Short notes on: The lost wax process

The lost wax process-

The lost wax process is a relatively simple and inexpensive way of producing acrylic dentures and cast restorations. A wax pattern is embedded in a mould material (such as plaster or investment) and the wax is then eliminated either by melting it away with hot, running water or heating it to such high temperatures in a furnace that it is incinerated.

We can then force molten metal or acrylic down a channel or directly into the cavity, filling the void left by our original wax pattern. Thus a metal substructure or acrylic denture is produced.

The mould materials for casting alloy structures must be capable of withstanding very high temperatures without disintegrating. In addition, upon heating the mould must undergo sufficient expansion to counteract the contraction of the alloy on cooling to normal room temperatures in order to produce an accurate fitting metal substructure. This mould cannot be reused as it's destroyed when removing the pattern.

The wax pattern for a dental alloy casting may be created in two different ways:

1. The duplicate refractory cast technique. Here, the master model is surveyed, the path of insertion selected and undesirable undercuts waxed out. A duplicate model is produced in refractory investment material and the wax pattern produced on this duplicate model. The wax pattern is invested on the duplicate model. This technique is commonly used in the production of partial or full metal denture bases.
2. The "lift-off" technique. The wax pattern is formed on the master cast or die, lifted off the model and then invested. This technique is only used in simple designs (like crowns and inlays) because complex patterns are likely to distort.