This document discusses principles of tooth preparation for fixed partial dentures. It covers biologic, mechanical, and esthetic considerations. On the biologic side, it emphasizes conservation of tooth structure, avoidance of overcontouring, and protection of the pulp. Mechanically, it focuses on providing adequate retention and resistance form through proper taper, surface area, and stress distribution. Esthetically, it notes the goals of minimizing metal display and ensuring porcelain thickness and contours. Overall, the key principles discussed are preservation of tooth structure and surrounding tissues, achieving durable marginal integrity, and allowing for a functional occlusion.

1. DR ACHYUT SINHA
1ST YEAR PG
1

2. INTRODUCTION
2

3. PARTS OF FIXED PARTIAL DENTURE
RETAINER
ABUTMENT
PONTIC
CONNECTOR

4. Teeth do not posses the regenerative ability found
in most other tissues. Therefore, once enamel or
dentin is lost as a result of caries, trauma, or wear,
restorative materials must be used to reestablish
form and function. Teeth require preparation to
receive restorations, and these preparations must
be based on fundamental principles from which
basic criteria can be developed to help predict the
success of prosthodontic treatment.
4

5. The principles of tooth preparation may be divided
into three broad categories:
1. Biologic considerations, which affect the
health of the oral tissues
2. Mechanical considerations, which affect the
integrity and durability of the restoration
3. Esthetic considerations, which affect the appearance
of the patient
(ROSENSTIEL)
5

6. BIOLOGIC
• CONSERVATION OF TOOTH
STRUCTURE
•AVOIDANCE OF OVERCONTOURING
•SUPRAGINGIVAL MARGINS
•HARMONIOUS OCCLUSION
•PROTECTION AGAINST
FRACTURE
MECHANICAL
• RETENTION FORM
• RESISTANCE FORM
• DEFORMATION
ESTHETIC
• MINIMUM DISPLAY OF METAL
•MAXIMUM THICKNESS OF
PORCELAIN
•PORCELAIN OCCLUSAL SURFACE
•SUBGINGIVAL MARGINS
6

7. PRESERVATION OF TOOTH STRUCTURE
RETENTION & RESISTANCE FORM
STRUCTURAL DURABILITY
MARGINAL INTEGRITY
PRESERVATION OF THE PERIODONTIUM
(SHILLINGBURG)
7

8. BIOLOGIC
CONSIDERATIONS
8

9. PREVENTION OF DAMAGE DURING
TOOTH PREPARATION
-ADJACENT TEETH
-SOFT TISSUES
-PULP
9

10. 1. ADJACENT TEETH :-
Iatrogenic damage to adjacent tooth
Plaque retention in damaged area
Increased caries
10

11. PREVENTION:-
 Use of metal matrix band around adjacent tooth
structure.
 Use of proximal enamel of tooth being prepared for
protection of adjacent structure.
11

12. Damage to adjacent
teeth is prevented
by making
a thin "lip"
of enamel as the
bur passes through a
proximal contact.
12

13. 2. SOFT TISSUE DAMAGE
PREVENTION
By careful retraction with
 Aspirator tip
 Mouth mirror
 Flanged saliva ejector
13

14. Mouth mirror protecting
the soft tissues during
tooth preparation.
14

15. 3. PULP :-
Heat produced during tooth reduction/chemical irritation/
Microorganisms
Cause reversible/irreversible pulp hyperemia
Which may lead to pulp damage
15

16. PREVENTION
1. Evaluation of radiograph
2. Proper cooling system must be used with water spray
16

17. Causes of Injury
1. Temperature ,
2. Excessive Pressure ,
3. Rotational speed ,
4. Chemical action of
restorative material,
5. Bacterial Action
17

18. TEMPERATURE:
 Heat is generated by friction between rotary
instrument and surface being prepared.
 Other factors which may lead to increase in
temperature
-Excessive pressure
-Higher rotational speed
-Type,Shape,Condition of cutting instrument
18

19. PREVENTION:
 Use of water spray.
 Use of slow speed hand piece or hand instrument.
 Care should be taken while preparing grooves or pin
holes, as coolant cannot reach the cutting edge of bur
 With a high-speed handpiece, a feather-light touch
allows efficient removal of tooth material with
minimal heat generation.
19

20. CHEMICAL ACTION:
Chemical action of certain DENTAL MATERIALS (bases,
restorative resins, solvent) may cause pulpal damage
particularly when applied to freshly cut dentin.
PREVENTION
-Use of Cavity varnish or Dentin bonding agent will
form effective barrier.
20

21. BACTERIAL ACTION:
 Microleakage may cause bacteria to enter the dentin and
may cause pulp damage.
PREVENTION
-Use of zinc phosphate cement, as it provide anti- Bacterial
effect to vital dentin which seems to resist infection.
NOTE ;all carious dentin should be removed before placing a
restoration that will serve as a foundation for a fixed
prosthesis.
21

22. CONSERVATION OF TOOTH STRUCTURE
 USE OF PARTIAL COVERAGE
CROWN RATHER THAN
COMPLETE COVERAGE.
 PREPARATION OF TEETH
WITH MINIMUM PRACTICAL
CONVERGENCE ANGLE (taper)
B/W AXIAL WALLS
22

23.  PREPARATION OF THE
OCCLUSAL SURFACE SO
REDUCTION FOLLOWS THE
ANATOMIC PLANES TO GIVE
UNIFORM THICKNESS IN THE
RESTORATION.
PREPARATION OF AXIAL
SURFACES SO TOOTH STRUCTURE
IS REMOVED EVENLY; IF
NECESSARY,TEETH SHOULD BE
ORTHODONTICALLY
REPOSITIONED
23

24. 24

25.  SELECTION OF CONSERVATIVE
MARGIN.
 AVOIDANCE OF
UNNECESSARY
APICAL EXTENSION
OF THE PREPARATION.
25

26. CONSIDERATIONS AFFECTING
FUTURE DENTAL HEALTH
AXIAL REDUCTION
INSUFFICIENT AXIAL REDUCTION –
OVERCONTOURED RESTORATION –PERIODONTAL
DISEASE/DENTAL CARIES.
OCCLUSAL REDUCTION
Inadequate occlusal reduction may result in
occlusal dysfunction.
MARGIN LOCATION
Poor margin placement such as in the area of
occlusal contact, may lead to chipped enamel or cusp
fracture.
26

27. SUFFICIENT TOOTH STRUCTURE MUST BE REMOVED TO
ALLOW THE DEVELOPMENT OF CORRECTLY FORMED AXIAL
CONTOURS –IN INTERPROXIMAL AND FURCATION AREAS OF
POSTERIOR TEETH.
27

28.  MARGIN PLACEMENT
MARGIN OF PREPARATION SHOULD BE
SUPRAGINGIVAL
ADVANTAGES-
-CAN BE EASILY FINISHED
-EASIER TO PREPARE ACCURATELY
WITHOUT TRAUMA TO THE SOFT TISSUE
-MORE EASILY KEPT CLEAN
-IMPRESSIONS ARE MORE EASILY MADE
-RESTORATIONS CAN BE EASILY
EVALUATED AT RECALL APPOINTMENTS
28

29.  If finish line is given SUB-GINGIVALLY it
will result in :-
Gingival inflammation
Loss of alveolar crest height
Periodontitis
Periodontal pocket
29

30. SUBGINGIVAL MARGINS
(INDICATIONS)
 DENTAL CARIES , CERVICAL EROSION
,RESTORATIONS EXTEND SUBGINGIVALLY
OR WHEN CROWN LENGHTHENING
PROCEDURE IS NOT INDICATED
 PROXIMAL CONTACT AREA EXTEND TO
THE GINGIVAL CREST.
 ADDITIONAL RETENTION IS NEEDED.
 THE MARGIN OF METAL-CERAMIC CROWN
IS TO BE HIDDEN BEHIND THE
LABIOGINGIVAL CREST.
30

31.  Root sensitivity cannot controlled by conservative
procedure.
 Modification of axial contour is indicated.
31

32. MARGINAL INTEGRITY:
 The restoration can survive in the biological
environment of the oral cavity
 The configuration of the preparation finish
line dictates the shape & bulk of restorative
material in the margin of the restoration
32

33. Marginal Integrity..
Incompetent
Adaptation
Gingival impingement
Periodontal
deterioration
OVER EXTENSION
33

34. OVER EXTENSION
34

35. Marginal Integrity..
Incompetent
Adaptation
UNDER EXTENSION
Sensitivity
Accumulation of Debris
Plaque formation
Marginal leakage
35

36. UNDER EXTENSION
36

37. UNDER EXTENSION
37

38. Marginal Integrity..
Incompetent Adaptation
THICK
Accumulation of debris
Plaque formation
Periodontal deterioration
Susceptibility to root
38

39. Incompetent Adaptation…
THICK
39

40. Incompetent Adaptation
Marginal Integrity..
OPEN
Sensitivity
Accumulation of debris
Marginal leakage
Periodontal deterioration
40

41. Incompetent Adaptation
41

42. MARGINAL 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.
 The more accurately the restoration is adapted to the
tooth, the lesser the chance of recurrent caries or
periodontal disease .
42

43.  ACCEPTABLE MARGINAL ADAPTATION
FOR CASTING - 10μm
FOR PORCELAIN - 50μm
(BELSER – 1985)
A WELL DESIGNED PREPARATION HAS A
SMOOTH AND EVEN MARGIN
43

44. 44

45. MARGIN GEOMETRY
(GUIDELINES)
 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.
 SUFFICIENT BULK OF MATERIAL
 CONSERVATION OF TOOTH STRUCTURE.
45

46. FINISH LINE
 The peripheral extension of a
tooth preparation
 The planned junction of
different material
 The terminal portion of a
prepared tooth
 Line of demarcation
46

47. Finish line..
Types of finish lines
•Featheredge
• Chisel edge
•Chamfer
•Shoulder
•Sloped shoulder
• Shoulder with bevel 47

48. Finish line..
FEATHEREDGE
Advantage
•Conservative of tooth
structure
Disadvantage
* Does not provide sufficient bulk
Indication
* Not recommended 48

49. CHISEL EDGE
Advantage
* Conservative of tooth structure
Disadvantage
* Location of margin difficult to
control
Indication
* On tilted teeth
Finish line..
49

50. CHAMFER
Advantage
* Distinct margin, adequate bulk
Disadvantage
*care needed to avoid unsupported lip of
enamel
Indication
* Cast metal restoration, lingual margin of
metal-ceramic crowns
Finish line..
50

51. CHAMFER FINISH LINE
Full Veneer Crown Preparation
51

52. BIOMECHANICS OF CROWN & BRIDGE
HEAVY CHAMFER LINE
All Ceramic Crown
52

53. Finish line..
SHOULDER
Advantage
* Bulk of restorative material
Disadvantage
* Less conservative of tooth structure
Indication
* Facial margin of metal ceramic crowns,
complete ceramic crowns
53

54. SHOULDER FINISH LINE
All ceramic crown (PJC)
54

55. Finish line..
SLOPED SHOULDER
Advantage
•Bulk of restorative material,
Advantage of bevel
Disadvantage
* Less conservative of tooth structure
Indication
* Facial margin of metal ceramic crowns
55

56. SHOULDER WITH BEVEL
Advantage
•Bulk of restorative material, removes
unsupported enamel , allows finishing
of the metal
•Disadvantage
* Less conservative of tooth structure,
Extends preparation apically
Indication
* Facial margin of posterior metal ceramic
crowns with supragingival margins
Finish line..
56

57. OCCLUSAL CONSIDERATION
 TOOTH PREPARATION SHOULD ALLOW
SUFFICIENT SPACE FOR DEVELOPING
FUNCTIONAL OCCLUSAL SCHEME IN THE
FINISHED RESTORATION.
 CONSIDERABLE REDUCTION IS NEEDED TO
COMPENSATE FOR THE SUPRAERUPTED
ABUTMENT TEETH
57

58. A, Nonreplacement of missing teeth has led to supraocclusion and a protrusive
interference (arrow). B, Teeth reduced with the help of trial tooth preparations and
diagnostic waxing. C, Restorations with anterior guidance.
58

59. PREVENTING TOOTH FRACTURE:
 RESTORED TOOTH FRACTURE CAN BE LESSENED
IF TOOTH PREPARATION IS DESIGNED TO
MINIMIZE POTENTIALLY DESTRUCTIVE STRESSES.
 PROVIDING A CUSPAL COVERAGE RESTORATION
RATHER THAN AN INLAY LESSENS THE CHANCE
OF FRACTURE
 A COMPLETE CROWN IS OFTEN A BETTER
SOLUTION,BECAUSE IT OFFERS THE GREATEST
PROTECTION AGAINST TOOTH FRACTURE,
TENDING TO HOLD THE CUSP OF THE TOOTH
TOGETHER.
59

60. A, An intracoronal cast restoration (inlay) can act as a wedge during cementation or
function.If the cusps are weakened, fracture will occur. B, A cuspal-coverage onlay
provides better protection but often lacks retention. C, A complete crown provides the
best protection against fracture. It also has the best retention.
60

61. MECHANICAL
CONSIDERATIONS
61

62. MECHANICAL CONSIDERATIONS
• PROVIDE RETENTION FORM
• PROVIDE RESISTANCE FORM
• PREVENTING DEFORMATION OF THE
RESTORATION
62

63. RETENTION FORM
 RETENTION – THE QUALITY OF A
PREPARATION THAT PREVENTS THE
RESTORATION FROM BEING DISLODGED BY
FORCES PARALLEL TO THE PATH OF
WITHDRAWL.
63

64. FACTORS FOR ADEQUATE
RETENTION
• MAGNITUDE OF DISLODGING FORCES
• GEOMETRY OF THE TOOTH PREPARATION
• ROUGHNESS OF THE FITTING SURFACE OF THE
RESTORATION
• MATERIALS BEING CEMENTED
• FILM THICKNESS OF THE LUTING AGENT
64

65. MAGNITUDE OF DISLODGING
FORCES
 Forces that tend to remove a cemented restoration
along its path of withdrawal.
DEPENDS ON –
 THE STICKINESS OF THE FOOD
 SURFACE AREA AND TEXTURE OF THE
RESTORATION BEING PULLED
65

66. GEOMETRY OF TOOTH
PREPARATION
 Most fixed prostheses depend on the geometric form
of the preparation rather than on adhesion for
retention because most of the traditional cements
(e.g., zinc phosphate) are nonadhesive (i.e., they act by
increasing the frictional resistance between tooth and
restoration).
 CEMENT IS EFFECTIVE ONLY IF THE RESTORATION
HAS A SINGLE PATH OF WITHDRAWL.
66

67.  THE RELATION SHIP B/W TWO BODIES , ONE
RESTRAINING MOVEMENT OF THE OTHER – CLOSED
LOWER PAIR OF KINEMATIC ELEMENTS.
 IN FPD – SLIDING PAIR- i.e FORMED BY TWO
CYLINDRICAL SURFACES CONSTRAINED TO SLIDE
ALONG ONE ANOTHER
 A tooth preparation will be cylindrical if the axial
surfaces are prepared by a cylindrical bur held at a
constant angle.
67

68.  However, if one wall of the complete crown
preparation is over-tapered, it will no longer be
cylindrical, and the cemented restoration will not be
constrained by the preparation because the restoration
then has multiple paths of withdrawal.
68

69. TAPER
 The axial walls of the preparation must taper
slightly to permit the restoration to seat…..
That is..
 Two opposing external walls must gradually
converge..
69

70.  The term Angle of Convergence can be used to
describe the relationship of the two opposing
walls of a preparation,
 The more nearly parallel the opposing walls of
the preparation, the greater should be the
retention.
70

71. 71

72. SURFACE AREA
 The greater the surface area for the
preparation, the greatest its retention.
 The preparation on larger teeth are more
retentive than preparation on small teeth.
 Surface area can be increased by adding
boxes and grooves
72

73. A full crown preparation is more
retentive on a molar than on a
premolar
73

74. STRESS CONCENTRATION
 STRESSES ARE NOT UNIFORM THROUHOUT THE
CEMENT BUT CONCENTRATED AROUND THE
JUNCTION OF THE AXIAL AND OCCLUSAL
SURFACES.NICHOLLAS (1974)
 ROUNDING OF INTERNAL LINE ANGLES –
REDUCE STRESS CONCENTRATION
74

75. TYPE OF PREPARATION
 Different types of preparation have different retentive
values that correspond fairly closely to the surface area
of the axial walls, as long as other factors (e.g., taper)
are kept constant.
 PREPARATION IN WHICH ADDITION OF A GROOVE
LIMITS THE PATH OF WITHDRAWL ,RETENTION IS
INCREASED
75

76. RETENTION OF DIFFERENT
PREPARATION DESIGN.
76

77. INTERNAL FEATURES
Retention from an excessively tapered preparation can be
increased by adding grooves and pinholes,because this will
limits path of with drawl.
77

78. ROUGHNESS OF SURFACE BEING
CEMENTED:
 RETENTION WILL BE INCREASED IF
RESTORATION IS ROUGHENED OR
GROOVED.SMITH(1970).
 AIR ABRADING THE FITTING SURFACE WITH 50μm
OF ALUMINA – INCREASE RETENTION BY 64 %.
78

79. MATERIALS BEING CEMENTED:
 THE MORE REACTIVE THE ALLOY IS THE MORE
ADHESION THERE WILL BE WITH LUTING
AGENTS.
 BASE METAL ALLOYS ARE BETTER RETAINED
THAN LESS REACTIVE HIGH GOLD CONTENT
METALS.SAITO C et al (1976)
79

80. TYPE OF LUTING AGENTS:
 ADHESIVE RESIN CEMENTS ARE MOST
RETENTIVE
 FOLLOWED BY GLASS IONOMER –
POLYCARBOXYLATE CEMENT – ZINC OXIDE
EUGENOL
80

81. 81

82. RESISTANCE FORM:
 THE QUALITY OF PREPARATION THAT PREVENT
THE ROTATION OF THE RESTORATION THAT
ARE PLACED IN COMPRESSION – RESISTANCE
 DEPENDS ON –
-MAGNITUDE AND DIRECTION OF THE
DISLODGING FORCES
- GEOMETRY OF THE TOOTH PREPARATION
- PHYSICAL PROPERTIES OF THE LUTING AGENT.
82

83. MAGNITUDE AND DIRECTION OF
DISLODGING FORCE:
 In one laboratory study,-" a complete crown cemented
on a nickel-chromium test die was found to be capable
of withstanding over 13,500 N (1400 kg) -a
far greater force than would occur in the mouth before
becoming displaced.
 In a normal occlusion, biting force is distributed
over all the teeth; most of it is axially directed. If a
fixed prosthesis is carefully made with a properly designed
occlusion, the load should be well distributed
and favorably directed.
83

84. GEOMETRY OF TOOTH PREPARATION:
 The tooth preparation must be shaped so that
particular areas of the axial wall will prevent rotation
of the crown.
 Lateral forces tend to displace the restoration by
causing rotation around the gingival margin. Rotation
is prevented by any areas of the tooth preparation that
are placed in compression, called resistance areas .
Multiple resistance areas cumulatively make up the
resistance form of a tooth preparation.
84

85. 85

86.  increased preparation taper and rounding of axial
angles tend to reduce resistance.
 Short tooth preparations with large diameters were
found to have very little resistance form.
 In general, molar teeth require more parallel
preparation than premolar or anterior teeth to achieve
adequate resistance form.
86

87.  A partial-coverage restoration may have less resistance
than a complete crown because it has no buccal
resistance areas.
 Resistance must be provided by boxes or grooves and
will be greatest if they have walls that are
perpendicular to the direction of the applied force.
 The resistance form of an excessively tapered
preparation can be improved by adding grooves or
pinholes, because these interfere with rotational
movement and in so doing subject additional areas of
the luting agent to compression.
87

88. Resistance form of partial and complete crowns. A, The buccoaxial wall (RA) of a complete
crown should provide good resistance to rotation around a lingual axis. B, In a partial
crown, resistance must be furnished by mesial and distal grooves. C, In a short or
excessively tapered complete crown, resistance form is minimal because most of the buccal
wall is missing. A mesiodistal groove should be placed to increase resistance form. D, Poor
resistance form is less a problem in a short partial crown, provided the grooves have
sufficient definition. However, lack of retention form may indicate the need
for complete coverage. 88

89. The resistance of short
preparation can be improved by
adding grooves 89

90. 90

91. DEFORMATION:
 MAY BE DUE TO –
• IN APPROPRIATE ALLOY SELECTION
• IN ADEQUATE TOOTH REDUCTION
• POOR FRAMEWORK DESIGN
91

92. ALLOY SELECTION:
 TYPE III AND TYPE IV GOLD ALLOYS ARE
APPROPRIATE FOR CROWNS AND FPD.
 IN LONG SPAN FPD’S – HIGH NOBLE METAL
ALLOYS OR NICKEL CHROMIUM ALLOYS.
92

93. ADEQUATE TOOTH
REDUCTION
93

94.  A restoration must contain a bulk of
material that is adequate to withstand the
forces of occlusion..
 This bulk must confined to the space created
by the tooth preparation. This helps in
Harmonious occlusion, Axial contours normal,
Preventing periodontal problems around the
restoration.
94

95. OCCLUSAL CLEARANCE:
 Occlusal clearance is an important feature for
providing adequate bulk of metal and strength.
TYPE OF FUNCTIONAL CUSP NONFUNCTIONAL
RESTORATION REDUCTION CUSP REDUCTION
 GOLD ALLOYS 1.5mm 1mm
 METALCERAMIC 1.5-2mm 1-1.5mm
 ALL CERAMIC 2mm 2mm 95

96.  The basic inclined pattern of the occlusal surface
should be duplicated to produce adequate clearance
without over shortening the preparation whose length
is already minimal to provide adequate retention
 Inadequate clearance makes a restoration weaker
96

97. FUNCTIONAL CUSP BEVEL:
 It provides space for an adequate bulk of
metal in an area of heavy occlusal contact
 If bevel is not given than deflective occlusal
contact & unnecessary destruction of the
tooth structure will likely to occur.
97

98. 98

99. 99

100. 100

101. 101

102. 102

103. 103

104. AXIAL REDUCTION:
 It secures space for an adequate thickness of
the restorative material
 If reduction is not proper then it will lead to
distortion.
 Other feature that provide space for metal
that will improve rigidity and durability of the
restoration: Offset , The Occlusal
Shoulder, The Isthmus, The Proximal
Groove, and The Box.
104

105. MARGIN DESIGN:
 Distortion of the restoration margin is prevented by
designing the preparation outline to avoid occlusal
contact in this area.
 Also, tooth reduction should provide sufficient room
for bulk of metal at the margin to prevent distortion.
105

106. ESTHETIC
CONSIDERATIONS
106

107. ESTHETIC CONSIDERATIONS
 The restorative dentist should develop skill in determining
the esthetic expectations of the patient
 Patients prefer their dental restorations to look as natural
as possible
 At the initial examination it is important to make a full
assessment of the appearance of each patient noting which
areas of which teeth show during smiling talking and
laughing
107

108. MINIMUM METAL DISPLAY
 When mandibular partial cast crowns are made metal
display is unavoidable because the occlusal surface of
mandibular teeth can be seen during speech
 Anterior partial coverage restoration can be fabricated
to show no metal but their preparation require
considerable care
108

109. MAXIMUM THICKNESS OF
PORCELAIN:
 The poor appearance of some metal –ceramic restorations
is often due to insufficient porcelain thickness
 On the other hand adequate porcelain thickness is
sometimes obtained at the expense of proper axial contour
 To correct all these deficiencies certain principles are
recommended during tooth preparation
109

110.  If there is to be sufficient bulk of porcelain for
appearance and metal for strength adequate reduction
of the facial surface is essential.
 A minimum reduction of 1.5 mm typically is required
for optimal appearance
 An incisal reduction of 2 mm is recommended for
good esthetics
 The proximal surfaces of anterior teeth will look most
natural if they are restored as the incisal edges without
metal backing
110

111. Adequate porcelain thickness is essential for
preventing direct light reflection from the
highly pigmented opaque porcelain. The
most critical areas are the gingival and
incisal thirds; in practice, opaque modifying
stains are often used in these areas.
111

112. PARTIAL COVERAGE RESTORATIONS
 Esthetic partial –coverage restorations depend on
accurate placement of the potentially visible facial and
proximal margins
 Many patients will not readily accept a visible display
of metal
 Place margin buccal to the proximal contact area
where metal will be hidden by the distal line angle of
the neighboring tooth
112

113.  The facial margin should be extended just beyond the
occlusofacial line angle
 A short bevel is needed to prevent enamel chipping
113

114. PORCELAIN OCCLUSAL SURFACES
 The mandibular occlusal surfaces are visible during
speech. Hence metal display is unavoidable.
to avoid unaesthetic appearance, a metal-ceramic
restoration with porcelain coverage on occlusal surface
can be made.
114

115. ACCEPTABLE RESULTS
115

116. CONCLUSSION
 THE PRINCIPLES OF TOOTH PREPARATION CAN
BE CATEGORIZED INTO BIOLOGIC , MECHANICAL
, AND ESTHETIC CONSIDERATIONS.EACH TOOTH
PREPARATION MUST BE MEASURED BY DEFINED
CRITERIA ,WHICH CAN BE USED TO IDENTIFY
AND CORRECT PROBLEMS.THUS SUCCESSFUL
PREPARATION CAN BE OBTAINED MOST EASILY
BY SYSTEMATICALLY FOLLOWING THE STEPS.
116

117. REFERENCES
 Contemporary fixed prosthodontics – Rosenstiel, Land
and Fujimoto 3rd 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
 Ayad ME et al: Influence of tooth surface roughness
and type of cement on retention of complete cast
crowns, J Prosthet Dent 77:116,1997.
117

118.  el-Mowafy OM et al: Retention of metal ceramic
crowns cemented with resin cements: effects of
preparation taper and height, J Prosthet Dent 76:524,
1996.
 Wilson AH, Chan DC: The relationship between
preparation convergence and retention of extracoronal
retainers, J Prosthod 3:74, 1994.
118