2016 dr ghazy handout of principles of tooth preparations
TRANSCRIPT
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By
Dr. Mohamed Hamed Ghazy
Professor of Fixed Prosthodontics
Faculty of Dentistry,
Mansoura University, Egypt
OCTOBER 31, 2015
Principles of Tooth PreparationWHAT IS A TOOTH PREPARATION?
a clinical procedure consisting of removal of
tooth structures and / or shaping of the tooth
to accommodate a fixed restoration
TOOTH REPLACEMENT WHY
Problems in Fixed Restorations
Esthetic Problem
Occlusal Problem
Marginal Leakage
Crown Dislodgement / Non-retention
Periodontal Problem
Crown Perforation
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Problems in Fixed Restoration
Can be avoided by
Correct Tooth Preparation
What is a Correct Tooth Preparation?
What are the principles that govern
Tooth Preparation
WHAT IS A CORRECT TOOTH PREPARATION?
• Removal of tooth structure does not weaken the tooth• Amount of reduction follows the requirements of restoration• Resist displacement in all directions• Presence of optimum tooth height• Finish line that can accommodate robust margin with close adaptation• Provide optimal space for crown which is sufficiently thick to prevent fracture, distortion or perforation
• Unnecessary reduction• Endangers the pulp• Lack of retention and resistance features• Finish line that cause micro leakage• Inadequate space for crown which is thin and may cause fracture, distortion or perforation
Incorrect Tooth PreparationCorrect Tooth Preparation
I- Diagnosis & treatment plane
phase.
II- Active Phase of Treatment:-
→ Tooth preparation.
→ Impression making.
→ Working cast & die.
→ Wax pattern.
→ Investing.
→ Casting.
→ Intra-oral try-in.
→ Cementation.
III- follow-up & maintenance.
The principles of tooth preparation are divided into 3 basic categories:-
1) Biologic considerations… which affect the health of the oral tissues.
2) Mechanical considerations… which affect the integrity and durability of the restoration.
3) Esthetic considerations… which affect the appearance of the patient.
What is Optimal ?
≠ Ideal ?
≠ Acceptable?
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Biological Principles
of
Tooth Preparation
maintenance of pulp vitality, adjacent teeth & soft tissues and
conservation of tooth structure
1) Prevention of damage during tooth preparation:-
1- Adjacent teeth.
2- Soft tissue.
3- Pulp.
2) Conservation of tooth structures.
3) Consideration affecting future dental health:-
1- Axial reduction.
2- Margin placement.
3- Margin adaptation.
4- Margin geometry.
5- Occlusal considerations.
6- Preventing tooth fracture.
Biological Principles
of Tooth Preparation:-
A. Prevention of damage during tooth preparation:
1- Adjacent teeth:-
- NEVER damage the adjacent tooth ….. Why ??
Prevention of damage during tooth preparation
1- Adjacent teeth.
2- Soft tissue. 3- Pulp.
Conservation of tooth structures.
Consideration affecting future dental health:-
A. Prevention of damage during tooth preparation:
1- Adjacent teeth:-
To prevent damage to adjacent tooth:-
Metal matrix band
Tooth being prepared
Prevention of damage during
tooth preparation:-
1- Adjacent teeth.
2- Soft tissue.
3- Pulp.
Prevention of damage during tooth preparation
1- Adjacent teeth.
2- Soft tissue. 3- Pulp.
Conservation of tooth structures.
Consideration affecting future dental health:-
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A. Prevention of damage during tooth preparation:
2- Soft tissue:-
Mirror or saliva ejector To protect
tongue, lips & checks.
Prevention of damage during tooth preparation
1- Adjacent teeth.
2- Soft tissue. 3- Pulp.
Conservation of tooth structures.
Consideration affecting future dental health:-
Zekrya,s gingival retractorRetraction cord
A. Prevention of damage during tooth preparation:
3- Pulp:-
- Care is needed to prevent pulpal injuries
Pulpitis pulpal degeneration.
- Freshly sectioned dentinal tubules (during
tooth preparation)
Provide a source for irritant to easily reach
pulpal tissues.
Irritant may be:-
- Temperature.
- Chemicals.
- Bacterial.
Prevention of damage during tooth preparation
1- Adjacent teeth.
2- Soft tissue. 3- Pulp.
Conservation of tooth structures.
Consideration affecting future dental health:-
A. Prevention of damage during tooth preparation:
3- Pulp:-
The morphology of the pulp must be considered before
tooth preparation.
Pulp size (seen in x-ray) … … … decrease with age.
Pulp morphology … … … related to the coronal contour.
occlusocervically ≠ faciolingually
Prevention of damage during tooth preparation
1- Adjacent teeth.
2- Soft tissue. 3- Pulp.
Conservation of tooth structures.
Consideration affecting future dental health:-
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A. Prevention of damage during tooth preparation:
3- Pulp:-A- Temperature.
Heat generation is affected by:-
1- Excessive pressure
2- High rotational speed
3- Coolant type
4- Cutting instrument
(shape &condition)
• Use feather-light touch.
• Never without air-water cooling.
• Use low-speed with pin preparation.
•Use air-water cooling system
•Instrument with suitable abrasives.
•Avoid dull instrument.
Prevention of damage during tooth preparation
1- Adjacent teeth.
2- Soft tissue. 3- Pulp.
Conservation of tooth structures.
Consideration affecting future dental health:-
Pin preparation must be done with low-speed
…. Why ???
Prevention of damage during tooth preparation
1- Adjacent teeth.
2- Soft tissue. 3- Pulp.
Conservation of tooth structures.
Consideration affecting future dental health:-
A. Prevention of damage during tooth preparation: 3- Pulp:-
B- Chemical action.
Avoid use of chemicals to clean the tooth after preparation.
… because … it cause pulpal irritation.
Chemicals (e.g., base, resin, luting agent) placed over freshly
Cut dentin … … cause pulpal irritation.
Varnish or dentin bonding agent form a barrier against
these chemicals … but … it affect retention.
Prevention of damage during tooth preparation
1- Adjacent teeth.
2- Soft tissue. 3- Pulp.
Conservation of tooth structures.
Consideration affecting future dental health:-
A. Prevention of damage during tooth preparation:
3- Pulp:-C- Bacterial action.
When bacteria reaches the pulp … … can cause pulpal damage.
Incomplete caries removal.
caries must be removed completely.
In-direct pulp capping is not recommended.
Microleakage under cemented restoration.
Use cement with minimal microleakage
& with anti-bacterial action.
Prevention of damage during tooth preparation
1- Adjacent teeth.
2- Soft tissue. 3- Pulp.
Conservation of tooth structures.
Consideration affecting future dental health:-
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A. Prevention of damage during tooth preparation.
B. Conservation of tooth structure.
Conserve as much tooth structure as possible (i.e. Avoid unnecessary removal of tooth structure).
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
B. Conservation of tooth structure.
Tooth structure is conserved by:-
1) Use of partial coverage rather than complete coverage.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
B. Conservation of tooth structure.
Tooth structure is conserved by:-
2) minimal practical convergence angle (taper) between axial walls.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
B. Conservation of tooth structure.
Tooth structure is conserved by:-
3) preparation of the occlusal surface must follow the anatomical planes.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
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B. Conservation of tooth structure.
Tooth structure is conserved by:-
4) preparation of the axial walls should be done evenly.if necessary, tooth should be repositioned orthodontically.
Q: preparation done // long axis or ┴ occlusal plane ?
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
B. Conservation of tooth structure.
Tooth structure is conserved by:-
5) selection of margin geometry that is
conservative & compatible with other principles of
tooth preparation.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
B. Conservation of tooth structure.
Tooth structure is conserved by:-
6) Avoid unnecessary apical extension of the preparation.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
A. Prevention of damage during tooth preparation.
B. Conservation of tooth structure.
C.Considerations affecting future dental health.
1) Axial reduction.
2) Margin placement.
3) Margin adaptation.
4) Margin geometry.
5) Occlusal considerations.
6) Preventing tooth fracture.
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A. Considerations affecting future
dental health.
1. Axial reduction.
- Over-contoured restorations is associated
with gingival inflammation.
… So … Preparation must provide sufficient space
to construct anatomically correct axial contour.
Over-contoured rest+ Inflamed gingiva
Insufficient tooth reductionRe-contoured rest+ healthy gingiva.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
1. Axial reduction.
The inter-proximal & furcation area of posterior teeth must beProperly contoured.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
2. Margin placement.
The preparation margin should be supra-gingival (whenever possible).
Adv.,:- Easily prepared with superior accuracy.
Easily finished without soft tissue trauma.
Facilitate impression making with less soft tissue trauma.… with CAD/CAM … facilitate optical capture.
Restoration margins can be easily evaluated during try-in & at recall appointments.
More easily kept clean & plaque free.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
2. Margin placement.
Sub-gingival margins are indicated in the following:-
Caries, cervical erosion or restoration extend subgingivally (crown lengthening is contra-indicated).
Axial contour modification is needed ( undercut for RPD clasp).
Root sensitivity (can not be managed by more conservative procedure e.g., dentin bonding agent).
The margins of an esthetic restoration is to be hidden subgingivally.
Additional retention & resistance are needed.
The proximal contact area extends apically to the level of gingival crest.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
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A. Considerations affecting future
dental health.
3. Margin adaptation.
Junction between cemented restoration &
the tooth is the potential site for recurrent
caries … … … Why ??
•The margin must be properly designed,
smooth & minimal marginal gab.
• Marginal gab range:10 µm … … for casting50 µm … … for porcelain
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
4. Margin geometry.
Cross-sectional configuration of the margin
= Finish line
= Line of demarcation between
prepared and unprepared
tooth structure.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
4. Margin geometry.
Guidelines for margin design:-(Requirement)
1. Ease of preparation.
2. Ease of identification in impression or optical scan.
3. Wax pattern can be easily finished & handled without distortion.
4. Conservation of tooth structure.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
4. Margin geometry.
1- Feather edge margin
Advantages
-Conservation of tooth structure.
Disadvantages
- Fail to provide adequate bulk at the margin.
Indication:
NOT recommended(historically was used with copper band
Imp tech before development of elastomericImpression materials.
2- Chisel edge margin
Advantages
Conservation of tooth
structure,
Disadvantages
Location of margin
difficult to control.
Indication:
- occasionally on tiltedtooth.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
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A. Considerations affecting future
dental health.
4. Margin geometry.
3- Beveled margin
Advantages
- Removes unsupported enamel.- Allow finishing of metal.
Disadvantages
- Extends preparation into the sulcus (if used on apical margin)
Indication:
- Facial margins of partial coverage - inlay / onlay margins
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
4. Margin geometry.
4- Chamfer margin
Instrument:
Using tapered diamond with a rounded tip
The gingival margin is prepared with the diamond held
precisely in the intended path of withdrawal of the
restoration
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
4. Margin geometry.
4- Chamfer margin
Advantages
• Distinct and easily identified.
• Provide adequate bulk of material at the margins
Disadvantages
• Care is needed to avoid leaving a ledge of unsupported
enamel
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
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Indication
A. Considerations affecting future
dental health.
4. Margin geometry.4- Chamfer margin
Cast metal rest. ,Lingual margin of metal-ceramic
restoration
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
4. Margin geometry.
5- Shoulder margin
Preparation
Using tapered diamond with a flat end.It should form 90 degree angle with unprepared tooth surface.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
Advantages
- Provide adequate bulk of material
Disadvantages
- Less conservative to tooth
structure
Indication
- Facial margin of metal ceramic restoration.
- All ceramic crown.
A. Considerations affecting future
dental health.
4. Margin geometry.
5- Shoulder margin
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
4. Margin geometry.
5- Shoulder with bevel margin
Advantages
Provide adequate bulk of material, in addition
to advantage of bevel.
Disadvantages
Less conservative to tooth structure.
Extend preparation apically.
Indication
Facial margin of posterior metal ceramic
restoration in which facial metal collar is
used.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
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Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A. Considerations affecting future
dental health.
4. Margin geometry.
6- Sloped Shoulder margin
Advantages
Provide adequate bulk of material,
in addition to advantage of bevel
Disadvantages
Less conservative to tooth
structure.
Indication
Facial margin of metal ceramic
restoration.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
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5. Occlusal considerations.
Sometimes compromising the principle of conservation is preferable to the potential harm that result from traumatic occlusion.
c) Considerations affecting future
dental health.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
A satisfactory tooth preparation allows sufficient space to develop a functional occlusal scheme in the finished restoration.
c) Considerations affecting future
dental health.
6. Preventing tooth fracture.
No tooth is unbreakable
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
6- Preventing tooth fracture
Tooth preparation should be designed to prevent fracture of
restored teeth.
Providing a cuspal coverage restoration (onlay) rather than an
inlay lessens the chance of such fracture.
However, although not conservative of tooth structure, a complete
crown is often a better solution.
Prevention of damage during tooth preparation
Conservation of tooth structures.
Consideration affecting future dental health:-
1.Axial reduction.
2.Margin placement.
3.Margin adaptation.
4.Margin geometry.
5.Occlusal considerations.
6.Preventing tooth fracture.
c) Considerations affecting future
dental health.
By
Dr. Mohamed Hamed Ghazy
Professor of Fixed Prosthodontics
Faculty of Dentistry,
Mansoura University, Egypt
November 7, 2015
Principles of Tooth Preparation
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MECHANICAL CONSIDERATIONS
Biological principles
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
1- magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
Esthetic principles
1- Providing Retention form
2- Providing Resistance form
3- Preventing deformation of restoration
(structure durability)
Biological principles
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the
restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
1- Magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
Esthetic principles
PRINCIPLES OF TOOTH PREPARATIONS
Definition:
The quality of a preparation that prevents
the restoration from becoming dislodged by
such forces parallel to the path of withdrawal
Biological principles
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Deformation
Esthetic principles
RETENTION FORM
Forces that tend to remove a cemented restoration along its path of withdrawal are small compared to those that tend to seat or tilt it.
eg. Sticky food
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration1. Magnitude of the dislodging forces:
RETENTION FORM
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a) Taper: Is the convergence of two opposing external
walls of a tooth preparation as viewed in a given plane.
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
External Internal
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
Axial walls of a preparation must taper slightly to permit the restoration to seat Two opposing surfaces, each with a 3degree inclination (diamond held parallel to the intended path of insertion) 6 degree taper
The more nearly parallel the opposing walls of a preparation, the greater should be the retentionWalls are tapered:
-visualize preparation walls -prevent undercuts -compensate fabrication inaccuracies -permit complete seating during cementation
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
What is the definition of Tipping Path?
It is the path along which the restoration, could be displaced under the displacing occlusal force
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
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Path of insertion
DefinitionThat direction through which the restoration could beprecisely seated on the corresponding tooth or teeth
Parallel to the long axis of the tooth Parallel to the incisal 2/3 of the tooth
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
b) Limiting number of paths of insertion
path of insertion: it is the direction through which the restoration could be precisely seated on the prepared teeth.
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
PATH OF INSERTION OF A PREP. MUST PARALLEL
THE ADJACENT PROXIMAL CONTACTS
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
c) Type of preparation:
Complete coverage has closed curve while the grooves of the partial
coverage prevents movement to the long axis of the tooth
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
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Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
d) Undercuts
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
√ X
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3-Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
PREP. IN THE MOUTH IS VIEWED THROUGH
A MOUTH MIRROR USING ONE EYE
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3-Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
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e) Surface area:
i) Preparation length:
Longer walls interfere with tipping displacement
Tipping path: It is the path along which the restoration
could be displaced under the displacing occlusal force
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3-Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
Short prep. can be improved by adding grooves
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
ii) Preparation diameter
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
f) Stress concentration
Sharp line angles
→ ↑ stress
→ ↑ failure
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration2. Geometry of the tooth Preparation:
RETENTION FORM
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Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3-Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration
3. Roughness of the fitting surface of the
restoration.
RETENTION FORM
The more reactive the alloy is, the more adhesion to the selected
cement.
Base metal alloys > noble alloys.
Amalgam core > composite and cast gold
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration4.Materials being cemented
RETENTION FORM
Resin cement > conventional ones
Adhesive resin > glass ionomer > polycarboxylate > zinc
phosphate > zinc oxide-eugenol.
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration5. Type of luting cement
RETENTION FORM
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration5. Type of luting cement
RETENTION FORM
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Retention form
1.Magnitude of the dislodging forces
2.Geometry of the tooth preparation
3. Roughness of the fitting surface of the restoration
4.Materials being cemented
5.type of luting cement
6.Film thickness of the luting agent (uncertain)
6. Film thickness of the luting agent
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3-Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
Preventing deformation of the restoration
RETENTION FORM
RESISTANCE FORM
Def. It is the features of the tooth preparation
that enhance the stability of a restoration
and resist dislodgement along an axis other
than the path of withdrawal. (apical, oblique and
horizontal direction).
Biological principles
Mechanical principles
Retention form
1- Magnitude of dislodging forces
2- Geometry of tooth preparation
3- Roughness of the fitting surface of the restoration
4- Material being cemented
5- Type of luting agent
6- Film thickness of the luting agent
Resistance form
1- Magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
Esthetic principles
-Normal occlusion→ biting
forces ,well distributed and
axially directed → greater
resistance.
-Biting habits (pipe smoking-
bruxism) → large oblique
force →lower resistance.
Biological principles
Mechanical principles
Retention form
Resistance form
1- Magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
Esthetic principles
A. Magnitude and direction of the dislodging
force.
RESISTANCE FORM
Tooth preparation must be shaped so that particular areas
(resistance areas) of the axial wall prevent rotation of the
crown
1. Taper
Biological principles
Mechanical principles
Retention form
Resistance form
1- Magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
Esthetic principlesB. Geometry of tooth preparation:
RESISTANCE FORM
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2. Diameter
Small (premolar) > large (molar).
Biological principles
Mechanical principles
Retention form
Resistance form
1- Magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
Esthetic principlesB. Geometry of tooth preparation:
RESISTANCE FORM
3. Height:
Long > short.
Biological principles
Mechanical principles
Retention form
Resistance form
1- Magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
Esthetic principlesB. Geometry of tooth preparation:
RESISTANCE FORM
4. Preparation type:
Complete coverage > Partial coverage (as no buccal resisting areas)
Biological principles
Mechanical principles
Retention form
Resistance form
1- Magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
Esthetic principlesB. Geometry of tooth preparation:
RESISTANCE FORM
Adhesive resin > Glass ionomer > Zinc phosphate > Zn
polycarboxylate > Zinc oxide-eugenol
C. Physical properties of the luting cement:
Biological principles
Mechanical principles
Retention form
Resistance form
1- Magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
Esthetic principles
RESISTANCE FORM
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A restoration must have sufficient strength to
prevent permanent deformation during function.
Otherwise, it will fail.
Biological principles
Mechanical principles
Retention form
Resistance form
1- magnitude and direction of dislodging forces
2- Geometry of tooth preparation
3- Physical properties of luting agent
Deformation
Esthetic principles3. Preventing deformation of the restoration
DEFORMATION MAY BE A RESULT OF:
1. Inappropriate alloy selection.
2. Inadequate tooth preparation.
3. Poor margin design.
4. Poor metal-ceramic framework design.
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles
3. Preventing deformation of the restoration
Type I and Type II gold alloys are
too soft for crowns and fixed partial
dentures.
Type III or Type IV gold alloys are
harder
1. Alloy selection
3. Preventing deformation of the restoration
There should be a minimum alloy thickness
of about 1.5 mm over centric cusps
1 mm over non centric cusp
2. ADEQUATE TOOTH REDUCTION
3. Preventing deformation of the restoration
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles
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Occlusal reduction should be as uniform, following
the cuspal planes of the teeth thus will give
rigidity to the crown because of the "corrugated
effect" of the planes.
2. ADEQUATE TOOTH REDUCTION
3. Preventing deformation of the restoration
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles
The supraerupted tooth may need considerably
more than 1.5 mm of reduction to result in
adequate clearance
2. ADEQUATE TOOTH REDUCTION
3. Preventing deformation of the restoration
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles
Putty index made before tooth preparation
facilitates evaluation of tooth reduction
uniformity.
2. ADEQUATE TOOTH REDUCTION
3. Preventing deformation of the restoration
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles
Distortion of the restoration margin is
prevented by:
1. Sufficient tooth reduction that provide
sufficient room for metal at the margin as
in case of a chamfer preparation.
3. MARGIN DESIGN
3. Preventing deformation of the restoration
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles
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2. The grooves and ledges incorporated in a partial coverage
restoration provide essential strengthening for the casting,
particularly on anterior pinledge retainer.
3. MARGIN DESIGN
3. Preventing deformation of the restoration
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles
Proper framework design allows:
a. Even thickness of porcelain veneer.
b. Proper porcelain metal interface in framework design to allow
distinct margin.
3. Preventing deformation of the restoration
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles4. METAL-CERAMIC FRAMEWORK DESIGN
c. Good connector design
d. Optimally placed occlusal contact:
The centric stops can be located on either porcelain or metal, 1- 1.5
mm away from the junction
3. Preventing deformation of the restoration
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles4. METAL-CERAMIC FRAMEWORK DESIGN
Existing restorations in the opposing arch can influence framework
design.
A porcelain restoration with a cast crown will abrade the gold.
3. Preventing deformation of the restoration
Biological principles
Mechanical principles
Retention form
Resistance form
Deformation
1- Alloy selection
2- Adequate tooth reduction
3- Margin design
4. metal-ceramic framework design
Esthetic principles4. METAL-CERAMIC FRAMEWORK DESIGN
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By
Dr. Mohamed Hamed Ghazy
Professor of Fixed Prosthodontics
Faculty of Dentistry,
Mansoura University, Egypt
November 21, 2015
Principles of Tooth Preparation
PRINCIPLES OF TOOTH PREPARATION
Biological considerations
Affect the health of the oral tissues
Mechanical considerations
Affect of the integrity and durability of the restoration
Esthetic considerations
Affect the appearance of the patient
ESTHETIC CONSIDERATIONS Determination of patient expectations and needs.
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
High esthetic but less conservative (1-1.2mm)
All ceramic restorations
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
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Esthetic restorations includes:Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
PRINCIPLES OF TOOTH PREPARATIONS
Biological principles
Mechanical principles
Esthetic principles All ceramic restorations
Metal –ceramic restorations
1- Facial surface reduction
2- Incisal reduction
3- Proximal reduction
4- Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial margin
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Can mimic original tooth color better than the
other restorative options can.
Includes :- inlays – onlays – veneers – crowns.
High esthetic but less conservative (1-1.2mm)
… so can not be used with thin teeth or teeth with
large pulps.
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
All ceramic restorations
The exact amount of reduction
depends to some extent on the
physical properties of the alloyused for the substructure, and on the
manufacturer and the shade of
the porcelain.
Minimum 1-1.3mm
Prepared in two distinct planes
Lower incisors → pulp exposure Or →
less than ideal esthetic
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Metal ceramic restorations
1. Facial tooth reduction
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-Adequate thickness of porcelain is needed to
create a sense of color depth and
translucency
-Minimum reduction of 1.5 mm is required
-Shade problems incisal and cervical 3rd
of
restoration (here direct light reflection from
the opaque layer can make the restoration
appear very noticeable
-Opaque porcelain generally have a
different shade from body porcelain,
they often need to be modified with
special stains in these areas with
very thin teeth like mandibular
incisors.
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Metal ceramic restorations
1. Facial tooth reduction
Incisal edge with no metal backing → increase esthetic
Incisal edge no metal backing.
So, it can be made with a
translucency similar to that of
natural tooth structure
-reduction 2 mm
-Excessive reduction – reduces retention
and resistance
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Metal ceramic restorations
2. Incisal reduction
Metal ceramic junction is 1mm. lingual to the contact for better esthetic
- Esthetics depends on exact location of the metal ceramic junction in
complete restoration
- Proximal surface of anterior tooth will look most natural if they are
restored as the incisal edges without metal backing.
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Metal ceramic restorations
3. Proximal reduction
The margin should follow the contour of the free gingiva
Supragingival margin placement has many biologic advantages.
Nevertheless,
High lip line → Subgingival finishing line
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Metal ceramic restorations
4. Labial margin placement
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Mesial → just buccal to the proximal contact.
Angulation → follow the long axis of posterior teeth and incisal
2/3 of facial surface of anterior teeth
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Partial coverage restorations
1. Proximal margin
Esthetic partial-coverage restorations depend
on accurate placement of the potentially
visible facial and proximal margins.
Distal → further buccally as it is less
visible to all proper preparation,
finishing and access to oral hygiene
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Partial coverage restorations
1. Proximal margin
Maxillary:
Just beyond the occluso-facial line angle
Short bevel to prevent enamel chipping.
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Partial coverage restorations
2. Facial margin
Mandibular:
Facial chamfer as appearance is impaired by the
occlusal reduction.
Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
Partial coverage restorations
2. Facial margin
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Biological principles
Mechanical principles
Esthetic principles
All ceramic restorations
Metal ceramic restorations
1. Facial tooth reduction
2. Incisal reduction
3. Proximal reduction
4. Labial margin placement
Partial coverage restorations
1- Proximal margin
2- Facial Margin
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