FR2863478A1 - Dental restoration prosthesis comprises a rigid core surrounded by a sheath made of a material that loses its mechanical bonding characteristics when subjected to a stimulus - Google Patents

Abstract

Dental restoration prosthesis comprises a rigid core surrounded by a sheath that provides a mechanical bond between the core and a receiving site and is made of a material that loses its mechanical bonding characteristics when subjected to a stimulus.

Description

1 2863478

  The present invention relates to a prosthetic element for dental restoration and in particular a post, an implant or a pillar. The present invention relates more particularly to such an element capable, after implantation, to be removed without causing trauma to the surrounding tissue.

  At the origin, the metal dental posts were made so that they could withstand the high mechanical stresses to which they are subjected during use. Due to their nature, these metal studs however have a certain number of drawbacks, some of which are related to corrosion phenomena and others to their excessive resistance (modulus of elasticity) in the transverse direction with respect to the resistance clean of the dentine in which they are implanted, which sometimes leads them to unseal and / or to cause a fracture of the root.

  In order to avoid this type of disadvantage, it has been proposed to produce tenons having a high mechanical strength in the longitudinal direction so that they can withstand the significant forces to which they are subjected during use, while possessing resistance. much lower, close to that of the dentine, in the transverse direction, which prevents their inadvertent loosening. To obtain such a result it has been proposed to make the dental studs no longer of metal but of composite material. These tenons thus consist of a core formed of fibers, in particular carbon or glass fibers, which are equitended and embedded in a biocompatible resin support matrix. European Patent EP-B-0 432 001 discloses such a stud and its method of manufacture.

  However, whether they are metallic or made of a fiber composite material, the dental posts have the disadvantage of being difficult to remove after use, for example when a new intervention is necessary on the tooth. Implants or abutments in titanium or ceramic are even more difficult to remove in the case of such a re-intervention or simply in case of partial fracture. Moreover, it is also known that this difficulty is further increased when the prosthetic elements are screwed into the tooth.

  The present invention aims to provide a dental prosthetic element of the aforementioned type which, once implanted in the tooth, can be removed easily without the practitioner being forced to implement a destructive intervention of the tenon and therefore, accordingly, without taking the risk of also damaging the integrity of the surrounding tissues.

  The subject of the present invention is thus a prosthetic element for dental restoration, in particular a post, an implant or a pillar, intended to be implanted in a recipient site, characterized in that it consists of a rigid core, conferring on the prosthetic element the essential of its mechanical characteristics, surrounded, at least partially, a sheath ensuring the mechanical connection of maintenance between the core and the receiving site, this sheath being made of a suitable material, under the action of a stimulus, to lose at least temporarily sufficiently its mechanical characteristics so that the connection it provides with the rigid core and / or the recipient site is interrupted so, when implanted in the recipient site, to allow its withdrawal .

  In one embodiment of the invention, the material constituting the sheath may be a so-called shape memory material, and in particular a polyurethane or an oligocaprolactone.

  It will be recalled that the memory effect of polymers is the capacity of these polymers to undergo a deformation in order to take a provisional form then a given form that is stable under the action of an external stimulus.

  In another embodiment of the invention, the outer surface of the sheath will be in the form of screw threads, which will make it easier to position the prosthetic element in the receiving site.

  Advantageously, the stimulus may consist of a variation in temperature, illumination or pH.

  An embodiment of the present invention will be described hereinafter by way of non-limiting example, with reference to the appended drawing in which: FIG. 1 is a schematic view of a first example of a prosthetic element according to the invention, consisting of a pin, - Figure 2 is a partial schematic and enlarged in axial cross section of a detail of the embodiment shown in Figure 1, - Figure 3 is a view schematic partial and enlarged in axial cross section of a detail of another embodiment of the invention, - Figure 4 is a schematic longitudinal sectional view of another application of the prosthetic element according to the invention, consisting of a dental implant.

  FIG. 5 is a perspective view of the application shown in FIG. 4, before the abutment is placed in the implant.

  FIG. 6 is a diagrammatic view in longitudinal section of another application of the prosthetic element according to the invention, consisting of a dental implant.

  FIG. 7 is a curve representative of the variation of the modulus of elasticity of a shape memory type material as a function of a stimulus constituted by the temperature.

  - Figure 8 is a partial schematic view and enlarged in axial cross section of a detail of another embodiment of the invention consisting of a dental abutment.

  FIRST EXAMPLE OF EMBODIMENT: Dental Tenon Firstly, an application of the present invention to a dental tenon 1 will be described.

  In this first embodiment, which is shown in Figures 1 and 2, the post 1 consists of two parts, namely a central core 3 and a peripheral sheath 5. The central core 3 is made of a material composite consisting of an organic resin matrix in which is embedded a bundle of long fibers, optionally tensioned during the polymerization of the resin. This resin matrix may be chosen from those commonly used in dental composites such as methacrylic, polyurethane or epoxy resins. The fibers may consist of carbon, glass, quartz, silica or polyethylene.

  The core 3 is then machined to give it the precise shape and dimensions required by the application concerned, namely in the present embodiment, a dental tenon. In order to promote the adhesion of the outer sheath 5 to the central core 3, the latter may be subjected to chemical treatment, such as, for example, the application of a silane, or to a physical treatment, for example a treatment. by plasma.

  The sheath 5 of the post 1 may be made by overmoulding, and in particular for example by the technique of thermoplastic injection. To do this, after machining, the central core 3 will be placed in a mold having the definitive shape of the tenon inside which a polymeric material, such as a polyurethane material shape memory, will be injected for example to a temperature of 110 C and then cooled to about 0 C.

  Depending on the shape of the mold used, it will be possible to impart an external shape to the pin in accordance with the application that one wishes to make and, for example, this outer shape may be present, as shown in FIGS. 1 and 2, in the form of a thread.

  The establishment of such a dental tenon in the root canal will be done in a conventional manner by the practitioner following the usual techniques of conventional sealing or bonding, setting up which will be greatly facilitated by the existence of a screw thread .

  Polymeric materials which, in known manner, have a vitreous state and a rubbery state in which the transition between these two states is carried out rapidly in a small temperature range and in which the module in the vitreous state is about 100 to 1000 × 2863478 times higher than the modulus of elasticity in the rubbery state.

  FIG. 7 thus shows a schematic curve showing the variation of the modulus of elasticity E of such a polymer as a function of temperature. It can thus be seen on this curve that below a so-called glass transition temperature TV, the modulus of elasticity E of the material has a certain value EV corresponding to a significant rigidity thereof. As soon as the temperature increases and exceeds the glass transition temperature Tv, it can be seen that the modulus of elasticity drops sharply and reaches, at a temperature TC1, a value of modulus of elasticity Ec, much lower than that of the modulus of elasticity EV wherein the material is in the rubbery state. It maintains this state until a maximum temperature TC2 beyond which it loses all consistency.

  If a polymer material whose glass transition temperature Tv is at about 45 ° C. is used and this material is used to form the sheath 5, it is found that the tenon retains its adhesion when it is in contact with it. place in the mouth of the patient since in any case, the temperature at which the polymeric material memory effect is subjected, is lower than its glass transition temperature.

  When it is desired to remove such a tenon, unlike the tenons of the prior art, it is not forced to proceed to the destruction of it, risking thereby causing damage to the channel root of the tooth. According to the invention, it suffices to apply to the tenon an external stimulus of bringing the temperature thereof to a temperature above the glass transition threshold T "(namely here 45 C) thus passing the sheath 5 of the tenon of the vitreous state in the rubbery state and thus allowing the thread of the latter to have sufficient flexibility to allow it to be easily extracted from the root canal and without the need to resort to mechanical drilling operations , with the risk of causing accidental perforation of the surrounding tissues.

  SECOND EXEMPLARY EMBODIMENT: Dental Tenon In this embodiment, shown in FIG. 3, the prosthetic element also consists of a tenon formed of a central core 3 and of a peripheral sheath 5. The material forming the central core 3 consists of a metal alloy, and more specifically of a titanium alloy. This core 3 is formed by machining and, as in the previous example, it is covered by overmolding on its periphery by the sheath 5 made of a polymeric material of the shape memory type.

  In such an embodiment, the shape memory polymer used fulfills three functions, namely a first protection function of the metal core 3 against corrosion which does not usually fail to occur because of the establishment of galvanic current phenomena between the metal and the dental tissues, a second structure modification function under the action of a stimulus that allows the removal of the tenon and a third function of masking the unsightly color of the titanium.

  As in the previous example, a re-intervention will be made possible by the application to the tenon of an external stimulus such as temperature.

  The memory materials that can be used according to the invention may, for example, be made of polyurethane with shape memory. Such copolymer blocks are obtained by condensation of a macrodiol and a diisocyanate. The macrodiols are of the polyetherdiol or polyether diol type and the diisocyanate is preferably aliphatic rather than methylene diisocynate. The macrodiols of ε-caprolactone are obtained from ecaprolactone, ethylene glycol and di-n-butyl tin oxide. The increase in the molar mass is then carried out by adding a diol of low mass (butane

diol for example).

  It is known that such polymers are characterized by the existence of two transitions: that of the macrodiol (vitreous or crystalline transition) and that of the rigid polyurethane phase of the low mass diol.

  With polycaprolactone diols having a mass of between 2000 and 8000 Da acting as a flexible segment, diphenylmethane diisocyanate and butane diol, as rigid segment ensuring the stability of the temporary form, polyurethanes are obtained that can withstand temporary deformations of 100 to 600. The mechanical properties strongly depend on the proportion of oligomers used but also on the molar mass of the copolymer blocks. Increasing the proportion of macrodiol in the reaction leads to increase also the modulus of elasticity.

  It is also possible to use a polystyrene block copolymer whose glass transition temperature Tv 9 2863478 is 100 ° C. and a transpolybutadiene block having a crystalline melting at 60 ° C. The polymer is molded at 120 ° C. The interval between 60 ° C. and 60 ° C. 100 C defines a rubbery plate to give the material a stable temporary shape below 60 C.

  Of course the external stimulus could be other than the temperature and could also for example be an electrical pulse, a certain wavelength of illumination or a chemical stimulus such as for example the pH, which would be able to bring the polymer material to pass in an elastic transition phase allowing it to retract during the traction exerted during its withdrawal and allowing it to be released from the element to which it is linked.

  It will also be noted that the screw thread made of shape memory polymer, by reducing the cross-section of the titanium core 3, reduces the modulus of elasticity of the post 1, which has the effect of damping the apical stresses. by distributing them at the joint of the latter.

  THIRD EXAMPLE OF IMPLEMENTATION: DENTAL IMPLANT In this example, shown in Figures 4,5 and 8, the prosthetic element 10 consists of a dental implant 11. It is known that the disassembly of such a prosthesis, after a certain time of use, is mostly problematic due in particular to the presence of hydroxypatite following the osseointegration thereof. The present invention overcomes such a problem.

  The dental implant consists of an actual titanium alloy implant 11 intended to be screwed into the maxillary bone 12 of the jaw of the patient with which a pillar 18 is associated. The implant 11 is pierced axially with a cavity internal cylindrical upper 15 whose wall is coated with a sleeve 16 of shape memory material whose inner surface forms a thread in which is screwed into the threaded lower cylindrical portion 17 of the pillar 18.

  In these conditions, it is understood that in order to disassemble the prosthetic element 10, it will be sufficient for the practitioner to apply a stimulus appropriate to the implant 11, and in particular a thermal stimulus, so as to exceed the glass transition temperature Tv of the material shape memory 16 which constitutes the internal thread of the implant so that the modulus of elasticity thereof drops sharply to a value Ec, so that the maintenance of the abutment 18 in the implant 11 is not more assured.

  One could of course according to the invention realize the threading on the cylindrical portion 17 of the pillar 18. One could also, as represented in FIG. 6, use an intermediate sleeve 20 made of a shape memory material provided with an external thread 22 ensuring its fixing in the implant 11 and an internal thread 22 'ensuring the maintenance of the pillar 18.

Claims (9)

  1. prosthetic element for dental restoration, in particular a tenon, an implant or a pillar, intended to be implanted in a recipient site, characterized in that it consists of a rigid core conferring on the prosthetic element the essential of its mechanical characteristics, surrounded, at least partially, by a sheath (5, 20) providing the mechanical connection for holding between the core and the receiving site (11), this sheath being made of a suitable material, under the action of a stimulus, at least temporarily to sufficiently lose its mechanical characteristics so that the connection it provides with the rigid core and / or the recipient site is interrupted, so, when implanted in the recipient site, to authorize its withdrawal.   2.- prosthetic element according to claim 1, characterized in that the material constituting the sheath is a type of said shape memory material.   3.- prosthetic element according to claim 2 characterized in that the shape memory material is a polyurethane material.   4. The prosthetic element according to claim 2, characterized in that the shape memory material is an oligocaprolactone.   5.- prosthetic element according to one of the preceding claims, characterized in that the outer surface of the sheath is in the form of screw thread.   6. Prosthetic element according to one of the preceding claims, characterized in that the stimulus consists of a temperature variation.   7.- prosthetic element according to one of claims 1 to 5 characterized in that the stimulus consists of a variation of illumination.   8.- prosthetic element according to one of claims 1 to 5 characterized in that the stimulus consists of a pH variation.   9.- prosthetic element according to one of claims 1 to 5 characterized in that the stimulus consists of an electrical pulse.