2. INITIAL TOOTH PREPARATION
Mesio-occlusal class II preparation
• Occlusal outline form:
Enter the pit nearest the involved proximal
surface with a punch cut using a No. 245
bur.
• Viewed from the proximal and lingual
aspects, the long axis of bur should be
parallel to the long axis of tooth crown
during cutting.
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Bur position for
entry;proximal view
3. 3
• Proper depth of the initial entry cut is
1.5-2mm.The pulpal depth is usually
0.1-0.2 mm in to the dentin.
While maintaining the same depth and
orientation ,bur is moved to extend the
outline to include the central fissure and
opposite pit ,if necessary.
Completed occlusal
step
Occlusal view
4. • Include all the carious occlusal pits and fissures in such a
manner that sharp angles in the marginal outline are avoided.
• The isthmus width should be as narrow as possible, ideally
should be 1/4th of the intercuspal distance
• Enameloplasty should be used where indicated to conserve
tooth structure.
•
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5. Before extending into the involved proximal marginal ridge, the final
location of the facial and lingual walls of the proximal box relative to
the contact area should be visualized ,to prevent overextension of the
occlusal outline form (i.e., occlusal step) where it joins the proximal
outline form (i.e., proximal box).
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Visualization of final location of
proximo-occlusal margin
6. 6
While maintaining the established pulpal depth
and with the bur parallel to the long axis of the
tooth crown, the preparation is extended mesially, stopping
approximately 0.8 mm short of cutting through the marginal ridge
into the contact area.
Removing remaining
undermined enamel
Breaking proximal contact
Isolating proximal
enamel
7. PROXIMAL OUTLINE FORM
• Again we visualizes the desired final location of the facial and
lingual walls of the proximal box relative to the contact area.
• The objectives for extension of proximal margins are to:
• Include all caries, faults, or existing restorative material.
• Create 90-degree cavosurface margins (i.e., butt joint margins).
• Establish (ideally) not more than 0.5 mm clearance with the
adjacent proximal surface facially, lingually, and gingivally.
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8. • The initial procedure in preparation of
outline form is the isolation of the
proximal enamel by giving the proximal
ditch cut.
• Allow the end of the bur to cut a ditch
gingivally along the exposed DEJ, two
thirds at the expense of dentin and one
third at the expense of enamel. The
0.8-mm diameter bur end will cut
approximately 0.5 to 0.6 mm into
dentin and 0.2 to 0.3 mm into enamel.
• The ditch is extended gingivally just
beyond the caries or the proximal
contact, whichever is greater.
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9. • When extension places the gingival margin in cementum, the
initial pulpal depth of the axiogingival line angle should be 0.7
to 0.8 mm (the diameter of the tip end of the No. 245 bur is 0.8
mm). The bur may shave the side of the wedge that is
protecting the rubber dam and underlying gingiva.
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10. 10
Ideally the extension of facial and lingual margins of proximal
box should be such that ,it provides clearance of 0.2-0.3 mm
from the adjacent tooth.
but this clearance greater than 0.5 mm is
excessive unless indicated to include caries,
undermined enamel, or existing restorative material.
Ideally the gingival margin should
clear the adjacent tooth by only
0.5mm ,which may be measured
with the side of explorer.
11. Preparation of Axial wall-
• It is an internal prepared wall that is parallel to the long
axis of the tooth & It is always placed in dentin to obtain:
It is always placed in the dentin to obtain:-
• Resistance & elasticity of dentin
• Bulk of the restoration.
• Placement of retentive locks.
• Length of the axial wall :- 0.4-0.6 mm from the axio-pulpal line
angle to the axio-gingival line angle.
• the axial wall should be straight or convex but it should
never be concave.
• It should follow the contour of proximal surface .
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12. 12
PREPRATION OF GINGIVAL SEAT:-
It is an external cavity wall that is perpendicular to the long
axis of the tooth.
It is extended beyond the contact area or up to the proximal
lesion whichever is more. This also help in providing a
contact clearance gingivally.
It is made flat so that the masticatory forces are distributed
equally.
The width of gingival seat:- 0.6-0.8mm(premolars)
0.8-1.0mm(molars)
It consists of 2/3rd of dentin and 1/3rd of enamel.
13. GINGIVAL DIVERGENCE OF FACIAL AND LINGUAL WAALS OF
PROXIMAL BOX
The proximal ditch cut may be diverged gingivally to ensure that
the faciolingual dimension at the gingival is greater than at the
occlusal.
This gingival divergence :
- Increases the retention form .
- Provides desirable extension of the facial and lingual proximal
margins to include defective tooth structure or old restorative
material at the gingival level.
- Conserve the marginal ridge strength.
- Provides 90-degree amalgam at the
margins on this ridge .
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14. • In completing the proximal extensions,
next make two cuts, one starting at the
facial limit of the proximal ditch and the
other starting at the lingual limit,
extending toward and perpendicular to
the proximal surface (until the bur is
nearly through the enamel at contact
level).
• The side of the bur may emerge slightly
through the surface at the level of the
gingival floor.
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15. • a matrix band may be used around the adjacent tooth
to prevent marring its proximal surface.
• The isolated enamel, if still in place, may be fractured
out with a spoon excavator or by additional
movement of the bur.
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16. • To protect the gingiva and the rubber dam when
extending the gingival wall gingivally, a wooden wedge
should already be in place in the gingival embrasure to
depress the soft tissue and rubber dam.
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Rounded toothpick
wedge Triangular wedge
Indicated in deep
Gingival extension
17. • With the enamel hatchet, the bin-angle chisel, or both, cleave
away any remaining undermined proximal enamel, establishing
the proper direction to the mesiolingual and mesiofacial walls.
.
• Proximal margins having cavosurface angles of 90 degrees are
indicated. 17
18. PRIMARY RESISTANCE FORM
1. Pulpal & gingival walls being flat and perpendicular to
the forces directed to the long axis of the tooth.
2. Restrict the extension of the walls to allow strong
cusps & ridges to remain with sufficient dentin
support.
3. Restricting the occlusal outline form to areas receiving
minimal occlusal contact.
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19. 4.Reverse curve optimizing the strength of both the amalgam and
tooth structure at the junction of the occlusal step and
proximal box.
5. Rounding off the internal line angles.
6.Providing enough thickness of the restorative material.
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20. REVERSE CURVE
• When the direction of the mesiofacial wall is parallel to the
direction of the enamel rods, thus creating a ‘s’ shaped curve in
the proximal outline.
It is created to:
• Provide butt joint in the preparation margin.
• To relieve the contact
• To place the proximal margins in a self cleansing area.
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21. PRIMARY RETENTION FORM
• Occlusal convergence of facial & lingual walls
• Dovetail design of occlusal step(when present).
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22. FINAL TOOTH PREPARATION
• Removal of any remaining defective enamel and infected
carious dentin
• Accomplished in the same manner as in the Class I
preparation.
• Infected carious dentin is removed with a slowly revolving
round bur of appropriate size or a discoid-type spoon
excavator or both.
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. A, Infected carious dentin extending beyond ideal pulpal wall position. B, Incorrect
lowering of pulpal wall to include infected carious dentin. C, Correct extension facially and
lingually beyond infectedcarious dentin.
23. • The presence of infected carious dentin on a portion of either the
pulpal wall (floor) or axial wall does not indicate deepening the
entire wall.
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. Infected carious
dentin on axial wall
does not call for
preparing axial wall
toward pulp as shown
by dotted lines. It
should be removed
with round bur
24. • A partial extension of a facial or lingual wall is
permissible if:
• The entire wall is not weakened
• The extension remains accessible and visible
• Sufficient gingival seats remain to support the
restoration
• A butt joint fit at the amalgam and enamel margin
(90-degree amalgam angle and 90-degree cavosurface
angle) is possible.
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25. PULP PROTECTION
It is desirable to have approx 2mm bulk beneath the pulp and
metallic restoration which may be Dentin, Liner or a Base.
• Liner/Base- Mechanical, Chemical, Thermal Pulp protection
and act as a barrier that protects the dentin.
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26. • Remaining Dentin Thickness 0.5-1 mm -Zinc Phosphate
Cement, Glass Ionomer Cement base is used followed by
calcium hydroxide liner.
The base insulates the pulp from thermal changes, bonds
to the dentin, releases fluoride, and is strong enough to
resist the forces of condensation.
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27. SECONDARY RESISTANCE AND
RETENTION FORMS
• Using the gingival margin trimmer
to bevel or round the axiopulpal line angle.
• Proximal retention locks:
• Placed on axiofacial and axiolingual line angles.
• Terminate at axiopulpal point angle.
• Prepared with No. 169L bur or No. ¼ bur
• There are four characteristics or determinants of proximal locks:
(1) position, (2) translation, (3) depth, and (4) occlusogingival
orientation
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28. Proximal retention locks
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A, Position of No. 169L bur
and pulpally. B, Lingual lock..
C, Completed locks. D, Locks prepared
with No. '/, bur. E, Completed locks
29. • Retention grooves:
• Placed on axiofacial and axiolingual line
angles.
• Extend from the gingival floor to the occlusal
surface
• Prepared with No. ¼ round bur with head
diameter of 0.5mm or No. 1/8 bur with head
diameter of 0.4mm
• In preparation with deep proximal box
grooves should be in the proximal walls just
inside the DEJ and not in the corners of the
box
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30. • Circumferential slots:
• Prepared with No. 33 ½ inverted cone bur
• 0.5 to 1 mm deep inside DEJ
• 0.6 mm deep
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31. • Amalgapins:
• Depth of 1.5 to 2mm is adequate
• Diameter 0.8 to 1mm
• Prepared with No.1156, No.1157, No.330 or No.56 burs
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32. • Amalgam bonding agents:
• Should have auto-polymerizing property as amalgam
does not allow light transmission
• Ex: All bond-2, Amalgam bond plus, etc.
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33. PROCEDURE FOR FINISHING EXTERNAL
WALLS:
1. There should be no unsupported enamel and
marginal irregularities present.
2. There should be a butt joint relation between the
tooth & amalgam
3. Cavosurface bevel [20°] at the gingival margin can
be given by G.M.T , to remove the unsupported
enamel rods.
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34. 34
• When the gingival margin is positioned gingival to the
cementoenamel junction (CEJ) on the tooth root, the
bevel is not indicated.
35. Final procedures: cleaning,
inspecting, desensitizing,
and bonding
• First step includes removing all chips and loose debris and then
drying the preparation(not dessicating) and check for any
infected dentin and any unsound enamel margins.
• Cleaning is to free the preparation of visible debris with warm
water from syringe and then to remove moisture with a few
light surges of air syringe.
• Varnishes should be applied on all the preparation walls to
prevent the microleakege.
• GLUMA desensitizer can also be used to reduce the
postoperative sensitivity.
• Disinfection of the preparation walls can be done by silver
nitrate, phenol,ethyl alchol (short duration). 35
