Direct Filling Gold: Forms, Manipulation, Applications, and Advantages in Dentistry

Direct Filling Gold

Pure gold can be used as a restorative material. It is the noblest metal and rarely tarnishes in the oral cavity. Gold in its pure form is very soft. Its malleability and lack of surface oxide layer permit increments to be welded in the oral cavity. This unique characteristic of gold to be welded at room temperature (cold welded) allows gold to be used as a direct filing gold.

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Following are the forms of direct gold filing:

1. Foil (Fibrous gold):

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

2. Electrolytic precipitate (mat gold):

• Mat gold
• Mat foil
• Alloyed or gold-calcium alloy

3. Granulated gold (encapsulated powder gold).

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 range in numbers 2, 3, 4, 5, 6, 8, and 10. Higher numbers are rolled by manufacturers from an 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. 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 known as cohesive gold.
• Although it is free from surface contaminants some of the gases are still adsorbed during storage so degassing is required.

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.

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.
• Non-cohesive gold is rarely used currently but it can be used to build up the bulk of direct gold restoration.
• 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 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.
• 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 and tried 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 are enclosed in gold foil No. 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.
• 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 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.

Applications of Direct Filling Gold:

• Pits and small class I restorations.
• For repair of casting margins.
• For class II, class V, and class VI restorations.
• Repair of cement vent holes and perforation in the gold crown.

Disadvantages of Direct Filling Gold:

• Poor esthetics (it is not tooth-colored)
• High coefficient of thermal conductivity
• Manipulation is difficult
• The problem of temperature sensitivity if not insulated with base.

Advantages of Direct Filling Gold:

• Tarnish and corrosion resistance
• Good mechanical properties
• Good biocompatibility.

Contraindications of Direct Filling Gold:

• In disto-occlusal cavities in molars
• Teeth with large pulp chambers
• In periodontally weak teeth with poor prognosis
• In low socioeconomic status individuals
• In root canal filed teeth as they are brittle
• In handicapped patients who are unable to sit for long dental appointments needed for this procedure.
• If the skill of the operator is questionable.

Manipulation of Direct Filling Gold

Manipulation of direct filing consists of the following steps:

1. Desorbing or degassing
2. Compaction.

1. Desorbing or Degassing:

• The heating process which removes surface gases and ensures a clean surface is known as degassing or desorbing
• Degassing removes the surface gases like oxygen, nitrogen, ammonia, moisture, or sulfur dioxide which may be present due to improper storage.
• Direct filing gold may be heated by one of two methods as follows:
  • In bulk on a tray heated by either a gas-flame or electricity
  • Piece by piece, in a well-adjusted alcohol flame

In practice all but the powder gold may be desorbed on a tray:

• An electric annealer should be maintained at a temperature between 340°C (650°F) and 370°C (700°F). The time required varies from 5 to 20 minutes depending on the temperature and the quantity of gold on the tray.
• Powder gold must be heated in a flame to ensure the complete burning away of the wax.
• In flame desorption, there is picking up each piece individually, heating it directly in the open flame, and placing it in the prepared cavity.
• The fuel for the flame may be alcohol or gas, but alcohol is preferred as there is less danger of contamination. The alcohol should be pure methanol or ethanol without colorants or other additives.
• Underheating could not adequately remove the impurities and thus results in incomplete cohesion, pitting, and flaking of the surface while overheating leads to overwintering and possible contamination from the tray, instruments, or flame.
• This results in incomplete cohesion, embrittlement of the portion being heated, and poor compaction characteristics.

2. Compaction: 

The gold is compacted by following methods, i.e.

1. Hand mallet
2. Condensors
3. Mechanical condensors.

• Hand Mallet: Earlier gold was compacted entirely with a mallet.
  • Starting points are cut in the prepared cavity.
  • The first pieces of foil are wedged into these areas and compacted.
  • 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.
• Condensers:
  • The original foil condensers had a single pyramid-shaped face, but current instruments have a series of small pyramidal serrations on the face.
  • These serrations act as swaggers, exerting lateral forces on their inclines in addition to providing direct compressive forces.
  • They also cut through the outer layers to allow air trapped below the surface to escape.
  • Each increment of gold should be carefully stepped by lacing the condenser point in successive adjacent positions, as the compaction force is applied.
  • The stepping may be more readily accomplished and standardized by mechanical condensers.
• Size of the Condenser Point:
  • The diameter of circular points should be 0.5 mm and 1 mm. The size of the condenser point determines the effectiveness of compaction.
  • The force distribution to the gold depends on the area of the point.
  • Small condenser points are indicated in order to get the desired compaction without using forces that might damage oral structures.
• Pressure Application:
  • The pressure was applied by the use of a special mallet. In recent years, there has been a tendency to apply condensation pressure by hand.
  • Compaction with mechanical devices like electromagnetic or spring loading condensers is quite rapid and is accomplished with greater comfort for the patient.

3. Mechanical Condensers:

Electromagnetic or spring-loaded have provided a mechanical means of applying force. The mechanical devices consist of points activated by comparatively light blows that are repeated with frequencies that range from 360–3600/minute. Vibrations can be produced either pneumatically (air driven) or electrically. They are faster and more comfortable for the patient.

Question 2. Enumerate the tooth-colored restorative material 
Answer:

Tooth-colored restorative materials are:

• Composite resin
• Glass ionomer cement
• Acrylic resin
• Porcelain.