Direct Filling GoldGold was one of the earliest materials available forrestoration of teeth. “Direct golds” are those gold restorativematerials that are manufactured for directly compacting theminto prepared cavities. This noble metal is a superiorrestorative material for small defects and lesions in teeth.Direct gold restorations are highly durable if proper caseselection, cavity preparation and careful manipulation of thematerial are done. Direct gold restorations exhibit excellentmarginal integrity and biocompatibility in the oral environment.
TYPES OF DIRECT FILLING GOLDS There are several forms of direct gold available for restorativepurposes. All of there are cohesive and are 99.9% pure. Direct filling golds maybe categorized as follows. I. Gold foil A. Sheets B. Pallets (hand rolled and preformed) C. Cylinders. D, Corrugated foil. E. Platinized foil. F. Laminated foil. II. Electrolytic precipitated gold A. Mat gold. B. Mat foil. C. Gold calcium alloy. III. Powdered gold A. Goldent.
PROPERTIES OF DIRECT FILLING GOLD1.Pure gold is soft, malleable and ductile and does not oxidize under normal atmospheric conditions.2. It has a rich yellow colour and a strong metallic luster.3. Gold fuses at 1063 C and boils at 2200 C4. Density of pure gold is 19.0-19.3g / cm3 but this is reduced by voids incorporated during restoration to 14-15g / cm3.5. The Brinnell hardness number for gold is 25. This makes it very soft. However during compaction the hardness increases to 58-82 making it a strong material.6. The coefficient of thermal expansion of gold is 14.4 x 16-6/ C which is close to that of tooth structure (11.4x10-6/ C).7. Gold exhibits high thermal conductivity.8. Gold is the noblest of all metals. It does not undergo tarnish and corrosion in the oral environment.9. Even small mounts of impurities can affect the mechanical properties of gold. Very small amounts of lead, bismuth or mercury advesely affect the properties of gold. However minute amounts of calcium, palladium and platinum can improve the properties of gold.10 The most important property of gold which has enabled its use as a direct filling material is its ability to be “cold welded” at room temperature. When two clean pieces of gold are pressed firmly together under sufficient force at mouth temperature they got welded together.11.Gold exhibits excellent marginal integrity and biocompatibility with the oral tissues.
Cohesive goldDirect gold materials that are coated with a layer of ammonia gas which is removed just before insertion of the gold into the cavity preparation.Non-cohesive goldPure gold which is contaminated with phosphorous or sulfurous gases or other deleterious oxides. This is not cohesive.
ADVANTAGES OF DIRECT GOLD1. When properly placed, direct gold is the most durable restorative material available.2. As pure gold is a noble metal, it does not undergo tarnish or corrosion in the oral cavity.3. Direct gold restorations are insoluble in the oral fluids and exhibit thermal expansion similar to that of dentin.4. When proper case selection is done and the cavity preparation is kept ideal, it is atraumatic to the dental pulp and supporting structures.5. Direct gold exhibits good adaptation to the cavity walls. Being ductile it can be burnished against the cavity margins to create excellent marginal integrity.6. The surface of direct gold can be polished well and the smoothness will last indefinitely. Thus plaque accumulation is negligible over direct gold filling.7. The density and hardness of compacted gold provide adequate compressive strength.
DISADVANTAGES OF DIRECT GOLD1. The yellow colour of pure gold is not esthetically acceptable to most patients.2. The manipulation of gold is very exacting and difficult to master.3. Placement of direct gold is time consuming requiring a lot of attention to detail.4. Direct gold is a very expensive material.5. Thermal conductivity of gold is high. So pulp protection is necessary under gold restorations.
INDICATIONS FOR DIRECT FILLING GOLD RESTORATIONS.1. Class I cavity: Direct gold is indicated for small carious lesions in pits and fissures of posterior teeth and lingual surfaces of anterior teeth.2. Class II cavity: Direct gold is indicated for minimal proximal caries in posterior teeth especially premolars when marginal ridges are not subjected to heavy occlusal stresses.3. Class III cavity: Direct gold can be used for small carious defects in anterior teeth when the defect is only on the proximal surface and esthetics will not be affectd.4. Class V cavity: For minimal caries in the cervical 1/3rd of teeth direct gold can be used. It is also indicated for small abrasion, erosion or abfraction defects on the facial surfaces of teeth.5. Class VI cavity: For restorations involving incisal edges or cusp tips, direct gold may be used, provided there is no heavy occlusal stress.6. Defective crown margins: Defective crown margins of cast gold crowns may be repaired with direct gold. Whenever access opening are done through existing cast gold crowns, they may be sealed with direct gold after the endodontic therapy.
CONTRAINDICATIONS FOR DIRECT FILLING GOLD RESTORATIONS1. Young patients: In young patients because of the presence of large pulp chambers direct gold is contraindicated as the malleting forces of direct gold may not be tolerated by the pulp.2. Poor periodontal status: In periodontally weakened teeth, direct gold is not employed because of questionable prognosis.3. Heavy occlusal stresses: For moderate to large carious defects direct gold is not used as it canot withstand heavy occlusal loading.4. Economics: Direct gold is not indicated when cost is the limited factor.5. Handicapped patients: Long appointments are necessary for direct gold. Hence, it is contraindicated in handicapped patients.6. Esthetics: When esthetics is the main concern for the patient direct gold is not recommended.7. Access and isolation difficulties: Direct gold is contraindicated in inaccessible regions and areas where isolation cannot be adequately
GENERAL PRINCIPLES OF CAVITY PREPARATION FOR DIRECT GOLD RESTORATIONS The principles of cavity preparation for direct gold restorations are veryexacting and require careful attention The outline form should include all structural structure. The outline should besmooth and designed to be esthetically pleasing. Resistance form is achieved by creating flat pulpal floors perpendicular toocclusal forces. The walls must be smooth and flat. Enamel walls must be supportedby sound dentin. The cavity width must be minimal while providing adequateconvenience form. Retention form is achieved by parallel or slight occlusal convergence of thefacial and lingual walls. The depth of the cavity should be 0.5 mm into dentin. Thepresence of sharp internal line angles resist the movement of the restoration.Convenience form for direct gold cavity preparations require suitable access and adry field. The width of the cavity preparation should be minimal. Separators may beused to provide convenient access for Class III cavity preparations. Sharp internalline and point angles in dentin serve as convenient “starting” points for compacting ofdirect gold. Other principles like removing remaining caries, finishing the cavity walls,debridement and pulp protection are similar to other cavity preparations.
CLASS III CAVITY PREPARATION FOR DIRECT GOLD RESTORATIONS Several designs have been advocated for Call III cavity preparations for direct gold. These include the Ferrier design, Loma Linda design, Woodbury design and Ingraham design. Of these, the Ferrier design is most popular because of the following reasons:1. It conserves tooth structure.2. It provides good access for compaction of gold.3. The final restoration would be esthetically pleasing.
GENERAL STEPS FOR DIRECT GOLD RESTORATIONS 1) Build- up of the restorationa) Tie Formation: This involves connecting two opposing point angles or starting points filled with gold with a transverse bar of gold. This “tie” forms the foundation for any restoration in direct gold.b). Banking of the walls: This consists of covering each wall from its floor or axial wall to the cavosurface margin with the direct gold material. Banking should be done simultaneously on the surrounding walls of the preparation.c) Shoulder formation: This consists of connecting two opposing walls with the direct gold material to completely fill up the restoration.
2. “Paying’ of the restorationTo overfill the preparation every area of the cavofurface margin should beindividually covered with excess cohesive gold foil. This is condensed with arectangular “foot” condenser. 3. Surface hardening of the restorationThe rectangular condenser is used with the highest possible condensation pressure in all directions on the surface of the restoration to strain harden the surface gold. 4. BurnishingThis is done with a suitable burnisher moving from the gold to the tooth surface. This enhances the surface hardening and also produces good marginal adaptation of the gold. 5. MarginationThis step uses sharp gold knives to remove excess gold from the surface to the tooth.
6. BurnishingIt is important to burnish the surface of the gold restoration after margination so as to eliminate marginal discrepancies and to strain haredn the surface. 7. ContouringThis step uses knives, files or finishing burs to create the proper occlusal anatomy. Burnishing. 8. Finishing and polishingDirect gold restorations require very little finishing if the previous steps are property done. Finishing can be done using tin oxide powder on soft bristle brushes or rubber cups. 9. Final burnishingThis is done after polishing to make the surface of the restoration smooth and free from voids.