Casting Machines in Dentistry – A Review Part I

ABSTRACT

Dental casting machine is an electrical device used to extrude molten materials to fabricate dental prostheses such as crowns, bridges, intracoronal and extracoronal restorations, and removable partial dentures. The casting process basically include melting and casting. Firstly, the solid material is heated in a crucible in temperature-controlled conditions to melt the material to its smelled form. The dental casting process is a complex one with multifaceted steps and equipment. Different types of casting machines are available to produce heat using different sources and techniques. It includes Arc melting, Open flame casting, and Electrical resistance. Arc melting involves the application of an electric or gas discharge on tungsten electrodes, causing the metal base to melt utilizing the heat produced by arcing. Open flame casting or induction melting employs water-cooled alternate current induction coils to induce heat. However, resistance heating uses electric current to melt precious metals.

INTRODUCTION

The primary objective of modern dental prosthetic rehabilitation is to create prostheses that are more aesthetically pleasing, functional, and bio-compatible.[1] Casting is the most common method of molding a metal restoration extraorally. Although the technique of lost wax casting has been employed for millennia to produce metal objects, W.H. Taggart was the first to introduce it into dentistry in 1907, and it is still a valid technique to be employed.[2] The technique is commonly used in dentistry to produce inlays, onlays, and metal crowns. Additionally, it is used to create all copings for metal crowns fused to porcelain, as well as elements for partially removable dentures.[1,2]

Casting procedures have been the focus of extensive research by many investigators. The principles of casting have been extensively discussed in the literature, and numerous techniques have been proposed for this process over the years by those who have studied the subject. It is often claimed that one or another of these methods would be more effective.[3] Nevertheless, the utilization of a dental casting machine within the dental laboratory is essential for all casting applications, regardless of the type of metal used.

Earlier studies have demonstrated that the selection of a casting machine has a significant influence on the mechanical characteristics of castings of base and noble metals, regardless of the alloy(s)/technique(s) employed.[4,5,6] In this review article, the purpose, principles, specifications and applications of dental casting machines are discussed.

History

1. The utilization of dental casting machines to create cast metal reconstructions is attributed to the inhabitants of ancient China during the Bronze Age.[7]

2. The practice of dental casting has its roots in Black Smithey, which can be traced back to the ancient civilizations of Mesopotamia and Egypt, where Brans alloy was cast using crimple techniques.[8]

3. The use of cast restorations was highly esteemed among the inhabitants of Ancient Egypt and the Indus Valley Civilization, as evidenced by the human skulls excavated from these locations.[9]

4. Benvenuto Cellini (1558) claimed to have attempted the use of wax and clay to prepare castings.[10]

5. Martin was the inaugural individual to employ wax to create gold inlays. According to Martin’s methodology, employing a foil liner was deemed unnecessary. He filled the void with wax, extracting it following solidification, investing, incinerating it, and finally, pouring molten gold into the mold shaped within the investment.[11]

6. The modern dental casting machines came into existence only in the year of1907, W.H. Taggart introduced the last wax casting technique.[2]

7. This was followed by Jameson, who introduced the centrifugal-casting machine, and Solbrig, who introduced the steam pressure casting machine.[12]

8. “William Justin Kroll” in 1930 invented useful metallurgical processes for Ti and is considered the father of Ti dentistry. B.G. Waterstrat, in 1977, introduced the world’s first titanium dental casting. Ti and Ti alloys made casting nearly feasible for fabricating sound-cast dental prosthesis.[13]

Since then, various casting machines have been introduced in dentistry.

Casting procedure [Figure 1]

Figure 1.

Steps in casting procedure

Glossary of prosthodontic Terms—9 defines casting as the process by which an object is formed by solidifying a fluid in a refractory mold. The most frequently utilized heat sources for alloy melting include the Flame, Induction process, or Electric arc. Centrifugal and vacuum/pressure systems are the main ways the material is deposited onto the casting cylinder.[14]

Flame

A correctly calibrated torch will generate an appropriate temperature of 1000°C for dental alloys with melting ranges within this temperature range. When the correct ratio of gas and air is blended and ignited, the resulting flame will display distinct zones of flames/combustion areas[15] [Table 1 and Figure 2].

Table 1.

Zones of flame

Zones	Name of Zones	Colour	Nature of Zones	Indication
1st	Fusion zone	No color	No heat	Not recommended
2nd	Ignition zone	Green color	Oxidizing in nature	Keep it at a distance from the alloy
3rd	Deoxidizing zone	Light blue color	Reducing in nature	Used to melt the alloy
4th	Oxidizing zone	-	Oxidizing in nature	Keep it at a distance from the alloy

Figure 2.

Zones of flame

Electrical

Electricity can be used to melt alloys in two distinct ways: through electrical resistance and induction melting machine. Electrical resistance is achieved by passing a current through a resistive heating conductor, and the alloy is then melted in a graphite crucible through the induction process.

Induction melting machine: It operates by generating electric currents within the metal core through electromagnetic induction induced by a magnetic field. Induction casting consists of a crucible around which the copper coil is circularly wound. High-density alternating current is passed through the copper coil at a frequency of 1500 KHz. A magnetic field is then generated around the coil, bringing the alloy to the casting temperature. Once at the casting temperature, the alloy is forced into a mold. Induction melting machines are used to melt base metal alloys.[16]

Despite its popularity, the main issues with gas oxygen torches are the inability to control the temperature precisely and the risk of changing the alloy composition through overheating. The induction system, however, allows perfect control over the melting temperature as it produces a homogeneous weight of all alloy constituents by molecular agitation. This means that the rapid increase in temperature reduces the risk of oxidizing and contaminating the molten alloy.[17]

CONCLUSION

Casting machines have revolutionized the field of dentistry, offering precision, efficiency, and reliability in the creation of dental prosthetics. These machines have enabled dental professionals to craft intricate and customized restorations with utmost accuracy, meeting each patient’s unique needs.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.