Pressing

Problem / Question

The zirconia framework can not be completely covered by pressed ceramic(ingot) after pressing.

Cause (1)

Either sprue is too narrow or too long.

Solution / Answer (1)

The sprue diameter should be 8 gauge( 3.3 mm in diameter) and its length should be 2-3mm.

Cause (2)

Investments and foreign debris are attached to pedestal base and sprue connectors.

Solution / Answer (2)

Always ensure that the pedestal base is clean without the attachment of investments or foreign debris.

Cause (3)

Sprues are attached not to the edge of the pedestal base, but to the center.

Solution / Answer (3)

Attach the wax sprue to the edge of the ring former (pedestal base) at an angle of 30-60　degrees.

Cause (4)

The wax patterns are too thin.

Solution / Answer (4)

The wax pattern thickness should be more than 0.8mm.

Cause (5)

Press time is too short. Pressing pressure is not enough. Press temperature is too low.

Solution / Answer (5)

Observe the specified press time, pressing pressure and pressing temperature.

Cause (6)

Sprue connection is not smooth enough.

Solution / Answer (6)

The connector between sprue and wax pattern should not be too narrow. The sprue shape to be connected to wax pattern and pedestal base should be as trumpet mouth-like.

Cause (7)

The sprue connecting side of the pedestal base is raised like a hill all over.

Solution / Answer (7)

The pedestal side should always be flat.

Problem / Question

The pressed ceramic has flashes after pressing.

Cause (1)

When more than two wax patterns are stood, the distance between the wax patterns is too short.

Solution / Answer (1)

The distance between the wax patterns should be at least 5mm.

Cause (2)

When more than two wax patterns are stood, the wax patterns are not of the same height at the margin.

Solution / Answer (2)

Position the margins of the wax patterns at the same height.

Cause (3)

Noritake press investment is not used or the specified liquid is not used.

Solution / Answer (3)

Use the specified investment and the liquid.

Cause (4)

Press time is too long.

Solution / Answer (4)

Observe the specified press time.

Cause (5)

After burn-out of the investment ring, it takes too long before pressing.

Solution / Answer (5)

After burn-out of the investment ring, set the ring quickly to the press furnace.

Cause (6)

The thickness of the zirconia framework is too thin.

Solution / Answer (6)

The minimum zirconia framework thickness is more than 0.4mm. Please note that zirconia's strength is low at a high temperature zone and the strength comes back to the original level when the temperature is back at room temperature. If the zirconia framework is too thin and has cracks, those cracks may be propagated to the press ceramic.

Cause (7)

The investment ring is cooled rapidly after pressing.

Solution / Answer (7)

The investment ring should not be cooled too rapidly or cooled in the water. Leave it to cool at room temperature until it is held by hand.

Cause (8)

The investment ring is left too long in the press furnace after pressing.

Solution / Answer (8)

The investment ring should be taken out from the press furnace immediately after pressing.