CONNECTORS FOR FIXED PARTIAL DENTURES

Dr.K.V.Pratheep

• Connectors are those parts of a fixed partial denture (FPD) that join the individual retainers and pontics together. (GPT 8)

Types Of Connectors

I. Rigid connectors

II. Nonrigid connectors

I. Rigid Connectors

• Rigid connections in metal can be made by casting, soldering or welding

• Rigid connectors must be shaped and incorporated into the wax pattern after the individual retainers and pontics have been completed to final contour

Cast Connectors

They are shaped in wax as part of a multiunit wax pattern (one-piece casting)

• Convenient, minimizing laboratory stepsDisadvantages :• Liability to distortion during wax pattern removal

from the cast• Restricted to simple restorations

I. Rigid Connectors

• Soldered connectors

Soldering involves the joining of metal components by the use of a filler metal or solder alloy having a lower melting temperature than the parts to be joined

The parts being joined are not melted during soldering but must be thoroughly wettable by liquefied solder

I. Rigid Connectors

• Soldering- the filler metal has a melting point

below 450° C (842° F), and

• Brazing- the filler has a melting point above

450° C.

• Rigid connections in dentistry are generally

fabricated above 450° C.

• Connectors to be soldered are waxed to final shape and then sectioned with a thin ribbon saw

• The surfaces to be joined should be flat and parallel• An even gap width of 0.25 mm is recommended• Cleanliness of the surfaces is very important to allow

good wetting by the solder alloy

I. Rigid connectors

Soldering • Joining components of fixed partial dentures

• Building up proximal contacts

• Repairing casting voids or broken joints

Requirements of solder alloys

• Lower fusion temperature than parent alloy• High tarnish and corrosion resistance• Flow freely during the soldering procedureLower fineness gold solders are more fluid and

so used for joining castingsHigher fineness solders tend to flow less freely

and are used for building up contacts

• High strength comparable to parent alloy• Non pitting• Color matching to parent alloy.• Solder should possess a fusion temperature

about 60 degrees C (100-150 F) below that of the metal being soldered

Requirements of solder alloys

Soldering flux

• It is applied on a metal surface to remove oxides or prevent their formation

• The solder will be then free to wet and spread over the clean metal surface

Ideal properties of flux

• Easy to apply and stay where it is applied.• Withstand heating without loosing its protective

properties.• Lower fusion temperature than the alloy being

melted.• Flow easily over the surface of the alloy when

melted• Prevent the formation of oxides• Prevent the absorption of gases into the molten

alloy

Types of fluxes

• For gold alloys: borax glass because of its affinity to copper oxides

• Borax 50-60%,boric acid 12%, silica5% and a fine carbon25%.

• the silica makes the glass a little stiffer for use on higher melting metals.

• The fine carbon adds some carbon monoxide at melting temperatures to protect the metal.

• For base metal alloys: fluoride fluxes to dissolve stable oxides of chromium, cobalt and nickel.

• Composition: potassium fluoride: 50%-60% boric acid : 25%-35% borax glass : 6%-8% potassium carbonate: 8%-10%

Soldering Antiflux

• Used to limit the spreading of the solder alloy. It is placed on the casting before flux application

• Graphite pencil• Iron oxide (rouge)

Soldering investment

• Similar in composition to casting investments• High strength• Should withstand heat without cracking• Quartz investments are better than

cristoballites because of lower thermal expansion

Soldering All-Metal FPDs

• Type III and type IV gold retainers are soldered with gold solders of 615 to 650 fineness

Soldering Metal-Ceramic FPDs• Pre-ceramic solderingAllows for the try-in step and any necessary adjustments can be

madeSag can be a problem with high-gold content ceramic alloys

• Post-ceramic solderingNecessary when regular gold is combined in an FPD with metal-

ceramic unitsAll the porcelain construction steps must be completed before

soldering

Heat sources

• Torch soldering

• Oven soldering

• Infrared soldering

Torch soldering

• Low heat soldering: gas-air torch

• High heat soldering: gas-oxygen torch

• Reducing portion of the flame is used to prevent oxidation

• Flame is never concentrated in one area but kept in constant motion for even heat distribution

• Maximum visibility, accessibility and control

Torch soldering

Oven soldering

• Can be done under vacuum or in air inside a porcelain furnace

• A piece of solder is placed at the joint space and the casting and solder are heated simultaneously

• Vacuum firing is not needed for soldering gold alloys

• Air firing is preferred with post-ceramic soldering. With vacuum, there is chance for drawing entrapped gases to the surface of glazed porcelain

• Provides uniform heating and accurate temperature control

Oven soldering

Infrared soldering

• Can be used for low-fusing connectors as well as pre-ceramic soldered joints

• Infrared source produces concentrated heating by optically collecting infrared energy and directing it to the connector area

Welding

• Welding depends on melting adjacent surfaces with heat or pressure. Sometimes a filler metal whose melting temperature is about the same as that of the parent metal can be used

I. Rigid connectors

Types of welding

• Laser welding.• Plasma welding.

Laser Welding

• Laser welding is a welding technique making use of the strong thermal effect of laser beam concentrated on a minute spot

• Relative ease and time saving• Can be done directly on the cast• Less distortion, higher strength and reduced

corrosion• High cost and technique sensitive• Hazardous effects

Laser Welding

Plasma welding

II. Nonrigid Connectors

• Indicated when it is not possible to prepare abutments for FPD with a common path of insertion

• Complex, large FPDs can be segmented into shorter components to minimize the induced stresses.

• In case of pier abutments.

• Designs : -Tenon mortise or key key-way. -split pontic design. -cross pin and wing. -Beyler ‘s attachment.

Mortise tenon: Indications :• when it is not possible to prepare two abutments for an FPD

with a common path of insertion.• Pier abutment• A non-rigid connector on the middle abutment isolates force

to that segment of the fixed partial denture to which it applied.• Complex mandibular FPD that consists of anterior and

posterior segments

• Selcuk Oruc et al.• The area of maximum stress concentration at

the pier abutment was decreased by the use of a nonrigid connector at the distal region of the second premolar. (J Prosthet Dent 2008;99:185–192).

A case report

Contemporary clinical dentistry oct 2011;vol 2

Contraindications:

• Abutment not suitable for attachment retainer- - short clinical crown - Narrow bucco-lingual crown -Large pulp horn -Insufficient bone support

• Improper mucosal condition- -No room for attachment (vertical and horizontal). - Inflammation. - No bone support ( wiry ridge).

• Split pontic design:

-attachment entirely in the pontic.-in tilted abutment cases.-mesial segment which is cemented first, has a distal shoe which is the gingival portion of the pontic.-distal segment of the pontic covers the mesiogingival part of the pontic when the distal retainer cemented .

• Cross pin and wing:• wing should parallel the path of

insertion of the mesial abutment preparation.

• extends out 3.0 mm mesially from the distal retainer, have a 1.0-mm thickness facio-lingually.

• Its 1.0 mm short of the occlusal surface, and have an undersurface that follows the intended contour of the underside of the pontic.

• Beyeler attachment:• Intracoronal, precision,

slide attachment. • Frictional retention

with 2° taper, not adjustable

• Gold alloy male and female

• Dovetail design for strength and lateral stability

• Chayes attachment:

• Schatzmann attachment:

Connector Design

• Size

• They should be sufficiently large to withstand stresses and prevent distortion or fracture during function

• If small failure

• If too large small embrasures hygiene is impeded

• Hamid et al 2008• Effect of connector width on stress distribution in

all ceramic fixed partial dentures.• compared three different widths, 3 mm, 4 mm, 5

mm for connectors.• Concluded that an increase in the width of

connector reduces the stress concentration and improves the likelihood of long-term prognosis.

• Shape • Tissue surface should be highly polished and curved

faciolingually to facilitate cleansing

• Mesiodistally, it is shaped to create smooth transition from one component to the other

• Buccolingually elliptical in shape to provide strength

Connector Design

• Anusavice et al 2002.• Studied the effect of connector design on the

fracture resistance of all-ceramic fixed partial dentures.

• As the radius at the gingival embrasure increased from 0.25 to 0.90 mm, the mean failure load increased by 140%.

• The radius of curvature at the occlusal embrasure had only a minor effect on the fracture susceptibility of 3-unit FPDs

• Position

Connectors are normally placed towards the lingual to improve appearance without affecting plaque control

Connector Design

Miscellaneous

• Loop connector /Spring cantilever.• Cast rest joint movable connector.

Loop connector

International journal of dental clinics 2010:2(3):61-63

Cast rest joint movable connector

Int chin j dent 2007:7;65-68

Reference

• Fundamentals of Fixed Prosthodontics 3rd edition Shillinburg.• Contemporary Fixed Prosthodontics, 4th Edition by

Rosenstiel • Review of fixed partial denture: Lovely M 1st edition 2006.• Planning and making of crowns and bridges. Bernard gn

smithleslie c howe.• J prosthet dent.1986 aug;56(2):249-51. Use of the split

pontic nonrigid connector with the tilted molar abutment. O'connor rp, caughman wf, bemis c.

• Anterior spring cantilever fixed partial denture: a simple solution to a complex prosthodontic dilemma pavan kumar, shivkumar.N.Puranik . international journal of dental clinics 2010:2(3):61-63 .

• Cast rest joint used as movable connector between single restoration and adjacent pontic. Int chin j dent 2007:7;65-68.

• Non Rigid Connector : A Boon for Pier Abutment Fixed Partial Denture - A Case Report JIDA, Vol. 5, No. 7, July 2011.• J Prosthet Dent. 2002 May;87(5):536-42.Effect of connector

design on the fracture resistance of all-ceramic fixed partial dentures. Oh WS Anusavice KJ.

• Journal of Prosthetic DentistryVolume 99, Issue 3, Pages 185-192, March 2008 Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments Selcuk Oruc et al