Connectors in fpd / dental continuing education

Connectors in FPD
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INDIAN DENTAL ACADEMY
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Contents
• Introduction
• Types of connectors –
Rigid&Nonrigid
• Types of Rigid connectors
• Types of Nonrigid connectors
• Connector design
• Heat sources for soldering
• Step by step procedure-Soldering
• Conclusion
• Bibliography

Connector is that part of a Fixed
Partial Denture (FPD) that joins
the individual
components(pontics and
retainers) together.

This can be accomplished by
• Rigid connectors
• Non rigid connectors

Rigid connectors can be made by
Casting - shaped in wax
Soldering - intermediate metal alloy
Welding - joining with heat

Non Rigid Connectors
Any connector that permits
Limited Movement
between otherwise
independent members of
F.P.D

TYPES OF RIGID CONNECTORS:-

Cast Connectors
• Cast Connectors are shaped
in wax as part of a multiunit
wax pattern.

Advantages
• Cast connectors are convenient
and minimize the number of
steps involved in the
laboratory fabrication.

Disadvantages
• The fit of the individual
retainers may be adversely
affected because distortion
occurs more easily when a
multiunit wax pattern is
removed from the die system.

Restrict cast connectors to
• Complete coverage
restorations which can be
gripped buccolingually.

Soldered Connectors
• Soldering is used to describe
most metal joining process
that involve the flow of a filler
metal between two or more
metal components

• Here the use of an
intermediate metal alloy is
used whose melting
temperature is lower than
that of the parent metal

• Connectors to be soldered are
waxed to final shape and
sectioned with a thin ribbon saw.
• So that when the components are
cast, the surfaces to be joined
will be flat,parallel, and a
controlled distance apart.
• This ensures accurate soldering
with a minimum of distortion.

Ribbon saw

SOLDERING GAP WIDTH:-
• The liquid solder is drawn into the
joint through capillary action
• Thus an optimum gap is necessary
for proper flow and strength of the
joint and to avoid distortion of the
assembly
• Gap width ranging from 0.13 to 0.3
have been suggested as optimum

LOOP CONNECTORS:-
Existing diastema

Loop on the lingual aspect of the prosthesis
that connects adjacent retainers and /or pontics

Welding Connectors
• is another method of rigidly
joining metal parts.
• The joining of two or more
metal pieces by applying
heat,pressure or both ,without a
filler metal ,to produce a
localized union across the
interface.

• Can be done by Spot welding
by passing of electric current
• Laser Welding based on a
pulsed high power neodymium
laser with a very high power
density.

• The units consists of a small
type of glove box that contains
the laser tip, an argon gas
source, and a stereomicroscope
with lens crosshairs for precise
alignment of the laser beam
with the components.
• The maximum penetration
depth of these laser welding
units is 2.5 mm.

• Since only a small amount of
heat is generated, the parts can
be hand-held during the welding
procedure.
• Welding can be performed
close to ceramic or resin
veneers without causing
damage to these materials.

TYPES OF NON RIGID CONNECTORS:-

Non rigid connectors
Indications
1. When it is not possible to
prepare two abutments for an
FPD with a common path of
placement.
2. Segmenting large, complex
FPDs into shorter
components that are easier
to replace or repair
individually.

3. Pier abutment

4.Mal aligned abutment
Difficult to prepare along long axis
- might result in devitalisation

5.Questionable distal
abutment- only a portion of
the FPD may be remade.

Used to
• Relieve stress
• Accommodate malaligned
FPD abutments
• FPD with anterior & posterior
segments
• Abutments with uncertain
prognosis

• During the mandibular opening
and closing stroke, the
mandible flexes mediolaterally.
• Rigid fixed partial dentures
have been shown to inhibit
mandibular flexure and
extensive splints have been
shown to flex during forced

• The associated stresses can
cause dislodgement of complex
FPD’s.
• Segmenting complex mandibular
FPD's can minimize this risk .
• Hence Non rigid connectors are
favorable here.


Types of Non Rigid Connectors
• Dovetail (Key – Keyway)
• Split pontic(connector inside
the pontic)
• Cross Pin & Wing

Dovetail (Key – Keyway)
• Align Path of insertion of the
keyway with that of the distal
abutment

Pontic
Deep wax box-
distal surface
Of wax pattern
Mortise/Female
/Keyway

A- the mesial segment ,with the keyway,is cemented first
B- the distal segment ,with the key
,is cemented immediately after
A B
distal aspect of the anterior retainer

Mortise can be prepared by
• Incorporation of prefabricated
inserts
• Wax Patterns
• Custom milling
• Prefabricated plastic patterns
Pulp size and clinical crown
height can be limiting factors in
the design of non rigid connectors

•Prefabricated plastic patterns

Split Pontic
• This is an attachment that is
placed entirely within the pontic
• Useful in tilted abutment cases
where the use of of a
conventional dovetail would
require the preparation of a
very drastic box.

A B
A- The mesial segment , has a distal shoe that is
the gingival portion of the pontic
B- The distal segment covers the mesiogingival
part of the pontic

Cross pin and Wing
These are the working elements
of a two piece pontic system
This allows the two segments to
be rigidly fixed after the
retainers have been cemented

•A-The distal retainer and wing are
cemented first
•B- The retainer and pontic is seated last
A B

•A tapered pin is driven through the
pontic ,the wing and back out from
pontic

• Used primarily in
accommodating abutment
teeth with disparate long axis
• The path of insertion of each
tooth is made parallel

CONNECTOR DESIGN

• The size, shape, and
position of connectors all
influence the success of the
prosthesis.
• Adequate access ( i.e.
Embrasure space) must be
available for oral hygiene aids
cervical to the connector.

• Connectors must be
sufficiently large to prevent
distortion or fracture during
function
• But not too large otherwise, it
will interfere with effective
plaque control and contribute
to periodontal breakdown over
time.

• Metal-ceramic fixed partial
dentures are usually fabricated
as a single unit, sometimes it is
necessary to solder the units
together.

This may occur if
1.There is distortion in a single-
piece fixed partial denture
casting
2.One retainer has inadequate
margins and must be redone
3. The FPD length is too great for
an accurate single-piece
casting www.indiandentalacademy.com

PRECERAMIC SOLDERING
• Preveneer soldering uses a
high-fusing solder that is
melted by torch before
porcelain is added.

• Once a metal – ceramic
framework has been assembled
by Pre ceramic soldering, the
subsequent procedures are the
same as if it had been cast in
one piece.

Advantages
• Allows the connected prosthesis to
be tried in the mouth in the
unglazed state & any necessary
adjustments can be made to the
porcelain.

Disadvantages
• Having to apply the porcelain
to a longer structure which
needs support
• It is also difficult to contour
the proximal embrasures so
that the units look like
natural teeth.

Post Ceramic Soldering
In post veneer soldering,a
low-fusing solder is melted in
the oven after porcelain has
been baked on the fixed
partial denture.

Post ceramic soldering
compensates for any tooth
movement in the mouth
between final impression and
restoration and it eliminates the
significance of any distortion
that might occur during
porcelain firing.

• All porcelain adjustment and
firing must be completed before
soldering.
• The proximal areas are shaped
before soldering, therefore it
looks more natural than a
presoldered or cast connector.

SOLDERING ALL- METAL FPD's:-
Soldering such retainers permits
the retainers to be shaped and
adjusted individually with
improved access for finishing
procedures.

• Advantage-Soldering simplifies that
manipulation of wax patterns.
• Disadvantage -it requires an
additional step, compared to a one-
piece casting.

Staffanou et al Strength properties of soldered joints
from various ceramic metal combinations JPD1980
• Staffanou et al in found that
20 % of post ceramic
soldered joints involving
base metal alloys had to be
resoldered because they
were so weak that they
broke with finger pressure.

Anusavice et al :flexure test evaluation of
presoldered base metal alloys JPD1985
• Anusavice et al showed
great variability in solder
joint quality with these
alloys , with no consistent
relationship of strength to
gap width.

• These authors found that
most failures occurred
through the solder and were
attributable to voids caused
by gas entrapment or
localized shrinkage.

Fehling et al Cast connectors :an alternative to soldering
JPD1987
• However, because of the
problems of soldering base
metal alloys, various
alternative procedures have
been advocated.
• These include making the
soldered joint through the
center of the pontic to
increase the area soldered.

• Another alternative is
connecting the parts by a
second casting procedure
with the molten metal
flowing into undercuts in the
sectioned pontic.

Cast Joining
• A process of joining two
components of a FPD by
means of casting molten metal
into interlocking region
between the invested
components .
• This procedure is sometimes
preferred for base metal alloys
because of technique sensitivity

• This was proposed by Weiss
and Munyon (1980) as an
alternative method for joining
cast components of FPD
• Cast joined components are
held together purely by
mechanical retention

Heat Sources for Soldering

Torch Soldering
Portion of flame used for
soldering should be neutral or
slightly reducing because this
produces the most efficient
burning process and most heat
.

• The flame should never
concentrated in one area but
kept in constant motion to
prevent uneven heat
application ,which could
result in fracture.

• Some researchers believe
the flow of solder is more
controllable during torch
soldering because a slight
temperature differential can
be created and the solder
always flows toward the
hotter point .

OVEN SOLDERING
Furnace or Oven soldering is
performed under vacuum or in
air.
A piece of solder is placed at
the joint space and the
casting and solder are heated
simultaneously.

• The method does not allow the
moment of the solder fusion to
be observed.
• This may be important, because
the longer the solder remains
molten, the more it will dissolve
the parent metal and
consequently weaken the joint

• In the porcelain furnace the
soldering assembly is heated
above the fusion point of the
solder, the muffle door is opened ,
and the solder is fed into the joint
space.
• Some furnaces have a observation
window

INFRARED SOLDERING
A specially designed unit
that uses an infrared
energy from a tungsten
iodine lamp that operates
at 3400 C

The operator observes the
soldering procedure
through a dark screen and
cuts off the electrical supply
when solder flow is
observed

• Good accuracy is possible with
the system.
• It requires more time than
conventional soldering .
• The joints have similar strength
to conventional soldering.

LASER WELDING
• Laser Energy is extensively
used for welding in many
industries and has been
described in described in
dentistry since the 1970s

• Laser assembly has reported
higher strength and reduced
corrosion in comparison to
conventional soldering
• Although laser welding does
seem susceptible to fatigue
failure.

• Laser welding may be a
practical way to joint cast
titanium components
(e.g. if these are to be used for
implant superstructures).

SOLDERING ACCURACY

Sarfati E Harter et al – Comparative accuracy of FPD
made as one piece castings or joined by solder IJP 1992
• Harter et al said that
Controversy exists as to the
relative accuracy of fixed
partial dentures that are cast
in one piece, preceramic
soldered, or post ceramic
soldered.

• The determining factor should
be the fit of the individual
abutment castings.
• In some situations it may be
impossible to cast a long- span
FPD with ideal retainer
dimensions and ideal
interabutment dimensions

• In such circumstances a
soldered connector may provide
better accuracy.

• The situation is reversed when
fabricating frame works for
implant supported prostheses
• An accurate, passively fitting
implant superstructure is critical
to avoid damaging forces.

Wee et al Strategies to achieve fit in implant
Prosthodontics .IJP 1999
• However, Wee at al have said
that it is not yet clear if accurate
implant superstructure are
most effectively made with
one- piece castings or
sectioned and soldered units.

SOLDERING TECHNIQUE

ARMAMENTARIUM.
Auto polymerizing acrylic
resin.
Zinc oxide- eugenol paste.
Impression plaster
Mixing bowl
Spatula
Small brush
 Waxing instrument
Sticky wax

Baseplate wax
Sprue wax
Soldering investment
Glass slab
Soldering tripod
 Flux
 Solder
 Tongs
. www.indiandentalacademy.com

Soldering Index

• Different methods can be used to
record the required relationships
of the parts to each other and to
the abutment teeth and ridge
tissues.
• When FPD’s are assembled by
soldering the relative position of
the components is recorded with
a Soldering Index on the

Advantages of an index
• After the soldering procedure
has been completed, the FPD
can be reseated in the index
and soldering accuracy can be
verified

AUTOPOLYMERIZING RESIN SOLDERING INDEX:-
• A Plaster Or ZnoE occlusal
index is less suitable for the
registration of anterior
restorations.
• The thinness of the incisal
edges of these units makes
them less stable, and accurate
repositioning is more difficult.

• For this reason, auto polymerizing
resin is recommended
• The resin burns offs during the
procedure.
• A small brush dipped in resin
monomer is touched to the
polymer powder.This forms a
bead .
• The resin should extend onto the
incisal edges of the retainers.www.indiandentalacademy.com

Step by Step Procedure

•Tongue depressor is soaked before using it to
hold the index

•Plaster is troweled onto the tongue depressor to
create a ridge that extends from one end of the
index to another

•The seated index is stabilized over the FPD until
the plaster sets

•Plaster index with components trapped in it

•Excess plaster around the FPD imprint is
trimmed off with a sharp blade

•The trimmed index exhibits shallow imprints of
the FPD components

•The gap width is measured by passing a business
card

•When the two surfaces to be soldered are
parallel ,there is less chances of distortion

•Wells are cut along the edges of the crown and
pontic imprints to provide space for sticky wax

•The periphery of the plaster index is trimmed on
the cast trimmer so that there will be a 3mm
apron around imprint of the FPD

•Sticky wax is used in the wells to attach the FPD

•A triangular shaped piece of utility
wax is extended facially and lingually .

•A strip of boxing wax 2.5 cm wide is
wrapped around the index

Investment is brushed into the
retainers

•After the investment has set ,the strip
of boxing wax is removed from the
index

•The index is pried loose from the
block of investment

•The index is separated from the
block of investment and inspected

•The Cast trimmer is used to remove
excess height from the block of
investment

•Buccal and lingual notches are carved
in the investment

•Pencil marks are used as an antiflux
on the occlusal surface of the castings

•Flux is placed in the solder joint area

•The invested casting is preheated
over a Fisher burner for 10 to 15
mins

•The flame is directed against the
investment from all sides

•Solder is placed into the lingual
notch later into buccal notch

•When the solder in the joint appears
to roll ,the flame is taken away

•The investment is removed after
placing it in water

•Any remaining investment is removed
with a sharp instrument

The finished solder joint

Evaluation
• No solder should run onto the
occlusal surface or cover the
margins.

• The joints must be tested for
strength any connector that
can be broken by force of
hand will not serve adequately
in the mouth.

• Because broken connectors
cannot be easily repaired
interiorly once the prosthesis
has been cemented.
• The entire restoration usually
must be remade.

Radiographic analysis of solder joint
quality
• When a FPD is delivered to the
dental office its processing
history is unknown
• Of particular importance is the
need to identify whether the
FPD was cast in one piece or
whether it was soldered or cast
joined.

• For either soldered or cast
joined structures, a radiographic
examination of the joined area
can be preformed
• The simplest method is to lay
the structure on a piece of
Intraoral film and expose the
film with a an X ray beam within
accelerating voltage of 90 kV
and a current of 10 mA for 1

• Another film should be exposed
after rotating the FPD at a 90 0
angle to the initial orientation .
• The flaws appear as radiolucent
areas in presoldered connectors
,whereas the cast metal
appears as a whole piece

SUMMARY and CONCLUSION

• Connectors join individual
retainers and pontics.
• Rigid or nonrigid connectors
can be used.
• Connector size,shape, and
position influence the success
of an FPD.

• The use of soldered
connectors can simplify the
fabrication of large fixed
prostheses, which may be cast
separately in groups of one or
two units and assembled after
their individual fit has been
verified.

• All debris must be removed
from the connector area
because it interferes with
surface wetting.
• Heat sources used for
soldering procedures include
gas – air torches gas- oxygen
torches, furnaces, infrared,

If the basic principles are
understood and the technique
has been mastered these
procedures are entirely reliable.

References
• Fundamentals of tooth preparation- 3rd
edition Herbert Shillingburg
• Tylman s Theory and Practice of Fixed
Prosthodontics
• Contemporary Fixed Prosthodontics-
Rosenstiel 3rd
edition
• Fixed Prosthodontics- Keith Thayer
• Johnston’s Modern Practice In Fixed
Prosthodontics - Roland W Dykema
• Science of dental materials - Anusavice

• Staffanou et al Strength properties of
soldered joints from various ceramic metal
combinations JPD 1980
• Anusavice et al :flexure test evaluation of
presoldered base metal alloys JPD 1985
• Fehling et al Cast connectors :an alternative
to soldering JPD 1987
• Sarfati E Harter et al – Comparative accuracy
of FPD made as one piece castings or joined
by solder IJP 1992
• Wee et al Strategies to achieve fit in implant
Prosthodontics .IJP 1999

Thank you
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Connectors in fpd / dental continuing education

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