Thermoformed copings or wax copings

Coping foils result in a stable and uniform wall thickness of the crowns. However, the setting expansion of the investment dies is decreased due to the hardness of the plastic copings. When using wax copings, the crowns are a bit wider after casting.

Investing with metal ring

When investing with a metal ring, a liner of thickness 1 mm or 2 mm (from ring size 6) must be used depending on the ring size. Metal rings keep the total expansion under control. With rema^® CC, always use the 2 mm liner.

Investing without metal ring

The use of silicone rings avoids the dirty metal chips, which are generated by used metal rings. Acrylic rings or silicone rings must be early removed during the setting process for an unhindered expansion of the mould.

Storage temperature

Phosphate-bonded investment materials should be stored in a climatic cabinet at approx. 18 – 20 °C / 64 – 68 °F. The mixing liquid contains silica sol, which is damaged under frosty terms.

Working temperature

The ideal temperature for processing is at 18 – 22 °C / 64 – 72 °F depending on the investment material.

Mixing concentration

The expansion can be controlled amongst other things by the concentration of the mixing liquid. The higher the concentration of the latter, the bigger is the expansion of the investment material.

Mixing time and vacuum stirring

Extended mixing times can result in an improved surface of the cast and an increased expansion. Indeed, two minutes should not be exceeded. Stirring too long can have the opposite effect in view of the expansion.

Investing

The mould should be filled by means of a vibrator using low vibration to avoid a segregation of the investment material and the rise of bubbles. Investing under pressure prevents formation of bubbles on the surface of the casting object. Working with too high pressure will cause a lower permeability and a decreased setting expansion.

Chemical and thermal expansion

All phosphate bonded investment materials have a chemical or setting expansion during the setting phase and a thermal expansion when they are preheated.

Preheating

• Conventional preheating: After the setting time according to the instructions for use, the muffle is put into the furnace at room temperature. Usually a holding time of 60 minutes is programmed at 250 °C / 482 °F for the cristobalite transformation. A second holding time of 30 minutes can be adjusted at 560 °C / 1040 °F for the quartz transformation to increase the thermal expansion in case of need.
• Speed preheating: The muffle is put into the furnace before the setting time is completely finished at final temperature 700 – 950 °C / 1292 – 1742 °F depending on the type of alloy. For safety reasons, the furnace door must be kept closed for the first 15 minutes!

Preheating furnace

A furnace, which is equipped with circulating air, multilateral heating and a ribbed base plate such as the Protherm oven from Dentaurum provides constant casting results.