Coating processes – Medical or dental purpose product; parts; subcombinations;... – Implantable permanent prosthesis
Patent
1993-01-12
1994-09-13
Lusignan, Michael
Coating processes
Medical or dental purpose product; parts; subcombinations;...
Implantable permanent prosthesis
2041921, 427255, 427527, 427529, 427530, 433218, 4332221, 433223, A01N 102
Patent
active
053467175
DESCRIPTION:
BRIEF SUMMARY
This invention concerns a method of preparing a surface of a dental ceramic body for subsequent fitting to a tooth, by means of improving the bond strength between the fitting surface of the body and certain commercially available dental cements.
Ceramics including high-alumina porcelains and glass ceramics are frequently used in restorative dentistry for the construction of, for example, jacket crowns, inlays or aesthetic veneers. Such materials are particularly useful for these purposes, being chemically inert and bio-compatible in the oral environment, and are aesthetically pleasing.
However, one disadvantage in the use of ceramics is that their inert chemical nature renders them unable chemically to bond directly to certain dental cements such as glass polyalkenoate cements. Consequently, mechanical retention techniques are often used for attachment. Whilst mechanical bonding may be enhanced by etching the fitting surface of the ceramic material to provide a "key" this tends to cause stress concentration locally and potentially weakens the rather brittle material.
One known technique developed to strengthen porcelain jacket crowns, has the additional advantage of overcoming the problem of bonding. It involves the preparation of a "thimble" of platinum foil, coated on both sides with a layer of tin oxide. The ceramic is fired onto the oxide coated outer surface of the thimble whilst the oxide coated inner surface provides a chemically reactive surface for bonding to the cement. Whilst this technique is effective, it involves a multi-stage process and the use of expensive platinum foil, and compromises the aesthetics of the restoration.
Other chemical methods of bonding to dental porcelain exist. The first is a group of chemicals called silane coupling agents, which can be initially effective in bonding to resin-based cements, but are subject to chemical degradation in the oral environment.
An object of the present invention is to provide a method of preparing the fitting surface of a dental ceramic body for subsequent bonding to a tooth using a dental cement, in which the aforementioned disadvantages are avoided. Such a method, according to the present invention, comprises the step of depositing by a vapour phase deposition technique, directly onto said fitting surface of the ceramic body, a strongly adherent coating of an inorganic substance which is capable of reacting with the cement to provide durable bonding to such cement.
Various chemically reactive species are available for this purpose, including, for example, metals and alloys; metal salts; metallic and nonmetallic compounds; glasses, particularly reactive or ion-leachable glasses; and other reactive ceramics. In a specific example, tin oxide is capable of being deposited as a microns-thin layer (ideally less than two microns) directly onto the fitting surface of the dental ceramic.
The selection of a coating material suitable for this purpose is determined such that it shall be bio-compatible, and, with reference to acceptable optical qualities, to be preferably white or off-white or colourless so as not to compromise the aesthetics of the restoration. Since the marginal regions of a ceramic body prepared in accordance with the invention will, in use, be subjected to saliva, acids of bacterial origin and acids originating from both foods and regurgitated gastric contents, it is important to avoid dissolution in the edge regions owing to chemical degradation, which in turn could lead to bond failure. The substance must be insoluble in both cold and hot water and should resist dissolution in low pH environments.
Various methods exist for vapour phase deposition of such materials onto ceramic surfaces, including physical vapour deposition techniques such as evaporation and sputtering, ion implantation and chemical vapour deposition.
Of sputtering techniques perhaps the most appropriate is the ion plating technique which incorporates partial ionisation of the deposition species thus increasing their average energy and enabling better integration
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Duvigneaud, P. H. et al, "Tin Oxide Coatings on Ceramics," Sprechsaal, vol. 118, No. 5, pp. 402-410, May, 1985.
Vispute, R. D. et al, "Deposition of Tin Oxide Films by Pulsed Laser Evaporation," Chemical Abstracts, vol. 110, No. 8, Feb. 20, 1989, Columbus, Ohio USA, p. 300.
Lusignan Michael
The Victoria University of Manchester
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