principles of tooth preparation - ann george final.pptx

1. Principles of Tooth
Preparation
Dr.Himanshu Tiwari
Senior Lecturer
Dept.of Prosthodontics and Crown and Bridge

2. CONTENTS
• Introduction
• PRINCIPLES OF TOOTH PREPARATION
 BIOLOGIC: Conservation of tooth structure
Considerations affecting dental health
Prevention of damage during preparation
 MECHANICAL: Retention form
Resistance form
Structural durability
 ESTHETIC: Metal ceramic
Partial coverage restoration
• SUMMARY
• REVIEW OF LITERATURE
• REFERENCES

3. Introduction
• Teeth do not possess the regenerative ability found in most other
tissues.
• Therefore, restorative materials are required to replace the lost
enamel or dentine as a result of caries, wear or trauma.
• Hence, teeth require preparation to receive such restorations.
• The longevity of all such restorations depends predominantly on
the preparation.
• So every effort must be made to prepare the tooth such that it
retains the restoration and does not harm the tooth or the
surrounding structures.

4. Tooth Preparation
• The process of removal of diseased &/or
healthy enamel and dentin & cementum to
shape a tooth to receive a restoration.
(G.P.T-9)
• The mechanical treatment of dental disease or
injury to hard tissues that restores a tooth to
original form.

5. Principles

7. Classification of principles of tooth preparation

8. Biologic Considerations :
1. Prevention of damage during tooth preparation
-Adjacent teeth
-Soft tissue
-Pulp
1. Conservation of tooth structure
2. Avoidance of overcontouring
-Axial reduction
1. Marginal integrity and preservation of periodontium
-Margin location
-Margin adaptation
-Margin geometry or Finish line configuration
1. Occlusal considerations
2. Preventing tooth fracture

9. PREVENTION OF DAMAGE
DURING TOOTH PREPARATION
• Adjacent teeth
• Iatrogenic damage to the adjacent tooth during tooth
preparation is a common error.
• A damaged proximal contact area even if reshaped and
polished will be more susceptible to dental caries.
• This is because the original surface enamel contains
higher fluoride concentrations and hence the damaged
layer is more prone to plaque retention

10. Prevention of damage to adjacent teeth
Thin "lip" of enamel
Matrix band

11. Prevention of soft tissue damage
Mouth mirror
Cotton rolls Rubber dam
Aspirator tip Flanged saliva ejector

12. Prevention of damage to pulp
Tooth preparations must not involve or irritate the
pulp chamber.
Causes of pulpal injury
• Temperature
• Chemical action
• Bacterial action

13. Temperature
• Extreme temperatures caused by excessive
pressure and high rotational speeds, condition of
cutting instrument and improper application of
coolants.
• Use of high speed handpiece intermittently with a
feather touch, sharp diamonds and directing water
spray to the area of contact between bur and tooth
, will prevent this.

14. Chemical action
• The chemical action of certain dental
materials (bases, restorative resins,
solvents, and luting agents) can cause
pulpal damage,particularly when they
are applied to freshly cut dentin.

15. Bacterial Action
• All carious dentin should be removed
before placing a restoration that will serve
as a foundation for a fixed prosthesis

16. 2. Conservation of tooth structure
• Use of partial coverage restorations rather than
complete coverage restorations.
• Preparation of teeth with the minimum
practical convergence angle (taper) between
axial walls

17. • Occlusal surface reduction should follow the
anatomic planes
• Selection of a conservative margin compatible
with the type of restoration.
• Avoidance of unnecessary apical extension
of the preparation unless indicated.

18. • Preparation of the axial surfaces so tooth
structure is removed evenly; if necessary,teeth
should be orthodontically repositioned.
Tooth structure is conserved by
uprighting a tilted FPD
abutment.

19. CONSIDERATIONS AFFECTING
FUTURE DENTAL HEALTH
• Insufficient axial reduction
results in overcontoured
restorations.
• Insufficient occlusal reduction
may cause occlusal
disharmony

20. AXIAL REDUCTION
• Gingival inflammation is commonly associated with
prosthetic abutments that have excessive axial contours.
• A crown should duplicate the contours and profile of
the original tooth.
• However if an error is made ,a slightly undercontoured
restoration is better.

21. • Tooth preparation with
adequate axial
reduction allow the
development of
properly contoured
embrasures.

22. 3. Margin integrity
• Margin: The outer
edge of a crown,
inlay, onlay or other
restoration (GPT 9).
• Finish line: Terminal
portion or peripheral
extension of the
prepared tooth (GPT
9)

23. • This integrity of the margin is
determined by the following:
• 1. Margin placement
• 2.Margin geometry
• 3. Margin adaptation

24. i. Margin Placement
• Whenever possible, the margin of the
preparation should be supragingival
• Subgingival margins often lead to the
periodontal disease

25. LOCATION OF RESTORATIVE
MARGINS
Supragingival
Equigingival
Subgingival

26. SUPRAGINGIVAL
MARGINS
• Cause trauma to gingiva as it
needs to be retracted before
making impression.
• Difficult to finish.
• Difficult to maintain hygiene.
• Difficult to evaluate at recall.
•Easy to prepare
accurately without
trauma to soft tissues.
•Easily finished.
•Easy to keep clean.
•Easy to evaluate at
recall appointment.
SUBGINGIVAL

27. INDICATION OF SUBGINGIVAL MARGIN
• Caries, erosion, restoration extending
subgingivally
• Additional retention is desired - in short crowns
• Esthetics - Metal Ceramic Restorations
• Root sensitivity
• Modification of axial contour is indicated

28. ii. Margin geometry
• This refers to the shape or configuration of the prepared
finish line.
• It should possess the following characteristics:
• • Ease of preparation
• Ease of identification in impression and die
• A distinct boundary to which the wax pattern can be finished.
• Sufficient bulk of material.
• • Conservation of tooth structures
• The shape of the diamond point/bur determines the
finish line configuration and the taper.

29. MARGIN DESIGNS
• Marginal accuracy depends on
having a high quality diamond
bur and good condition of
handpiece.
• The gingival margin is
prepared with the diamond
held in precisely the intended
path of withdrawal of the
restoration

30. • Tilting the diamond away
from the tooth will lead to
formation of an undercut.
• Tilting the diamond toward
the tooth will result in
excessive convergence.

31. Finish line configurations
• i. Chamfer
• ii. Heavy chamfer
• iii.Shoulder
• iv.Shoulder with bevel
• v.Radial shoulder
• vi.Sloped shoulder
• vii.Knife edge

33. Chamfer
• It is an obtuse-angled
finish line.
• It is distinct.
• Exhibits least stress.
• Most conservative.

34. • • Indicated where metal forms the margin of a
restoration, e.g. complete metal crown.
• Should not be given for porcelain restorations as the
obtuse angle produces shearing forces which is not well
tolerated by porcelain.

35. • • It is prepared using a
round-end tapering
diamond.
• This is produced by
sinking in half the
diamond into the tooth.
• The tip produces the
chamfer while the sides
give the necessary taper
to the axial surface
Round- end tapered diamond
and chamfer diamond.

36. Heavy chamfer
• • Similar to chamfer but
prepared with a
diamond of greater
diameter than that used
to produce the chamfer.
• • Indicated for all-
ceramic crowns.
• • Can produce an
unsupported lip of
enamel.
Heavy chamfer with diamond

37. Shoulder
• It is a right-angled finish line .
• • Produces a wide ledge which resists
compressive occlusal forces.
• • Requires more preparation, hence it is not
conservative.
• • Indicated for ceramic restorations – all ceramic
and metal ceramic (where ceramic forms the
margin).

38. • • It is prepared using a flat-end tapering diamond . This
is produced by sinking in the entire diamond into the
tooth.
• The tip produces the shoulder while the sides give the
necessary taper to the axial surface.
• End-cutting diamond is used to finish the shoulder.
• Sharp internal line angle can produce stresses in all-
ceramic crowns.

39. Shoulder with bevel
• It is a shoulder with a bevel
on the external edge
• It reduces the marginal discrepancy of the
restoration as it can be burnished;
however, only gold alloys can be
burnished.
• Protects the edge of finish line preventing
chipping.

40. • Indications
• Primarily indicated to hide the supragingival facial metal
margin of metal-ceramic restorations.
• It is also used as the gingival finish line on inlays and
onlays.
• as occlusal finish line for onlays and partial veneer
crowns.

41. Radial shoulder
• • It is a shoulder finish line with
rounded internal line angle .
• • The internal angle is rounded
using an end-cutting diamond
and finished with a bin-angle
chisel.
• • Indicated for all-ceramic
crowns.

42. Sloped shoulder
• Similar to shoulder
but with an obtuse
angle
• Indicated for facial
margin of metal-
ceramic crowns

43. Knife-edge
• It is a thin finish line .
• Highly conservative.
• It is difficult to wax and cast and
susceptible to distortion.
• It can lead to overcontoured
restorations.
• May be used for metal
restoration in adolescent
patients, lingual surface of
mandibular posteriors, very
convex axial surfaces and tilted
teeth where preparation is
minimal.
• Rarely used

44. • •. Chisel edge and feather edge are
similar to knife edge and they are rarely
used.

45. Feather edge
• Advantage: Conservation of tooth structure
• Disadvantage: Does not provide sufficient
bulk
• Indications: Not recommended

46. Chisel Edge
• Advantage: Conservation of tooth
structure.
• Disadvantage: Location of margin is difficult
thus produces
overcontouring
• Indication: Occasionally on the tilted tooth,
Not acceptable

48. a) Knife edge b) Bevel c) Chamfer
d) Shoulder e) Shoulder with bevel

49. TO BEVEL OR NOT TO BEVEL
• Controversial
• Trignometric analysis-
More acute the bevel-
-lesser the marginal discrepancy
-lesser the seating with cement
• So, bevel improves the marginal adaptation but
reduces the seating of restoration
• Empirical clinical results dictate that acute margin of
metal should continue to be used on metal
restorations but that angle should be in 30-45°

51. 3. Margin adaptation
• • The junction/space between a cemented restoration
and tooth is always a potential site for recurrent caries or
periodontal disease because of dissolution of luting
agent and inherent roughness.
• • Clinically acceptable marginal gap is 10 microns for
cast metal and up to 50 microns for ceramic restorations.

52. Poor preparation design

53. OCCLUSAL CONSIDERATIONS
• A tooth preparation
should allow sufficient
space for developing a
functional occlusal
scheme in the finished
restoration.
• Utility wax can used to
evaluate occlusal
reduction.

54. • While preparing supraerupted
and tilted teeth for
restoration,the eventual
occlusal plane should be
carefully analyzed and teeth
reduced accordingly.
• Endodontic treatment might
be needed.

55. PREVENTING TOOTH FRACTURE
• Although not conservative
of the tooth structure, a
complete crown is often a
better solution as it offers
greatest protection against
tooth fracture

56. MECHANICAL CONSIDERATION
• Providing Retention form
• Providing Resistance form
• Structural durability

57. • Retention form
Definition: The feature of a tooth preparation that
resists dislodgment of a crown in a vertical direction
or along the path of placement (GPT 9 ).

58. Factors To be considered For
Retention
Magnitude of the dislodging forces.
Geometry of the tooth preparation.
-Taper
-Surface area
-Stress concetration
-Type of preparation and secondary retentive features
Roughness of the fitting surface of the restoration.
Materials being cemented.
Film thickness of the luting agent.

59. 1. Magnitude & direction of dislodging
force
• Forces that tend to remove a restoration are
small compared to those tend to seat it.
• It depends on the stickiness of the food and the
surface area of the restoration being pulled

60. GEOMETRY OF TOOTH PREPARATION
ESSENTIAL ELEMENTS OF RETENTION
• Opposing vertical surfaces in same preparation.
• Path of insertion
• Area under shear stress
• Freedom of displacement
FACTORS
• Taper
• Surface area
• Stress concetration
• Type of preparation and secondary retentive features

61. OPPOSING VERTICAL SURFACES
IN SAME PREPARATION
1) External surfaces: Buccal & lingual walls of
full veneer crown. An extracoronal restoration is an
example of veneer, or sleeve retention.
Scan0001.jpg

62. 2) Internal surfaces - Buccal & lingual walls of the
proximal box of a proximo-occlusal inlay.
An intracoronal restoration resists displacement by
wedge retention.

63. PATH OF INSERTION
• It is an imaginary line along which the restoration will be
placed onto or removed from the preparation.
• It is of special importance when preparing teeth to be fixed
partial denture abutments, since the paths of all the
abutment preparations must parallel each other.
• Surveying visually, since it is the primary means of
insuring that the preparation is neither undercut nor over-
tapered.

64. • The path of insertion must be considered in two
dimensions:-
- Faciolingually
- Mesiodistally
• The faciolingual orientation of the path can affect the
esthetics of metal-ceramic or partial veneer crowns.

65. • The mesiodistal inclination of the path must parallel the
contact areas of adjacent teeth.
• So if path is inclined mesially or distally, the restoration
will be held up at the proximal contact areas & be
“locked out”.

66. CHARLES PARALLELING DEVICE:
Components Preclinical set up
Intra oral attachment

67. TECHNIQUE OF VISUALIZATION
To visually check a preparation for undercuts and taper, the centre
of occlusal surface of the preparation is viewed with one eye from
a distance of 30 cm or 12 inch.

68. INTRA ORAL VISUALIZATION

69. AREA UNDER SHEAR STRESS
– Most important feature for retention is that the total
surface area of cement which will experience
shearing rather than tensile stress.
– To achieve this the preparation must have opposing
walls nearly parallel to each other.

70. FREEDOM OF DISPLACEMENT
• 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.

71. Taper
• Definition:
• Taper is the convergence of two opposing
external walls of a tooth preparation as
viewed in a given plane.
• The extension of those average lines
within that plane form an angle described
as the angle of convergence (GPT 9).

72. • Theoretically the more nearly parallel the opposing
walls of a preparation, greater should be retention.

73. • The more nearly parallel the opposing walls of a
preparation, the greater should be the retention.
• Most retentive preparation should be one with parallel
walls, but parallel walls are impossible to create without
undercuts.
• An UNDERCUT is defined as a divergence between
opposing axial walls, or wall segments, in a cervical-
occlusal direction.

74. • Tooth preparation taper should be kept minimal because
of its adverse effects on retention.
ed taper ed retention
ed taper ed retention.
 Jogensen said that retention decreases as taper
increases.

75. • Ideal taper should be
within the range of 2- 6.5°.
• A taper of 6° have been
proposed as being
clinically achievable
while affording adequate
retention.

76. SURFACE AREA
• Provided the restoration has limited path of withdrawal,
Greater the surface area of a preparation, greater is its
retention.
• Length - crowns with long axial walls are more retentive
• Molar crowns are more retentive than premolar crowns of
same taper

77. STRESS CONCENTRATION
• If line angle between axial and occlusal surface is sharp,
it leads to concentration of stresses around that junction
• Induced stresses exceeds the strength of the cement
• Leads to cohesive failure of cement
• Rounding the internal line angles reduces the stress
concentration and thus increases the retention of
restoration

78. TYPE OF RESTORATION AND SECONDARY
RETENTIVE FEATURES
• Full veneer crown has excellent retention when
compared to partial veneer crown because reducing the
path of insertion to a narrow range.

79. SURFACE ROUGHNESS
• ADHESION of dental cements depends primarily on
projections of the cement into microscopic irregularities.
– Jorgensen found retention of castings cemented with
ZnPO4 cement on test dies with a 10° taper to be twice
as great on preparations with 40µm scratches than 10µm.
– Retention increases when restoration is roughened or
grooved.
– Failure rarely occurs at the cement tooth interface. So
roughening tooth preparation hardly influences retention.

80. • MATERIALS BEING CEMENTED:
– Retention is affected by both the casting alloy and the
core material.
– More reactive the alloy, more is adhesion.
– Base metal alloys are better retained than less reactive
high gold content metals.
• TYPE OF LUTING AGENT:
– Studies show that adhesive resin cements are more
retentive than compared to conventional ZnPO4 and
GIC cements.

81. FILM THICKNESS OF THE LUTING
AGENT
• Conflicting evidences
• Studies showed that increased thickness of the cement
film will have some effect on a restoration.
• This may be important if a slightly oversized casting is
made using die spacers.

82. • Resistance form
The feature of a tooth preparation that enhances the
stability of a restoration and resists dislodgment
along an axis other than the path of placement
(GPT 9).
• It prevents dislodgement of a restoration by forces
directed in an apical, oblique or horizontal direction.
• The geometric configuration of tooth structure must
place the cement in compression to provide the
necessary resistance.

83. • Lateral forces tend to displace the restoration
by causing rotation around gingival margin
• Rotation is prevented by any areas of the
tooth preparation that are placed in
compression and are called as RESISTANCE
AREA

84. FACTORS AFFECTING RESISTANCE FORM
• Magnitude and direction of dislodging forces
• Geometry of the tooth preparation
• Physical properties of luting agent

85. MAGNITUDE AND DIRECTION DISLODGING
FORCES
• Normal occlusion - axially directed forces
• Habits (pipe smoking and bruxing) – large oblique
forces to restoration
• Resistance decreases in following order:
- normal occlusion
- habits
- eccentric interferences
- anterior guidance

86. TYPE OF PREPARATION
• Partial coverage restoration may have less resistance
than a complete crown because it has no buccal
resistance area
PHYSICAL PROPERTIES OF LUTING AGENT
• Resistance to deformation is affected by physical
properties of the luting agent, such as compressive
strength and modulus of elasticity
• Adhesive resin >GIC > ZnPO4 > Polycarboxylate >
ZOE

87. Structural durability
• The ability of the restoration to withstand destruction due to
external forces is known as structural durability.
• Durability comes with thickness of the restoration , a
restoration should contain sufficient bulk to withstand forces.
• The amount of reduction required for structural durability
depends on the type of restorative material being used and the
design of the restoration.

88. FACTORS AFFECTING STRUCTURAL
DURABILITY
1. Adequate tooth reduction.
- occlusal reduction
- functional cusp bevel
- axial reduction
2. Alloy selection.
1. Metal-ceramic framework design.
2. Margin design

89. ADEQUATE TOOTH REDUCTION
OCCLUSAL REDUCTION
• An important feature for providing adequate bulk of metal
& strength to the restoration is occlusal clearance.
- Occlusal thickness varies with different restorative materials
TYPE OF
RESTORATION
FUNCTIONAL
CUSP
NON FUNCTIONAL
CUSP
METAL 1mm 1mm
METAL CERAMIC 1.5-2mm 1.5mm
ALL CERAMIC 2mm 2mm

90. - Firstly, opposing occlusal equilibration is to be achieved eg.
Plunger cusps to be rounded.
- Round the line and point angles, avoid deep grooves in the center
of the occlusal surfaces to prevent stress concentration and to
distribute the forces over a larger surface area.
- Uniform and planar
occlusal reduction should be done.

91. Functional cusp bevel
• A functional cusp bevel provides space for an adequate
bulk of restoration in an area of heavy occlusal contact.
• A wide bevel is placed on the functional cusps – palatal
cusps of maxillary posterior teeth and buccal cusps of
mandibular posterior teeth.
• Lack of this may lead to perforation, overcontouring with
deflective contact or overinclination of axial surface

92. • This ensures:
-Sufficient occlusal clearance
- Preservation of tooth structure
- Gives rigidity to crown because of
CORRUGATED EFFECT OF PLANE
• OCCLUSAL OFFSET can be given on posterior partial veneer
crown preparation to provide space for a TRUSS of metal to
form reinforcing strap
• INCISAL OFFSET can be given on anterior partial veneer
crown preparation to provide space for metal that helps to
strengthen the lingual-incisal margin

93. FUNCTIONAL CUSP BEVEL
• It is an integral part of the occlusal reduction.
• A wide bevel on the :
-Lingual inclines of the maxillary lingual cusps
- Buccal inclines of the mandibular buccal cusps provides
space for an adequate bulk of metal in an area of heavy
occlusal contact.

94. • If a wide bevel is not placed on the functional cusp, several
PROBLEMS may occur :
- If the crown is waxed & cast to normal contour it can
cause a thin area or perforation in the casting.
- To prevent this the crown may be waxed to optimal
thickness resulting in overcontouring & poor occlusion.

95.  If an attempt is made to obtain space for an adequate
bulk in a normally contoured casting without a bevel, it
will result in over inclination of the buccal surface which
will destroy excessive tooth structure while lessening
retention.

96. AXIAL REDUCTION
• It plays an important role in securing space for an adequate
thickness of restorative material.
• Inadequate axial reduction can cause thin walls & a weak
restoration subjected to distortion or a bulbous,
overcontoured restoration which will strengthen the
restoration but may have a disastrous effect on
periodontium.

97. Other features that provide space for metal and improve
the rigidity & durability of the restoration are:
 The offset
 The occlusal shoulder
 The isthmus
 The proximal groove
& the box.

98. ESTHETIC CONSIDERATIONS
• The restorative dentist should develop the skill in determining
the esthetic expectations of a patient.
• Esthetic considerations < patient’s long term oral health or
functional efficiency.
• Patient’s esthetic requirements must be discussed and related
to oral hygiene needs and the potential for disease.
• Final decision about appropriate restoration can be made with
informed consent of the patient

99. METAL CERAMIC RESTORATION
FOR GOOD ESTHETICS:
• Sufficient thickness of porcelain
• Proper placement of margins
Adequate facial reduction to provide sufficient
thickness of porcelain and metal for strength.
Minimum reduction of 1.5mm

100. • The margin should follow
the contour of free gingiva.
• FIG A :poor design,apical
margin doesn’t follow the
gingival contour.
• FIG B:restoration displays
metal collar labially.

101. • Adequate porcelain
thickness is essential
for preventing direct
light reflection from
highly pigmented
opaque porcelain.
• Critical areas:
Gingival and incisal third

102. • Proximal surfaces of
anterior metal ceramic
crown are restored
with porcelain which
allows light to be
transmitted for
maximum esthetics.

103. PARTIAL COVERAGE RESTORATION
• Esthetic partial coverage restorations depend on accurate
placement of potentially visible facial and proximal
margins.
• The proximal margin is placed just buccal to the
proximal contact area where it will be hidden by the
distal line angle of the neighboring tooth.

104. • The facial margin should
be shaped so that light is
not reflected directly to the
observer.

105. • To allow proper access
for finishing extend
just beyond the contact
area,but the metal must
remain hidden.

106. • The incisal margin of
a partial coverage
restoration is not
completely covered .
• The restoration margin
is located between the
highest point of incisal
contour and the
incisofacial angle.

107. REVIEW OF LITERATURE

108. • Jeffrey Nodlander, Dennis Weir, Warren Stoffer and Shigaro
Ochi, JPD, vol. 60, 1988.
• – Conducted a study to measure the convergence angles of a
full coverage preparations performed in a clinical
environment.
• Teeth were prepared by the participants to attempt a 4-10°
convergence angle.
• The convergence angles of all preparations were determined
by projecting the faciolingual and mesiodistal silhouttes of the
dies with an overhead projector.
• They concluded that, the ideal convergence angle of 4-10°
is seldom achieved.
• The convergence angle for mandibular preparations were
greater than maxillary.

109. • Steven M. Carter, Peter R. Wilson, IJP, vol. 9, 1996.-
• Conducted a study to see the effect on die spacing on pre and
post cementation crown removal and crown elevation.
• Different layers of die spacer was used.
• They observed that the force required to remove a crowns
before cementation decreased with increased layers of die
spacers.
• Following cementation the mean crown elevation decreased
and the removal force is increased

111. • Aim: To determine the effect of three different tooth
preparation techniques had on operator’s ability to
• appropriately and consistently prepare teeth for metal
ceramic crowns.
Ram, et al Evaluation of three different tooth preparation techniques
for metal ceramic crowns by comparing preparation depths:
An in vitro study
The Journal of Indian Prosthodontic Society | Apr-Jun 2015 | Vol 15 | Issue 2

112. • Materials and Methods:
• Ninety maxillary left central incisor typodont teeth were
allocated to three equal groups (A, B and C) of thirty and
mounted in standard working model one at a time.
• A freehand approach was used to prepare the teeth in
Group A, which acted as a control.
• Groups B and C were prepared with the assistance of
silicon index and suitable depth gauge burs, respectively.
• A silicon index of unprepared teeth, into which
contrasting colored silicon injected to occupy the space
created by tooth preparation, was sectioned in the
midline.

113. • Images of sectioned index were captured with optical
microscope attached to a personal computer.
• A calibrated image analysis software was used to
measure the depth of preparation (in millimeters) at five
points (labial-cervical, mid-labial, incisal, mid-palatal and
palatal cervical) on two occasions.
• These results were pooled and averaged to give a mean
labial, incisal and palatal preparation depths in mm.
• The data were analyzed by one-way analysis of variance
and Scheffe’s post-hoc statistical test.

114. • Results:
• The mean depth of labial and incisal preparation for
Groups A, B and C was 1.23 and 1.72 mm,1.45 and 1.96
mm, 1.47 and 1.95 mm, respectively.
• The difference between the groups’ labial preparation
depth was significant as well as the difference between
groups’ incisal preparation depth.
• The mean palatal preparation was 0.46 mm for Group A,
0.54 mm for Group B and 0.59 mm for Group C.

115. • Conclusion: Teeth preparation for metal ceramic crowns
without any assistance can lead to under-preparation of
labial and incisal surface.
• Clinical Significance: Whenever possible, considerable
importance should be given to the use of index or depth
gauge burs for preparing teeth for receiving metal
ceramic crowns.

116. • Periodontal and prosthetic outcomes on teeth prepared
with biologically oriented preparation technique: a 4-year
follow-up prospective clinical study
• Blanca serra-pastora, Ignazio loi etal
• JOURNAL OF PROSTHODONTIC RESEARCH
2019;63:415–420

117. • Purpose: To evaluate the clinicaland biological behavior
of full coverage restorations on teeth prepared without
finish line during a 4-year follow-up.
• Methods: This prospective study included 149 teeth
treated using biologically oriented preparation technique
(BOPT). The sample (149 teeth) was divided into two
groups: Seventy four teeth restored with crowns, and 75
teeth supporting fixed partial dentures (FPD).
• Restorations were fabricated with zirconium oxide cores
and ceramic coverings.
•

118. • Patients attended regular annual check-
ups when probe depth, presence of
inflammation with bleeding on probing,
presence of plaque, gingival
thickness,marginal stability, biological or
mechanical complications, and the
patient’s level of satisfaction were
• registered over a 4-year follow-up.

119. Prosthetic treatment needed to be replaced
due to biological and esthetic problem.
a) Teeth prepared with conventional chamfer.
Vestibular view.
(b) Teeth prepared with conventional
chamfer. Occlusal view

121. BOPT preparation technique. From left to right:
• First step introduce the bur with an angulation of 10-15 with respect to the dental
axis (tip of the bur in the direction of the tooth);
• second step, introduce the bur parallel to the dental axis;
• third last step, introduce the bur with a 3-6 angulation with respect to the dental
axis.

122. BOPT technique, immediately after preparation

123. (a) Maturation of gingival tissue after a provisional phase of 8–12 weeks. (b)
Gingival sulcus in teeth prepared with BOPT. (c) Emergence profile with BOPT
provisional restoration

125. • Results: After the 4-year follow-up, 2.1% of teeth
underwent increases in probing depth; 12% of the
sample
• presented inflammation and bleeding on probing; 20% of
the restored teeth presented plaque; gingival
• thickening increased a 32.5%; 98.6% of teeth presented
marginal stability; the restoration survival rate
• was 96.6%, with 2% of biological complications and
1.4% of mechanical complications. General
• satisfaction score was 80.73.
• Conclusions: Restorations placed on teeth prepared
using BOPT present good periodontal behavior,
• increase of gingival thickening, and marginal stability
over a 4-year follow-up. High survival rates after

126. • Proper attention should be given during margin placement and
the principle of “Do no harm” to the soft tissues should be
followed.
• All preparations require the incorporation of factors to prevent
the dislodgement of restoration by functional stresses.
• If too much emphasis is given on any one of the principles
then the success of the procedure may be limited by a lack of
consideration of the other factors.

127. REFERENCES
1. Shillingburg HT. Fundamentals of fixed prosthodontics. 3rd ed
2. Rosenstiel SF. Contemporary fixed prosthodontics 4th ed
3. Gilboe DB. Fundamentals of extracoronal tooth preparation. J
prosthet Dent 2005;94:105-7.

128. THANK YOU !!