Fundamentals in Tooth Preparation

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Fundamentals in Tooth Preparation

• Dr. Ramesh Bharti
• Assistant Professor
• Conservative Dentistry Endodontics
• King Georges Medical University
• Lucknow

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Definition of Operative Dentistry

• Operative dentistry is the ART and SCIENCE of
  the diagnosis, treatment, prognosis of defects of
  teeth which do not require full coverage
  restorations for correction, such treatments
  should results in the restoration of proper tooth
  form, function, and esthetics while maintaining
  the physiologic integrity of the teeth in
  harmonious relationship with adjacent hard and
  soft tissue, all of which enhance the general
  health and welfare of the patient.

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Objectives of Cavity Preparation

• Remove all defects and give the necessary
  protection to pulp.
• Locate the margins as conservatively as possible.
• Form the cavity so that both the restoration and
  tooth can withstand the load of mastication.
• Allow for the esthetic and functional placement
  of a restorative material.

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Need of Restoration

• Caries
• Malformed, discolored or fractured teeth
• Restoration replacement

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Factors affecting tooth preparation

• 1. General Factors
• Pulpal periodontal status
• Occlusal relationship
• 2.Dental anatomy
• Direction of enamel rods
• Thichness of enamel /dentin
• Size and positionof pulp
• Relationship of tooth to its supporting tissues

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3.Patient factors

• Age
• Esthetic consideration
• Economic status
• Patients with high risk caries
• 4.Affected infected Dentine
• 5. Restorative material factors

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Approach of Operative. cont..

• Cavity preparation
• Matrix application
• Preparation of materials
• Insertion and carving of materials
• Finishing and Polishing

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Cavity Preparation

• The mechanical alteration of a defective,
  injured, or diseased tooth in order to best
  receive a restorative material which will
  re-establish a healthy state for the tooth
  including esthetic corrections where indicated,
  along with normal form and function.

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Cavity Structure

• walls
• angles
• Floor

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Classification of cavity

• Class I
• Class II
• Class III
• Class IV
• Class V
• Class VI

G.V.Black in 1908
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Cavity

• Simple cavity only one tooth surface is
  involved.
• Compound cavity two surfaces are involved.
• Complex cavity three or more surfaces are
  involved.

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Class 1
Class 6
Class 1
Class 4
Class 3
Class 2
Class 2
Class 5
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Stages and Steps in Cavity preparation

• Initial cavity preparation stage
• Final cavity preparation stage

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• Initial cavity preparation stage
• Step 1 Outline form and initial depth
• Step 2 Primary resistance form
• Step 3 Primary retention form
• Step 4 Convenience form

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Final cavity preparation stage

• Step 5 Removal of any remaining infected
• dentin if indicated
• Step 6 Pulp protection
• Step 7 Secondary resistance retention form
• Step 8 Procedure for finishing external walls
• Step 9 Final procedures

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Outline Form and Initial Depth

• Definition
• placing the cavity margins in the positions they
  will occupy in the final preparation.
• preparing an initial depth of 0.20.8 mm
  pulpally of the dentinoenamel junction position
  or normal root surface position.

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Maxillary Class ? outline form
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Mandibular Class ? outline form
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Maxillary Class ? outline form
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Mandibular Class ? outline form
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Common Error
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Outline Form and Initial Depth

• Principles
• all friable and/or weakened enamel should be
  removed
• all faults should be included
• all margins should be placed in a position to
  afford good finishing of
• the margins of the restoration.
• Margins of the preparation will be located on
  finishable, self cleansing area.

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Outline Form and Initial Depth

• Features
• preserving cuspal strength
• preserving marginal ridge strength
• minimizing facio-lingual extension
• using enameloplasty
• connecting two close faults or cavities
• restricting the depth of the preparation into
  dentin.

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Auxillary Factors

• Conservation
• Adjacent enamel cracks or decalcification could
  be involved in the preparation.
• Type of restorative material.
• Extension for access.
• anatomy and alignment.
• If possible, no margins will be in occlusion with
  opposing teeth.
• Esthetics

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Outline Form and Initial Depth for pit and
fissure cavities

• Controlled by three factors
• 1- Extension to which enamel has been involved by
  caries.
• 2- Extension to achieve sound and smooth margins.
• 3- Limited bur depth while extending the
  preparaton

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Rules

• Capping of cusp should be done when cavity
  extension is two-third from central fissure to
  cuspal eminence.
• Include all fissures that cannot be eliminated by
  enameloplasty.
• Restrict the depth.
• Join two lesions if they are less than 0.5 mm
  apart.

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Outline Form and Initial Depth for smooth surface
cavities

• Extension of cavity.
• Sufficient access.
• Depth.
• Sufficient clearance with adjacent tooth.

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• Initial cavity preparation stage
• Step 1 Outline form and initial depth
• Step 2 Primary resistance form
• Step 3 Primary retention form
• Step 4 Convenience form

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Primary Resistance Form

• Definition
• The shape and placement of the cavity walls
  that best enable both the restoration and the
  tooth to withstand, without fracture,
  masticatory forces delivered principally in the
  long axis of the the tooth.

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Primary Resistance Form

• Principles
• To utilize the box shape with a relatively flat
  floor to resist occlusal loading by virtue of
  being at right angles to mastication force.
• To restrict the extension of the external walls
  (keep as small as possible) to allow strong cusp
  and ridge areas to remain with sufficient dentin
  support.

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Primary Resistance Form

• Principles
• To have a slight rounding of internal line angles
  to reduce stress concentration in tooth
  structure
• The presence of sharp internal line angles in
  GOLD FOIL resist the movement of the restoration
• Sharp internal line and point angles in dentin
  serve as convenient starting points for
  compacting of direct gold.
• To provide enough thickness of restorative
  material to prevent its fracture under load.

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Primary Resistance Form

• Feature
• Box shape
• Relatively flat floors
• Inclusion of weakened tooth structure
• Preservation of cusps and marginal ridges
• Rounded internal line angles
• Adequate thickness of restorative materials
• Reduction of cusps for capping if indicated

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Primary Resistance cont.

• Designing the outline form so that minimal of
  restoration is exposed to occlusal stress.
• Seat on sound dentin.

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Vale Experiments

• 1 MR at 1/4th ICD -10 Loss of FR
• 2 MR at 1/4th ICD - 15 Loss of FR
• 1 MR at 1/3th ICD -30 Loss of FR
• 2 MR at 1/3th ICD -35 Loss of FR
• 1 MR at 1/2 of ICD -40 Loss of FR
• 2 MR at ½ of ICD -45 Loss of FR

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• Initial cavity preparation stage
• Step 1 Outline form and initial depth
• Step 2 Primary resistance form
• Step 3 Primary retention form
• Step 4 Convenience form

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Primary Retention Form

• Definition
• The shape or form of the prepared cavity that
  resists displacement or removal of the
  restoration from tipping or lifting forces.

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Primary Retention Form

• Principles depending on the materials
• Amalgam restoration
• developing external cavity walls that
  converge occlusally and dovetail design

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The devotail design provide retention form to
the occlusal portion of the cavity. The occlusal
convergence of the walls offers retention in
the proximal portion of the cavity against
displacement occlusally.
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Primary Retention Form

• Principles depending on the materials
• Composite restoration
• a mechanical bond between the material
• and conditioned, prepared tooth structure.

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Dentin etched with 32 phosphoric acid Collagen
exposed by the acid.
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FIG
Bonding of resin to dentin, using a "total-etch"
technique
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16 Bonding to dentin using a self-etching primer.
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Scanning electron micrograph of the transition
between composite resin (C) adhesive (A),
adhesive-hybrid layer (H), and hybrid
layer-dentin.
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• Initial cavity preparation stage
• Step 1 Outline form and initial depth
• Step 2 Primary resistance form
• Step 3 Primary retention form
• Step 4 Convenience form

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Convenience Form

• Conception
• The shape or form of the cavity that provides
  for adequate observation, accessibility, and ease
  of operation in preparing and restoring the
  cavity.

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Convenience Form

• Principles
• Allow access for caries removal
• Allow access for restoration placement
• Allow access to margins for finishing,
• evaluation and cleaning

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Convenience Form
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• Final cavity preparation stage
• Step 5 Removal of any remaining infected
• dentin if indicated
• Step 6 Pulp protection
• Step 7 Secondary resistance retention form
• Step 8 Procedure for finishing external walls
• Step 9 Final procedures

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Removal of any remaining infected dentin if
indicated

• Definition
• The elimination of any infected carious tooth
  structure or faulty restorative material left in
  the tooth after initial cavity preparation.

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Removal of dentinal caries using round burs and
spoon excavators
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Pulp protection

• Using liners or bases to protect the pulp or
  to aid pulpal recovery or both.
• If the infected dentin more than 2 mm deeper
  from the initial pulpal or axial wall then a
  Liner is indicated.

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• Final cavity preparation stage..
• Step 5 Removal of any remaining infected
• dentin if indicated
• Step 6 Pulp protection
• Step 7 Secondary resistance retention form
• Step 8 Procedure for finishing external walls
• Step 9 Final procedures

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Secondary resistance and retention forms

• Most compound and complex cavity preparations
  require additional resistance and retention form.
• The exception being those preparations that are
  very conservative.

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Secondary resistance and retention forms

• Mechanical forms
• Cavity wall conditioning form

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• Mechnical form
• Proximal locks
• Proximal slots

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Proximal locks
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Slot on gingival wall
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• Final cavity preparation stage.
• Step 5 Removal of any remaining infected
• dentin if indicated
• Step 6 Pulp protection
• Step 7 Secondary resistance retention form
• Step 8 Finishing external walls
• Step 9 Final procedures

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Finishing the external walls

• Definition
• Finishing the preparation walls is the further
  development of a specific cavosurface design and
  degree of smoothness that produces the maximum
  effectiveness of the restorative material being
  used.

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Finishing the external walls

• Objectives
• To create the best marginal seal possible
  between the restorative material and tooth
  structure
• To afford a smooth marginal junction
• To provide maximum strength of both the tooth
  and the restorative material at and near the
  margin.

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The strongest enamel margin is that margin which
is composed of full-length enamel rods that are
supported on the cavity side by shorter enamel
rods, all of which extend to sound dentin.
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Finishing the external walls

• The design of the cavosurface angle
• The degree of smoothness of the wall

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The design of the cavosurface angle depending on
the material

• Amalgam 90
• Composite beveling 30 40

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• Final cavity preparation stage..
• Step 5 Removal of any remaining infected
• dentin if indicated
• Step 6 Pulp protection
• Step 7 Secondary resistance retention form
• Step 8 Procedure for finishing external walls
• Step 9 Final procedures

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Final procedures

• cleaning
• inspecting
• varnishing
• conditioning

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Multiple Choice Questions

• Q.1. In cavity prepartion cavo-surface margin
  will be a junction between
• a) Cavity wall/floor and adjacent tooth surface.
• b) Cavity wall and floor.
• c) Floor of the occlusal box and aproximal box
• d) Axial wall and occlusal floor.

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• Q.2 Toilet of the cavity is
• a) Removal of debris by washing with water
• b) Removal of debris by cold air
• c) Removal of debris by hot air
• d) Washing the cavity with water.

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• Q.3 Most common fracture seen in amalgam
  restoration at
• a) Cavosurface margin.
• b) Contact area
• c) Isthmus area
• d) Proximal box

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• Q 4 G. V Black concluded that following area of
  tooth surface are relatively non-selfcleansing
• A) Pit and fissures
• B) Tips and cusps
• C) Fossa
• D) Marginal ridge

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• Q.5 Class III amalgam restorations areusualy
  prepared on
• a) Distal surface of anterior teeth
• b) Mesial surface of canine
• c) Distal surface of canine
• c) Mesial and distal surface of all teeth.