BIOLOGICAL
PRINCIPLES IN FPD
PRESENTED BY:
SUCHETA.P
POST GRADUATE STUDENT
DEPARTMENT OF PROSTHODONTICS
INTRODUCTION
The principles of tooth preparation may be divided
into:
1. Biological considerations
2. Mechanical considerations
3. Esthetic considerations
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 209
BIOLOGIC
Conservation of tooth
structure
Avoidance of over contouring
Supragingival margins
Harmonious occlusion
Protection against tooth
fracture
ESTHETIC
MECHANICAL
Retention form
Resistance form
Deformation
Minimum display of
metal
Maximum thickness of
porcelain
Porcelain occlusal
surfaces
Subgingival margins
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 210
BIOLOGICAL CONSIDERATIONS
1. Adjacent teeth
2. Soft tissues
3. The tooth being prepared
4. Periodontium
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 210
ADJACENT TEETH
1. Iatrogenic damage
2. A metal matrix band
3. Use of proximal enamel
Damage to
adjacent
tooth
Plaque
retention
Increased
caries
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 210
Progression of Approximal Caries in Relation to
Iatrogenic Preparation Damage V. Qvist, L.
Johannessen, and M. Bruun. J Dent Res
71(7):1370-1373, July, 1992
•Iatrogenic preparation damage is a frequent sideeffect and represents a dental health problem, since
the damage increases caries progression and the
perceived need for restorative therapy of the
adjacent teeth.
SOFT TISSUES
Prevention
1. Aspirator tip
2. Mouth mirror
3. Flanged saliva ejector
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 210
PULP
• Extreme temperature
• Chemical irritation
• Microorganisms
• Reversible pulpitis
• Irreversible pulpitis
• Pulpal damage
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 211
•Pulp size decreases with age.
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 211
TEMPERATURE
•Excessive pressure
•Higher rotational speeds
•The type, shape, and condition of the cutting
instrument
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 211
Clinical and histological evaluation of thermal
injury thresholds in human teeth: a preliminary
study. P. Baldissara, S. Catapano & R. Scotti. Journal of
Oral Rehabilitation 1997 24; 791-801
•The preparation of full crowns with air-cooled high
speed instruments can generate an average
temperature increase of 8.8°C.
•Preliminary results suggest that average increases
of 11-2°C do not damage the pulp, since no signs of
inflammation.
•Results suggest that heat plays a secondary role in
the generation of pulp pathologies during the
postoperative period of dental treatment and
prosthetic treatment in particular.
•Crown preparations, made with an adequate
air/water spray, showed no initial reaction.
•If, the air/water spray was deficient, the sections
showed burned dentin on the surface of the
preparation.
•The reaction was not exclusively influenced by the
rotational speed of the engine, but by the diameter
and shape of the rotating instrument, the
relationship of the spray jet to the instrument/tooth
contact area, and the air pressure at which the
spray was operated.
Pulp reactions to crown preparation, impression,temporary crown fixation, and
permanent cementation. Kaare Langeland and Leena Kaarina Langeland. J. Pros.
Den. Jan.-Feb., 1965. 129 -138
A large wheel or disk or, particularly, a grinding
surface not facing the spray would deflect the spray,
thus preventing it from lubricating the instrument tooth
contact area.
EFFECT OF COOLANTS
•An air/water spray with adequate pressure, directed
at the point of instrument-tooth contact will prevent
pulp injury
•Crown preparation is generally attained with larger
instruments which will tend to “run dry.” This may be
alleviated by using an adjustable spray which will
cover the entire rotating instrument.
Pulp reactions to crown preparation, impression,temporary crown fixation, and
permanent cementation. Kaare Langeland and Leena Kaarina Langeland. J. Pros.
Den. Jan.-Feb., 1965. 129 -138
•The pressure of the spray should be sufficiently
strong to penetrate the centrifugal forces of high
speed rotating instruments.
•The spray nozzle should be close to the shank of
the instrument and should lubricate small burs as
well as long diamond points.
•Disks present a special problem. If the spray is
directed toward the side of a disk which revolves
away from the tooth, it offers no protection.
Pulp reactions to crown preparation, impression,temporary crown fixation, and
permanent cementation. Kaare Langeland and Leena Kaarina Langeland. J. Pros.
Den. Jan.-Feb., 1965. 129 -138
TEMPERATURE RESPONSE IN THE PULPAL
CHAMBER DURING ULTRAHIGH-SPEED TOOTH
PREPARATION WITH DIAMOND BURS OF
DIFFERENT GRIT. Peter Ottl and Hans-Christoph
Lauer. J Prosthet Den 1998;80:12-9
1. This study demonstrated that the coarser the grit
of diamond bur, the more pronounced the
temperature elevation within a pulpal chamber
during tooth preparation.
2. The temperature of cooling water of 38° to 43° C
did not result in a cooling effect at tooth
temperatures of 37° C.
The temperature of the cooling water rose during
tooth preparation. The temperature of cooling
water and the temperature increases in the pulpal
chamber were directly proportional, so a thermal
hazard to the dental pulp was conceivable when
the spray was not sustained for a sufficient length
of time at an appropriate temperature, especially
if ultra coarse burs are selected.
3. Lower cooling water temperatures (30° to 32°C),
ensured pulpal vitality during tooth preparation
CHEMICAL ACTION
•Chemical action of certain dental materials can
cause pulpal damage when they are applied to
freshly cut dentin.
•Chemical agents are used for cleaning and
degreasing tooth preparations.
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 214
BACTERIAL ACTION
•Bacteria that were left behind or gained access to
the dentin because of microleakage.
•Many dental materials like zinc phosphate cement
have an antibacterial effect.
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 214
CONSERVATION OF TOOTH STRUCTURE
Thickness of remaining dentin inversely
proportional to the pulpal response
DEPTH OF REDUCTION
Tylman’s theory and practice of fixed prosthodontics. 8th edition. 148
Fundamentals of fixed prosthodontics. Herbert T Shillingburg. 4th edition. 150
GUIDELINES TO CONSERVE TOOTH
STRUCTURE
1. Use of partial coverage rather than complete
coverage restorations
2. Preparation of teeth with the minimum practical
convergence angle (taper) between axial walls
3. Preparation of the occlusal surface so that
reduction follows the anatomic planes to give
uniform thickness in the restoration
4. Preparation of the axial surfaces so that a
maximal thickness of residual tooth structure
surrounding pulpal tissues is retained.
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition.
214-5
5. Selection of a margin geometry that is
conservation and yet compatible with the other
principles of tooth preparation.
6. Avoidance of unnecessary apical extension of the
preparation.
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition.
214-5
Axial reduction
Occlusal
considerations
Contour
CONSIDERATIONS
AFFECTING
FUTURE DENTAL
HEALTH
Preventing
Margin
tooth fracture
placement
Margin
adaptation
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 215
AXIAL REDUCTION
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 215
Fundamentals of fixed prosthodontics. Herbert T Shillingburg. 4th edition. 138
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 222
1. Retention is influenced by occlusogingival length
of the axial walls
2. Proximal walls should be nearly equal in vertical
length because the retention of the retainer is
only as effective as the shortest wall
3. Proximal walls ideally possess a 5 to 8⁰ taper
4. Facial and lingual walls are more convergent
from the occlusal one – third to provide a
narrowed occlusal table.
5. Short axial walls require accessory methods of
retention
Tylman’s theory and practice of fixed prosthodontics. 8th edition. 123-4
CONTOUR
•Crown contours represent a group of
characteristics critical to the longevity and success
of any dental restoration.
• In restoring the gingival third of a crown, a flat
emergence profile should be developed at the
marginal area.
• A uniform continuance of the two structural phases
(tooth-restoration) is biologically and technically
necessary for controlled reestablishment of
harmony in the tooth periodontium environment.
Clinical crown contours: contemporary view. Petros T . Koidis, James G.
Burch, Rudy C. Melfi. JADA, Vol. 114, June 1987; 792
CURRENT THEORIES OF CROWN CONTOUR,
MARGIN PLACEMENT, AND PONTIC DESIGN.
Curtis M. Becker and Wayne B. Kaldahl. J Prost
Dent 1981; 45; 3: 268- 277
Crown contours should follow these guidelines:
(1)Buccal and lingual contours are flat
(2)Embrasure spaces should be open
(3)Contacts should be high (incisal one third) and
buccal to the central fossa (except between first
and second molars)
(4)Furcations should be “fluted” or “barreled out.”
AXIAL CROWN CONTOURS
Morton L Perel
J Prosthet Dent 25;642;1971
1. Axial tooth surface undercontouring of various
types did not produce any significant changes in
the circumscribed gingiva in health.
2. Overcontouring of similar surfaces produced
inflammatory and hyperplastic changes in the
marginal gingiva. Such changes were seen, both
clinically and microscopically, after 4 weeks.
CROWN CONTOURS AND GINGIVAL RESPONSE
Lee M, Jameson, and William F. P. Malone.
J Prosthet Dent 1982; 47;6: 620
1. Deflective contours and/or overcontouring should
be avoided in the cervical third and the interproximal
surfaces of tooth restorations.
2. Overcontouring of the interproximal region is
common and harmful to periodontal health.
3. Adequate tooth reduction at the gingival margin
and interproximally provides for restorative materials
and lessens the potential for overcontouring.
4. Fluting or barreling of exposed furcations
eliminates plaque shelves and promotes
accessibility for hygiene.
5. Minimal disruption within the intracrevicular
space during tooth preparation allows a more
predictable, favorable periodontal response to
satisfactorily contoured restorations.
FACIAL AND LINGUAL CONTOURS OF
ARTIFICIAL COMPLETE CROWN
RESTORATIONS AND THEIR EFFECTS ON THE
PERIODONTIUM RALPH A. Yuodelis, James D.
Weaver and Stanley Sapkos. J. Prosthet. Dent.
January, 1973;29;1;61
•The final restoration should not follow the original
anatomic crown and should recreate the original
contours of the root portion.
•The modification of the anatomic coronal form
entails reduction of unnecessary bulges in order to
create additional accessibility to the gingival third of
the fluted and furcation regions .
•This will eliminate the triangular region that is
created by the roots and the cervical bulge and
which is the area most difficult to maintain in a
plaque-free condition by normal brushing.
•Flattened facial and lingual contours of restorations
and have observed excellent gingival response:
most probably because the cervical region is made
more accessible for routine home care.
MARGIN PLACEMENT
•The margin of the preparation should be
supragingival whenever possible.
Advantages of supragingival margins:
1. Easily finished without associated soft tissue
trauma
2. More easily kept plaque free
3. Impressions are more easily made, with less
potential for soft tissue damage
4. Restorations can be easily evaluated at the time of
placement or at recall appointments.
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 217
Periodontal conditions in patients treated with
dental bridges. III The relationship between the
location of the crown margin and the periodontal
conditions. John Silness. J Periodont Res 5;225;
1970
Not only is complete removal of plaque in the
porosities and spaces of subgingival cement areas
impossible, but when attempts are made to obtain
healing in pockets around subgingival restorations,
the soft deposits may also remain undetected on
clinical examination.
Periodontal conditions in patients treated with
dental bridges. V Effects of splinting adjacent
abutment teeth. John Silness and Elizabeth Ohm. J
Periodont Res 9;121- 126
•The results discourage the use of bridge designs
with two or more end abutments in cases where
subgingival retainer margins have to be used
especially in recipients who do not participate
appropriate tooth cleansing methods.
Effect of crown margins on periodontal conditions
in regularly attending patients.
James D. Bader, R. Gary Rozier, Walter T. McFall and
Diane L. Ramsey. J Prosthet Dent 1991;65;1;75-9
•Intact surfaces in patients with cast restorations were
not significantly different from the same surfaces in
patients without cast restorations. Even among
patients receiving regular preventive dental care,
subgingival margins are associated with unfavorable
periodontal reactions.
Restorative margins and periodontal health: A
new look at an old perspective. P. L. Block. J
Prosthet Dent 1987;57;683
•The indiscriminate placement of the margins of
dental restorations into the gingival crevice for the
purpose of esthetics or protection from decay can no
longer be considered good practice.
•The junctional epithelium and the supracrestal
fibers, together, have been called the biologic width,
which is considered to have a length of 2 mm. A
more accurate term for the biologic width, one that
expresses the function and diversity of the
component tissues while avoiding reference to
dimension, is the “subcrevicular attachment
complex.”
•The most accurate anatomic structure from which
to take measurements for margin placement is the
healthy, stable gingival margin. It is clinically visible,
unlike the biologic width, and should replace the
latter as the landmark of choice for placing dental
margins. Surgical crown lengthening will be
necessary when restorations will end at or below the
alveolar crest.
Subgingival margin indications :
1. Dental caries, cervical erosion, or restorations extend
subgingivally.
2. The proximal contact area extends to the gingival
crest
3. Additional retention and/or resistance is needed.
4. The margin of a metal- ceramic crown is to be hidden
behind the labiogingival crest
5. Root sensitivity cannot be controlled by more
conservative procedures, such as the application of
dentin bonding agents
6. Modification of the axial contour is indicated, as to
provide an undercut to provide retention for the clasp
of a partial removable dental prosthesis
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 217-8
MARGIN ADAPTATION
•A well designed preparation has a smooth and even
margin.
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 219
Fundamentals of fixed prosthodontics. Herbert T Shillingburg. 4th edition. 140
Effect of in vivo crown margin discrepancies on
periodontal health. D. A. Felton, B. E. Kanoy, S. C.
Bayne, and G. P. Wirthman. J PROSTHET DENT
1991;66:357-64.
•An increase in marginal discrepancy between the
casting and prepared tooth resulted in an increase
of gingival inflammation measured by a gingival
index and crevicular fluid volume. There is strong
evidence to support supragingival margins for
artificial crowns and FPDs.
MARGIN GEOMETRY
Guidelines for margin design:
1. Ease of preparation without overextension or
unsupported enamel
2. Ease of identification in the impression and on the
die
3. A distinct boundary to which the wax pattern can
be finished
4. Sufficient bulk of material
5. Conservation of tooth structure
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 219
Finish line
Advantages
Disadvantages
Chamfer
Minimal tooth destruction
Minimal stress
Reduces crown strength
Poor esthetics
Deep chamfer
Moderate tooth destruction
Minimal stress in tooth
Reduces crown strength
Potential lip formation
Classic shoulder
Maximal esthetics
Maximal crown strength
Prevents overcountouring
Maximal destruction
Maximal tooth stress
Radial shoulder
Maximal esthetics
Excellent crown strength
Less stress than classic
shoulder
Destructive of tooth
More stress than chamfer
Radial shoulder with a
bevel
Excellent crown strength
Less strength than classic
shoulder
Destructive of tooth
More stress than chamfer
Poor esthetics
Knife edge
Minimal destruction
Overcontouring
Poor esthetics
Weaker crown margin
Fundamentals of fixed prosthodontics. Herbert T Shillingburg. 4th edition. 144
The effect of various finish line preparations on
the marginal seal and occlusal seat of full crown
preparations
J. R. Gavelis, J. D. Morency, E. D. Riley, and R. B.
Sozio
J Prosthet Dent 1981;45;138
•The featheredge and parallel bevel preparations
demonstrated the best marginal seal, followed in
order by the full shoulder, 45-degree shoulder, and
finally the 90- degree shoulders with 30-degree and
45-degree bevels.
•With regard to seating of the restoration, the 90degree full shoulder demonstrated the best seat,
followed in order by the 45-degree shoulder, 90degree shoulder with 45-degree bevel,
featheredge, 90-degree shoulder with 30-degree
bevel, chamfer with parallel bevel, and finally 90degree shoulder with parallel bevel.
OCCLUSAL REDUCTION
To provide adequate bulk to the material and
strength to the restoration.
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 223
Fundamentals of fixed prosthodontics. Herbert T Shillingburg. 4th edition. 138
FUNCTIONAL CUSP BEVEL
Fundamentals of fixed prosthodontics. Herbert T Shillingburg. 4th edition. 138-9
PREVENTION FROM TOOTH FRACTURE
Contemporary fixed prosthodontics. Rosensteil, Land, Fujimoto. 4th edition. 223-6
Review Endodontically treated teeth:
Characteristics and considerations to restore
them. Adriana Cla´udia Lapria Faria, Renata Cristina
Silveira Rodrigues, Rossana Pereira de Almeida
Antunes, Maria da Gloria Chiarello de Mattos, Ricardo
Faria Ribeiro. Journal of Prosthodontic Research 55
(2011) 69–74
•Endodontically treated teeth are more brittle due to
loss of structural integrity associated with access
preparation or caries.
•Because of the brittleness of these elements,
planning will be associated to remaining tooth
structure and functional demands, once load received
depends on tooth position in the arch, occlusion and
rehabilitation planning.
SUMMARY
REFRENCES
1. Contemporary fixed prosthodontics. Rosensteil, Land,
Fujimoto. 4th edition.
2. Progression of Approximal Caries in Relation to
Iatrogenic Preparation Damage V. QVIST, L.
JOHANNESSEN, and M. BRUUN. J Dent Res
71(7):1370-1373, July, 1992
3. Clinical and histological evaluation of thermal injury
thresholds in human teeth: a preliminary study. P.
Baldissara, S. Catapano & R. Scotti. Journal of Oral
Rehabilitation 1997 24; 791-801
4. Pulp reactions to crown preparation, impression,
temporary crown fixation, and permanent cementation.
Kaare Langeland and Leena Kaarina Langeland. J. Pros.
Den. Jan.-Feb., 1965. 129 -138
5.Temperature response in the pulpal chamber during
ultrahigh-speed tooth preparation with diamond burs of
different grit. Peter Ottl and Hans-Christoph Lauer. J
Prosthet Den 1998;80:12-9
6. Tylman’s theory and practice of fixed prosthodontics.
8th edition.
7. Fundamentals of fixed prosthodontics. Herbert T
Shillingburg. 4th edition.
8. Clinical crown contours: contemporary view. Petros T .
Koidis, James G. Burch, Rudy C. Melfi. JADA, Vol.
114, June 1987; 792
9. Current theories of crown contour, margin placement,
and pontic design. Curtis M. Becker and Wayne B.
Kaldahl. J Prost Dent 1981; 45; 3: 268- 277
10. Axial crown contours. Morton L Perel. J Prosthet Dent
25;642;1971
11.Crown contours and gingival response. Lee M,
Jameson, and William F. P. Malone. J Prosthet Dent 1982;
47;6: 620
12. Facial and lingual contours of artificial complete crown
restorations and their effects on the periodontium. Ralph A.
Yuodelis, James D. Weaver and Stanley Sapkos. J.
Prosthet. Dent. January, 1973;29;1;61
13. Periodontal conditions in patients treated with dental
bridges. III The relationship between the location of the
crown margin and the periodontal conditions. John Silness.
J Periodont Res 5;225; 1970
14. Periodontal conditions in patients treated with dental
bridges. V Effects of splinting adjacent abutment teeth.
John Silness and Elizabeth Ohm. J Periodont Res 9;121126
15. Effect of crown margins on periodontal conditions in
regularly attending patients. James D. Bader, R. Gary
Rozier, Walter T. McFall and Diane L. Ramsey. J Prosthet
Dent 1991;65;1;75-9
16. Restorative margins and periodontal health: A new look
at an old perspective. P. L. Block. J Prosthet Dent
1987;57;683
17. Effect of in vivo crown margin discrepancies on
periodontal health. D. A. Felton, B. E. Kanoy, S. C. Bayne,
and G. P. Wirthman. J PROSTHET DENT 1991;66:357-64.
18. The effect of various finish line preparations on the
marginal seal and occlusal seat of full crown preparations.
J. R. Gavelis, J. D. Morency, E. D. Riley, and R. B. Sozio. J
Prosthet Dent 1981;45;138
19. Review Endodontically treated teeth: Characteristics
and considerations to restore them. Adriana Cla´udia
Lapria Faria, Renata Cristina Silveira Rodrigues, Rossana
Pereira de Almeida Antunes, Maria da Gloria Chiarello de
Mattos, Ricardo Faria Ribeiro. Journal of Prosthodontic
Research 55 (2011) 69–74
20. Iatrogenic Damage to the Periodontium Caused by
Fixed Prosthodontic Treatment Procedures. PV Harish,
Sonila Anne Joseph, Syed Sirajuddin, Veenadharini
Gundapaneni, Sachidananda Chungkham and Ambica.
The Open Dentistry Journal, 2015, 9, (Suppl 1: M4) 190196