Docstoc

Cavity Preparations

Document Sample
Cavity Preparations Powered By Docstoc
					      Presented By:
       Rahul Mishra,
    Junior Resident-I,
UP Dental College &
     Research Centre,
            Lucknow.
                     1
           DEFINITION OF CAVITY
               PREPARATION
Cavity preparation is the mechanical alternation of a
tooth to receive a restorative material, which will return
the tooth to proper anatomical form, function, and
esthetics. The procedure of the preparing the tooth is
the removal of the defective or friable tooth structure.
Any remaining infected or friable tooth structure may
result of further carious progression, sensitivity or pain
or fracture of the tooth and / restoration.

                                                       2
Cavity preparation is the mechanical alternation of
defective, injured or diseased tooth in order to best
receive a restorative material that will reestablish a
healthy state for the tooth including esthetic correction
when indicated, along with normal form and function.

The reason of the need for restoration as follow:

• To restore the integrity of the tooth surface.
• To restore the function of the tooth.
• To restore the appearance of the tooth.
• To remove the diseased tissue from the tooth.
                                                       3
          OBJECTIVES OF CAVITY
             PREPARATION
• To remove diseased tissue as necessary and at the
same time provides the protection to the pulp.
• To locate the margins of the restoration as
conservative as possible.
• To ensure the cavity form, it should not be under the
force of mastication of the tooth.
• To allow the functional placement of the restorative
material.

                                                     4
PRINCIPLES OF CAVITY PREPARATION

 •Gain access to caries.
 •Removal of all carious lesions.
 •Cut away all significantly unsupported enamel.
 •Extended margins so that they are accessible for
 instrumentation and Cleaning.




                                                     5
                 CLASSIFICATION
                (G.V. BLACK CLASSIFICATION)
Black suggested that it was necessary to

•Remove additional tooth structure to gain access and
visibility .
•Remove all trace of demineralized enamel and dentin
from the floor, walls and margins of the cavity.
•Make room for the insertion of the restorative material in
sufficient bulk to provide strength.
•Provide mechanical interlocking retentive designs.
•Extend the cavity to self-cleansing areas to avoid
recurrent caries.
                                                        6
CLASS I
             The lesions involving the occlusal surfaces of
molars and premolars, the occlusal 2/3 of buccal and
lingual surfaces of molars, and the palatal pits in anterior
teeth.
CLASS II
            The lesions involving the proximal surfaces of
the posterior teeth with access established from the occlusal
surface.
CLASS III
             The lesions involving the proximal surfaces of
anterior teeth which may or may not involve a labial or a
lingual extension & not involving incisal edge.         7
CLASS IV
             The lesions involving all proximal surfaces of
anterior teeth which involves the incisal edge.

CLASS V
             The lesions involving the cervical third of all
teeth, including the proximal surface of posterior teeth
where the marginal ridge is not included in the cavity
preparation.


                                                          8
          ACCORDING TO SITE INVOLVED

Site 1 . Pits, fissures and enamel defects on occlusal
surfaces of posterior teeth or other smooth surfaces.
Site 2 . Approximal enamel in relation to areas in contact
with adjacent teeth.
Site 3 . The cervical one third of the crown or, following
gingival recession, the exposed root surface.




                                                       9
ACCORDING TO THE SIZE AND EXTENT OF THE LESION AT
          THE TIME OF IDENTIFICATION

Size 0 . The earliest lesion that can be identified as the initial
stages of demineralisation. This needs to be recorded but will be
treated by eliminating the cause and should therefore not require
further treatment,
Size 1 . Minimal surface cavitation with involvement of dentine
just beyond treatment by remineralisation alone. Some form of
restoration is required to restore the smooth surface and prevent
further plaque accumulation,
Size 2 . Moderate involvement of dentine following cavity
preparation. Remaining enamel is sound, well supported by
dentine and not likely to fail under normal occlusal load. The
remaining tooth is sufficiently strong to support the restoration,
                                                               10
Size 3 . The lesion is enlarged beyond moderate. Remaining
tooth structure is weakened to the extent that cusps or incisal
edges are split, or are likely to fail if left exposed to occlusal
load. The cavity needs to be further enlarged so that the
restoration can be designed to provide support to the remaining
tooth structure,

Size 4 . Extensive caries or bulk loss of tooth structure e.g. loss
of a complete cusp or incisal edge has already occurred.




                                                                  11
      DESIGN AND PREPARATION OF
              CAVITIES
• The design and preparation of cavities are based on
Black’s principles that have been determined and re-
applied with importance directed towards protection
of tooth in preparation rather than only on the
material.
• Each diseased tooth has an individual cavity form
determined by caries involvement, morphology of
tooth and its location in oral cavity – leading to new
conservative cavity designs.

                                                     12
    STEPS IN THE CAVITY PREPARATION
                (Given by G V Black)
Obtaining Outline Form
Obtaining Primary Resistance Form
Obtaining Primary Retention Form
Obtaining Convenience Form
Removal of Remaining Carious Dentin
Obtaining Secondary Resistance & Retention Form
Providing Pulp Protection
Finishing of Enamel Walls & Margins
Performing the Toilet of the Cavity
                                                   13
               ARMAMENTARIUM

• Basic Instruments – mouth mirror, explorer, tweezer,
etc.
• Hand Instruments – Excavators, enamel hatchet,
monoangle or biangle chisels, Gingival Marginal
Trimmer.
• Rotary Instruments –
         •Burs No.-carbide burs 55, 56, 57.
         • Ultraspeed and conventional speed contrangle
         handpiece.
         • Safety glasses.
                                                    14
Definition:
These are pit and fissure type cavities
that involve the occlusal surfaces of
molars and premolars, the occlusal 2/3
of buccal and lingual surfaces of molars,
and the palatal pits in anterior teeth.

                                        15
 These are self-cleansable areas.
  However, they may get involved by
  caries due to their inherent defective
  structure. These areas are retentive
  for food and thus invite caries.



                                       16
     These lesions are
 clinically characterized
             by:
1. A small surface opening which may
   remain unnoticed until the lesion
   becomes of a considerable size.
2. A conical spread in both enamel and
   dentin, with the bases of cones at the
   Dentinoenamel Junction.
3. It is rapid burrowing at the dentinoenamel
   junction. These lesions may involve one
   or more surfaces and hence a simple or
   compound cavity should be prepared.
                                                17
             Simple occlusal
                cavities

Designing the Outline Form

The outline form of a routine class I cavity should
describe a symmetrical design running in sweeping
curves along all pits, fissures, and angular grooves
between the cusps and with a minimum width.

                                                18
Marginal ridge walls should be 1/2 distance from
mesial and distal pit to the crest of each marginal
 ridge and in a direction parallel to these ridges.
 The mesial and distal wall should
  have a slant or slight divergence
  from the pulpal floor outward to
  avoid undermining the marginal
  ridges.


                                  20
PERPENDICULAR IN MESIAL-
    DISTAL DIRECTION
 •Pulpal Floor mesio-distally is flat and
perpendicular to the long axis of the tooth
In a bucco-lingual direction, the cavity
 is extended just sufficient to eliminate
 the defective and susceptible tissues.
 The lingual and the buccal wall should
 be parallel to the respective tooth
 surface.



                                        23
•INTERNAL FORM                BUCCO-LINGUAL VIEW


•Buccal and Lingual Walls
are Parallel to each other
and to the Long Axis of the
Crown (Provides retention)
•Buccal, Lingual, and
Proximal Walls meet Pulpal
Floor at sharp angle
•Buccal and Lingual Walls
meet Proximal in smooth,
rounded form.
LONG AXIS
   OF
  THE
 TOOTH
 LONG
AXIS OF
  THE
CROWN
 It must be reemphasized that the
 outline form for class 1 cavities
 should be very conservative since
 they involve cleansable areas.
It is governed only by the extent of
 caries in both enamel and dentin and
 the amount of extension or need to
 eliminate pits and fissures to secure
 smooth margins.
                                         27
Isthmus just wide enough to accept
         instrumentation


           1/4th intercuspal
               distance
29
CORRECT OUTLINE FORM




                       30
  Obtaining the Resistance
   and Retention Forms
 The resistance form here consists
  chiefly of a pulpal wall parallel to
  the occlusal plane with dentin walls
  at right angles to it., i.e. Boxing the
  preparation.

 The form of this cavity provides
  automatically for effective retention
  and, therefore, no special retentive
  features are required.
                                            31
    Removal of remaining
      Carious Dentin
 In small size cavities, the carious dentin
  should have been removed during making the
  cavity extensions.
 In moderately deep and deep cavities, the
  carious dentin is peeled off carefully at the
  sides using large spoon excavators, and then
  scooped out in few and large pieces.
 Only light pressure in a direction parallel to
  that of the pulp is utilized. This is continued
  until a sound dentin floor is reached.
                                               32
     Planning of Enamel
           Walls
The enamel walls of the cavity should be
 finished free from any loose, short, or
 undermined enamel, and trimmed to meet the
 tooth surface at a right cavo-surface angle.
This may be done by sharp and regular edged
 chisels and hatchets, plane fissure burs,
 stones, or sand-paper discs.
All sharp corners in enamel must be rounded,
 as they may contain short enamel rods.
                                            33
Performing of the toilet
     of the cavity

A sharp explorer is then used to check
the details of the prepared cavity and to
loosen the tooth debris which are then
blasted out with warm air.



                                            34
        Procedure

The outline form is performed by first
 gaining access through the enamel to
 the carious dentin floor of the cavity
 followed by making the necessary
 cavity extensions.


                                          35
• In case of initial carious lesions, access is
  obtained by employing a small round bur #330.
• In big carious lesions, access is obtained easily
  by breaking down the undermined enamel
  overlying the carious dentin, using a suitable size
  chisel.
• In either case, access is started at the most
  defective area of enamel, i.e., a carious pit or
  fissure.



                                                  36
     The bur is held at a right angle to the
    involved surface of the tooth and light
    pressure in an in-and-out direction is
    exerted. Cutting is continued until the
    Dentinoenamel Junction is reached.




                                                37
 The necessary cavity extensions through
pits, fissures, and deep developmental
grooves are made using a
#330 round bur held at
Right Angle To The
Surface Of The Crown.

The     bur is rotated, and carefully
introduced through the opening just
obtained, so that its weak corners do not
touch the enamel and get dulled.        38
With the bur seated in the cavity just
below the dentinoenamel junction 1/2-1 mm.
Gentle pressure is applied in the direction
of required extension.


During cutting, the bur should be kept
moving in-and-out of the cavity and at
right angle to the tooth surface. In this
way, the bur will undermine and lift the
cut enamel, and at the same time unclog
itself.                                  39
Provision of ample resistance and
 adequate retention through boxing of
 the preparation could be obtained.

This is obtained by using a #56 fissure
 bur held perpendicular to the surface of
 the tooth. All the line angle in dentin
 must be squared up by help of the HOE
 Excavators.
                                            40
•Deepest or most carious pit entered with a
punch cut using No. ½ round bur or No.245
inverted cone bur oriented perpendicular to
long axis of tooth.

•Depending on cuspal incline, depth of
prepared external walls is 1.5 – 2 mm and
1.5mm pulpal depth measured at central
fissure.

•Desired pulpal depth – 0.1 to 0.2 mm into
dentin.                                  41
•Maintaining depth, cavity extended to include all
defective supplemental and developmental
grooves (No.57 plain St. fissures carbide bur).

•Isthmus width of 1/4th intercuspal distance so
that it does not reduces the strength of tooth
(Diameter of bur should be considered).

•If fissure extends farther into marginal ridge,
slight occlusal divergence is given, to prevent
undermining of marginal ridge & to provide
dentinal support.
                                                42
•Pulpal floor remains at initial ideal depth,
relatively flat, in dentin and provides a strong
stable seat for restoration.

•Enameloplasty done on terminal ends of
shallow fissures to conserve tooth structure.

•Final tooth preparation includes removal of
remaining defective enamel / infected dentin,
pulp protection and finishing of external walls
accomplished with hand instruments.          43
44
45
     Buccal Pit Cavities

•The outline of these cavities usually
describes a triangle with its base facing
the gingival wall and its sides forming
the mesial and distal walls.

•The gingival wall is placed at or slightly
occlusal to the height of contour of the
tooth.
                                              46
OUTLINE FORM FOR PIT RESTORATIONS



                                    47
All walls are extended just enough
to eliminate defective enamel and
dentin.

The enamel walls are planed in the
direction of enamel rods           and
perpendicular to the axial wall.


                                         48
Hoe excavators are used to smooth
 the axial wall and make it parallel with
 the external surface of the tooth.

It should be re-emphasize that the
 shape of the cavity will be governed by
 the extension of caries, accordingly
 the outline of these cavities may be a
 rounded or oval in shape.

                                            49
       Buccal and Lingual
          Extensions

In case of occluso-buccal and occluso-
 lingual cavities extensions are made
 through the fissures and towards the
 respective surfaces.
The cutting is done in dentin at the
 dentinoenamel junction using a #56 bur
 until the occlusal ridge is undermined
 and removed.
                                      50
If the caries is still gingival to the
 level of the pulpal seat, a step is
 indicated: a #330 or 56 bur is used
 to cut the dentin at the
 dentinoenamel junction, applying
 pressure in a gingival direction and
 at the same time moving the bur
 mesio-distally.
                                      51
The enamel thus undermined, is broken
 down with chisels.

Retentive grooves are then made in
 dentin along the axio-mesial and axio-
 distal line angles. The cavity walls and
 margins are finished as previously
 described.

                                        52
In case of deeply-seated caries,
 where removal of the carious dentin
 will leave a round cavity floor,
 flattening of which to obtain the
 required resistance form, will
 expose the pulp.


                                   53
The following technique is
          used:


a) The cavity floor is covered with
  a sub base followed by a base or
  base alone which fills it to the
  routine cavity depth.


                                      54
b) A ledge is cut on the expense of
  the buccal and lingual side walls
  of the cavity for obtaining the
  required resistance in sound
  dentin.


                                      55
56
  Principles          Rationale

I. OUTLINE FORM –    Angular irregularities in
   Smooth flowing,   the outline are
   regular curves.   susceptible to fracture
                     during condensation – a
                     smooth flowing outline is
                     easier to visualize and
                     carve following
                     condensation.



                                             57
II. EXTENSIONS (Extension for Prevention)
Conservation of tooth structure is the basis for
all cavity preparations in order to preserve the
strength of the tooth.
However, sufficient extension of cavity
preparations is necessary to ensure access
(convenience form) for instrumentation, removal
of defective tooth structure, insertion and
finish of the restorative material, and
maintenance of the restoration (prevention).


                                               58
      Principles            Rationale
A. Extensions consist of:
a.    Caries and            eliminates defective
     decalcifications       tooth structure and
b. Enamel unsupported by    eliminates areas (pits,
   sound dentin             fissures, etc.) which are
                            susceptible to recurrent
c.   Pits and fossae        caries and facilities oral
d. Major fissures and       hygiene procedures
   grooves                  (extension for
                            prevention).
e. Existing restorations


                                                   59
   Principles                   Rationale
B. Bucco – lingual extension
1. Extend fully in areas of      to allow a smooth
   buccal and lingual grooves    tooth-restoration
   to terminate on smooth        margin to be created
   surfaces.                     (easier to finish and
                                 keep clean).




                                                    60
    Principles               Rationale

2. Extend minimally in       to preserve the
   areas of triangular       strength and function
   ridges (optimal isthmus   of the cusps while
   width is ¼ intercuspal    eliminating susceptible
   distance or less)         grooves or defective
   terminating on smooth     tooth structure (must
   surfaces.                 be wide enough to allow
                             condensation).




                                                  61
    Principles                       Rationale

C. Mesio-distal extension
1. Stop short of the                to preserve strength of
   marginal ridge crest             marginal ridges.
    Marginal ridge walls should
   be 1/2 distance from mesial
   and distal pit to the crest of
   each marginal.




2. Parallel to the contour of       to preserve a uniform
   the marginal ridge.              bulk (strength) to the
                                    mariginal ridges.
                                                             62
    Principles                Rationale

3. Groove extensions are      to preserve strength of
   kept narrow (mesio-        cusps while eliminating
   distally) where possible   susceptible grooves
   terminating on smooth      and/or defective tooth
   tooth structure.           structure (must be at
                              least as wide as the
                              narrowest condenser).




                                                   63
   Principles               Rationale



4. If marginal ridge is     If not included the
   unsupported or very      marginal ridge may
   thin it should be        fracture. (amalgam will
   included, resulting in   be stronger than the
   a Class II               unsupported enamel)
   preparation.




                                                  64
   Principles               Rationale

III. RESISTANCE/ RETENTION FORM


A. Depth = 0.1-0.2mm into   Minimum depth is
   dentin (approx. 2 mm     required to provide
   measured at triangular   sufficient bulk to
   ridges).                 prevent fracture and
                            retain the amalgam.




                                               65
    Principles                Rationale
B. Pulpal floor

                              Uniform thickness of
1. Smooth and flat            restorative material.


2. Parallel to the occlusal   resists occlusal stress
 plane                        (resistance form) and
                              forces of condensation.




                                                      66
    Principles                Rationale
C. Buccal and lingual walls


1. Smooth and curved          Facilitates adaptation
   mesio-distally.            of amalgam and
                              elimination of weak
                              tooth structure.
2. Smooth and straight
   pulpo-occlusally.




                                                  67
    Principles             Rationale



3. Converge slightly     To provide mechanical
   pulpo-occlusally in   lock or retention to the
   areas of triangular   occlusal portion and
   ridges (60).          create bulk at the
                         margins.




                                                    68
   Principles              Rationale



4.Diverge slightly      protects buccal and lingual
  pulpo-occlusally in   surfaces from being
  buccal and lingual    undermined (RESISTANCE
  groove extensions     FORM).
  (60).




                                                 69
   Principles               Rationale

D. Mesial and distal wall


1. Smooth and straight      facilitates adaptation
                            of amalgam and
                            elimination of weak
                            tooth structure.




                                                     70
   Principles           Rationale


2. Diverges slightly   protects marginal ridge
   pulpo-occlusally    from being undermined or
   (forms an obtuse    weakened (enamel must
   angle with pulpal   be supported by dentin)
   floor).




                                             71
72
   Principles                Rationale

IV. CAVITY FINISH


A. Pulpo-occlusal line     increases retention of the
   angle is well defined   amalgam restoration and
   (no point angles are    preparation is more easily
   present) and follows    visualized.
   general
   configuration of
   cavosurface outline.



                                                  73
   Principles               Rationale

B. Cavosurface margins

                            easier to visualize and
1. Sharp (well defined)     carve.


2. Sound (well supported)   provides marginal
                            integrity.




                                                  74
    Principles                Rationale

C. Cleanliness – cavity   facilitates adaptation of
   is free of debris      amalgam to the cavity and
   and moisture.          improves the physical
                          properties of the
                          restoration by elimination of
                          void or foreign material.




                                                     75
   Principles                 Rationale
V. TISSUE RESERVATION

                               preserves isolation,
A. Rubber dam is intact        eliminates moisture.


B. Adjacent tooth structure    conservation of tooth
   and restorations are        structure.
   intact

                               prevention of post-
C. Adjacent soft tissue        operative pain and
   (periodontium) is intact    inflammation.
                                                      76
                     REFERENCES

1. ART & SCIENCE OF OPERATIVE DENTISTRY- STURDEVANT.
2. OPERATIVE DENTISTRY- WEINE
3. OPERATIVE DENTISTRY- MARZOUK
4. DENTISTRY FOR THE CHILD AND ADOLESCENT- MCDONALD.
5. ESTHETICS IN DENTISTRY- GOLDSTEIN.
6. CLASSIFICATION & CAVITY PREPARATION FOR CARIOUS
   LESION- G J MOUNT & W R HUME.
7. MINIMALLY INVASIVE DENTISTRY- JADA, Vol. 134, January 2003
8. CARIES    PREVENTION        CURRENT      STRATEGIES-    NEW
   DIRECTIONS- JADA, Vol. 127, October 1996




                                                             77

				
DOCUMENT INFO
Shared By:
Categories:
Stats:
views:139
posted:10/13/2012
language:English
pages:77
Description: Principles of Cavity preparations in different classes for amalgam restoration