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PRINCIPLES OF TOOTH PREPARATION ppt given
1. Principles of Tooth Preparataion
in Fixed Partial Dentures
Presented By
Shabeena Mustafa
PG-II Year
2. Contents
• Introduction
• Objectives of tooth preparation
• Principles of tooth Preparation
• Definition of FPD
• Types of Fixed prostheses
• Retainers
• Conservation of tooth structure
• Margin placement and Design
• Restorations and margins
• Porcelain fused metal crowns
3. INTRODUCTION
• Tooth preparation may be defined as the mechanical
treatment of dental disease or injury to hard tissue that
restores a tooth to the original form (Tylman).
• The mechanical preparation or the chemical treatment of
the remaining tooth structure, which enables it to
accommodate a restorative material without incurring
mechanical or biological failure.(Marzouk)
• The current focus is on conservative tooth preparation that
is noninvasive and that minimally involves dentin.
PRINCIPLES OF TOOTH PREPARATION . NAIR RR
4. • Black’s principles of cavity preparation and Tylman’s
principles of tooth preparation are both presently
being modified to accommodate imaginative
approaches i.e., acid etching with minimum reduction.
• Dentistry is changing from macro tooth preparation
to an environment of molecular chemistry i.e., esthetic
bonding.
• These techniques are not presently supported by any
longitudinal studies, but are exciting and promising
5. • Despite these advances, traditional crowns are still
indicated for majority of patients.
• Diagnosis and disciplined tooth preparation are
essential to successful fixed prosthetics.
6. OBJECTIVES OF TOOTH PREPARATION
• 1.Reduction of the tooth in miniature to provide
retention.
• 2.Preservation of healthy tooth structure to secure
resistance form.
• 3.Provision for acceptable finish line.
• 4.Performing pragmatic axial tooth reduction to
encourage favorable tissue responses from artificial
crown contour.
8. FIXED PARTIAL DENTURES
According to Glossary of Prosthodontic Terms - GPT 9th
edition (2005) fixed prosthodontics is defined as,
“The branch of prosthodontics concerned with
the replacement and/ restoration of the teeth by
artificial substitutes that not readily removed
from the mouth.”
9. TYPES OF FIXED PARTIAL PROSTHESES
a. All metal crowns.
b. Porcelain Fused Metal crowns
c. All ceramic crowns.
d. Acrylic crowns.
e. Porcelain veneers.
i Full veneer
ii Partial Veneer
g. Laminates
h. Post and core
i.Resin Bonded
i. Resin Retained
J .Anterior partial coverage Crowns
k. Posterior Partial coverage crowns
l.Cantilever Bridges
10. Retainers.
“The part of a fixed dental prosthesis that unites the
abutment(s) to the remainder of the restoration.” GPT – 9
18. • In 1923 Prothero indicated
that the convergence of
surfaces should be 2-5◦
• In 1955 Jorgenson tested
the retention of crown
and concluded that
maximal retention was
recorded at 5º.
19. Preparation of the occlusal surface:
reduction follows the anatomic planes to
give uniform thickness to the restoration.
20. • Preparation of the
axial surfaces:
- tooth structure is
removed evenly.
- if necessary, teeth
should be
orthodontically
repositioned
21. Selection of a conservative margin compatible
with the other principles of tooth preparation
23. MARGIN PLACEMENT
Whenever possible, the margin of the preparation
should be supragingival.
Advantages of supragingival margins:
1. They can be easily finished without trauma to soft
tissues.
2. They are more easily kept clean.
3. Impressions are more easily made, with less potential
for soft tissue damage.
4. Restorations can be easily evaluated at recall
appointments.
24. Indications of subgingival margin
1. Dental caries, cervical erosion, or restorations extending
subgingivally and a crown-lengthening procedure is not
indicated.
2. The proximal contact area extends to the gingival crest.
3. Additional retention is needed.
4. The margin of a metal-ceramic crown is to be hidden
behind the labiogingival crest.
5. Root sensitivity cannot be controlled by more conservative
procedures.
6. Modification of the axial contour is indicated (undercuts).
25. MARGIN ADAPTATION
The junction between a cemented
restoration and the tooth is always a potential
site for recurrent caries because of dissolution
of the luting agent and inherent roughness.
A well-designed preparation has a margin that
is smooth and even.
26. • Rough, irregular, or
"stepped" junctions greatly
increase the length of the
margin and substantially
reduce the adaptation of
the restoration.
27. RATIONALE FOR COMPARISON OF PLAQUE-RETAINING PROPERTIES
OF CROWN SYSTEMS
JOHN A. SORENSEN(1989)
The factors that mediate plaque accumulation and influence gingival health at
the tissue-restoration interface are:
Surface roughness: Since bacterial colonization originates in the protected
sites of microscopic grooves, the crown micro-topography is crucial. The
linearity of the marginal finish line, if irregular, increases roughness and hence
plaque accumulation.
Marginal fit: Marginal discrepancy determines the amount of exposed
cement retaining plaque and/or the plaque niche between the crown and
tooth. The degree of marginal rounding determines the area of exposed
cement and possible plaque habitation.
Contour: An over-contoured margin compromises oral hygiene and hinders
professional scaling.
28. MARGIN GEOMETRY
Guidelines for margin design:
1. Ease of preparation without overextension.
2. Readily identifiable in the impression and on the die.
3. A distinct boundary to which the wax pattern can be
finished.
4. Sufficient bulk of material (to enable the wax pattern to be
handled without distortion as well as give the restoration
strength and, when porcelain is used, esthetics).
5. Conservative of tooth structure (provided the other
criteria are met).
29. PROPOSED MARGIN DESIGN
CHISEL EDGE
• Advantage:
conservative
• Disadvantage:
location of margin
difficult to control
• Indication
occasionally on tilted
teeth
30. PROPOSED MARGIN DESIGN
• FEATHER EDGE
- Advantage: conservative
- Disadvantage:
does not provide
sufficient bulk
- Not recommended.
31. BEVEL EDGE
• Advantages:
unsupported enamel
removed, allows finishing of
metal
• Disadvantage:
extends preparation into
sulcus if used on apical
margin
• Indication:
facial margin of maxillary
partial coverage crowns
32. CHAMFER
• Advantage
distinct margin,
adequate bulk,
easier to control
• Disadvantage
care needed to avoid
unsupported lip of
enamel
• Indications
cast metal restorations,
lingual margin of metal
ceramic crowns
33. SHOULDER
• Advantage
bulk of restorative
material,
• Disadvantage
less conservative
• Indication
facial margin of metal
ceramic crowns, complete
ceramic crowns
34. SLOPED SHOULDER
• Advantage
bulk of material,
• Disadvantage
less conservative
• Indication
facial margin of metal
ceramic crowns
35. SHOULDER WITH BEVEL
Advantage
bulk of material,
advantages of bevel
Disadvantage
less conservative,
extends preparation
apically
Indication
facial margin of posterior
metal ceramic crowns with
supragingival margins
36. A study was conducted by Jung-zen et. al.in (1993IJP) on
the influence of finish line geometry on the fit of the
crown.
• Three tooth preparation were considered that had
different labial finish line configuration shoulder, shoulder
with bevel and chamfer.
• Result:
marginal fit was not influenced by the type of finish line.
Castings with well-fitting margins exhibited axial wall
space between 15 and 33 μm.
37. Grooves and boxes incorporation
• Adding grooves or boxes to a preparation with a
limited path of withdrawal does not markedly affect
its retention because the surface area is not increased
significantly(Rosenstiel).
• However other authors have reported that, where the
addition of grooves or boxes limits the path of
withdrawal, retention is increased
38.
39.
40. RETENTION AND RESISTANCE
• Retention prevents removal of the
restoration along the path of
insertion or long axis of the tooth
preparation.
• Resistance prevents dislodgement
of the restoration by forces
directed in an apical or oblique
direction and prevents any
movement of the restoration
under occlusal forces.
• Retention and resistance are
interrelated and often inseparable
qualities.
47. FULL VENEER CROWN
INDICATIONS :
1. Extensive coronal destruction due to caries
or trauma.
2. Endodontically treated tooth.
3. Necessity for maximum retention and
strength.
4. To correct minor malinclination.
5. To correct occlusal plane.
48. FULL VENEER CROWN
Contra-indication :
Full coverage should not be used in mouths with
uncontrolled caries.
It does not protect the tooth against the
biological causes of caries.
Caries must be controlled by other means
before any restoration can be successful.a
49. FULL METAL CROWN PREPARATION
ARMAMENTARIUM :
1. Hand piece
2. No : 171L bur
3. Round-end tapered
diamond
4. Short needle diamond
5. Torpedo diamond
6. Torpedo bur
7. Red utility wax
50. FULL METAL CROWN PREPARATION
STEP NO :1
OCCLUSAL REDUCTION
1.5 mm of clearance of
functional cusp and 1mm
on the nonfunctional cusp.
Depth orientation grooves are
placed on the occlusal
surface with round end
tapered diamond.
51. Full metal crown preparation
• Occlusal reduction :
A round-end tapered diamond
is used to place the grooves
on the ridges and the
primary grooves of the
occlusal surface.
If there is already some
clearance with the opposing
tooth because of
malposition- grooves should
not be made as deep.
52. Full Metal Crown Preparation
OCCLUSAL REDUCTION :
The occlusal reduction should
follow the configuration of
the geometric inclines that
make the occlusal surface of
any posterior teeth.
53. Full Metal Crown Preparation
STEP NO : 2
Functional cusp bevel with
round-end tapered
diamond.
A wide bevel is placed on the
functional cusp-depth
orientation grooves are also
helpful in this reduction.
Functional cusp bevel is
integral part of occlusal
reduction.
Failure to place this bevel can
produce thin casting or poor
morphology.
54. Full Metal Crown Preparation
OCCLUSAL CLEARANCE :
Is checked by having the
patient to close on red
utility wax held over the
preparation.
55. Full Metal Crown Prep
STEP NO : 3
Buccal and lingual walls are
reduced with the round-end
tapered diamond.The sides
of the diamond will produce
the desired axial reduction
while the tip forms the
chamfer.
56. Full Metal Crown
Preparation
STEP NO : 4
Initial proximal axial
reduction with short
needle diamond
followed by the round-
end tapered diamond.
57. Full Metal Crown Preparation
STEP NO : 6
Seating groove with 171L
bur.
59. Full Veneer Crown Preparation
STEP NO : 5
Axial finishing- round-end
tapered diamond.
All axial surfaces are
smoothed including all
point angles. The finish
line should be smooth
and continuous.
