Atypical Tooth Preparation
Transcript of Atypical Tooth Preparation
ATYPICAL TOOTH PREPARATION
SEMINAR BY
Dr.VINAMRA DHARIWAL
CONTENTS
Part 1 – Basics of tooth preparation
a. Definition
b. Caries control
c. Preparation objectives
d. Finish lines
e. Principles of tooth preparation
f. instrumentation
Part 2 –
a. Preparation modification for damaged teeth
b. Atypical tooth preparation
c. preparation modification for special situation
d. preparation for periodontally weak teeth
TOOTH PREPARATION
Tooth Preparation is defined as the
mechanical treatment of dental
disease or injury to hard tissues
that restores a tooth to original
form.
CARIES CONTROL
Why important
Removal procedure
Sequence of removal
PREPARATION OBJECTIVES
1. Reduction of the tooth in miniature to provide retainer
support.
2. Preservation of healthy tooth structure to secure
resistance form
3. Provision for acceptable finish lines
4. Performing pragmatic axial tooth reduction to
encourage favorable tissue responses from artificial
crown contours, i.e., fluting of molars.
1. Sequence of tooth preparation
2. Contour
3. Intracoronal Vs Extra coronal
4. Tooth structure conservation
5. Gingival termination of
preparation
CLINICAL CONSIDERATION
Errors in tooth preparation
Selection of retainer
Occlusion and tooth preparation
Difficult restorative treatment
OTHER CONSIDERATION
FINISH LINES
1. Supragingival Vs Subgingival Margins
2. Types of finish lines
PRINCIPLES OF TOOTH PREPARATION
1. Preservation of tooth structure
2. Retention and resistance form
3. Structural durability of the
restoration
4. Marginal integrity
5. Preservation of the
periodontium
RETENTION
Taper and retention
Surface area
Area under shear
Surface roughness
RESISTANCE
Method to analyze resistance form
Factors influencing resistance
1. Leverage
2. Length
3. Width
4. Taper
5. Rotation around vertical axis
6. Path of insertion
INSTRUMENTATION
1. Water colling
2. Diamond stones
3. Tungsten carbide burs
4. Twist drills
5. Diamond burs
MANAGEMENT OF DAMAGED
TEETH
Depends on : a. Amount of damage
b. Location of damage
Golden rules of management of
damaged teeth:a. Protecting the vital core
b. Avoiding excessive reduction
Approaching the damaged vital teeth
1. Evaluate the condition of the pulp and
periodontal tissues and make a preliminary
decision on the design of the restoration.
2. Remove all caries and old restorations.
3. Reevaluate the strength of the remaining walls
and decide on the final preparation design
4. Execute the chosen design.
PULPAL CONSIDERATION
# Capping
# Pulpotomy
# Pulpectomy
PERIODONTAL CONSIDERATION
CARIES CONTROL
REVALUATION
PROTECTION OF REMAINING TOOTH STRUCTURE
CONVERTION OF DEFECTS INTO RETENTIVE
FEATURE
• Blocks form
• Orientation of sloping surface
ADDITION OF RETENTION BAR RESSTANCE
FEATURES
Grooves
Pinholes
Core build-up
SOLUTION FOR COMMON PROBLEMS
Over-tapered axial wall
Short axial wall
Undercut in axial wall
Over extended box form
Fractured cusp
One missing cusp
Two missing cusp
ELECTIVE DEVITALISATION
ENDO TREATED TOOTH MANAGEMENT
• Crown
• Dowel core
• Reference: Sorensen and Martin
Hoag and Dwyer
ATYPICAL TOOTH PREPARATION
Teeth that deviate from the anatomical
average or have suffered from carious
attack, erosion or traumatic injury,
sufficient to destroy the outline form of a
typical porcelain veneer crown preparation
will be classified as atypical.
DESIGN FACTORS
Achieving uniform
stress distribution
Retention form
Class 1: Crowns larger than anatomical average.
Class 2: Crowns smaller than anatomical average.
Class 3: Crowns which show marked anatomical deviation from
normal.
Class 4: Crowns with loss of enamel and dentine on either the mesial
or distal surfaces.
Class 5: Crowns with loss of enamel and dentine on both the mesial
and distal surfaces.
Class 6: Crowns with loss of enamel and dentine at the incisal edge,
e.g. traumatic injury or abrasion.
Class 7: Crowns with loss of enamel and dentine at the cervical
margins.
Class 8: Crowns with generalised loss of surface enamel.
Class 9: Length of clinical crown greater than anatomical crown, i.e.
loss of supporting gingival tissue.
TYPES OF ATYPICAL TOOTH PREPARATION
CLASS-1
CLASS-2
• Maxillary lateral
• Mandibular incisor
CLASS-3
Absence of
cingulum
Thin teeth Conical teeth Excess labial
curvature
CLASS-4
Mesial Distal Middle
third
Cervical
third
CLASS-5
CLASS-6
Attrition
Trauma
CLASS-7
CLASS-8
CLASS-9
SUMMARY OF REQUIREMENTS
1.
2. 1. Optimum retention form may be provided for the atypical
preparation by preserving the maximum amount of dentine at the
cervical one third of the preparation. This area should be prepared so
that near parallelism is obtained on both the approximal, lingual and
labial axial walls, thereby ensuring that the crown only has one path of
insertion.
3.
4. 2. Additional retention form and strength may be given to the
porcelain veneer crown by providing an artificial cingulum step in cases
where the tooth preparation would tend to be conical. This cingulum
step will lessen the degree of taper of the lingual surface and bring it
nearer to parallelism with the labial surface.5.
3. Approximal areas of missing tooth structure should not be
entirely restored with cement but should be prepared to form
small lingual steps in the preparation. These steps must be
slightly rounded at all line or point angles and provide an anti-
rotational locking mechanism for the porcelain veneer crown. It
is recommended that high fusing aluminous core porcelain is
used to restore these areas, thereby providing greater strength
than a conventional cement lining. Alternatively the missing
area can be built up with a cast metal coping when a metal-
ceramic crown is fitted.
4. Additional anchorage for the porcelain veneer crown may
be provided by constructing thin gold copings or pinlays which
will restore the missing areas of incisal dentine. The use of
accessory gold anchorage in porcelain veneer crown work is
limited by the amount of space available, and should only be
used as a last resort it a strong and aesthetic result is to be
obtained. The metal-ceramic crown or platinum bonded
alumina crown will often provide more suitable alternatives.
The use of pins with a composite resin core is not satisfactory
on front teeth due to the risk of shearing of the pins or micro-
leakage at the resin tooth interface due to the low modulus of
elasticity and low shear strength of the composite fillings.
MODIFICATION FOR SPECIAL SITUATION
# For Fixed bridge abutment
# For Removable partial abutment Cingulum rest
Occlusal rest
RESIN BONDED BRIDGES
Anterior bridge
Posterior bridge
FIXED PROSTHESIS FOR PERIODONTALLY
COMPROMISED TOOTH
Tooth mobility situation by LINDHE
Situation I – Increased mobility of a tooth with
increased width of the periodontal ligament, but
normal height of the alvealor bone.
Situation II – increased mobility of a tooth with
increased width of the periodontal ligament and
reduced height of the alveolar bone.
Situation III – increased mobility of a tooth with
reduced height of the alveolar bone and normal width of
the periodontal ligament.
Situation IV – Progressive (increasing) mobility of a
tooth (teeth) as a result of gradually increasing width of
the periodontal ligament in teeth with a reduced height
of the alveolar bone.
Situation V – increased bridge mobility despite
splinting.
SPLINTS
Temporary
Intermediate
Permanent
CONNECTORS
Rigid
Non-rigid
TELESCOPIC CROWN
By Peeso in 1916
• Advantages
• Disadvantages
ORTHODONTIC THERAPY
• Occlusal consideration
• Alteration in periodontal environment
OTHER CONSIDIDERATION
• Complete/Partial coverage
• Marginal placement
• Wound healing consideration
• Atraumatic preparation
• Furcation treatment