HI

2. CONTENTS
1. Introduction
2.
Definition
3.
Preparatio
n
objectives
4.
Principles
of tooth
preparation
5. various
Finish lines
6.
Instrumentation
7. Summary
and
conclusion

3. Introduction
Tooth
-- Don’t regenerate as other tissue
-- therefore require replacement by tooth
preparation
----longevity depends on tooth prep.
--so through knowledge + attention =prediction
of successful Prosthodontic treatment

4. TOOTH PREPARATION
Tooth Preparation is defined as the mechanical
treatment of dental disease or injury to hard tissues
that restores a tooth to its original form. (GPT)

5. PRINCIPLES OF TOOTH PREPARATION
According to shillingbergh
1. Preservation of tooth structure
2. Retention and resistance form
3. Structural durability of the restoration
4. Marginal integrity
5. Preservation of the periodontium

6. According to Rosenstiel
BIOLOGIC MECHANICAL
ESTHETIC

7. 1. Preservation of tooth structure(Biological)
A tooth structure can be preserved by means of
1. Partial coverage of the tooth structure instead of
full coverage.
2. By preparing the minimum taper of the tooth
structure.

8. 3. By fallowing the anatomical contour of the occlusal
surfaces while preparing the tooth
4. Preparation of axial surfaces so that tooth surface
removed evenly and if required the tooth can be
repositioned orthodontically.
5. Selection of conservative margins compatible
with the restoration .eg.feather edge,chamfer etc.
6. By avoiding unnecessary apical extension of the
restoration

9. 7. By using metal matrix bands to Prevent
Iatrogenic damage to the adjacent tooth while
preparation
or
---By using a thin tapered diamond passed
through the interproximal contact area to leave a
slight lip of enamel without causing excessive
tooth reduction

10. 8.Prevention of Pulpal degeneration
 Extreme temperature, chemical irritation
or microorganisms can cause an
irreversible pulpitis, especially when they
occur on freshly sectioned dentinal tubule .
 It’s better to prepare grooves or pinholes at low
speed because the coolant cannot reach the
cutting edge of the burs.

11. • Should examine the morphology of the pulp
chamber in the radiograph and the preparation
should fallow the pulp chamber

12. • Prevention of Damage to the soft tissues of
tongue and cheeks can be prevented by careful
retraction with an
Aspirator tip
Mouth mirror or
Flanged saliva ejector.

13. RETENTION FORM-
----- it is the feature of a tooth preparation that resists
dislodgement of crown in a vertical direction or along
the path of placement. GPT-8
2. RETENTION AND RESISTANCE(Mechanical)

14. Retention
Factors to be considered
1.Magnitude of dislodging forces
2.Geometry of the tooth preparation
1.Degree of Taper
2.Surface Area
3. Area under Shear Stress
4.Type of restoration
3.PATH of insertion
4.Roughness of the surface being cemented
5.Material being cemented
6.TYPE of the luting agent

15. Retention
stickiness of the food
surface area under contact
texture of the restoration
1.Magnitude of dislodging forces
Depends upon

16. Retention
2. Geometry of the tooth prepn
a. if preparation is cylindrical- more retentive
b. cylindrical without groove –less retentive
c. cylindrical with groove- more retentive

17. Retention -:
i.Degree of Taper:
• The more nearly parallel the
opposing walls of a preparation,
the greater will be the retention.
• Recommended taper 3-6 degrees

19. Retention
For a constant
prep
height
As the degree of taper of a preparation INCREASES,
its ability to retain the restoration DECREASES.

20. Retention
ii.Roughness of the fitting surface of the
restoration
• smooth surface less retentive
• Rough/grooved surface more retentive
Roughness created by air abrasion i.e
sand blasting with 50 micron alumina

21. Retention
iii.Material being cemented
Base metal alloys –more retentive
Noble metal alloys- less retentive
Amalgam restoration –better retention
Composite restoration-less better retentive-
shrinkage—gap creation in microtags

22. Retention
iv. Type & Film thickness of the luting agent
• The type of luting agent chosen affects the
retention of a cemented restoration.
• Adhesive resin cements are the more
retentive than any other cements

23. Retention ----
5.Surface Area & its detail
• The greater the area of the cement film bound to both
the preparation and the internal detail of the casting, the
greater the retention of the restoration.
• Therefore, crowns with long axial walls are more
retentive than those with short axial walls
e.g.. molars are more retentive than premolars
• Adhesion of dental cements depends primarily on
projections of the cement into microscopic irregularities
axial surface-rough •margins-smooth

24. Diff Diam / Same Ht. Same Diam / Diff Ht.
The GREATER the surface area, the GREATER
the retention

25. Retention ----
Length of Preparation
• The longer the preparation inciso-gingivally,the
greater its retention due to greater surface area.
Surface Area

26. Retention ----
6. Type of Stress concentration
• Better shear – than tensile! Stress concentration
• Changes in the geometry of the preparation (e.g.,
rounding the internal line angles) may reduce stress
concentrations and hence increase the retention of the
restoration.

27. • TENSILE AWAY FROM
TOOTH
• SHEAR PARALLEL TO
CEMENT FILM
• TENSILE+SHEAR AT AN
ANGLE – AWAY
• COMPRESSION
TOWARD TOOTH

28. COMPARISON OF RETENTION AND RESISTANCE FOR
DIFFERENT TYPES OF PREPARATION

29. RESISTANCE FORM
Resistance is defined as per GPT-8
As the feature of a tooth preparation that enhances
the stability of a restoration and resists dislodgement
along an axis other than the path of placement
• According to shilling burgh Resistance is defined as
the ability of the preparation to resist removal by
forces acting in directions other than the path of
insertion
Resistance prevents dislodgement of the restoration
by forces directed in an apical or oblique direction

30. Factors Affecting Resistance
---- Geo-mechanical factors that influence resistance:
• Magnitude and direction of he dislodging surfaces
• Geometry of the tooth preparation
• Physical properties of the luting agent
• Leverage and Resistance:
• Preparation Length and Resistance
• Resistance and Tooth Width
• Taper and Resistance

31. 1.Magnitude and direction of he dislodging forces
Normally occlusion the biting forces are
distributed over all teeth
But a pt having bruxism,
pipe smoking habit ,large oblique
forces are applied to a restoration
So the restoration may get dislodged
and it depends upon the magnitude of
the forces

32. 2.Geometry of the tooth preparation
• Short tooth preparations with large diameters
have very less resistance
• A partial coverage restoration has less
résistance than full coverage because it has no
buccal résistance area
• Thus U shaped grooves provide more
resistance than V Shaped

33. 3.Physical Properties of luting agent:
• Modulus of elasticity and compressive strength
of the luting cement have an effect on resistance
to deformation
• Silicophosphate cements have higher
compressive strengths than GIC, RESIN,

34. Resistance
4.Preparation/restoration Length and
Resistance:
• Shortening a preparation will produce a
proportionally greater diminution of the
resisting area.

35. A short restoration on a short preparation is less likely to
fail through tipping than is along restoration on the same
preparation.
The resistance of this preparation inadequate to prevent the
crown from tipping under the
applied force (A).
Although the preparation and the
applied force in (B) are identical
to those in (A), the crown fails
because of the greater height of the
crown
Tipping for long restoration

36. Resistance ----
5.Tooth (Prep) Width and Resistance:
• A wide preparation has greater retention than a
narrower one of equal height - but the narrow
preparation has better resistance - due to
smaller arc of rotation -creating a larger area of
resistance.

37. Because of the small diameter, the tangent line of this
narrow preparation falls low on the wall opposite the axis of
rotation, resulting in a large resisting area (A).
Preparation B is wider than preparation A, but its height and
taper are the same.
Because of the much greater radius of the arc of rotation, its
resisting area is smaller than that of the narrower preparation.

38. Resistance ----
6.Taper and Resistance:
• The more tapered a preparation, the less
its resistance.

39. Resistence
The resisting area decreases as the preparation
taper increases
For a cylinder with no taper, the resisting area
would cover half the axial walls (A).
 For an ideally-tapered tooth preparation, the
resisting area covers somewhat less than half the
axial walls (B).
An over-tapered (20 degrees) preparation has
only a small resisting area near the occlusal
surface (C).

40. B---Addition of parallel sided grooves limits path of
insertion to one direction , increases retention and
resistance
SINGLE PATH
MULTIPLE PATHS

41. Resistence
• In addition
• Parallel internal walls,
grooves, boxes,
and post holes
can be used to enhance the retention and
resistance form of these three tooth preparations

42. Recommendation
• Routinely use axial grooves and boxes
when mandibular molars are prepared

43. 3.Path of Insertion
The path of insertion is an imaginary line along
which the restoration will be placed on to or
removed from the preparation.
• Retention is improved by geometrically limiting
the numbers of paths along which a restoration
can be removed from the tooth preparation.
• Maximum retention is achieved when there is
only one path.

44. Path of Insertion
• Evaluate using monocular (one
eye closed) vision from a distance
of 12”
• Visualize the entire finish line
when the preparation is viewed
from the occlusal /incisal view
• The widest dimension occlusally
should be within the confines of
the prepared margin ,
E.g. deepest portion of
shoulder/chamfer

45. The Path of Insertion created by the preparation is
dependent upon
• Approximating contacts/contours
• Tooth inclination
• Esthetics
• Path of insertion of other abutment teeth
• Planned restoration contour
• Pulp size and location

46. A tooth has migrated into the space formed
by a long-standing carious lesion (A).
A vertical path of insertion will not permit
seating without removal of surface of the
adjacent tooth (B).
The problem can be solved less
destructively by inclining the path of
insertion slightly to the mesial,and
removing small amounts of enamel from
both adjacent teeth (C).

47. Sufficient tooth structure must be removed to create
space for an adequate bulk of restorative material.
This must be accomplished without departing from
the normal contours of the tooth.
3.Structural Durability of the Restoration

48. Structural Durability
Factors affecting the structural durability are
• Occlusal Reduction
• Functional Cusp Bevel
• Axial Reduction

49. Occlusal Reduction
Occlusal thickness varies with the type
of restorative material
a. Gold requires:
- 1.5 mm over the functional cusps
(mand buccal - max lingual)
- 1.0 mm over nonfunctional cusps
(mand lingual - max buccal)
b. Porcelain over metal: Add 0.5 mm.
clearance
(because of combination of two
materials.

50. Structural Durability
• Reduction - Incisal

51. Functional Cusp Bevel
1. Functional cusps
Mn - buccal
Mx – lingual/palatal
2. Extension of the occlusal reduction
(totally for strength of casting)

53. Structural Durability
CROSSBITE
• Cross bite reverses
functional cusps
(but all prep features
are same)

54. Axial Reduction
Should provide space
for an adequate bulk &
thickness of restorative
material.
inadequate axial
reduction, they will have
thin walls that will be
subject of distortion.
e.g.—feather edge finish
line

55. Structural Durability
Inadequate Reduction
Thin flexible restoration Difficulty in fabrication
Perforation---- Distortion Over-contoured
Gingival Loss of seal inflammation
Loss of seal Loss of seal

56. 4.Marginal Integrity
• There are three requirements for
successful restoration margins:

57. A. Must fit as closely as possible against the
finish line of the preparation.
AVOID rough, irregular & stepped FINIS LINES
B. Must have sufficient strength to withstand the
forces of mastication.
C. Be located in areas where the dentist can finish
and inspect them, and the patient can clean
them.

59. 5.Preservation of the Periodontium(esthetic)
Healthy Periodontium

60. Historical Perspective
1. Traditionally - restoration margins were placed
subgingivally
2. Past mistaken belief was that the gingival sulcus
represented a caries-free zone

61. Modern Perspective
FROM RESEARCH:
1. Accepted research has shown that the subgingivally
placed margins can result unhealthy gum tissue
WHY NOT SUBGINGIVALLY ?
a. Harbours & Increase the gram-negative bacteria
(disturbance in balance of microorganisms)
b. Direct irritation (bump from tooth to crown)
c. Plaque retention

62. Modern Perspective
MODERN TECHNIQUE:
2. Margins of cast restorations should be
placed supragingivally whenever possible
That’s good ! However,

64. Subgingival margins
where Indicated ?
1. Existing caries
2. Previous restorations
new margin must extend subgingival to the old
margin
(two margins would cause gingival inflammation)
3. Need for Retention and Resistance Form

65. 4. Esthetics
ANTERIOR CROWN
(showing margin is unsightly)
5. Subgingival tooth fracture
6. Root sensitivity—gingival recession
(cover root in hope of insulating dentin, pulp)

66. FINISH LINES

67. Finish lines in fpd
• Definition: It may be well defined as
• I. Line of demarcation
• II. Peripheral extension of tooth preparation
• III. The planned junction of different materials

68. Features of finish lines:
• must be distinct, uniform, and smooth and
should follow alveolar bone crest and free
gingival margin.
• Requirements of finish lines:
• it should be Easy to prepare, easy to
duplicate in impression, conservative and
provide sufficient strength to restoring
material.

69. Classification of finish line
design configuration
I. Based on configuration of finish line
• a. Feather edge
• b. Knife edge
• c. bevel
• d.shoulder
• e. chamfer

70. ii. Based on location of finish line
• a. Supragigival
• b. Equigingival
• c. subgingival

71. Feather Chisel •Chamfer •Bevel Butt Shoulder
Sloped shoulder
Beveled /radial should

72. Not recommended now
INDICATIONS
I. Large pulp chambered tooth
ii. Finish line on cementum
iii. MOD onlay

73. Knife edge finish line
ADVANTAGES
• I. Easy to prepare
• ii. Most conservative
• iii. Burnishable type
of finish line
• iv. Ideal for marginal
adaptation
DISADVANTAGES
I. Indistinct margin
II. Over contoured
restoration
iii. Marginaldistortion
iv. Difficult to wax
and cast

74. CHISEL EDGE
Advantage
conservative
Disadvantage
location of margin difficult to
control
Indication
occasionally on tilted teeth
After periodontal surgery that
results in long clinical crowns
termination apically on the tooth
structure.

75. Chamfer finish line
• A chamfer is an obtuse
angled gingival
termination.
• It is a concave extra
coronal finish line that
possesses greater
angulations than a knife-
edge with less width than
a shoulder.

76. • A chamfer is the preferred cervical finish line for
fixed Prosthodontics and should be utilized
whenever possible because it is easily
developed and visually intact.
• The chamfer also enhances accurate die
trimming for technical fabrication of the cast
restorations.

77. • A chamfer should not be wider than half the bur
used to form it ,otherwise a lip o enamel will be
left

78. Chamfer
Advantages - Distinct margin
- Adequate bulk
- Easier to control
Disadvantages
• Care needed to avoid unsupported lip
of enamel
Indications - Cast metal restorations
- Lingual margin of metal
ceramic crowns

79. Shoulder
Advantages
I. Aesthetically acceptable
ii. Good crown contour
iii. Adequate bulk
iv. Less distortion
- Provides Bulk to restorative material
- Preparation produces fewer sensitive teeth after cementation
Disadvantages
I. Arduous to prepare
II. Least conservative
III. Danger of pulp exposure
IV. Inferior marginal integrity
V. Lacks sliding joint fit more destruction of tooth structure
Indications - facial margins of metal ceramic crowns
- All ceramic crowns

81. Shoulder with bevel
Advantages - Bulk of material
- Removes unsupported enamel
- Allows finishing of the restoration
Disadvantages - Less conservative
- Extends preparation apically
Indication - Facial margins of posterior metal ceramics
crowns with super gingival margins,
• proximal box of inlays and onlays and occlusal
shoulder of onlays and mandibular three fourth
crowns

82. SLOPED SHOULDER
Advantage
-bulk of material,
- advantages of bevel
Disadvantage
-less conservative
Indication
facial margin of metal ceramic
crowns
finish line design for tooth preparation in which the
gingival floor meets the external axial surfaces at
approximately 120

83. Radial shoulder:
Shoulder finish line with rounded gingivoaxial line
angle and 90 cavosurface angle.
Radial shoulder on all ceramic preparation
combines the support of ceramic with stress
reducing radial shoulder

84. Armamentarium
 The instruments are generally available in
course, medium and fine grit with wide range of
shapes and diameters.
 The coarse the medium grit --for removal of
tooth structure
 -- fine grit diamond instrument FOR finishing

87. METAL CERAMIC CROWN
INDICATION
• Esthetics
• If porcelain jacket crown is contraindicated
• Gingival involvement
CONTRAINDICATION
• Large pulp chamber
• Intact buccal wall
• When more conservative retainer is technically feasible

88. ADVANTAGE
• Superior esthetics as compared to cast gold restoration
DISADVANTAGE
• Removal of substantial tooth structure
• Subject to fracture because porcelain is brittle
• Difficult to obtain accurate occlusion in glazed porcelain
• Shade selection can be difficult
• Inferior esthetics as compared to porcelain jacket crown
• Expensive

89. Salient features of metal ceramic tooth
preparation

91. ALL CERAMIC CROWN
INDICATION
• High esthetic requirement
• Considerable proximal caries
• Incisal edge reasonably intact
• Endodontically treated teeth with post and core
• Favorable distribution of occlusal load
CONTRAINDICATION
• When superior strength is required
• Thin teeth faciolingually
• Unfavorable distribution of occlusal load

92. ADVANTAGE
• Esthetically unsurpassed
• Good tissue response
DISADVANTAGE
• Reduced strength compared to metal ceramic
crown
• Proper preparation extremely critical
• Brittle nature of material

93. Salient features of all ceramic tooth
preparation

94. CONCLUSION
• The biomechanical principles of tooth preparation
have been discussed in relation to biological,
mechanical, and esthetic considerations
• These principles must be applied within the
context of the external dimensions of the tooth
being prepared, pulp size, tooth-soft tissue
relationship, and available sound tooth structure.

95. • A thorough understanding of tooth morphology and
principles is essential for developing preparations
that will permit the restorations placed upon them to
be functionally durable, provide optimal esthetics,
and be biologically compatible with the
periodontium.

96. REFERENCES
– Contemporary Fixed Prosthodontics; 3rd
edition; H.T.Shillingburg.
– Planning and Making Crown and Bridges;
3rd edition; Bernard G.N. Smith
– Inlays Crowns and Bridges – A clinical Hand
book; George F.kantorowikz.

97. – Fundamentals of Fixed Partial Denture ;
Stephen F.Rosensteil; 3rd edition
– Gnathologic Tooth Preparation; Charles E.
Stuart
– Tooth Preparation in Fixed Partial Denture;
H.T.Shillingburg.
– Tooth preparation for complete crowns; an art
form based on scientific principles; jpd; 2001;
85; 363-76

98. • Charles J Good acre ; Guillermo; Clinical Complications in
Fixed Prosthodontics ; jpd; 2003; 90; 31-41
• VALDERHAUG J.M. BIRKELAND; Periodontal conditions in
patients 5 years following insertion of fixed prostheses ; Journal of
Oral Rehabilitation, 1976, Volume 3, pages 237-243
• J Charles T. Smith, 'John J. GUT, And Herby L. Franks;
Effective Taper Criterion for the Full Veneer Crown Preparation in
Preclinical Prosthodontics ; Journal of Prosthodontics.;Val 8,
(September), 1999: pp 196-200
•

99. • E. OHM and J. SILNESS ; The convergence angle in teeth prepared
for artificial crowns Journal of Oral Rehabilitation, 1978, Volume 5,
pages 371-375
• Aaron H. Wilson, and Daniel C. N. Chan, ; The Relationship Between
Preparation Convergence and Retention of Extra coronal Retainers J
Prosthodontics vol3;1994:74-78...
• T.HEGDAHL J. SILNESS; The Preparation areas resisting
Displacement of artificial crowns; Journal of Oral Rehabilitation, 1977,
Volume 4, pages 201-7
• Merle H. Parker, Gunderson et al; New Guidelines for Preparation
Journal of Prosthodontics VoL 2, 1997:61- 66
• Dennis B.Gilboe; Walter .R. Teteruck ; Fundamentals of extra
coronal tooth preparation part-1;Retention and resistance form
;J.Prosthet.Dent ;2005;94;105-107