investment the pattern, such a
condition may result
 Prevention --- wetting agent, pattern should not be moved,
jarred or vibrated after investing.
 Avoid too high liquid : powder ratio
J.Anusavice.page339

Phillip’s science of dental materials-11th edition by Kenneth J.Anusavice page339

 Rapid heating results in fins or spines on the
casting or may result as a characteristic surface
roughness may be evident because of flaking of
the investment when the water or steam pours
into the mold.
 Furthermore, such a surge of steam or water
may carry some of the salts used as modifiers
into the mold.

 Salts are left as deposits on the walls after
water evaporates and leads to surface
roughness
Remody
 The mold should be heated gradually; at least
60 minutes should elapse during the heating of
the investment- filling ring from room
temperature to 7000c.
 The greater the bulk of the investment, the
more slowly it should be heated
Phillip’s science of dental materials-11th edition by Kenneth J.Anusavicepage339

Contemporary fixed prosthodontics-4th edition by
Rosenstiel.Land.Fujimoto.page702
 Fins are also caused by
cracks in the investment
that have been filled
with molten metal
 Cracks due to over
vibration during
investment or disturbing
ring during setting

Introduction to metal-ceramic technology-2nd edition by W.Patric Naylor.page100
Fin caused by excess wax pattern cleaner or improper heating of the
mold

 Incomplete elimination of wax residues may occur if
the heating time is too short or if insufficient air is
available in the furnace.
 These factors are particularly important with the low-
temperature investment techniques.

 Voids or porosity may occur in the casting from the
gases formed when the hot alloy comes in contact with
the carbonaceous residues.(due to incomplete wax
elimination)
 Occasionally, the casting may be covered with a
tenacious carbon coating that is virtually impossible to
remove by pickling.
Phillip’s science of dental materials-11th edition by Kenneth J.Anusavice

 The amount of water and investment should be
measured accurately.
 The higher the L: P ratio, the rougher the casting.
 However, if too little water is used, the investment may
be unmanageably thick and cannot be properly applied
to the pattern.
 Both leads to rough surface
The science and art of dental ceramics-volume ii bridge esign and laboratory
procedures in dental ceramics by John W.McLean.page232

 When the high –heat casting technique is used, a
prolonged heating of the mold at the casting
temperature is likely to cause a disintegration of the
investment, and the walls of the mold are roughened as
a result
 Furthermore, the products of decomposition are sulfur
compounds that may contaminate the alloy to the
extent that the surface texture is affected.
Phillip’s science of dental materials-11th edition by Kenneth J.Anusavicepage.340

 Such contamination may be the reason that the surface
of the casting sometimes does not respond to pickling.
 When the thermal expansion technique is employed,
the mold should be heated to the casting temperature-
never higher than 7000c – and the casting should be
made immediately.

 If an alloy is heated to too high temperature before
casting, the surface of the investment is likely to be
attacked, and a surface roughness of the type described
in the previous section may result.
 As previously noted, in all probability the alloy will
not be overheated with a gas – air torch when used
with the gas supplied in most localities.
 If other fuel is used, special care should be observed
that the color emitted by the molten gold alloy, for
example, is no lighter than a light orange.

 Casting Pressure : Too high pressure during
casting produces a rough surface on the
casting. A gauge pressure of 0.10 to 0.14 Mpa
(15 to 20 psi) in an air pressure casting
machine or three to four turns of the spring in
an average type of centrifugal casting is
sufficient

 The ratio of the binder to the quartz influences the
surface texture of the casting.
 In addition, coarse silica causes a surface roughness.
 If the investment meets ADA specification no.2, the
composition is probably not a factor in the surface
roughness

 When foreign substances get into the mold, a surface
roughness may be produced. For example, a rough
crucible former with investment clinging to it may
roughen the investment on its removal so that bits of
investment are carried into the mold with the molten
alloy.
 Carelessness in the removal of the sprue former may be
a similar cause.

 Usually, contamination results not only in surface
roughness but also in incomplete areas or surface
voids.
 Any casting that shows sharp, well- defined
deficiencies indicates the presence of some foreign
particles in the mold, such as pieces of investment and
bits of carbon form a flux.

 Bright- appearing concavities may be the result of flux
being carried into the mold with the metal.
 Surface discoloration and roughness can result from
sulfur contamination, either from investment
breakdown at elevated temperatures or from a high
sulfur content of the torch flame.
 The interaction of the molten alloy with sulfur
produces black castings that are brittle and do not clean
readily during pickling.

 The direction of the sprue former should be such that
the molten gold alloy does not strike a weak portion of
the mold surface.
 Occasionally, the molten alloy may fracture or abrade
the mold surface on impact, regardless of its bulk, it is
unfortunate that sometimes the abraded area is smooth
so that it cannot be detected on the surface of the
casting, such a depression in the mold is reflected as a
raised area on the casting, often too slight to be noticed
yet sufficiently large to prevent the seating of the
casting.

1. The science and art of dental ceramics-volume ii bridge esign and laboratory
procedures in dental ceramics by John W.McLean.page224

 This type of surface roughness or irregularity can be
avoided by proper Spruing so as to prevent the direct
impact of the molten metal at an angle of 900 to the
investment surface.
 A glancing impact is likely to be less damaging and at
the same time an undesirable turbulence is avoided.

 Likewise, too many patterns positioned in the same
plane in the mold should be avoided,
 If several pattern are invested in the same ring they
should not be placed too close together.
 The expansion of wax is much greater than that of the
investment, causing breakdown or cracking of the
investment if the spacing between patterns is less than
3mm.
The science and art of dental ceramics-volume ii bridge esign and laboratory procedures
in dental ceramics by John W.McLean page230

 Carbon, as form a crucible , an improperly adjusted
torch or a carbon-containing investment, can be
absorbed by the alloy during casting.
 These particles may lead to the formation of carbides
or even created visible carbon inclusions.

 There are certain surface discolorations and roughness
that may not be evident when the casting is completed
but that may appear during service.
 For example, various gold alloys, such as solders, bits
of wire, and mixtures of different casting alloys should
never be melted together and reused.
 The resulting mixture would not posses the proper
physical properties and might form eutectic or similar
alloys with low corrosion resistance.
 Discoloration and corrosion may also occur.

 Porosity may occur both within the interior region of a
casting and on the external surface.
 The latter is a factor in surface roughness, but also it is
generally a manifestation of internal porosity.
 Not only does the internal porosity weaken the casting
but also if it also extends to the surface, it may be a
cause for discoloration.
 If severe, it can produce leakage at the tooth-
restoration interface, and secondary caries may result.
 Although the porosity in a casting cannot be prevented
entirely, it can be minimized by use of proper
techniques

I. Solidification defects -
A. Localized shrinkage porosity
B. Microporosity
II. Trapped gases -
A. Pinhole porosity
B. Gas inclusions
C. Subsurface porosity.
III. Residual air

 Localized shrinkage is generally caused by
premature termination of the flow of molten
metal during solidification.
 The linear contraction of noble metal alloys -
changing from a liquid to solid is at least
1.25%.
 Localized shrinkage generally occurs near the
sprue-casting.

1. Restorative dental materials -8th edition by Robert G.Craigpage472

Cause:
 Diameter of the is too narrow
 Length of the sprue is too long
 Absence of reservoir
 Direction of sprue at 90 degree

 This type of void may also occur externally,
usually in the interior of a crown near the area
of the sprue, if a hot spot has been created by
the hot metal impinging from the sprue channel
on a point of the mold wall.
 This hot spot causes the local region to freeze
last and results in what is called suck-back
porosity

 Suck-back porosity often
occurs at an occlusoaxial line
angle or incisoaxial line angle
that is not well rounded.
 The entering metal impinges
onto the mold surface at this
point and creates a higher
localized mold temperature in
this region, known as a hot
spot

Introduction to metal-ceramic technology-2nd edition by W.Patric Naylorpage85

 A hot spot may retain a localized pool of
molten metal after other areas of the casting
have solidified. This in turn creates a
shrinkage void, or suck-back porosity.
Remody
 Suck-back porosity can be eliminated by
flaring the point of sprue attachment and
reducing the mold-melt temperature
differential, that is lowering the casting
temperature by about 30 degree C.

 Surface Porosity of Different Investment Materials with
Different Mixing Techniques
 Ahmed A et al. Al–Rafidain Dent J. 2009; 9(2): 307–314
 Conclusion: Manual technique showing higher value of surface
area and number of porosities than the Vacuum technique.

 The effect of sprue attachment design on castability and
porosity.
 Verrett RG, Duke ES. J Prosthet Dent. 1989 Apr;61(4):418-24.
 Conclusion: Flared and straight sprue attachments showed
optimized castability and minimized porosity than compared to
abrupt constriction, and gradual constriction

 Occurs from solidification shrinkage but is
generally present in fine-grain alloy castings
when the solidification is too rapid for the
microvoids to segregate to the liquid pool.
 This premature solidification causes the
porosity shown in the form of small, irregular
voids.

 Such phenomena can occur from rapid
solidification if the mold or casting
temperature is too low.
 Unfortunately, this type of defect is not
detectable unless the casting is sectioned

 Both pinhole and the gas inclusion porosities
are related to the entrapment of gas during
solidification.
 Both are characterized by a spherical contour,
but they are decidedly different in size.
 The gas inclusion porosities are usually much
larger than pinhole porosity.

 Many metals dissolve or occlude gases while they are
molten. For example, both copper and silver dissolve
oxygen in large amounts in the liquid state.
 Molten platinum and palladium have a strong affinity for
hydrogen as well as oxygen. On solidification, the absorbed
gases are expelled and pinhole porosity results
 The larger voids may also result from the same cause, but it
is more logical to assume that such voids are caused by gas
that is mechanically trapped by the molten metal in the
mold or by gas that is incorporated during the casting
procedure

 Subsurface porosity occurs on occasion. At
other times, it may be particularly evident.
 The reasons for such voids have not been
completely established.

 They may be caused by the simultaneous
nucleation of solid grains and gas bubbles at
the first moment that the alloy freezes at the
mold walls.
 As has been explained, this type of porosity
can be diminished by controlling the rate at
which the molten metal enters the mold.

 Entrapped –air porosity on
the inner surface of the
casting, sometimes referred to
as back-pressure porosity,
can produce large concave
depressions.
 This is caused by the
inability of the air in the mold
to escape through the pores in
the investment or by the
pressure gradient that
displaces the air pocket
toward the end of the
investment via the molten
sprue and button

 Since back pressure porosity occurs more generally in
full crown type castings, insertion of a wax rod into the
core of the investment when investing the pattern will
provide a good means of venting the hot gases quickly
 Use of reservoir

 The dinstance from the top of the pattern to the outside
of the investment is kept to ¼ inch
 Furnace temperatures above 1100ºF help eliminate this
back pressure porosity condition
Introduction to metal-ceramic technology-2nd edition by W.Patric Naylorpage231

 Increasing the number of turns on a centrifugal
machine and increasing the casting pressure

 Performing the casting operation in a vacuum
 Using more metal when casting so that a good size
button is left as an important precaution.
 Hygroscopic low burn out technique produces more of
this porosity than high heat techniques

 The entrapment is frequently found in a
“pocket” at the cavity surface of a crown or
mesio-occlusal-distal casting.
 Occasionally it is found even on the outside
surface of the casting when the casting
temperature or mold temperature is so low that
solidification occurs before the entrapped air
can escaped.

 The incidence of entrapped air can be increased
by the dense modern investments, an increase
in mold density produced by vacuum investing,
and the tendency for the mold to clog with
residual carbon when the low-heat technique is
used.
 Each of these factors tends to slow down the
venting of gases from the mold during casting.

 Proper burnout, an adequate mold and casting
temperature, a sufficiently high casting
pressure, and proper L: P ratio can help to
eliminate this phenomenon.
 It is good practice to make sure that the
thickness of investment between the tip of the
pattern and the end of the ring not be greater
than 6mm.

 Occasionally, only a partially complete casting
or perhaps no casting at all is found.
 The obvious cause is that the molten alloy has
been prevented, in some manner, from
completely filling the mold.
 At least 2 factors that may inhibit the ingress
of the liquefied alloy are insufficient venting of
the mold and high viscosity of the fused metal

• Insufficient venting of the mold
• High viscosity of the fused metal
• Incomplete elimination of wax residues from the mold
• Low W/P ratio less porosity
• Inadequate spruing
• Mold is too cold
• Insufficient alloy is used
• Sprues are blocked
• Insufficient casting force
• Back pressure of gases in the mold
• Metal not completely molten
• Wax pattern thin
Notes on dental materials-6th edition by E C.Combe page203

Incomplete casting resulting from incomplete
wax elimination characterized by rounded
margins and shiny appearance

J.Anusavicepage348

 The first consideration, insufficient venting, is
directly related to the back pressure exerted by
the air in the mold.
 If the air cannot be vented quickly, the molten
alloy does not fill the mold before if solidifies.
 In such a case, the magnitude of the casting
pressure should be suspected.

 If insufficient casting pressure is employed, the
back pressure cannot be overcome.
 Furthermore, the pressure should be applied
for at least 4 seconds.
 The mold is filled and the metal is solidified in
1 second or less, yet it is quite soft during the
early stages point.
 Therefore the pressure should be maintained
for few seconds beyond this point
 These are usually exemplified in rounded
incomplete margins.

 A second common cause for an incomplete casting is
incomplete elimination of wax residues from the mold.
 If too many products of combustion remain in the
mold, the pores in the investment may become filled so
that the air cannot be vented completely.
 If moisture or particles of wax remain, the contact of
the molten alloy with these foreign substances
produces an explosion that may produce sufficient
backpressure to prevent the mold from being filled.
z

 It can be seen as rounded margins with quite
shiny rather than dull appearance. The strong
reducing atmosphere created by carbon
monoxide left by the residual wax causes this
shiny condition of the metal.
 The possible influence of the L: P ratio of the
investment has been discussed. A lower L: P is
associated with less porosity of the investment.
 An increase in casting pressure during casting
solves this problem.
Phillip’s science of dental materials-11th edition by Kenneth J.Anusavice page347-349

 Different alloy composition and temperature
probably exhibit varying viscosities in the
molten state, depending on composition and
temperature, however, both the surface tension
and the viscosity of a molten alloy are
decreased with an increase in temperature.
 An incomplete casting resulting from too great
a viscosity of the casting metal can be
attributed to insufficient heating..

 The temperature of the alloy should be attributed
to insufficient heating.
 The temperature of the alloy should be raised
higher than its liquidus temperature so that its
viscosity and surface tension are lowered and it
does not solidify prematurely as it enters the mold.
 Such premature solidification may account for the
greater susceptibility of the white gold alloys to
porosity because their liquidus temperatures are
higher, thus, they are more difficult to melt with a
gas-air torch flame

 Prevention:
 Proper time and temperature adapted during
burnout.
 Too large size casting is due to excessive mold
expansion and this is prevented by the use of
correct type of investment and correct
temperature.
 Too small casting is due to, too little mold
expansion and it is prevented by heating the
mold sufficiently
Notes on dental materials-6th edition by E C.Combe.page203

 Naylor (1986) described in detail the "Laws of
Casting" as they pertain to spruing, investing and
burnout, and casting. The seventeen laws are as
follows:
 1. Attach the sprue to the thickest cross-sectional
area of the wax pattern.
 2. Orient the margins of the wax pattern to the
right and mark their location. This assures that the
centrifugal, rotational, and gravitational forces on
the molten alloy are used to their proper
advantage.

 3. Place the wax pattern in a cold zone of the
investment mold, and position the reservoir in the
heat center of the ring. This improves the
likelihood that casting porosity will occur in the
reservoir rather than in the restoration.

 4. The reservoir must have enough molten metal
available to fill the shrinkage that occurs within
the restoration.
 5. Do not cast a button if a runner bar, or other
internal reservoir, is used.

 6. Turbulence must be minimized, if not totally
eliminated. Use smooth gradual pathways. Avoid
sharp turns, restrictions, and impingement on flat
surfaces.
 7. Select a casting ring of sufficient diameter and
length to accommodate the pattern or patterns to
be invested. The patterns should be spaced 1/4"
apart with at least 3/8" of investment between the
patterns and the ring liner.

 8. The surface tension of the wax pattern must be
reduced. This enables the casting investment to
wet the patterns more completely.
 9. Weigh all casting investment powder and
measure all investment liquids to assure a precise
and consistent liquid-powder ratio

 10. Eliminate the incorporation of air in the casting
investment during mixing and pouring. Vacuum
mixing is highly recommended.
 11. Allow the casting investment to set completely
before beginning the burnout procedure.
 12. Use a burnout technique that is specific for the
type of patterns used (wax versus plastic) and
suitable for the particular casting alloy selected.

 13. Adequate heat must be available to properly
melt and cast the alloy selected for use.
 14. Use the REDUCING ZONE of the casting
torch to melt the alloy and NOT the oxidizing zone
when torch casting.

 15. Enough force must be provided to cause the
liquid alloy to flow into the heated mold,
regardless of the type of casting machine used.
 16. Cast to your margins. In a centrifugal casting
machine the margins should be oriented downward
and to the right.
 17. Allow the ring to bench cool before quenching.
Introduction to metal-ceramic technology-2nd edition by W.Patric Naylor
page97-103

1. Phillip’s science of dental materials-11th edition by Kenneth
J.Anusavice
2. Contemporary fixed prosthodontics-4th edition by
Rosenstiel.Land.Fujimoto
3. Introduction to metal-ceramic technology-2nd edition by
W.Patric Naylor
4. Restorative dental materials -8th edition by Robert G.Craig
5. The science and art of dental ceramics-volume ii bridge esign
and laboratory procedures in dental ceramics by John
W.McLean
6. Materials in dentistry –priciples and applications by Jack
L.Ferracane
7. Notes on dental materials-6th edition by E C.Combe
8. Applied dental materials-9th edition by John F.McCabe and
Angus W.G.Walls

9.Effect of wax melting range and investment liquid concentration on
the accuracy of a three-quarter crown casting by Michio Ito et al,The
Journal of Prosthetic Dentistry Volume 87, Issue 1, January 2002, Pages
57–61

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