Metal working – Means to assemble or disassemble – Puller or pusher means – contained force multiplying operator
Patent
1994-10-26
1995-12-19
Echols, P. W.
Metal working
Means to assemble or disassemble
Puller or pusher means, contained force multiplying operator
433223, H61C 510
Patent
active
054759129
DESCRIPTION:
BRIEF SUMMARY
FIELD OF APPLICATION
The invention relates to a method for making ceramic dental crowns, inlays or onlays to replace lost dental natural substance. The tooth is prepared by a dentist, and a copy of the prepared surface is used as a base for building a replacement part of fired ceramic in a dental laboratory. Because of the way the copy is made or utilized, previously known methods cause problems with precision, colour matching and time delays, which are avoided by the present invention.
DISCUSSION OF RELATED ART
Among known methods for making crowns, the most common method is making a copy of the prepared tooth surface by pressing a gold foil against it, removing the foil and firing a ceramic layer on the foil in the laboratory in one or more layers at temperatures low enough not to melt the gold foil. The metal-ceramic part is then secured to the tooth by ionomer or phosphate dental cement. Problems with this method are that the adhesion of the gold foil is weak, requiring that the sides of the prepared surface are steep or parallel, requiring a thin gold foil which is easily damaged and may have inadequate strength for building-up of the ceramic layers. Its edge will be visible as a thin line between the crown and the natural tooth. Platinum foils have higher melting point but otherwise the same problems.
Other known methods create a higher strength base for the crown by making negative and positive models of the prepared surface in several steps, followed by making a metal base by casting or electrolytic deposition, or by copy milling from a block of ceramic material. To facilitate milling, the ceramic block may be fired at a lower temperature than final, or may consist of a pressed but not sintered body of ceramic powder such as aluminium oxide as described in the patent SE 464 908. Disadvantages with these methods are loss of precision because of the number of steps and the shrinkage of the ceramic during final firing or sintering.
It has also been described how to make an impression of the prepared tooth surface with fiberglass weave prepreg, which is subsequently hardened to a base part according to the patent U.S. Pat. No. 5,062,799. With this method there is a great risk of deformation of the weave before hardening, and the ceramic can not be fired directly on the weave.
For all metallic bases, the choice of ceramic is limited by the requirement that the firing temperature must not be so high that the metal softens or deforms.
SUMMARY OF THE INVENTION
According to the invention an impression of the prepared tooth surface is made from soft aluminium metal foil which is subsequently converted to hard and heat-resistant alpha-corundum by electrochemical methods. The corundum foil can then be used as a base for building a ceramic crown or onlay. Since the same foil that was used to make the original impression becomes part of the crown or onlay many copying operations are avoided and the precision is retained. Because of the strength of alpha-corundum a high grade ceramic enamel can be used without firing temperature restrictions. The shape and surface structure of the metal foil can be so closely controlled that the requirement for parallel or very steep prepared tooth surfaces can be relaxed. The metal foil can be relatively thick, up to 0.5 mm, without a visual metal edge on the finished crown.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section of a tooth being repaired according to present invention;
FIG. 2 is a view of a foil in a bath;
FIG. 3 is a view of a ceramic top mounted on the foil; and
FIG. 4 illustrates a method of attaching a crown to a mounted post.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a cross-section of a tooth (11) where an upper surface (13) has been prepared after loss and removal of tooth substance (12). An aluminium foil is formed by pressing a first major part (14) of it into contact with the prepared surface (13). A second part (15) of it can advantageously be pressed against the remaining outside of the tooth to increase the sti
REFERENCES:
patent: 5062799 (1991-11-01), Duncan et al.
patent: 5106303 (1992-04-01), Odeet al.
Echols P. W.
Sandvik AB
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