Drug – bio-affecting and body treating compositions – Whole live micro-organism – cell – or virus containing – Animal or plant cell
Reexamination Certificate
2001-04-12
2003-07-08
Witz, Jean C. (Department: 1651)
Drug, bio-affecting and body treating compositions
Whole live micro-organism, cell, or virus containing
Animal or plant cell
C435S289100, C435S303100
Reexamination Certificate
active
06589525
ABSTRACT:
This is a continuation of co-pending international application No. PCT/FR99/02462 filed on Oct. 12, 1999, which designated the United States of America.
The present invention relates to integrated periodontal implants comprising cementum on the surface of the root and a ligament to connect the cementum to the bone alveolus, as in a natural tooth.
The invention pertains to a method for preparing the implant by bringing the implant into contact with undifferentiated mesenchymal stem cells under culture conditions to allow adhesion of cementoblasts and of alveolodental ligament to the root portion of the implant and implanting the implant carrying differentiated tissue cells.
The invention also relates to a cell culturing apparatus for preparing a dental implant. Finally, it relates to a method for replacing lost or compromised teeth with implants to which biological tissues and cells have been affixed using a suitable cell culture technique, to then obtain mouth cicatrisation by cementum and ligaments between the bone alveolus and implanted roots.
Dental transplants and implants have been carried out for several decades and a variety of techniques have been described.
Implanting techniques in current use include the following:
a) prostheses on osteo-integrated implants, artificial titanium roots which are stabilized by bony ankylosis. The force of mastication is transmitted to the bone with no dampening because of the absence of alveolodental ligament which is an important factor in protecting teeth against shock, overload and the risk of fracture;
b) transplants or other dental grafts which do not have the disadvantages of the preceding approaches but require extraction of a donor tooth which is available and generally non-functional.
Before embarking on the description of the present invention, a reminder of the physiological conditions regarding the connections of the natural tooth is necessary. The tooth is anchored in a cavity termed the alveolus, in the alveolar bone. The root and bone are anchored together by a ligament principally constituted by bundles of collagen fibers with one end anchored in the bone and the other end in the cementum, a mineralised layer resulting from differentiation of undifferentiated mesenchymal cells to cementoblasts which produce the organic and mineral matrices constituting the cementum. Collagen fibers are perpendicularly inserted in this cementum, and are included parallel to the cementum surface, forming a network.
In order to be functional and accepted, ideally, implanting an artificial tooth must anatomically and histologically reproduce the support structures of natural teeth, i.e., the cementum, the alveolodental ligament, and the alveolar bone, with all of their components: differentiated or undifferentiated cells, collagenic fibers and other fibers (elastic, oxytalan, elauin), the basic substance, mineralised tissues, vascularisation and innervation.
The patent application EP-A-734712 (Kanebo Ltd) describes a method for carrying out an implant by applying a layer of cementum particles to the surface. However, such implant does not present collagen fibers perpendicularly inserted in the surface of the neoformed cementum, necessary to the attachment of said implant with the alveolar cavity.
In order to stimulate the reformation of alveolodental ligaments on the curetted dental roots, Hanes et al. (“Cell and Fiber attachment to demineralised cementum from normal root surfaces” Vol. 60, no. 4, pages 188-198), have studied the effect of citric acid on its surface; the cementum or dentin fibers removed by demineralisation can bind by “splices” to the collagen fibers in the surrounding tissues. But there is no “neo-cement” and the fibers stand much less dense than a normal desmodont The fibroblasts, ligament generators, cementoblasts and osteoblasts bordering the alveolar bone result from differentiation of undifferentiated mesenchymal stem cells which are normally sited in the connective tissues surrounding the blood vessels. They can be found on the surface of the roots of extracted teeth and/or in the alveolus of extracted teeth or in the ligaments of a tooth or in other tissues, which may or may not be buccal connective tissue.
The invention results from a demonstration that under certain biological and mechanical stimulation conditions, the natural physiological environment of the root described above can be reconstituted from a culture of undifferentiated mesenchymal stem cells.
The proposed invention can thus enable teeth lost in the majority of clinical situations to be replaced with permanent artificial teeth connected to the jaws by the same tissue elements as natural teeth, i.e., a cementum, an alveolodental ligament and an alveolar bone and enabling normal attachment of the gingivae to the neck of the implant. These four elements are constituents of the periodontal tissue which can thus fulfil its normal physiological role, namely dampening the stresses of mastication, preventing overloads, and adapting the position and mobility of the tooth to the average load it receives.
The present invention provides a method of manufacturing a dental implant comprising:
preparing an implant composed of a root portion and a crown portion and constituted by a biocompatible material in a shape which is adapted to an extracted tooth;
immersing the root portion of said implant in a culture of undifferentiated mesenchymal stem cells in a culture medium the composition of which allows differentiation into cementoblasts and fibroblasts, over a period which is sufficient for said differentiation and for adhesion of cementoblasts to the root portion and the formation of a first layer of cementum and an alveolodental ligament primordium attached to said cementum;
recovering the implant carrying differentiated tissues affixed to its root portion.
The choice of implant is governed by different criteria. The first criterion is its morphology. This depends on the volume of dentin (ivory) in the tooth to be replaced, i.e., the total volume less the enamel and cementum. The desired shape is obtained, for example, by comparison with the extracted tooth; it is then customised to the exact shape of the tooth to be replaced. The desired shape can also be obtained from radiological or tomodensitometric data or the like. The implant is then shaped from a block constituted by a selected material using an N/C machine or any other means. A few basic shapes may also be satisfactory in a majority of cases; they will have a variety of lengths, diameters or tapers, with round or oval cross sections.
The choice of implant material in the method of the invention is guided firstly by the biological and immunological acceptability of said material in the mouth, and secondly by its performance as a support for cementoblast adhesion. The material of the implants must be biocompatible and must be sufficiently strong mechanically to avoid the risk of fracture; the surface must also be roughened to facilitate cell adhesion, and finally its color must be close to that of the natural tooth. Known materials can be envisaged for the material of the implant, such as titanium, alloys or ceramics, for example zirconia. Natural devitalised teeth obtained from any source may also be used. Such materials have been described in Periodontology 2000 (1998) 17: 7-21.
In addition to the root portion which is brought into contact with the undifferentiated mesenchymal culture, the dental implant used in the method of the invention comprises a crown portion which can be capped by a crown of resin, a composite, or a metal or ceramic alloy. Grooves are provided in the crown portion of the implant to stabilise the sutures which hold the implant in its alveolus on placing it in the mouth. With the implant viewed occlusally a groove can, for example, occupy one diameter and two others can cross this diameter at a right angle at a point equidistant from the center and from the circumference. However, these grooves can be disposed differently without disturbing the ergonomics of the system, as will be
Societe Anonyme Natural Implant
Witz Jean C.
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