The preparation of teeth for a full coverage restoration involves reduction of teeth to provide adequate mechanical and aesthetic properties in the restoration.

1. Tooth Preparation
for Full Coverage
Restorations

2. 1.
Introduction

3. Principles of Tooth Preparation
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4. • Complete (Full) veneer crown
• A restoration that covers all of the tooth clinical crown surfaces
(mesial , distal, facial, lingual and occlusal)
• Partial coverage crown
• This is a crown that leaves one or more axial surfaces uncovered.
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5. When to use full coverage
restoration?
1. Extensive tooth destruction—as a result of caries, trauma,
or existing previous restorations
2. Need for superior retention and strength
3. Endodontically treated tooth
4. Recontour axial surfaces or correct minor malinclinations.
5. Alter the occlusal plane within limits.
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6. Full veneer crown
All
metal
PFM
Full
veneered
Labial
veneered
All
ceramic

7. Indications
Maximum retention and resistance
are needed where esthetics isn’t a
concern e.g.: posterior
Esthetic demands are significant (e.g., the anterior teeth).
Single crowns
Short span FPD
⬩ Favorable distribution of
⬩ occlusal load
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As a retainer, particularly for long-span FPD
Support a removable prosthesis (surveyed crowns)
Bruxer
Short crown

8. Types of Finish Lines
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Feather edge
Chisel chamfer Beveled Shoulder Sloped
shoulder Beveled
shoulder

9. The objective in beveling is threefold:
(1)to allow the cast metal margin to be bent or burnished against
the prepared tooth structure
(2)to minimize the marginal discrepancy caused by a complete
crown that fails to seat completely
(3)to protect the unprepared tooth structure from chipping (e.g., by
removing unsupported enamel).
Of note is that when access for burnishing is limited, there is little
advantage in beveling
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10. Finish Lines
Full metal
According to material And size of
the tooth:
• 0.5mm nobel metal
• 0.3mm base metal
Metal ceramic
Labial veneered
• Facial Shoulder F.L. 1.2mm
sub‐gingival for esthetic
• Lingual chamfer F.L. 0.5mm.
Full veneered
Shoulder F.L. 1.2mm all axial.
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11. All metal crown
preparation
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12. Minimum recommended occlusal clearance
 1 mm on nonfunctional cusps
 1.5 mm on functional cusps.
 The occlusal reduction should follow
normal anatomic contours
Axial reduction should parallel the long axis of
the tooth but allow for the recommended 6-
degree taper.
The preparation margin
 Chamfer configuration
 Ideally supragingival.
 Allow for approximately 0.5 mm of metal
thickness at the margin.
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13. Preparation Steps
• Depth grooves for occlusal reduction
• Occlusal reduction and functional cusp bevel
• Axial alignment grooves
• Axial reduction, second plane reduction
• Finishing of chamfer margin
• Additional retentive features if needed
• Finishing
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15. Alignment Grooves for Axial Reduction
1. The shank of the diamond is parallel to
the proposed path of placement of the
restoration.
2. The diamond tip should not cut into the
tooth beyond its midpoint.
Axial Reduction
• Concurrent with axial reduction, 0.5mm
chamfer finish line
• At least 0.6mm clearance
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16. Finishing
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Finishing of the chamfer margin
- Even thickness
- Continuous & smooth
- Following gingival contour
Roundation of all sharp line
angles and transition lines
Addition of retentive features:
When opposing axial walls are
excessively tapered, to
improve resistance form.

17. Metal-ceramic
crown preparation
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18. They consist of a complete-coverage metal crown substructure that is veneered with a
layer of fused porcelain.
This restoration offers a predictable esthetic result, coupled with sound physical
properties.
The extent of the veneer can vary. Full veneered / Labial veneered
D i s a d v a n t a g e
Requires substantial additional tooth reduction for the porcelain veneer to have a certain
minimum thickness for esthetics and to mask the dark metal colour .
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19. Preparation Steps
1. Depth grooves
2. Incisal or occlusal reduction
3. Labial or buccal reduction in the area to be
veneered with porcelain
4. Axial reduction of the proximal and lingual
surfaces
5. Final finishing
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20. Finish line
Occlusal / incisal
reduction
Axial reduction
All metal 0.5mm chamfer
Functional cusp 1.5mm
non FC 1mm.
0.5mm
Metal
ceramic
Lingual metal collar
0.5mm
Labial 1.2mm shoulder
or heavy chamfer
1.5-2mm if occlusal is
porcelain
Full veneered 1.2mm
Labial veneered 1.2mm
labial
0.5 lingual

21. Metal ceramic
Two plane reduction
• The cervical plane
determines the path of
placement of the completed
restoration.
• The incisal or occlusal plane
provides the space needed
for the porcelain veneer;
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22. Winged vs Wingless
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The “wingless” variation does not exhibit the defined
transition from chamfer margin to shoulder margin.
Rather, the shoulder margin gradually narrows toward
the lingual side
It is contraindicatedIf tooth excessively tapered, to
avoid over convergence.
The chamfer margin is distinct and blends smoothly
into the facial shoulder or sloped shoulder margin.
Proximal wings is done to
• allow conservation of tooth structure
• provides some resistance to rotation
Contraindicated if proximal caries exists
Proximal Reduction

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Brittle
Enamel
abrasive

26. Porcelain is brittle
• The metal substructure must be designed so that any
tensile stresses in the porcelain are minimized
• The veneering surface must be finished to a smooth
texture with rounded internal angles to allow proper
wetting by the opaque porcelain.
• The thickness of a ceramic veneer
• Minimum 1 mm & not exceed 2 mm
• The metal framework must be thick enough to prevent
distortion during firing.
• Minimum thickness
▫ noble metal alloys 0.3 mm
▫ base metal alloys 0.2 mm
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porcelain-metal interface is carved
to a distinct 90-degree butt joint.
• Ideal porcelain thickness is ensured by waxing to the full anatomic contour and cutting back.
• The metal should be shaped to support an even thickness of porcelain.

28. The framework should be shaped to allow for a
distinct margin so that the porcelain is not
overextended and ensures a smooth transition from
porcelain to metal.
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29. Occlusal Analysis
• The centric stops of any metal-ceramic restoration
can be located on either porcelain or metal
• at least 1.5 mm away from the junction
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30. • Opposing restorations must be
carefully planned so that
contacting surfaces are of the
same material
(i.e., metal opposing metal,
porcelain opposing porcelain).
• Because sliding contact of a
porcelain restoration with a cast
crown abrades the gold
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Existing Restorations In The Opposing Arch
Can Influence Framework Design:

31. PFM Opposing gold crown
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32. Disadvantages of occlusal
porcelain
Porcelain is enamel abrasive
• Especially when the porcelain is not glazed or
highly polished
• Restorations with porcelain occlusal coverage
results in restorations with lower strength,
• Anatomically correct occlusal form with sharp
cusps can be difficult to obtain in dental porcelain.
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33. Connector Design
Connectors should be in locations where they do not
impede oral hygiene measures
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34. CAD Wax

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36. Chemical
bonding
Compressive
fit
Mechanical
retention
Bond

37. Mechanical Bonding
• Airborne-particle abrasion with 50 μm of aluminum
oxide is routinely performed on alloy castings to
create surface irregularities and to provide
mechanical interlocking with the opaque dental
porcelain.
• The viscosity of opaque dental porcelain is low
enough in the firing temperature range that the
material can flow into these microscopic openings. 37

38. Chemical Bonding
• To establish the chemical bond between metal and porcelain, a
controlled oxide layer must be created on the metal surface.
• Oxide layer also helps in masking the metal colour
• This oxide layer should have an optimum thickness for a strong metal-
ceramic interfacial bond.
• In casting alloy compositions, manufacturers incorporate small amounts
of certain base metals that form oxides and contribute chemical bonding
to the metal-ceramic adherence
• For base metal alloys in which the principal elements are nickel and
cobalt, chromium oxidation provides chemical bonding
• In noble-metal alloys -> iron, tin, indium, and gallium
• Titanium oxidation fulfills this role for titanium casting alloys.
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39. De-
investing
Oxide
removal
• must be
partially
removed with
either acid or
airborne-
particle
abrasion with
50 μm of
aluminum
oxide
Metal
finishing &
cleaning
Oxidizing
• Creation of a
controlled
oxide layer on
the metal
surface to
establish
chemical bond
between metal
and porcelain.
Acid
pickling
Heating in
the air
Mechanical
bonding
Chemical
bonding
Gold alloy

40. Heating under partial vacuum
/Oxidizing
• During firing, the ceramic is taken above its glass
transition temperature such that it can flow and
fuse with the oxides on the metal surface by
migration of the metal oxides into the ceramic.
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41. Compressive fit
• Small miss match in coefficient of thermal expansion
between metal & porcelain (by 0.5 x 10 -6 ⁰C) The
metal being slightly higherOn cooling, the metal will
try to contract more than the ceramic
• Causing the ceramic to be in a beneficial state of
residual compressive stress at room temperature
• If the mismatch is too big, internal stresses created
during cooling could cause the ceramic to fracture,
with the most likely place for failure being the
interface between the metal and the ceramic
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42. Possible modes of failure of
alloy-porcelain restorations
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43. All ceramic
crown preparation
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46. To prevent stress concentrations in the ceramic, all internal line
angles should be rounded. The shoulder margin should be as
smooth as possible to facilitate the technical aspects of
fabrication.
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47. Finish line
Occlusal / incisal
reduction
Axial reduction
All metal 0.5mm chamfer
Functional cusp 1.5mm
non FC 1mm.
0.5mm
Metal
ceramic
Lingual metal collar
0.5mm
Labial 1.2mm shoulder
or heavy chamfer
1.5-2mm if occlusal is
porcelain
Full veneered 1.2mm
Labial veneered 1.2mm
labial
0.5 lingual
All ceramic 1mm rounded shoulder 1.5mm 1mm

48. Intraoral Repair
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