Crown-and-root reconstruction assembly made of a composite mater

Details Crown-and-root reconstruction assembly made of a composite mater Crown-and-root reconstruction assembly made of a composite mater

1997-05-09

1999-02-16

O'Connor, Cary E.

Dentistry

Method or material for testing, treating, restoring, or...

Crown

A61C 508

Patent

active

058713590

DESCRIPTION:

BRIEF SUMMARY
PRIOR ART

This invention deals with a crown-and-root reconstruction assembly for a dental prosthesis, comprised of a physiological securing post and a crown reconstruction base made of composite material tightly connected to the post and applied without any gap to the tooth or to a laboratory model reproduction of the healthy remaining portion of the tooth.
In dentistry, crown-and-root reconstructions generally use posts made out of various metallic alloys that are either prefabricated or cast via indirect technique. The use of metallic posts presents many disadvantages resulting from electro-chemical corrosion and oxidation phenomena or from the clustering of metallic ions in the body. When the crown reconstruction base is cast simultaneously with the post, the crown-and-root reconstruction assembly is homogeneous but its mechanical behavior is far from that of a natural tooth, a fact which results in root fractures in reconstructed teeth.
Posts made out of composite material are also available, in particular those made from high solidity fibers that may possibly be included in organic matrices as composite materials. Such posts are described in documents FR-A-2588181 and EP-A-432001. The reconstruction base is made directly inside the mouth on the natural tooth, with a charged resin or ionomer glass. A carbon fiber and epoxy resin post has a modulus of elasticity (110 GPA) that is identical to that of titanium when it is stressed along the axis of the fibers. The posts can be fabricated by machining cylindrical bars, or they can be made from axial carbon fibers assembled in an organic matrix.
The method consists of lining what remains of the tooth to be reconstructed and inserting the reconstruction product in a pasty state using a spatula or with the fingers. The reconstruction product is composed of two pastes to be mixed at the time of use, and one of the two pastes includes the catalyst. However, in mixing the two pastes, there is the risk of air bubbles becoming incorporated in the mixture, which results in inhibiting the polymerization around each bubble, thus creating areas in which there remain free monomers that are toxic to dental tissues. These poorly polymerized areas are the source of a significant reduction in the reconstruction's mechanical qualities and, are choice areas for discolorations and bacterial growth; they are also a source of cracks and fractures. The double mixture does not allow for the strict control of the components proportions which would ensure complete polymerization.
It is also difficult to use photo-polymerizable reconstruction paste inside the mouth because the product used is very thick. Indeed, the degree of polymerization of a resin is inversely proportionate to the square of the distance to the light source.
When the reconstruction material is manually inserted, the reconstruction paste must have characteristics that allow for easy handling. The resin must be charged with particles or ultra short fibers so that the material retains some viscosity and pegosity in order to ensure easy manual handling. The mechanical characteristics of such a material are weak, with the modulus of elasticity usually in the 4 to 12 Gpa range and tensile resistance does not exceed 60 to 70 Mpa.
Inventors have determined that in a crown-and-root reconstruction assembly, the root dentine, the favored locus for fractures, must be stressed as little as possible. The post must be in a passive state and its role is to maintain the crown portion of the reconstruction base. In the case of a metallic post, in particular, a titanium post, or of a post made of carbon-epoxy fibers, the application of evenly spread pressure on the occlusal face of a root reconstruction causes deformation of the base of the charged resin root reconstruction with a low modulus of elasticity (4 to 12 Gpa). The post will very quickly have to support the entire load, with the risk that it may cause the root to explode in the event of significant pressure on the tooth, particularly. when the force is applied along the

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patent: 5518399 (1996-05-01), Sicurelli, Jr. et al.
patent: 5564929 (1996-10-01), Alpert

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