Direct Filling Gold: Types, Properties, and Applications in Restorative Dentistry

Direct Filling Gold

Following are the forms of direct gold filing:

1. Foil (Firous gold):

• Sheet
  • Cohesive
  • Non-cohesive
• Ropes
• Cylinders
• Laminated
• Platinized.

2. Electrolytic precipitate (Mat gold):

• Mat gold
• Mat foil
• Alloyed.

3. Granulated gold (encapsulated powder gold)

“Types Of Direct Filling Gold Used In Restorative Dentistry”

Gold Foil of Direct gold filing:

Gold is malleable. A cast ingot of 15 mm thickness is beaten to the submicroscopic thickness of 15 to 25 µm. This is known as gold foil. Gold foils are made from pure metal by beating and rolling. Beating produces lightweight foils and rolling produces heavy-weight foils.

Fibrous gold is supplied in the form of sheets about 4 inches square which ranges in numbers 2, 3, 4, 5, 6, 8, and 10. Higher numbers are rolled by manufacturers from ingot, while lower numbers are beaten by machinery.

Gold Restorations In Dentistry

These numbers are indicative of the number of grains in a sheet, for example, No. 5 gold sheet contains 5 grains. Gold foil or fibrous gold is available in form of sheets, rolls, cylinders, and pellets of various sizes. Sheets of gold foil are of two types, i.e. cohesive and non–cohesive.

“Understanding The Role Of Direct Filling Gold In Restorative Dentistry”

“Best Ways To Understand Direct Filling Gold Properties”

1. Cohesive Gold Foil:

• Cohesive gold is also known as sticky gold.
• This is the gold foil that the manufacturer supply to the dentist is free from any surface contaminant and can be placed directly in cavity preparation is known as cohesive gold.
• Although it is free from surface contaminants some of the gases are still adsorbed during storage so degassing is required.

Dental Gold Fillings

Various types of cohesive gold foils are:

• Soft type: This gets annealed before trimming and is treated in ammonia fumes for reducing the cohesion. As this type is cut and rolled in desired sizes, ammonia gas is driven off
• Dead soft type: This is not annealed and is soft. This is less cohesive than soft type.
• Extra or special soft: This is deliberately alloyed by a trace of silver for limiting cohesiveness. This is moderately cohesive after annealing.
• Platinized soft gold foil: In this, a sheet of pure platinum foil is sandwiched between two sheets of pure gold foil and then malleated again till the original thickness is established. Platinum increases hardness and wear resistance.

“Importance Of Direct Filling Gold In Cavity Restorations”

2. Non-cohesive Gold Foil:

• Non-cohesive gold foil is subjected by the manufacturer to a volatile agent such as ammonia which is adsorbed on the surface of gold.
• This adsorption of ammonia gas on the surface of gold prevents gold foil from adhering.
• It is rarely used currently but it can be used to build up the bulk of direct gold restoration.
• It can also be used with cohesive gold for beginning restoration on the gingival wall in the proximo-occlusal cavity or on the pulpal wall in occlusal cavities as a timesaver.

Electrolytic Precipitated Gold

• Crystalline gold powder is formed by electrolytic precipitation. The powder is formed into strips and shapes by sintering.
• Electrolytic precipitated gold is available as mat gold, mat foil, and alloyed electrolytic precipitate.
• Mat Gold: Mat gold is electrolytically precipitated gold sandwiched between sheets of foil and then formed into strips. Strips can be cut by the dentist into the desired size. It is used to build up the bulk of the restoration, as it can be more easily compacted and adapted to the cavity. However, mat gold has lots of voids and results in a pitted external surface. Therefore, foil gold is used to cover the mat gold and form the surface of the restoration.

Restorative Dentistry Gold

“Risk Factors For Failure Of Direct Filling Gold Restorations”

• Mat Foil: It is a sandwich of electrolytic precipitated gold powder between sheets of No. 3 gold foil. The sandwich is sintered and cut into strips of differing widths. The dentist can then cut these to desired lengths. Mat was sandwiched between foil sheets to try to eliminate the need to veneer the restoration with a layer of foil. This type is no longer marketed.
• Alloyed Electrolytic Precipitates: A form of electrolytic gold is an alloy of gold and calcium (0.1% by wt.) called ‘Electraloy RV’. For greater ease of handling, the alloy is sandwiched between two layers of gold foil. Calcium produces stronger restorations by dispersion strengthening which locks in cold work strengthening. Thus, alloying with calcium changes the crystalline structure and makes it harder and stronger.

Powdered Gold:

• Powdered gold is also known as EZ gold.
• It is known as EZ gold because its manipulative characteristics are similar to very stiff amalgam and is more sticky than gold foil.
• Powdered gold is a blend of atomized and precipitated powder that is embedded in a wax-like organic matrix.
• This is available in pellets of various sizes which are mixed with wax and enclosed in gold foil N o. 3 wrappers and packed for their usage.
• The usage of pellets of powdered gold increases cohesion at the time of compaction and decreases the time needed for placing the restoration.

Gold In Direct Restorations

“Early Signs Of Problems With Direct Filling Gold”

• Commercially available pellets of powdered gold wrapped in a gold foil are known as Golden. The ratio is 95% powder and 5% foil.
• It is provided in a cohesive form.
• The powdered particles are mixed with soft wax and held in a No. 3 gold foil.

“The Role Of Direct Filling Gold In Improving Marginal Integrity”

• The gold foil acts as a container for the powdered particles and facilitates their condensation.
• Each pellet contains approximately ten times more gold than a pellet of gold foil of comparable size.
• The hand method of compaction is better than mechanical compaction for powdered gold.