A presentation on fundamentals in tooth preparation. book referred : Sturdevant's

1. Definition (STURDEVANT) :
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.

2. INITIAL TOOTH PREPARATION STAGE:
 Step 1: Outline form and initial depth
 Step 2: Primary resistance form
 Step 3: Primary retention form
 Step 4: Convenience form
FINAL TOOTH PREPARATION STAGE:
 Step 5: Removal of any remaining infected dentin and/or old restorative
material, 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 procedures: cleaning, inspecting, sealing

3. ‘Initial tooth preparation is 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 the tooth,
and retain the restorative material in the tooth.’
-
Sturdevant

4. Step 1: Outline Form and Initial Depth
Step 2: Primary Resistance Form
Step 3: Primary Retention Form
Step 4: Convenience Form

5. OUTLINE FORM AND INITIAL DEPTH
DEFINITION

6. PRINCIPLES
1. All friable and/or weakened enamel 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
restoration.

7.  Extent of carious lesion, defect or faulty old restoration.
 Esthetic considerations.
 Occlusal requirements.
 Adjacent tooth contour.
 Cavosurface marginal configuration which varies with type
of restorative material used.

8.  Preserving cuspal strength
 Preserving marginal ridge strength
 Minimizing faciolingual extension
 Using enameloplasty
 Connecting two close(less than 0.5 mm apart) faults or tooth
preparations
 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

9. FACTORS CONTROLLING OUTLINE FORM IN PIT-AND-FISSURE LESIONS
The extent to which the enamel has been involved by the carious
process
The extensions that must be made along the fissures to achieve sound
and smooth margins
The limited bur depth related to the tooth’s original surface while
extending the preparation
to sound external walls that have a pulpal depth of approximately 1.5 to
2 mm and usually a maximum depth into dentin of 0.2 mm

10.  Extend the preparation margin until sound tooth structure is obtained
and no unsupported and/or weakened enamel remains.
 Avoid terminating the margin on extreme eminences such as cusp
heights or ridge crests.
 If the extension from a primary groove includes one half or more of
the cusp incline, consideration should be given to capping the cusp. If
the extension is two-thirds, the cusp-capping procedure is most
often the proper procedure which removes the margin from the area
of masticatory stresses.
 Extend the preparation margin to include all of the fissure that cannot
be eliminated by appropriate enameloplasty.

11.  Extend the preparation margin to include all of the fissure that cannot
be eliminated by appropriate enameloplasty
 Restrict the pulpal depth of the preparation to a maximum of 0.2 mm
into dentin
 When two pit-and-fissure preparations have less than 0.5 mm of sound
tooth structure between them, they should be joined to eliminate a
weak enamel wall between them.
 Outline form should be extended to provide sufficient access for proper
tooth preparation, placement of restorations and finishing procedures.

12. Rule for cusp capping: If extension from a primary groove toward the cusp tip is no
more than half the distance, then no cusp capping; if this extension is from one half
to two thirds
of the distance, then consider cusp capping; if the extension is more than two thirds
of the distance, then usually cap the cusp.

13. A, Enameloplasty on area of imperfect coalescence of enamel.
B, No more than one-third of the enamel thickness should be
removed.

14. Smooth-surface lesions occur in two very different locations:
(1) proximal surfaces or
(2) gingival portion of the facial and lingual surfaces
Rules for establishing outline forms for proximal surface tooth preparations
(class II, III, and IV):
 Preparation margins should be extended until sound tooth structure is
obtained and no unsupported and/or weakened enamel remains.
 Avoid terminating the margin on extreme eminences such as cusp heights
or ridge crests.
 Extend the margins to allow sufficient access for proper manipulative
procedures.
 Restrict the axial wall pulpal depth of the proximal preparation to a
maximum of 0.2 to 0.8 mm into dentin.

15.  Provide minimal clearance of 0.5 mm between the gingival margins
and adjacent tooth.
 Place the facial and lingual margins in proximal preparations into
respective embrasures to provide specified clearance between
margins and adjacent tooth.
 Axial wall should follow the contour of the external tooth surface or
the curvature of the DEJ buccolingually and occlusogingivally.
 In Class III preparations, the incisal margin may be placed in the area
of contact, especially when an esthetic restorative material is used or
when the incisal embrasure is not large enough to allow extension
incisal of contact and still have a strong incisal angle of the tooth.

16. FACTORS CONTROLLING OUTLINE FORM OF CLASS V TOOTH PREPARATION:
 Extent of the lesion (except pulpally)
RULES FOR ESTABLISHING OUTLINE FORM FOR CLASS V LESION:
 Extend the preparation mesially, distally, gingivally and occlusally (incisally) till the
sound tooth structure is reached.
 The axial wall pulpal depth at the gingival wall without an enamel portion should be
0.8 mm
 The axial wall pulpal depth at the occlusal wall should be more, i.e. 0.5 mm
extension into dentin

17.  DEFINITION (Sturdevant)
Primary resistance form may be 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 the tooth.

18.  To use the box shape with a relatively 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
 To restrict the extension of the external walls to allow
strong cusp and ridge areas to remain with sufficient
dentin support
 To have a slight rounding of internal line angles to
reduce stress concentrations in tooth structure
PRINCIPLES

19. To cap weak cusps and envelope or include enough of the
weakened tooth structure within the restoration in extensive
tooth preparations to prevent or resist fracture of the tooth
by forces in the long axis and obliquely directed forces
To provide enough thickness to restorative material to
prevent its fracture under load
To bond the material to tooth structure when appropriate

20. FACTORS AFFECTING RESISTANCE FORM
 Assessment of the occlusal contact on the
restoration and remaining tooth structure.
Amount of remaining tooth structure ( eg. In class IV
restorations , the cavity is kept narrow faciolingually to
obtain resistance form)
All weakened , friable tooth structure should always be
removed.

21. Enhancement of the resistance form by bonding the
restoration to the remaining tooth.
Type of restorative material- The minimum thickness
of restorative material required for restoration with :-
amalgam 1.5 mm, cast restoration 1 mm ,ceramics 2
mm; to resist fracture.
Occlusal stresses on the tooth ( Greater the occlusal
force , the greater is the potential for future fracture)

22. FEATURES
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

23. Resistance forms must consider resistance of tooth to fracture from forces exerted on
restoration.
Flat floor (A) will help prevent restoration movement, whereas rounded pulpal floor
( B) may allow a nonbonded restoration rocking action producing a wedging force,
which may result in shearing of tooth structure

24.  DEFINITION (Sturdevant)
Primary retention form is the shape or form of the
conventional preparation that resists displacement or
removal of the restoration by tipping or lifting forces.
Although they are separate entities,the same prepared form
may contribute to both resistance and retention qualities of the
preparation.

25. PRINCIPLES
For Amalgam restorations :-
 In most class I and all class II preparations, the amalgam is retained
in the tooth by developing external tooth walls that converge
occlusally
 Occlusal convergence of the proximal portion helps in conserving
the marginal ridges
 The cavosurface angle where the proximal facial and lingual surfaces
meet the marginal ridge is a desirable 90 degrees because of the
occlusal convergence of the preparation
 Adhesive systems provide some retention by micromechanically
bonding amalgam to tooth structure and reducing or eliminating
microleakage.

26. For Composite restorations :-
Composite restorations are retained in the tooth by a
micromechanical bond that develops between the material
and the etched and primed prepared tooth surface.
The enamel and dentin are etched by an acid ,and the
dentin is primed with a dentin bonding agent before
placement of the composite.
Other conventional- type composite restorations may
require a separate enamel bevelling procedure that would
be done in final tooth preparation.

27. For Cast Metal restorations :-
Close parallelism of the opposing walls, with small angle of
divergence (2-5 degrees) from the line of draw , helps in
enhancing retention.
The degree of divergence needed primarily depends on
the length of the prepared walls: the greater the vertical
height of the walls , the more divergence is permitted , but
within the range mentioned.
In class II preparations , an occlusal dovetail may aid in
preventing the tipping of the restoration by occlusal forces.

28. Basic primary retention form in Class II tooth preparations
for amalgam
(A) with vertical external walls of proximal
and occlusal portions converging occlusally and for inlay
( B) with similar walls slightly diverging occlusally.

29. DEFINITION (Sturdevant)
 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.

30. FEATURES
• Obtaining this form may necessitate extension of distal,
mesial, facial or lingual walls to gain adequate access to
the deeper portion of the preparation.
• Occlusal divergence of vertical walls in class II cast
restorations.
• Extending proximal preparations beyond proximal
contacts ie. Proximal clearance of contact area