CROWN-2019 (Fifth Impact)
CROWN-2019 (Fifth Impact)
CROWN-2019 (Fifth Impact)
Definition of terms:
1
Introduction (crown and bridge classification)
- Crown and
Bridges
2
Introduction (crown and bridge classification)
Notes:
§ Intra radicular prosthesis: in endodontically treated tooth
formed of:
1) Post
2) Core
3) Crown
Types of posts:
1) Attached one piece (post crown)
2) Dethatched 2 pieces (custom made post)
"post + core / + crown"
3) Dethatched3 pieces (readymade post)
3
Introduction (crown and bridge classification)
Crown:
artificial replacement of an existing tooth structure
Indications:
§ Heavily fracture tooth
§ Heavily discolored tooth
§ Badly decayed tooth
§ Heavy attrition of teeth
Classification:
according to coverage:
4
Introduction (crown and bridge classification)
3) Combination:
§ Veneered metal crown: it's a full metallic crown with
only one or two surfaces covered with porcelain.
"porcelain fused to metal"
§ Full veneered metal crown: it's a full metallic crown
with all surfaces covered with porcelain "metal
ceramic crown"
5
Introduction (crown and bridge classification)
6
Introduction (crown and bridge classification)
7
Introduction (crown and bridge classification)
Notes:
Types of abutments:
1) Primary abutment: the tooth next to the missing tooth
2) Secondary abutment: in case the primary abutment is weak
3) Remote abutment: the abutment is far from the missing
tooth
4) Pier abutment: missing teeth on both sides "mesial and
distal" of the abutment
Classification:
→ According to material
1) Metallic
2) Non metallic
3) Combination
8
Introduction (crown and bridge classification)
→ According to retention:
àRemovable bridge
9
Introduction (crown and bridge classification)
It's the bridge in which the pontic is fixed and takes its support
from one or double retainers at one end only while the other end
is unsupported and free.
It's the bridge that gets all of its retention from cement
"retainers are palatal or proximal"
2) Compound bridge:
It's a combination type bridge composed of two or more of
simple bridges.
10
Introduction (crown and bridge classification)
→ According to site
11
Instruments
Introduction:
- needs.
- skills.
- personal preferences.
1
Instruments
cutting instruments:
- definition:
2
Instruments
The handle:
- it’s the part grasped in the operator’s hand.
- It’s commonly eight sided and serrated to facilitate control
The shank:
- It connects the handle to the working end
- It’s smooth, rounded and tapered
- It may have one or more bends to avoid twisting of the instrument
in use, when force is applied, to facilitate access for the cutting
edge.
3
Instruments
4
Instruments
NB.
All angle hand pieces have had an air-water spray to provide cooling,
cleansing and improved visibility.
- Ineffective.
- Time consuming.
- Requires a heavy force application, which results in heat production
at the operating site.
- Vibrations causing patient discomfort.
- Burs do not last long and they tend to roll out of the tooth.
5
Instruments
- Cleaning teeth.
- Occasional caries
- Excavation
- Finishing and polishing procedures.
6
Instruments
Common design:
1. Shank
2. Neck
3. Head
Shank:
7
Instruments
Uses:
Neck:
It’s the intermediate portion that connects the head to the shank.
Head:
It’s the working part of the instrument, the cutting edges that
perform shaping of tooth structure.
8
Instruments
Dental burs:
9
Instruments
Abrasive instruments:
- They have had great clinical importance because of their long life
and high effectiveness in cutting enamel and dentin.
- They consist of three parts:
1. Metal blank
2. Powdered diamond abrasive (covering the metal blank)
3. Metallic bonding material (holds the diamond powder onto the
blank)
- Classification: according to
head shapes and sizes:
more than 200 shapes and sizes are currently marked, so they are
selected from a catalogue
10
Instruments
diamond particles:
1. Size
2. Spacing
3. Uniformity, of the diamond particles.
B. Rubber stones:
- They have flexible heads.
- Used for finishing and polishing procedures
- Formed by molding rubber with abrasive particles as carborundum.
11
Instruments
C. Un-mounted instruments:
- They are formed of:
1. Mandrel (shank)
2. Screw (attach the mandrel to the interchangeable working parts)
3. Interchangeable working parts
- This design permits the instrument to be changed easily and
discarded economically
- Example of un-mounted instruments:
1. Un-mounted wheel stones
2. Un-mounted discs:
->They are coated by a thin layer of abrasive material.
->The common discs have diameters of 3/8, ½, 5/8 and ¾ inch.
->The most commonly used types are:
1) sand paper discs for producing smooth surface of preparation
2) carborundum discs: black in color, termed separating discs
NB.
The mounted types of instruments are those in which the working part
is attached to the shank.
12
Principles of tooth preparation
I. Biological principles:
Procedures involving living tissues must be carefully
executed to avoid unnecessary damage.
The adjacent teeth, soft tissues & the pulp of the
tooth being prepared are easily damaged n tooth
preparation.
If poor preparation leads to inadequate marginal fit
or deficient crown contour, plaque control around fixed
restorations will become more difficult which will impede
the long term maintenance of dental health.
1
Principles of tooth preparation
2
Principles of tooth preparation
3
Principles of tooth preparation
2. Chemicals:
- The chemical action of certain dental
materials (base, restorative resins, solvents &
luting agents) can cause pulpal damage
particularly when they are applied to freshly
cut dentin.
- Cavity varnish or dentin bonding agents will form an
effective barrier, but their effect on the retention of
a cemented restoration is controversial.
- Some chemical agents used for cleaning &
degreasing tooth preparations have shown to be
pulpal irritant so their use is contraindicated,
particularly because they don’t improve the
retention of cemented restorations.
4
Principles of tooth preparation
3. Bacterial agents:
- Pulpal damage under restoration has been
attributed bacteria which
Were left behind
Gained access due to micro leakage
However, many dental materials, including
zing phosphate cement have an antibacterial
effect
- All carious dentin should be removed before
placing a restoration. "endotreatment is also
applied if caries are very close to pulp."
- Indirect pulp cap is not recommended.
5
Principles of tooth preparation
5) Occlusion:
TMJ and muscle of mastication health must be considered
proper occlusion is achieved by Proper contour
Good occlusal reduction
Considerations affecting future dental health:
6
Principles of tooth preparation
7
Principles of tooth preparation
8
Principles of tooth preparation
2. Margin geometry:
Different shapes of margins have been described &
advocated for evaluation, the following guidelines for
margin design should be considered
Ease of preparation without over extension or
unsupported enamel
Ease of identification in the impression or on the
die
A distinct boundary to which the wax pattern can
be finished
Sufficient bulk of material to allow handling of was
pattern without distortion & to give the
restoration strength, and esthetics when porcelain
is used.
Conservation of tooth structure "provided that the
other criteria are met"
3. Finish line configuration
Finish lines are classified acc. To the type of
restoration used, whether it's metal, ceramics "non-
metal" or combination.
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Principles of tooth preparation
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Principles of tooth preparation
Advantage:
- Provides sufficient bulk
- Provides butt joint (flat seat)
which gives support for porcelain
Disadvantage:
- Less conservation of tooth structure
- Internal angle is sharp (90) stress
concentration & chipping of porcelain
Indication: not commonly used in all ceramics
restoration used with:
- Veneered crowns: on buccal surface
- Full veneered crowns
2) Rounded shoulder (radial shoulder) finish line:
Thickness: 0.8-1 mm
Formed by: tapered with rounded end stone, &
radial fissure bur for roundation of internal angle
Advantages:
- Provides sufficient bulk
- No sharp internal angle
o Less stress concentration
o No chipping of porcelain
Disadvantage: less conservation of tooth
structure
Indication: all ceramics crowns
3) Heavy chamfer (deep chamfer) finish line:
Thickness: 0.8-1 mm
Formed by: trapped with rounded end stone (half
thickness)
Advantage:
- Easy preparation
- Provides sufficient bulk
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Principles of tooth preparation
Indication:
- Less conservation of tooth
structure
- Care should be provided to not increase
the thickness of this line as this may
lead to fracture
Indication: all ceramic crowns (most common)
With porcelain fused to metal restoration
(combination):
1) Shoulder (conventional / classic shoulder) finish
line)
2) Sloped shoulder finish line:
Thickness: 1-1.5 mm
Formed by: tinker stone or torbado stone
Advantage:
- Provides sufficient bulk fo
o Metal: strength
o Porcelain: esthetics
- Internal angle is 120
o Less stress concentration
o No chipping
Disadvantage: less conservation & may extend
apically (subgingivally)
Indication: facial margin of PFM
3) Beveled shoulder finish line:
Thickness: 1-1.5 mm
Formed by: tapered with flat end stone then
bevel by tinker stone
Advantages:
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Principles of tooth preparation
14
Principles of tooth preparation
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Principles of tooth preparation
Taper:
Theoretically, maximum retention is obtained if
a tooth preparation has parallel walls. However, it's
impossible to prepare a tooth this way using current
techniques & instruments; slight undercuts are
created that prevent the restoration from seating.
A slight convergence or taper is necessary in
completed preparation as long as the taper is small
the movement of cemented restoration will be
effectively restrained by the preparation this is
known as limited path of withdrawal.
The recommended convergence bet. Opposing walls
is 3.6 degrees for each surface "total convergence
is 6-12 degrees"
How is it produced?
The rotary instrument is moved through a
cylindrical path & the taper of the instrument
should produce the desired axial wall taper.
If the convergence increase multiple paths of
withdrawal free movement of restoration &
retention will be reduced
Note: too small taper undercuts
To large taper no good retention
The recommended is slight convergence
Divergent walls (reverse taper) the crown won't
fit into the prepared tooth.
Surface area:
Provided the restoration has a limited path of
withdrawal, its retention depends on surface area in
sliding contact "length of withdrawal path”. The
length of the prepared tooth must not be less than
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Principles of tooth preparation
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Principles of tooth preparation
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Principles of tooth preparation
2. resistance form:
definitions:
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Principles of tooth preparation
1-Taper:
2- Surface area:
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Principles of tooth preparation
Alloy selection:
For gold alloys:
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Principles of tooth preparation
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Principles of tooth preparation
Esthetic properties:
The dentist should be able to achieve the esthetical
expectations of the patient, as most of the patients
prefer their dental restorations to look as natural as possible.
However, care must be taken that esthetic considerations are
not pursued at the expense of a patient’s long-term oral health
or functional efficiency.
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Principles of tooth preparation
Partial-coverage restoration:
It is more preferred to use partial-coverage
restorations whenever it is possible not only because the
tooth structure is conserved but also because no
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Principles of tooth preparation
-facial margin:
The facial margin of the partial-coverage restoration
should extend just beyond the occluso-facial line angle. a
short bevel is needed to prevent the chipping of enamel.
also a chamfer finish line can be placed when appearance
is less important (as in molars) which will provide greater
bulk of metal for strength. anterior partial-coverage
restorations can be fabricated to show no metal, the
facial margin extends just beyond the highest contour of
the incisal edge but not quite to the inciso- labial line
angle, here the metal will prevent the tooth from chipping
but will not be visible.
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Full veneer metal crown
_________________________________________________________________________________________
Definition:
Advantages: Disadvantages:
1
Full veneer metal crown
_________________________________________________________________________________________
Indications :
Contra-indications:
2
Full veneer metal crown
_________________________________________________________________________________________
1. Occlusal preparation :
non-functional cusps: 1 mm
central groove: 1 mm
should follow the anatomy (to give sufficient bulk and structural
durability)
- Fleximeter strips
3
Full veneer metal crown
_________________________________________________________________________________________
NB.
2. axial reduction:
amount: 0.3 - 0.5 mm
how to check the reduction?
- Using index
- Thickness of the stone : half thickness of stone
Technique :
- Free hand technique
- Guiding grooves
4
Full veneer metal crown
_________________________________________________________________________________________
technique:
how to check ?
using a probe
4. finish line:
Type: chamfer finish line
Position: supra-gingival (0.5 – 1 mm above gingiva)
Thickness: 0.3 -0.5 mm
Avoid enamel lip formation
The finish line should follow the
contour of CEJ, continuous and
smooth
Function of finish line: marginal
adaptation and integrity
how to check?
By looking from occlusal view
5
Full veneer metal crown
_________________________________________________________________________________________
NB.
-Thin finish line -> no marginal adaptation, leading to dissolution
of cement and recurrent caries
-Thick finish line -> enamel lip formation, leading to fracture
-No finish line -> no proper seating of the crown and no marginal
adaptation, leading to dissolution of cement and recurrent caries
-Irregular finish line -> cement dissolution, plaque accumulation
and recurrent caries
-Unnecessary apical extension -> over reduction and violation of
the biological principles.
technique:
using a fine diamond stone
6
Full veneer metal crown
_________________________________________________________________________________________
1. The occlusal reduction must allow adequate room for the alloy
used. Minimal recommended clearance is 1 mm on non-
functional cusp and 1.5 mm on functional cusps
2. The occlusal reduction must follow the normal anatomic
contour to be conservative
3. Axial reduction should be parallel to the long axis of the tooth,
allowing 6 degrees of convergence between opposing axial
surfaces
4. The margin should be located sup gingivally, the chamfer
should be smooth, distinct and allow for 0.5 mm of metal
thickness at the margin
5. Functional cusp bevel:
The bevel must be angled to be about 45 to the long axis. This
reduction of the functional cusp will provide optimum
restoration contour with maximum durability and conservation
of tooth structure
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Veneered crown
________________________________________________________________________
Definition :
- It’s a full coverage crown (metal-ceramic) that consists of a
cast metal substructure with one or two surfaces covered
with porcelain ( veneered ) OR with all surfaces covered with
porcelain ( full veneered ).
- It combines both advantages of
1. Metal strength & durability.
2. Porcelain mimic natural teeth ( esthetics)
- Complete coverage by metal .
- Extention varies .
- Need Major requirements :-
1
Veneered crown
________________________________________________________________________
Indications:-
1. Esthetics demands.
2. Durability ( better than all ceramic as its supported by metal
so better used in patients with para-functional habits)
3. Marginal fit ( better than all ceramics).
4. Crown & bridges ( connectors)
In metal ceramic bridge the connectors are thinner
(2.5-3 mm) than in all ceramic bridge ( 4 mm ).
N.B. so better used in patients with short teeth.
5. Support a removable partial denture ( allow placement of
rests, if RPD is a part of treatment).
6. Extensive tooth destruction ( caries – trauma – extensive
erosion – endodontically treated )
7. Correction of malocclusion.
8. Correction of occlusal plane.
Contra indications :-
1. Patients with active caries ( contra indicated to any fixed
restoration, so removable restorations are preferred unless
the patient changed his mentality ) .
2. Untreated periodontal diseases ( mobility – pocket depth).
3. Young patients with large pulp champers due to high risk of
pulp exposure so porcelain & composite laminates are
preferred.
4. If more conservative restoration is possible.
5. If facial wall is intact partial veneer is possible &
favorable .
N.B
Partial coverage Dec. surface area Dec. retention &
resistance.
2
Veneered crown
________________________________________________________________________
Advantages :-
1. Strength of metal ( reinforcement & support to brittle
ceramic).
2. Mimic natural teeth appearance.
3. Provides excellent retention & resistance ( full coverage ).
4. Easier preparation than partial coverage .
Disadvantages:-
1. No conservation for tooth structure.
2. To achieve better esthetics, the facial margin needed to be
placed subgingivally which increase risk of periodontal
disease.
3. Fracture due to brittleness of ceramic material.
4. Inferior esthetics compared to all ceramics.
5. Difficulty in accurately selection of shade.
6. Many procedural steps ( casting – porcelain adaptation ) so
its expensive.
3
Veneered crown
________________________________________________________________________
2. Incisal reduction
amount : 1.5 - 2 mm ( to give bulk for porcelain for good
esthetics& translucency )
incisal bevel
Upper anteriors -> palatally directed
Lower anteriors -> buccaly directed
3. Buccal reduction
amount : 1.5 mm
in 2 planes
1) cervical ( // to long axis) determines path of
withdrawal
2) incisal or middle ( inclination) provides space for
porcelain veneer.
4
Veneered crown
________________________________________________________________________
5. Proximal reduction
contact area should be opened without injury of adjacent
teeth .
should be slightly converge 6 degree avoid undercut.
6. Lingual reduction
cingulum // to cervical 1/3 retention & resistance.
fossa concave structural durability .
7. Wing preparation
transition between chamfer finish line lingually & shoulder
buccaly.
claimed to give strength but considered to be stress line.
so wingless prep is preferred ( no definite Trancession from
chamfer to shoulder ) shoulder gradually narrows lingually.
8. Finishing
by red or yellow stone
smooth glass like
rounded line angles
no scratches
use gingival retraction.
5
Veneered crown
________________________________________________________________________
Criteria of preparation :-
Chamfer
- marginal integrity.
wing
- retention & resistance
-preservation of tooth structure .
incisal notch
- structural durability.
shoulder
-marginal integrity
-structural durability
axial reduction
- retention &resistance
- structural durability
6
Veneered crown
________________________________________________________________________
Criteria of preparation :-
Chamfer
- marginal integrity.
- structural durability .
Lingual axial reduction
-retention & resistance
-structural durability.
wing
- retention & resistance
-preservation of tooth structure .
functional cusp bevel
- structural durability.
Gingival bevel
- marginal integrity .
shoulder
-marginal integrity
facial axial reduction
- retention &resistance
- structural durability
planer occlusal reduction
- structural durability.
Evaluation:-
1. incisal or occlusal reduction 2mm in centric & eccentric
movements.
2. Axial wall restricted angle of convergence
3. Facial wall exhibit two plane reductions
4. Shoulder finish line provide 1.2-1.5 mm & chamfer .5mm
5. Smooth & rounded preparation .
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All ceramics restoration
NB.
Veneers :
1
All ceramics restoration
Advantages:
1. Best esthetics
2. Excellent translucency, resembles natural teeth
3. Good tissue response (ceramics are inert and bio-compatible and
plaque is easily removed form it)
4. More conservative preparation of facial surface (compared to
veneered crowns)
5. Higher color stability in comparison to composite
6. Low thermal conductivity in comparison to metal
7. Shade (color) can be modified by the shade of the underlying
luting cement
Disadvantages:
2
All ceramics restoration
Indications:
Contra indication:
NB.
3
All ceramics restoration
Incisal reduction:
- Approximately 1.5 mm
- Creation of bevel (lingually in upper teeth and labially in lower
teeth)
- Roundation
Labial reduction
lingual reduction
4
All ceramics restoration
finish line:
Finishing:
5
All ceramics restoration
NB.
Veneers :
1
All ceramics restoration
Advantages:
1. Best esthetics
2. Excellent translucency, resembles natural teeth
3. Good tissue response (ceramics are inert and bio-compatible and
plaque is easily removed form it)
4. More conservative preparation of facial surface (compared to
full-veneered crowns)
5. Higher color stability in comparison to composite
6. Low thermal conductivity in comparison to metal
7. Shade (color) can be modified by the shade of the underlying
luting cement
Disadvantages:
2
All ceramics restoration
Indications:
Contra indication:
NB.
3
All ceramics restoration
Incisal reduction:
- Approximately 1.5 mm
- Creation of bevel (lingually in upper teeth and labially in lower
teeth)
- Roundation
Labial reduction
lingual reduction
4
All ceramics restoration
finish line:
Finishing:
NB.
5
All ceramics restoration
some definitions:
6
All ceramics restoration
why ceramics??
History: (read)
In 1887, Dr. Land was the first who made the first porcelain jacket crown , It
consisted of feldspathic porcelain baked on a thin platinum foil.
In 1889, Dr. Land was the first who made the first porcelain crown , It consisted
of feldspathic porcelain baked on a thin platinum foil
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All ceramics restoration
But he came up against the problem that the crowns would break too easily, which
limited their use to anterior teeth.
Porcelain:
glassy
crystalline
It has 3 constituents:
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All ceramics restoration
Composition of porcelain:
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All ceramics restoration
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All ceramics restoration
NB.
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All ceramics restoration
-Advantages of porcelain:
1. Inert during firing
2. Its melting point is higher than the firing temp of porcelain, so
no distortion occurs.
3. supplied in soft sheets that can be easily adapted to the die.
NB.
The foil is adapted to the facial surface of the die, then folded
around the lingual surface and burnished.
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All ceramics restoration
Objectives of condensation:
1- Removal of excess water to dec. firing shrinkage
2- Most compact arrangement will adapt the paste to the required
form
3- Lack of void spaces and inc. strength
Methods of condensation:
1- Vibration: gentle vibration which causes the porcelain particles to
settle closer, while excess water is absorbed by a napkin or
blotting paper.
2- Spatulation: smoothening and burnishing the wet porcelain by a
spatula, until excess water is brought to the surface and
absorbed
3- Brush/capillary action: dry porcelain powder is applied by a brush
to remove excess water by capillary action.
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All ceramics restoration
3. Porcelain firing:
-In a furnace, at a specific temp. for a specific time
-Either air firing or vacuum firing.
-Technique:
Firstly, water is gradually lost form the workable mass by warming
the mix, to prevent sudden steam formation
Secondary change then occurs as the mass is placed in a furnace and
the temp. is raised, the free and combined water is lost causing the
particles to fuse together in a process known as sintering
(continuous mass)
No firing is perfect from the first trial
If firing cycles are increased/repeated multiple times, porcelain’s
crystalline phase increases “devitrification” resulting in a milky
appearance -> inc. opacity (bad esthetics).
4. Glazing:
Glaze is a thin, translucent, low fusing porcelain which may be
applied to the surface as the final stage in the firing cycle and
has the effect of filling surface defects (smoothening the
surface), leading to:
better esthetics and translucency.
color stability
no plaque accumulation
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All ceramics restoration
if metal ceramic:
if all ceramic:
NB.
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All ceramics restoration
Properties of porcelain:
5. Resist devitrification:
vitreous = glass
vitrification = creation of the glassy phase
devitrification = creation of the crystalline phase.
- porcelain feldspar: glassy phase
quartz: crystalline phase
porcelain should have resistance to devitrification by avoiding
repeated firing cycles.
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All ceramics restoration
Recent cements:
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All ceramics restoration
2. Pressable ceramics:
Impression/intra-oral scan
Model
Wax
Spruing
Investment
Wax elimination
Pressing (instead of casting) in the pressing furnace
pressure and firing
- Ceramic ingots are used with a plunger which is pressed inside the
crown.
Notes:
- In case of absence of an intra-oral scanner, a normal impression
is taken, the impression is sent to the lab to form a model which
is then scanned and then used in milling.
- All new ceramics are low fusing
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Working casts and dies
1. Impression
2. Cast and die formation
3. Formation of wax pattern
4. Casting and investing
Definitions:
1
Working casts and dies
NB.
Types of casts:
1) Primary and
secondary cast of
the teeth to be
restored 1ry cast 2ry cast die
2) Primary impression
of the opposing teeth
3) Die: for easier handling during wax pattern fabrication and
finishing of inaccessible areas of the cast
2
Working casts and dies
9. Economic.
3
Working casts and dies
2. Metals:
• Electroformed/electroplated.
• Sprayed metals.
• Amalgam.
4
Working casts and dies
3. Polymers:
• Epoxy.
4. Cements:
• silicophosphate or
Gypsum:
by heating
(hemihydrate) (dihydrate)
5
Working casts and dies
Gypsum products:
Advantages
1. Inexpensive
4. Easy to use
Disadvantage
Overcome by:
6
Working casts and dies
Mixing of gypsum:
1. Manual mixing.
2. Vacuum mixing (to remove any air
bubbles)
Resin:
Resin are used as a die material to overcome the low strength and
abrasion resistance of die stone.
Types:
1. Epoxy resin
2. Polyurethane
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Working casts and dies
Advantages
High strength
Disadvantages
Expensive
4. Electroplated die:
Advantages
1. High accuracy.
2. High strength.
4. Dimensional stability.
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Working casts and dies
Die system:
3) Single Die
-> The first pour is to obtain the separate die (pouring the stone to
the side of prepared teeth in impression in small increments)
-> Then, the second pour is to obtain the full arch cast.
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Working casts and dies
1 2 3 4
- So we obtain:
Full arch cast for proximal contact and occlusion.
Sectional cast (Separate die) for wax coping and margins.
- Advantages:
1) Easy to fabricate.
- Disadvantages:
1) Wax pattern must be transferred from die to cast:
10
Working casts and dies
a. Retained by pins:
Dowel pin system
Pindex system
b. Not retained by pins:
Di-lock tray system
11
Working casts and dies
pre-pour technique:
12
Working casts and dies
Post-pour technique
Here, the cast is poured up to the level of the crowns of the teeth
in the impression.
Subsequently, small holes are drilled within the first pour in the
required places and the dowel pins are cemented into the holes
The remaining part of the cast is poured and the dies are sectioned
as described in the pre-pour technique.
b. Pindex system:
Technique:
1. Base of the cast is flat and smooth and parallel to the occlusal
plane
2. Cast is 15-20 mm thick from gingival crest to the base
3. Each segment must have at least 2 pins (Long pin toward facial,
Short pin toward lingual) for stability and to prevent rotation
4. Parallel pin channels are made, at least 5 mm apart (base is placed
on the drill, press and drill holes are prepared in the under
surface of the base (down penetration) of the cast using the pilot
light as a guide.)
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Working casts and dies
This is done:
Advantages:
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Working casts and dies
Die preparation:
The grooves on the base of the cast formed by the di-lock tray are
used as a guide to die sectioning and will ensure that the die will be
positioned correctly in its place after its removal.
15
Working casts and dies
Copper band are supplied in different sizes and diameter to fit for
anterior, premolars and molars.
1. Stone die
2. Amalgam die
4. Refractory die
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Alloys
Alloys
Alloys selection:
Type of instrument
Type of sprue
Casting method
Temperature
Alloys classification:
1
Alloys
ruthenium (Ru)
rhodium (Rh)
palladium (Pd)
silver (Ag) ¾ crowns are made
osmium(Os) by gold only for
iridium (Ir) good marginal
platinum (Pt) adaptation
titanium alloys:
2
Alloys
3
Spruing
Spruing
1. The sprue must allow the molten wax to escape from the mold
(wax elimination).
2. The sprue must enable the molten metal to flow into the mold
with as little turbulence as possible (casting).
3. The metal within it must remain molten slightly longer than
the alloy that has filled the mold. This provides a reservoir to
compensate for the solidification shrinkage that occurs during
casting.
1. Wax sprue:
- Wax sprues are preferred for most casting as they melt at
the same rate as the pattern, thus allow easy escape of the
molten wax, leaving no residues.
- Prefabricated wax sprue formers are available with
different shape and gauges to meet the needs of individual
cases.
1
Spruing
3. Metal sprue:
- They are often hollow to increase the contact surface area and
Strengthen the attachment between the sprue & pattern.
They should be made of non-rusting metal to avoid possible
contamination of the wax.
They are usually removed from the investment before wax
elimination. special care must be taken to examine the orifice
for small particles of the investment that may break off when
such a sprue is removed because these can cause an incomplete
casting if detected.
2
Spruing
3
Spruing
4. length of the sprue: -> very short sprue < 2mm must be avoided
as it may place the mould space too far from the end of the
ring, so the gases can’t escape easily resulting in backpressure
porosity.
very long sprue > 6mm must be avoided as the molten metal
inside the sprue may solidify first preventing full mould
feeding by the molten alloy.
5. Sprue former diameter: -> a sprue of sufficient size should be
selected to supply the volume of alloy required of the pattern
to be cast. In general, a relatively large diameter sprue is
recommended because this improves the flow of molten metal
into the mold and ensures a reservoir during solidification.
with indirect spruing, the reservoir should be equal or larger
than the thickest cross-sectional area of the largest pattern
(this requirement is especially critical when metal pontics and
large molar retainers are sprued).
when using air pressure casting machines a narrow sprue is
essential.
4
Spruing
NB. The greater the density of alloy, the greater the sprue pattern
access must be.
-resilient liner is placed inside the ring leaving 2-3mm at both ends
to allow for supporting contact of the investment with the ring.
5
Spruing
Ringless investment:
- When more than 2 units are being cast together, each is joined to
a runner bar. A single sprue is used to feed the runner bar.
- Two units may be cast with a runner bar or each unit may be fed
from a separate sprue.
6
Spruing
a. Direct spruing:
b. Indirect spruing:
- The molten alloy doesn’t flow directly from the casting crucible
into the pattern area in the heated mould.
- the casting alloy takes a circuitous (indirect) route before it
reaches the pattern area this called indirect spruing.
- the connector or runner bar is often a large in diameter, round
wax to which the wax pattern sprue formers are attached on one
side with 2 large sprue formers on the other side. the bars large
volume houses molten metal so the pattern area fill with metal
first and are able to draw upon the reservoir, if additional alloy is
needed due to solidification shrinkage.
Consequently, the connector “runner “bar is often referred to as a
“reservoir” bar.
7
Spruing
NB.
- The composition of an alloy will influence the manner in which it
fills the mold. for instance a palladium silver alloy fills the mold
unidirectionally, whereas, type 3 gold fills in random “scattered”
fasluion)
- Expansion of wax during heating = shrinkage of alloy during
cooling “solidification shrinkage”.
- A wax sprue could result in imitability when handling the wax
pattern thus a plastic or metal sprue is preferable when handling a
multiple unit wax pattern.
- Direct spruing is used for Nobel metal alloys and indirect spruing
is for base metal alloy as it allows the oxides to be removed / lost
on the way to the casting unit.
-sprue attachment in anteriors should be away from line angles to
avoid distortion. Spruing is easier for anteriors as only a thin
coping layer needs to obtained “thickest at the incisal edge”.
- Oven heating:
wax elimination
thermal expansion of the investment
8
Casting and investing
Casting:
recovery and
cleaning of casting burn out
casting
Casting assembly:
1
Casting and investing
1. Crucible former: it’s the part to which the sprue is attached, and
it helps in guiding the flow of the molten metal.
They are available as rubber, metal or plastic
pressing of ceramics
2
Casting and investing
NB.
NB.
- We may use more than one liner for more venting and
expansion.
3
Casting and investing
expansion.
Investing:
Phosphate bonded
silica bonded
4
Casting and investing
a. Gypsum bonded investment: mainly used with gold alloys, not used
with base metal as it can’t withstand the high melting temp.
(causes fracture and chemical decomposition)
Formed of:
1. Binder: gypsum
2. Refractory material: silica (in the form of quartz or
cristobalite, and is responsible for the thermal expansion)
Properties:
1. Weak
2. Can’t withstand temp. higher than 650, so used with gold
alloys
3. High porosity (more porous than phosphate bonded investment)
Types of expansion:
5
Casting and investing
Properties:
NB.
6
Casting and investing
Types of expansion:
1. Setting expansion: it’s affected by:
Heat from the setting reaction increases setting expansion
Mixing the powder with colloidal silica increases setting
expansion
2. Thermal expansion: expansion occurs when the mold is heated
to eliminate the wax.
The silica refractory material is principally responsible for this
because of the solid-state phase reaction (changing form to
form)
multiple wax patterns: large ring (oval ring), and the wax patterns
are placed near the center of the ring.
7
Casting and investing
Investment bridge:
It’s the distance from the end of wax pattern to the end of the ring.
In GBI Each 100gmpowder -> 26-27ml water Vacuum mixing (flowy mix)
- bench setting for 20-30 mins then placing the ring in burn out
furnace
- place on the vibrator, to remove any air bubbles.
- Then remove excess material and crucible former
8
Casting and investing
NB.
hygroscopic expansion.
Burn out:
- To start wax elimination, the mold is set upside down, with the
sprue hole placed downward (in the furnace) at first for
approximately half an hour, so that all the wax is eliminated.
- To start the wax elimination procedure:
1. set the furnace to to a temp. of 200-250C and hold it for
around 30 mins. During this time, most wax is eliminated.
2. Then, raise the temp. gradually to either 480C or 650C
- 480 -> corresponds to the low heat technique.
- 650 -> corresponds to the high heat technique.
NB. For any method of those to be used, once the desired temp.
respective for each technique is reached, a plateau is held (constant
temp.) This temp. should be held for 45 mins (heat soak).
The heat soak ensures the investment remains at the desired high
temp. for casting, as if it gradually cools down, there will be premature
solidification of the alloy, leading to incomplete casting.
9
Casting and investing
-> This technique is only possible with phosphate bonded and not
gypsum bonded investment since Gypsum bonded investment,
undergoes thermal decomposition at temp. > 650C
NB.
10
Casting and investing
NB.
11
Casting and investing
1. heat:
single-orifice tip
12
Casting and investing
Red -> Orange -> white (dull) -> white (mirror like)
Fluxes:
The previous fluxes can’t be used with base metals, since charcoal may
cause discoloration of the base metal, and borax is not sufficient to
remove all the oxides form the base metal.
13
Casting and investing
2. Electric:
The electric machines are expensive and more appropriate for larger
dental laboratories.
15
Casting and investing
Casting Defects:
16
Casting and investing
- Concavity
- Convexity
- Roughness
17
Casting and investing
Defects by addition:
18
Casting and investing
NB. If the nodules are in the fitting surface or margin and upon
removal result in perforation, the crown (restoration) needs remaking
19
Casting and investing
3. Fins:
Mainly due to crack in the investment
20
Casting and investing
Negative defects:
causes:
2. inclusion porosity:
due to entrapment of small fragments in the
mould (mainly form the investment)
3. using the oxidizing red zone not the blue reducing zone
which causes oxides formation
21
Casting and investing
causes:
discoloration:
due to:
dimensional changes:
22
Casting and investing
marginal discrepancy:
causes:
Law no 1:
Violation of this law will lead to → short margins and incomplete castings.
Law no 2:
Orient wax patterns such that the margins are facing the ring trailing edge
when the ring is in the casting machine
Law no 3:
Cold zone → the coolest part of the ring present at the ring end and at the
periphery.
Heat zone → the hottest part of the ring present in the center.
23
Casting and investing
Law no 4:
Violation of this law will lead to → shrinkage porosity and/or suck back
porosity.
Law no 5:
A button can draw available molten alloy from the runner bar → shift the
heat center and reduce the feed of metal to the restorations.
Law no 6:
Eliminate turbulence
Pathway for the flow of metal should be smooth, gradual with no sharp turns,
restrictions or points that leads to:
Increase rate of flow of metal and abrading the mold surface (mold wash)
24
Casting and investing
Law no 7:
Casting ring should have sufficient length and diameter to accommodate the
wax pattern to be invested
Wax pattern should be 6mm away from the end of the ring,6 mm apart from
each other and 9mm from the ring liner.
If too much investment → air will not escape and the wax pattern will be
placed in the heat zone.
Violating this law, Shrinkage porosity and Back pressure porosity will lead to
→ Mold fracture, Fins.
Law no 8:
If too little wetting agent → investment will not wet properly and inclusion
of air will occur.
If too much wetting agent → weaken the investment → bubbles and fins.
Violating this law will lead to → Bubbles, Nodules, Rough casting and Fins.
25
Casting and investing
Law no 9:
Law no 10:
Mix the phosphate bonded investment under vacuum to eliminate air and
ammonia gas by-product
Areas of the mold that contain dense, bubble free investment will expand
differently from areas containing large voids.
Violating this law will lead to → Surface nodules, Weak mold and Distortion
of casting.
Law no 11:
Procedure
If the ring is placed in burn out furnace before the end of the setting time
→ weak mold that cannot withstand steam expansion during burn out.
Violating this law will lead to → Mold cracking → Fins or Mold blowout and
fracture.
26
Casting and investing
Law no 12:
Use two stage burnout with low rate of temperature rise (allow for uniform
expansion with no plastic residues).
Violating this law will lead to → Short margins, Mold cracks and Casting fins.
Law no 13:
Too much heat or too high temperature → burn off minor alloy elements
through vaporization and/or oxidation.
Violating this law will lead to → Incomplete casting and Short margins (Low
heat) OR Rough casting and investment breakdown (High heat).
Law no 14:
Use the reducing zone and not the oxidizing zone of the casting torch.
Violating this law will lead to → Gas porosity and/or change in the alloy
coefficient of thermal expansion due to alloy contamination).
27
Casting and investing
Law no 15:
Provide enough force to cause the liquid alloy to flow into the heated mold
Violating this law will lead to → Incomplete casting and short margins (Low
force) OR mold fracture and fins (High force)
Law no 16:
Uneven cooling between the alloy and investment → apply tensile forces to
the casting and the restoration could tear.
Law no 17:
In a centrifugal casting machine, the metal will flow downward and to the
right, taking advantage of the centrifugal, rotational and gravitational
forces on the molten alloy.
Violating this law will lead to → Cold shuts, Short margins and incomplete
castings.
28
Casting and investing
Instruments:
29
Casting and investing
30
Casting and investing
The area/point form where the marking agent was ripped / removed
identifies the site for relief using a small carbide bur.
31
Casting and investing
32
Casting and investing
In case of bridge:
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Casting and investing
NB.
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Casting and investing
35
Casting and investing
- High gold alloys: contain tin, indium and iron as trace elements to
create the required oxide layer
- Base metal alloys: can already form the required oxide layer for
bonding, but if it becomes too thick, failure takes place (if the
oxidation process is too long)
- The oxidation / degassing process should be performed according
to manufacturer’s instructions
NB. Gold alloys generally take longer time to obtain the required
oxide layer compared to base metals.
Bridges:
36
Metal-Ceramic restoration (PFM)
Structure:
-> if the porcelain covers all the surfaces of metal -> full veneered
crown
-> if the porcelain in applied only on the esthetic area -> veneered
crown
underneath
- initiates the development of the shade
1
Metal-Ceramic restoration (PFM)
NB. These areas are not supported by dentin so they have higher
translucency than the other parts of enamel
2
Metal-Ceramic restoration (PFM)
NB.
2. Melting range of the alloy: The melting range of the alloy used in
the coping must be 170 to 280 C higher than the fusing
temperature of the porcelain applied to it. If the difference
between the two materials is less than 170 distortion (sagging)
or melting of the coping will occur during firing and glazing of the
porcelain. The greater the difference, the fewer the problems
that encountered during firing.
3. Rigidity (stiffness / modulus of elasticity) of the metal: The
metal should be rigid enough i.e. should not flex during seating or
when subjected to occlusal forces. Any flexing will lead to
shearing of the porcelain.
NB.
Base metals have higher rigidity than gold alloys that’s why they only
require 0.2 - 0.3mm thickness
3
Metal-Ceramic restoration (PFM)
1. Low fusing temperature, being about 170 to 280 more than the
melting range of the metal
2. Should be of high viscosity, i.e. they require a high resistance to
slumping in order to maintain their basic shapes during firing
3. Should resist devitrification, when porcelain is fired too many
times it may devitrify, thus becomes milky and difficult to glaze
4. Coefficient of thermal expansion should be slightly lower than
the metal by 1 x 10 -6 C to enhance the bond strength and avoid
crack formation
5. It must be chemically and optically stable over a series of firing
cycles.
The design of the metal coping has an important effect on the success
or failure of the restoration, and since porcelain is a brittle material,
it’s stronger in compression than in tension so the coping must allow the
porcelain to remain in compression by supporting the incisal region, the
occlusal table and the marginal ridges.
It includes:
4
Metal-Ceramic restoration (PFM)
5.
6
Metal-Ceramic restoration (PFM)
NB.
7
Metal-Ceramic restoration (PFM)
NB.
If the porcelain extends only to the cusp tip -> shear forces due to
load, leading to fracture of porcelain
If the distance between the porcelain and the central groove is less
than 1.5 – 2 mm -> fracture of porcelain (due to flexure of metal)
So, porcelain should extend over the cusp tip and about half of the
ways down the lingual incline of the facial cusp (1.5 – 2 mm away from
central groove)
4) Facial margin
8
Metal-Ceramic restoration (PFM)
NB.
NB. The crown remover is a device used for removing the crown, it
depends on the fact that the cement is a brittle material, if it was
applied on the porcelain margin it will lead to its fracture, so the
presence of a metal collar lingually allows it to remove the restoration
without fracture
10
Metal-Ceramic restoration (PFM)
Metal preparation:
1. Investment removal:
11
Metal-Ceramic restoration (PFM)
-> gypsum bonded investment: used only with low fusing gold alloys (not
suitable for metal-ceramic restoration)
12
Metal-Ceramic restoration (PFM)
2. Oxide removal:
The oxide layer that has been formed on the metal surface during
casting must be removed, again with either acid or air-abrasion
(sand blasting). If the metal-porcelain bond is to be maximized, the
alloy manufacturer’s directions should be followed as the bonding
depends on a controlled metal-oxide layer. (the thinner the oxide
layer the better the bonding).
3. Metal finishing:
- The metal surface should be smooth, convex, with no
irregularities and no sharp line angles.
- Finishing is done by:
Carbide burs
Ceramic bonded stones (non contaminated ceramic bonded
stones)
6. Cleaning:
- The substructure can be cleaned by immersion in a cleaning
solution in an ultrasonic unit. The duration of the cleaning cycle
will depend on the unit, but in most cases approximately 5 minutes
is adequate.
- Steam cleaning is an excellent and timesaving alterative to
ultrasonic cleaning. Residual soap can be removed by a rinse in
distilled water.
- The veneering surface should not touch once the cleaning
procedures have been completed.
14
Metal-Ceramic restoration (PFM)
15
Metal-Ceramic restoration (PFM)
16
Alternatives to casting techniques:
1. High chemical reactivity (react with the surrounding air, with the
investment material so should be casted under vacuum)
2. High melting temperature (1700 C melting range)
3. Low density (needs a strong centrifugal casting machine)
1
Alternatives to casting techniques:
2. Electroforming.
3. Capillary technology.
4. Machining.
5. Rapid prototyping.
2. Elector-forming:
Similar to electroplating, but In electroforming, the metal can
be grown as thick as the customer wants (used with gold)
Example: Heliform 600
2
Alternatives to casting techniques:
3
Alternatives to casting techniques:
4. Machining:
a. MAD-MAM
b. CAD-CAM
4
Alternatives to casting techniques:
Steps:
Scanning:
Intra oral: by camera, at first accessibility
and saliva were the main disadvantage.
however, intra-oral scanners can give like
real-life image / videos of the condition.
It can gives images of restorations and
opposing teeth…
Extra oral: impressions or casts scanned extra-orally, for better
accuracy
Designing:
Different designs are found in the library of the software, so
that the technician can choose the most suitable design for the
case.
1. Settings (parameters):
Insertion axis.
Margin placement
Margin thickness.
Spacer and cement space
connector thickness
5
Alternatives to casting techniques:
Veneering thickness
Pontic design
occlusal &wall thickness
2. software suggests the best
design form data fed in
3. operator can modify this design:
any modification is made by the
mouse (making a surface convex,
flat or removal of excess)
how to know what to modify?
->The software gives color codes for the areas to be modified
and the operator will modify them.
6
Alternatives to casting techniques:
Additive manufacturing:
Process:
1. 3D scanner
2. CAD model
3. STL file format
4. Slicing STL file
5. Prototype grows in layers
Advantages:
Fast.
Material formed:
Techniques: