V Ideal Requirements

Soldering  Definition  Uses  Ideal requirements  Properties  Composition  Classification  Procedures

• If solder joint done properly there should be no fusion or alteration of the two components joined. • Fusion welding is the process whereby the pieces that are joined are melted or fused together without solder (filler).

Prerequisites of soldering • To achieve Bonding – Cleanliness – Wetting of the surfaces

Ideal requirements of dental solder  Ability to resist tarnish and corrosion.  Fusion temperature 100-150°F (60°C) below that of the parts to be joined.  To be free flowing when melted.  Resistance to pitting.  At least as strong as the parts being joined.  Color compatible with parts to be joined.

Properties • Fusion Temperature. • Strength • Resistance to tarnish and corrosion. • Solder gap. • Free flowing.

Classification of Gold Solder • Fineness • Carat • Fusion Temperature

Carat  It is the amount of gold in parts per 24.  an alloy that is 18 K is 18 parts gold per 24 (18/24) = 75% gold .

FLUX  Is placed on the surfaces to be soldered before they are heated.  Added to the metal surface to  improve solder flow,  prevent oxidation (actually flux dissolves oxides),  prevent contamination.  Oxidation of metal surfaces during soldering procedures can prevent both flow and wetting of solder.

• 1st, displaces gases and removes oxides from surface by reduction or dissolution • 2nd, is displaced by the solder

FLUX  Borax, Boric Acid, Silica, or Sodium tetraborate  Used with noble alloys (gold alloys for crown and bridge and ceramo-metal alloys).  Fluoride Fluxes are need for Chrome-Nickel metals (base metal alloys) since Borax based flux does not dissolve chromium oxide. Anti-Flux  A material used to outline the area to be soldered in order to restrict the flow of solder (limit spreading of solder).  Placed on casting before flux application.  Most common types:  Soft graphite pencil  Polishing rouge (Iron Oxide)  Whiting compound (a calcium based compound). Soldering Procedure • Indexing • Investing • Soldering

Pre-soldering  Preveneer soldering.  Refers to soldering the metal framework before the addition of porcelain.  A high fusing solder (1100°C) is used because the solder joint must withstand subsequent heating during the addition and firing of porcelain. Post-soldering • Refers to soldering after the porcelain is added. • A low fusing solder is used because soldering must be done at a lower temperature than the maturation of porcelain. • All staining and glazing of ceramic units must be done prior to soldering. • The porcelain should not contact the investment or flux, and the units should not be quenched. 3. Make soldering index : fast-setting impression plaster in impression carrying tray or tongue depressor.

4. Make soldering block: Box index and pour soldering investment Trim to uniform shape and notch soldering block , Flush boiling water, Place flux and antiflux

REPAIRING CASTING VOIDS

• Solder cannot be used to repair deficient margins or occlusal holes. • CAN be used to repair PITS and HOLES in axial surfaces. • Platinum foil over hole on inside of casting: acts as matrix for solder.

NON-RIGID CONNECTORS

Used to: 1. Solve problems of malaligned abutments. 2. Relieve stress in pier abutment cases. NON-RIGID CONNECTORS

Different types: *Dovetails (key-keyway) *Split pontics *Cross-pin and wing

Dovetail Technique Use supplied plastic pattern and surveyor. or Fabricate keyway and key in lab.

Split pontic technique  Attachment placed entirely within pontic  Use With tilted abutments to avoid cutting deep box on distal of mesial retainer.  Plastic key or keyway is placed in gingival third of pontic using surveyor.

Cross-Pin and Wing  Two-piece pontic allows the two segments of FPD to be rigidly joined after luting.  Use with non-parallel abutments.  Path of insertion of each tooth preparation is made to parallel the long axis of that tooth.