different designs of dental bridges

Different designs
of bridges
Yasmin Mohammed
Group E2

Fixed Partial Dentures
Fixed partial dentures (FPDs) are "dental
prostheses that are luted, screwed, or
mechanically attached or otherwise securely
retained to natural teeth, tooth roots, and/or
dental implant abutments."1
During the past
decades, many types of FPDs or "bridges"
have been used to replace missing teeth. With
the introduction and widespread use of
osseointegrated implants, many missing teeth
are now being replaced in this manner rather
than with FPDs. Dental bridges can, of course,
still be used successfully, and this article will
briefly review the many methods of bridge
construction and relate them to their
applicability and current acceptance of the
practicing dentist and the treated patient.
These will include: cast-gold, stress-broken
bridges; resin-bonded, etched retainers;
porcelain-fused-to-metal (PFM) bridges; and
all-ceramic bridges, including zirconia.

THE BRIDGE CONSISTS OF :
1. Retainer : it is the part of the bridge
which is cemented to the abutment
teeth .it could be full metal ,full
veneer with facing , partial veneer ,
post crown or inlay … etc
2.Pontic : Is the part of the bridge
which represent the missing tooth and
it connected to the retainer by a
connector
3. connector : is the part of the bridge
which connect the pontic and the
retainer , it maybe rigid (solid joint )
or movable joint (precision attachment
, key and key way )
4. abutment : Is the natural tooth
which support the bridge and on
which the retainer is cemented (tooth
or root )
.

Bridge compnents
Types of connectors : Connectors are those
parts of a fixed partial denture (FPD) or
splint that join the individual retainers and
pontics together. Usually this is
accomplished with rigid connectors ,
although nonrigid connectors are used
occasionally. The latter are usually
indicated when it is impossible to prepare

a common path of insertion for the
abutment preparations for an FPD.
The main types
•1. Rigid
•2. non rigid
•_tenon mortise conectors
•_loop connectors
•_split pontic connectors
•_cross pin and wing connectors

Rigid connectors
Rigid connections in metal can be made by
casting, soldering, or welding. Cast
connectors are shaped in wax as part of a
multiunit wax pattern. Cast connectors are
convenient and minimize the number of
steps involved in the laboratory
fabrication. However, the fit of the
individual retainers may be adversely
affected because distortion more easily
results when a multiunit wax pattern is
removed from the die system. Soldered
connectors involve the use of an
intermediate metal alloy whose melting
temperature is lower than that of the parent
metal .The parts being joined are not
melted during soldering but must be
thoroughly wettable by liquefied solder.'
Dirt or surface oxides on the connector
surfaces can reduce wetting and impede
successful soldering; for example, the
solder may melt but will not flow into the
soldering gap. Welding is another method
of rigidly joining metal parts. Here the

connection is created by melting adjacent
surfaces with heat or pressure. A filler
metal whose melting temperature is
about the same as that of the parent
metal can be used during welding. In
industrial metalworking, a distinction is
made between soldering, in which the
filler metal has a melting point below
450° C (842° F), and brazing, in which the
filler has a melting point above 450° C.2
Rigid connections in dentistry are
generally fabricated above 450° C, but the
process has almost always been referred to
in the dental literature as soldering.
However, a proposed international
standard uses the term brazing. With time
the latter term may become more generally
accepted. In this text, however,
the term soldering will be used.
NONRIGID CONNECTORS
Nonrigid connectors are indicated when
it is not possible to prepare two
abutments for an FPD with a common
path of placement. Segmenting the

design of large, complex FPDs into
shorter components that are easier to
replace or repair individually is
advisable. This can be helpful if there is
uncertainty about an abutment's
prognosis. If the abutment fails, only a
portion of the FPD may need to be remade.
In the mandibular arch, nonrigid
connectors are indicated when a
complex FPD consists of anterior and
posterior segments. During
themandibular opening and closing
stroke, th mandible
flexesmediolaterally.
3 Rigid fixed partial dentures have been
shown to inhibit mandibular flexure,
and extensive splints have been shown
to flex during forced opening. The
associated stresses can cause
dislodgment of complex FPDs.
Segmenting complex mandibular FPDs
can minimize this risk Nonrigid
connectors are generated through
incorporation of prefabricated inserts in
the wax pattern

or through custom milling procedures
after the first casting has been obtained.
The second part is then custom-fitted to
the milled retainer and cast. They are
often made with prefabricated plastic
patterns. The retainers are then cast
separately and fitted to each other in
metal.
connector design The size, shape,
and position of connectors all influence
the successof the prosthesis. Connectors
must be sufficiently large to prevent
distortion or fracture during function but

not too large; otherwise, they will
interfere with effective plaque control and
contribute to periodontal breakdown over
time. Adequate access (i.e., embrasure
space) must be available for oral hygiene
aids cervical to the connector. If a
connector is too large incisocervically,
hygiene is impeded, and over time
periodontal failure will occur . For esthetic
FPDs, a large connector or inappropriate
shaping of the individual retainers
may result in display of the metal
connector, which may compromise the
appearance of the restoration and lead to
patient dissatisfaction In addition to being
highly polished, the tissue surface of
connectors is curved faciolingually to
facilitate cleansing. Mesiodistally, it is
shaped to create a smooth transition from
one FPD component to the next. A
properly shaped connectorhas a

configuration similar to a meniscus
formed between the two parts of the
prosthesis. In a buccolingual cross section,
most connectors have a somewhat
elliptical shape. Such an elliptical
connector is strongest if the major axis of
the ellipse parallels the direction of the
applied force. Unfortunately, because of
anatomic considerations, this can not
always be achieved. In fact, due to space
constraints, most connectors have their
greatest dimension perpendicular to the
direction of applied force, which tends to
result in a weaker connector. For ease of
plaque control, the connectorsshould
occupy the normal anatomic interproximal
contact areas because encroaching on the
buccal, gingival, or lingual embrasure
restricts access. However, to improve
appearance without significantly affecting

plaque control, anterior connectors are
normally placed toward the lingual.
depicts typical locations for connectors on
selected teeth.Pulp size and clinical crown
height can be limiting factors in the design
of nonrigid connectors. Most
prefabricated patterns require the
preparation of a fairly sizable box. Fhis
allows incorporation of the mortise in the
cast restoration without overcontouring
of the interproximal emergence profile.
Short clinical crowns do not provide
adequate occlusocervical space to ensure
adequate strength. Most manufacturers
recommend 3 to 4 mm of vertical height

RIGID CONNECTORS
Rigid connectors must be shaped and
incorporated into the wax pattern after
the individual retainers and pontics have
been completed to final contour but
before reflowing of the margins for
investing
Cast Connectors. Connectors to be cast
are also waxed on the master cast before
reflowing and investing of the pattern. The
presence of a cast connector makes the
latter somewhat more awkward. Access to
the proximal margin is impeded, and the
pattern cannot be held proximally during
removal from the die. Restricting cast
connectors to complete coverage
restorations is therefore advisable, which
can be gripped buccolingually. Partial-
coverage wax patterns are easily distorted

when they are part of a single-cast FPD.
One-piece castings often appear to
simplify fabrication but tend to create
more problems than do soldered
connectors, especially as pattern
complexity increases.
Soldered Connectors. As with cast
connectors, connectors to be soldered are
waxed to final shape but are then
sectioned with a thin ribbon saw
therefore, when the componentsare
cast, the surfaces to be joined will be flat,
parallel, and a controlled distance apart.
This allows accurate soldering with a
minimum of distortion . Molten solder
will flow toward the location where
the temperature is highest. In metal, the
two flat surfaces previously created in wax

retain heat, ensuring that the highest
temperature is in the connector
area.
Soldering Gap Width. As gap width
increases, soldering accuracy decreases.
Extremely small gap widths can prevent
proper solder flow and lead to an
incomplete or weak joint.' An even
soldering gap of about 0.25 mm is
recommended. If a connector
area has an uneven soldering gap width,
obtaining a connectorof adequate cross-
sectional dimension without resulting
distortion is more difficult.
Loop Connectors . Although they are
rarely used, loop connectors are
sometimes required when an existing
diastema is to be maintained in a planned
fixed prosthesis. The connectorconsists

of a loop on the lingual aspect of the
prosthesis that connects adjacent
retainers and/or pontics. The loop may be
cast from sprue wax that is circular in
cross section or shaped from a platinum-
goldpalladium (Pt-Au-Pd) alloy wire.
Meticulous design is important so that
plaque control will not be impeded.
NONRIGID CONNECTORS
The design of nonrigid connectors that are
incorporated in the wax pattern stage
consistsof a mortise (also referred to as
the female component) prepared
within the contours of the retainer and a
tenon (male) attached to the pontic The
mortise is usually placed on the distal
aspect of the anterior retainer. Accurate
alignment of the dovetail or cylindrically
shaped mortise is critical; it must

parallel the path of withdrawal of the
distal retainer. Paralleling is normally
accomplished with a dental surveyor.
When aligning the cast, the path of
placement of the retainer that will be
contiguous with the tenon is identified
The mortise in the other retainer is then
shaped so its path of insertion permits
concurrent seating of the tenon and its
corresponding retainer.
The mortise can be prepared freehand in
the wax pattern or with a precision milling
machine. Another approach is to use
prefabricated plastic componentsfor the
mortise and tenon of a nonrigid
connector. As an alternative, a special
mandrel can be embedded in the wax
pattern and the abutment retainer can be
cast, with refinement of the female
component as necessary; the male key is
then fabricated of autopolymerizing

acrylic resin and attached to the
pontic.
Tenon mortise
Loop connector

split pontic
Cross pin and wing connector

Crown_ root ratio
Is the measurementof the length of tooth
occlusal to the alveolar crest of the bone
compare with the length of root
embedded in the bone . The ideal crown
root ratio for a tooth to be used as a
bridge abutment is 1:2 , and the minimum
ratio acceptable for prospective abutment
under normal circumstances is 1:1 .

•
• The root surface area (pericemental
area )of the abutment teeth should be
more or at least equal to the root
suface area (pericemental area )of the
missing teeth being replace .

Types of bridges
• There are 4 main type of bridges
• 1. fixed _ fixed bridge
• 2. fixed movable bridge
• 3.cantilever bridge
4.resin bonded bridge (conservative
bridge )
Fixed _fixed bridge
In this type the pontic is attached to the
retainers (mesial and distal)by rigid
connector(solid joint) so they should have
one path of insertion . This is the most
commonly used FPD
.

Advantages
• 1. maximum retention and support .
• 2. abutment teeth are splinted
together .
• 3. the design is most practical for
larger bridges .
disadvantages
1.require preparation to be parallel
2. All the retainers are major retainers
and require extensive ,destructive
preparation of the abutment teeth .
3.Has to be cemented in one piece .
Fixed movable bridge
• In this type the pontic is attached to
one distal major retainer (distal end of
the pontic )by fixed connectorwhile
the other end is attached to the minor
retainer (in front of pontic )by

movable joint .it s indicated in case of
drifted abutment teeth and difficulty
to obtaining parallel abutments.
Advantages:
• 1. preparations do not need to be
parallel to each other .
• 2. more conservative of tooth tissue
because preparations for minor
retainers are less destructive .
• 3. parts can be cemented separately .
Disadvantages
• 1.more complicated to constructin
laboratory than fixed fixed bridge .
• 2.difficult to make temporary bridge .

Cantilever bridge
n areas of your mouth that are under less
stress, such as your front teeth, a cantilever
dental bridge may be used. A cantilever
dental bridge is when the “false tooth” is
only supported on one side. The result is
just as aesthetic but has the benefit that
fewer teeth have to be treated.
resin bonded bridge
A resin-bonded fixed partial denture is a
prosthetic construction which can replace
I or several teeth in an occlusal system
and which comprises a pontic element
which is adhesively attached to 1 or more
abutment teeth. To compensate for the
limited shear strength of the adhesive

layer, the Jixed partial denture is
occlusally supported by the abutment(s).
A direct resin-bonded fixed partial
denture is made of composite, reinforced
or not by a frame of flexible metal or
fiber material. For an indirect resin-
bonded fixed partial denture, a metal,
fibre-reinforced composite or ceramic
substructure is fabricated in a dental
laboratory. The basic principle of a resin-
bonded fixed partial denture is minimal
invasiveness. However, a restoration in
an abutment tooth requires a certain
occlusal space which is realized by tooth
preparation. Resistance preparations may
be performed to improve the longevity of
resin-bonded fixed partial dentures. Both
financially and biologically, a resin-
bonded bridge is a cost-effective
prosthetic construction. The longevity is
limited, but when the construction fails
the negative consequences for the

abutments are generally limited, which
leaves open several types of other
treatments.
Spring Cantilever
It is a tooth and tissue supported bridge. A
pontic is supported at some distance from
the retainer (). It is a type of cantilever
bridge. Strong retention is required as for
all cantilever bridges and double
abutments are usually necessary. The
retention of a spring bridge is severely
tested when force is exerted in
apicoincisal direction as seen on biting
sticky food as the retainer is subjected to
detrimental stresses. To avoid this, two
retainers in adjacent teeth are used
together to give added strength. This
bridge design is used while replacing
anteriors with diastema or in case of
existingexisting endodontically treated
tooth posteriorly. This design cannot be

used in lower arch because of lack of
suitable tissue support. The bar should
follow the natural contours of the rugae in
the palate, so that it lies obscurely in the
valleys and its lateral margins do not
represent an attraction to the tongue. The
cross – section of the bar should be a flat,
oval or a rounded – T shape[8]. The model
should be lightly scraped to ensure firm
seating on the soft tissue and minimize
food trapping. High platinized gold or
spring metal is used. Class IV casting gold
is ideal. The Achilles heel with this design
is the junction of retainerand the bar and
the leverage on the abutment.
Resin retained bridges
1. Bonded pontic
2. Rochette bridge
3. Viginia bridge
4. Maryland bridge
5. Adhesive bridge

1. Bonded pontic
Introduced by Ibsen and Portnoy in 1973,
these are the earliest resin retained
prosthesis[9]. They are the resin tooth or
patient’s natural tooth bonded directly to
the etched enamel. These are meant for
short term replacements. The limiting
factor was the weakness of the
composite resin connector.
2.Rochette bridge
CAST PERFORATED RESIN-
RETAINED FPDS (MECHANICAL
RETENTIO In 1973, Rochette
introduced the concept of bonding
metal to teeth using flared perforations
of the metal casting to provide
mechanical retention. He used the
technique principally for periodontal
splinting but also included pontics in his
design. Howe and Denehy recognized

the metal framework's improved
retention (as compared to bonded
pontics) and began using FPDS with
cast-perforated metal retainers bonded
to abutment teeth and metal-ceramic
pontics to replace missing anterior
teeth. Their design recommendation,
extending the framework to cover a
maximum area of the lingual surface,
suggested little or no tooth preparation.
Patient selection limited these FPDs to
mandibular teeth or situations with an
open occlusal relationship.
The restorations were bonded with a
heavily filled composite resin as a luting
medium. This concept was expanded to
replacement of posterior teeth by
Livaditis. Perforated retainers
were used to increase resistance and
retention. The castings were extended
interproximally into the edentulous
areas and onto occlusal surfaces. The
design included a defined
occlusogingival path of insertion by
tooth modification, which involved

lowering the proximal and lingual
height of contour of the enamel on the
abutment teeth. These restorations
were placed in normal occlusion; many
have survived and have been seen on
recall for up to 13 years Despite this
success, the perforation technique
presents the following limitations:
• Weakening of the metal retainer by
the perforation Exposure to wear of the
resin at the perforations Limited
adhesion of the metal provided by the
Perforations Clinical results with the
perforated technique were followed for
15 years in a study at the University of
Iowa.'-' The results from this well-
controlled study suggest that for
anterior fixed partial dentures, 63% of
the perforated retainer prostheses fail in
about 130 months.'6 Later data'-'

indicate that 50% fail in about 110
months .
ETCHED CAST RESIN-RETAINED FPDS
(MICROMECHANICAL RETENTION-
"MARYLAND
BRIDGE")
Based on the work of Tanaka et al" on
pitting corrosion for retaining acrylic resin
facings and the metal etching studies of
Dunn and Reisbick," Thompson and
Livaditis at the University of Maryland
developed a technique for the electrolytic
etching of Ni-Cr and Cr-Co alloys. Etched
castm retainers have definite advantages

over the castperforated restorations: •
Retention is improved because the resin-
toetched metal bond can be substantially
stronger than the resin-to-etched enamel.
The retainers can be thinner and still resist
flexing. The oral surface of the cast
retainers is highly polished and resists
plaque accumulation. During the course of
this work, the need for a composite resin
with a low film thickness for luting the
casting became apparent. This led to the
first generation of resin cements, which
permitted micromechanical bonding into
the undercuts in the metal casting created
by etching while providing adequate
strength and allowing complete seating of
the cast retainers. Comspan,* the first of
these cements, was moderately filled
(60% by weight) with a film thickness of
approximately 20 um.21 Such cements are
not chemically adhesive to the metal.

Electrolytic etching of base metal alloys
proved to be critically dependent on the
base metal alloy and attention to detail in
the laboratory. Initial etching methods
were developed for a Ni-Cr alloy* and a
Ni-Cr-Mo-Al-Be alloy. These methods were
followed by simplified techniques,
chemical etching, 23 or attemptsat gel
etching. 24 They all yield similar results,
provided the technique is optimized for a
specific alloy. Proper etching requires
evaluation of the alloy surface with a
scanning electron microscope. The degree
of undercut created by this etching
process can be seen in Figure 26-3. Lack of
attention to detail can result in
electropolishing or surface contamination
.26 With time, both severely degrade
bond strengthsin a moist environment.
Highly variable results were reported for
dental laboratories when etching the

same alloy . Etchingand bonding
techniques were adopted based on
bond strengthtesting of specimens only
subjected to 24 hours or 7 days of water
exposure. When resin-tometaltest
specimens were aged for 6 months in
water and then thermally stressed by
10,000 or more thermal cycles, large
reductions in bond strengths were
recorded . Therefore, data from
specimens that have not been aged and
thermally stressed should be viewed
skeptically. Even particle abrasion
will provide initially high resin-to-metal
bonds, which can degrade to almost zero
with time . Well-researched and tested
resin systems for direct adhesion to metal
surfaces have now completely supplanted

metal etching as retention mechanisms.
MACROSCOPIC MECHANICAL RETENTION
RESINRETAINED FPDS ("VIRGINIA
BRIDGE")
As a result of concerns about etching base
metal and the desire to use alternative
alloys, several methods have been
developed to provide visible macroscopic
mechanical undercutson the inner surface
of FPD retainers. The first was developed
at the Virginia Commonwealth University
School of Dentistry and is known as the
"Virginia Bridge. It involves a "lost

salt crystal" technique. On the working
cast, the abutments are coated with a
model spray, and a lubricant is then
applied. Within the outlines of the
retainers, specially sized salt crystals* (150
to 250 um) are sprinkled over the surface
in a uniform monolayer, leaving a 0.5-mm
border without crystals at the periphery of
the pattern. This is followed by application
of a resin pattern. After pattern
investment, the salt crystals are dissolved
from the surface of the pattern. Adequate
bond strengthsare possible with this
method, but the thickness of the casting
must be increased to allow for the
undercut thickness. Although no long-
term results have been reported with this
technique, it does permit the use of
almost any metal-ceramic alloy An
alternative technique for macroscopic
retention is the use of a cast mesh pattern

on the internal surface of the retainers.
The mesh, usually made of nylon,* should
be adapted to the lingual and proximal
surfaces of the abutments. The mesh is
then covered by wax or resin; this must
be done carefully to prevent occluding
the mesh with the pattern material.
Investing and casting then followThis
method is technique sensitive but
can provide adequate retention with a
resulting thick lingual casting. The cast
mesh and the lost salt crystal method
have been supplanted by direct adhesion
with resin, which is possible for most
casting alloys if the correct surface
treatment is provided .
Cast mesh fixed bridge

Virginia bridge
Adhesive Bridges5.
Inspite of electrochemical etching being
very popular in America, alloy etching and
macroscopic retention is obsolete in Japan
since 1980s . As a result of extensive
research chemically active adhesive
cements were developed for direct bonding
to metal . These cements rely on chemical
adhesion to the metal and not on
microretention in the surface of the metal
for bond strength. Etching was no longer
necessary[19] Adhesive bridge shows
chemical bonding between the metal and
the resin luting agent. Direct bonding
involves the chair side and lab systems.
Metabond is first of these resin systems. It
is based on formulation of Methylmetha
acrylate (MMA) polymer powder and

MMA liquid modified with adhesion
promoter 4- META (4-methacryloxyethyl
trimellitate anhydride). Unique tributyl
borane catalyst is added to liquid. On base
metal alloys, Superbond has highest initial
bond strengths of any adhesive resin
systems[20]. But, it gives weak bond with
high gold alloys and the bond shows
hydrolytic instability. Introduction of
Metabond was followed by Panavia which
can be used both with high gold ( after tin
plating) and base metal alloy. Tin plating
can be done in lab, chair side or
intraorally. Intraoral tin plating is done by
tin amide solution. Adhesive monomer
used in Panavia is MDP(10-
methacrylolyloxydecyl dihydrogen
phosphate). The phosphate end reacts with
Calcium of tooth and with the metal oxide.
Bond strength to etched base metal is
greatly exceeded to that of tooth. Lab
system for adhesive bonding have been
developed. Silicoater Classical ( Tiller et.
al , 1984) is based on the need for an
intermediate layer containing silica as this
provides sufficient bonding of the resin via
a silane bonding agent. New version of
Silicoater MD was introduced in 1998.

This uses a special oven that burns a
chrome endowing silica layer onto the
surface. Pyrosil Pen Technology (1998) is
the chairside version of silicoater. Rocatec
System is a novel acrylic and metal
bonding system which uses a
tribochemical and thermal embedding of a
silica layer by means of sand blasting on
the metal surface[22]. Metal is thus
rendered more reactive to resin via silane.
It is unfortunate that this treatment
modality is not very popular amongst
dentist but if the case selection is proper it
offers outstanding conservatism with
tremendous bond strength.

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