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1. Good
Morning
Good morning

3. Contents
 Introduction
 Classification
 Biological requirements
 Mechanical requirements

4. Esthetic requirements
 Planning and evaluating tooth
preparation
 Frequently encountered errors in
tooth preparation
 Conclusion
 References

5. Introduction
Carious, traumatised or worn out teeth
require preparation
Preparations based on fundamental
principles
A good preparation ensures that subsequent
techniques can be accomplished

6. Tooth preparation -“ mechanical treatment of
dental disease or injury to hard tissues that
restore a tooth to original form”
Perceptive diagnosis and disciplined tooth
preparation determine success

7. Objectives of tooth preparation
Reduction of tooth in miniature to provide retainer
support
Preservation of healthy tooth structure to secure
resistance form
Provision for acceptable finish lines
Performing axial tooth reduction to encourage
favourable tissue responses from artificial crown
contours

8. Factors to be considered before
preparing teeth
•Size and position of the pulp
•Rotation or tilting of teeth
•Provision of space for connectors
•Use of precision retainers

9. •Finishing margin
•Degree of metal to be displayed
•Treatment of any opposing teeth

10. Classification
According to Rosenstiel, Land and
Fujimoto (1988)
biologic mechanical
esthetic

11. According to Shillingburg et al (1987)
•Preservation of tooth structure
•Retention and resistance
•Structural durability
•Marginal integrity
•Preservation of periodontium

12. The Rosenstiel classification

13. Biological considerations
I. Prevention of damage during tooth preparation
II.Conservation of tooth structure
III.Considerations affecting future dental
health

14. I.Prevention of damage during
tooth preparation
Adjacent teeth-
 A metal matrix band around adjacent tooth
 A thin tapered diamond - interdental area
 Leave a slight lip or fin of enamel on the
proximal side

16. Soft tissues-
 Prevent damage to tongue and cheeks
Careful retraction with aspirator tip and
mouth mirror or flanged saliva ejector

17. Pulp-
Extreme temperature, chemical irritation or
micro organisms cause irreversible pulpitis
Pulp size decreases with age

18. Causes of injury-
Temperature -
excessive pressure
high rotational speeds
type, shape, condition of cutting instrument
all increase generated heat

19. water spray prevent
overheating of the tooth
removes debris
prevents clogging
prevents dessication of dentin

20. Chemical action-
bases, restorative resins, solvents and luting
agents-cause pulpal damage
Bacterial action-
all carious dentine should be removed

21. II.Conservation of tooth structure
 partial coverage
complete coverage
 Axial walls - minimal taper
 Occlusal reduction - anatomic planes

22.  Retain maximal thickness surrounding
pulpal tissues
 conservative margin geometry
 Avoid unnecessary apical extension

24. III.Considerations affecting
future dental health
Axial reduction-
 sufficient space for good axial contours
 margin - smooth and free of ledges
 anterior crowns –maintain the interproximal
papilla

25. adequate less over
reduction reduction reduction

26. Margin placement-
Supra gingival margins –
 No trauma to soft tissues
 On enamel
 Kept plaque free
 Impressions made easily with no soft tissue
damage
 Easy evaluation after placement or at recall
appointments

27. Equigingival margins-
At the level of the crest of the gingiva
Maintain the health of periodontium

28. Subgingival margins-
dental caries,cervical erosion extend subgingivally
crown lenghthening procedure not indicated
 proximal contact area extends to gingival crest
 additional retention /resistance needed

29. margin of metal ceramic crown to be hidden
 root sensitivity
 modification of the axial contour indicated

30. Margin adaptation-
casting to fit within 10 micrometre
porcelain margin to fit within 50 micrometre
smooth and even margin
rough , irregular increased margin
stepped junctions length & reduced
adaptation accuracy

32. Margin geometry-
Ease of preparation without overextension or
unsupported enamel
Ease of identification in the impression and on
the die
A distinct boundary to which the wax pattern
can be finished

33. Sufficient bulk of material
Conservation of tooth structure

34. margin design advantages disadvantages indications

35. margin design advantages disadvantages indications

36. margin design advantages disadvantages indications

37. Feather edge chisel edge chamfer beveled shoulder 120 deg sloped beveled
shoulder shoulder

39. Occlusal considerations-
Reduction to compensate for supra erupted or
tilted abutment teeth
Reduced retention and resistance
Endodontic treatment needed
Prevent traumatic occlusal scheme

40. Preventing tooth fracture-
The tooth preparation design- minimise the
potentially destructive stresses

43. Mechanical considerations
I. Providing retention form
II.Providing resistance form
III.Preventing deformation of the restoration

44. I. Providing retention form
Retention
The quality of a preparation that prevents the
restoration from becoming dislodged by such
forces parallel to the path of placement

45.  Magnitude of dislodging forces
 Geometry of tooth preparation
 Roughness of the fitting surface of the
restoration
 Materials being cemented
 Type of luting agent
 Film thickness of the luting agent

46. A)Magnitude of the dislodging forces-
Pulling with floss under the connectors
When exceptionally sticky foods( caramel ) is
eaten
Magnitude depends on -stickiness of foods
-surface area
-surface texture

47. B) Geometry of the tooth preparation-
 A single path of placement
 Preparation restrains free movement
 The occlusoaxial line angle - a replica of the
gingival margin geometry

48. Taper:
Convergence of two opposite external walls of
a tooth preparation as viewed in a given plane
Angle of convergence
Maximum retention - parallel walls

49. Undercut- any irregularity in the wall of the
prepared tooth that prevents the withdrawal or
seating of a wax pattern or casting
If cervical diameter at the margin
narrower than at occluso axial junction
The recommended convergence between opposing
walls is 6 degrees

51. Surface area:
Crowns with tall axial walls - more retentive
Wider tooth – more retentive

53. Stress concentration:
Stresses are not uniform throughout the
cement
Are concentrated around the junction of axial
and occlusal surfaces
Sharp occlusoaxial line angles should be
rounded to minimise these stresses

54. Type of preparation:
Retention of complete crown is more than
double of that of partial coverage
Addition of grooves and boxes limit the path
of placement

57. Roughness of the surfaces being cemented:
Retentive failure -cement restoration interface
Air abrading the fitting surface with 50 micron
of alumina
Avoid abrading the polished surfaces or margins

58. Materials being cemented:
type of casting alloy
core build up material
Base metal alloys better retained
Cement adheres better to amalgam

59. Type of luting agent:
Film thickness of the luting agent:
Important if slightly oversized casting is made

60. II. Providing resistance form
Lateral forces displace by causing rotation
Rotation is prevented by resistance areas

61. Depends on:
•Magnitude and direction of the dislodging
forces
•Geometry of tooth preparation
•Physical properties of the luting agent

62. A)Magnitude and direction of dislodging
forces-
 In normal occlusion , biting force mostly is
axially directed
 If patient has a habit of pipe smoking or
bruxism, large oblique forces are generated

63. B) geometry of tooth preparation-
 Taper of 5 to 22 degrees
 Short tooth with large diameters- less
resistance
 On molar crown minimum preparation wall
height - 3.5 to 4 mm

64.  Increasing taper and rounding off axial angles
reduce resistance
 Proximal grooves and boxes enhance resistance
 Partial coverage crowns have less resistance

69. C) Physical properties of luting agents-
Properties such as compressive strength and
modulus of elasticity
Adhesive resin  glass ionomer  zinc
phosphate  polycarboxylate  zinc oxide
eugenol

70. III. Preventing deformation
A)Alloy selection-
 Type I and II gold alloys -intra coronal cast
restorations
 Type III and IV gold alloys -crowns and FDPs
 Nickel chromium alloys - for long span FDPs

71. B) Adequate tooth reduction –
 Alloy thickness of 1.5 mm over functional
cusps and 1 mm over non functional cusps
 Occlusal reduction should be uniform following
cuspal planes of teeth

74. Esthetic considerations
Determining the esthetic expectations of the
patient
At the initial examination, a full assessment is
made of the appearance of the patient ,noting
teeth shown in speech , smiling and laughing
Related to oral hygiene needs and the potential
for development of future disease

75. All ceramic restorations –
 most pleasing esthetic restoration
 mimic tooth original color better
 greater risk of brittle tooth fracture
 minimum material thickness of 1 to 1.2 mm

77. Metal ceramic restorations-
 a metal cast sub structure that in visible areas
has an esthetic porcelain veneer
 a minimum reduction of 1.5 mm facially
 sub gingival margins
 porcelain coverage on occlusal surface

79. Partial coverage restorations-
 maintain an intact labial or buccal surface
 tooth structure is conserved

81. Planning & evaluating tooth
preparations
Diagnostic tooth preparations-
 selecting path of placement
deciding on the amount of tooth reduction
determining the location for the facial and proximal
margins

82. Diagnostic waxing procedures-
establish the optimum contour and occlusion
Alteration of occlusal scheme or anterior
guidance

83. Evaluative procedures during tooth
preparation-

85. Detecting undercuts during tooth
preparation

87. Complex preparations - evaluated by making an
alginate impression and pouring it in fast setting
stone.
A dental surveyor - precisely measure the axial
inclinations of the tooth preparation.

88. Checking occlusal reduction -

90. use the contra angle handpiece as both a
cutting and measuring instrument.
top surface of the turbine head is
perpendicular to the shank of the bur.
If the top surface is kept parallel to the
occlusal surface of the tooth being prepared ,
the bur is automatically in correct orientation.

92. Patient and operator positioning-
Direct view preferred
Having the patient rotate the head -improves
visibility of molar teeth
partially open jaw -cheek retracted easily
lateral excursion - distobuccal line angle and
buccal third of the distal wall seen directly
the mirror view - visualizing distal surface

93. Maxillary right posterior –
buccal or buccal half of occlusal-
operator at 9 to 11 o’clock position
patient turns head to left
palatal or palatal half of occlusal-
operator at 11 o’çlock position
patient turns head to right

94. Maxillary left posterior-
buccal or buccal half of occlusal-
operator at 9 o’clock position
patient turns head to right
palatal or palatal half of occlusal-
operator at 9 o’clock position
patient turns head to left
 distal surface reduction-
operator at 9 o’clock position
patient’s mandible in left lateral excursion

95. Frequently encountered errors in
tooth preparations
Inadequate tooth reduction on incisal or
occlusal surfaces
Inadequate tooth reduction on the
preparation’s axial walls
Over reduction of tooth structure
Excess taper on the tooth preparation

96. Inadequate build ups
Indistinct margins
Excess gingival extension
Undercuts in the preparation’s axial
walls
Sharp angles on the preparation

97. Conclusion
Successful restoration- accurate diagnosis
thoughtful Rx planning
preparation design

98. On tooth preparation depends-
pulp vitality
periodontal health
good esthetics
proper occlusion
protection of remaining tooth
longevity of the restoration

99. References
•Contemporary fixed prosthodontics –
Rosenstiel, Land and Fujimoto
4th edition pages 209- 257
•Fundamentals of fixed prosthodontics –
Shillingburg et al
3rd edition pages 119 – 138
•Fundamentals of tooth preparation for cast
metal and porcelain restorations – Shillingburg
et al. 1991 ed pages 13-45

100. •Tylman’s fundamentals of fixed
prosthodontics
8th edition pages 113-143
•JADA oct 2007 vol 138 pages 1373- 1375
•JPD june 2006 vol 95 no 6 pages 456-461
•JPD aug 2005 vol 94 no 2 pages 105 -107
•JPD dec 2004 vol 92 no 3 page 302
•JPD may 2004 vol 91 no 5 pages 499-500
•JPD may 2001 vol 85 no 5 pages 521-522
•JPD april 2001 vol 85 no 4 pages 363-375

101. Thank you
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