1. PRINCIPLES OF CAVITY
PREPARATIONS
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كنزارف س 3

2. PRINCIPLES OF CAVITY
PREPARATIONS
The principles of modern cavity preparation
were first defined in 1896 by Dr. G.V .
Black , a man considered by many to be the
" father of modern restorative dentistry"
when his original sequence of cavity was
one of the most important considerations of
. cavity design
2 Ass.Prof.Dr.Mohamed ALsakkaf

3. However the degree of cavity extension is
considerably less today , because of the
realization that caries , primary or secondary ,
can be more effectively controlled and
prevented by greater emphasis on oral hygiene
. by the patient
3

4. Although techniques have been refined and
outlines have been modified , Black's
principles are still used as the basic steps in
the process of designing and preparing a
cavity . The adherence to these principles
will facilitate the procedure of cavity
preparation . and decay removal
4

5. BIOLOGICAL CONSIDERATION: 'Pulp
:protection
Avoid over cutting of dentin and ( 1)
unnecessary deeping of the cavity
because the deeper the cavity the
.more irritated pulp
Unnecessary application of ( 2)
pressure in scooping out
soft dentin at the bottom of a deep
cavity, only gentle pressure, using
. sharp excavators
5

6. Unnecessary or excessive cutting of enamel, ( 3)
in order to expose only a small area of dentin
.to irritation
.Avoid heat generation( 4)
Injudicious use of rotary instruments in ( 5)
. removing soft dentin at the bottom
Don’t use chemical irritants in performing ( 6)
the toilet of the cavity. No cavity sterilization
. should be done
6

7. :STEPS
.Obtain the required outline form. 1
.Obtain the required resistance form. 2
.Obtain the required retention form. 3
.Obtain the required convenience form. 4
.Remove any remaining carious dentin. 5
.Finish the enamel wall. 6
Cleanse and medicate the cavity . 7
. preparation
7

8. Normally, these principles of cavity preparation
are followed in the sequence as Outlined
above. However , occasionally situations arise
when the operator may have to deviate from
. this sequence
8

9. In very deep Lesions, where a pulp expose is
feared or when there is gross destruction of
the tooth structure because of caries, it is
often advisable to remove the carious dentin
)Principle #5( resistance and retention from
)Principles #2 and #3(, or in extreme cases,
even before obtaining the outline form
((.))Principle #1
9

10. These principles of cavity preparation should
be understood on a biomechanical basis .
They are concerned with both the biological
structure that complement the physical and
chemical properties of the restorative
.material
10

11. The basic biological objectives of cavity
preparation procedures are the removal of
a carious lesion , and the preservation of the
optimum amount of remaining healthy
tooth structure . Within these parameters
the cavity preparation assumes a design
that includes the actual carious lesion and
the potential f . or it's future occurrence
11

12. This is reflected by the location of the cavity
margins in areas easily cleansable by the
patient and readily accessible examination
.by the dentist
The mechanical factors included in cavity
preparation are basically concerned with
the retention of the restoration and the
.continued vitality and function of the tooth
12

13. OUTLINE FROM
Obtaining or establishing the outline from
means carrying the margin of the cavity to
the position it will occupy upon completion
of the cavity. The outline should encompass
the carious lesion and may include portions
of caries – susceptible areas on the surface
.being restored
13

14. The outline form should follow a gently,
sweeping curve, especially on the occlusal
surface. Many factors govern the outline
.form of the cavity
14

15. LOCATION AND EXTENT OF THE
CARIOUS LESION
The cavity preparation must be extended
sufficiently to include the entire carious
area and the enamel which is not supported
by sound dentin. Enamel which is
unsupported is subject to fracture. This
conservation of tooth structure is of
paramount importance for the preservation
of esthetic, prevention of irritation to the
dental pulp, and the maintenance of the
natural relationship between the tooth and
.the supporting tissues 15

16. 16

17. The areas of tooth with caries susceptibility
are usually included in the outline form.
This principle is known as "extension for
prevention“. The importance of the concept
of conservation of tooth structure must be
considered. An occlusal outline form on
posterior teeth may include the fissured
primary (developmental) grooves, and in
some cases secondary grooves, as well as
buccal and lingual extensions of these
. grooves
17

18. Cavity preparation should not automatically
extend into all the developmental and
supplementary grooves, especially if : 1)
they are not carious, 2)they are not fissured
and are unlikely to become carious
18

19. RELATIONSHIP OF SELF-CLEANING
AREAS TO OUTLINE
All cavity preparations normally have their
Cavosurface margins located in areas that
are self-cleaning or are easily-cleansable by
the patient. Recurrent decay is more likely
to occur in areas of the tooth that are not
cleaned naturally by the action of the lips,
.cheek and tongue
19

20. Therefore, the dentist must design the cavity
so that all margins are located in areas
easily cleansed by the patient. These areas
are found on smooth surfaces above the
height of contour, incisal edges and cusp
.tips
20

21. PRESERVATION OF HEALTHY
TOOTH STRUCTURE
Healthy tooth structure should not be removed
unless justified since tooth structure removed
cannot be put back. However establishing the
margins of cavity preparation sometimes
necessitates the removal of some healthy tooth
structure. This may conflict with locating the
cavity margins in easily-cleansable areas since
it necessitates the removal of healthy tooth
structure. However compromise can be
.reached
21

22. 22

23. RESTORATIVE MATERIAL
Individual properties of each material utilized
to restore tooth, demand certain design
factors that must be incorporated into each
cavity preparation. For example , the
marginal strength ( also called "edge-strenght")
of dental cement and amalgam is
relatively weak , so their Cavosurface
margins must be prepared at an angle of
approximately "90d" with the tooth surf ace
to provide maximum edge strength for both
.the restorative material and the enamel
23

24. Placing a bevel and etching the enamel at the
Cavosurface angle of composite
preparations improves the marginal seal. In
some cases, the bevel may also aid in
improving the contour and esthetic qualities
.of the composite restorations
24

25. 25

26. TOOTH MORPHOLOGY
Tooth size and arch position may influence
the design of a cavity preparation.
Malpositioned and rotated teeth may
require unusual outline form because they
must be restored where they contact the
.adjacent teeth
26

27. AREAS OF ENAMEL
DECALCIFICATION
These areas may have to be included in the
outline form. Areas of decalcified or chalky
enamel are usually included in the outline
form. This prevents future marginal
breakdown and recurrent caries. The most
common areas for decalcified enamel is in
the cervical one-third of the crown, and is
associated with class five cavity
.preparations
27

28. HOME CARE
Lack of patient motivation, salivary and
dietary problems may influence the quality
of cleaning the tooth. More extension for
prevention may be required when these
. factors cannot be controlled
28

29. RESISTANCE FORM
Resistance form is the design given to a cavity
preparation to help prevent fracture of the
restorative martial and the tooth.
Resistance form is obtained by giving the
cavity "box form" .The factors that
contribute : to resistance form include
29

30. WALL ANGULATION
Masticatory forces are directed primary
along the long axis of the teeth. Since the
teeth and the restorative materials resist
compressive forces best, the cavity
preparation should be designed to minimize
tensile . and shear stresses
30

31. This is done by preparing the internal walls of
the cavity perpendicular or parallel to the
direction of the force ,which is along the
long axis. Thus, pulpal and gingival walls
should be horizontal or perpendicular to
the long axis. The other walls, including the
axial, are vertical or parallel to the long
.axis
31

32. DEPTH OF THE CAVITY
PREPARATION
The depth of the pulpal and axial walls must
be sufficient for the restorative material to
have enough bulk to resist fracture. Placing
these walls just within dentin is usually
adequate for this purpose. Increasing the
width of a cavity will not significantly
increase the resistance of the restoration to
fracture but it will decrease the strength of
.the tooth
32

33. The restorative material is more likely to fail
if the cavity is too shallow rather if it is too
.narrow
It is important that the pulpal and axial walls
be maintained at their ideal depth just
.within the dentin if at all possible
33

34. The contours of the pulpal and axial walls are
important in preserving the interadjacent
dentin. Ideally the pulpal wall is flat and the
axial wall is convex, paralleling the
curvature of the surface of the tooth and the
dentinoenamel junction. The axial wall
should . not be flat or concave
34

35. INTERNAL LINE ANGLES
Well defined internal line angles delineate the
walls of the cavity preparation, aid in
establishing uniform depth, and contribute
to retention form by preventing rotation of
restoration. Line angles such as the pulpo-axial
should be slightly rounded to
minimize stress concentration on the
.restoration
35

36. RESTORATIVE MATERIAL
Brittle material that have low tensile strength,
such as amalgam and cement, require good
box form and strict adherence to proper
.preparation
Less brittle materials such as composite can
be used in shallower or rounded
preparation when other means of retention
are used in addition to wall friction
36

37. RETENTION FORM
Retention form refers to the features of a
cavity preparation that prevent
dislodgment of the restoration. Retention
form is achieved through:
1) WALL FRICTION: Friction
between the restorative material and the
walls of the cavity preparation acts to retain
all types of restoration. Frictional retention
is improved by increasing the area of the
walls (cavity depth) and making opposing
).walls parallel (proper box form
37

38. Consequently, good resistance form also
contributes retention form to the cavity by
enhancing wall friction. Walls are not
intentionally roughened to increase
retention, since normal instrumentation
leaves the walls sufficiently rough.
2) UNDERCUT POIENTS AND
GROOVES: Undercuts are confined to the
dentin to avoid . undermining enamel
38

39. They are usually placed in the facial and
lingual walls of occlusal preparation, the
buccal and lingual proximal walls of class 2
preparation, and the incisal and gingival
walls of class 5 preparation. They are not
normally placed in the pulpal or axial walls
in order . to avoid approaching the pulp
AUXILIARY RETENTION: They are;
Dovetails, Grooves, Pins and etching of
enamel
39

40. 40

41. CONVENIENCE FORM
This means that the dentist must create
sufficient access to the lesion to facilitate
visibility and instrumentation in
preparation of the cavity and insertion of
.restorative material
Proper convenience form is a requirement for
.all operative procedures
41

42. REMOVAL OF REMAINING CARIOUS
DENTIN
Cavity preparations are designed to remove
carious tooth structure. Preparations that
are designed according Blacks principles
will automatically include those lesions that
have just penetrated the dentin. Moderate
or gross amounts of carious tooth structure,
however, are not removed by ideal cavity
designs and therefore caries removal in
these instance becomes a separate and
.significant step
42

43. FINISHING OF THE ENAMEL WALL
It is necessary to refine the enamel walls of a
cavity preparation to ensure the best
possible adaptation between the restorative
.material and enamel
43

44. An other objective of this procedure is the
removal of any unsupported enamel which
may fracture later, and lead to secondary
caries. Adequate planning of all enamel
walls will result in a smooth Cavosurface
margin which enhances the condensability
and adaptability of the restorative material,
thereby increasing the strength of the
.restoration
44

45. CLEANSE AND MEDICATE
No cavity preparation should be restored that
has not been properly cleaned and dried for
inspection. It may also be necessary to place
certain medicaments in the cavity
.preparation
45

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