WO2001010336A1 - Method and apparatus for the photopolymerization of a mass for reconstructing a dental prosthesis - Google Patents

Method and apparatus for the photopolymerization of a mass for reconstructing a dental prosthesis Download PDF

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Publication number
WO2001010336A1
WO2001010336A1 PCT/FR2000/002246 FR0002246W WO0110336A1 WO 2001010336 A1 WO2001010336 A1 WO 2001010336A1 FR 0002246 W FR0002246 W FR 0002246W WO 0110336 A1 WO0110336 A1 WO 0110336A1
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Prior art keywords
polymerization
irradiation
mass
light
photochemical
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PCT/FR2000/002246
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French (fr)
Inventor
Arnaud Delahaye
Didier Poussin
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Arnaud Delahaye
Didier Poussin
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Application filed by Arnaud Delahaye, Didier Poussin filed Critical Arnaud Delahaye
Priority to EP00956619A priority Critical patent/EP1202680A1/en
Priority to AU68503/00A priority patent/AU6850300A/en
Publication of WO2001010336A1 publication Critical patent/WO2001010336A1/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C19/00—Dental auxiliary appliances
    • A61C19/003—Apparatus for curing resins by radiation

Definitions

  • “latest generation composite material” is used to refer to composite materials used for making dental prostheses and in particular described in document EP-B-0 667 765. This document describes the application of composite materials to the mass for restoring dental prostheses, this mass, after polymerization, having a flexural strength at least equal to 100 MPa and a Vickers hardness at least equal to 450 N / mm 2 .
  • Latest generation composite materials are, for example, the "Colombus” and "Cristobal” materials from International Dental Research.
  • Such a “latest generation composite material” has a polymeric binder formed by photochemical polymerization of monomers containing methacrylate esters.
  • a mineral filler contained in the polymeric binder is in the form of a finely ground borosilicate glass, having an average particle size of between 0.02 and 2 ⁇ m, possibly with a small proportion of silica, advantageously treated with a silane. .
  • This "latest generation composite material” has a flexural strength and Vickers hardness which are markedly increased when it is subjected to prolonged irradiation annealing, after the polymerization of the polymeric binder.
  • the flexural strength increases from 25 to 30% by annealing.
  • the hardness increases by about 20% by annealing.
  • photopolymerization apparatuses for composite materials of previous generations that is to say composite materials which do not have flexural strength properties, were already known. and of sufficient hardness for the mass of reconstitution of real prostheses. These composite materials were mainly used for dental restorations.
  • a "Labolight LV” device described in document US-A-4 645 649 was known and comprising a housing in which a turntable rotates on which are placed one or more dental restorations which thus pass in front of fluorescent lamps intended to cause minimum internal heating of the restorative mass of dental restorations.
  • the documentation accompanying the device indicates that this minimum internal heating is obtained on the one hand by ventilation and on the other hand by "special" fluorescent lamps with cathode emission by electric field.
  • Document US-A-4 645 649 specifies that the lamps can be of any type capable of giving radiation of activation energy.
  • the documentation for this device indicates in particular that other known devices, such as "Dentacolor XS" and "Morita", having xenon or halogen lamps, cause excessive heating of the reconstitution mass during photopolymerization.
  • FIG. 2 represents the emission spectrum 1 of the cold cathode lamp of the "Biophoton” device and the emission spectrum 2 of a halogen lamp.
  • the spectrum of the halogen lamp increases regularly towards long wavelengths, in accordance with the emission spectrum of so-called "incandescent" lamps.
  • This controlled polymerization preferably uses light essentially between 460 and 520 nm and preferably having a maximum of the emission spectrum between 480 and 500 nm.
  • the inventor then determined the conditions under which these characteristics should be used, and he thus discovered a method and an apparatus which give particularly optimal results on composite materials of the latest generation.
  • the invention relates, in a first aspect, to a process for the polymerization of a reconstitution mass of a dental prosthesis which comprises a support and at least one reconstitution mass fixed to the support, the reconstitution mass being formed, at least for the most part, superimposed layers of a composite material containing a polymeric binder in which a mineral filler is dispersed and which, after polymerization, has a flexural strength at least equal to 100 MPa and a Vickers hardness at less than 450 N / mm 2 , the method being of the type which comprises a step in which the reconstitution mass undergoes polymerization by irradiation with visible light.
  • the method comprises, for each layer, a first essentially photochemical polymerization step at low temperature until the polymerization rate of the layer reaches about 50 to 60%, and a second essentially thermal polymerization step comprising a heating of the layer to a temperature above the glass transition temperature, for a time sufficient for the polymerization rate to increase by approximately 10%, then, for several layers or all the layers, an additional photochemical annealing step and thermal simultaneously, such that the rate of polymerization further increases by at least 10%.
  • the first essentially photochemical polymerization step is carried out by irradiation with visible light, most of the spectral energy of which is between 460 and 520 nm. It is advantageous that, during the first step, the temperature of the layer is less than 35 ° C., and the duration of the step is of the order of 1 to 2 min.
  • the temperature is greater than approximately 50 ° C., and this second stage has a duration of approximately 1 to 2 min.
  • the additional step of photochemical and thermal annealing is advantageously carried out at a temperature of the reconstitution mass of between approximately 90 and 140 ° C. and it has a duration of at least 5 min.
  • a layer of the reconstitution mass may be formed of several sublayers which each undergo the first photochemical polymerization step, but which only undergo the second thermal polymerization step when all the sublayers of the layer have been superimposed.
  • the invention also relates, in a second aspect, to an apparatus for polymerizing a restoring mass of a dental prosthesis which comprises a support and at least one restoring mass fixed to the support, the mass of reconstitution being formed, at least for the most part, of a composite material containing a polymeric binder in which a mineral filler is dispersed, the apparatus comprising an apparatus for irradiating the composite material with polymerization light.
  • the device for irradiation with polymerization light comprises a first device for photochemical irradiation with light, the major part of the spectral energy of which is between 460 and 520 nm, and a second device. irradiation emitting a continuous spectrum at least in the visible and intended to ensure a mainly thermal polymerization, and the apparatus further comprises a prosthesis displacement device in front of the two irradiation devices.
  • the first irradiation device is a fluorescent lamp with electric field emission, and the maximum of the spectrum of the first irradiation device is between 480 and 500 nm.
  • the second irradiation device is a halogen lamp.
  • the apparatus includes a device for mounting the first irradiation device and the second irradiation device such that, during most of the first irradiation step, the composite material is not irradiated with light from the second irradiation device.
  • the apparatus comprises a control device intended to control the first irradiation device and the second irradiation device separately, each for a time and with an intensity which are suitable for the corresponding step of polymerization of the composite material.
  • the apparatus may include an irradiation regulation device intended to irradiate the reconstitution mass in at least half of the solid angle of the entire space.
  • This irradiation regulation device may include a reflector device which envelops a radiation irradiation chamber. the device intended to contain the prosthesis having the reconstruction mass.
  • This irradiation regulation device may also include a device intended to move the prosthesis in the irradiation chamber of the device, preferably a turntable which moves the prosthesis in front of the irradiation device.
  • the invention also relates, in a third aspect, to a set of irradiation apparatus which comprises on the one hand a first polymerization apparatus as defined in the preceding paragraphs, and on the other hand a second irradiation apparatus by annealing light.
  • This second device for irradiation with annealing light advantageously comprises at least one halogen lamp.
  • the first device is intended to ensure the polymerizations of the first two steps of the process according to the invention, and the second device is intended to carry out the additional annealing step.
  • FIG. 1 previously described, represents the emission spectrum of a fluorescent lamp from the device
  • FIG. 2 represents the emission spectrum of the lamps of a “Biophoton” device; and FIG. 3 represents the emission spectrum of an irradiation device according to the invention.
  • the subject of the invention is the determination of the polymerization conditions which give the best results with the latest generation composite materials for dental prostheses, so that the properties of the prostheses produced are increased and that the duration and the cost of the polymerization cycles of the prostheses dental can be reduced, and the means to obtain them.
  • a bonding layer often based on acid and methacrylic esters, is formed by treatment of the support. Then a layer called "opaque" is applied.
  • This layer which may be double, comprises for example a very opaque material intended to hide the color of the metal of the support.
  • Each layer has for example a thickness of 100 ⁇ ⁇ .
  • Each layer is polymerized separately, preferably at a temperature which hardly exceeds the temperature of use of a prosthesis in the mouth.
  • This mass is built up in successive layers. These layers are relatively thin, because they hardly ever exceed 2 mm in thickness and most often have a thickness of a few tenths of a millimeter. The layers, after polymerization of each of them, are built one on top of the other until a final stage of polymerization.
  • this layer is subjected to a first and then to a second polymerization step.
  • the first polymerization step is an essentially photochemical polymerization step, and it is carried out at low temperature below 35 ° C, preferably at room temperature.
  • the irradiation is preferably carried out with light having a spectrum of which most of the energy is between 460 and 520 nm.
  • This first polymerization step lasts long enough for the polymerization rate of the layer material to reach a value of the order of 50 to 60%. This time is generally of the order of 1 to 2 min.
  • the layer undergoes a second, especially thermal, polymerization step which involves heating of the layer to a temperature above 50 ° C.
  • the irradiation is preferably carried out with light a halogen lamp. Its duration is generally of the order of 1 to 2 min.
  • This second thermal polymerization step increases the polymerization rate of the reconstitution mass by approximately 10%.
  • the process comprises an additional step of both photochemical and thermal annealing. More precisely, the entire mass for reconstituting the prosthesis is photochemically irradiated and heated, to a temperature preferably between 90 and 140 ° C., for example of the order of 120 ° C. This temperature is greater than or equal to the glass transition temperature of the material. This additional annealing step increases the polymerization rate of the reconstitution mass by at least 10%.
  • the photochemical irradiation used in the first step can comprise a simple irradiation with light having a spectrum of which the largest part of the energy is between 460 and 520 nm and the maximum of which is preferably between 480 and 500 nm .
  • This first irradiation step is preferably carried out with one or more fluorescent lamps with electric field emission.
  • the advantage of emission by electric field is not new since it has already been implemented in the aforementioned device "Labolight LV" and other known devices.
  • the important feature is that this first photopolymerization step (creation of free radicals, essentially peroxide) must be carried out at low temperature.
  • This condition of photopolymerization at low temperature is advantageously combined with a second new characteristic which is irradiation with light, most of the spectral energy of which is between 460 and 520 nm.
  • cathode fluorescent lamps working by emission by electric field give a combination of the aforementioned characteristics (low heating of the material, spectrum essentially between 460 nm and 520 nm).
  • the cathode working by emission by electric field reduces the heating of the lamp in which the cathode emits electrons towards vapors of mercury, present in small quantity in the lamp.
  • the mercury atoms, excited by the electrons coming from the cathode emit ultraviolet radiation (essentially at 254 nm) which arrives on an electroluminescent material carried by the walls of the body of the lamp. This electroluminescent material, excited by ultraviolet rays from mercury atoms, emits visible fluorescent light.
  • This electroluminescent material is preferably chosen so that the greatest amount of visible light is emitted between 460 and 520 nm and that the maximum emission is between 480 and 500 nm.
  • Such an electroluminescent material once the desired spectrum is known, can be easily determined by a person skilled in the art, in this case specialists in atomic emission lamps.
  • An example giving a useful spectrum in the context of the invention contains, in addition to europiu and other rare earth elements, tantalum, strontium or zirconium compounds.
  • the second thermal polymerization step is advantageously carried out with a simple halogen lamp, for example a 300 W lamp, fitted with an overhead projector.
  • a simple halogen lamp for example a 300 W lamp
  • Such a lamp has a significant thermal effect on the composite material (heating), but also contains radiation with photochemical action on the material.
  • the device used for carrying out this process is preferably a single device which successively performs the two steps, ie that is to say first the photochemical polymerization step, then the especially thermal polymerization step. It is therefore important that these steps are carried out successively and not simultaneously.
  • the appliance comprises a irradiation control device so that the composite material is irradiated in at least half of the solid angle of the entire space.
  • the regulation device can be either passive or active, or a combination of active and passive devices.
  • a passive device essentially comprises one or more reflectors which surround the irradiation chamber. It is possible, for example, to use known devices for mounting reflectors which, depending on the geometrical configuration of the light source, allow omnidirectional irradiation. We know for example the use of cylinders of ellipsoidal section, having a light source at one focal point and one element to be irradiated at the other focal point. This arrangement is suitable for photopolymerization by omnidirectional irradiation of a single prosthesis of relatively small extent.
  • the radiation regulation device may also include a device for moving the prosthesis with respect to one or more lamps, so that the various parts of the prosthesis are irradiated in a relatively homogeneous manner.
  • a device for moving the prosthesis with respect to one or more lamps so that the various parts of the prosthesis are irradiated in a relatively homogeneous manner.
  • the device advantageously includes a suitable control device which can be of known type and which is therefore not described in detail.
  • This control device can control all the active components of the device, in particular the first irradiation device, the second irradiation device and, if necessary, the displacement device.
  • This control device can, for example, separately adjust the time and intensity of each of the irradiation devices, and can control any desired treatment cycle by combining the controls of the various components in the manner that best suits the polymerization of the material. composite. Each treatment cycle can then be best adapted to the particular layer of material to be polymerized.
  • the whole of the mass is subjected to an additional stage of polymerization, both photochemical and thermal.
  • This step is preferably carried out in a separate device. Indeed, it is desirable for the reconstitution mass to reach a relatively high temperature since this temperature must be greater than the glass transition temperature of the composite material, reaching, for such polymerization rates, a value which is generally between 90 and 140 ° C, for example of the order of 120 ° C.
  • the duration of this additional step of both photochemical and thermal polymerization is at least 5 min and preferably of the order of 10 min. As it is only used once for the entire prosthesis, it does not excessively lengthen the duration of the total manufacturing process.
  • the device used can be a special oven, for example provided with three very common halogen lamps "ELH" from Philips, each having a power of 100 W.
  • the lamps are advantageously placed in a triangle so that the prosthesis is irradiated in several directions and can thus undergo a relatively homogeneous treatment.
  • the invention also relates to a set of apparatuses for carrying out the method of the invention and comprising a first apparatus which ensures the photochemical polymerization and the thermal polymerization of each layer, and a second apparatus which ensures the additional step final annealing. It has been realized that the prostheses produced by the process according to the invention had a fracture toughness at least 80% greater than that of the masses for reconstituting composite materials produced without carrying out the process. It should be noted that this fracture toughness obtained using the process of the invention is also almost 50% higher than that of the best ceramics for dental application.
  • the reconstitution masses obtained by the process of the invention have a wear resistance greater by a factor at least equal to 2.2 than that given by the composite materials polymerized by the conventional processes.
  • the method of the invention implements steps which minimize these withdrawals.
  • the photochemical polymerization at low temperature allows a reduction in physical shrinkage since the mass undergoes practically no rise in temperature in the first step.
  • the material can have a constant rearrangement, so that the final shrinkage obtained is very low.
  • the total shrinkage after the end of the polymerization is always less than 2.5% and in general of the order of 1.9 at 2.2%.
  • Composite materials of other embodiments exhibit shrinkages of the order of 4.5 to 5% and which are never less than 3.3%. This reduction in the withdrawal of the reconstitution mass greatly reduces the stresses existing at the interface of the mass and the support.
  • the invention allows the production of dental prostheses whose durability is greatly increased compared to prostheses produced by other methods, because, for a given material, the shrinkage is greatly reduced and the toughness is significantly increased. These two phenomena combine to considerably increase the durability of prostheses when they are subjected to the stresses which are applied to them during use. It should also be noted the reduction in wear which is due in particular to an increase in hardness obtained simultaneously by implementing the method of the invention.
  • the invention relates to improvements to the methods and apparatuses applicable to the dental prosthesis manufacturing industry.

Abstract

The invention concerns composite materials. It concerns an apparatus for polymerising a dental prosthesis comprising a support and a reconstruction mass attached to the support and formed, for the major part, of a composite material containing a polymeric binder wherein is dispersed a mineral filler. The apparatus comprises a first device for irradiating the composite material with polymerising light whereof the major part of the spectral energy ranges between 460 and 520 nm and which provides a polymerising index between 50 and 60 %, and a second device irradiating with polymerising, particularly thermal, light which increases the polymerisation rate by about 10 %. The material is then annealed. The invention is useful for making dental prostheses.

Description

Procédé et appareil de photopolvmérisation d'une masse de reconstitution d'une prothèse dentaireMethod and apparatus for photopolvmerization of a reconstruction mass of a dental prosthesis
La présente invention concerne un procédé et un appareil de polymérisation de matériaux composites de dernière génération entrant dans la composition de la masse de reconstitution de prothèses dentaires.The present invention relates to a process and an apparatus for polymerizing last generation composite materials used in the composition of the mass for restoring dental prostheses.
Dans le présent mémoire, on appelle "matériau composite de dernière génération" des matériaux composites utilisés pour la confection de prothèses dentaires et notamment décrits dans le document EP—Bl—0 667 765. Ce document décrit l'application de matériaux composites à la masse de reconstitution de prothèses dentaires, cette masse, après polymérisation, ayant une résistance à la flexion au moins égale à 100 MPa et une dureté Vickers au moins égale à 450 N/mm2. Des matériaux composites de dernière génération sont par exemple les matériaux "Colombus" et "Cristobal" de International Dental Research.In the present specification, “latest generation composite material” is used to refer to composite materials used for making dental prostheses and in particular described in document EP-B-0 667 765. This document describes the application of composite materials to the mass for restoring dental prostheses, this mass, after polymerization, having a flexural strength at least equal to 100 MPa and a Vickers hardness at least equal to 450 N / mm 2 . Latest generation composite materials are, for example, the "Colombus" and "Cristobal" materials from International Dental Research.
Un tel "matériau composite de dernière génération" a un liant polymère formé par polymérisation photochimique de monomères contenant des mëthacrylates esters. Une charge minérale contenue dans le liant polymère est sous forme d'un verre de borosilicate finement broyé, ayant une dimension particulaire moyenne comprise entre 0,02 et 2 μm, avec éventuellement une petite proportion de silice, avanta- geuse ent traitée par un silane.Such a "latest generation composite material" has a polymeric binder formed by photochemical polymerization of monomers containing methacrylate esters. A mineral filler contained in the polymeric binder is in the form of a finely ground borosilicate glass, having an average particle size of between 0.02 and 2 μm, possibly with a small proportion of silica, advantageously treated with a silane. .
Pour l'obtention de la dureté nécessaire du "matériau composite de dernière génération", la quantité de charge minérale est au moins égale à 50 % en volume et à 70 % en poids de la masse de reconstitution, et de préférence à 75 % en poids de la masse de reconstitution.To obtain the necessary hardness of the "latest generation composite material", the quantity of mineral filler is at least equal to 50% by volume and to 70% by weight of the reconstitution mass, and preferably to 75% by weight of the reconstitution mass.
Ce "matériau composite de dernière génération" a une résistance à la flexion et une dureté Vickers qui sont nettement accrues lorsqu'il est soumis à un recuit par irradiation prolongée, après la polymérisation du liant polymère. Ainsi, la résistance à la flexion augmente de 25 à 30 % par recuit. De même, la dureté augmente de 20 % environ par recuit. Antérieurement aux enseignements du document précité EP—Bl—0 667 765, on connaissait déjà des appareils de photopolymérisation de matériaux composites de générations précédentes, c'est-à-dire de matériaux composites ne possé- dant pas des propriétés de résistance à la flexion et de dureté suffisantes pour la masse de reconstitution de véritables prothèses. Ces matériaux composites étaient essentiellement utilisés pour des restaurations dentaires. Ainsi, on connaissait un appareil "Labolight LV" décrit dans le document US—A—4 645 649 et comprenant un boîtier dans lequel tourne un plateau tournant sur lequel sont disposées une ou plusieurs restaurations dentaires qui défilent ainsi devant des lampes fluorescentes destinées à provoquer un chauffage interne minimal de la masse de reconstitution des restaurations dentaires. La documentation accompagnant l'appareil indique que cet échauffement interne minimal est obtenu d'une part par ventilation et d'autre part grâce à des lampes fluorescentes "spéciales" à émission cathodique par champ électrique. Le document US—A—4 645 649 précise que les lampes peuvent être de tout type capable de donner le rayonnement d'énergie d' activation. En outre, la documentation de cet appareil indique en particulier que d'autres appareils connus, tels que "Dentacolor XS" et "Morita" , ayant des lampes à xénon ou des lampes à halogène, provoquent un échauffement excessif de la masse de reconstitution pendant la photopolymêrisation.This "latest generation composite material" has a flexural strength and Vickers hardness which are markedly increased when it is subjected to prolonged irradiation annealing, after the polymerization of the polymeric binder. Thus, the flexural strength increases from 25 to 30% by annealing. Similarly, the hardness increases by about 20% by annealing. Prior to the teachings of the abovementioned document EP-B1-0 667 765, photopolymerization apparatuses for composite materials of previous generations, that is to say composite materials which do not have flexural strength properties, were already known. and of sufficient hardness for the mass of reconstitution of real prostheses. These composite materials were mainly used for dental restorations. Thus, a "Labolight LV" device described in document US-A-4 645 649 was known and comprising a housing in which a turntable rotates on which are placed one or more dental restorations which thus pass in front of fluorescent lamps intended to cause minimum internal heating of the restorative mass of dental restorations. The documentation accompanying the device indicates that this minimum internal heating is obtained on the one hand by ventilation and on the other hand by "special" fluorescent lamps with cathode emission by electric field. Document US-A-4 645 649 specifies that the lamps can be of any type capable of giving radiation of activation energy. In addition, the documentation for this device indicates in particular that other known devices, such as "Dentacolor XS" and "Morita", having xenon or halogen lamps, cause excessive heating of the reconstitution mass during photopolymerization.
Les appareils précités ont été réalisés pour les matériaux composites de générations antérieures, et, en particulier, l'appareil "Labolight LV" donne un spectre d'émission ayant un maximum du spectre d'émission autour de 450 nm (voir la figure 1 qui représente le spectre d'émission d'une lampe fluorescente de l'appareil "Labolight LV").The aforementioned devices were made for composite materials of previous generations, and, in particular, the "Labolight LV" device gives an emission spectrum having a maximum of the emission spectrum around 450 nm (see FIG. 1 which represents the emission spectrum of a fluorescent lamp from the "Labolight LV" device).
Lors de l'utilisation de matériaux composites de dernière génération pour la réalisation de prothèses den- taires objets du document précité EP—Bl—0 667 765, on s'est rendu compte que les appareils d'irradiation des types précités n'étaient pas bien adaptés à ces matériaux composites de dernière génération. On a donc essayé d'utiliser des appareils donnant des spectres différents. Ainsi, on a proposé un appareil "Biophoton" , comprenant, dans une première chambre, au moins une lampe dite "à cathode froide", c'est-à-dire une lampe à cathode à émission par champ électrique destinée à assurer la polymérisation. L'appareil, qui est décrit dans le document WO 99/39 657 qui n'est opposable au présent mémoire qu'au titre de l'article 54(3) de la CBE, comporte en outre une lampe à halogène destinée à être utilisée dans des "applications spéciales", telles que le "durcissement des matières opaques et la cuisson de finition" . La figure 2 représente le spectre d'émission 1 de la lampe à cathode froide de l'appareil "Biophoton" et le spectre d'émission 2 d'une lampe à halogène. On note deux axima dans le spectre d'émission 1 de la lampe à cathode froide autour de 420 nm et 540 nm. La quantité de lumière émise entre 450 nm et 520 nm est très réduite. Le spectre de la lampe à halogène augmente régulièrement vers les grandes longueurs d'onde, conformément au spectre d'émission des lampes dites "à incandescence".When using the latest generation of composite materials for the production of dental prostheses which are the subject of the aforementioned document EP-B-0 667 765, it has been realized that the irradiation devices of the aforementioned types are not well suited to these latest generation composite materials. We therefore tried to use devices giving different spectra. Thus, a "Biophoton" device has been proposed, comprising, in a first chamber, at least one lamp called "cold cathode", that is to say an electric field emission cathode lamp intended to ensure polymerization. . The apparatus, which is described in document WO 99/39657 which can only be relied on in this specification under Article 54 (3) of the EPC, furthermore comprises a halogen lamp intended for use in "special applications", such as "hardening of opaque materials and finishing firing". FIG. 2 represents the emission spectrum 1 of the cold cathode lamp of the "Biophoton" device and the emission spectrum 2 of a halogen lamp. There are two axima in the emission spectrum 1 of the cold cathode lamp around 420 nm and 540 nm. The amount of light emitted between 450 nm and 520 nm is very small. The spectrum of the halogen lamp increases regularly towards long wavelengths, in accordance with the emission spectrum of so-called "incandescent" lamps.
Cependant, on s'est rendu compte que des prothèses dont la masse de reconstitution est constituée de certains matériaux composites, autres que ceux du document précité EP—Bl—0 667 765, qui sont polymérisës avec les appareils précités, ne possédaient pas la durabilité à long terme nécessaire à cause d'une fracturation à l'interface de la masse de reconstitution et du support.However, it has been realized that prostheses whose reconstitution mass consists of certain composite materials, other than those of the aforementioned document EP-B-0 667 765, which are polymerized with the aforementioned devices, did not have the durability long term necessary due to fracturing at the interface of the reconstruction mass and the support.
L'inventeur a étudié ce problème et en a attribué la cause à de mauvaises conditions de polymérisation. Il s'est alors rendu compte qu'il était possible d'obtenir de meilleurs résultats, c'est-à-dire une résistance à la flexion et une dureté Vickers accrues, avec une réduction de la durée des temps de traitement par utilisation d'un procédé de "polymérisation ménagée" en plusieurs étapes. Cette polymë- risation ménagée met en oeuvre de préférence de la lumière essentiellement comprise entre 460 et 520 nm et ayant de préférence un maximum du spectre d'émission entre 480 et 500 nm. Cette découverte est surprenante dans la mesure où les photons de la lumière des lampes fluorescentes de l'appareil "Labolight LV" et des lampes de l'appareil "Biophoton" ont une énergie supérieure à celle des photons de la lumière comprise entre 460 et 520 nm, alors que les spectres d'absorption des matériaux composites de dernière génération sont très semblables à ceux des matériaux composites des générations précédentes .The inventor has studied this problem and attributed the cause to poor polymerization conditions. He then realized that it was possible to obtain better results, that is to say increased flexural strength and Vickers hardness, with a reduction in the duration of the treatment times by using d 'a process of "gentle polymerization" in several stages. This controlled polymerization preferably uses light essentially between 460 and 520 nm and preferably having a maximum of the emission spectrum between 480 and 500 nm. This discovery is surprising since the photons of light from fluorescent lamps of the "Labolight LV" device and lamps from the "Biophoton" device have an energy higher than that of photons of light between 460 and 520 nm, while the absorption spectra of last generation composite materials are very similar to those of composite materials of previous generations.
L'inventeur, ayant noté que les concepteurs des appa- reils "Labolight LV" avaient déjà observé qu'il était essentiel d'éviter une élévation excessive de température du matériau composite pendant la polymérisation, et ayant lui- même observé que la lumière comprise entre 460 et 520 nm était bien plus efficace pour la photopolymérisation que la lumière aussi bien de plus courte que de plus grande longueur d'onde, en a déduit que, pour la polymérisation des masses de reconstitution des prothèses, il était avantageux d'utiliser des lampes fluorescentes à cathode à émission par champ électrique émettant de la lumière essentiellement entre 460 et 520 nm et ayant de préférence un maximum du spectre d'émission entre 480 et 500 nm.The inventor, having noted that the designers of the “Labolight LV” devices had already observed that it was essential to avoid an excessive rise in temperature of the composite material during polymerization, and having himself observed that the light included between 460 and 520 nm was much more effective for photopolymerization than light, both shorter than longer wavelength, deduced therefrom that, for the polymerization of the masses for restoring prostheses, it was advantageous to use cathode fluorescent lamps with electric field emission emitting light essentially between 460 and 520 nm and preferably having a maximum of the emission spectrum between 480 and 500 nm.
L'inventeur a alors déterminé les conditions dans lesquelles il convenait d'utiliser ces caractéristiques, et il a ainsi découvert un procédé et un appareil qui donnent des résultats particulièrement optimaux sur les matériaux composites de la dernière génération.The inventor then determined the conditions under which these characteristics should be used, and he thus discovered a method and an apparatus which give particularly optimal results on composite materials of the latest generation.
Plus précisément, l'invention concerne, dans un premier aspect, un procédé de polymérisation d'une masse de reconstitution d'une prothèse dentaire qui comprend un support et au moins une masse de reconstitution fixée au support, la masse de reconstitution étant formée, pour sa plus grande partie au moins, de couches superposées d'un matériau composite contenant un liant polymère dans lequel est dispersée une charge minérale et qui, après polymérisation, a une résistance à la flexion au moins égale à 100 MPa et une dureté Vickers au moins égale à 450 N/mm2, le procédé étant du type qui comprend une étape dans laquelle la masse de reconstitution subit une polymérisation par irradiation par de la lumière visible. Selon l'invention, le procédé comprend, pour chaque couche, une première étape de polymérisation essentiellement photochimique à basse température jusqu'à ce que le taux de polymérisation de la couche atteigne environ 50 à 60 %, et une seconde étape de polymérisation essentiellement thermique comprenant un échauffement de la couche à une température supérieure à la température de transition vitreuse, pendant un temps suffisant pour que le taux de polymérisation augmente d'environ 10 %, puis, pour plusieurs couches ou toutes les couches, une étape supplémentaire de recuit photochimique et thermique simultanément, telle que le taux de polymérisation augmente encore d'environ 10 % au moins.More specifically, the invention relates, in a first aspect, to a process for the polymerization of a reconstitution mass of a dental prosthesis which comprises a support and at least one reconstitution mass fixed to the support, the reconstitution mass being formed, at least for the most part, superimposed layers of a composite material containing a polymeric binder in which a mineral filler is dispersed and which, after polymerization, has a flexural strength at least equal to 100 MPa and a Vickers hardness at less than 450 N / mm 2 , the method being of the type which comprises a step in which the reconstitution mass undergoes polymerization by irradiation with visible light. According to the invention, the method comprises, for each layer, a first essentially photochemical polymerization step at low temperature until the polymerization rate of the layer reaches about 50 to 60%, and a second essentially thermal polymerization step comprising a heating of the layer to a temperature above the glass transition temperature, for a time sufficient for the polymerization rate to increase by approximately 10%, then, for several layers or all the layers, an additional photochemical annealing step and thermal simultaneously, such that the rate of polymerization further increases by at least 10%.
De préférence, la première étape de polymérisation essentiellement photochimique est effectuée par irradiation par de la lumière visible dont la plus grande partie de l'énergie spectrale est comprise entre 460 et 520 nm. Il est avantageux que, au cours de la première étape, la température de la couche soit inférieure à 35 °C, et la durée de l'étape soit de l'ordre de 1 à 2 min.Preferably, the first essentially photochemical polymerization step is carried out by irradiation with visible light, most of the spectral energy of which is between 460 and 520 nm. It is advantageous that, during the first step, the temperature of the layer is less than 35 ° C., and the duration of the step is of the order of 1 to 2 min.
De préférence, au cours de la seconde étape de polymérisation thermique de la couche, la température est supérieure à 50 °C environ, et cette seconde étape a une durée d'environ 1 à 2 min. L'étape supplémentaire de recuit photochimique et thermique est avantageusement exécutée à une température de la masse de reconstitution comprise entre 90 et 140 °C environ et elle a une durée d'au moins 5 min.Preferably, during the second stage of thermal polymerization of the layer, the temperature is greater than approximately 50 ° C., and this second stage has a duration of approximately 1 to 2 min. The additional step of photochemical and thermal annealing is advantageously carried out at a temperature of the reconstitution mass of between approximately 90 and 140 ° C. and it has a duration of at least 5 min.
Dans une variante, une couche de la masse de recon- stitution peut être formée de plusieurs sous-couches qui subissent chacune la première étape de polymérisation photochimique, mais qui ne subissent la seconde étape de polymérisation thermique que lorsque toutes les sous-couches de la couche ont été superposées . L'invention concerne aussi, dans un second aspect, un appareil de polymérisation d'une masse de reconstitution d'une prothèse dentaire qui comprend un support et au moins une masse de reconstitution fixée au support, la masse de reconstitution étant formée, pour sa plus grande partie au moins, d'un matériau composite contenant un liant polymère dans lequel est dispersée une charge minérale, l'appareil comprenant un appareil d'irradiation du matériau composite par de la lumière de polymérisation. Selon l'invention, le dispositif d'irradiation par de la lumière de polymérisation comporte un premier dispositif d'irradiation photochimique par de la lumière dont la plus grande partie de l'énergie spectrale est comprise entre 460 et 520 nm, et un second dispositif d'irradiation émettant un spectre continu au moins dans le visible et destiné à assurer une polymérisation surtout thermique, et l'appareil comporte en outre un dispositif de déplacement de prothèse devant les deux dispositifs d'irradiation. De préférence, le premier dispositif d'irradiation est une lampe fluorescente à émission par champ électrique, et le maximum du spectre du premier dispositif d'irradiation est compris entre 480 et 500 nm.In a variant, a layer of the reconstitution mass may be formed of several sublayers which each undergo the first photochemical polymerization step, but which only undergo the second thermal polymerization step when all the sublayers of the layer have been superimposed. The invention also relates, in a second aspect, to an apparatus for polymerizing a restoring mass of a dental prosthesis which comprises a support and at least one restoring mass fixed to the support, the mass of reconstitution being formed, at least for the most part, of a composite material containing a polymeric binder in which a mineral filler is dispersed, the apparatus comprising an apparatus for irradiating the composite material with polymerization light. According to the invention, the device for irradiation with polymerization light comprises a first device for photochemical irradiation with light, the major part of the spectral energy of which is between 460 and 520 nm, and a second device. irradiation emitting a continuous spectrum at least in the visible and intended to ensure a mainly thermal polymerization, and the apparatus further comprises a prosthesis displacement device in front of the two irradiation devices. Preferably, the first irradiation device is a fluorescent lamp with electric field emission, and the maximum of the spectrum of the first irradiation device is between 480 and 500 nm.
De préférence, le second dispositif d'irradiation est une lampe à halogène.Preferably, the second irradiation device is a halogen lamp.
Il est en outre avantageux que l'appareil comporte un dispositif de montage du premier dispositif d'irradiation et du second dispositif d'irradiation tel que, pendant la plus grande partie de la première étape d'irradiation, le matériau composite n'est pas irradié par la lumière du second dispositif d'irradiation.It is also advantageous for the apparatus to include a device for mounting the first irradiation device and the second irradiation device such that, during most of the first irradiation step, the composite material is not irradiated with light from the second irradiation device.
De préférence, l'appareil comporte un dispositif de commande destiné à commander séparément le premier dispositif d'irradiation et le second dispositif d'irradiation, chacun pendant un temps et avec une intensité qui conviennent à l'étape correspondante de polymérisation du matériau composite.Preferably, the apparatus comprises a control device intended to control the first irradiation device and the second irradiation device separately, each for a time and with an intensity which are suitable for the corresponding step of polymerization of the composite material.
Il est en outre avantageux que l'appareil comporte un dispositif de régularisation d'irradiation destiné à irra- dier la masse de reconstitution dans au moins la moitié de l'angle solide de la totalité de l'espace. Ce dispositif de régularisation d'irradiation peut comporter un dispositif réflecteur qui enveloppe une chambre d'irradiation de l'appareil destinée à contenir la prothèse ayant la masse de reconstitution. Ce dispositif de régularisation d'irradiation peut aussi comporter un dispositif destiné à déplacer la prothèse dans la chambre d'irradiation de l'appareil, de préférence un plateau tournant qui déplace la prothèse devant le dispositif d'irradiation.It is also advantageous for the apparatus to include an irradiation regulation device intended to irradiate the reconstitution mass in at least half of the solid angle of the entire space. This irradiation regulation device may include a reflector device which envelops a radiation irradiation chamber. the device intended to contain the prosthesis having the reconstruction mass. This irradiation regulation device may also include a device intended to move the prosthesis in the irradiation chamber of the device, preferably a turntable which moves the prosthesis in front of the irradiation device.
L'invention concerne aussi, dans un troisième aspect, un ensemble d'appareils d'irradiation qui comprend d'une part un premier appareil de polymérisation tel que défini dans les précédents paragraphes, et d'autre part un second appareil d'irradiation par de la lumière de recuit. Ce second appareil d'irradiation par de la lumière de recuit comporte avantageusement au moins une lampe à halogène. Le premier appareil est destiné à assurer les polymérisations des deux premières étapes du procédé selon l'invention, et le second appareil est destiné à la mise en oeuvre de l'étape supplémentaire de recuit.The invention also relates, in a third aspect, to a set of irradiation apparatus which comprises on the one hand a first polymerization apparatus as defined in the preceding paragraphs, and on the other hand a second irradiation apparatus by annealing light. This second device for irradiation with annealing light advantageously comprises at least one halogen lamp. The first device is intended to ensure the polymerizations of the first two steps of the process according to the invention, and the second device is intended to carry out the additional annealing step.
D'autres caractéristiques et avantages de l'invention ressortiront mieux à la lecture de la description qui va suivre d'un exemple de mise en oeuvre de l'invention faite en référence aux dessins annexés sur lesquels : la figure 1, précédemment décrite, représente le spectre d'émission d'une lampe fluorescente de l'appareilOther characteristics and advantages of the invention will emerge more clearly on reading the description which follows of an example of implementation of the invention made with reference to the appended drawings in which: FIG. 1, previously described, represents the emission spectrum of a fluorescent lamp from the device
"Labolight LV" ; la figure 2, précédemment décrite, représente le spectre d'émission des lampes d'un appareil "Biophoton" ; et la figure 3 représente le spectre d'émission d'un dispositif d'irradiation selon l'invention."Labolight LV"; FIG. 2, previously described, represents the emission spectrum of the lamps of a "Biophoton" device; and FIG. 3 represents the emission spectrum of an irradiation device according to the invention.
L'invention a pour objet la détermination des conditions de polymérisation qui donnent les meilleurs résultats avec les matériaux composites de dernière génération pour prothèses dentaires, afin que les propriétés des prothèses réalisées soient accrues et que la durée et le coût des cycles de polymérisation des prothèses dentaires puissent être réduits, et les moyens permettant leur obtention.The subject of the invention is the determination of the polymerization conditions which give the best results with the latest generation composite materials for dental prostheses, so that the properties of the prostheses produced are increased and that the duration and the cost of the polymerization cycles of the prostheses dental can be reduced, and the means to obtain them.
On considère d'abord un exemple de mise en oeuvre de l'invention, lors de la réalisation d'une prothèse dont la masse de reconstitution est formée d'un matériau composite de la dernière génération.We first consider an example of implementation of the invention, when making a prosthesis whose reconstitution mass is made of a latest generation composite material.
Après qu'un support métallique a été préparé, une couche d'accrochage, souvent à base d'acide et d'esters méthacryliques, est formée par traitement du support. Ensuite, une couche dite "opaque" est appliquée. Cette couche, qui peut être double, comprend par exemple un matériau très opaque destiné à cacher la couleur du métal du support. Chaque couche a par exemple une épaisseur de 100 μ→ . Chaque couche est polymérisée séparément, de préférence à une température qui ne dépasse guère la température d'utilisation d'une prothèse dans la bouche.After a metal support has been prepared, a bonding layer, often based on acid and methacrylic esters, is formed by treatment of the support. Then a layer called "opaque" is applied. This layer, which may be double, comprises for example a very opaque material intended to hide the color of the metal of the support. Each layer has for example a thickness of 100 μ → . Each layer is polymerized separately, preferably at a temperature which hardly exceeds the temperature of use of a prosthesis in the mouth.
Après réalisation de cette couche opaque commence la construction de la masse de reconstitution proprement dite. Cette masse est construite par couches successives. Ces couches sont relativement minces, car elles ne dépassent pratiquement jamais 2 mm d'épaisseur et ont le plus souvent une épaisseur de quelques dixièmes de millimètre. Les couches, après polymérisation de chacune d'elles, sont construites les unes sur les autres jusqu'à une étape finale de polymérisation.After completion of this opaque layer, the construction of the actual reconstruction mass begins. This mass is built up in successive layers. These layers are relatively thin, because they hardly ever exceed 2 mm in thickness and most often have a thickness of a few tenths of a millimeter. The layers, after polymerization of each of them, are built one on top of the other until a final stage of polymerization.
Selon l'invention, après application de chaque couche, cette couche est soumise à une première puis à une seconde étape de polymérisation. La première étape de polymérisation est une étape de polymérisation essentiellement photochimique, et elle est exécutée à basse température inférieure à 35 °C, de préférence à température ambiante. L'irradiation est effectuée de préférence avec de la lumière ayant un spectre dont la plus grande partie de l'énergie se trouve entre 460 et 520 nm. Cette première étape de polymérisation dure suffisamment pour que le taux de polymérisation du matériau de la couche atteigne une valeur de l'ordre de 50 à 60 %. Ce temps est en général de l'ordre de 1 à 2 min. Ensuite, la couche subit une seconde étape de polymérisation surtout thermique qui comporte un échauffement de la couche à une température supérieure à 50 °C. L'irradiation est effectuée de préférence avec de la lumière d'une lampe à halogène. Sa durée est en général de l'ordre de 1 à 2 min. Cette seconde étape de polymérisation thermique augmente le taux de polymérisation de la masse de reconstitution d'environ 10 %. Le taux de polymérisation est déterminé par comparaison de spectres, de préférence Raman, qui indiquent l'évolution de la concentration de doubles liaisons acryliques —C=C— à des longueurs d'onde particulières. Cette évolution est déterminée par le rapport des intensités à plusieurs longueurs d'onde qui dépendent du liant particulier du matériau composite et sont bien connues des hommes du métier. Dans un exemple, pour le matériau composite précité "Cristobal", le taux de polymérisation est défini par le rapport normalisé de l'intensité du spectre Raman à 1 639 cm-1 et 3 069 cm"1.According to the invention, after application of each layer, this layer is subjected to a first and then to a second polymerization step. The first polymerization step is an essentially photochemical polymerization step, and it is carried out at low temperature below 35 ° C, preferably at room temperature. The irradiation is preferably carried out with light having a spectrum of which most of the energy is between 460 and 520 nm. This first polymerization step lasts long enough for the polymerization rate of the layer material to reach a value of the order of 50 to 60%. This time is generally of the order of 1 to 2 min. Then, the layer undergoes a second, especially thermal, polymerization step which involves heating of the layer to a temperature above 50 ° C. The irradiation is preferably carried out with light a halogen lamp. Its duration is generally of the order of 1 to 2 min. This second thermal polymerization step increases the polymerization rate of the reconstitution mass by approximately 10%. The polymerization rate is determined by comparison of spectra, preferably Raman, which indicate the evolution of the concentration of acrylic double bonds —C = C— at particular wavelengths. This evolution is determined by the ratio of the intensities at several wavelengths which depend on the particular binder of the composite material and are well known to those skilled in the art. In one example, for the aforementioned composite material "Cristobal", the polymerization rate is defined by the normalized ratio of the intensity of the Raman spectrum at 1,639 cm -1 and 3,069 cm -1 .
Lorsque toutes les couches nécessaires ou un certain nombre de couches ont été empilées, le procédé comporte une étape supplémentaire de recuit à la fois photochimique et thermique. Plus précisément, l'ensemble de la masse de reconstitution de la prothèse est irradié photochimiquement et chauffé, à une température de préférence comprise entre 90 et 140 °C, par exemple de l'ordre de 120 °C. Cette température est supérieure ou égale à la température de transition vitreuse du matériau. Cette étape supplémentaire de recuit augmente le taux de polymérisation de la masse de reconstitution d'environ 10 % au moins.When all the necessary layers or a number of layers have been stacked, the process comprises an additional step of both photochemical and thermal annealing. More precisely, the entire mass for reconstituting the prosthesis is photochemically irradiated and heated, to a temperature preferably between 90 and 140 ° C., for example of the order of 120 ° C. This temperature is greater than or equal to the glass transition temperature of the material. This additional annealing step increases the polymerization rate of the reconstitution mass by at least 10%.
L'irradiation photochimique utilisée dans la première étape peut comprendre une simple irradiation par de la lumière ayant un spectre dont la plus grande partie de l'énergie est comprise entre 460 et 520 nm et dont le maximum est de préférence compris entre 480 et 500 nm.The photochemical irradiation used in the first step can comprise a simple irradiation with light having a spectrum of which the largest part of the energy is between 460 and 520 nm and the maximum of which is preferably between 480 and 500 nm .
Cette première étape d'irradiation est de préférence exécutée avec une ou plusieurs lampes fluorescentes à émis- sion par champ électrique. L'avantage de l'émission par champ électrique n'est pas nouveau puisqu'il a déjà été mis en oeuvre dans l'appareil précité "Labolight LV" et d'autres appareils connus. La caractéristique importante est que cette première étape de photopolymerisation (création de radicaux libres, essentiellement peroxydiques) doit être réalisée à basse température. Cette condition de photopolymérisation à basse température est avantageusement combinée à une seconde caractéristique nouvelle qui est l'irradiation par de la lumière dont la plus grande partie de 1 ' énergie spectrale est comprise entre 460 et 520 nm.This first irradiation step is preferably carried out with one or more fluorescent lamps with electric field emission. The advantage of emission by electric field is not new since it has already been implemented in the aforementioned device "Labolight LV" and other known devices. The important feature is that this first photopolymerization step (creation of free radicals, essentially peroxide) must be carried out at low temperature. This condition of photopolymerization at low temperature is advantageously combined with a second new characteristic which is irradiation with light, most of the spectral energy of which is between 460 and 520 nm.
Certaines lampes fluorescentes à cathode travaillant par émission par champ électrique donnent une combinaison des caractéristiques précitées (faible échauffement du matériau, spectre essentiellement entre 460 nm et 520 nm) . La cathode travaillant par émission par champ électrique réduit 1 ' échauffement de la lampe dans laquelle la cathode émet des électrons vers des vapeurs de mercure, présentes en petite quantité dans la lampe. Les atomes de mercure, excités par les électrons provenant de la cathode, émettent un rayonnement ultraviolet (essentiellement à 254 nm) qui parvient sur une matière électroluminescente portée par les parois du corps de la lampe. Cette matière électroluminescente, exci- tée par les rayons ultraviolets provenant des atomes de mercure, émet de la lumière visible de fluorescence.Certain cathode fluorescent lamps working by emission by electric field give a combination of the aforementioned characteristics (low heating of the material, spectrum essentially between 460 nm and 520 nm). The cathode working by emission by electric field reduces the heating of the lamp in which the cathode emits electrons towards vapors of mercury, present in small quantity in the lamp. The mercury atoms, excited by the electrons coming from the cathode, emit ultraviolet radiation (essentially at 254 nm) which arrives on an electroluminescent material carried by the walls of the body of the lamp. This electroluminescent material, excited by ultraviolet rays from mercury atoms, emits visible fluorescent light.
Cette matière électroluminescente est de préférence choisie de manière que la plus grande quantité de la lumière visible soit émise entre 460 et 520 nm et que le maximum d'émission se trouve entre 480 et 500 nm. Une telle matière électroluminescente, une fois connu le spectre voulu, peut être facilement déterminée par l'homme du métier, en l'occurrence les spécialistes en lampes d'émission atomique. Un exemple donnant un spectre utile dans le cadre de l'invention contient, en plus d'europiu et d'autres éléments des terres rares, des composés de tantale, de strontium ou de zirconium.This electroluminescent material is preferably chosen so that the greatest amount of visible light is emitted between 460 and 520 nm and that the maximum emission is between 480 and 500 nm. Such an electroluminescent material, once the desired spectrum is known, can be easily determined by a person skilled in the art, in this case specialists in atomic emission lamps. An example giving a useful spectrum in the context of the invention contains, in addition to europiu and other rare earth elements, tantalum, strontium or zirconium compounds.
La seconde étape de polymérisation thermique est avantageusement mise en oeuvre avec une simple lampe à halogène, par exemple une lampe de 300 W, munie d'un rétroprojecteur. Une telle lampe a un effet thermique important sur le matériau composite (échauffement) , mais contient aussi un rayonnement à action photochimique sur le matériau. Bien que la première et la seconde étape du procédé selon 1 ' invention puissent être exécutées successivement dans deux appareils séparés, l'appareil utilisé pour la mise en oeuvre de ce procédé est de préférence un appareil unique qui exécute successivement les deux étapes, c'est-à-dire d'abord l'étape de polymérisation photochimique, puis l'étape de polymérisation surtout thermique. Il est donc important que ces étapes soient réalisées successivement et non simultanément. Cependant, il est possible qu'il existe un certain recouvrement entre la fin de la première étape et la seconde, car on s'est rendu compte que la durée totale du cycle des deux étapes pouvait alors être encore réduite. En particulier, l'irradiation utilisée pour la première étape peut être maintenue pendant la seconde étape. Etant donné que les prothèses dentaires réalisées en matériaux composites ont souvent une forme orientée sinon vers tout l'espace, tout au moins dans la moitié de l'angle solide de la totalité de l'espace, il est souhaitable que l'appareil comporte un dispositif de régularisation de l'irradiation afin que le matériau composite soit irradié dans au moins la moitié de l'angle solide de la totalité de 1 ' espace.The second thermal polymerization step is advantageously carried out with a simple halogen lamp, for example a 300 W lamp, fitted with an overhead projector. Such a lamp has a significant thermal effect on the composite material (heating), but also contains radiation with photochemical action on the material. Although the first and second steps of the process according to the invention can be carried out successively in two separate devices, the device used for carrying out this process is preferably a single device which successively performs the two steps, ie that is to say first the photochemical polymerization step, then the especially thermal polymerization step. It is therefore important that these steps are carried out successively and not simultaneously. However, it is possible that there is some overlap between the end of the first stage and the second, since it has been realized that the total duration of the cycle of the two stages could then be further reduced. In particular, the irradiation used for the first step can be maintained during the second step. Since dental prostheses made of composite materials often have a shape oriented if not towards the entire space, at least in half of the solid angle of the entire space, it is desirable that the appliance comprises a irradiation control device so that the composite material is irradiated in at least half of the solid angle of the entire space.
Le dispositif de régularisation peut être soit passif, soit actif, soit une combinaison de dispositifs actif et passif.The regulation device can be either passive or active, or a combination of active and passive devices.
Un dispositif passif comprend essentiellement un ou plusieurs réflecteurs qui enveloppent la chambre d'irradiation. On peut par exemple utiliser des dispositifs connus de montage de réflecteurs qui, en fonction de la confi- guration géométrique de la source de lumière, permettent une irradiation omnidirectionnelle. On connaît par exemple l'utilisation de cylindres de section ellipsoïdale, ayant une source lumineuse à un foyer et 1 ' élément à irradier à l'autre foyer. Cette disposition convient pour la photo- polymérisation par irradiation omnidirectionnelle d'une prothèse unique d'étendue relativement petite.A passive device essentially comprises one or more reflectors which surround the irradiation chamber. It is possible, for example, to use known devices for mounting reflectors which, depending on the geometrical configuration of the light source, allow omnidirectional irradiation. We know for example the use of cylinders of ellipsoidal section, having a light source at one focal point and one element to be irradiated at the other focal point. This arrangement is suitable for photopolymerization by omnidirectional irradiation of a single prosthesis of relatively small extent.
Le dispositif de régularisation d'irradiation peut aussi comprendre un dispositif de déplacement de la prothèse par rapport à une ou plusieurs lampes, afin que les diverses parties de la prothèse soient irradiées de manière relativement homogène. Ainsi, on connaît déjà des appareils à plateau tournant, utilisés avec des sources étendues, de manière que la lumière reçue par chaque partie de prothèse, intégrée sur la durée du cycle de traitement, soit pratiquement constante.The radiation regulation device may also include a device for moving the prosthesis with respect to one or more lamps, so that the various parts of the prosthesis are irradiated in a relatively homogeneous manner. Thus, devices with a turntable are already known, used with extended sources, so that the light received by each prosthesis part, integrated over the duration of the treatment cycle, is practically constant.
Bien entendu, l'appareil comporte avantageusement un dispositif de commande convenable qui peut être de type connu et qu'on ne décrit donc pas en détail. Ce dispositif de commande peut commander tous les composants actifs de l'appareil, notamment le premier dispositif d'irradiation, le second dispositif d'irradiation et, le cas échéant, le dispositif de déplacement. Ce dispositif de commande peut par exemple régler séparément le temps et 1 ' intensité de chacun des dispositifs d'irradiation, et peut commander tout cycle voulu de traitement par combinaison des commandes des divers composants de la manière qui convient le mieux à la polymérisation du matériau composite. Chaque cycle de traitement peut alors être adapté au mieux à la couche particulière de matériau qui doit être polymérisée.Of course, the device advantageously includes a suitable control device which can be of known type and which is therefore not described in detail. This control device can control all the active components of the device, in particular the first irradiation device, the second irradiation device and, if necessary, the displacement device. This control device can, for example, separately adjust the time and intensity of each of the irradiation devices, and can control any desired treatment cycle by combining the controls of the various components in the manner that best suits the polymerization of the material. composite. Each treatment cycle can then be best adapted to the particular layer of material to be polymerized.
Lorsque toutes les couches de la masse de reconstitution ont subi la polymérisation photochimique et la polymérisation thermique, l'ensemble de la masse est soumis à une étape supplémentaire de polymérisation à la fois photochimique et thermique. Cette étape est de préférence mise en oeuvre dans un appareil séparé. En effet, il est souhaitable que la masse de reconstitution atteigne une température relativement élevée puisque cette température doit être supérieure à la température de transition vitreuse du matériau composite, atteignant, pour de tels taux de polymérisation, une valeur qui est en général comprise entre 90 et 140 °C, par exemple de l'ordre de 120 °C.When all the layers of the reconstitution mass have undergone photochemical polymerization and thermal polymerization, the whole of the mass is subjected to an additional stage of polymerization, both photochemical and thermal. This step is preferably carried out in a separate device. Indeed, it is desirable for the reconstitution mass to reach a relatively high temperature since this temperature must be greater than the glass transition temperature of the composite material, reaching, for such polymerization rates, a value which is generally between 90 and 140 ° C, for example of the order of 120 ° C.
La durée de cette étape supplémentaire de polymérisa- tion à la fois photochimique et thermique est au moins égale à 5 min et de préférence de l'ordre de 10 min. Comme elle n'est utilisée qu'une fois pour l'ensemble de la prothèse, elle n'allonge pas excessivement la durée du processus total de fabrication.The duration of this additional step of both photochemical and thermal polymerization is at least 5 min and preferably of the order of 10 min. As it is only used once for the entire prosthesis, it does not excessively lengthen the duration of the total manufacturing process.
L'appareil utilisé peut être un four spécial, muni par exemple de trois lampes à halogène très courantes "ELH" de Philips, ayant chacune une puissance de 100 W. Les lampes sont avantageusement placées en triangle afin que la prothèse soit irradiée dans plusieurs directions et puisse ainsi subir un traitement relativement homogène.The device used can be a special oven, for example provided with three very common halogen lamps "ELH" from Philips, each having a power of 100 W. The lamps are advantageously placed in a triangle so that the prosthesis is irradiated in several directions and can thus undergo a relatively homogeneous treatment.
L'invention concerne aussi un ensemble d'appareils destiné à la mise en oeuvre du procédé de l'invention et comprenant un premier appareil qui assure la polymérisation photochimique et la polymérisation thermique de chaque couche, et un second appareil qui assure l'étape supplémentaire de recuit final. On s'est rendu compte que les prothèses réalisées par le procédé selon l'invention présentaient une ténacité à la fracture supérieure d'au moins 80 % à celle des masses de reconstitution de matériaux composites réalisées sans mise en oeuvre du procédé. Il faut noter que cette ténacité à la fracture obtenue grâce au procédé de l'invention est aussi supérieure de près de 50 % à celle des meilleures céramiques d'application dentaire.The invention also relates to a set of apparatuses for carrying out the method of the invention and comprising a first apparatus which ensures the photochemical polymerization and the thermal polymerization of each layer, and a second apparatus which ensures the additional step final annealing. It has been realized that the prostheses produced by the process according to the invention had a fracture toughness at least 80% greater than that of the masses for reconstituting composite materials produced without carrying out the process. It should be noted that this fracture toughness obtained using the process of the invention is also almost 50% higher than that of the best ceramics for dental application.
En outre, les masses de reconstitution obtenues par le procédé de l'invention ont une résistance à l'usure supé- rieure d'un facteur au moins égal à 2,2 à celle que donnent les matériaux composites polymérisés par les procédés classiques .In addition, the reconstitution masses obtained by the process of the invention have a wear resistance greater by a factor at least equal to 2.2 than that given by the composite materials polymerized by the conventional processes.
Bien que l'invention ne soit pas limitée par une théorie quelconque, on considère que le procédé de polymé- risation selon l'invention donne les résultats particulièrement avantageux précités par son effet sur le retrait présenté par la masse de reconstitution.Although the invention is not limited by any theory, it is considered that the polymerization process according to the invention gives the particularly advantageous results mentioned above by its effect on the shrinkage presented by the reconstitution mass.
En effet, on sait que, en cours de polymérisation, une masse constituée du seul liant du matériau composite pré- sente un retrait total de l'ordre de 10 %, correspondant à 3 % de retrait chimique et 7 % de retrait physique (dilatation) . Lorsque le liant est chargé, le matériau composite a un retrait total de l'ordre de 5 %, correspondant à la somme d'un retrait chimique d'environ 1,5 % et d'un retrait physique (dilatation) d'environ 3,5 % .Indeed, it is known that, during polymerization, a mass consisting of the only binder of the composite material exhibits a total shrinkage of the order of 10%, corresponding to 3% chemical shrinkage and 7% physical shrinkage (dilation ). When the binder is loaded, the composite material has a total shrinkage of around 5%, corresponding to the sum about 1.5% chemical shrinkage and about 3.5% physical shrinkage (dilation).
Le procédé de 1 ' invention met en oeuvre des étapes qui réduisent au minimum ces retraits. Ainsi, la polymérisation photochimique à basse température permet une réduction du retrait physique puisque la masse ne subit pratiquement pas d'élévation de température dans la première étape. En outre, comme la polymérisation est progressive, le matériau peut présenter un réarrangement constant, si bien que le retrait final obtenu est très faible. Par exemple, on constate que, avec les matériaux composites de dernière génération "Colombus" et "Cristobal", le retrait total après la fin de la polymérisation est toujours inférieur à 2,5 % et en général de l'ordre de 1,9 à 2,2 %. Des matériaux composites d'autres réalisations présentent des retraits de l'ordre de 4,5 à 5 % et qui ne sont jamais inférieurs à 3,3 %. Cette réduction du retrait de la masse de reconstitution réduit fortement les contraintes existant au niveau de 1 ' interface de la masse et du support. Ainsi, l'invention permet la réalisation de prothèses dentaires dont la durabilité est fortement accrue par rapport à des prothèses réalisées par d'autres procédés, car, pour un matériau déterminé, le retrait est fortement réduit et la ténacité est notablement accrue. Ces deux phénomènes se conjuguent pour augmenter considérablement la durabilité des prothèses lorsqu'elles sont soumises aux contraintes qui leur sont appliquées pendant l'utilisation. Il faut en outre noter la réduction de l'usure qui est due notamment à une augmentation de la dureté obtenue simulta- nément par mise en oeuvre du procédé de l'invention.The method of the invention implements steps which minimize these withdrawals. Thus, the photochemical polymerization at low temperature allows a reduction in physical shrinkage since the mass undergoes practically no rise in temperature in the first step. In addition, as the polymerization is progressive, the material can have a constant rearrangement, so that the final shrinkage obtained is very low. For example, it can be seen that, with the latest generation composite materials "Colombus" and "Cristobal", the total shrinkage after the end of the polymerization is always less than 2.5% and in general of the order of 1.9 at 2.2%. Composite materials of other embodiments exhibit shrinkages of the order of 4.5 to 5% and which are never less than 3.3%. This reduction in the withdrawal of the reconstitution mass greatly reduces the stresses existing at the interface of the mass and the support. Thus, the invention allows the production of dental prostheses whose durability is greatly increased compared to prostheses produced by other methods, because, for a given material, the shrinkage is greatly reduced and the toughness is significantly increased. These two phenomena combine to considerably increase the durability of prostheses when they are subjected to the stresses which are applied to them during use. It should also be noted the reduction in wear which is due in particular to an increase in hardness obtained simultaneously by implementing the method of the invention.
La réduction du temps de polymérisation des matériaux composites de dernière génération est très importante en pratique. En effet, les prothèses sont formées par application successive de couches qui sont polymérisées les unes après les autres. Chacune des couches est mince et doit être polymérisée séparément. Comme le nombre total de couches est couramment de dix à quinze, le nombre de polymérisations est équivalent. On apprécie donc pleinement l'intérêt que pré- sente la réduction de la durée de chaque cycle de polymérisation. Possibilités d'application industrielleReducing the polymerization time of latest generation composite materials is very important in practice. Indeed, prostheses are formed by successive application of layers which are polymerized one after the other. Each layer is thin and must be polymerized separately. Since the total number of layers is commonly ten to fifteen, the number of polymerizations is equivalent. We therefore fully appreciate the interest that pre- feels the reduction in the duration of each polymerization cycle. Industrial application possibilities
L' invention concerne des perfectionnements aux procédés et appareils applicables à l'industrie de fabrication des prothèses dentaires. The invention relates to improvements to the methods and apparatuses applicable to the dental prosthesis manufacturing industry.

Claims

REVENDICATIONS
1. Procédé de polymérisation d'une masse de reconstitution d'une prothèse dentaire qui comprend un support et au moins une masse de reconstitution fixée au support, la masse de reconstitution étant formée, pour sa plus grande partie au moins, de couches superposées d'un matériau composite contenant un liant polymère dans lequel est dispersée une charge minérale et qui, après polymérisation, a une résistance à la flexion au moins égale à 100 MPa et une dureté Vickers au moins égale à 450 N/mm2, le procédé étant du type qui comprend une étape dans laquelle la masse de reconstitution subit une polymérisation par irradiation par au moins de la lumière visible, caractérisé en ce qu'il comprend, pour chaque couche, une première étape de polymérisation essentiellement photochimique à basse température jusqu'à ce que le taux de polymérisation de la couche atteigne environ 50 à 60 %, et une seconde étape de polymérisation surtout thermique comprenant un échauffement de la couche à une température supérieure à la température de transition vitreuse, pendant un temps suffisant pour que le taux de polymérisation augmente d'environ 10 %, puis, pour plusieurs couches ou toutes les couches, une étape supplémentaire de recuit, photochimique et thermique simultanément, telle que le taux de polymérisation augmente encore d'environ 10 % au moins.1. Method for the polymerization of a reconstruction mass of a dental prosthesis which comprises a support and at least one reconstruction mass fixed to the support, the reconstruction mass being formed, for the most part at least, of superimposed layers d '' a composite material containing a polymeric binder in which a mineral filler is dispersed and which, after polymerization, has a flexural strength at least equal to 100 MPa and a Vickers hardness at least equal to 450 N / mm 2 , the method being of the type which comprises a stage in which the reconstitution mass undergoes polymerization by irradiation with at least visible light, characterized in that it comprises, for each layer, a first stage of essentially photochemical polymerization at low temperature up to that the polymerization rate of the layer reaches approximately 50 to 60%, and a second, especially thermal, polymerization step comprising a heating the layer to a temperature above the glass transition temperature, for a time sufficient for the polymerization rate to increase by approximately 10%, then, for several layers or all the layers, an additional step of annealing, photochemical and simultaneously, such that the polymerization rate further increases by at least about 10%.
2. Procédé selon la revendication 1, caractérisé en ce que la première étape de polymérisation essentiellement photochimique est effectuée par irradiation par de la lumière visible dont la plus grande partie de l'énergie spectrale est comprise entre 460 et 520 nm.2. Method according to claim 1, characterized in that the first essentially photochemical polymerization step is carried out by irradiation with visible light, most of the spectral energy of which is between 460 and 520 nm.
3. Procédé selon l'une des revendications 1 et 2, caractérisé en ce que, au cours de la première étape, la température de la couche est inférieure à 35 °C.3. Method according to one of claims 1 and 2, characterized in that, during the first step, the temperature of the layer is less than 35 ° C.
4. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce que, au cours de la seconde étape de polymérisation surtout thermique de la couche, la température est supérieure à 50 °C environ. 4. Method according to any one of claims 1 to 3, characterized in that, during the second especially thermal polymerization step of the layer, the temperature is above about 50 ° C.
5. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que l'étape supplémentaire de recuit photochimique et thermique est exécutée à une température de la masse de reconstitution comprise entre 90 et 140 °C environ.5. Method according to any one of the preceding claims, characterized in that the additional step of photochemical and thermal annealing is carried out at a temperature of the reconstitution mass of between 90 and 140 ° C approximately.
6. Appareil de polymérisation d'une masse de reconstitution d'une prothèse dentaire qui comprend un support et au moins une masse de reconstitution fixée au support, la masse de reconstitution étant formée, pour sa plus grande partie au moins, d'un matériau composite contenant un liant polymère dans lequel est dispersée une charge minérale, l'appareil comprenant un dispositif d'irradiation du matériau composite par de la lumière de polymérisation, caractérisé en ce que le dispositif d'irradiation par de la lumière de polymérisation comporte un premier dispositif d'irradiation photochimique par de la lumière dont la plus grande partie de l'énergie spectrale est comprise entre 460 et 520 nm, et un second dispositif d'irradiation émettant un spectre continu dans le visible et destiné à assurer une polymé- risation thermique, et l'appareil comporte en outre un dispositif de déplacement de prothèse devant les deux dispositifs d'irradiation.6. Apparatus for the polymerization of a reconstitution mass of a dental prosthesis which comprises a support and at least one reconstruction mass fixed to the support, the reconstruction mass being formed, for the most part at least, of a material composite containing a polymeric binder in which a mineral filler is dispersed, the apparatus comprising a device for irradiating the composite material with polymerization light, characterized in that the device for irradiation with polymerization light comprises a first photochemical light irradiation device, most of the spectral energy of which is between 460 and 520 nm, and a second irradiation device emitting a continuous spectrum in the visible and intended to ensure thermal polymerization , and the apparatus further comprises a prosthesis displacement device in front of the two irradiation devices.
7. Appareil selon la revendication 6, caractérisé en ce que le premier dispositif d'irradiation est une lampe fluorescente à émission par champ électrique, et le maximum de son spectre est compris entre 480 et 500 nm.7. Apparatus according to claim 6, characterized in that the first irradiation device is a fluorescent lamp with emission by electric field, and the maximum of its spectrum is between 480 and 500 nm.
8. Appareil selon l'une des revendications 6 et 7 , caractérisé en ce qu'il comporte un dispositif de montage du premier dispositif d'irradiation et du second dispositif d'irradiation tel que, pendant la plus grande partie de la première étape d'irradiation, le matériau composite n'est pas irradié par la lumière du second dispositif d'irradiation.8. Apparatus according to one of claims 6 and 7, characterized in that it comprises a device for mounting the first irradiation device and the second irradiation device such that, during most of the first step d irradiation, the composite material is not irradiated by the light of the second irradiation device.
9. Appareil selon l'une quelconque des revendications 6 à 8, caractérisé en ce qu'il comporte un dispositif de commande destiné à commander séparément le premier dispositif d'irradiation et le second dispositif d'irradiation, chacun pendant un temps et avec une intensité qui conviennent à 1 ' étape correspondante de polymérisation du matériau composite.9. Apparatus according to any one of claims 6 to 8, characterized in that it comprises a control device intended to separately control the first irradiation device and the second irradiation device, each for a time and with a intensity which are suitable for the corresponding step of polymerization of the composite material.
10. Ensemble d'appareils d'irradiation, caractérisé en ce qu'il comprend d'une part un premier appareil de polymérisation selon l'une quelconque des revendications 6 à 9, et d'autre part un second appareil d'irradiation par de la lumière de recuit. 10. Set of irradiation devices, characterized in that it comprises on the one hand a first polymerization device according to any one of claims 6 to 9, and on the other hand a second device for irradiation with annealing light.
PCT/FR2000/002246 1999-08-06 2000-08-04 Method and apparatus for the photopolymerization of a mass for reconstructing a dental prosthesis WO2001010336A1 (en)

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EP00956619A EP1202680A1 (en) 1999-08-06 2000-08-04 Method and apparatus for the photopolymerization of a mass for reconstructing a dental prosthesis
AU68503/00A AU6850300A (en) 1999-08-06 2000-08-04 Method and apparatus for the photopolymerization of a mass for reconstructing a dental prosthesis

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FR9910286A FR2797173B1 (en) 1999-08-06 1999-08-06 METHOD AND APPARATUS FOR PHOTOPOLYMERIZATION OF A RECONSTRUCTIVE MASS OF A DENTAL PROSTHESIS
FR99/10286 1999-08-06

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EP1264581A3 (en) * 2001-06-07 2003-09-03 Firma Ivoclar Vivadent AG Artificial tooth and manufacturing method thereof

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AU6850300A (en) 2001-03-05
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FR2797173A1 (en) 2001-02-09

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