HK1008925B - A polymer-fiber prepreg, a method for the preparation thereof as well as the use of said prepreg - Google Patents

Description

Polymer-fibre prepreg, method for the production thereof and use thereof

Technical Field

The invention relates to a method for producing a fibre product (prepreg) pre-impregnated with a polymer. The invention further relates to a novel prepreg, a method for the manufacture of fibre-reinforced composites based on the use of such prepregs, to such novel composites and to their use.

Background

The literature and other materials used to illuminate the background of the invention, particularly those that provide additional details respecting the practice, are incorporated herein by reference.

Dental devices made from polymers are prone to breakage under oral conditions. For example, it is possible to verify that a movable dental base is broken after wearing for several years (1-4). Thus, ideal reinforcement of the tray is necessary either in the manufacture of new trays or in the restoration of old trays, and polymer devices and structures in dentistry are conventionally reinforced with metal inclusions of polymers (5-7). However, the strength effect of these metal wraps in polymeric devices and structures is insufficient. There have been attempts to develop a polymer-fiber composite that can be readily used for reinforcement of dental abutments. Prior to the present invention, although there was a fiber tape-like article (ribbon) for dental use on the market^Fiber-composite articles have never been obtained that satisfy dental clinical needs and dental laboratory techniques, Ribbon inc. It is known from dentistry for restorative purposes that polymer-fibre composites have been made by impregnating fibre bundles, fibre tapes or fibre braids in Methyl Methacrylate (MMA) monomer or in a mixture of polymethyl methacrylate (PMMA) powder and its monomer (MMA). However, the compound obtained in this way is not suitable for use in a dental abutment due to the following drawbacks: 1) insufficient adhesion between PMMA and fibres, especially for repairing dental abutments PMMA i.e. autokineticThis is especially true for polymerized PMMA (8), 2) inadequate impregnation of the fibers with PMMA (9-11), 3) when the PMMA is compression molded, the fibers disperse into the area of the dental base where it is not intended (12), 4) in the dental laboratory, the fibers are difficult to handle (13), and 5) mechanical irritation of the soft tissue in the oral cavity is caused by the fibers protruding from the surface of the dental base (14).

There have also been attempts to make pre-impregnated fiber bundles with polymers (known as polymer-fiber prepregs). There have been three reports of the general method of making such thermoplastic polymer-fiber prepregs: 1) an in-situ polymerisation process, which is a resin injection moulding process whereby monomers are combined with fibre-containing preforms, 2) a film lamination process whereby fibre layers are laminated between polymer film layers, and 3) a powder coating process whereby polymer powder is impregnated into fibres and then melted.

However, these methods have some drawbacks with respect to dental requirements. While PMMA can be used in situ, its composite structure has pores created by shrinkage of the polymerization reaction, which will be filled with saliva and bacteria in the mouth. The film lamination process results in a composite with low impregnation (i.e., the fiber bundles are not sufficiently impregnated with polymer). Insufficient impregnation will also result in voids in the composite structure. The powder coating process involves melting a powder of the polymer. This process results in a prepreg of dense structure which is difficult to plasticize prior to treatment with the dissolved polymer. Therefore, any method used in the general plastic industry for manufacturing fiber composites is not suitable for the manufacture and repair of dental abutments,

objects and summary of the invention

Clinical dentistry and dental technology have the following requirements for prepregs for dental reinforcement: 1) the prepreg must be readily shaped to the anatomical shape of the mouth, i.e., it must be a molding substance at room temperature when used in the manufacture or repair of dental abutments. 2) When the prepreg is covered with unfilled (i.e., fiber-free) polymer, it must remain intact, 3) the polymer in the prepreg must polymerize with the surrounding polymer, 4) the polymer matrix must chemically react with the surrounding polymer, whether it is a thermally cured polymer or an autopolymerized polymer, and 5) the fibers in the prepreg must be able to bond to the thermally cured polymer and the autopolymerized polymer.

One object of the present invention is to satisfy the above requirements 1) to 5) of prepregs.

Another object of the invention is the use of the prepreg in the manufacture of fibre-reinforced composites. The composite is suitable for use in any technical field, in particular in the dental or medical field.

Thus, in accordance with one of the objects of the present invention, there is provided a method for making a fibrous article (prepreg) pre-impregnated with a polymer. The method comprises i)

a) With at least one polymer and optionally capable of initiating polymerization of the polymer

The powder including the agent coats the fibers,

b) adding a solvent to the composition obtained in step a), the solvent being soluble

Which polymer is depolymerized but not initiated to polymerize, and

c) evaporation of the solvent, or ii)

a) Comprising at least one polymer and optionally capable of initiating the polymerization of the polymer

The powder of the agent (A) is dissolved in a solvent which dissolves the polymer used but does not initiate its polymerization

In the solvent of the synthesis reaction, and

b) contacting the fibres with the solution obtained in the preceding step, and

c) the solvent was evaporated.

Although the prepreg can be formed in the form of a continuous roll, it can be easily formed into its intended shape for many applications. In this case, the composition obtained in step a) is introduced into a mold before the addition of the solvent, and the completed prepreg is removed from the mold after the solvent has evaporated.

According to a preferred embodiment, the surface of the fibres is treated in order to facilitate the bonding of the polymer to the fibres, and the polymer powder is then applied to the fibres which have been surface-treated. An agent that facilitates the bonding of the polymer to the surface of the fiber is preferably applied to the surface of the fiber prior to coating the fiber with the polymer powder.

In another aspect, the present invention provides a loose prepreg comprising fibers and a polymer, wherein the polymer is present between individual fibers and is distributed between the fibers as a solution, and the solvent is evaporated from the solution.

In a particularly preferred prepreg, the fibers are glass fibers and the polymer is Polymethylmethacrylate (PMMA), ethylene dimethacrylate (EGDMA), 2-BIS [4- (2-hydroxy-3-methacryloyloxy) -phenyl ] -propane (BIS GMA), or hydroxyethyl methacrylate (HEMA); and a silane compound, preferably gamma-methacryloxypropyl-trimethoxysilane, is applied to the surface of the fibers.

In a further aspect, the present invention provides a method of making a fiber-reinforced composite based on the use of the prepreg of the present invention. The method comprises the following steps: -adding a plasticizer to an optionally pre-prepared prepreg, -shaping the plasticized prepreg into a desired shape, -embedding the prepreg in a simple polymer of the composite or a mixture of the polymer and a monomer, and-polymerizing the polymer in the prepreg and the simple polymer in the composite simultaneously.

The reinforced composite may be used at once, or alternatively, as a raw material for making blocks of a desired shape. In this way, dental composites can be processed into, for example, dental restorations and dental or medical implants.

According to another preferred embodiment, the polymer in the prepreg and the unfilled polymer in the composite are the same.

The present invention further provides a fiber-reinforced composite comprising the prepreg of the present invention, which has been plasticized by impregnation with a monomer and shaped into a desired shape to embed the polymer alone in the composite, wherein the polymer in the prepreg and the polymer alone in the composite are polymerized simultaneously.

The composite may be used in any technical aspect. However, it is particularly suitable for use in medical or dental structures, for example, for prosthodontics, orthodontics or orthopaedic appliances; a framework of the movable denture base, a fastener or a precise accessory of the movable denture base; permanent or temporary prostheses, including dental and implant prostheses; dental or medical implant interchange; a sulcus filling of a endodontically treated tooth; a support post, core, filling or crown for a tooth, a protective cover for the mouth, and the like.

Brief Description of Drawings

Figures 1A to 1C illustrate the use of prepregs for repairing a complete set of dental abutments.

FIGS. 2A and 2B show two examples of fiber orientation in the prosthetic abutment (FIG. 2A is the full set of abutments and FIG. 2B is the upper portion of the abutments), an

FIG. 3 shows the bending properties of GF-PMMA composites.

Detailed description of the invention

The fibers suitable for use in the present invention may be either inorganic or organic. The choice of fibres is highly dependent on the technical field of use of the composite reinforced with such fibres. Fibers that have been tested for reinforcement of dental abutments in dentistry include E-glass (conductive glass) fibers (10), S-glass (high strength glass) fibers (16), carbon/graphite fibers (12, 17, 18), aramid fibers (19) and ultra-high modulus polyethylene (8, 13, 20-23), the black color of carbon/graphite fibers making it less suitable for dentistry. It has been reported that the adhesion between the organic fiber and the dental polymer is insufficient (8). Thus, glass fibers appear to be the most cosmetically and adhesively acceptable dental fibers.

The fibers can be made in various forms. For example, the fiber bundles described above, woven fiber bundles, woven glass fiber mats, chopped glass fiber mats, short fibers, whiskers, or fiber particles (fillers), and fiber products may be selected depending on the intended use of the composite, and various types of fiber mixtures may be used.

The polymer in the prepreg may be any polymer. Thermoplastic polymer materials may be preferred for medical and dental use. Preferably, the polymer in the prepreg is the same as the polymer surrounding the prepreg in the final composite. The preferred polymer for use in the dental field is Polymethylmethacrylate (PMMA), either thermally cured or auto-polymerized. Thermally cured PMMA is polymerized in a water bath at 70 to 100 ℃. The polymerization is carried out, for example, initiated with a benzoyl peroxide initiator (24). Thermally cured PMMA may also be polymerized under microwave energy. Auto-polymerized PMMA polymerizes at a lower temperature (35 to 50 ℃) than thermally cured polymerized PMMA, and thus requires a compound such as dimethyl-p-toluidine to activate the initiator (24) of the reaction. Among other preferred polymers, there may be considered, for example, ethylene dimethacrylate (EGDMA), 2-BIS [4- (2-hydroxy-3-methacryloyloxy) phenyl ] propane (BIS GMA), polyethylene terephthalate (PETG), 1, 4-cyclohexylenedimethylene terephthalate (PCTG), hydroxyethyl methacrylate (HEMA) and the like.

The ratio of the amounts of fibres and polymer is preferably chosen so that after evaporation of the solvent a prepreg with good porosity is obtained. A high porosity is advantageous because it allows the plasticizer to easily penetrate the prepreg. When glass fibers and PMMA are used, the fibers and polymer are in equal amounts to achieve the best porosity.

The surface of the fibers may optionally be treated, either physically or chemically, for example with an agent, in order to facilitate bonding of the polymer to the fibers. The choice of agent (i.e., coupling agent) that facilitates bonding of the polymer to the fiber depends on the fiber and polymer matrix used. In dentistry, coupling agents that generally improve the adhesion between glass fibers and PMMA are silane-based compounds. A particularly preferred silane compound is gamma-Methacryloxypropyltrimethoxysilane (MPS). The bonding between the carbon fibers and the polymer matrix can be improved by oxidative methods, radiation methods, and the use of silane compounds. Polyethylene fibers can be plasma etched, for example, on the surface of the fiber to increase its adhesion to the polymer matrix. However, the results obtained so far are still relatively poor (21).

According to a preferred embodiment of the invention, the coupling agent is pre-impregnated on the surface of the fibre before it contacts the polymer. This method enables the use of heat cured polymers and autopolymerized polymers. According to known methods, the curing of the silane compound will be carried out simultaneously with the polymerization of the thermally cured PMMA. There is no report on the successful application of silane compounds to improve the adhesion between the autopolymerized PMMA and the glass fibers.

The polymerization initiator is added to, for example, the polymeric material in the prepreg or to the plasticizer used to plasticize the prepreg prior to use of the plasticizer. The initiator may be any suitable known polymerization initiator. Most common initiators are peroxides, such as benzoyl peroxide.

The solvent used to prepare the prepreg may be any solvent that is capable of dissolving the polymeric material but is not capable of initiating the polymerization reaction therein. Tetrahydrofuran (THF) is one of the suitable solvents. Its dissolution of the polymer material and subsequent evaporation of the solvent results in a very good impregnation of the fibre product with the polymer, which will later on, as disclosed in the examples, result in a final composite with excellent strength properties. The solvent preferably evaporates relatively quickly, which is advantageous for obtaining a porous structure of the substance in the prepreg.

The plasticizer to be used for plasticizing the prepreg may use a monomer, which may be a monomer of the polymer powder contained in the prepreg, or a different monomer. Preferably the same monomers are used. In the case where the polymer is PMMA, this monomer will be MMA.

The invention is illustrated by the following examples. In these examples, the invention is explained according to its preferred embodiments and only in the field of restorative dentistry techniques, although the invention is also relevant to other medicine and techniques.

EXAMPLE 1 preparation of prepreg

E-glass fibers in the form of continuous non-oriented fiber bundles (Ahlstrokm, Karhula, Finland) were treated with 1.5mol/l sulfuric acid (H)₂SO₄) Washed, washed with distilled water and then dried at +22 ℃ for 48 hours.

To improve the adhesion of the Polymer (PMMA) on the fiber surface, the surface of the fiber was treated with gamma-Methacryloxypropyltrimethoxysilane (MPS) (A174, Union carbide, Versoix, Switzerland). Dilute MPS (30% MPS, 70% methanol) was pre-dried on the glass fiber surface for two hours at 100 ℃. Commercially available surface-treated glass fibers can also be used.

Glass fibers that have been treated with a silane compound are coated with dental heat-curable polymethyl methacrylate (PMMA) powder (Pro Base Hot, Ivoclar, Schaan, Liechtenstein) that has contained benzoyl peroxide as a polymerization initiator, the weight of the PMMA powder used being equal to the weight of the glass fibers.

A set amount of chopped glass fibers was placed in a mold having a cavity corresponding to the shape of the prepreg. The milled fibers were wetted with the solvent Tetrahydrofuran (THF), which dissolves the PMMA but does not initiate polymerization of the dissolved PMMA. At this step, the dissolved PMMA bonds the individual fibers and interconnects to form a rigid prepreg of predetermined shape. The solvent (THF) was allowed to evaporate and the prepreg was finally taken out of the mold and packaged for use.

Another method of making prepregs is to dissolve a set amount of PMMA in THF, to impregnate a ribbon or braid of fibers in the mixture, or to draw the fiber bundles or braids through the mixture. The ratio of PMMA and THF should be optimized to give a porous glass fiber-PMMA prepreg that can be easily wetted and plasticized by MMA when in use.

Prepregs based on autopolymerized PMMA (Pro Base Cold, Ivoclar, Schaan, Liechtenstein) may be prepared in the same manner as described above.

EXAMPLE 2 use of prepregs for reinforcement in the manufacture of dental abutments

Acrylic-based dental bases can be made from heat-cured PMMA using compression molding techniques. The weakened portion in the tray may be reinforced with the prepreg obtained from example 1 by: 1) after initially filling the mold of the dental base with PMMA, the PMMA dough is pressed out of a concave portion using a plastic sheet having the same size as the prepreg as a spacer, 2) the prepreg is plasticized by wetting with a heat-curable PMMA monomer and placed in a concave portion of the acrylic resin dough, 3) the final filling of the acrylic resin dough can be performed according to a conventional method in dentistry (25), 4) the PMMA and PMMA dough in the prepreg are simultaneously polymerized in a water bath. The final product thus obtained is a set of dental abutments comprising an oriented continuous fibre reinforcement covered by a layer of unfilled PMMA.

EXAMPLE 3 use of prepregs in denture repair

A broken dental base on a dental casting may be reshaped by a method described in the dental literature. In addition (see fig. 1A-1C), the size of the grooves 10 and glass fibers of the prepreg 11 made of autopolymerized PMMA are just as large as the site where the dental base is set (fig. 1C). The prepreg 11 is plasticized by wetting with a monomer of auto-polymerized PMMA and placed into a channel in a dental base. The trench is then filled with autopolymerized PMMA and allowed to polymerize simultaneously with the PMMA in the prepreg on a water bath. This results in a pair of abutments (see figures 2A-2B) reinforced with oriented fibres. EXAMPLE 4 use of prepregs as a Movable set of dental base framework materials

The prepreg is plasticized with a monomer of the polymer matrix and then placed over the gum casting to cover the skeletal site. The prepreg was placed so that the fiber direction was oriented against the expected fracture line of the denture base, and the surface of the prepreg was coated with PMMA powder so that the unfilled PMMA covered the fibers. Alternatively, a mixture of PMMA powder and MMA fluid (i.e., a dough of PMMA) is coated onto the surface of the prepreg. The cast block is placed in a curing unit to allow the PMMA to polymerize. After curing, the composite skeleton is obtained. The composite framework can be used for manufacturing movable dental base brackets like a universal metal framework.

EXAMPLE 5 use of prepreg as clasp for removable denture

Prepregs shaped as denture hooks and shaped as tooth color are plasticized with a monomer of polymer matrix (PMMA). A plasticized prepreg is placed at a set location in the cast denture base, which is bonded to the extended base of the removable denture base, and this prepreg is coated with a tooth-colored PMMA powder prior to being fed into the curing unit for polymerization. Alternatively, the prepreg is coated with a dental-colored PMMA dough prior to polymerization.

EXAMPLE 6 use of prepregs to manufacture permanent, semi-permanent or temporary prostheses

Prepregs comprising colorless or tooth-colored PMMA (alternatively, polybutylmethacrylate or ethyl methacrylate, etc.) are plasticized with monomers of the polymer matrix. The plasticized prepreg was placed in a silicon mold to which the prosthesis was fixed, the mold having been filled with a portion of PMMA dough. The PMMA dough was then coated with the plasticized prepreg and the mold was placed on a cast plaster of the adjacent teeth. After curing the PMMA, the fixed prosthesis is finished using conventional dental laboratory procedures.

The solid prosthesis includes non-directional glass fiber reinforcement to increase bridge strength and its attachment to the crown unit, and additionally includes glass fiber woven reinforcement or short fiber reinforcement to increase the strength of the crown unit and the fixed prosthesis.

Properties of the fiber composite obtained in example 7

The method discussed in the earlier process, i.e. the method of impregnating the fiber bundle in a mixture of PMMA powder and its monomers, gives an impregnation degree (amount of dental PMMA/amount of continuous non-oriented E-glass fibers) of 0.4 to 0.8. For fiber bundles with a higher specific fiber count (fibers), the degree of impregnation is lower. The degree of impregnation of the composite made of continuous E-glass fibers and PMMA using the prepreg of the invention was 0.91 for PMMA cured with heat and 0.98 for PMMA auto-polymerized. Furthermore, the degree of impregnation is not affected by the amount of specific fibres in the fibre bundle.

The flexural properties of the non-oriented glass fiber reinforced dental PMMA composites made according to the prior art method and the flexural properties of the composites made according to the present invention are shown in table 1 and fig. 3. The test specimens tested in the preceding examples have a fiber concentration which makes them easy to use both in the production process according to the prior art and in the process according to the invention.

Simulated chewing (150N closure force, 300ms interval in 37 ℃ water) produced bending fatigue resistance 15 times higher for the glass fiber reinforced active topical denture according to the invention than for the conventional wire reinforced denture. The glass fiber-reinforced dental PMMA according to the invention has an impact strength of 70KJ/m measured on a Charpy-type impact tester (WPM, Lepidium, Germany)²The impact strength is greatly higher than that of PMMA reinforced by metal wires, and the three-unit fixed PMMA is brokenThe muscle closure force required for a local denture made of dental PMMA is 91N. Whereas the prepreg according to the invention strengthens the three-unit bridge, the bridge resistance increases to 350N.

The conversion of MMA into PMMA in the prepregs reinforced with glass fibres is as high as in the case of non-reinforced PMMA, as determined by the amount of residual MMA released from the composite (high performance liquid chromatography, according to ISO1567 standard). The water absorption and solubility of the glass fiber for reinforcing PMMA also meet the ISO technical standard. TABLE 1 flexural Strength (MPa) and flexural modulus (GPa) (measured according to ISO1567 standard three-point load) of autopolymerized PMMA and non-oriented GF-PMMA composites prepared according to conventional techniques and according to the novel prepreg method

Flexural Strength flexural modulus non-reinforced PMMA 89.12.83 GF-PMMA composite 231.27.12 GF-PMMA composite 335.012.56 made by the general technique of prepreg

It is understood that the methods of the present invention can be combined in several different embodiments, only a few of which are disclosed herein. It will be apparent to those skilled in the art that other arrangements exist without departing from the spirit of the invention. Accordingly, the discussed embodiments are for illustration only and should not be taken as a limitation.

Reference documents: smith dc acrylic denture: mechanical determination of midline rupture, journal of british dentistry, 1961, 110: 257-67. Wetherell JD., Smalles RJ., partial denture failure: long-term clinical investigation j.dent, 1980, 8: 333-40. Valittu PK, Lassila VP., Lappalainen R, the number and type of removable denture damages available in Finland, Acta Odontol Scand 1993, 51: 363-9. Darbar UR., hugette r, Harrison a, damage to dental abutments-review. British journal of dentistry, 1994, 176: 342-5. Ruffino ar, effect of steel reinforcement on the burst resistance of acrylic denture dentures, jprosthet, dent, 1985, 54: 75-86. Vallititu PK., influence of certain properties of metal reinforcement on the structural failure resistance of acrylic denture base materials, J.Oral Rehabil., 1993, 20: 241-8. Schwickrath H., Werkstoffe in der Zahnheilkunde Grundlardlagen Verarbaiitung, Beansprucung und Verhalten im Klinische Einstz Quinception Publ, Berlin, 1977: 189-94. Vallititu PK., as an ultra high modulus polyethylene tape for autopolymerized polymethylmethacrylate reinforcement, short news, dental material, printing. Grave amh, Chandler HD., wolfarardt JF., denture acrylic resin reinforced with high modulus fibers, dental materials, 1985, 1: 185-7. Vallititu PK., Lassila VP., Lapplaimen R., acrylic resin-fiber composite-I part: effect of fiber concentration on damage resistance, j.prosthet.dent, 1994, 71: 607-12. Williamson DL., Boyer db, Aquilino SA, Leary JM., effect of polyethylene fiber reinforcement on denture base strength polymerized by microwave energy, j.prosthet dent, 1994, 72: 635-8. Yaznodie n., Mahood m., carbon fiber acrylic resin composite: study of transverse strength, j. prosthet. dent, 1985, 54: 543-7. Ladizesky NH., Ho cf., Chow TW., reinforcement of complete denture trays with continuous high performance polyethylene fibers, j.prosthet.dent., 1992, 68: 934-9. Causton BE., denture tray polymer and liner, in O' Brien WJ. braids "dental materials: properties and selection ", Quessence Publ, Chicago, 1989, 167-9. Cogswell FN., component of composites of thermoplastic structure, in Cogswell FN., eds "composites of thermoplastic structure", Butterworth Heinemann, Oxford, 1992, 38-57. Goldberg aj, Burnstone cj, use of continuous fiber reinforcement in the dental field. Dental materials, 1992, 8: 197-202. Wylegala RT., denture tray material reinforced with carbon fibers, dental technique, 1973, 26: 97-100. Ekstrand k, Ruyter IE., wellandorf h. carbon/graphite fiber reinforced polymethylmethacrylate: properties under dry and wet conditions. Journal of biomedical materials research, 1987, 21: 1065-80. Mullarky RH., aramid fiber reinforcement of acrylic devices, journal of clinical stomatology, 1985, 19: 655-8. Gutteridge DL., comprising the effect of ultra-high modulus polyethylene fibers on the impact strength of acrylic resins, journal of british dentistry, 1988, 164: 177-80. Gutteridge DL., reinforcement of polymethylmethacrylate with ultra-high modulus polyethylene fibers, journal of dentistry, 1992, 20: 50-4. Ladizesky NH., Chow TW., effect of highly drawn polyethylene fibers on mechanical properties of denture resin, clinical materials, 1990, 68: 934-9. Ladizesky NH., Cheng YY., Chow TW., Ward IM., acrylic resins reinforced with chopped high performance polyethylene fibers: performance and base structure, dental material, 1993, 9: 128-35. Phillips RW., the science of the Scandinavian of dental materials (Skinner's science of dentalmaterials), WB Saunders Company, Philadelphia, 1982, 170-3. Winkler s., basis for a complete set of denture prosthetics, WB saunders company, toronto, 1979: 416-505.

Claims (19)

1. A method of making a fibrous article pre-impregnated with a polymer, the pre-preg being porous and readily formable at room temperature after the addition of a plasticizer; wherein, the method comprises the following steps: i)

a) polymerization with a polymer comprising at least one polymer and optionally an initiator for the polymerization

The powder of the respective agent coats the fibres,

b) adding a solvent to the composition obtained in step a), the solvent being soluble

Which polymer is depolymerized but not initiated to polymerize, and

c) evaporation of the solvent, or ii)

a) Comprising at least one polymer and optionally capable of initiating polymerization of the polymer

The powder of the reagents of the reaction being dissolved in a solvent capable of dissolving the polymer used but not capable of initiating its progress

In a solvent in which the polymerization is carried out, and

b) contacting the fibres with the solution obtained in the preceding step, and

c) the solvent was evaporated.

2. A process according to claim 1, wherein the composition obtained in step i) a) is added to a mould before the solvent is added thereto.

3. A method according to claim 1 or 2, which comprises surface treatment of the fibres to facilitate polymer-to-fibre bonding, the surface treated fibres thereafter being coated with the polymer powder.

4. A method according to claim 1 or 2, wherein the fibres are glass fibres.

5. A process according to claim 4 wherein the polymer is polymethyl methacrylate, ethylene glycol dimethacrylate, 2-bis [4- (2-hydroxy-3-methacryloyloxy) phenyl ] -propane or hydroxyethyl methacrylate and wherein the agent which facilitates polymer bonding to the glass fibre is a silane compound which is immobilised on the fibre at elevated temperature.

6. A process according to claim 5, wherein the silane compound is γ -methacryloxy-trimethoxysilane.

7. A porous prepreg comprising fibres and a polymer, the prepreg being porous and readily formable at room temperature after addition of a plasticizer, wherein the polymer is present between individual fibres and is distributed between the fibres as a solution from which solvent is evaporated.

8. The prepreg according to claim 7 wherein the porous prepreg comprises an agent capable of initiating polymerization of the polymer.

9. A prepreg according to claim 7 or 8 wherein the fibres are in the form of fibre tows, woven glass fibre mats, chopped glass fibre mats, staple fibres, whiskers or are processed into particulate form, or a mixture of the above forms.

10. A prepreg according to claim 7 or 8 wherein the fibre surfaces are treated to facilitate bonding with the polymer.

11. The prepreg according to claim 7 or 8, wherein the fiber is a glass fiber, the polymer is polymethyl methacrylate, ethylene glycol dimethacrylate, 2-bis [4- (2-hydroxy-3-methacryloyloxy) phenyl ] -propane or hydroxyethyl methacrylate, and a silane compound is coated on the surface of the fiber.

12. A process according to claim 11 wherein the silane compound is gamma-methacryloxypropyltrimethoxysilane.

13. A method of preparing a fibre-reinforced composite in which a prepreg according to any one of claims 7 to 12 is used, the method comprising the steps of:

adding a plasticizer to the prepreg in question, which may optionally be pre-prepared,

shaping the plasticized prepreg into a predetermined shape,

embedding the prepreg in a simple polymer of a composite or in a mixture of the polymer and a monomer, and

-allowing the polymer in the prepreg and the pure polymer in the composite to polymerize simultaneously.

14. A method according to claim 13, wherein the composite obtained in a later step is processed into one or more defined blocks or into defined shapes.

15. A method according to claim 13 or 14, wherein the plasticizer is a monomer of the polymer used in the prepreg.

16. A method according to claim 13 or 14, wherein the polymer in the prepreg is the same as the polymer alone in the composite.

17. A fiber reinforced composite comprising the prepreg according to any one of claims 7 to 12, wherein said prepreg is plasticized by impregnation with a monomer, shaped into a given shape, and embedded in a simple polymer in the composite; the polymer in the prepreg and the pure polymer in the composite are polymerized simultaneously.

18. Use of a composite according to claim 17 in a medical or dental component; a framework of the movable denture base, a fastener or a precise accessory of the movable denture base; permanent or temporary prostheses, including dental and implant supported prostheses; a dental or medical implant; endodontically treating a sulcus filling of a tooth; a support post, core, filling or crown of a tooth; a mouth shield, etc.

19. Use according to claim 18, wherein the component for medical or dental purposes is a device for prosthodontics, orthodontics or orthopedics.