Using precious metals in Dentistry for dental casting goes back to the first time Jean Darcet used low-fusing metal alloy in 1789. This was a huge step leading to the noble metal casting. Use of Metals was brought in for various types of dentistry uses such as onlays, inlays, crowning, bridging, and partial dentures. There are two types of metals used in dentistry. The Noble Metal, which is resistant to any chemical reactions and has the properties of higher densities, cannot rust for a very long time. High densities allow them to sit properly as casting. Due to its firm properties, it was an ideal solution to introduce its infusion into dentistry. Some precious noble metals include Gold, Palladium, and Platinum. These metals are mixed with Iridium and ruthenium to form an alloy which gives stronger resistance as alloys are known to be stronger than pure metals. However, Silver is more reactive to fluoride toothpaste; therefore, Silver is not recommended. These Alloys are used for the formation of the crown of the teeth. The rest of the Alloys are used for what is called to be the ‘cementing’ of the teeth.
Gold
Gold is the only precious metal used frequently for all noble metal alloys because of its weight. It is a soft yellow metal with the most ductile and malleable properties. Due to its hardness and strength, it is mixed with alloy and used in crowning to resist the wear and friction of the opposing tooth. Because of its high melting point, gold is used for metal-ceramic restoration as this process involves high heating temperatures. Gold is sterilized several times before undergoing the mixing process. This prevents any granular unhygienic particles which may be present from infusing into an alloy. Such allergic particles in the alloy may cause abrasion, wear, and tear, or any chemical reaction affecting the neighboring tooth. Gold-based alloys are also classified under their strength, softness, flexibility, and malleability. Higher the strength, the use will be for denture frameworks or the formation of bridges. Meanwhile, the higher the softness, conventional inlays and Onlays or full mouth crowns are used.
Platinum
Platinum is a bluish-white precious metal with a boiling point of 1755 degrees Celsius. It is very high melting point helps in processes such as. It also helps prevent discoloration of the teeth by any oxidation process as it gives the white color and sheen to the alloy. Like palladium, it requires a minute amount because of white color as too much white color may disturb the color of the neighboring tooth. It is advised not to add more than 6 percent of platinum and palladium.
Other notable Noble Metals (Type 1):
Other noble metals include Iridium and ruthenium, mixed with gold, palladium, and platinum to form alloys. They are to be used in minute amounts because of their higher reactivity in air and bright whitening color component. Another metal used is Rhodium mixed with platinum to form an alloy that can withstand the shapes. Mentioning the shapes, this alloy is used in the weights attached along with the braces wiring and used to reshape a faulty gum. These weights, which are to attach with each tooth continuously, have the properties to resist any reaction with the enamel or foods and drinks of any temperatures. This is because both Platinum and Rhodium have high boiling points.
Base Metals (Type 2)
The metal alloys used for base metals are Silver, Copper, Zinc, Indium, Tin, Gallium, and Nickel. Silver, however, has some unfavorable properties, such as reacting with the acidic Ph or discoloring the teeth, which is called Greening. So it is usually not recommended. Some common uses of base metal alloys are the fabrication of partial denture framework. A denture is a fake rootless tooth glued to the gum to fill in the incomplete set of teeth. Enough, the tooth to be glued requires a ‘throne’ or framework rich enough to settle the tooth permanently. Therefore base metal alloys form a firm, thick, cloudy seat for the tooth to settle perfectly. Another use of Base Metals is the casting of the tooth. Tooth casting is pouring the liquid form of base metal alloy over the patient’s tooth to take the accurate size, shape, and three-dimensional model to form a new fake tooth.
Similarly, these base metal alloys are used in surgical instruments in dentistry as they can withstand pressure and heat and bend properties. Another common use is a periodontal splint, where teeth are placed with firmness to avoid the mobility and thus friction with the neighboring teeth. Base metals are usually biocompatible, so they will not react with any food remains left in the teeth.
Classification of Noble Metal Alloys:
Noble metal alloys are further divided into three types—the high type in which there is a 60 percent composition of noble metals. Type 2 belongs to a rather lower composition of Noble Metals, mainly around 25 percent, and the last one is type 3, which contains the alloys made by base metals with the composition of 25 percent here. There are yet another type, type 4, which has the properties of very tough strength, high tensile toughness, and hardness, which is beneficial for casting, and dentures. The alloys used for all-metal or resin veneer prostheses are the metal-ceramic restorations alloys. However, the alloys for metal-ceramic restorations should never be used for all-metal resin veneer. This is because the alloys may not form thin stable oxide layers to promote atomic bonding to porcelain. Adding to it, their melting range may be too low to resist sag deformation. Furthermore, their thermal contraction coefficients may not be close enough to those of commercial porcelains.
Conclusion
The use of precious metals in dentistry has been great progress. It requires extensive research. Many more alloy metals have been introduced so far. For example, Cobalt, Chromium, Titanium, and Tungsten require deep insight and further research to get complete recognition. It is recommended that dentists develop a deep understanding of precious metals before practicing their use.