Direct Gold Restorations: Types, Properties, and Applications in Dentistry

Direct Gold Restorations

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. These numbers are indicative of the number of grains in the sheet. for example. No. 5 gold sheet contains 5 grains.

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Gold foil or fibrous gold is available in the form of sheets, rolls, cylinders, and pellets of various sizes. Sheets of gold foil are of two types, i.e. cohesive and non–cohesive

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 but some of the gases still adsorbed during storage so degassing is required.

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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.

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2. Non-cohesive Gold Foil:

1. Non-cohesive gold foil are subjected by the manufacturer to a volatile agent such as ammonia which is adsorbed on the surface of gold.
2. This adsorption of ammonia gas on the surface of gold prevents gold foil from adhering.
3. Non–cohesive gold is rarely used currently but it can be used to build up the bulk of direct gold restoration.
4. Non-cohesive gold 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 timesaver.

Carbonized or Corrugated Gold Foil:

• Corrugated foil is obtained by placing the gold foil in between sheets of paper and igniting it in closed container.
• On igniting paper gets charred, but the gold foil remains unharmed except that it becomes corrugated. This is due to shriveling of paper while oxidizing in an airtight safe.
• The condenser is placed against the foil and struck sharply with a small mallet.
• Subsequently, additional foil is wedged in the same manner till the cavity is filed.
• Each increment of gold must be carefully ‘stepped’ by placing the condenser point in successive adjacent positions.
• This permits each piece to be compacted over its entire surface so that voids are not bridged.

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Supply of Gold Foil:

• Flat square sheets (of varying thickness) in booklet form, 12 sheets (each 10 cm × 10 cm) per booklet.
  • No. 4 wt 4 grains (0.259 gram) 0.51 um thick.
  • No. 3 wt 3 grains (0.194 gram) 0.38 um thick.
• The number denotes the weight of the gold. Other sheets also available are Nos. 20, 40, 60, and 90. No. 3 foil is used to manufacture electrolytic and powder gold.

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• Performed cylinders and ropes. These are made by cutting the No. 4 gold foil sheets into strips of varying widths (3.2,4.8, etc.) and then rolling and compressing them into pellets or cylinders. They may be carbonized
• A number of sheets of foil may be placed one top of each other to form laminated gold foil. One type of laminated foil is platinized foil which is a sheet of pure platinum foil sandwiched between two sheets of pure gold foil.