OPERATIVE DENTISTRY

1. Tooth
Preparatio
n
B Y D R A M B A L I K A R A J

2. Contents
• Definition
• Objectives
• Terminology
• Tooth preparation terminology
• Classification of tooth preparation
• Initial stage of tooth preparation
• Final stage of tooth preparation
• Additional concepts in tooth preparation

3. Definition
• Tooth preparation is the mechanical alteration of a defective, injured, or diseased tooth such that
placement of restorative material reestablishes normal form (and therefore function) including
esthetic corrections, where indicated. ( Sturdevant )

4. Objectives
conserve as much healthy tooth structure as possible,
Conserve
remove all defects while simultaneously providing protection of the pulp–dentin complex,
Remove
form the tooth preparation so that, under the forces of mastication, the tooth or the restoration
(or both) will not fracture and the restoration will not be displaced, and
Form
allow for the esthetic placement of a restorative material where indicated.
Allow

5. Terminology
1. Anatomic crown
2. Clinical crown
3. Crystalline restorative material
4. Polymeric restorative material
5. Intracoronal tooth preparation
6. Extracoronal tooth preparation

6. Extracoronal preparation

7. Simple tooth preparation - only one tooth surface is involved ,eg, O
Compound - two or three surfaces are involved , e.g. MO
Complex – 4 or more surfaces involved , e.g. MODL

8. 4. Internal wall – A prepared surface that
does not extend to the external tooth surface.
E.G. axial wall , pulpal wall.
A. Axial wall - an internal wall that is oriented
parallel to the long axis of the tooth.
B. Pulpal wall - an internal wall that is oriented
perpendicular to the long axis of the tooth and
is located occlusal to the pulp.
5. External wall - A prepared surface that
extends to the external tooth surface.

9. 6. Enamel wall - that portion of a prepared external wall consisting of
enamel.
7. Dentinal wall - that portion of a prepared external wall consisting of
dentin, in which mechanical retention features may be located .
8.Tooth preparation features or sections that are parallel (or nearly so)
to the long axis of the tooth crown are commonly described as vertical,
such as vertical height of cusps, or vertical walls. The term longitudinal
may be used in lieu of vertical.
9.Tooth preparation features that are perpendicular (or nearly so) to the
long axis of the tooth are termed horizontal or transverse.

11. 10. A line angle is the junction of two planar
surfaces of different orientation along a line .
a. An internal line angle is the line angle
whose apex points into the tooth.
b. The external line angle is the line angle
whose apex points away from the tooth.
11. The point angle is the junction of three
planar surfaces of different orientation.

13. 12. Cavosurface angle - The angle of tooth
structure formed by the junction of a prepared wall
and the external surface of the tooth. The actual
junction is referred to as cavosurface margin.

14. Classification of
tooth
preparation

15. G.V. Black's Classification

17. Stages of cavity
preparation
Initial tooth
preparation
stage
Final tooth
preparation
stage

18. Initial tooth preparation stage is defined as the extension and initial design of the
external walls of the preparation, at a specified , limited depth so as to provide access
to the caries or defect , reach sound tooth structure ( except for later removal of
infected dentin on the pulpal or axial walls), resist fracture of the tooth or restorative
material from masticatory forces principally directed with the long axis of tooth , and
retain the restorative material in the tooth ( except for a class V preparation ) -
Sturdevant

19. Steps in initial tooth
preparation
Step 4 Covenience form
Step 3 Primary retention form
Step 2 Primary resistance form
Step 1 Outline form and initial depth

20. Step 1 – Outline form and initial
depth
• Establishing the outline form means
(1) placing the preparation margins in the positions they will occupy in the final preparation except
for finishing the enamel walls and margins
(2) preparing an initial depth of 0.2 to 0.8 mm pulpally of the DEJ position or normal root – surface
position ( no deeper initially whether in tooth structure , air , old restorative material , or caries unless
the occlusal enamel thickness is minimal , and greater dimension is necessary for strength of the
restorative material ).

21. Principles -
(1) All friable or weakened enamel usually
should be removed.
(2) All faults should be included.
(3) All margins should be placed in a position
to afford good finishing of the margins of the
restotation.

22. FEATURES OF OUTLINE FORM -
(1) Preserving the cuspal strength
(2) Preserving marginal ridge strength
(3) Minimizing faciolingual extensions
(4) Using enameloplasty
(5) Connecting two close ( <0.5 mm apart ) faults or tooth
preparation
(6) Restricting the depth of the preparation into dentin to a
maximum of 0.2 mm for pit and fissure caries and 0.2 to 0.8 mm
for the axial wall of smooth surface caries.

23. • 1. Outline form for pit and fissure
caries
• Avoid terminating the margin on extreme
eminence such as cusp height.
• Extend to include all fissure mot
eliminated by enameloplasty.
• Restrict the depth to 0.2mm into dentin .
• For amalgam , depth of 1.5 mm prepared
first .
• If < 50 % enamel pit or fissure on pulpal
floor present - removed in final tooth
preparation stage.
• If enamel pit and fissure on > 50% of
pulpal floor , entire flor is deepened.

24. • Outline form for conventional amalgam preparation is = butterfly type preparation
• As much of the cuspal incline as possible should be preserved in any preparation
involving the occlusal surface.
• All developmental grooves should be included.This may necessitate extending onto the
facial or lingual SURFACES.

25. 2.Outline form for smooth surface lesion
• In 2 locations -
 Proximal surfaces
 Gingival portion of facial and lingual surfaces
A. Proximal surface -
• Extend preparation to sound tooth structure
• Avoid terminating margins on extreme eminences
• Restrict axial wall pulpal depth of proximal preparation to 0.2 to 0.8 mm into dentin.
• Gingival margins = apical to proximal contact to provide a clearance of atleast 0.5 mm between
adjacent teeth.
• Facial and lingual margins of proximal preparation extended into embrasures ( self cleansing)

26. B. Gingival portion of facial and lingual surfaces ( Class V ) -
• Outline form is determined by extent of caries except pulpally.
• Depth of 0.8 to 1.25 mm pulpally.
• In class III restoration , when extending the proximal surface
incisally , the incisal margin may be placed in the area of contact
, esp .when an esthetic material is used.

27. To do
enameloplast
y or not -
A fissure is removed by normal
procedures if it penetrates to more
than one third the thickness of the
enamel in the area.
If one third or less area is
involved , the fissure may be
removed by enameloplasty.
Also enameloplasty done when a
shallow fissure appraoches or
crosses a lingual or facial ridge.

28. Step 2 – Primary resistance
form
• It is defined as the shape and placement of the preparation walls that best enable the restoration
and the tooth to withstand , without fracture , masticatory forces delivered principally in the long
axis of tooth.

29. Stress bearing areas on tooth

30. Intracoronal cavity
can be done in box,
cone or inverted
truncated cone
shapes.
If possible walls of
preparation should
be parallel to loading
forces to minimize
shear stress.

31. • Principles of resistance form -
1. Box shaped cavity with flat floor ( resist forces by being at right angles to masticatory loads )
2. Restrct the extension of external walls to preserve ridge and cusp.
3.Slight rounding of internal line angle
4. Cap weak cusps
5. Provide enough thickness of restorative material to prevent its fracture under load.
6.Bond the material to tooth structure.( whenever possible )
- Conventional and bevelled conventional preparation have these features- require a specific form ,
depth andmarginal configuration, eg. Amagam , cast meatl and ceramic.
- Modified preparation design – small, medium composite restoration , no uniform depth – scooped
design.

32. Modified cavity preparation

35. • Minimally extended facial and lingual walls conserve dentin supporting the cusps and facial and
lingual ridges.
• Amalgam - 1.5 mm
• Cast metal - 1 to 2 mm
• Porcelain – 2mm
• Composite – 1 to 2 mm usually ( acute marginal angles )

36. Factors to consider while preparing the resistance form -
1. Occlusal contact on the restoration
2. Amount of remaining tooth structure
3. Type of restorative material used.
4. Bonding of restoration

37. Features of resistance form -
1 . Relatively flat floor
2. Box shape
3. Inclusion of weakened tooth structure
4. Preservation of cusps and marginal ridges
5. rounded internal line angles
6. Adequate thickness of restorative material
7. Reduction of cusps for capping when indicated

39. Step 3 – Primary retention form
• Primary retention form is the shape or form of the preparation that prevents displacement or
removal of the restoration by tipping or lifting forces.
• Principles -
- Depends on the restorative material used,
- Hence different principles for different material.

40. 1. Amalgam
Walls are made that converge occlusally ( class I and class II
)
Walls diverge outwardly to provide strong enamel margins (
class III and V )
Adhesive system may be used – eliminates microleakage
Occlusal dovetail
90 degrees cavosurface margin
Undercuts

41. • 2. Composite -
>90 degrees cavosurface angle
Micromechanical bond between material and etched tooth structure.
• 3. Cast metal -
Almost parallel vertical walls
Greater vertical height of walls
Occlusal divergence in inlay and onlay preparation.

42. Step 4 – Convenience form
• Convenience form is the shape or form of the preparation that provides for adequate observation,
accessibility, and ease of operation in preparing and restoring the tooth.
• Ideally a tooth preparation fulfilling all requirements for outline , resistance , retention form will be
convinient to instrumentation.
• E.g. Extension of the proximal walls, so as to obtain clearance with an adjacent proximal
surface, may aford better access for the inishing of preparation walls, the placement of the matrix,
and the inishing of the restoration margins.

43. 1.Modifications in tooth preparation for
convenience - Flaring some walls more than
necessary for retention , resistance form in order
to decrease distoretion errors in intermediate
materials during casting.
2. Modification in instruments like introduction
of contra angling , addition of several angles
to shank to facilitate access and force
application in proper direction
3. Separation – wedging teeth away from each
other to make interproximal instrumentation
convenient.