connectors in fpd
TRANSCRIPT
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