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Untitled Prezi

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by

Raghad Al Hammad

on 9 April 2014

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Fundamental principles of tooth preparation
Definition of Tooth Preparation
The mechanical alteration of defective, injured, or diseased tooth to best receive a restorative material that will reestablish a healthy state for the tooth, including esthetic corrections where indicated, along . with normal form and function
Objectives of Tooth Preparation
Remove all defects & provide necessary protection to the pulp
Form the tooth preparation so that under masticatory forces the tooth or restoration will not fracture or the restoration will not be displaced
Allow for functional & esthetic placement of restorative material
Extend the restoration as conservatively as possible
Operative Treatment Goals
should preserve & restore:
Tooth morphology

should preserve & restore:
Function
Aesthetics
Pulpal health

should preserve & restore:
should preserve & restore:
Factors Affecting Tooth Preparation
knowledge of
dental anatomy
patient factor
conservation of
tooth structure
restorative material
factor
diagnosis
G . V black calcification
Class I
In the early 1900’s, a dentist by the name of G.V. Black devised a method of classifying dental caries according to its location on the tooth surface. This method is known as Black’s Classification of Cavities and is used in dentistry today
The father of operative dentistry
Class II
Class III
Class IV
Class V
Class VI
never described by Black, added later by others
Principle of tooth preparation

Biological form

Mechanical form

BIOLOGICAL FORM OF TOOTH PREPARATIONS:

I. PROTECTION OF THE PULP
Cutting must be parallel to the recessional lines of the pulp.
Unnecessary pressure is unacceptable.
Limiting the exposed amount of dentin.
Unnecessary heat generation should be avoided during cutting.
Large round burs should be used at low speed while removing soft dentin cavity floors.
No Cavity caustics, chemicals or sterilizers should be used.

II. PREVENTION OF CARIES RECURRENCE
Removing all carious enamel or dentin.
Extension of the cavity margins to include all areas susceptible to caries as pits and fissures.
Removal of all undermined enamel.
Correct Cavo-surface angle according to the physical characteristics of the restoration type must be performed.

1-OUTLINE FORM & INITIAL DEPTH
placing the preparation margins in the positions they will
occupy in final preparation and Preparing an initial depth of 0.2 - 0.8mm
pulpally of DEJ


6- esthetics
It is important to maximize the conservation of tooth structure, because the natural tooth is the most esthetic

3- Relationship of self cleansable areas to outline form
all margins are located in areas easily cleansed by the patient, These areas are found on :
Smooth surfaces above the height of contour.
occlusal cusp inclines.
incisal edges.
cusp tips.

1- Location and extent of carious lesion
The cavity preparation must be extended sufficiently to include the entire carious area
Unsupported enamel (Undermined Enamel) should be removed during cavity preparation, since it is liable to fracture creating open marginal areas which may lead to secondary decay
Conservation of tooth structure must be considered .
Two separate cavities should not be united unless the separating ridgeis less than 0.5mm

FACTORS
PRINCIPLES
All friable or/and 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 restoration

2- Position of pits & fissures
areas of tooth with caries susceptibility are usually included "extension for prevention"

4- Preservation of healthy and vital tooth structure
The dentin surrounding the pulpal horns should be conserved to insulate- and strengthen the restored tooth. The outline is curved and flowing and is constricted as it curves around the cusps.

5- Restorative material
Individual properties of each material utilized to restore teeth demand certain design factors that must be incorporated into each cavity preparation
7- Functional requirements of the restoration
A restoration cannot be considered successful unless it fulfills the functional requirements of the tooth.

Amalgam
Box-shaped cavities, flat walls parallel with or perpendicular to the tooth surface.
Thickness of amalgam should be in the range of 2mm
composite resin
Placing a bevel and etching the enamel at the cavo-surface angle to improve the marginal seal
2-Performing resistance &retention form

primary retention form
Primary resistance form

It is the shape and placement of the cavity walls that enable the tooth and restoration to withstand Masticatory forces without fracture.

It is that shape or form of the conventional preparation that resists displacement or removal of the restoration from tipping or lifting forces

secondry resistance & retention form
PRINCIPLES

box shape

Keep the cavity as small as possible.

rounding of internal line angles

cap week cusps

provide enough thickness of restorative materials

provide enough thickness of restorative materials

Factors
Cavity wall angulations

Cavity preparation depth

Internal line angles

Type of restorative material used

Features

Relatively horizontal floor

Inclusion of weakened tooth structure

Preservation of cusps and marginal ridges

Adequate thickness of restorative material

Reduction of cusps for capping

Rounded internal line angles

Box-like
shape

principles
Vary depending on the
restorative material used..

composite
Micromechanical bond
to enamel & dentin by acid itching
Indirect restoration

Porcelain
& Cast

-Diverging wall with taper
-occlusal dovetail
-using 2ry retintion form coves, skirts& dentin slots
amalgum
-Convergence occlusal
-Undercuts .
-Conserve the marginal ridge.
-dovetail.
-elastic deformation of dentin
Direct restoration

Factors
Amount of masticatory stresses falling on the restoration
Thickness of the restoration

Total surface area of the restoration exposed to masticatory forces
the amount of remaining tooth structure
3- Convenience form

Definition: The form of cavity preparation that the dentist must create adequate observation & accessibility to facilitate visibility in preparing & restoring the cavity
4- Removing of
any remmaning infected dentine
It is the elimination of any infected carious tooth structure or  faulty restorative material that is left in the tooth after tooth preparation
Affected dentine
This is the deeper layer which is hard and dark brown in color. It does not contain bacteria. Therefore this layer preserved (don't remove )

Also considered as secondary dentine that prevent invasion of caries
Infected dentine
superficial layer which is soft and light brown in color.
high concentration of bacteria . (must be removed)

States of dentine

Providing adequate depth and proximal extension for tooth preparation to access deeper parts of the cavity
Providing proximal clearance from adjacent tooth enhances  convenience form

Occlusal divergence for cast restoration class II preparation

Features
In large preparation with extensive soft caries , the removal of infected dentine may be accomplished early in initial tooth preparation
FEATURES
pit-and-fissure lesion
Controlled by three factors:

1. The extent to which the enamel has been involved by the carious process
2. The extensions that must be made along the fissures to achieve sound and smooth margins
3. The limited bur depth related to the tooth's original surface

smooth-surface lesion
smooth-surface lesion occure in two very different location:

1. Proximal surfaces
2. The gingival portion of the facial and lingual surfaces

Remove of the
soft caiers
( infected dentine )


Large area of soft caries usually are best removed with spoon excavator by flaking up the caries around the periphery of the infected mass and peeling it off in layers
5- Finishing of enamel & external cavity wall

Finishing of the enamel should be done irrespective of restorative material used.
It has been shown that better marginal adaptation of restoration to the walls and the margins is obtainable when enamel is smooth.
Also, maximum effectiveness of the restoration
so we get
1- Better marginal seal between restoration and tooth structure.

2- Increased strength of both tooth structure and restoration
Factors
1- Direction and support of enamel rods at DEJ and cavity margins.
2- Type of restorative material to be used.
3- Location of the margin.
4- Degree of smoothness / roughness desired.
Flushing the cavity with warm water to remove debus
Lightly air drying the cavity with the air syringe
Using a sealer when indicted (e.g. dentin bonding agent)
6- Cleaning & toileting


Many preparation require additional retentive features .When the tooth preparation include both occlusal and proximal surfaces each of those area should have independent retention and resistance features
Mechanical features
Retention locks, grooves and coves
Grooves extension
skirts
Beveled
enamel margins
Conditioning procedures-etching and bonding
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