This document provides information on dental soldering, welding, and brazing. It defines the different metal joining techniques and discusses ideal requirements, types, and compositions of solders/brazing materials. The document outlines the soldering process, including cleaning surfaces, using flux, selecting the proper heat source (flame or oven), and following technical considerations like maintaining an optimal gap between parts. Applications of soldering in dentistry and different welding methods are also summarized.

1. Dental Soldering,
Welding and Brazing
Dr. Abhidha Tripathi
MDS First Year

2. 1. Definition
2. Ideal requirements
3. Types of Solders
4. Composition
5. Properties
6. Flux and Antiflux
7. Techniques
8. Welding
9. Cast Joining
10. References
Contents

3. Definition
 Metal joining operations are usually divided into four categories: welding, brazing,
soldering and cast-joining.
 WELDING : The term welding is used if two pieces of similar metal are joined
together without the addition of another metal that is, the metal pieces are heated
to a high enough temperature so they join together by melting and flowing.
 BRAZING AND SOLDERING : The words soldering and brazing are used if two pieces
of metal are joined by means of a third metal called as filler.

4. Definition
 Soldering operation at or above 450 degree C is generally termed
brazing.
 Most dental soldering procedures are actually brazing but the
names are used interchangeably in dentistry.
 Brazing is defined as a joining by the fusion of filler metals between
them at a temperature below the solidus temperature of metals
being joined and above 450 degree C.

5.  It should melt at temperatures below the solidus temperature of the
parent metal.
 When melted, it should be wet and flow freely over the parent
metal.
 Its color should match that of metal being joined.
 It should be resistant to tarnish and corrosion.
 It should resist pitting during heating and application.
IDEAL REQUIREMENTS OF A BRAZING MATERIAL (DENTAL
SOLDER)

6. The Soldering Process

7.  For soldering to be successful basic practical steps should be
followed:
1. The surface of the alloy should be free from dirt and oxides.
2. If using soldering investment use the smallest amount possible. This
will maintain the proper position of the parts during the procedure.
3. Place flux in the joint to be soldered.
4. Select a suitable solder which melts 50°C-100°C below the melting
point of the components.
6. Heat the components evenly by either using the reducing zone of the
flame or a furnace.
7. When the flame is evenly cherry red, apply the solder.
The Soldering Process

8. 6. The parts being joined are not melted during soldering but must be
thoroughly wettable by liquefied solder.
7. The careful and skillful use of the soldering torch flame is important
to a high quality soldered joint. A well-defined, not-too-large pointed
flame is advisable for the final heating of solder in a localized area, but
a larger, less well defined flame of the “brush” type may be used for the
initial heating.
8. The operation should be completed in the shortest time possible to
avoid oxidation of the base metal ingredients of the alloys involved and
to prevent damage to the microstructures of the alloys.
The Soldering Process

9. They may be divided into two major groups:
1. Soft solders 2. Hard solders
SOFT SOLDERS : have low melting range of about 260°C. They can be applied by
simple means like hot soldering iron. They lack corrosion resistance and so are
not suitable for dental use, e.g., lead-tin alloys (plumbers solders).
HARD SOLDERS These have a higher melting temperature and greater strength
and hardness. They are melted with the help of gas blowtorches or occasionally in
an electric furnace. Hard solders are more commonly used in dentistry. They are
also used for industrial purposes and in the jewelry trade, e.g., gold solders and
silver.
TYPES OF SOLDERS OR BRAZING MATERIAL

10. Soldering is often used in construction of dental appliances.
Components of solder joint
1.Parent metal
2.Flux
3.Antiflux
4.Solder/ filler metal
Composition

11. The parent metal is the metal or alloy to be joined.
It is also known as substrate metal or base metal.
The composition of parent metal determines :
Melting range
Oxide that forms on the surface during heating
Wettability of the substrate by the molten metal
Parent Flux

12. The Latin word ‘flux’ means flow.
For a solder to wet and flow properly, the parent metal must be free of oxides.
This is accomplished with the help of a flux.
FUNCTION OF FLUX
1. To remove any oxide coating on the parent metal.
2. To protect the metal surface from oxidation during soldering.
Fluxes

13.  TYPES
• Fluxes may be divided into three activity types.
1. Protective - This type covers the metal surface and prevents access to oxygen so
no oxide can form.
2. Reducing - This reduces any oxide present to free metal and oxygen.
3. Solvent - This type dissolves any oxide present and carries it away.
 Most fluxes are usually combination of two or more of the above.
Fluxes

14. COMMONLY USED DENTAL FLUXES
1.Boric and borate compounds
Used with noble metal alloys. They act as protective and reducing
fluxes.
2. Fluoride fluxes
Fluoride fluxes like potassium fluorides are used on base metal
alloys and are usually combined with borates.
They help to dissolve the more stable chromium, nickel and cobalt
oxides.
Fluoride fluxes should be used carefully around porcelain as it can
attack the porcelain.
Note: Excess flux should be avoided as it can get entrapped within
the filler metal and result in a weak joint.

15. The flow can be controlled by use of an antiflux material. Solder will
not flow into an area where antiflux has been applied.
It is applied before the flux or solder is appalied.
Examples of antiflux are graphite (soft lead pencil), rouge (iron oxide)
or whiting (calcium carbonate) in an alcohol and water suspension.
ANTIFLUX

16. The heat source is a very important part of brazing.
In dentistry, two heat sources may be used:
1. Flame
2. Oven
HEAT SOURCE

17.  The most commonly used heat source is a gas-air or gas-oxygen
torch.
 The flame must provide enough heat not only to melt the filler metal
but also to compensate for heat loss to the surroundings.
 Thus, the flame should not only have a high temperature but also a
high heat content.
FLAME BRAZING OR SOLDERING

18.  The Various Gases Used are
 Hydrogen : It has the lowest heat content and therefore
heating would be slow. It is not indicated for soldering of
large FPDs.
 Natural gas : It has a temperature of 2680°C and heat
content is four times that of hydrogen. However, normally
available gas is nonuniform in composition and frequently
contains water vapor.

19.  The most commonly used heat source is a gas-air or gas-oxygen
torch.
 The flame must provide enough heat not only to melt the filler metal
but also to compensate for heat loss to the surroundings.
 Thus, the flame should not only have a high temperature but also a
high heat content.
FLAME BRAZING OR SOLDERING

20. Torch Soldering

21. Acetylene :
It has the highest flame temperature and a higher heat content than
H2 or natural gas.
Temperature from one part of its flame to another may vary by more
than 100°C.
Therefore, positioning the torch is critical and proper part of the
flame should be used.
It is chemically unstable and decomposes readily to carbon and
hydrogen. The carbon may get incorporated into the Ni and Pd alloys,
and hydrogen may be absorbed by the Pd alloys.

22. Propane : It is the best choice. It has the highest heat content (2385
Btu) and a good flame temperature (2850°C).
Butane : It is more readily available and is similar to propane. Both
propane and butane are uniform in quality and water-free.

23.  An electric furnace with heating coils may be used for
brazing.
 The furnace also provides heated surroundings, so less heat
is lost to other parts of the fixed partial denture and the
atmosphere.
OVEN BRAZING (FURNACE BRAZING)

24. Two techniques of dental soldering are employed to assemble dental
appliances:
A. FREE HAND SOLDERING : In free hand soldering the parts are
assembled and held in contact manually while the heat and solder are
applied.
B. INVESTMENT SOLDERING : In investment soldering, the parts to
be joined are mounted in a soldering type of investment. The hardened
investment holds it in position while the heat and solder are applied.
TECHNIQUE OF SOLDERING

25. 1.Selection of solder
2. Cleaning and polishing of components
3.Assembly of the prosthesis in soldering investment
4. Application of flux
5. Preheating the bridge assembly
6. Placement of solder
7. Application of hot gas flame to joint and solder
8.Cooling of assembly followed by quenching in water
STEPS IN SOLDERING PROCEDURE

26.  Cleanliness—Metal should be free of oxides
 Gap between parts
 Selection of solder—Proper color, fusion temperature, and flow
 Flux-type and amount Flame—Neutral or reducing in nature
 Temperature
 Time
TECHNICAL CONSIDERATIONS FOR SUCCESSFUL SOLDERING

27.  The liquid solder is drawn into the joint through capillary action.
Therefore, an optimum gap is necessary for proper flow, strength of
the joint and to avoid distortion of the assembly.
 Gap width ranging from 0.13 to 0.3 have been suggested.
 If the gap is too narrow, strength is limited due to
— Porosity caused by incomplete flow
— Flux inclusion
 If the gap is too great
— The joint strength will be the strength of the solder.
— There is a tendency for the parts to draw together as the solder
solidifies.
Gap between parts

28. Flame
 The flame has multiple zones .
 The portion of the flame that is used should be neutral or slightly
reducing.
 An improperly adjusted or positioned flame can lead to oxidation
and/or carbon inclusion.
 Once the flame has been applied to the joint area, it should be
removed until brazing is complete.
 Due to its reducing nature, the flame gives protection from
oxidation.

29. Temperature
 The temperature used should be the minimum required to
complete the brazing operation.
 Prior to the placement of the solder, the parent metal is heated till
it is hot enough to melt the filler metal as soon as it touches.
 A lower temperature will not allow the filler to wet the parent
metal.
 A higher temperature increases the possibility of diffusion
between parent and filler metal.

30. Time
 The flame is held until the filler metal has flowed completely into the
connection and a moment longer to allow the flux or oxide to separate
from the fluid solder.
 Insufficient time increases chances of incomplete filling of joint and
possibility of flux inclusion in the joint.
 Excessive time increases possibility of diffusion. Both conditions
cause a weaker joint

31. Applications Of Soldering
1. Assemble long span fixed partial dentures.
2. Joining wrought wire clasps arms to cast partial dentures
framework.
3. Joining precision attachments. 4.
4. Joining sections of metal superstructure for implant supported
restorations etc.
5. To overcome distortion in multiunit cast fixed prostheses,.
6. Repair of perforated crown and bridges.
7. Develop contacts points in crown.
8. Cutting and rejoining of ill fitted distorted bridge.

32.  The term welding is used if two pieces of similar metal are joined
together without the addition of another metal. It is usually used to
join flat structures such as bands and brackets.
WELDING

33. INDICATIONS
1. In orthodontics to join flat structures like bands and
brackets.
2. In pedodontics, to weld bands and other appliances.
3. In prosthodontics, to join wrought wire clasps and repair
of broken metal partial dentures.

34. Cold welding is done by hammering or pressure. An example
of cold welding is the gold foil filling.
Hot welding uses heat of sufficient intensity to melt the
metals being joined.
The heat source is usually an Oxyacetlyene flame or high
amperage electricity.

35. Basically two methods are followed :
1.Fusion welding : where the parts are melted and joined
but pressure is ot applied.
E.g: Gas welding, Laser welding
1.Pressure welding : where parts are heated and pressed but
not melted.
E.g: Spot welding.

36. Spot welding
Pressure welding
Laser welding
Laser micro welding
Methods

37. The two clean metal surfaces to be welded are placed together under
pressure.
Two ends of wire or band to be welded are placed between two copper
electrodes of welder and pressed together
When switch is pressed large current passes through the wires or band
on the copper electrode.
Combined heat and pressure fuses the metal pieces at that point.
1. Spot welding

38. This is also called cold welding and does not require heat application.
Gold foil is welded by pressure or cold welding
Two layers of gold foil are joined by application of pressure at room
temperature.
2. Pressure welding

39.  LASER welding is stronger than solder joints of comparable size.
 The laser micro welder is high power industrial laser capable of
delivering 20J/pulse for maximum of 6 mili seconds at a wire.
 Used for orthodontic appliances such as space maintainers,
retention devices etc.
3. LASER Welding

40. Spot welding maybe used as method of fusing
Stainless steel strip for making bands
Securing attachments to the bands
Attaching springs to a rigid bow wire, or to bands
It is used more in the construction of fixed prosthesis
Application of Spot Welding

41. 1. Ryge G: Dental soldering procedures. Dent Clin North Am1958;2:747-757 [2].
2. American Dental Association: Dentists’ Desk Reference:Materials, Instruments
and Equipment (ed 2). Chicago, ADA,1983, pp. 261-268 [3].
3. JM Ney Company: Ney Basic Cast Restorations. Bloomfield,CT, Ney, 1984, pp 86-
91 [4].
4. Shillingburg HT, Hobo S, Whitsett LD, et al: Fundamentals ofFixed
Prosthodontics (ed 3). Chicago, Quintessence, 1997,pp. 509- 534 [7].
5. Rosenstiel SF, Land MF, Fujimoto J: Contemporary FixedProsthodontics (ed 4). St.
Louis, Mosby/Elsevier, 2006,pp. 843-866
References