Metal ceramics /certified fixed orthodontic courses by Indian dental academy

METAL CERAMICS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


1.HISTORY.
2. TERMINOLOGY.
3. CHEMISTRY & COMPOSITION.
4. ALLOYS FOR THE METAL CERAMICS.
5.TOOTH PREPARATION FOR THE METAL
CERAMIC RESTORATION.
6. METAL CERAMIC SUB STRUCTURE DESIGN.

7. FUNDAMENTALS OF THE SPRUING,
INVESTING&CASTING.
8. BONDING BETWEEN THE METAL
&POCELAIN.
9. SOLDERING &FINISHING OF THE
METAL SUB STRUCTURE
10. PORCELAIN APPLICATION METHODS

11.FURNACE
12. FIRING PROCEDURES.
13. FINISHING &ADJUSTMENTS


Chinese were the first to introduce porcelain in
1000A.D.
D’Entrecolles is first person to use porcelains in
the dentistry.
Dental porcelains were used first to fabricate the
complete dentures.
The technology for the metal ceramics introduced
in 1950’s
Dechaeteau 1985 was the first person to make a
pair of complete dentures for himself.

Italians in 1808 made porcelain teeth.

Claudius Ash 1985 created an artificial tooth that
could be placed over the complete dentures & fixed
partial dentures.

Land Went 1985 developed low fusing porcelains
& porcelain jacket crown

TERMINOLOGY:METAL CERAMIC RESTORATION:-A fixed
restoration that employs a metal substructure on
which a ceramic veneer is fused.
ALLOY:-A mixture of two or more metals that are
mutually soluble in the molten state, distinguished
as binary,tertnary,quaternary.
NOBLE METAL:-A term applied to metal that are
corrosion and oxidation resistant because of
inherent chemical inertness. (Craig 1989)

There are at least seven noble metals used in
dentistry.Gold,Platinum,Palladium,Iridium,Osmium,
Rhodium,Ruthenium & Silver.
NON NOBLE:-Alloys that composed of metal that are not
noble.
E.g.:-nickel,chromium,cobalt & aluminum.
COPING:-A term used to describe the metal sub structure.
DEGASSING:-A term used to describe the process of
heating a metal structure believed to release entrapped
gases and burn off organic surface impurities.

 OXIDATION:-The

process of heat treating a
metal ceramic alloy to produce an oxide layer
for porcelain bonding.

 OXIDE

LAYER:-The colored film that forms on
a metal ceramic alloy after the metal has been
heated .

 VACCUM

FIRING:-The firing of dental
porcelain in a furnace in which the air or
atmosphere in order to create denser porcelain
restoration.

COMPONENTS OF METAL CERAMIC
RESTORATION
1.METAL SUB STRUCTURE
.
2.THE OXIDE LAYER.
3.THE OPAQUE PORCELAIN LAYER.
4.THE DENTIN PORCELAIN.
5.THE ENAMEL PORCELAIN.
6.THE EXTERNAL GLAZE.

CHEMISTRY OF THE DENTAL
PORCELAIN
 The

chemical components of the porcelain: 1.Feldspar:-feldspar is the primarily responsible
to the glass matrix.
 It occurs in a pure form but is a mix of two
substances.
 Potassium aluminum silicate & sodium
aluminum silicate.
 This is also called as albite.

 Potassium

feldspar:-it adds translucent qualities
to fired restorations.

 When

melted between 2280°c to 2730°c potash
fuses with the kaolin & quartz to become glass

 The

potash form of feldspar increases the
viscosity & controls the pyroplastic flow of the
porcelain.

 Sodium

feldspar:-lowers the fusion temperature
of the porcelain.

QUARTZ:
 This

has high fusion temperature and serves as a
frame work around the other ingredients can flow.

 It

helps to prevent the porcelain build up from
slumping on the metal substructure by stabilizing
the mass at high temperature

 Quartz

also strengthen the porcelains.


ALUMINA
It

is considered as hardest & strongest
oxide.

Its

CTE is similar to the low fusing
porcelains.

It

also strengthens the porcelain.

KAOLIN: This

particular ingredient of the porcelain is

clay.
 This

is formed from the igneous rock
containing alumina.

 It

is not include in the enamel porcelains
because of the opaque character of the kaolin.


BASIC COMPONENTS
The

basic components of a traditional porcelain
kit include 1.opaque porcelain.
2.dentin porcelains
3.enamel porcelains
Modifiers,stains &glazes.

Newest

products has high fusing shoulder
porcelains.

OPAQUE
PORCELAINS:These porcelains made opaque by the addition of
the insoluble oxides like,
Tin.
Titanium.
Zirconium.
Cerium oxides.
Such oxides have high refractive,so they scatter
light.

The opaque layer serves three primary functions:1.It masks the color of the metal substructure.
2.It wets the metal surface &establishes the metal
porcelain bonding.
3.It initiates the development of the selected
shade.

DENTIN PORCELAINS
The dentin porcelains correspond to the dentin of
the natural teeth.

The dentin porcelain is the major component of the
porcelain restoration.

ENAMEL PORCELAIN
Enamel porcelains are more translucent than dentin
porcelains.

The enamel porcelains are usually in the violet to
grayish range &impart a combination of true
translucency & the illusion of the translucency by
virtue of their grayish or some times bluish
appearance.

TRANSLUCENT PORCELAIN
Translucent porcelains are not transparent.they do
not allow the transmission of all lights.
They are applied as a veneer over nearly the entire
surface of the typical porcelain build up.
The translucent enamel imparts the depth & enamel
like translucency without substantially altering the
body shade that is being overlaid

BODY MODIFIERS
These porcelains are more color concentrated &
were designed to aid in the achieving internal color
modifications.
They are used to distinguish the
dentin,enamel&translucent porcelains,because they
have the same basic physical &chemical
properties.
All these powders are basically same
materials,they do differ in the appearance because
of the modifiers.

STAINS & GLAZES
Stain powders contain less silica or alumina &more
sodium &potassium oxides.

They contain high concentration of metallic oxides.

They are created by mixing the metallic oxides
with lower fusion point glasses

Glazes are generally colorless,low fusing
porcelains.

They possess considerable fluidity at high
temperatures.

They fill small surface porosities &
irregularities.when fired helps to recreate the
external glazy appearance of the natural tooth

ALLOYS FOR THE METAL
CERAMICS


 REQUIREMENTS.

(skinners 10th &Naylor's)

 CLASSIFICATION.
 A)BASED

ON COLOR & COMPOSITION.
 B)BASED ON FUNCTION.
 C)AN ALTERNATIVE CLASSIFICATION.
 D)ADA CLASSIFICATION.
 DIFFERENT

CONSTITUENTS &THEIR ROLE

 DIFFERENT

ALLOY SYSTEMS THEIR
ADVANTAGES & DISADVANTAGES

Requirements of the alloys:1.A ceramic alloy must be able to produce surface
oxides for chemical bonding with dental porcelain.
2.A metal ceramic alloy should be formulated so its
coefficient of thermal expansion is slightly greater
than that of the porcelain veneer to maintain the
metal porcelain attachment.Even though oxides
form & and the metal chemically bonds to the
porcelain,fracture of the ceramic veneer may occur
if the metal & the porcelain are not thermally
compatible.

The alloy must have melting range considerably
higher than the fusing range of the dental
porcelain fired on to it.
The alloy must not under go distortion at the the
firing temperatures of the porcelain.
The first four requirements must be balanced with
technicians need for ease of handling.
A casting alloy should be biocompatible.

CLASSIFICATION OF THE DENTAL
CASTING ALLOYS
They are classified based on :1.Alloy classification based on function.
2.Alloy classification based on color
&composition.
3.The ADA classification for cast alloys.
4.An alternative classification system for metal
ceramic alloys.

CLASSIFICATION BASED ON
FUNCTION
One of the oldest & simplest methods used to
categorize casting alloys was devised by the
NATIONAL BUREAU OF STANDARDS IN
1932.
The gold based crown & bridge metals of that time
were organized according to function into only
four categories & described type1,2,3,or4alloys
Alloys in each classification or type were arranged
based on their gold &platinum group composition
as well as the associated VHN.



TYPE –1– SOFT.--- USED FOR THE SMALL
INLAYS




TYPE –2– MEDIUM.--- USED FOR THE
THREE QUARTER CROWN,THIN
BACKINGS.

 TYPE

–3– HARD.--- USED FOR THE FULL
CROWNS, ABUTMENTS & PONTICS.



TYPE –4—EXTRA HARD---DENTURE BASE
BARS,PARTIAL DENTURE FRAME WORK,
LONG SPAN FIXED PARTIAL DENTURE.

ALLOY CALSSIFICATION BASED
ON COLOR &COMPOSITION
A second method of classification is to describe
alloys according to their color & principal element.
1.Yellow golds:- yellow color,greater than 60% of
the gold content.
2.White golds:-white color but more than 50%of
the gold content.
3.Low golds:-usually yellow colored with less than
60%of the gold.

High palladium:-white colored ,with palladium the
major component.also contains small amount of
gold &copper,cobalt.
Silver- palladium:-white colored predominantly
silver with substantial amounts of the palladium to
provide nobility &to help control tarnish.
Palladium- silver :-white colored with palladium
the major component ,plus substantial component
of silver.

ADA CLASSIFICATION
In 1984 ADA prepared a new classification for
cast alloys.
The system was devised for the identification in
dental procedure codes,where the intrinsic value
of the metals in the castings provided to patient
would influence the amount of reimbursement
from insurance carriers.
This system of the classification was not intended
to indicate usage or performance levels.

ADA CLASSIFICATION
 HIGH

NOBLE:CONTAINS 40% GOLD,60%
OF THE NOBLE METALS.(Au-Ir-Os-Pt-Ru)

 NOBLE

METAL:CONTAINS 25% OF THE
NOBLE METAL ELEMENTS.

 PREDOMINANTLY

BASE
METAL:CONTAINS LESS THAN 25% OF
THE NOBLE METAL ELEMENTS.

AN ALTERNATIVE CLASSIFICATON
SYSTEM
With this method the alloys are classified based on
composition & level of the constituent of the
major content.
The alloys are first divided into two groups,
1.Noble metal
2.Non noble metals.
Each system further divided into constituent
groups.

THE ROLE OF DIFFERENT
CONSTITUENT ELEMENTS
 Aluminum:-lowers

the melting range of the

nickel based alloys.
 It acts as a hardening agent.
 It influences the oxide layer formation.
 With cobalt chromium alloys used for the metal
ceramic restoration, aluminum is one of the
element that is etched from the alloy surface to
create micro mechanical retention for resin
bonded retainers.
 Melting range:660 degree centigrade; CTEwww.indiandentalacademy.com
o.236

IRON: Iron

is added to some gold based porcelain for
hardening & oxide production.
 Melting range:1527degree centigrade; CTE0.123
 NICKEL:-it

is base for the porcelain alloys.
 Its CTE similar to the gold
 It provides resistance to corrosion.
 Melting range:1453degrees; CTE-0.133.

PALLADIUM: Palladium

added to increase the corrosion,
strength,hardness,tarnish resistance of the gold
based alloys.
 It increases the melting temperature.
 Improves the sag resistance.
 M.T.-1552; CTE-0.0188
 PLATINUM:-It increases the strength,hardness,of
the gold based alloys.
 It improves the corrosion,tarnish &sag resistance.
 It improves the density of the gold & non gold based
alloys.
 M.T.-1769; CTE-0.089

SILICON: Silicon

primarily as an oxide scavenger.
 It also act as a hardening agent.
 M.T.-1410; CTE-0.073.
 SILVER: It

lowers the melting range,improves the
fluidity,&helps to control the CTE.
 It has high affinity for the oxygen, which can lead to
the porosity&gassing of the casting.
 It is not universally regarded as noble in the oral
cavity.
 M.T.-960.8; CTE– 0.197.

TIN: Tin

is the hardening agent that acts as a
lower melting range of the alloy.

 It

also assists in oxide layer production for
the porcelain bonding in gold based &
palladium based alloys.

 Tin

is the one of the key trace elements for
the oxidation of the palladium silver alloys.
 M.T.-231.9;CTE-0.23

BERYLLIUM:Lowers the melting temperature of the nickel
based alloys.
It improves the castability,improves polish ability.
Helps to control the oxide layer formation.
BORON:Boron is a de oxidizer.
It reduces the surface tension there by increases
the castability.
Reduce the ductility & increase the hardness.

CHROMIUM: Chromium

is a solid solution hardening agent that
contributes to corrosion resistance.
 M.T.-1875; CTE– 0.062.
 COBALT:-used

as alternative to the nickel based

alloys.
 Cobalt included in the high palladium alloys to
increase the CTE.
 It also acts a strengthener.
 M.T.-1495; CTE– 0.138.

COPPER: The

properties of the copper is same like aluminum.
 M.T.—1083; CTE– 0.165.
 GALLIUM: Gallium

is added to silver free alloys to compensate the
decreased CTE.

 GOLD:-it

provides the high levels of the tarnish
&corrosion.
 It increases melting range.
 It improves the wettability,burnishability &increases the
density.
 M.T.—1063; CTE– 0.142.

DIFFERENT ALLOY SYSTEMS
THEIR ADVANTAGES
&DISADVANTAGES


HIGH NOBLE ALLOY
SYSTEMS


Au-Pt-Pd








Advantages
Excellent
castability&porcelain
bonding
Easy to adjust &finish
Tarnish&corrosion
resistance
Biocompatible
Not technique sensitive

 disadvantages
 Poor

sag resistance
 Low hardness
 Low density
 High cost


COMPOSITION:Gold:75%-88%
Platinum:-8%
Palladium:-11%
Silver:-5%


Au-Pd-Ag
Composition:Gold:39%-53%
Palladium:25%-35%
Silver:12%-22%


 Advantages

 Disadvantages

 Less

 Silver

expensive
 Improved rigidity&sag
resistance
 High nobility level

content creates
potential for porcelain
discoloration.
 High cost
 High CTE
 Tarnish &corrosion
resistance


GOLD-PALLADIUM ALLOY
SYSTEMS
Gold:44%-55%
Palladium:35%-45%
Gallium:5%
Indium & tin:8%-12%

 Disadvantages

Advantages
 Excellent

castability
 Good bond strength
 Corrosion & tarnish
resistance
 Improved hardness &
strength
 Low density.

 Not

thermally
compatible with
expansion
 High cost


NOBLE ALLOY SYSTEMS.


PALLADIUM – SILVER ALLOY SYSTEM
Composition:
Palladium:55%-60%
Silver:28%-30%
Indium & tin are used.
The melting range of the this alloy system is
1021degrees-1099degrees centigrade.

 Advantages

 Disadvantages

 Low

 Discoloration

cost & density
 Good castability &
porcelain bonding
 Low hardness
 Excellent sag ,tarnish
& corrosion resistance
 Suitable for long span
fpd’s

 Pd-Ag

prone to absorb

gases
 High CTE
 May form internal
oxides.
 Should not be cast in
carbon crucible


NICKEL-CHROMIUM-BERYLLIUM
ALLOYS
COMPOSITION:
Nickel:62%-82%
Chromium:11-20%
Beryllium:2%

 Advantages



 Low



cost
 Low density
 High resistance
 It can produce thin
castings
 Poor thermal
conductor
 Can be etched.







Disadvantages
Cannot be used with Ni
sensitive patients
Beryllium may be toxic to
the technician & patients
Bond failure may occur
High hardness
Difficult to solder
Difficult to cut through
cemented castings


NICKEL-CHROMIUM ALLOYS
Composition:
Nickel :62%-77%
Chromium :-11%-22%


•Advantages
 Do

not contain
beryllium
 Low cost
 Low density means
more castings per
ounce.

 Disadvantages
 Cannot

be use with
nickel sensitive
patients
 Produce more oxides
than Ni-Cr-Be alloys.
 May not cast as well
as Ni-Cr-Be alloys


COBALT – CHROMIUM ALLOYS
Composition:
Cobalt:53%-68%
Chromium:25%-34%
Trace elements of molybdenum ruthenium are
added.

 Advantages



 Do



not contain nickel
 Do not contain
beryllium
 Poor thermal
conductors
 Low density
 Low cost





Disadvantages
More difficult to process
than Ni base alloys
High hardness
Oxide more than both Ni
based alloys
No information on long
term clinical studies.


 THE

MELTING TEMPARATURE OF THE
HIGH NOBLE ALLOYS IS 1271DEGREE
CENTIGRADE TO 1304 DEGREE
CENTIGRADE.

 FOR

NOBLE METALS 1232 DEGREE
CENTIGRADE TO 1304 DEGREE
CENTIGRADE.


TOOTH PREPARATION FOR
THE METAL CERAMIC
RESTORATION


 Depth

orientation
grooves flat end
tapered diamond.


 Make

at least two
vertical cuts in the
incisal portion of the
facial surface.


 Next

align the flat end
tapered diamond with
the gingival portion of
the facial surface.


 Sink

the side of the
diamond into the
mesiodistal center of
the facial
surface,maintain the
instrument alignment
parallel to the gingival
surface of the facial
segment.


 Make

two incisal
orientation grooves
that are 2mm deep.The
diamond should be
parallel to the incisal
edge faciolingally.


 Incisal

reduction is
done with the flat end
tapered diamond.


 Facial

reduction;
incisal half,flat end
tapered diamond.


 If

there sound tooth
structure inter
proximally, wing
preparation is done.


 Begin

the lingual
reduction with the
small round diamond
with diameter of
1.4mm. Sink this
instrument into the
lingual tooth structure
up to 0.7mm.


 Lingual

axial
reduction torpedo
diamond and carbide
finishing bur.


 Lingual

reduction is
done with the small
wheel diamond.


 Smooth

the entire
facial surface with
no.171 bur .Round
over the any sharp
angles on the incisal
angle or along the
edges of the incisal
notches with no.171
bur.


 After

the tooth preparation gingiva has to be
retracted,impression is made with materials
such as rubber base,which is the best material
available for the impression procedures.

 After

this the working cast is obtained and the
die pins are placed .

 Apply

die hardener,then die spacer and die
separator.
 Now the die ready for the wax pattern
fabrication.

METAL SUB STRUCTURE
DESIGN.


 FUNCTIONS.
 DESIGN.
 WAX

PATTERN FABRICATION.


ESSENTIALS OF METAL CERAMIC
SUB SRUCTURE
 FUCTIONS

OF THE METAL CERAMIC
SUBSTRUCTURE:
 1.Primary functions: The casting provides fit of the restoration to the
prepared tooth.
 The metal forms oxides that bond chemically to
the dental porcelain.
 The coping serves as a rigid foundation to which
the brittle porcelain can be attached for increased
strength & support.

 The

sub structure restores the tooth's proper
emergence profile.


 Metal

SECONDARY
FUNCTIONS:-

occlusal & lingual articulating surfaces
generally less destructive to the enamel of the
opposing natural tooth.
 Fabrication of the restoration with minimal
occlusal clearance has more potential for the
success with metal substructure than all ceramic
alloys.
 Occlusal surfaces can be easily adjusted &
 repolished intraorally.
 The metal axial walls can support the removable
partial denture.

SUB STRUCTURE DESIGN FOR
THE SINGLE UNIT RESTORATIONS.
 Procedure

for the maxillary anterior sub

structure:
 When restoring anterior teeth,more emphasis is
placed on esthetics than any other single
requirement.
 There important factors to be considered for the
restoration of the anterior teeth:
 1.Location of the occlusal contacts.
 2.Amount of the clearance.

LOCATION OF OCCLUSAL
CONTACTS:
 The

mandibular anterior teeth contact the lingual
surfaces of the lingual surfaces of the maxillary
anterior teeth in the centric occlusion.
 The location of the those contact areas should be
identified with articulating film.
 When these occlusal contacts appear in the
incisal one half of the restoration,then the
porcelain veneer may be extended over incisal
edge for the occlusion in the porcelain.

 According

to the concept of the mutually
protected occlusion in centric occlusion the
anterior teeth are out of the contact by
approximately 25 microns or two thickness of
shimstock.

 The

design of the lingual aspect of the metal
ceramic depend on the clinician & patient.


 When

the anterior
teeth contact in the
incisal region,it is
often necessary to
consider a design with
lingual surface in
porcelain to avoid
functioning on or over
the porcelain metal
junction.


 Do

not design the sub
structure so contact
occurs at the porcelain
metal junction.


 When

the anterior
teeth occlude in the
gingival half of the
maxillary teeth or
when the lingual tooth
reduction is less than
1mm it is best to
design the sub
structure with
occlusion in the metal.


AMOUNT OF THE CLEARENCE
 One

of the advantage of the restoring the lingual
occlusion in the metal is less tooth reduction is
required than for the full ceramic restoration.

 It

is depend on the clinician & dentist to give
ceramic or the metal.


WAX PATTERN FABRICATION .


 THERE

ARE THREE METHODS OF
WAX PATTERN FABRICATION:

 1.CUT

BACK METHOD.

 2.PLASTIC

SHELL TECHNIQUE.

 3.DIPPING

MEHTOD.


STEP BY STEP PROCEDURE


CUT BACK PROCEDURE


 Scribe

a line across the
labial surface between
0.5-1mm above the
marginal finish line.Also
scribe a line across the
labial surface 1.5mm
from the incisal edge


 After

completing the
full contour wax up
determine the location
of the patient’s centric
& eccentric occlusal
contacts, then scribe a
line for the porcelain
metal junction.


 Remove

the die & wax
pattern form the
master cast.connect
the lines drawn for the
porcelain metal
junction.


 Reduce

the incisal
edge by at least 1.5mm
to provide sufficient
space to re-create the
appearance of natural
translucency yet avoid
un supported
porcelain.


 The

wax pattern is
now ready to be cut
back.The objective of
the cut back procedure
is to remove a uniform
thickness of
approximately 1mm
wax from all proximal
surfaces of the
substructure to receive
porcelain.


use discoid carver,or
similar instrument to
refine the porcelain
metal junction on the
labial&lingual
surfaces.


 Evaluate

the cut back
in the master cast for
proper extension &
adequate clearance by
viewing it from all
anglelabial,lingual&incisal.


 Measure

the thickness
of the wax pattern
with the rounded tips
of the Iwanson wax
pattern.


 Smooth

any sharp line
angles to produce
rounded contours.A
cotton swab or Q-tip
moistened with
debubblizer and
warmed by a flame
can be used for this
procedure.


 Finished


wax pattern.

The

recommended thickness of the
wax pattern is0.3mm-0.5mm.

It

may vary the type of the alloy is
used.


PROCEDURE FOR THE
POSTERIORTEETH(CERAMIC
FACING)


 WAX

THE
RESTORATION TO
FULL CONTOUR &
ASSES ITS
CONTOUR FROM
OCCLUSAL &
FACIAL VIEWS.


 SCRIBE

A LINE ON
ON THE INNER
INCLINE OF THE
BUCCAL CUSP
FROM DISTAL TO
MESIAL THAT IS
2MM FORM ANY
AREA OF THE
OCCLUSAL
CONTACT.


 Scribe

the gingival &
inter proximal lines for
the proposed cut
back.remove the die &
wax pattern from the
master cast and connect
the occlusal inter
proximal scribe line for
the cut back.


 Complete

the cut back
then view the
completed wax pattern
from the occlusal and
facial views.


 Carefully

examine the
cut back to make
certain enough wax
has been removed to
ensure that ceramic
veneer will be uniform
in all areas


If the interproximal contact area is to
be restored in porcelain rather than
metal extend the cut back of the
porcelain metal junction further
lingually.




The

disadvantage of cut technique

are
 Thinning the wax in the areas to be
veneered with porcelain can create
problems.
The wax become fragile & breaks
easily.
Forces generating during th4e cut back
procedure may distort the adaptation
of the pattern.

WAX PATTERN
FABRICATION FOR THE
FIXED PARTIAL DENTURES.


 First

full contour of
the wax pattern is
made.carefully inspect
the inspect the wax
pattern for the proper
contours,& inter
proximal areas.


 Mark

the occlusion
scribe line on the
lingual surface of the
wax up .


 Place

a scribe line on
the facial surface to
indicate the extent of
the incisal cut back.


 Place

depth cuts in
each unit & perform
the facial cut.


 Refine

the lingual
surfaces with a carving
instrument


 After

the cut back,view
the sub structure form
the facial,incisal, and
lingual views.There
should be a 1mm gap
between the pontics area
and the soft tissue which
will be covered by
ceramic later


PALSTIC SHELL
TECHNIQUE


Armamentarium
1.

4.0 cm spacer disks
2. 4.0 cm coping disks
3. Wire holding frame
4. Iris scissors


 Spacer

disk is placed
over the coping disk.


 Place

the coping
material and the spacer
disk onto a wire
holding frame


 Heat

the disk slowly
and evenly by holding
them, approximately
10 cms above the
flame.


 Place

the heated
coping disk and the
spacer over the mouth
of the moulding
apparatus, a plastic jar
filled with silicone
putty.


 Press

the trimmed die
forcefully against the
softened spacer and
the coping disk until
the finished line of the
preparation
completely submerges.




 This

closely adapts the two disks over the tooth
preparation.continue to exert the pressure against
the disks with die until the sheet becomes
cloudy.This will take approximately 10seconds.


• Heating the coping disk
stretches it to the desired
thickness of 0.3mm.


 Three

cuts are made in
the unadapted skirt of
the disks with pair of
iris scissors.


 The

disks are pulled of
the tooth preparation
die.


 The

spacer disks are
peeled out of the
coping shell.


 Excess

border material
is cut off 1.0mm above
the preparation line.


 The

trimmed shell is
placed over the.the
edges of the copings
are about 1.0mm short
of the finish line on
the die.


 The

1.0mm gap
between the shell and
the finish line is filled
with the wax.


 The

benefits of the using plastic shell
copings becomes apparent during the cut
back stage.
 The plastic coping provides rigidity & resist
distortion.


FUNDAMENTALS OF
SPRUING,INVESTING&
CASTING




SPRUING

 TECHNIQUES
 A)Methods

(1)direct spruing.

(2)indirect spruing.
 Sprue former placement.
 Sprue former gauge.
 Sprue former length.
 Orientation of wax pattern.
 Location of the reservoir.

 Sprue

former composition:wax Vs plastic.

 Prefabricated

Sprue former.


TECHNIQUES
A

spruing system is intended to create a
channel or series of channels in the set
investment though which molten alloy flows to
reach the pattern areas.

 There

is no single method of spruing that is
universally accepted.

 The

manufacturer’s recommendations has to be
followed for their alloy productions.

METHODS

 Wax

patterns can be sprued in one of two
different methods.each method has it’s
advantages & disadvantages.


DIRECT SPRUING
With the direct spruing the flow of the molten
metal is straight from the casting crucible to
pattern area in the ring.
 This method requires less time


PROCEDURE:
 A straight Sprue former is luted to the thickest
part of the wax pattern.
 One end is to the wax pattern & other end is
secured to the crucible former.


 The

sprue former can be modified by placing a
ball or round reservoir between the pattern and
the button.
 Even with the ball reservoir, the spruing method
is still direct.
 Direct spruing is used to most frequently for the
single units.
 The

draw back of this method is the potential
suck back porosity at the junction of the
restoration & the sprue.

INDIRECT TECHNIQUE
 With

the indirect spruing,the molten metal does not flow
directly form the casting crucible into the pattern area.

 The

casting alloy takes a circuitous root before it
reaches the pattern areas.

 With

this method of spruing,the connector bar is 6gauge or 8-gauge round wax to which the wax pattern
sprue formers are attached on one side with two larger
ingot sprue formers on the other side.

 Here

the connector acts as a reservoir.

 The

composition of the alloy will influence the
manner in which it fills the mold.

 For

Example: Palladium-Silver alloy fill the mold
unidirectionally.
 Type III gold fills the mold in a random fashion.

 The

value of the indirect spruing for single
crowns&bridges.

 Although

direct spruing can produce acceptable
results, in many instances indirect spruing offers
advantages such as greater predictability &
reliability in the casting plus enhanced control of
solidification shrinkage.

SPRUE FORMER PLACEMENT
 The

sprue former attached to the wax up should
be luted to the thickest part of the pattern to
allow the molten alloy to flow from regions
large volume to lesser volume.

 Placing

the sprue former else where may result
in the improper casting.

 The

most practical sprue location is the mid
incisal area.

SPRUE FORMER GAUGE
A

pattern sprue former of the sufficient size
should be selected to supply the volume of alloy
required of the patterns to the cast.

 The

round wax sprue former are conveniently
identified with gauge No.10,8,6.

 The

larger the No. smaller the size of the sprue
formers diameter.

SPRUE FORMER LENGTH.
 With

the direct spruing method, the sprue former
should be long enough to position the wax
patterns out side the heat center of the ring.
 The length of the sprue former should be vary
with the type & size of the crucible former & the
casting ring used.
 5mm of the pattern sprue former is often
sufficient to connect the wax pattern & the
connector bar.

ORIENTATION OF THE WAX
PATTERN.
 Attach

the sprue to the thickest portion of the
wax pattern.
 Do not cerate sharp 90 degrees angles between
the sprue former and the wax pattern or position
the pattern so the alloy would have to flow back
towards the ring entrance.
 It is essential to take advantage if the
gravitational force and the centrifugal forces by
positioning the wax pattern such that the alloy is
cast towards the thinner sections.

 Position

the margins trailing edge of the casting

ring.


LOCATION OF THE RESERVOIR
 The

reservoir of the spruing system,should be
placed in the heat center of the ring.
 This permits the reservoir to remain molten
longer & enables it to furnish alloys to the
patterns until they complete the solidification
process.
 This should have the largest mass of any part of
the sprue system.


SPRUE FORMER COMPOSITION
WAX Vs PLASTIC


Casting wax melts out by leaving 0.1%
residue.



PRE FABRICATED SPRUE
FORMERS.
 READY SPRUES:
 The design of the prefabricated indirect

sprue formers permits rapid placement
of the pattern in the accompanying
sprue former & consistent location of
the reservoir bar in the oval casting
ring.

TRI WAX SYSTEM:
 The

pre fabricated TRI WAX system from
Williams dental company available as direct
and indirect sprues.

 Three

sizes are available 6,8,10 gauge number.

 The

large indirect patterns are useful for the
large pontics and thick molar wax patterns.

CASTING
 TORCH

SELECTION.
 CHOICE OF THE FUELS.
 CRUCIBLES.
 LAWS

OF CASTINGS.


TORCH SELECTION.
 There

are two types of the torches when
selecting for the casting equipment.
 1.Multi orifice torch.
 2.Single orifice torch.
 The tip mostly used for the metal ceramics is
multi orifice.
 Its main advantage is the distribution of heat
over a wide area for more uniform heating of a
alloy.
 The single unit orifice concentrate more heat in
one area.

CHOICE OF FUELS
 ACETYLENE:
 This

is a colorless gas with distinctive garlic
odor.

 It

will burn in air & can generate a flame
approaching 3000 degrees.

 Acetylene

is usually contaminated with the
carbon and other elements.so it should not be
used for the metal ceramic alloys.

 NATURAL

GAS:

 This

fuel is a by product of the natural
decomposition of the organic matter.

 When

mixed with air the natural gas flame
approaches 2,200degrees.

 Replacing

the air with oxygen enables natural
gas to attain temperatures required to melt high
fusing noble & base metal alloys.



Inadequate pressure in the gas lines,fluctuations
in pressure levels,water contamination,
variations in the compositions among the
companies are some of the problems
encountered by the natural gas users.


 PROPANE:

 The

problems with the natural gases are avoided
when using bottle propane gas.

 The

constant regulated mix of
pure,uncontaminated propane & oxygen provides
a clean,consistent burn leading to a more ideal
melt.

CASTING CRUCIBLES
 Either

zircon-alumina or quartz casting crucible
are recommended for noble & base metal alloys.

 Carbon

crucible well suits for the gold alloys.

 But

there is chance of the carbon contamination
leads to lessen the strength of the alloys.


 After

selecting the appropriate type of the casting
crucible,pre heat it in the oven to avoid spalling
& prolongs the life of the crucible.

 Never

cast different alloys in the same crucible
as this causes contamination.

 Carve

the alloy name on the crucible for
identification.

 Do

not use the asbestos liner in the crucible or
flux in the molten metal.

THE LAWS OF CASTING
 INGERS0LL

& WANDLING formulated an
expanded set of 17 separate recommendations for
spruing, investing, burnout, melting & casting.
Collectively, these guide lines are referred to
LAWS OF CASTING.


THE FIRST LAW OF CASTING
 Attach

the pattern sprue former to the thickest
part of the wax pattern.
 As the molten alloy moves from the reservoir to
the pattern margins it should flow from greater
volume to lesser volume areas.
 Lute the pattern sprue former to the most
practical portion wax pattern.
 Molten metal flowing form a thin area to a
thicker region may solidify before the mold is
completely filled.

 The

penalty for not obeying this law are cold
shuts, short margins, & incomplete castings


SECOND LAW OF CASTING.
 Orient

wax patterns so all the restorations margin
will face the trailing edge when the ring is
positioned in casting machine.

 To

identify the orientation add a wax dot to the
crucible former.This helps as guide to place the
ring in the crucible.

 The

penalties for not obeying this laws are cold
shuts, & short margins.

THIRD LAW OF CASTING
 Position

the wax pattern in the cold zone of the
investment mold & the reservoir in the heat
center of the casting.
 The coolest part of the mold are at the end of ring
& along the ring periphery.
 The hottest portion of the casting ring is located
near the center of the ring.
 Limit the amount of the investment covering the
pattern to no more than ¼ in.
 The penalty for not obeying this law shrinkage,
porosity in the restoration.

FOURTH LAW OF CASTING
A

reservoir must have sufficient molten metal to
accommodate the shrinkage that occurs with in
the restoration.
 Alloy that fills the restoration solidify first.as that
solidifies,it shrinks and create a vacuum.For
completing casting , the vacuum must be able to
draw additional metal form an adjacent source –
the reservoir.
 The penalties for not obeying this law are
shrinkage porosity& suck back porosity.

FIFTH LAW OF CASTING
 Do

not cast a button if a connector bar or other
internal reservoir,is used.
 With indirect spruing, largest mass of the metal
should be the reservoir.A button is counter
productive because it can draw available molten
alloy from the bar.
 Shift the heat center & reduce the feed of the
metal to the restorations.
 Like wise the wax patterns should not be larger
than connector bar.

 The

penalties not obeying this law are
shrinkage porosity, distortion, & suck back
porosity.


SIXTH LAW OF CASTING
 Turbulence

must be minimized if not totally

eliminated.
 Pathways for the flow of the metal should be
smooth, gradual & with out impediments.
 Eliminate sharp turns retractions,points,or
impingements.
 That might create turbulence & occlude air in the
casting.
 The penalties not obeying this law are
voids,surface pitting,mold wash.

SEVENTH LAW OF CASTING
 Select

a casting ring of a sufficient length &
diameter to accommodate the patterns to be
invested.
 The casting ring should permit the patterns to be
¼ in.apart & 1/4in from the top of the investment
with minimum 3/8in of the investment between
them & the ring liner.
 Less investment-alloy break through the
investment.
 Too much investment-impairs the escape of the
gases.

 Mold

fracture casting fails & shrinkage porosity.


EIGHTTH LAW OF CASTING
 Increase

the wettability of the wax patterns.
 A wetting agent should be brushed or sprayed
on the patterns and dry before investment.
 A clean wax surface better enables the casting
investment to wet the patterns more completely.
 Too much of the wetting agent-weaken the
investment & produce bubbles.
 The penalties for not obeying this law are
:bubbles

NINTH LAW OF CASTING
 Weigh

the bulk of the investment & measure the
investment liquid for a precise powder:liquid
ratio.
 The correct proportions of powder to liquid and
any dilution of the liquid with distilled water
should be established for each alloy.
 Thick mix of the investment-more expansionloose fittings.
 Thin mix of the investment-less expansion-tight
fittings.

TENTH LAW OF CASTING

 Eliminate

the incorporation of air in the casting
investment and remove the ammonia gas by
product of phosphate bonded investment by
mixing under vacuum.


11th LAW OF CASTING
 Allow

the casting investment to set completely
before initiating the burnout procedure.

 The

penalties for not obeying this law are mold
cracking, blow out.


12th LAW OF CASTING.
 Use

a wax elimination (burnout) procedure that
is specific for the type of pattern involved &
recommended for the particular type of casting
alloy selected.
 Plastic sprues has to be heated slowly so they can
soften gradually & not exert pressure on the
mold.
 If burnout is incomplete,the spruing system
channels may be blocked by plastic or wax
residue.

 The

penalties for not obeying this law colds
shuts, short margins, cold welds, mold
cracks.


13th LAW OF CASTING
 Adequate

heat must be available to properly
melt and cast the alloy.
 Prolonged heating-by improperly adjusted torchprevent the alloy from attaining the fluidity.
 Too much of heat or too high temperature can
off minor alloying elements.
 The penalties for not obeying this law are cold
shuts, short margins, cold welds, rough castings,
investment break down.

14th LAW OF CASTING
 When

torch casting, use the reducing zone of the
flame to melt the alloy & not the oxidizing zone.
 Improperly adjusted torch-adds carbon.
 Reducing zone- minimize the gas absorption.
 Penalties:gas

porosity,change in alloy’s CTE


15th LAW OF CASTING
 Provide

enough force to cause the liquid alloy to
flow in to the heated mold.
 Adjust the casting machine to the requirements of
each alloy.
 Low density metal generally needs 4 winds of a
centrifugal casting arm.
 Penalties:cold

shuts, short margins, cold welds,

mold fracture.

16th LAW OF CASTING
 Cast

towards the margins of the wax patterns.
 Place the heated in the casting cradle using the
orientation dot.So the pattern margin face the
trailing edge.
 In the centrifugal casting machine the metal will
flow downwards and to the right,taking
advantage of centrifugal, rotational, gravitational
forces on the molten alloy.
 Penalties: cold shuts, short margins, incomplete
castings.

17th LAW OF CASTINGS
 DO

NOT QUENCH THE RING
IMMEDIATELY AFTER CASTING.

 UNEVEN

COOLING-APPLY TENSILE
FORCES TO THE CASTING.

 AFTER

CASTING THE ALLOY MAY NOT
HAVE THE SUFFICIENT STRENGTH TO
RESIST THESE FORCES & RESTORATION
COULD TEAR.

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