WO2003105785A1

WO2003105785A1 - Antimicrobial prepreg, composite and their use

Info

Publication number: WO2003105785A1
Application number: PCT/FI2003/000468
Authority: WO
Inventors: Pekka Vallittu; Tuomas Waltimo; Johanna Tanner
Original assignee: Stick Tech Oy
Priority date: 2002-06-12
Filing date: 2003-06-12
Publication date: 2003-12-24
Also published as: FI20021126A0; AU2003240904A1

Abstract

The invention relates to a prepreg comprising an antimicrobial agent, fibers and a curable matrix, said matrix consisting of at least a first curable material. The invention is characterized in that said matrix contains pores and in that 0,5-95 % of the volume of said pores is filled with said antimicrobial agent. The invention also relates to a method for producing said prepreg, to a composite obtainable by curing said prepreg and to the use of said prepreg and said composite.

Description

ANTIMICROBIAL PREPREG, COMPOSITE AND THEIR USE

FIELD OF INVENTION

The present invention relates to a prepreg comprising an antimicrobial agent, fibers and a curable matrix, said matrix consisting of at least a' first curable material. The invention also relates to a method for preparing said prepreg, a composite obtainable from said prepreg as well as to the use of the prepreg and the composite.

BACKGROUND OF THE INVENTION

Different composite materials have been developed for dental use and the most recent composites are based on the use of fibre reinforcements as described in several patent publications (US 4,717,341; US 5,987,376; US 5,759,029, US 6,197,410; US 5,846,640). The successful combination of fiber reinforcement with highly viscous denture resins requires polymer pre-impregnation of the glass fibers as described in patent by Vallittu et al. (US 5,846,640). Incorporation of fibres instead of or additionally to the particulate fillers can considerably increase the mechanical properties of the composite. The odontological needs for a composite material include general biocompatibility, nontoxicity as well as adequate mechanical and cosmetic properties. In addition, a dental material should not promote oral microbial adhesion. Adhesion of microbes to host tissues or surfaces is essential for the pathogenesis of all infectious diseases. Oral microbes can adhere to tooth tissues as well as to restorative materials. In previous studies composites with different fibres have been shown to differ from each other with regard to microbial adhesion. Polyethylene fibers are found to bind more caries associated Streptococcus mutans than other fibers or restorative materials. The salivary pellicle formed on E-glass fibers was found to contain high amounts of S. mutans binding proteins and may thus promote adhesion of the organism in the oral environment.

Oral Candida species, especially C. albicans, are often associated with denture stomatitis. These yeasts together with bacterial flora of denture plaque adhere to and accumulate on the denture surface that acts as a reservoir of micro-organisms being a chronic source of mueosal irritation. Earlier studies have shown that incubation of a denture base polymer in chlorhexidine digluconate solution decreases the number of adherent yeasts in vitro (Ellepola ANB, Samaranayake LP. Adjunctive use of chlorhexidine in oral candidoses: a review. Oral Diseases 2001; 7: 11-17). This effect appears to be based on the perfusion of chlorhexidine into the denture base polymer and its subsequent diffusion from the polymer. A significant disadvantage of the use of the mentioned preliminary method of saturating the denture polymer with said solution is that the patient cannot wear the denture during the immersion of the denture in said solution. This causes major discomfort for the patient. In addition, if the denture is fixed on teeth or implants, the removal of the denture for immersion in antimicrobial agent is difficult to perform.

OBJECT AND SUMMARY OF INVENTION

An object of the invention is thus to provide a material suitable to act as a carrier material for antimicrobial agent offering simultaneously a reinforcing effect for use in dentistry and medicine. A further object of the invention is to provide a material of the above-mentioned kind that would be able to contain an antimicrobial agent for a significant period of time and at the same time, being able to release said agent at a predetermined rate.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates the weight increase of a prepreg according to the invention during immersion in water.

Figure 2 illustrates the weight increase of a prepreg according to the invention during immersion in a solution of water and chlorhexidine digluconate.

DETAILED DESCRIPTION OF THE INVENTION

By "curing" in this application it is meant both polymerising and crosslinking. Furthermore, by dendrimers large spherical hyper-branched polymers are meant.

The present invention relates to a prepreg comprising an antimicrobial agent, fibers and a curable matrix, said matrix consisting of at least a first curable material, said prepreg being characterized in that said matrix contains pores and in that 0,5-95 % of the volume of said pores is filled with said antimicrobial agent.

The prepreg according to the present invention thus fulfils an object of the invention, i.e. it is a material suitable to act as a carrier material for antimicrobial agent offering simultaneously a reinforcing effect for use in dentistry and medicine, since said antimicrobial agent is present in the pores of a porous matrix but do not fill the pores entirely. Thus, the prepreg comprising an antimicrobial agent still has a porous matrix. According to the present invention, 0,5-95 % of the volume of said pores is filled with said antimicrobial agent. It is obvious to a person skilled in the art that the amount of antimicrobial agent in the pores is selected such as to obtain the desired result. Factors influencing the amount of antimicrobial agent are for example the use of the prepreg, i.e. how long it is going to be used, where and eventually with what other materials. For example, 0,5-10 % of the volume of said pores may be filled with said antimicrobial agent. On the other hand, also percentages such as 1- 15, 4-25, 40-95, 23-55, 80-90, 4-8, 50-60, 90-95, 40-70 and 30-80 may be used.

According to an embodiment of the present invention, the prepreg further comprises a second curable material. This second curable material advantageously fills up the pores after the antimicrobial agent has partially filled said pores. This embodiment thus fulfils the further object of the invention, i.e. it provides a material that is able to contain an antimicrobial agent for a significant period of time and at the same time, is able to release said agent at a predetermined rate.

The antimicrobial agent used in the present invention may be any known antimicrobial agent. Antimicrobial agents include also antibiotics. Antibiotics include agents that are active against bacteria, such as betalactams, tetracyclins and metronidazoles, as well as agents that are active against fungi, such as polyenes and azole-group agents. Other examples of antimicrobial agents are biguanides such as chlorhexidine, halogen releasing agents, betaine, fluorides, delmopinol and antimicrobial monomers such as methacrloyloxydodecylpyridinium bromide as disclosed in the publication by Imazato S, Walls AWG, Kuramoto A, Ebisu S. "Penetration of an antibacterial dentine-bonding system into demineralised human root dentine in vitro" (Eur J Oral Sci 2002;110:168-174).

According to the present invention, the fibres of the prepreg may be any known fibers that are compatible with the matrix used. The fibers may for example be selected from a group consisting of inert glass fibers, bioactive glass fibers, silica fibers, quartz fibers, ceramic fibers, carbon/graphite fibers, aramid fibers, poly(p- phenylene-2,6-benzobisoxazole) fibers (PBO), poly(2,6-diimidazo(4,5-b4',5'- e)pyridinylene-l,4(2,5-dihydro)phenylene fibers (PIPD), polyolefin fibers, polyester fibers, polyamide fibers, polyacrylic fibers, sol-gel processed silica fibers, collagen fibers, cellulose fibers and modified cellulose fibers. Any combination of said fibers may be used. Poly(p-phenylene-2,6-benzobisoxazole) fibers and poly(2,6-diimidazo(4,5-b4' ,5 ' -e)pyridinylene- 1 ,4(2,5-dihydro)phenylene fibers belong to a group called rigid-rod polymer fibers. It is obvious to a person skilled in the art that any other known fibers may be used in the present invention, provided it is possible to obtain a suitable adhesion between said fibers and matrix, in order to achieve the desired mechanical properties. In dental applications the most suitable fibres are, at the moment, glass fibres.

The matrix of the prepreg as well as the second curable material may be made of any suitable monomer or polymer or mixture of them. Indeed, said prepreg is further cured to make a finished product and by curing it is here meant both polymerization and cross-linking. When polymers are used as matrix, they are advantageously linear polymers. The material of the matrix and the second curable material may be identical or not. They may for example both comprise two components, one of which is common.

The matrix of the prepreg may comprise monomers selected from the group consisting of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, tetrahydrofurfuryl methacrylate, benzyl methacrylate, morpholinoethyl methacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate (TEGDMA), diurethane dimethacrylate, 2,2-bis(4-(2-hydroxy-3- methacryloxy)phenyl)propane (BisGMA), acetoacetoxy ethyl methacrylate (AAEM), methacrylate functionalized dendrimers, other methacrylated hyperbranched oligomers and mixtures thereof. The matrix may also be made of crosslinkable monomers or polymers such as ε-caprolactone, polycaprolactone, polylactides, polyhydroxyproline, and other biopolymers as well as polyamides, polyurethane, polyethylene, polypropylene, other polyolefins and polyvinyl chloride. The matrix may naturally also consist of a mixture of a monomer(s) and a polymer (s).

A typical and preferred polymer in dental and medical applications at the moment is polymethylmethacrylate (PMMA), especially PMMA having a molecular weight between 13 000 and 990 000 g/mol. More preferably the molecular weight is between 20 000 and 300 000 g/mol, such a molecular weight allowing an especially easy formation of a dense polymer matrix for the finished composite when the prepreg is used with dental resins as first and/or second material.

The invention also relates to a method for preparing a prepreg, said method being characterized in that the antimicrobial agent is incorporated in a prefabricated porous prepreg in a first step. According to a preferred embodiment of the present invention, the antimicrobial agent is incorporated into the prepreg in solution form. In this embodiment, the solvent used should thus not essentially dissolve the matrix of the prepreg. According to an embodiment of the invention, a solution of water and chlorhexidine digluconate is used. Said solution has the advantages of having a wide spectrum of antimicrobial action, resistance development is rarely encountered and irritation to host tissues is minor. In this embodiment of the invention, the porous polymer structure is filled with the antimicrobial agent solution by capillary force after the porous prepreg has been immersed in said solution. After evaporation of the water of the antimicrobial solution, the antimicrobial agent, i.e. chlorhexidine remains in the pores of the prepreg.

According to a further embodiment of the invention, a second curable material is incorporated in the prepreg in a second step after said first step of incorporating the antimicrobial agent. Said second step is advantageously carried out once the solvent has evaporated from the pores of the prepreg, thus allowing for said second curable material to fill up the pores of the prepreg. It is also possible to firstly make a prepreg impregnated with said antimicrobial agent, cure the matrix and then re- impregnate the cured material with a second curable material.

The curing, i.e. polymerizing and/or cross-linking may be initiated by any known method, such as by heat, light, ultra-sound or microwave energy.

The invention further relates to a composite obtainable by curing a prepreg according to the present invention. The invention thus provides a combination of fibre-reinforcement and antimicrobial agent for one appliance by the use of a prepreg according to the invention.

The invention yet further relates to the use of a prepreg or a composite according to the present invention in dental and/or medical devices.

Examples of such devices are removable dentures, permanent partial dentures, temporary fixed partial dentures, orthodontic appliances, root canal fillings, root canal posts, periodontal splints, tooth fillings, crowns, maxillofacial prostheses and endosseal implants, such as dental implants, orthopaedic implants and surgical plates. In medicine any devices penetrating into the parenteral space or blood vessels are potential infection pathways. Examples of devices to be used in medicine are therefore any kind of canyles and catheters for temporary and long- term use. Orthopaedic external supporting devices are also applications suitable for the material according to the present invention. The antimicrobial agent modified prepreg according to the invention can also be used in fabrication of another type of prepreg, such as described in the patent US 6,197,410. After the appliance made of the antimicrobial agent containing prepreg or composite is in use, the water of saliva, or water of body fluid diffuse into the polymer matrix and diffusion of the antimicrobial agent occurs from the device. The antimicrobial effect of the agent can be clinically used to heal microbe induced denture stomatitis, periapical infections or periodontal infections. Furthermore, it can also be used against caries prevention particularly in immuno-compromised patients. In addition, the release of antimicrobial agent from the device inhibits the adhesion of oral microbes on the material surface.

EXPERIMENTAL PART

Manufacture of a prepreg and a composite according to the invention

A fibre prepreg made of woven glass fibres and polymethyl metacrylate (Mw 220 000 g/mol) by the process described in US 5,846,640, the prepreg Stick Net™ (by Stick Tech Ltd., Turku, Finland; lot 1990906- W-0037) was used. Said prepreg has a porous structure wherein the pores (pore size: 1 to 50 micrometres) are located between the glass fibres. The prepreg was immersed in a solution of water and chlorhexidine digluconate (80:20 wt%) (medical grade, lot 9901028, University Pharmacy, Turku, Finland) for one minute and dried before preparation of the composite test specimens. During the one minute immersion time the porous matrix of the prepreg was saturated with the chlorhexidine digluconate solution which was evidenced by the weight increase by water (Fig. 1 and 2).

The prepregs impregnated with said solution were further impregnated with a mixture of polymer powder and monomer liquid of Palapress® (Palapress®, Heraeus Kulzer, Wehrheim, Germany; powder lot 012151, liquid lot 010984) resin, after which the prepregs were embedded into the resin mixture. The Palapress® resin contained methylmethacrylate (MMA) and butanedioldimethacrylate (BDMA) monomers with a barbituric acid - copper ion initiator system. The powder/liquid ratio of the resin was 1.90/1.00 by weight and polymerization of the resin was carried out in water at (55±1)°C under air pressure of 300 kPa for 15 min. Thickness of the glass fibre reinforcement was 0.06 mm and one layer of reinforcement was incorporated to the rhombic test specimens of a size 5,0 x 5,0 x 0,8 mm. Control material was made of the same denture base resin without any fibre prepregs. The test specimens were stored in water for 24 hours before yeast adhesion assay. Microbiological testing of the materials

Organisms and growth conditions

Candida albicans strains were used: Cal (ATCC 90028), Ca2 (LCA03, OBU stock strain), Ca3 (LCA07), and Ca4 (LCA14). The organisms were identified by a germ tube test as disclosed in Berardinelle S., Opheim D:J: (1985), "New germ tube medium for the identification of Candida albicans, J. Clin. Microbiol. 22:861-862. The organisms were also identified by a commercially available API 20C Aux identification kit (Analytical Profile Index; Bio Merieux SA, France). Stock cultures were maintained at 4°C. After recovery these were maintained on Sabouraud dextrose agar (Oxoid Ltd, Basingstoke, Hampshire, England), stored at 4-6°C during the experimental period. Purity of the cultures was ensured by regular random identification of isolates by techniques described above. A loopful of stock culture was incubated on a Sabouraud agar plate in air at 37°C for 18 h. Four loopfuls of this culture were transferred to Sabouraud dextrose broth (Oxoid Ltd, Basingstoke, Hampshire, England) enriched with sucrose (500 mmol/litre) (KEBO Lab, Oslo, Norway) and incubated at 37°C for 24 h. The culture was centrifuged at 1500 g for 10 min and the deposit washed twice with phosphate buffered saline (PBS). A final, spectrophotometrically standardized, yeast suspension of approximately 1 x 10⁷ cfu/ml was prepared in PBS.

Adhesion assay

The prepared test specimens were placed vertically in the wells of a sterile serology plate (Corning Glass Works, Corning, NY, USA), each well measuring 5 mm in diameter. The yeast suspension with an inoculum size of lxlO⁷ cells/ml was prepared by haemocytometric counts as described previously. Approximately 0,4 ml of this suspension was added to each well to completely immerse the test specimen and the whole plate placed in a shaker incubator for 1 h at 37°C, with gentle agitation at 75 rpm. The test specimens were then removed from the wells, washed with sterile distilled water, air dried, and stained using a modified Gram stain, without counter staining. Thereafter, the test specimens were dried at room temperature and mounted on glass slides with Permount (Fisher Scientific, Fair Lawn, NJ, USA). Randomly selected twenty fields were counted for each sample at 400x magnification using light microscopy. The mean number of adherent yeast cells per field was expressed as cells per microscope field (approximately 1,6 mm^). Each experiment with each isolate / test specimen combination was performed on two separate occasions, with two strips on each occasion. Adherence of yeasts to the composite and control specimens

In the control group, the mean number of yeasts / unit area was 59,81 whereas in the antimicrobial agent containing test group the mean number was of yeasts was 38,69. Thus, there was significantly more adherent C. albicans cells found in the control group without chlorhexidine than in the group containing the composite according to the present invention with chlorhexidine antimicrobial agent.

The use of a prepreg according to the invention in the manufacturing of temporary fixed partial denture

The fibre prepreg described above was used in the manufacturing of a temporary fixed partial denture made of polymethyl methacrylate powder and butyl methacrylate monomer liquid (Dentalon Plus, Heraeus Kulzer, Wehrheim, Germany). A model of the denture was made of wax and the shape was copied by polyvinyl siloxane impression material. The prepreg containing glass fibres, a matrix and an antimicrobial agent was further impregnated with the Dentalon Plus resin. The impression was filled with the resin and the further-impregnated prepregs were placed to the impression. The impression was pressed to a dental cast having the shape of the abutment teeth. The resin was polymerized in water bath and the denture was finished in conventional way. By this procedure, a temporary fixed partial denture with antimicrobial agent and fibre reinforcement was obtained.

In this specification, except where the context requires otherwise, the words "comprise", "comprises" and "comprising" means "include", "includes" and "including", respectively. That is, when the invention is described or defined as comprising specified features, various embodiments of the same invention may also include additional features.

Claims

1. A prepreg comprising an antimicrobial agent, fibers and a curable matrix, said matrix consisting of at least a first curable material, characterized in that said matrix contains pores and in that 0,5-95 % of the volume of said pores is filled with said antimicrobial agent.

2. The prepreg according to claim 1, characterized in that it further comprises a second curable material.

3. The prepreg according to claim 2, characterized in that the second curable material is contained in the pores of said matrix.

4. The prepreg according to any of the preceding claims, characterized in that said antimicrobial agent is selected from the group comprising antibiotics, chlorhexidine, betaine, fluoride, delmopinol, methacrloyloxydodecylpyridinium bromide and mixtures thereof.

5. The prepreg according to any of the preceding claims, characterized in that the fibers are selected from a group consisting of inert glass fibers, bioactive glass fibers, silica fibers, quartz fibers, ceramic fibers, carbon/graphite fibers, aramid fibers, poly(p-phenylene-2,6-benzobisoxazole) fibers, poly(2,6- diimidazo(4,5-b4' ,5 ' -e)pyridinylene- 1 ,4(2,5-dihydro)phenylene fibers, polyolefin fibers, polyester fibers, polyamide fibers, polyacrylic fibers, sol-gel processed silica fibers, collagen fibers, cellulose fibers, modified cellulose fibers and combinations thereof.

6. The prepreg according to any of the preceding claims, characterized in that the first and/or second curable material comprises at least one monomer selected from the group consisting of methyl methacrylate, ethyl methacrylate, n- butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, tetrahydrofurfuryl methacrylate, benzyl methacrylate, morpholinoethyl methacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, diurethane dimethacrylate, 2,2-bis(4-(2-hydroxy- 3-methacryloxy)phenyl)propane, acetoacetoxy ethyl methacrylate, methacrylate functionahzed dendrimers, methacrylated hyperbranched oligomers and mixtures thereof.

7. The prepreg according to any of the preceding claims, characterized in that the first and/or second curable material comprises crosslinkable polymers selected from the group consisting of ε-caprolactone, polycaprolactone, polylactides, polyhydroxyproline, polyamides, polyurethane, polyethylene, polypropylene, polyvinyl chloride and mixtures thereof.

8. A method for preparing a prepreg according to any of the claims 1-7, characterized in that the antimicrobial agent is incorporated in a prefabricated porous prepreg in a first step.

9. The method according to claim 8, characterized in that the antimicrobial agent is incorporated in said prefabricated porous prepreg in solution form.

10. The method according to claim 8 or 9, characterized in that a second curable material is incorporated in the prepreg in a second step.

11. A composite obtainable by curing a prepreg according to any of the claims l to 7.

12. Use of a prepreg or a composite according to any of the claims 1-7 or 11 in dental and/or medical devices.

13. Use according to claim 12, characterized in that said device is selected form the group consisting of a removable denture, a permanent partial denture, a temporary fixed partial denture, an orthodontic appliance, a root canal filling, a root canal post, a periodontal splint, a tooth filling, a crown, a maxillofacial prostheses, a canyle, a catheter, an orthopaedic external supporting device and endosseal implants.