2. DEFINITION OF TOOTH PREPARATION
Tooth preparation is the mechanical alteration of a defective, injured, or
diseased tooth to receive a restorative material that re-establishes a healthy
state for the tooth, including esthetic corrections: where indicated and
normal form and function.
3. OBJECTIVES OF TOOTH PREPARATION
Remove all defects and provide necessary protection to the pulp
Extend the restoration as conservatively as possible.
Form the tooth preparation so that under the force of mastication the tooth
or the restoration orboth will not fracture and the restoration will not
fracture & the restoration will not displaced, and (4) allow for the esthetic
and functional placement of a restorative material.
4. TOOTH PREPARATION TERMINOLOGY
Tooth preparation walls
Internal wall-An internal wall is prepared surface that does not extend to
external tooth surface.
Axial Wall – An axial wall is an internal wall parallel with the long axis of the toot
Pulpal Wall- A pulpal wall is an internal wall that is perpendicular to the long axis
of the tooth and occlusal of the pulp.
5. External Wall An external wall is a prepared (cut) surface that extends to the
external tooth surface. Such a wall takes the name of the tooth surface (or
aspect) that the wall is toward
Floor (or Seat)- A floor (or seat) is a prepared wall that is reasonably flat and
perpendicular to the occlusal forces that are directed occlusogingivally
(generally parallel to the long axis of the tooth Examples are the pulpal and
gingival walls.
Enamel Wall The enamel wall is that portion of a prepared external wall
consisting of enamel
Dentinal Wall: The dentinal wall is that portion of a prepared external wall
consisting of dentin, in which mechanical retention features may be located.
6.
7. TOOTH PREPARATION ANGLES
Line angle. A line angle is the junction of two planal surfaces of different
orientation along a line.
An internal line angle is a line angle whose apex points into the tooth
An external line angle is a line angle whose apex points away from the tooth
Point angle- a point angle is the junction of three planal surface of different
orietation
8. CLASSIFICATION OF TOOTH PREPARATION
Class I Restoration
All pit rand-fissure restoration are class I and they are assigned to three groups.
Restoration on Occlusal Surface of Premolars & Molars.
Restorations on Occlusal Two Thirds of the Facial and lingual surfaces of Molars.
Restoration on lingual Surface of Maxillary Incisor
class II Restorations,
Restorations on Proximal surface of posterior teeth are Class II
9. Class III Restorations
Restorations on the proximal surface of anterior teeth that do not involve the incisal angle are Class III.
Class IV Restoration
Restorations on the proximal surfaces of anterior teeth that do involve the incisal edge are class IV
Class V Restorations
Restoration on the gingival third of the Facial or lingual surface of all teeth(except pit-and-fissure lesions) are Class V
Class VI Restorations
oRestorations on the incisal edge of anterior teeth or the occlusal cusp height of posterior teeth are class VI
10. INITIAL AND FINAL STAGES OF TOOTH
PREPARATION
Initial tooth preparation stage
Step 1: Outline form and initial depth
Step2 Primary resistance form
Step3 Primary retention form
Step4 Convenience form
11. Final tooth preparation stage
Step 5 Removal of any remaining infected dentin or
oldrestorative material (or both), if indicated
Step 6: Pulp protection, if indicated
Step 7: Secondary resistance and retention forms
Step 8: Procedures for finishing external walls
Step 9: Final procedure-cleaning, inspecting sealing
12. INITIAL TOOTH PREPARATION STAGE
Initial tooth preparation is the extension and initial design
of external walls of preparation at a specified limited
depth so as to provide access to the caries or defect,
reach sound tooth Structure, resist fracture of the tooth
restorative material from masticatory forces principally
directed with the long axis of the tooth, and retain the
restorative material in the tooth.
13. STEP 1: OUTLINE FORM AND INITIAL
DEPTH
Def
Establishing the outline form means(1) placing the
preparation margins in the positions they will occupy in the
final preparation except for Finishing enamel walls and
margins and (2) preparing an initial depth of 0.2 to 0.8 mm
pulpally of the Postion or root-surface position
14. PRINCIPLE
All friable or weakened enamel should be removed
All faults should be included and
All margins should be in a position to afford good
finishing of the margin of the restoration.
15. FEATURES…
1) Preserving cuspal strength
2) preserving marginal ridge strength
3) Minimizing faciolingual extension
4) using enamelopasty
5) Connecting two close faults or tooth preparation
6) Restricting the depth of the preparation into dentin to a
maximum of 0.2mm for pit & fissure caries and 0.2 to 0.8
mm for axial wall of smooth surface caries.
16. STEP 2. PRIMARY RESISTANCE FORM
Def:
Primary Resistance form may be defined as the shape and
placement of preparation walls that best enable the
restoration and the tooth to withstand, without Fracture,
masticatory forces delivered principally in the long axis of
the tooth.
17. PRINCIPLE
1) To use the box shape with a relativity flat floor which helps the tooth resist
occlusal loading by virtue of being at right angles to the forces of mastication
that are directed in the long axis of the tooth
2) to restrict the extension of the external walls to allow strong cusp and ridge
areas to remain with sufficient dentin support
3) to have a slight rounding of internal line angles. To reduces stress
concentration in tooth structure
4) to cap weak cusps and envelope
5) to provide enough thickness of restorative material to prevent its Fracture
under load and
6) to bond the material to tooth structure when appropriate.
18.
19. FEATURES:
Relatively flat floors
Box shape
Inclusion of weakened tooth structure
Preservation of cusps & marginal ridges
Rounded internal line angles
Adequate thickness of restorative material
Reduction of cusps for capping when indicated
20. STEP3: PRIMARY RETENTION FORM
Def:
Primary Retention form is the shape or form of the
conventional preparation that resists displacement or
removal of restoration by tipping or lifting forces.
21.
22. STEP4: CONVENIENCE FORM
Convenience form is the shape or form of
preparation that provide for adequate
observation, accessibility and ease of operation in
preparing & restorating the tooth.
23. STEP 5: REMOVAL OF ANY REMAINING ENAMEL
PIT OR FISSURE, INFECTED DENTIN, OR OLD
RESTORATIVE, IF INDICATED.
Removal of any remaining enamel pit or fissure
infected dentin, or old Restorative material is the
elimination of any infected carious tooth
Structure or faulty restorative material left in the
tooth after initial tooth preparation..
24. ANY REMAINING OLD RESTORATIVE MATERIAL
SHOULD BE REMOVED IF ANY OF THE
FOLLOWING CONDITIONS ARE PRESENT
The old material may affect negatively the esthetic result
of the new restoration.
the old material may compromise the amount of
anticipated needed retention.
Radiographic evidence indicates caries is Under the old
material.
The tooth pulp was symptomatic preoperatively
The periphery of the remaining old restorative material is
not intact.
25. STEP 6: PULP PROTECTION, IF INDICATED
The reason for using traditional liner or bases is to protect
the pulp or to aid pulpal recovery or both.
Other pulpal irritants that affect operative procedure Are:
Some ingredients of various materials
thermal changes conducted through restorative
force transmitted through material to the dentin
Galvanic shock and most importantly
The ingress of noxious products & bacteria through
microleakage.
26. Liners also may provide
1) A barrier that protects the dentin from noxious agents
from restorative material oral fluids
2) Initial electrical insulation
3) Some thermal protection
Ex-of bases include zinc phosphate, zinc oxide eugenol
calcium hydroxide, polycarboxylate & glass ionomer
27. STEP 7… SECONDARY RESISTANCE &
RETENTION FORMS
The secondary retention and resistance form are of two types…
1. Mechanical preparation feature –
Retention locks, Grooves & Coves ,
Groove Extensions, Skirts
Beveled Enamel Margins
Pins, Slots, Steps, Amalgampins
2.Treatments of preparation walls with etching,priming & adhesive
materials-
Enamel Wall Etching
Dentin Treatment.
28. STEP 8: PROCEDURE FOR FINISHING THE
EXTERNAL WALLS
Finishing the preparation wall is the further development,
when indicated, of a specific Cavosurface design & degree of
smoothness or roughness that produces the maximum
effectiveness of the restorative material being used.
Objectives: -
create the best marginal seal possible between the
restorative material and the tooth strcture.
Afford a smooth marginal junction and
provide maximal strength of the tooth & the restorative
material at & near the margin
29. FEATURES
1) the design of the cavosurface angle &
2) The degree of smoothness or roughness of wall.
Cavosurface angle of 90° produces maximal Strength for
the amalgam & the tooth. No bevels placed at the
cavosurface margin.
Beveling can serve useful purpose in tooth preparation
1) It produces a strong enamel margin
2) It permits a marginal seal in slightly undersized Casings.
30. STEP. 9: FINAL PROCEDURE: CLEANING,
INSPECTING. & SEALING
The usual procedure in cleaning is to free the
Preparation of visible debris with warm water
from the syringe & then to remove the visible
moisture with a few light surges of air from the
air syringe.
