INTRODUCTION:

Gold is possibly the oldest and best-documented dental treatment for filling cavities for more than 4000years. These early dental application were based on aesthetics, rather than masticatory ability. Several types of dental restorative materials are currently available. Generally they are grouped into categories such as amalgam, cast gold, tooth coloured material that is manufactured for compaction directly into prepared cavities.

Gold has been the undisputed king of restorative materials. In spite of the more recently introduced materials and techniques, gold foil still holds the leading position in choice of materials [1]. In this modern age of dentistry with the high speed and other up to date equipment, we have a tendency to forget the fine art of cavity preparations. Gold foil more than any other type of procedures offers the best results.

The use of gold in dentistry remains significant today, with annual consumption typically estimated to be approximately 70 tonnes worldwide [2]. However, with an increasingly wide range of alternative materials available for dental filling, it is considered appropriate to review the current gold based technology available today and there by highlight the exceptional performance that competing materials must demonstrate if they are to displace gold from current uses. New gold-based dental technologies are also highlighted. For the patient, gold foil restoration means no second appointment, no second administration of local anesthetic, and no second application of the rubber dam. Lastly as quoted by Brue B Smith, it may serve the tooth for a lifetime. [3]

Giovanni Arcolani published in 1483 his treaty ‘Pratica Chirurgica’ where first he described the use of gold to fill teeth. String fellow introduced in 1839 the technique of plugging metal in dental cavities, [4] and Arthur [5] introduced in 1855 the cohesive gold foil for direct gold restorations. So why is it rarely – if ever – part of the curricula at dental schools and why have dentists almost abandoned it as a choice dental procedure for caries

This article aims to explore the various applications and uses of gold restoration. Gold foil restorations, even if not performed, should be well understood in their principles by general practitioners in order to improve the quality of their restorations of any kind.

Why Gold?

In this modern era of dentistry, with the use of high end equipments, we have a tendency to forget the fine art of cavity preparation. Gold foil, more than any other type of procedure, offers an answer to this problem. It is an exacting preparation and tests the skill of the operator. When well done, no other restoration can compare to it [6].

Over the years, many new filling materials have been developed, under a variety of trade names, but, to date, none have been satisfactory as a restorative material [7]. The resilience of dentine and the adaptability of gold allow an almost perfect seal between the tooth structure and gold. The malleability of gold, which is the property of being worked into very thin foils, make it possible to add gold in very small amounts that are building up the filling.

Gold is resistant to corrosion, shows no shrinkage or expansion, and therefore is an ideal dental filling material. Two types of gold restorations are used in dentistry, which are direct and indirect gold restorations.

Direct gold restoration:

Direct gold restoration is one of the oldest gold restorations. It is available as sheets or pellets of 99.99% of pure gold. The most common forms of direct gold are gold foil and powdered gold which can be used alone or in combinations. Gold foil is an example of cohesion in dentistry and can be easily cold worked during filling a cavity [9].

Gold used for conservative procedures is classified as crystalline and fibrous, according to its microscopic structure. The former is produced by melting of pure gold ingots that appear made up of interwined fibers, giving great strength. The latter is produced by electrolytic precipitation, and appears granular under microscope magnification.

Gold foil is produced by fibrous gold ribbons, which can be either flattened using round head mallets to produce five square inches foil, or by rolling mills to produce rolled gold foil.

Gold foils are classified as cohesive and non-cohesive, which means that the cohesive property has to be obtained by slow heating, the annealing process [10]

Non- cohesive gold foils are more flow able and are used basically in the proximal portions of class 2 restorations and class 3 lingually. Its use prevents the possible damages to enamel rods involved in the use of the mallet necessary for cohesive gold foil. Cohesive gold is used for all surfaces subject to wear.

Indications and Contraindications:

Generally gold foil restorations are indicated for incipient or early lesions, generating small cavities in non-stress bearing areas, and where aesthetic concern is limited. The technique is also used to repair of endodontic openings in gold crowns or for gold crown margins, onlays and inlay. They are not generally used in children and young adults. Rex Ingram in his ‘Atlas of Gold foil and Rubber Dam Procedures’ offers guidelines on class ! pits and fissures restorations, class 5 restorations, maxillary class 3 restorations, labio- invisible class 3 restorations, mandibular class 3 restorations and class 2 restorations. [15]

Direct gold restorations are contraindicated in some patients whose teeth have very large pulp chambers, in patients with severely periodontally weakened teeth with questionable prognosis, in patients for whom economics is a severely limiting factor, and in handicapped patients who are unable to sit for long dental appointments required for this procedure [14]. Root canal filled teeth are generally not restored with direct gold because these teeth are brittle, although in some cases gold may be the material of choice to close access preparations [for root canal therapy] in cast gold restorations.

Types

Dental gold foil is available in several types:

1. Sheets, usually for preparation in the dental off Ice

2. Manufactured pellets or cylinders

3. Ropes

4. Laminated-varying thicknesses of foil stacked and slightly precondensed.

1. Crystalline, sponge, or mat gold:

In use for many years, mat is a microcrystalline form, produced by electrodeposition, the crystals being dendritic or fern-like in shape about 0. 1 mm long. It can be used plain or sandwiched in gold foil to make it easier to handle, in which form it is designated as mat foil.

2. Granular or powdered gold:

They are irregularly shaped, precondensed pellets or clumps of particles [Biotil, Filoro, Karat], which were prepared by basic methods: chemical precipitation, or atomization from the molten state. Volatile liquid was provided to act as a carrying medium to carry the pellet to the cavity. In general they are difficult to control [11].

1. Goldent:

Type of granular gold developed in USA about 1962. The individual particles or granules, averaging 15 micrometers, are gathered into conglomerate masses of Irregular shape ranging in diameter from 1 to 3 mm, lightly precondensed to facilitate handling. The masses are encased in an envelope of foil to make it easier to carry them to the cavity. The present form has some spherical atomized particles mixed with the granules to improve compacting properties.

2. Electraloy R V:

It is the newest form of gold. All compacted gold develop increased hardness with the introduction of stresses. However, greater hardness occurs with the introduction of minute quantities of other elements, such as palladium, platinum, indium, silver. and calcium, without lessening desirable manipulative characteristics. Here, the granular gold, alloyed with a trace of calcium, is manufactured electrolytically. Sintering [a method of heating under controlled pressure and time] changes the alloy into a mat. These strips of mat, of varying widths are sandwiched between foil to improve handling properties [12]

3. E-Z gold:

It is a new direct filling gold material that is similar to existing powdered gold formulations but more user friendly. It is a mixture of pure gold powder and wax, wrapped in gold foil introduced to the dental profession in the Kate 1980s and similar metallurgic ally to gold foil and powdered gold in that when properly and thoroughly compacted it has comparable properties like inertness and permanence. E-Z gold's manipulative characteristics are similar to that of a very stiff amalgam but more sticky than gold foil and hence the name E-Z gold. [13]

Advantages and Disadvantages:

Direct gold is one of the old restoration material and it has many advantages. It is insoluble and non-oxidizable by the oral fluids, capable of adaptation to cavity walls with great force, immediately and permanently sustains force, the resistance of hammered gold makes it hard and tough [16]. Low tendency to molecular change makes it free from objectionable shrinkage or expansion [17]. Cohesive gold is capable of receiving and retaining its polish to a much higher degree than the other restoration materials [18].

The disadvantage of cohesive gold is in the difficulty of learning to properly manipulate it. Its use develops and demands quantities of cleanliness, exactness, precision, concentration, patience and perseverance. The inharmonious color may be objectionable in certain areas of the mouth. High conductivity of gold can lead to sensitivity to hot and cold. Difficulty of manipulation if it filled by inexperienced dental surgeons. Non-cohesive gold may be used on account of its rapidity of manipulation in simple cavities with four strong walls, located on surfaces not subject to wear. It may also be used in combination with cohesive gold, for beginning restorations on the gingival wall in class I cavities or in the class II cavities. It is not indicated on surfaces subjected to stress of mastication or for contour work [18].

Indirect gold restorations:

Indications and Contraindications:

Cast gold is beneficial in large restorations and teeth at risk for fracture. Endodontically treated teeth are restored to their original function using cast gold. Ultimate in both efficiently replacing lost tooth structure and supporting remaining tooth structure. As an adjacent to successful periodontal therapy 1] Physiologically restoring the dimensions of the contact contour, marginal ridges and embrasures 2] splinting of teeth loosened by periodontitis to a better bone supported teeth. The rigid connection of several cast restoration assures distribution of the applied forces to the best supported teeth and minimizes force on disabled teeth(19].

It is contraindicated in physiologically young dentitions with large pulp chambers are poor candidates for cast restoration.Cast gold restorations cannot be used on developing and deciduous teeth. It is not appealing aesthetically and is not suitable for small restorations [20]

Advantages and Disadvantages:

Cast gold when handled properly has many advantages. ,the edges of gold crowns and restorations can be finished down nearly imperceptibly with the tooth and it is less likely to decay. The gold does not chip fracture or change color due to its wear resistant and durability. Gold onlays and partial crowns prevents the tooth from fracturing and strengthens the tooth. The life span of a gold restoration can be as much as 50+ years making it the best value. It also does not contain toxic substances such as Mercury [17]. The cast gold restoration will not fracture in the isthmus or other areas [16].

One of the disadvantages of that the treatment is time consuming for both the dentist and the patient. Because of the extra time involved, gold crowns and restorations necessarily cost more up front. However, given their predictable life expectancy, they are the best value in restorative dentistry today.The technique for preparation and placement of gold crowns and restorations must be done meticulously. If it is not done with a real concern for excellence, it probably is not as satisfactory as other restorative options [16].

Indirect gold are weak, soft, ductile and malleable and resist tarnish and corrosion. They are yellow in colour with a melting temperature of 1083 degree Celsius.

Alloying elements in in gold alloys for ceramometallic restorations:

1. Platinum, palladium – To obtain surface oxides

2. Iron, tin, Indium – Strength, hardness and stiffness

3. Platinum and palladium – solution hardening

4. Iron – Reacts with platinum forming intermetallic compound, which precipitated within the solid solution.

5. Neither silver nor copper is added because they produce greenish discolouration to ceramic.

Characteristics of cast gold alloy:

Type 1 – Soft gold alloys – For restorations subject to very slight stress such as inlays.

Type 2 – Medium gold alloys – For restorations subject to moderate stress such as onlays.

Type 3 – Hard alloys – For high-stress situations, including onlays, crowns, thick veneer crowns and short span fixed partial dentures.

Type 4 – Extra hard alloys – For extremely high stress states such as endodontic posts and cores, thin veneer crowns, long span fixed partial dentures and removable partial dentures

Future of gold in dentistry:

The historical development work concerning the use of gold in conservative and restorative dentistry has provided the industry with a variety of gold-based dental alloys suitable for application in an wide range of uses. If longevity, functionality, aesthetics, and biocompatibility, together with ease of manufacture are considered as the most important requirements, the material for dental restorations will be a well-approved high gold alloy. In all testing and development of competing materials, gold is defined as the standard element. The practising dentists with a few exceptions always prefer gold for restorations. [20]

Nevertheless, attention is mainly focused on the extensive range of alternative materials. These new materials include titanium and cobalt/nickel based alloys and all-ceramic crowns. The latter have excellent aesthetic properties, but do not have the long-term clinical approval that gold has. For example, zirconia has only passed clinical tests during the last few years. In addition, the CAD/CAM techniques associated with the use of these materials are, in many instances, prohibitively expensive. Furthermore, the problems of poor aesthetics often associated with porcelain-fused-to-metal techniques might be addressed through the use of extremely high gold content alloys, which have recently been granted. It is considered that as CAD/CAM technology progresses, special high gold alloys should be developed, which are well suited to milling and grinding operations and have sufficiently high strength for long span bridges and small cross sections [21].

Of the other competing materials, there are problems with casting titanium which prevents the widespread use of this material. Long-term use of cobalt/chromium alloys are increasing, and there are fewer problems with casting compared to titanium. Besides long term clinical approval and longevity, the most important advantages of gold alloys are easy workability, biocompatibility, aesthetics and maximum range of indications.

The development of electroforming technology with pure gold offers new opportunities for future research. For highly stressed parts in dental restorations, electroformed pure gold is still too soft and thus has limited uses. Efforts have been made in recent years to develop increased strength through dispersion strengthening by incorporating a suspension of ceramic particles [15]. Another area for electroforming research may focus on the deposition of multilayers by electrochemical structure modulation. Both of these research efforts should have the objective of developing thick deposits of pure gold with high strength [21].

REFERENCES:

1. Smith B.B. Broader concepts of gold foil- J Pros. Den 1956. 6:563

2. ‘Gold Survery 2002’ Gold fields Mineral Services Ltd,London,2002

3. Ferrier W.I. Gold foil operations Seattle University of Washington Press.1959

4. Stringfellow, S.L, on Plugging teeth.Amer J Dent Science 1 [1^st ser]: 111-112,1839

5. Arthur R, A New Method of using Gold Foil. Amer J Dent science 5 [2^nd ser]: 606-605,1855

6. Why Gold Foil? Norwood E.Lyons, D.D.S, American Academy of Gold Foil Operators, Vol. XI, No. 1, April 1968

7. Coy. HD (1957) The selection and purpose of dental restorative materials in operative dentistry dental clinics of North America March 65-80

8. Grainger, D A (1971) Gold foil- its future in dental education and state boards journal of the American academy of gold foil operators 77-88

9. ‘Lets Make Another Restorative Available – The Direct Restorative Gold’, Paul K. Blaser, Indiana University School of Dentistry,1979

10. Hodson, J T (1961)Microstructure of gold foil and mat gold. Dental Progress, 2, 55-58.

11. Hodson, J T (1964) Current studies on the physical properties of the various forms of pure gold. Journal of the American Academy of Gold Foil Operators, 7, 5-16.

12. Direct Golds in Dental Restorative Therapy, Gerald D Stibbs, Operative Dentistry, 1980, 5,107-114.

13. Alperstein KS, et al. Open Dent ' E-Z Gold: the new Goldent' 1996 Jan-Feb.

14. Gold Foil in today's Practice, Gerald D. Stibbs,, Operative Dentistry, 1976, 1, 1, 7-11.

15. Ingram R et a. An Atlas of Gold Foil and Rubber dam procedures Los Angeles 1961

16. McGeehee, True, Inskipp: A Textbook of Operative Dentistry. McGraw-Hill Book Co., The Blakiston Division, 1956, pp. 355-382.

17. W. J. Simon: Clinical Operative Dentistry. W. B. Saunders Co., Philadelphia, Pa., 1956, pp. 278-279.

18. G. V. Black: Operative Dentistry, Vol. II, Physical Properties of Filling Materials and Correlation of Forces Concerned, pp. 224-237. Medico-Dental Publishing Co., Chicago, Illinois, 1914.

19. “Old is gold”- A review of “Direct filling Gold”, Smita Govila, Minkle Gulati, 2013

20. Vimal K. Sikri Textbook of operative dentistry. 1^st Edition 2002.

21. Zielonka, A. and Fauser H., ‘Advanced Materials by Electrochemical Techniques’, Z. Phys. Chemie 208 (1999) 195.

Received on 28.07.2016 Modified on 08.08.2016

Research J. Pharm. and Tech 2016; 9(12):2354-2358.

DOI: 10.5958/0974-360X.2016.00470.4