The lost wax technique originally goes back to ancient times and is believed to have probably originated in China or Egypt. The method was employed to create figurines and objects in gold. Then in 1907, a centrifugal casting machine was invented by William H. Taggart. Although he patented his idea using the lost wax technique, he lost the patent when it was discovered another dentist had written a paper on the same idea some 25 years earlier.
Lost Wax Technique for Dental Crowns
Before a casting can be taken, the dentist drills out any decay and prepares the tooth for a crown. The dentist then takes an impression and sends this impression to the lab. At the lab, the impression is used to make a model of the prepared tooth and its neighbors. This is done by filling the impression with fine plaster called dental stone. The created model of the tooth requiring a crown is called a die. This die is coated in wax. That wax lump is then carved into the shape of a tooth that will fit with its neighbors.
A sprue (a small, bulbous wax rod) is attached to the carving. The sprue is an extension from the carved wax crown which goes downward toward the casting ring cap. The bulb in the hollow sprue functions as a gold reservoir and helps equalize pressure so the liquid gold flows evenly into the casting. The casting ring cap is positioned over the casting ring. The casting ring holds the plaster which flows around the casting.
Once the plaster has set, the casting ring cap is removed. This leaves the sprue protruding from the hardened plaster. The cylinder is then placed in an oven. As the wax melts, it leaves a space in the plaster in the shape of the original wax carved filling. This empty space, held in plaster, is filled with molten gold via a centrifugal casting machine.
The still-hot plaster is immersed in water, causing the plaster to shatter. All that is left behind is the gold crown casting and attached sprue. The sprue is removed. The gold casting is polished then cemented into the patient's mouth over the prepared tooth. The dental crown is finished.
Tags: casting ring, casting machine, centrifugal casting, centrifugal casting machine, Dental Crowns, Lost Technique Dental, prepared tooth