WO1990006733A1

WO1990006733A1 - Novel fitted dental prosthesis and process for the manufacture thereof

Info

Publication number: WO1990006733A1
Application number: PCT/FR1989/000652
Authority: WO
Inventors: Guillaume Malquarti; Mohamed Qasseem Saif; André OLIVIER; Daniel Treheux; Dominique Bois
Original assignee: Ecole Centrale De Lyon; Association Lyonnaise Pour Le Developpement De L'odontologie (A.L.D.O)
Priority date: 1988-12-16
Filing date: 1989-12-14
Publication date: 1990-06-28
Also published as: FR2640495A1; AU4807390A; EP0448587A1; CA2005628A1; FR2640495B1

Abstract

Novel fitted prosthesis comprising a support (1) surmonted by a porcelain cap (2). The support (1) is made from a sprayed and partially molten material.

Description

NEW FIXED DENTAL PROSTHESIS AND METHOD FOR PRODUCING THE SAME

TECHNICAL AREA :

The present invention relates to the dental field and it relates, more particularly, to fixed prostheses, as opposed to removable prostheses.

By fixed prostheses, it is necessary to consider, in particular, crowns, abutments, esthetic caps, inlay, onlay.

For economic reasons, fixed dental prostheses are currently most often made of a precious metal alloy, semi-precious or non-precious, such as a nickel-chromium alloy or a cobalt-based alloy. For obvious aesthetic reasons, the constitution of such a prosthesis, which was initially ensured solely on the basis of such an alloy, has evolved to involve the production of a screed, always of the same alloy, but covered with a porcelain cap (glazing process). The problems of manufacturing such prostheses are mastered, in particular with regard to the adhesion between the metal cap and the porcelain cap. Likewise, the problems of adaptation in the mouth are correctly resolved because the prosthetists know and perfectly master the characteristics of dimensional variations of the metal alloys during the production.

If such prostheses therefore give satisfaction on these two points, on the other hand, they pose significant problems of biocompatibility, due to the permanent contact between the metallic screed and the organic tissues. These problems are those of corrosion, galvanic coupling and diffusion of non-biocompatible metal ions. These various problems are at the origin of allergy phenomena, of toxicology by diffusion of dust which reduce the proliferation capacity of fibroblasts and impede the growth of epithelio- gingival.

It should also be pointed out that the presence of metallic screeds prevents the application or the implementation of modern and precise diagnostic methods, such as medical imaging by nuclear magnetic resonance. Indeed, the presence of such screeds is responsible, at the very least, for distortions of the images leading to an unusable reading.

PRIOR TECHNIQUE:

To overcome the above drawbacks, the prior art has made several proposals aimed at eliminating the presence of the metal screed.

Mention should be made, in this regard, of the proposal consisting in making the screed in alumina or aluminous porcelain. This technique gives rise to problems of realization which are difficult to overcome, originating from significant distortions of dimensions at the time of the firing of the porcelain. The products obtained are generally characterized by manufacturing tolerances that are too tight or too wide, making adaptation in the mouth respectively delicate, if not impossible, or responsible for the birth of bacterial foci.

Among the drawbacks of such a method, mention should also be made of the great fragility of the aluminous porcelain screed, even after covering the traditional cap. Furthermore, it does not currently seem possible to use such a method to produce a fixed type dental prosthesis.

Another proposal also consisted in making the glass ceramic prosthesis involving the use of transparent glass poured at high temperature. In such a process, it is necessary to have recourse to the definition of a negative impression for the entire tooth and to produce the prosthesis by the lost wax process, in order to obtain the formation of the entire tooth in glass-ceramic. The choice of such a raw material, with a fragile and transparent crystal structure, implies the obligation to resort to a thermal stabilization treatment which is responsible for dimensional distortions. Problems of adaptation and of bacterial focus are also to be considered. The imposed heat treatment is responsible for the opacification of the raw material which should therefore be masked by a surface bonding. Given that the method provides for making the entire tooth from a negative impression of the natural tooth, the bonding process can only be considered over a small thickness which does not have reliability over time.

All in all, therefore, the above techniques, although linked to an advantage of biocompatibility and neutrality of the base material, pose great practical difficulties which have limited their development.

It should also be noted that the above methods involve the use of very expensive specific equipment, generally not very affordable for a prosthetist practicing his profession as an individual in a liberal profession.

If all these drawbacks are responsible for a limited use of the above techniques, it must certainly be recognized that the most serious of them is that of the lack of control of the dimensional characteristics and, more particularly, of the risk of existence a hiatus between the prosthesis and the stump of the tooth, as well as between the gingival tissues and the skirt of the prosthesis. The existence of such a hiatus irreparably condemns the reconstitution of tissues in the more or less long term, because of the foci of bacterial infection which develop in a way that is difficult to control.

The object of the present invention is precisely to remedy the above drawbacks by proposing a new fixed prosthesis and a particular method for producing such a prosthesis, characterized by the elimination of metallic alloys in the mouth and by a very exact adaptation. to the tooth to be fitted, so that the following advantages are certain:

- elimination of corrosion and galvanic coupling problems, - elimination of diffusion of non-biocompatible metal ions responsible for cellular disorders,

- possibility of implementing diagnostic imaging procedures,

- removal of any hiatus responsible for development of microbial foci.

PRESENTATION OF THE INVENTION:

To achieve the above objectives, the new dental prosthesis is characterized in that the screed is made of a sprayed material and partially melted.

The subject of the invention is also a method for producing such a prosthesis, method consisting in:

- contour the tooth in a homothetic way by connecting the stump to the collar by a shoulder with leave,

- produce a positive mold on which a spacing varnish is deposited,

- constitute, on the positive mold and by projection, a ceramic screed of substantially constant thickness,

- and form a porcelain cap on the yoke, a replica of the tooth to be fitted, using a traditional method. Various other characteristics appear from the description given below with reference to the appended drawings which show, by way of nonlimiting example, an embodiment of the subject of the invention. BRIEF DESCRIPTION OF THE DRAWINGS:

Fig. 1 is a perspective, partly in section, of a new prosthesis according to the invention. Fig. 2 is a partial perspective illustrating

The adaptation of the prosthesis according to fig. 1 on a tooth to be paired.

Figs. 3 to 9 are schematic views illustrating the different phases of implementation of the method according to the invention.

BEST WAY TO IMPLEMENT THE INVENTION:

Fig. 1 shows the new prosthesis according to the invention which is characterized by a yoke 1 made of a powdered material sprayed and melted, having a substantially constant thickness which may be between 0.15 and 0.80 mm.

By pulverulent material, it should be considered, within the meaning of the invention, any ceramic or metallic material, non-ferromagnetic and projectable, such as titanium. By ceramic, it is necessary to consider all materials, monolithic or composite, meeting the characteristics of lightness, hardness, refractoriness, chemical inertia, thermal inertia and possibility of manufacturing from common elements. Among the ceramics meeting these characteristics, it is preferable to cite zirconia and, among this family, that sold under the reference 201 NS by the company METCO.

Such a composition comprises: - Zirconium oxide 93%

- 5% calcium oxide

- 0.5% aluminum oxide

- 0.4% silica dioxide

- Other oxides 0.1% - Complementary components 1% In such a composition having a melting point at 2,535 C, the powder is characterized by a cubic structure and The different oxides The component has a particle size between - 50 and + 10 μm. A yoke 1 of the above type is characterized by an internal surface precisely adapted to the tooth to be fitted.

A screed, such as 1, is completed by a porcelain cap 2, constituted in a conventional manner, that is to say involving a methodology similar to the mounting of such an aluminous porcelain cap on a metal screed.

A prosthesis, of the above type, can be adapted very easily, as illustrated in FIG. 2, by using a sceLLing or bonding method, by using a product, such as a glass-ionomer cement or a known composite bonding resin from those skilled in the art.

A prosthesis of the above type is characterized by very good mechanical strength and by a remarkable aesthetic appearance, due, in particular, to the elimination of the dark border frequently presented at the gingival interstice by prostheses having a metal alloy screed.

To perform a dental prosthesis of the type of fig. 1, the method of the invention consists, first of all, as illustrated by FIG. 3, to prepare a tooth to be fitted, such as I, so as to provide a stump 3 which is connected to the collar 4 by a shoulder at leave 5. Such a preparation, by trimming, is carried out to obtain a reduction occlusal of the homothetic type with the profile of the crown 6, up to the proximity of the collar 4 and over a thickness, for example close to 2.5 mm. The shoulder 5 is executed on the entire periphery over a thickness of 1.2 to 1.5 mm, having an angle of connection to the collar between 90 and 110 relative to a plane such as P, shown schematically in line mixed in fig. 3.

The preparation must be carried out in such a way as to avoid the presence of sharp angles and so as to give the stump 3 a state polished surface.

A second step, illustrated by FIG. 4, consists in making a negative impression 7 of the preparation or of the stump 3 by using traditional methods to do this. The imprint 7, as illustrated in FIG. 4, is, for example, made from usual impression materials.

According to a conventional method, the negative imprint 7 is used, as shown in FIG. 5, for obtaining a positive model 8, for example in plaster. Such a model 8, generally called the master model, is executed to preserve and preserve the shape of the preparation or of the stump 3 and is used to produce a duplicate positive model used for making the screed 1. For such a purpose, the master -model 8 is coated with a spacing varnish 9 deposited on a uniform thickness of approximately 20 μm, up to approximately 1 to 2 mm below the edge 10 reproducing that of connection between the collar 4 and the 'shoulder 6 of tooth I. Preferably, the layer of spacer varnish stops at the start of the leave. Such a spacing varnish is chosen from the usual conventional supplies. We then proceed to the constitution, over the spacing varnish 9, of a duplicative mass 11 intended to provide a negative imprint of the type produced by the imprint 7 of FIG. 4. The duplicative mass is generally made up of a material, such as that sold under the name VITA HI-CERAM by the VITA Company. Such material is prepared and deposited in accordance with the manufacturer's instructions regarding the method of constituting the duplicative mass 11 and the duration of hardening or polymerization. After demolding, it is important to carefully examine the internal peripheral surface of the negative duplication impression obtained, in order to check the presence or existence of surface defects. A "smooth" surface, free of bubbles, must imperatively be sought in order to proceed to the next operating phase consisting in filling the negative duplication imprint. with suitable refractory material to produce a duplicate positive mold 13, such as that shown in FIG. 7. The raw material used is, for example, that marketed by VITA. In general, use is made of a mixing or kneading with a spatula of the various components which must be brought together to obtain a paste which is deposited in the duplication impression.

The phase of obtaining the mold 13 is followed, before the duplicated mold has reached its hardening stage, by the installation of a pin 14 made of a refractory material, for example constituted by a cylindrical rod which is arranged to be coaxial with the axis _x_ of the stump 3 or of the preparation. The pin 14 is engaged so that its internal end is always placed at a distance from the stump 3 and, for example, between 4 to 6 mm.

The hardening conditions must take into account the manufacturer's instructions and be strictly followed to avoid any distortion detrimental to the quality of reproducibility of the duplicated model. After hardening, the duplicated model 13 is extracted from

The duplication impression to be subjected to a usual heat treatment phase, then to a preparation phase consisting in applying to it a layer of spacing varnish 15 deposited on a constant thickness of a few micrometers and always below the leave. Such a varnish is, for example, a refractory plaster milk sold by the company VITA. Such a varnish can be, for example, applied with a brush. The function of this spacing varnish is to produce a glossy surface, obscuring the surface micro-defects likely to be presented and to constitute a second thickness of spacing with respect to the first having been provided, due to the presence of Layer 9. Layer 15 is left to harden, then is subjected to a heat treatment according to the manufacturer's instructions. An important phase of the process then consists in make the screed 1 in ceramic. To this end. The positive duplicate mold 13 is adapted, by the spindle 14, to the mandrel 16 of a machine not shown capable of driving it in rotation on its axis. The machine is arranged so that the JK axis. of the model 13 makes an angle α between 20 and 50 with respect to the y axis of a torch 17, of known type, for example a plasma torch or any other projection device (flame projection, etc.). The torch 17 is supplied with a pulverulent composition, of the type described above and, in particular, by that sold under the reference 201 NS from the company METCO. The plasma projection, in order to produce the screed 1, is carried out using the following parameters:

- plasma gas flow rate, such as argon 30 l / min

- powder flow 12.5 g / min - distance between the duplicated mold 13 and the torch 17. 115 mm

- torch power 30 kW

- plasma gas pressure 0.13

The projection is carried out by rotating the mold 13 by the mandrel 16 at 4,000 rpm and by planning to move the mold relatively relative to the torch, so as to carry out a deposition of ceramic in several successive passes, for example 3 or 4 passes, making it possible to form the yoke 1 under the desired thickness, between 0.15 and 0.80 mm.

The above parameters allow the creation of a yoke 1 in about 30 seconds, after which the torch 17 is deactivated, without interrupting the rotation of the mandrel 16, so as to produce a slow and homogeneous cooling of the yoke 1 , in order to avoid, by internal tension, the appearance of structural defects, such as fractures, cracks. After cooling, the screed 1 obtained is completed by the formation, on its outer face, of the ceramic cap 2. The method used is, generally, that used for making ceramic prostheses and must be considered as possessed by Man of art. It is important, however, to specify that the mounting of the cap 2 is carried out on a yoke 1 in ceramic having, consequently, a low coefficient of expansion for temperature variations between 20 and 1000 C. In order to avoid damage to the yoke 1 When the material constituting the yoke 2 is cooling, iL is necessary proceed to the prior constitution of a bonding prelayer 20 by depositing several superimposed sublayers, for example three, of an aluminous opaque milk, rich in alumina, known under the English term "OPAQUER", which undergoes a cooking phase up to approximately 1,120. Prior to the baking phase, shrinkage preferences are provided in each sub-layer by proceeding, for example, with a fine spatula.

After baking of the aluminous opaque layers, the yoke 1 is removed from the mold 13 to undergo a machining phase of its skirt 18 brought back in coincidence with the edge 10. The yoke 1 is presented, as illustrated by FIG. . 9, in the definitive form of exact adaptation to the preparation or stump 3 of tooth I. The delimitation of the internal form, deduced from preparation 3, is, however, not identical to the latter, due to the prior presence layers of varnish 10 and 15 which make it possible to spare, as illustrated in FIG. 2, an interval 19 allowing the interposition, during assembly, of a layer or thickness of bonding or sealing material. The interval 19 is, however, of small importance and is spared by an internal surface condition of the yoke 1, rigorously homothetic to the preparation or to the stump 3, given the absence of dimensional distortions occurring during manufacturing. of screed 1, due to the use of the constitution of the latter by plasma projection.

Next, the cap 2 is made from an aluminous ceramic, usually used by following the usual prescriptions for this confection. The final prosthesis, as shown in fig. 1 is then obtained and can be implemented in the traditional way. A variant of the process consists in forming the yoke 1 in proceeding from the master mold, without providing for the production of the duplicated mold.

Another variant consists in reinforcing the mechanical strength of the screed by coating it, before the deposition of the opaque layers, with a layer of slip of silica and short fibers (type WHIS ERS, etc., in alumina, silicon, carbide silicon, silicon carbonitride). This slip is baked at around 1200 C for approximately 4 hours. An overshield is then projected to cover the layer of cooked slip, so as to obtain a laminated screed. The overshield is executed as said previously and then undergoes the phases already described for a simple projected screed.

The invention is not limited to the examples described and shown, since various modifications can be made without departing from its scope.

POSSIBILITY OF INDUSTRIAL APPLICATION:

The present invention finds a particularly interesting industrial application in the field of crowns, abutments and esthetic caps.

Claims

CLAIMS:

1 - Fixed dental prosthesis, of the type comprising a screed (1) covered with a porcelain cap (2), characterized in that the screed is made of a projected and partially molten material. 2 - Prosthesis according to claim 1, characterized in that the yoke is made of ceramic.

3 - Prosthesis according to claim 1, characterized in that the yoke is made of titanium.

4 - Prosthesis according to claim 1, characterized in that the yoke has a thickness between 0.15 and 0.80 mm.

5 - A method of making a fixed dental prosthesis, simple or complex, according to claim 1 or 4, of the type consisting in trimming a tooth to be fitted, in order to spare a stump, at. make a negative mold from this stump and produce a positive mold from this negative mold, characterized in that it consists of:

- contour The tooth in a homothetic way by connecting the stump (3) to the collar (4) by a shoulder with leave (5), - produce a positive mold (8, T3) On which a spacing varnish (15) is deposited ,

- constitute, on the positive mold and by projection, a screed (1) made of ceramic of substantially constant thickness, - and form on the screed a cap (2) made of porcelain, replica of the tooth to be fitted, using a method traditional.

6 - Method according to claim 5, characterized in that one produces, from the positive mold, called master mold, a replica model (8) on which is applied a spacing varnish (9 ⁾ .

7 - Method according to claim 5 or 6, characterized in that, during the projection, the positive mold is rotated on the axis Cx) of the stump. 8 - Method according to claim 7, characterized in that that the axis of rotation of the mold makes an angle between 20 and

50 ° from the projection direction.

9 - Method according to claim 5, 7 or 8, characterized in that the projection is carried out by scanning in several successive passes.

10 - Method according to one of claims 5, 7, 8 or 9, characterized in that the projection is carried out by maintaining a distance between 50 and 200 mm between the mold and the projection apparatus. 11 - Method according to one of claims 5 or 7 to 10, characterized in that the projection is ensured from a pulverulent mixture of Zr0 -, - Ca0 of particle size between

- 50 and + 10 ym.

12 - Method according to one of claims 5 or 7 to 11, characterized in that the projection is provided from a plasma gas consisting of argon or hydrogen.

13 - Method according to one of claims 5 or 7 to 12, characterized in that the plasma projection is ensured by involving the following parameters: - plasma gas flow rate Ar 30 l / min

- powder flow 12.5 g / min

- distance 115 mm

- torch power 30 kW

- plasma gas pressure 0.13 - mold rotation 4,000 rpm

- scan 3

14 - Method according to one of claims 10 to 13, characterized in that the screed is covered with a layer of slip, silica and fibers, this layer of slip is baked and an overspray is formed by projection.

15 - A method according to claim 5 or 14, characterized in that The formation of the porcelain cap, on the screed or the overlay, involves the formation of a prelayer based on baked aluminous opaque. 16 - Method according to claim 15, characterized in that that the precoat is obtained by depositing several sublayers in each of which, before cooking, shrink prefentes are cleaned.

17 - Process according to claim 15, characterized in that the skirt of the yoke and / or the overshield is machined to make its edge coincide with the connection edge between the preparation and the collar of the tooth to be fitted.