The document discusses the principles of tooth preparation for dental restorations. It covers biological principles like preventing damage, conserving tooth structure and considerations for future dental health. Mechanical principles discussed include providing retention form, resistance form and structural durability. Esthetic principles for metal-ceramic and partial coverage restorations are also covered. The objectives of tooth preparation are outlined as are factors like margin placement, adaptation and the biologic width. Current concepts in tooth preparation emphasize adequate occlusal reduction and resistance form.

1. PRINCIPLES OF TOOTH
PREPARATION
Dr. Dipal Mawani
PG

3. Contents
 Introduction
 Objectives of tooth preparation
 Principles of tooth preparation
• Biologic :
 Prevention of damage during tooth preparation
 Conservation of tooth structure
 Considerations affecting future dental health
• Mechanical :
 Retention form
 Resistance form
 Structural durability
• Esthetics :
 Metal ceramic
 Partial coverage restoration

4. Introduction
 What is tooth preparation?
Mechanical treatment of dental disease or injury to hard
tissues that restore a tooth to original form
The process of removal of diseased and/or healthy enamel
and dentin and cementum to shape a tooth to receive a
restoration

5. OBJECTIVES OF TOOTH PREPARATION
 Reduction of a tooth in miniature to provide
retainer support.
 Preservation of healthy tooth to secure
resistance form.
 Provision for acceptable finish lines.
 Performing pragmatic axial tooth reduction to
encourage favourable tissue responses from
artificial crown contours.

6. Principles Of Tooth Preparation
• Biologic :
• Mechanical :
• Esthetics :
Prevention of damage during tooth
preparation
Conservation of tooth structure
Considerations affecting future
dental health
Retention form
Resistance form
Structural durability
Metal ceramic
Partial coverage
restoration

8. Biologic Considerations
 Prevention of damage during tooth
preparation
1. Adjacent Teeth
-damaged tooth even if reshaped and recontoured is
always more susceptible to caries
Less fluoride content
More plaque retention

9. • AVOIDED BY:
• Placing a matrix band interproximally
• leaving thin lip/ fin of enamel intact
Interproximally.
2.Soft Tissues :Aspirator tip , mouth mirror.

10. 3.Pulp
Extreme Temperature
Chemical Irritation
Micro-organisms
AVOIDED BY:
Using correct technique of tooth preparation
Selecting correct materials (cements)
Pre-op Radiographs
Irreversible Pulpitis

11.  Causes of injury :
• Temperature : Friction – heat
• Zach &Cohen –
 rise of 5.5 o C - 15% necrosis
 rise of 11.1o C - 60% necrosis
 rise of 16.6o C - 100% necrosis
AVOIDED BY: Feather edge touch
Water –air spray coolant
Slow-speed handpiece
Special Care While Preparing Grooves/ Pinholes.

12. • Chemical Action
-Bases, Restorative Resins, Solvents, and Luting
Agents.
AVOIDED BY: Cavity Varnish / Dentin Bonding Agents
• Bacterial Action
-Due to bacteria left behind after preparation or having
gained access to dentin due to microleakage.
AVOIDED BY: Removal of all carious dentin before
tooth preparation.

13. Conservation Of Tooth Structure
Partial coverage.
Minimum convergence angle.
Anatomic reduction
Axial surface reduction.Apical extension.
Conservative margin

14. Considerations Affecting Future Dental
Health
 CAUSE
Insufficient Tooth
Reduction
Inadequate Occlusal
Reduction
Poor Margin Location
 EFFECT
Overcontoured
Restoration
Occlusal Dysfunction
Chipping of Enamel

15. Axial Reduction
-Sufficient space for Good axial contours.
-Must Duplicate the contours and profile
of the original tooth.

16. Margin geometry
• Preparation without unsupported enamel
• Ease of identification
• Distinct boundary
• Bulk of material
• Conservation of tooth

17. Title

18.  Margin Placement:
-A Supra-gingival Margin should be preferred over a Sub-
gingival Margin.
Advantages of a Supra-gingival Margin are:
 Easily finished
 Easily cleansible
 Ease of impressions
 Easy Evaluation
 No trauma to the soft tissues.

19. Indications of Subgingival preparation
• Dental caries , cervical erosion
• Contact areas extended to gingival crest
• Retention
• Margin has to be hidden
• Root sensitivity
A
C B

20.  Margin Adaptation –
• Recurrent caries – dissolution of cement
• Accurate adaptation
• Irregular or stepped junctions
BD

21. BIOLOGIC WIDTH

22. The distance from the epithelial attachment to the crest of
the alveolar bone is called as the “biologic width.” It is
normally about 2.04mm WIDE, INCLUDING THE
EPITHELIAL ATTACHMENT ( 0.97mm) AND THE
CONNECTIVE TISSUE ATTACHMENT (1.07mm).

23. When the margin of a restoration intrudes into the biologic
width, inflammatory and osteoclastic activity are stimulated.

24. Bone resorption will continue until the alveolar crest is at least 2.0mm
FROM THE RESTORATION MARGIN. The best outcome that can be
expected is that the epithelial and connective tissue attachments will
reestablish themselves at a more apical level. Continued inflammation
with pocket formation is likely.

25.  Preventing Tooth Fracture –
• Minimize - destructive stresses – inlay - wedge
- opposing walls
• Providing a cuspal coverage restoration -
complete crown.

26. Mechanical Considerations
 Retention Form
 Resistance Form
 Structural Durability

27. Title
 Retention : A+B
 Resistance: B+C+D

28. Retention Form :
Magnitude of the dislodging forces
Geometry of the tooth preparation
Roughness of the fitting surface of the
restoration
Materials being cemented
Film thickness of the luting agent

29. Magnitude of the dislodging forces
Depends on the stickiness of food
Geometry of the tooth preparation –
prostheses depend on the geometric form rather
than - cements
Cement is effective only if the restoration
has a single path of withdrawal

30. Closed lower pair of kinematic elements
- Formed by two cylindrical surfaces
- curve of a complete crown - closed - grooves -
partial crown - prevent movement at right angles -
complete crown - over tapered - no longer be
cylindrical,

31. Taper -
Theoretically, maximum retention - parallel walls –
undercuts
Taper small – limited path of withdrawal
Ward - first to recommend taper of 3 to 12 °
Jorgensen and Kaufman - 2.5.to 6.5 ° - optimum

32. Freedom of Displacement.
Maximum retention - when there is only one
path ….long parallel axial walls
Definite wall perpendicular to the direction of
the force ….
Proximal box - Buccal and lingual wall…meet
the pulpal wall …near 90°

33. Length
More surface area - more retentive
Length - enough to interfere with the arc of the
casting
The shorter the wall - more important its
inclination.
The shorter walls - little taper

34. Path of insertion
Imaginary line along which the restoration will
be placed.
Survey a preparation …..12 inches
….preparation to be surveyed in the mouth -
½ inch above the preparation

35. For metal ceramic crowns, the path - parallel -
long axis of the teeth.
Partial Coverage Restorations

36. • Roughness of the Surfaces Being Cemented
• If Internal surface of a restoration is very smooth-retentive
failure occurs at the cement restoration interface
• Restoration is roughened or grooved.
• Air-abrasion - with 50 µm of alumina – 64% retention
 Materials Being Cemented
• More reactive the alloy is, the more adhesion
• …Base metal alloys are better retained

37.  Type Of Luting Agent
Adhesive resin cements are the most adhesive followed by
cements which bond with the tooth and zinc phosphate
cement.
Adhesive resin cements-long term deterioration-resin
dentin interface-NANOLEAKAGE

38.  Resistance form:
 Depends on
• Magnitude and direction of the dislodging forces
• Geometry of the tooth preparation
• Physical properties of the luting agent

39. Magnitude and Direction of the Dislodging
Forces.
Properly designed occlusion, the load should be
well distributed …
Geometry of the Tooth Preparation
Concept of resistance area(RA)

40. Length Width

41. Hegdahl and Silness - Increased preparation taper and
rounding of axial angles tend to reduce resistance
Molar teeth require more
parallel preparation

42. Partial-coverage
Resistance must be provided
by grooves , boxes or pinholes

43. Tylman suggests - proximal grooves just buccal to the
junction of the buccal and middle third of the proximal.
Johnston and associates and Vale - the groove as
buccal as possible but still within the original contact area.
Bassett and associates, Jones, Baum, and Shillinburg -
groove placement as buccal as possible.

44. Anthony H.L. Tjan, Gary D. Miller… J.P.D. 1981
discussed about two groove flare designs
referred to as Type I and Type II.
Type I groove-flare :
Fishhook design
Encroachment on pulp
Type II groove-flare :
placed into the dentin paralleling a line tangent

45. Biologic factors which influence the
choice of groove location
size and location of the pulp chamber
thickness of the enamel
direction of the enamel rods
alignment of the tooth involved
physical properties of the dental structure.
Maximum length - 0.5 mm short of the gingival margin.

46. Bowley and Lai ......Both grooves and boxes provided
significant improvement of total surface area for both the
3- and 4-mm vertical preparation heights.
Cambagni , Bernal, Goodacre and Kim .....The most
effective method of enhancing resistance form in a tooth
preparation that lacks resistance is to decrease the total
occlusal convergence of the cervical portion of the
prepared axial walls.

47. Physical Properties Of Luting Agents
Compressive strength of re-inforced ZnOE is halved at
mouth temperature.
Zinc Phosphate has high modulus of elasticity so retention
depends less on taper when compared to Zn
Polycarboxylate
Adhesive resin>Resin>Glass Ionomer>Zinc
Phosphate>Polycarboxylate

48. Structural durability
A restoration must contain a bulk of material that
is adequate to with stand the forces of occlusion.
This bulk must be confined to the space created by
the tooth preparation.

49. Structural durability
Occlusal reduction.
Functional cusp bevel.
Axial reduction.

50. Occlusal reduction
One of the most important feature for providing
adequate bulk of metal and strength to the
restoration is occlusal clearance.

51. Occlusal reduction
Functional
cusp
Non functional
cusp
All metal 1.5 1.0
Metal
ceramic
1.5-2.0 1.0-1.5
All ceramic 2.0 2.0

52. FUNCTIONAL CUSP AND NON
FUNCTIONAL CUSP

55. AXIAL REDUCTION
Plays an important role in securing space
for an adequate thickness of the restorative
material.

56. Esthetic Considerations
Metal-ceramic restorations :
Facial tooth reduction :
Adequate reduction of the facial surface – Color
depth and translucency.
Minimum reduction of 1.5 mm

57. Incisal Reduction
incisal edge – no metal backing - translucency – 2mm
reduction.
Proximal Reduction
extent is contingent on the location of metal-
ceramic junction.
Proximal surface with no metal backing at the
incisal edge – looks most natural

58. Low lip line
Collarless Metal collar
Patient’s smile - initial examination
High lip line
Margins - not to be placed so far apically -
encroach on the attachment.

59. Supragingival margin - Easier to keep clean
Subgingival margins - Indicated for esthetic
reasons - when the patient has a high lip line

60. Partial-coverage restorations :
Proximal margin : …place the margin just buccal
to proximal contact area - metal - hidden by the
distal line angle.
Tooth preparation angulation

61. Facial margin :
Just beyond the occlusofacial line angle.
A short bevel is needed to prevent enamel chipping
If buccal margin - correctly shaped, no reflection of
light
Mandibular partial cast crowns - metal display is
unavoidable
A chamfer, rather than a bevel, is recommended for the
buccal margin

62. Current Concepts
 Tooth preparations for complete
crowns: An art form based on scientific
principles
Charles Goodacre

63. 1. The total occlusal convergence, ideally should range between 10
and 20 degrees.
2. 3 mm should be the minimal occlusocervical /incisocervical
dimension of incisors and premolars prepared within the
recommended 10 to 20 degrees of total occlusal convergence.
3. The minimal occlusocervical dimension of molars should be 4 mm
when prepared with 10 to 20 degrees total occlusal convergence.
4. The ratio of the occlusocervical/incisocervical dimension of a
prepared tooth to the faciolingual dimension should be at least 0.4 or
higher for all teeth.

64. 5. Whenever possible, teeth should be prepared so that the
facioproximal and linguoproximal corners are preserved.
6. Teeth without natural circumferential morphology after tooth
preparation (round teeth) or teeth that lack adequate resistance
form should be modified with the creation of grooves/boxes.
7. Many molars need auxiliary grooves or boxes to enhance
resistance form because of their short occlusocervical dimensions
and the unfavorable ratio of the occlusocervical dimensions to the
faciolingual dimensions.
8. Axial grooves/boxes should be used routinely when mandibular
molars are prepared for fixed partial dentures, and they should be
located on the proximal surfaces.

65. 9. When tooth conditions and esthetics permit, finish lines should
be located supragingivally.
10. When subgingival finish lines are required, they should not be
extended to the epithelial attachment.
11. Chamfer finish lines approximately 0.3 mm deep are well suited
for all-metal crowns.
12. Both shoulder and chamfer finish lines can be used with all-
ceramic crowns if the crowns are bonded to the prepared teeth.
Depths greater than 1 mm are not required when a
semitranslucent type of allceramic crown is used.

66. 13. Axial and occlusal reductions for all-metal crowns should be at
least 0.5 mm deep and 1.0 mm deep, respectively.
For metal-ceramic crowns, Facial /axial reductions in excess of 1
mm can compromise the remaining tooth structure external to the
pulp, whereas 2.0 mm of occlusal reduction is commonly
achievable even on a young tooth.
With all-ceramic crowns, it is not necessary to exceed 1 mm of
axial reduction with semitranslucent systems and higher value,
lower chroma shades.
2 mm incisal/occlusal reduction for allceramic crowns.

67. 14. Line angles should be rounded on all-ceramic tooth
preparations to reduce stress in the definitive
restoration.
With crowns that use metal, the primary purpose of line
angle rounding is to facilitate pouring impressions and
investing wax patterns without trapping air bubbles
and to facilitate removing casting modules.
15. Smooth tooth preparation appears to enhance the fit
of restorations. Surface roughness generally
increases retention with zinc phosphate cement, but
its effect with adhesive cements (polycarboxylate,
glass ionomer, resin) has not been as definitely
determined.

68. CONCLUSION
Successful restoration:
Accurate diagnosis
Thoughtful Rx planning
Preparation design

69. On tooth preparation depends
Pulp vitality
Periodontal health
Good esthetics
Proper occlusion
Protection of remaining tooth
Longevity of the restoration

70. Contemporary fixed prosthodontics ; Rosensteil, Lang,Fujimoto;3rd ed.
Fundamental of fixed prosthodontics ; Shillingburg et al,3rded.
Fundamental of Tooth preparation ,Shillingburg
Modern practice of Fixed prosthodontics – Johnston , 4th ed.
Theory & practice of fixed prosthodontics – Tylman
J.P.D. 1965 ; 15 : 129
J.P.D. 1976 ; 35 :538
J.P.D. 1979 oct.;42(4) : 405 – 10
J.P.D. 1981 ; 45 : 138
References

71. J.P.D. 1987 ; 57 : 411
J.P.D. 1989 ; 62 : 264
J.PD. 1991 ; 65 : 56
J.P.D. 1996 ; 75 : 129
J.P.D. 1998 ; 79 : 671
DCNA 2004 Apr.; 48(2) : 387-97
J.P.D 2001;85:363-76.
J.P.D 2009;101:7-12.
J.P.D 2003;89:565-71
J.P.D 2004;91:33-41
J.P.D 2007;98:436-444