FIXED PARTIAL DENTURE -DESIGN CONSIDERATION

DR VIKRAM
DESIGN OF FIXED PARTIAL
DENTURE

Introduction to Fixed
Prosthodontics
 Fixed prosthodontics treatment can range
from the restoration of a single tooth to the
rehabilitation of the entire occlusion.
 Missing teeth can be replaced with fixed
prostheses that will improve patient comfort
and masticatory ability, maintain the health
and integrity of the dental arches, and, in
many instances, elevate the patient’s self-
image.

 RESTORATION is a broad term applied to any
material or prosthesis that restores or replaces lost
tooth structure, teeth, or oral tissue.
Single tooth restorations include amalgams,
composite resins, inlays, onlays, crowns, and
veneers.The restoration of natural teeth with single
tooth restorations is frequently referred to as
RESTORATIVE or OPERATIVE DENTISTRY although
this treatment is included in the definition of
prosthodontics.

A FIXED PARTIAL DENTURE (FPD) is a Partial
denture that is luted to natural teeth or tooth
roots and/or affixed to dental implants that
furnish the primary support for the prosthesis
 .

Terminology
 Crown is a cemented or permanently affixed extracoronal
restoration that covers, or veneers, the outer surface of
the clinical crown. If it covers the entire clinical crown,
the restoration is called a full veneer, full
coverage,complete, or just a full crown
If only portions of the clinical crown are veneered, the
restoration is called a partial coverage or partial veneer
crown

Defnition
 A tooth or implant serving as an attachment for a fixed
partial denture is called an abutment
.
 The artificial tooth suspended from the abutments is a
pontic
 connectors between ( pontic and retainer )
-rigid (ie, solder joints or cast connectors)
- nonrigid (ie, precision attachments or stress breakers)


Indications of Fixed partial
Denture
 1. Short span edentulous arch
 2. Periodontally strong supporting teeth
(abutment)
 3. Inadequate tissue support ex. Excessive
ridge resorption
 4. Aesthetic Consideration

Contraindications of fixed
partial denture
1.Young patients with large pulp chamber
2. Patient attitude (uncooperative patients)
3. Recurrent/ grossly carious dentition
4. Congenitally malformed teeth
5. Bilaterally missing teeth which require cross
arch stabilization
6.Weak periodontal condition of abutment
teeth

Step 1a: Diagnosis
 • History of physical and medical conditions
 • Extraoral examination ofTMJ and muscles of
mastication
 • Intraoral examination of oral
hygiene,periodontium and any intraoral
pathologies
 • Radiograph to determine caries, alveolar
bone support, morphology of abutment and
presence of any underlying pathologies along
with examination of any existing prostheses

Step 1b: Treatment planning
• Construction of diagnostic casts
• Mount the cast on the articulator and assess
the height, rotation and inclination of
abutment teeth along with a general idea
about the present Occlusion.

Selection Criteria for abutment
 Vital tooth(if possible then good for abutment)
 Endodontically treated
- asymptomatic,
- radiographic evidence of a good seal
- complete obturation of the canal,
- sound,surviving coronal tooth structure to ensure longevity.
 Compromising coronal tooth structure can be compensated
by use of a dowel core or a pin-retained amalgam or composite

Special consideration
 Teeth that have been pulp capped in the process of
preparation should not be used FPD
 Supporting tissues surrounding the abutment teeth must
be healthy and free from inflammation
 Abutment teeth should not exhibit mobility
because they will be carrying an extra load.

Abutment Evaluation
 The roots and their supporting tissues should
be evaluated for three factors:
 1. Crown-root ratio
 2. Root configuration
 3. Periodontal ligament area

Root configuration
The optimum crown-root ratio 2:3;
a ratio of 1:1 is the maximum ratio
If the opposing tooth is artifical then a greatr ratio can
be acceptable
 As the level of the alveolar bone moves apically, the lever arm of the
portion out of bone increases, and the chance for harmful lateral
forces increases.

Important point in root
configuration
 Labiolingually conical root – more stable
compared to circular
 Multirooted posterior teeth with widely
separated roots than converge, fuse,
 irregular configuration than perfect taper.

Although the root surface area of
these teeth is similar, the root
configuration of the maxillary
premolar (a), with its greater
faciolingual dimension, makes it a
superior abutment to
the maxillary central incisor (b),
whose root is essentially circular in
cross section
The molar with divergent roots (a) will be a
better abutment tooth than one whose roots
are fused (b).

Annte law Ante’s Law by Johnston et al, the
root surface area of the abutment teeth had to equal or
surpass that of the teeth being replaced with pontics
The combined root surface area of the second
premolar and the second molar (A2p + A2m)
is greater than that of the first molar being
replaced (A1m).

Biomechanical Considerations
 Bending or deflection varies
- directly proportional (span length)3
- inversely with the cube of the
occlusogingival thickness of the pontic
To overcome this deflection (a higher yield strength, such as nickel-chromium and
increse hieght of pontics)
.

Bending or deflection directly
proportional (span length)3

The walls of facial and lingual grooves counteract
mesiodistal torque resulting from
force applied to the pontic.
Preparations should be
modified accordingly to produce greater
resistance and structural durability.

Double abutments are sometimes used as a means
of overcoming problems created by unfavorable
crown-root ratios and long spans
The retainers on secondary abutments will be
placed in tension when the pontics flex,
with the primary abutments acting as fulcrums.

When pontics lie outside the interabutment axis
line,(canine to canine involvement) the pontics act as a
lever arm, which can produce a torquing movement.
Secondary retention (R) must extend a distance
from the primary interabutment axial to the
distance that the pontic lever arm (P) extends in
the opposite direction

Special Consideration
 P ier abutments
 Tilted molar abutments
 Cantilever fixed partial dentures
 canine-replacement fixed partial dentures

the maxillary first premolar and molar
are missing, leaving the second premolar
as a pier abutment
it will create huge stress on the terminal
abutment and pier abutment will acts as a
fulcrum and failure of prosthesis
Rocking of retainer
– Bending of retainer
–Tension between abutment andretainer
– Intrusion of retainer on abutment

Pier abutment: the central abutment is subjected to torsion and
leverage, hence non rigid stress breakers should be used at pier
connector
A nonrigid connector on the middle abutment
isolates force to the segment of the fixed
partial denture to which it is applied

If a nonrigid connector is placed on the distal
side of the retainer on a middle abutment,
movement in a mesial direction will seat the key
into the keyway

If a nonrigid connector is placed on the mesial
side of the middle abutment, mesially
directed movement will unseat the key.

Cantilever (1st premolar pontic): adequate periodontal support
There is no need of non-rigid connector

Tilted molar abutment
 Initialy orthodontically( conservative)
 Modified preparation design ( if angle less than
25deg)
 Proximal half crown : ¾ crown
 Non-rigid connector on the distal aspect of the
premolar retainer compensates for the
inclination of the tilted molar
 Telescopic crown (A full crown preparation with heavy
reduction is made to follow the long axis of the tilted molar )

Tiled Crown treatment if orthodonticaly not possible
Proximal half crown : ¾
crown
Telescopic crown
Non-rigid connector on the distal
aspect of the premolar retainer
compensates for the inclination of
the tilted molar

cantilever can be used for replacing a maxillary lateral incisor .There
no occlusal contact on the pontic in either centric or lateral
excursions.The canine must be used as an abutment,There should be
a rest on the mesial of the pontic against a rest preparation in an inlay
or other metallic restoration on the distal of the central incisor to
prevent rotation of the pontic and abutment.

canine-replacement fixed
partial dentures
A fixed partial denture replacing a mandibular canine has a more favorable prognosis
than that replacing a maxillary canine because the forces are directed inward and the
pontic will be closer to the interabutment axis.
Difficult - it often lies outside the
interabutment axis
Maxillary more difficult than mandible due to
labially and lingually acting force respectively

Tooth preparation
 Tooth preparation: “The process of removal of diseased and/or
healthy enamel, dentin and cementum to shape a tooth to receive a
restoration.”

Principles of Tooth
Preparations
 The design of a preparation for a cast restoration
and the execution of that design are governed by
five principles:
 1. Preservation of tooth structure
 2. Retention and resistance
 3. Structural durability
 4. Marginal integrity
 5. Preservation of the periodontium

Preservation of Tooth
Structure
 restoration must preserve remaining tooth
structure.
 tooth structure should not be needlessly
sacrificed to the bur in the name of
convenience or speed
 Adequate for retention and resistance
.

No cements that are compatible with living tooth structure
and the biologic environment of the oral cavity possess
adequate adhesive properties to hold a restoration in place
solely through adhesion
The geometric configuration of the tooth preparation most
important for retention and resistance

Resistance and Retention
 Taper
 F reedom of displacement
 Length
 Substitution of internal features
 P ath of insertion

Taper :The terms angle of convergence and angle of
divergence can be used to describe the respective
relationships between the two opposing walls of a
preparation. Two opposing surfaces, each with a 3-degree
inclination, would give the preparation a 6-degree

A full crown preparation is more retentive on a molar than
on a premolar because the
molar preparation has greater surface area.

Freedom of displacement
 Maximum retention is achieved when there is
only one path
V-shaped grooves
Boxes
facial and lingual walls must meet the pulpal wall at
angles near 90 degree

(a)limiting the paths of withdrawal, retention is improved.
(b) A preparation with
unlimited freedom of displacement is much less retentive.

The walls of a groove that meet the axial wall at an
oblique angle do not provide the necessary resistance. (b)
The walls of a groove must be perpendicular to rotating
forces to resist
displacement.

Length
 Occlusogingival length is an important factor
in both retention and resistance
more longer prepration
more surface area
more retentive and resistance to rotation
 length must be great enough to interfere with
the arc of the
Length & taper = retention and resistance

The preparation with longer walls (a) interferes with the tipping
displacement of the
restoration better than the short preparation (B)

A preparation on a tooth with a smaller diameter (a)
resists pivoting movements better
than a preparation of equal length on a tooth of larger
diameter (b).

Substitution of internal
features

Path of insertion
 The path of insertion is an imaginary line along which the
restoration will be placed onto or removed from the
preparation.
 It is determined mentally by the dentist before the
preparation is begun, and all features of the preparation
are cut to coincide with that line
 correct technique must be used to survey a preparation
visually

approximately ½ inch above the preparation
one eye

(a) The path of insertion of a preparation for a
metalceramic crown should parallel the
long axis of the tooth. (b) If the path is directed
facially, the prominent facioincisal angle may
create esthetic problems of overcontouring or opaque show-
through. (c) However, if the path is
directed lingually, the facial surface will intersect the
lingual surface, creating a shorter
preparation. It also may encroach on the pulp

Structural Durability
Occlusal reduction
F unctional cusp bevel
Axial reduction
Marginal Integrity
F inish line configurations
Preservation of the Periodontium

Structural Durability
Occlusal reduction
 For gold alloys, there should be 1.5 mm of
clearance.
 Metal-ceramic crowns will require 2.0 mm of
clearance to receive ceramic coverage
 should be 2.0 mm of clearance on
preparations for all-ceramic crowns

Functional cusp bevel
 A wide bevel on the palatal inclines of the maxillary
palatal cusps and the facial inclines of mandibular facial
cusps
 If not given wide bevel-thin wax up -thin casting –failure
restoration
attempt may be made to wax the crown to optimal
thickness in this area
Overcontoured
high point

FIXED PARTIAL DENTURE -DESIGN CONSIDERATION

If lab worker maintain wax
thickness

If an attempt is made to obtain space for adequate
bulk in a normally contoured casting without a bevel,
the result will be an overcut axial surface In addition to
the unnecessary destruction of tooth structure, the
severe inclination of the surface renders it useless for
retention

Axial reduction
Inadequate axial reduction can cause thin walls
and a weak restoration (a) or a bulbous,
overcontoured restoration (b).

Marginal Integrity
 restoration can survive in the biologic
environment of the oral cavity only if the
margins are closely adapted to the
cavosurface finish line of the preparation
 finish line dictates the shape and bulk of
restorative material in the margin of the
restoration.
 It also can affect both marginal adaptation
and the degree of seating of the restoration

F inish line configurations
chamfer
 metal restorations
 least stress,
 so the cement underlying it will have less
likelihood of failure
 cut with the tip of a round-end diamond

deep chamfer
 90-degree cavosurface
 large-radius rounded internal angle .
 radius of curvature = depth of axial reduction.
 The shoulder >deep chamfer used in all ceramic
 A bevel can be added to the deep chamfer for use with a metal
restoration

Shoulder
 choice for the all-ceramic crown
 wide ledge provides resistance to occlusal forces
 The sharp,90-degree internal line angle associated with the classic
variety of this finish line concentrates stress in the tooth

Radial shoulder
 radial shoulder is a modified form of shoulder
finish line
 radius of curvature = 1/4 to 1/5 depth of the axial
reduction
 Stress concentration less than classic shoulder
 The deep chamfer will produce slightly less
stress than a radial shoulder
 Bevels have been advocated as a means of
diminishing marginal discrepancy

A radial shoulder on an all ceramic crown preparation combines maximum
support of the ceramic with a stress reducing, rounded gingivoaxial angle.
(b) Minimal radius of curvature
reduces stress.

Pontic
•The part of FPD that replaces the missing
teeth.

Pontic Classification ACCORDING TO (with)
MUCOSAL CONTACT
 Ridge lap pontic: resembles to natural tooth( Adapts
closely to the ridge)
 Modified ridge lap pontic: tissue contact on buccal
surface of ridge.
 Saddle pontic: overlaps the ridge buccaly and lingually.
 Ovate pontic: for defective/incompletely healed ridges.
 Spheroidal pontic: contact only on ridge crest.
 Bullet/Conical/Heart shaped pontic: contacts the tissue
in a single point without any pressure.

Pontic ClassificationACCORDING According TO
(with) MUCOSAL CONTACT

Pontic ClassificationACCORDING TO (without)
MUCOSAL CONTACT
•Hygienic/Sanitary pontic: don’t make any contact with ridge. Easy
to maintain but un-aesthetic.

Pontic ClassificationACCORDING TO
MATERIAL USED
 •Metal and ceramic veneered pointic
 •Metal and resin veneered pontic
 •All metal pontic
 •All ceramic pontic

Based on the method of fabrication pontics can be
classified
 • Custom made pontic
 • Prefabricated pontic
 —Trupontic
 — Interchangeable facing
 — Sanitary Pontic
 — Pin-facing Pontic
 — Modified Pin-facing Pontic
 — Reverse Pin-facing Pontic
 — Harmony Pontic
 — Porcelain Fused to Metal Pontic
 • Prefabricated Custom Modified Pontic

Connector
Portion of FPD that unites pontics and
retainers.

Type of Connector
 Non-rigid connector: indicated when single path of insertion can’t be achieved due to
unparallel abutments.
 –Tenon Mortise connector: it got male (Tenon) and
female(Mortise) components or dovetail.
 –Split pontic connector: connector incorporated within the
pontic. Pontic is split into mesial and distal segment which
are attached to their respective retainers.
 –Cross-pin/Wing connector: similar to the split connector.
Indicated on tilted abutments.
 –Loop connector: lingual loops is given to connect the
retainer/abutment; when existing diastema to be maintained.
 –

Diastema is to be maintained in a planned
fixed prosthesis.
platinum-gold palladium alloy
Spring cantilever FPDs
used for diastema cases
can be used in posterior
teeth to replace missing
incisors.

Split pontic connector: used in cases with a pier
abutment
The mesial segment, which is
cemented first,
has a distal shoe in the gingival
portion of the pontic
The distal segment of the pontic
covers the mesiogingival part of the
pontic when the distal retainer is
cemented

Cross-pin/Wing connector used for tilted abutments
The distal retainer
and wing should be
cemented first
The retainer-pontic
segment is seated
finally
Cemented cross-pin and
wing fixed partial
denture

References
 Shillingburg Fundamental of fixed
prosthodontics 4th edition
 Textbook of prosthodontics Nallawsamy
 Glossary of prosthodontic term chapter 1

FIXED PARTIAL DENTURE -DESIGN CONSIDERATION

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