Tooth preparation

1. Principle of Tooth
preparation
UNIVERSITY OF MOSUL
COLLEGE OF
DENTISTRY
Omar rahawi
2020-2021
Department of
Conservative
Dentistry
3rd YEAR

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. Extension for Prevention
GV Black noted that, in tooth preparations for smooth-
surface caries, the restoration should be extended to areas
that are normally self-cleansing to prevent recurrence of
caries. This principle was known as extension for prevention
and was broadened to include the extension necessary to
remove remaining enamel defects, such as pits and fissures.
extension for prevention to include the full length of enamel
fissures has been reduced by treatments that conserve tooth
structure; therefore restored teeth are stronger and more
resistant to fracture. Such treatments are enameloplasty of
pit-and-fissure sealant and the preventive resin or
conservative composite restoration.

4. Enameloplasty
procedure of reshaping the enamel surface
with suitable rotary cutting instruments is
Sometimes a pit or groove (fissured or not) does
not penetrate to any great depth into the enamel
and does not allow proper preparation of tooth
margins, except by undesirable extension. This is
always true of the end of a fissure. If such a
shallow feature is removed and the convolution
of the enamel is rounded or
"saucered," the area becomes cleanable,
finishable, and allows conservative placement of
preparation margins.

6. Step 1: Outline Form and Initial
Depth
Definition
Establishing the outline form means:
placing the preparation margins in the
positions they will occupy in the final
preparation,

7. Principles
The three general 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.

8. Rules for establishing outline form for tooth
preparation
1. Extend the preparation margin until sound
tooth structure is obtained and no unsupported
and/or weakened enamel remains.
2. Avoid terminating the margin on extreme
eminence’s such as cusp heights or ridge crests.
3. If the extension from a primary groove
includes one half or more of the cusp incline,
consideration should be given to capping the
cusp.

9. 4. Extend the preparation margin to include all of
the fissure that cannot be eliminated by
appropriate enameloplasty.
5. Restrict the pulpal depth of the preparation to a
maximum of 0.2 mm into dentin .
6. 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.
7. Extend the outline form to provide sufficient
access for proper tooth preparation, restoration
placement, and finishing procedure

10. 8. Restrict the axial wall pulpal depth of the proximal
preparation to a maximum of 0.2 to 0.8 mm into dentin
9. Usually, gingival margins of tooth preparations are
extended apically of the proximal contact to provide
a minimum clearance of 0.5 mm between the gingival
margin and the adjacent tooth
10. The facial and lingual margins in proximal tooth
preparations usually are extended into the respective
embrasures to provide specified clearance between the
prepared margins and the adjacent tooth.

11. Step 2: Primary Resistance Form
Definition.
Primary resistance form may be defined as that shape
and placement of the preparation walls that best
enable both the restoration and the tooth to withstand,
without fracture, masticatory forces delivered
principally in the long axis of the tooth. (For
protection principally against oblique forces,
The relatively flat pulpal and gingival walls prepared
perpendicular to the tooth's long axis help resist forces in the
long axis of the tooth and prevent tooth fracture from
wedging effects

12. Principles
The fundamental principles involved in
obtaining primary resistance form are:
(1) 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 those forces of
mastication that are directed in the long axis
of the tooth.
(2) 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.

13. (3). To have a slight rounding (coving) of
internal line angles to reduce stress
concentrations in tooth structure.
(4) in extensive tooth preparations, to cap weak
cusps and envelope or include enough of a
weakened tooth within the restoration to prevent
or resist fracture of the.
tooth by forces both in the long axis and
obliquely.
(5) To provide enough thickness of restorative
material to prevent its fracture under load.
( 6) Bond the material to tooth structure
when appropriate.

15. The design features of tooth preparation that
enhance primary resistance form are as follows
1. Relatively flat floors.
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.

16. Step 3: Primary Retention Form
Definition
Primary retention form is that shape or form of the
conventional preparation that resists displacement or
removal of the restoration from tipping or lifting forces.

18. Principles
Because retention needs are related to the restorative
material used, the principles of primary retention form vary
depending on the material:
(1)For amalgam restorations in most Class I and all
Class II conventional preparations, the material is retained in
the tooth by developing external tooth walls that converge
occlusally. In this way, once the amalgam is placed in the
preparation and hardens, it cannot dislodge without some
type of fracture occurring.
This convergence should not be overdone for fear of
leaving unsupported enamel rods on the cavosurface margin
of the occlusal surface.

19. Adhesive systems provide some retention by
micromechanically bonding amalgam to tooth
structure and also reducing or eliminating micro
leakage
Composite restorations primarily are
retained in the tooth by a micromechanical
bond that develops between the material and
etched and primed prepared tooth structure.
Cast metal (usually a gold alloy) intracoronal
restorations rely primarily on almost parallel
vertical (longitudinal) walls to provide
retention of the casting in the tooth. During
initial tooth preparation.

20. Step 4: Convenience Form
Convenience
form is that shape or form of the preparation
that provides for adequate observation
,accessibility, and ease of operation in preparing
and restoring the tooth.
obtaining this form may necessitate
extension of distal, mesial, facial, or lingual
walls to gain adequate access to the deeper
portion of the preparation.

21. FINAL TOOTH PREPARATION STAGE
Step 5: Removal of Any Remaining Enamel Pit or
Fissure, Infected Dentin, and/or Old Restorative
Material,
if Indicated:
Definition
Removal of any remaining enamel pit or fissure,
infected dentin, and/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.

22. Any remaining old restorative material should be
removed if any of the following conditions are present:
(1) the old material may affect negatively the
esthetic result of the new restoration (i.e., old
amalgam material left under a new composite
restoration).
(2) The old material may compromise the
amount of anticipated needed retention
(3) radiographic evidence indicates caries is
under the old material.

23. Step 6: Pulp Protection, if Indicated
Although the placement of liners and bases
is not a step in tooth preparation in the strict
sense of the word, it is a step in adapting the
preparation for receiving the final restorative
material.
The reason for using traditional liners or
bases is to either protect the pulp or to aid pulpal
recovery or both. However, often, neither liners
nor bases are needed. When the thickness of
the remaining dentin is minimal.

24. How to protect pulp
(1) removal of infected dentin should
continue until the remaining dentin
feels as hard as normal dentin.
(2) heavy pressure should not be
applied
(3) air or air water coolant.

25. Step 7: Secondary Resistance and Retention Forms:
After removal of any remaining enamel pit or fissure,
infected dentin, and/or old restorative material additional
resistance
and retention features may be deemed necessary for the
preparation. Many compound and complex preparations
require these additional features.
The secondary retention and resistance forms are of two
types:
(1) Mechanical preparation features and
(2) Treatments of the preparation walls with etching,
priming, and adhesive materials.

26. Mechanical Features.
A variety of mechanical alterations to the
preparation enhance retention form, and these
alterations require additional removal of tooth
structure.
Retention locks, grooves, and coves. Vertically
oriented retention locks and retention grooves.

27. Step 8: Procedures for Finishing the
External Walls
of the Tooth Preparation:
Finishing the preparation walls is the
further development, when indicated,
of a specific cavosurface design and
degree of smoothness or roughness
that produces the maximum
effectiveness of the restorative
material being used.

28. The following factors must be considered in the finishing of
enamel walls and
margins
The direction of the enamel
rod
The support of the enamel rods both at the DEJ and
laterally (preparation side).
The type of restorative material to be placed in the
preparation,
The location of the
margin
The degree of smoothness or roughness
desired.

29. The enamel rods radiate from the DEJ to
the external surface of the enamel and are
perpendicular to the tooth surface. All rods
extend full length from the dentin to the
enamel surface.
The design of the cavosurface angle is
dependent on the restorative material being
used. Because of the low edge strength or
friability of amalgam, a tooth preparation
cavosurface angle of 90 degrees produces
maximal strength for both the amalgam and
the tooth. Thus, no bevels are placed at the
cavosurface
margin.