G-c Dental Industrial Corp.

Gc Corporation

Shohei Hayashi

Hiroshi Kamohara

Nobukazu Ohi

Norio Kojima

Kenichi Iiyama

Yoshinobu Yamamura

Yasutaro Ito

Reiichi Okuda

Takashi Miyazaki

Takashi Inamochi

Masaaki Kitamura

A method for casting dental metals with a casting apparatus including a melting chamber in which there are located an arc electrode above and a crucible formed of an electrically conductive material positioned below the arc electrode, and a mold chamber divided from the melting chamber by a partition wall having a through-hole at a position below the crucible and housing a mold box receiving a mold provided with an extending open vent positioned below the through-hole, the melting chamber communicating hermetically with the mold chamber through the mold, which is characterized by positioning a dental metal ingot on the crucible, vacuumizing the melting and mold chambers, feeding a small amount of an inert gas into the melting chamber at such a pressure as to induce arc discharge all over the upper surface of the ingot, thereby melting the ingot placed on the crucible by arc discharge from the arc electrode, pouring the thus obtained molten metal into the mold through its inlet, and immediately feeding an additional amount of the inert gas into the melting chamber to increase its internal pressure to a level suitable for casting.

Casting of dental metals

A method for casting dental metals with a casting apparatus including a hermetically sealed casting chamber in which an arc electrode is located above, a crucible made of an electrically conductive material is positioned below the arc electrode, and a mold provided with a closed vent is disposed below the crucible, the method including by positioning a dental metal ingot on the crucible, evacuating the casting chamber to vacuum, feeding a small amount of an inert gas at such a pressure as to induce arc discharge all over the upper surface of the ingot, thereby melting the ingot placed on the crucible by arc discharge from the arc electrode, pouring the thus obtained molten metal into a mold through its inlet, and immediately feeding an additional amount of the inert gas into the casting chamber to increase its internal pressure to a level suitable for casting. Also the additional amount of the inert gas is rapidly fed into the casting chamber through a gas tank in the vicinity of the casting chamber.

A dental prosthesis comprises an inner layer portion and an outer layer portion. The outer layer portion is a dental porcelain material, while the inner layer portion is a sintered product which, after sintering, is composed of: (i) 40 to 95% by weight of one or (two or) more electric conductive ceramic materials selected from the group consisting of nitride ceramics, boride ceramics and carbide ceramics, all having a specific electric resistance of 10.sup.-1 .OMEGA..multidot.cm or below, and (ii) 5 to 60% by weight of the following (A) and/or (B):

Dental prostheses

An investment for dental casting comprises a mixture of at least one refractory selected from alumina, zirconia, magnesia clinker, quartz, cristobalite and fused quartz with either a mixture of a soluble phosphate with magnesium oxide or hemi-hydrate gypsum, which act as a binder. The investment of the invention further contains 0.5 to 5 parts by weight of raw starch (original starch) and 0.1 to 50 parts by weight of at least one selected from the group consisting of carbides, nitrides, borides, silicides and sulfides of transition metals of Groups IV, V and VI in the periodic table, which are added as expanding agents to 100 parts by weight of the aforesaid mixture. The investment of the invention may still further contain 0.1 to 1 part by weight of soluble starch.

Investments for dental casting

An investment material for dental casting comprises 100 parts by weight of a mixture of hemihydrate gypsum, quartz and/or cristobalite and 2 to 5 parts by weight of natural starch optionally with 0.1 to 1.0 part by weight of soluble starch.

Growing community of inventors

Tokyo, Japan

Shohei Hayashi