Dentistry – Method or material for testing – treating – restoring – or... – Endodontic
Reexamination Certificate
2000-02-29
2001-07-31
Wilson, John J. (Department: 3732)
Dentistry
Method or material for testing, treating, restoring, or...
Endodontic
C433S220000
Reexamination Certificate
active
06267597
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a tooth restoration system for restoring a tooth which has undergone root canal therapy.
BACKGROUND OF THE INVENTION
A human tooth comprises a crown and roots. The crown is the part of the tooth visible above the gumline while the roots are under the gums. The roots anchor the teeth to either the maxillary or mandibular bones. Within the roots are root canals which contain pulp. Pulp is live tissue which includes nerves and blood vessels.
The pulp may become infected and inflamed as a result of dental caries or physical trauma to the tooth. Endodontics is a branch of dentistry which treats teeth with diseased pulps. Endodontics is commonly referred to as root canal therapy. The goal of root canal therapy is to save the tooth by removing the diseased pulp. The root canal is then cleaned and filled. A crown or cap is typically placed on the tooth to protect the tooth and preserve its functionality.
In the prior art, porcelain fused metal (“PFM”) systems are commonly used. In a conventional PFM system, a post and core are fashioned from one of a variety of suitable precious and non-precious metals. The post is made to snugly fit the root canal void and serves to anchor the core and crown. The core is built up onto the post and forms the support for the crown which replaces the injured tooth. The crown may be fashioned from porcelain (ceramic) material.
PFM systems enjoy excellent strength due to the metal post and excellent wear resistance due to the porcelain. However, a major drawback to PFM systems is the aesthetic appearance of the completed restoration. The enamel and dentin of a normal human tooth are slightly translucent which determines the natural look of a tooth. The metal post and core used in a PFM system reflects light passing through the artificial crown which results in the restoration looking unnatural.
A solution to this drawback of PFM systems is to replace the metal post with a ceramic material which simulates the translucency of normal teeth. An example is the CosmoPost™ system available from Ivoclar Vivadent, Ivoclar North America Inc. The post in this system is a zirconium oxide based ceramic, resulting in an aesthetically pleasing restoration. However, this system suffers from certain drawbacks. The posts are only available in preformed posts of a certain size and diameter. As a result, the dentist must perform the root canal therapy such that the root canal is the exact fit of the pre-formed post and to do so requires the use of proprietary root canal reamers.
Another solution to the aesthetic drawback of PFM systems is to use a carbon fibre based material such as the Composipost™ system available from Biodent of Quebec, Canada. This prior art system shares the same drawback as the CosmoPost™ system in that the posts are only available in preformed sizes and diameters. Again, special proprietary drills must be used in the canal preparation.
The root canal void created for using such prior art pre-formed posts are typically circular in cross-section as is shown in prior art FIG.
6
A. As a result the dentist may not be able to remove all of the diseased pulp while retaining the necessary root canal void shape.
Posts are subject to high stresses once the restoration is complete and therefore the ceramic material used in the CosmoPost™ system and similar systems must be very strong. However, that strength prevents flexibility in fashioning the post. Other ceramic materials such as commonly available polymer/ceramic composites do not possess enough strength to be suitable material for root canal posts.
Therefore, it would be advantageous to have a tooth restoration system which combines the aesthetic qualities of an all-ceramic root canal restoration system with the strength of a conventional PFM system. It would be further advantageous for such a system to allow the convenient fabrication of a post which molds itself to the root canal and yet still possesses high structural strength.
SUMMARY OF THE INVENTION
In general terms, the invention in one aspect comprises a tooth restoration system for insertion into a tooth upon which root canal therapy has taken place, resulting in a root canal void having a certain shape; said system comprising a post, a core and a crown wherein:
(a) the post is formed from a fibre-reinforced composite material comprising a polymeric matrix and a reinforcing fibre component embedded within the matrix, said post having an upper end and a lower end wherein said lower end has previously been molded to the shape of the root canal void;
(b) the core is bonded to the upper end of the post and is formed from a ceramic material or a polymer/ceramic composite material; and
(c) the crown is bonded to and partially surrounds the core and is formed from a ceramic material or a polymer/ceramic composite material.
In another aspect of the invention, the invention comprises a method of preparing a dental prosthesis comprising a post, a core and a crown for restoring a tooth upon which root canal therapy has taken place. In one embodiment the method comprises the steps of:
(a) creating a post from an uncured or partially cured fibre-reinforced composite material comprising a polymeric matrix and a reinforcing fibre component embedded within the matrix;
(b) molding a lower end of the post to fit the root canal void;
(c) curing the post;
(d) building up a core onto the upper end of the post from a ceramic or polymer/ceramic composite material; and
(e) forming a crown around the core from a ceramic or polymer/ceramic composite material and shaping the crown to simulate the lost tooth.
The fibre reinforced composite material used in the present invention may comprise glass, carbon and/or graphite and polyaramid fibres. The polymeric matrix may include fully or partially polymerized thermoplastic materials. Suitable fibre reinforced composite materials are described in U.S. Pat. No. 4,894,012, although the present invention is not limited to those materials.
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