EP1984038A2

EP1984038A2 - Marking for medical instruments, method for marking medical instruments, medical instrument comprising a marking

Info

Publication number: EP1984038A2
Application number: EP07711170A
Authority: EP
Inventors: Viktor Hegedüs
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-02-08
Filing date: 2007-02-08
Publication date: 2008-10-29
Also published as: DE112007000877B4; WO2007090387A3; DE112007000877A5; WO2007090387A2

Abstract

The invention relates to, inter alia, a marking for medical instruments, a method for marking medical instruments, and a medical instrument comprising a marking. The method for marking a medical instrument, especially a ceramic or metallic surgical or dental instrument, especially a dental drill, is characterised in that a) a layer of a mixture of polymerisable acrylates or pethacrylates or of a solid partially polymerised mixture of polymerisable acrylates or methacrylates, is applied to the instrument, forming an outer partial surface thereof, b) the polymerisation of the mixture is initiated, and c) the mixture is hardened on the instrument, the layer forming an outer partial surface of the instrument being provided with a colour and/or being light-permeable in such a way that it appears coloured due to a coloured layer arranged below.

Description

- -

MARKING FOR MEDICAL INSTRUMENTS, METHOD FOR MARKING

MEDICAL INSTRUMENTS, MEDICAL INSTRUMENT WITH A MARKER

FIELD OF THE INVENTION

The invention relates to a marking for medical instruments, in particular surgical and dental instruments such as dental drills, a method for

Marking of medical instruments, in particular surgical and dental instruments such as dental drills, and an instrument, in particular a surgical and dental instrument with a marking. In particular, it relates to the use of color markers with pigments on medical instruments, in particular dental drills, of ceramic or metal.

BACKGROUND OF THE INVENTION

Dental drills differ e.g. in the design of the turret depending on its purpose such as drilling different fine holes, milling or polishing. Also, in other surgical instruments, color markers are desired, for example, to distinguish the age of the instruments, the material or manufacturer.

Various methods for marking medical instruments are known. For example, international patent application WO 2005/102204 A2 in order to identify different dental drills faster and easier to mark the dental drills with a colored Teflon ring.

However, the known markings have not proven to be satisfactory in practice in every respect. So they are sometimes very expensive, difficult to work, for example, to grind, and fade or burst in disinfection procedures such as autoclaving. Surgical instruments made of ceramic or metal are articles that are used several times on different patients under as germ-free conditions as possible. For thorough and thorough cleaning and sterilization you must therefore be able to withstand autoclaving, especially at high temperatures and pressures, typically above 12O ⁰ C and above 2 bar. Furthermore, the surgical instruments should be as biocompatible and non-toxic as possible.

Another problem, especially in dental instruments, is addressed in DE 20 2004 002 472 U1: the accidental or intentional multiple use of disposable instruments. Namely, a series of instruments is expressly designed for single use only and is not intended to be sterilized in the autoclave after use. DE 20 2004 002 472 U1 therefore proposes to apply a thermochromic ink with irreversible color change on disposable dental drillings, the color change being triggered, for example, by the heat prevailing in the autoclave, so that instruments that are sterilized inappropriately can be easily recognized and rejected. However, DE 20 2004 002 472 U1 lacks a concrete executable marking.

OBJECT AND SUMMARY OF THE INVENTION

The invention has for its object to facilitate the marking of surgical instruments made of ceramic or metal, in particular tooth drills and to provide easily manufacturable, durable and biocompatible medical, especially surgical and dental instruments such as dental drills with color markings or disposable instruments with a reliable mark with to provide irreversible color change.

For this purpose, the invention proposes a method for marking a medical

Instrument, in particular a surgical or dental instrument made of ceramic or metal, in particular a dental drill, before, which is characterized by: Applying to the instrument a layer forming an outer sub-surface of the instrument, a mixture of polymerisable acrylates or methacrylates or a solid partially polymerized mixture of polymerisable acrylates or methacrylates, - starting the polymerization of the mixture

Curing the mixture on the instrument, wherein the layer forming an outer partial surface of the instrument itself has a color and / or is transparent, so that it is colored by an underlying colored layer.

The use of the mixture of polymerized acrylates or methacrylates makes it possible to carry out a marking which is itself subject to drastic conditions such as e.g. prevail in a treatment in an autoclave, survives damage. Such markers are also biocompatible and non-toxic. The markings can be used on ceramic, metal, synthetic, organic or mineral surfaces.

Suitable mixtures and their application to metal and ceramic surfaces are shown in the patent application DE 197 09 280 A1, to the entire contents of which the disclosure of the invention reference is made.

Particularly advantageous methacrylates for the polymerization mixture used according to the invention are among the names

- EC No. 216-367-7, CAS no. 1565-94-2, BIS-GMA, bisphenol-A

Glycidyl methacrylate, (1-methylethylidene) bis (4, 1-phenylenoxy (2-3, 1-propanediyl)) bis-methacrylate, or 2-methyl-2-propenoic acid (1-methylethylidene) bis (4,1-phenyleneoxy (2-hydroxy-3, 1-propanediyl)) ester or

- (1-methylethylidene) bis [4,4-phenylenoxy (2-hydroxy-3,1-

Propanediyl)] bis-methacrylate or

EC No. 203-652-6, CAS no. 109-16-0, TEDMA, 2,2'-ethylenedioxyethyl dimethacrylate, or triethylene glycol dimethacrylate - -

known. As particularly advantageous methacrylates for the polymerization mixture used in the invention are also used

Urethane dimethacrylate, which is also covered by the CAS no. 72869-86-4, and

Tetraethylene glycol dimethacrylate, which is also covered by CAS no. 109-17-1,

from the mixture of which a polymer is formed and used according to the invention.

Further advantageous acrylates and methacrylates are defined in the subclaims.

The mixture may advantageously comprise a preferably non-crystalline filler such as

Silica sand, crystal-free fumed silica, alumina, ceramics, glass, silanized glass powder, glass-ceramic, or mixtures of these fillers.

A particularly preferred filler is CAS-No. 112945-52-5 designated crystal-free highly disperse silica or fumed silica.

Another particularly preferred filler is the CAS no. 100402-78-6 designated 0.7 micron fine barium glass with disperse silica. The filler is usually inorganic.

A particularly preferred mixture comprises 70 to 90 wt .-%, preferably 79 wt .-% BIS-GMA ₁ 10 to 30 wt .-%, preferably 20 wt .-% TEDMA and 0 to 3 wt .-%, preferably 1 wt % of crystal-free fumed silica such that the sum of the components of the mixture is 100% by weight.

The mixture is polymerized, for example, with a photoinitiator which starts the polymerization, in particular of acrylates and / or methacrylates, under blue light irradiation, especially with a wavelength of 400 to 500 nm. - o ~

The photoinitiator may be benzophenone, benzoin, an alpha-diketone, acylphosphine oxide, camphorquinone, one or more of their derivatives, and a mixture thereof.

It can also be used according to the invention, a mixture by

Pressure and / or temperature is polymerized. It can thus be used mixtures which are polymerized without photoinitiator. As a result, it can be safely ruled out that no residual photoinitiator or its reaction products are present in the mixtures used. Combinations of pressure and temperature values are then selected for the polymerization such that a cured mixture is obtained. Preference is given to the pressure above 1 bar, in particular over 2 bar, preferably between 2.5 and 5 bar. The temperature is preferably above 100 ^° C., preferably between 110 and 150 ^° C.

To obtain the desired pressure and temperature conditions, can also

Water vapor pressure can be applied. In particular, the desired pressure and temperature conditions can be obtained in a conventional autoclave as used to sterilize surgical or dental elements. This can advantageously be carried out in one step hardening and sterilization of an instrument. Sterile, possibly sterile packaged

Instruments are so easily available.

Preferably, color markers are used which are obtained by curing a solid partially polymerized mixture of polymerizable acrylates or methacrylates. Such a solid partially polymerized mixture has at

Room temperature and atmospheric pressure a non-liquid soft consistency, in particular a consistency such as butter, dough or gel.

Such a solid partially polymerized mixture, blended with pigments and optionally fillers to a mass, can be used for a color marking in at least one

Groove or a groove of an instrument to be marked are applied so that this groove is covered by the mass. Advantageously, the instrument for curing under pressure and temperature is so immersed in glycerol that the mass is completely immersed. It is then a pressure and Temperature range chosen such that the mass hardens. The cured polymer can then be abraded so that the color marking produced in the region of the recess is flush with the surface of the instrument.

Instead of glycerol, other suitable liquids or gels may be used, such as polyethylene glycol solutions, paraffins, mineral oils, silicone oils, etc .. It is preferred to use liquids or liquid mixtures which have a favorable effect on pressure-free and temperature curing of polymers on a gap-free filling of the well have the polymer. It is thus avoided on the marked instruments places where

To collect contaminants or sources of infection. Especially after the grinding of the cured polymer, a smooth, easy-to-clean surface of the instrument is obtained in the region of the groove. Liquids such as glycerol or gels may function to cause the cure to occur in a protected reaction environment. So can in a sterilizing autoclave with

Water vapor curing under glycerol proceed largely without the presence of water.

In particular, a solid partially polymerized mixture having a buttery consistency is preferably formed from a copolymer of the dimethacrylate monomers

Urethane dimethacrylate, CAS no. 72869-86-4, and tetraethylene glycol dimethacrylate, CAS No. 109-17-1 and if necessary the above with the CAS no. 100402-78-6 described filler. The partially polymerized mixture can be obtained from the monomers by photopolymerization and / or polymerization under pressure and / or temperature. The pigment may be added before or after production of the solid partially polymerized mixture. Preferably, the mixture composition is selected such that a density of the fully cured mixture of between 1.5 and 2.1 g / cm, preferably 1.6 and 1.7 g / cm is obtained.

Pigments are used, for example, in the colors white, for example in the form of titanium dioxide or in the colors yellow, orange, light red, dark red, light green, dark green, light blue, dark blue, black, transparent, UV red or UV blue. Pigment examples are known under the names CAS no. 38185-91-4 (deep black), CAS no. 910010-29-1 (pink), CAS no. 13463-67-7 (white), CAS no. 910010-35-5 (yellow), CAS no. 910010-15-7 (kiwi or deep yellow), CAS no. 57455-37-5 (deep blue), CAS no. 990001-08-8 (neon red), CAS no. 99001-09-9 (neon blue and neon green), CAS no. 99001-15-7, CAS no. 99001-02-9 (orange), CAS no. 99001-10-

0 (red, deep red), CAS no. 99001-06-7 (neon yellow), which are available, inter alia, from the company Heraeus Kulzer GmbH, Werheim, Germany.

It can be used organic or inorganic pigments.

For marking disposable instruments, the outer surface of the instrument forming layer of a mixture of polymerizable acrylates or methacrylates or a solid partially polymerized mixture of polymerizable acrylates or methacrylates serves as a protective layer for an underlying colored layer of a thermochromic paint with irreversible ■

Color change.

The protective layer ensures that the thermochromic paint does not reach a patient and can not detach from the instrument. A film as a protective layer allows a cost-effective production of disposable drill bits with thermochromic color, but can not always safely fulfill the protective function but possibly tear or damage.

Advantageously, the manufacture of a sterile instrument can be simplified in that UV radiation both for curing the protective layer and the

Sterilization of the instrument is applied. The steps of hardening and sterilization are thus standardized. UV radiation can also be applied to a prefabricated instrument in UV-transparent packaging to ensure sterility.

Advantageously, the thermochromic ink is introduced into a depression of the instrument and subsequently, if appropriate, furthermore the polymerization mixture into this depression. - -

The abrasion of a portion of the cured polymerization mixture protruding from the recess allows the production of a smooth flush surface of the instrument in the region of the protective layer. This avoids sticking or seizing of sources of infection after unpacking the sterile instrument.

The thermochromic paint can also be printed on an adhesive tape and glued to the instrument.

The thermochromic color can also be printed directly on the instrument.

Advantageously, the thermochromic ink is applied in the form of a symbol or a label. Thus, after color change, for example, a stop symbol or e.g. The word "NO" will be visible to sort out disposables that have been autoclaved in the autoclave, even without incoming

To ensure instruction of the staff.

For ease of processing, a partially polymerized, viscous polymerization mixture is advantageously used.

The polymerization mixture comprises acrylates and / or methacrylates and optionally pigments. From this acrylate polymers are available, which are particularly biocompatible and may come into contact with the body or mucous membranes of a patient. Pigments especially in a color that corresponds to the thermochromic color before the color change under heat, ensure that a label is visible only after color change. The polymerization mixture can thus be suitably adapted to different thermochromic colors.

EXAMPLES

EXAMPLE 1

The following mixture 1 is produced: - -

79% by weight BIS-GMA, 20% by weight TEDMA

1% by weight of crystal-free highly dispersed silica of the ACEMATT® TS 100/20 brand from Degussa.

The following mixture 2 is prepared: 98% by weight of the above mixture 1

2% by weight ultramarine blue L6498

To the mixture 2 0.03 wt .-% UV stabilizer (Tinuvin P, Ciba Geigy) are added and 0.25 wt .-% camphorquinone.

The mixture is stored under light for three days in the refrigerator at about 8 ° C.

The titanium metal surface of a dental drill is cleaned with acetone and dried in air for 2 minutes.

The preserved mixture is then applied with a brush to a ring section of the

Titanium metal surface of a dental drill applied.

It is irradiated for 60 seconds with a handheld device with a wavelength in the range of 400 and 600 nm and then cured for 20 minutes.

The color application remains stable even after several passes in an autoclave.

EXAMPLE 2

The mixture 3 from:

Urethane dimethacrylate, CAS no. 72869-86-4, tetraethylene glycol dimethacrylate, CAS-No. 109-17-1, 0.7 μm fine barium glass with disperse silica, CAS no. 100402-78-6

was purchased under the brand Novorit® from Heimerle + Meule GmbH, 75179 Pforzheim, Germany.

It is prepared by kneading with a spatula the following mixture 4: 98 wt .-% of the above mixture 3 2 wt .-% ultramarine blue L6498.

A titanium metal plate with a groove is cleaned with acetone and 2 minutes at the

Air dried.

The mixture is then applied with a spatula on the furrow and covered with hydrous 98% glycerol.

The titanium metal plate with the glycerine-covered mixture 4 is placed in the autoclave for 3 hours at 12O ⁰ C and 3 bar water vapor pressure to completely cure the mixture.

The mixture composition is chosen in this example such that a

Density of 1.63 g / cm is obtained. EXAMPLE 3

In a titanium metal plate, a blind hole with a depth of 5 mm and a diameter of 5 mm is drilled and cleaned with acetone.

The hole is partially filled with tert-butoxycarbonylated 9-aminoperylene-3,4-dicarboximide.

The following polymerization mixture is prepared:

79% by weight BIS-GMA, 20% by weight TEDMA 1% by weight of crystal-free highly dispersed silica of the ACEMATT® TS 100/20 brand from Degussa.

To this mixture 2 are added 0.03% by weight UV stabilizer (Tinuvin P, Ciba Geigy) and 0.25% by weight camphorquinone.

The hole is filled up with the polymerization mixture.

It is irradiated for 30 seconds at a wavelength of 470 nm and then cured for 20 minutes and irradiated again for 30 minutes.

Claims

- 2 -PATENT CLAIMS

1. A method for marking a medical instrument, in particular a surgical or dental instrument made of ceramic or metal, in particular a dental drill, characterized by:

Applying a layer forming an outer sub-surface of the instrument, a mixture of polymerizable acrylates or methacrylates or a solid partially polymerized mixture of polymerisable acrylates or methacrylates to the instrument,

Starting the polymerization of the mixture curing of the mixture on the instrument, wherein the layer forming an outer partial surface of the instrument itself has a color and / or is transparent so that it is colored by an underlying colored layer.

2. A method according to claim 1, wherein the layer forming an outer sub-surface of the instrument is translucent so as to be colored by an underlying colored layer, characterized in that the underlying colored layer is of a thermochromic color with irreversible color

Color change exists.

3. The method according to claim 1 or 2, characterized in that the outer part surface of the instrument forming layer and an optionally underlying colored layer in a recess, in particular a circumferential

Groove, is introduced in the instrument or be.

4. The method according to claim 3, characterized in that the outer part surface of the instrument forming layer are introduced into the recess such that it protrudes from the recess and after curing of the

Partially abraded polymerization mixture. - -

5. The method according to claim 2, characterized in that the thermochromic ink is printed on an adhesive tape and adhered to the instrument.

6. The method according to claim 2, characterized in that the thermochromic ink is printed on the instrument.

7. The method according to claim 2, characterized in that the thermochromic color is applied in the form of a symbol or a label.

8. The method according to any one of claims 1 to 7, characterized in that the mixture when applied to the instrument comprises a photoinitiator, which is preferably selected from the group formed by benzophenone, benzoin an alpha-diketone, acylphosphine, camphorquinone and their

Derivatives and mixtures of these photoinitiators.

9. The method according to claim 8, characterized in that the start of the polymerization by applying an activation wavelength of 400 to 500 nm, preferably 470 nm is carried out on the mixture.

10. The method according to claim 1, characterized in that the polymerization mixture is cured with UV radiation.

11. The method according to any one of claims 1 to 10, characterized in that the start of the polymerization of the mixture and / or the curing of the mixture by application of pressure and / or temperature.

12. The method according to claim 11, characterized in that the mixture is cured in an autoclave.

13. The method according to claim 11 or 12, characterized in that the mixture is cured under glycerol. - -

14. The method according to any one of claims 1 to 13, characterized in that the acrylates or methacrylates are monomers having at least two acrylate or methacrylate groups, preferably di- or trifunctional methacrylates.

15. The method according to claim 14, characterized in that the monomers are selected from the group formed by tetraethylene glycol dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate-forming monomers, butanediol dimethacrylate, hexanediol dimethacrylate, decanediol dimethacrylate, dodecanediol dimethacrylate, bisphenol A dimethacrylate,

Trimethylolpropane trimethacrylate, tetraethylene glycol diacrylate, diethylene glycol diacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate-forming monomers, butanediol diacrylate, hexanediol diacrylate, decanediol diacrylate, dodecanediol diacrylate, bisphenol A diacrylate, trimethylolpropane triacrylate, their derivatives and mixtures of these compounds.

16. The method according to claim 14, characterized in that the monomers comprise urethane dimethacrylate and / or tetraethylene glycol dimethacrylate.

17. The method according to claim 14, characterized in that the monomers are selected from the group formed by BIS-GMA and TEDMA, mixtures of these compounds and mixtures of these compounds with monomers selected according to claim 15.

18. The method according to any one of claims 1 to 17, characterized in that the mixture further comprises a preferably non-crystalline filler.

19. The method according to claim 18, characterized in that the filler is selected from quartz sand, crystal-free fumed silica, alumina, ceramics, glass, silanized glass powder, glass ceramic, barium

Glass and mixtures of these fillers.

20. The method according to claim 17 and 18, characterized in that the mixture 70 to 90 wt .-%, preferably 79 wt .-% BIS-GMA, 10 to 30 wt .-%, - -

preferably 20% by weight of TEDMA and 0 to 3% by weight, preferably 1% by weight, of crystal-free highly disperse silica such that the sum of the constituents of the mixture is 100% by weight.

21. Medical instrument, in particular surgical or dental

Instrument of ceramic or metal, with a marking, characterized in that the instrument is marked by a method according to one of claims 1 to 20.

22. Medical instrument according to claim 21, characterized in that the instrument is a dental drill.

23. Use of color markers with pigments on medical, in particular surgical and dental instruments made of ceramic or

Metal, in particular tooth drills, characterized in that the pigments are contained in a mixture of polymerized acrylates or methacrylates, the mixture forming an outer partial surface of the instrument, and / or in one of said layer sealed

Layer are included.

24. Use according to claim 23, characterized in that the acrylates or methacrylates are monomers having at least two acrylate or methacrylate groups, preferably di- or trifunctional methacrylates. ,

25. Use according to claim 24, characterized in that the monomers are selected from the group formed by tetraethylene glycol dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, polyethyleneglycol dimethacrylate-forming monomers,

Butanediol dimethacrylate, hexanediol dimethacrylate, decanediol dimethacrylate, dodecanediol dimethacrylate, bisphenol A dimethacrylate, trimethylolpropane trimethacrylate, tetraethylene glycol diacrylate, diethylene glycol diacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate-forming - -

Monomers, butanediol diacrylate, hexanediol diacrylate, decanediol diacrylate, dodecanediol diacrylate, bisphenol A diacrylate, trimethylolpropane triacrylate, their derivatives and mixtures of these compounds.

26. Use according to claim 24, characterized in that the

Monomeric urethane dimethacrylate and / or tetraethylene glycol dimethacrylate.

27. Use according to claim 24, characterized in that the monomers are selected from the group formed by BIS-GMA and

TEDMA, mixtures of these compounds and mixtures of these compounds with monomers selected according to claim 25.

28. Use according to any one of claims 23 to 27, characterized in that the mixture further comprises a preferably non-crystalline filler.

29. Use according to claim 28, characterized in that the filler is selected from quartz sand, crystal-free fumed silica, alumina, ceramics, glass, silanized glass powder, glass ceramic, barium glass and mixtures of these fillers.

30. Use according to claim 27 and 28, characterized in that the mixture 70 to 90 wt .-%, preferably 79 wt .-% BIS-GMA, 10 to 30 wt .-%, preferably 20 wt .-% TEDMA and 0 up to 3% by weight, preferably 1% by weight, of crystal-free highly disperse silica in such a way that the sum of the

Components of the mixture 100 wt .-% is.

31. Use according to one of the preceding claims, characterized in that the mixture is polymerized with a photoinitiator.

32. Use according to claim 31, characterized in that the photoinitiator has an activation wavelength of 400 to 500 nm, preferably 470 nm. - -

33. Use according to claim 31, characterized in that the photoinitiator is selected from the group formed by benzophenone, benzoin an alpha-diketone, acylphosphine oxide, camphorquinone and derivatives thereof and mixtures of these photoinitiators.

34. Use according to any one of claims 23 to 30, characterized in that the mixture is at least partially polymerized by pressure and / or temperature.

35. Use according to claim 34, characterized in that the mixture is at least partially polymerized at a pressure above 1 bar, in particular above 2 bar and a temperature above 100 ⁰ C.

36. marking a medical instrument, in particular a surgical or dental instrument made of ceramic or metal, in particular a dental drill, characterized in that the marking comprises a layer having an outer partial surface of the

Instruments and consists of a mixture of polymerizable acrylates or methacrylates or a solid partially polymerized mixture of polymerizable acrylates or methacrylates, wherein the layer itself has a color and / or is transparent, that it is colored by an underlying colored layer.

37. The marker of claim 36, wherein the layer is an outer

Partial surface of the instrument is so translucent that it is colored by an underlying colored layer, characterized in that the underlying colored layer consists of a thermochromic color with irreversible color change.

38. A marker according to claim 36 or 37, characterized in that the acrylates or methacrylates are monomers having at least two acrylate or methacrylate groups, preferably di- or trifunctional methacrylates. - -

39. The marker according to claim 38, characterized in that the monomers are selected from the group formed by tetraethylene glycol dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate-forming monomers, butanediol dimethacrylate, hexanediol dimethacrylate, decanediol dimethacrylate,

Dodecanediol dimethacrylate, bisphenol A dimethacrylate, trimethylolpropane trimethacrylate, tetraethylene glycol diacrylate, diethylene glycol diacrylate, ethylene glycol diacrylate, polyethyleneglycol diacrylate-forming monomers, butanediol diacrylate, hexanediol diacrylate, decanediol diacrylate, dodecanediol diacrylate, bisphenol A diacrylate, trimethylolpropane triacrylate;

Derivatives and mixtures of these compounds.

40. A marker according to claim 39, characterized in that the monomers comprise urethane dimethacrylate and / or tetraethylene glycol dimethacrylate.

41. A marker according to claim 38, characterized in that the monomers are selected from the group formed by BIS-GMA and TEDMA, mixtures of these compounds and mixtures of these compounds with selected according to claim 39 monomers.

42. A marker according to any one of claims 36 to 41, characterized in that the mixture further comprises a preferably non-crystalline filler.

43. A marking according to claim 42, characterized in that the filler is selected from quartz sand, crystal-free fumed silica,

Alumina, ceramics, glass, silanized glass powder, glass-ceramic, barium glass and mixtures of these fillers.

44. The marker of claim 41 and 42, characterized in that the mixture 70 to 90 wt .-%, preferably 79 wt .-% BIS-GMA, 10 to 30 wt .-%, preferably 20 wt .-% TEDMA and 0 to 3% by weight, preferably 1% by weight, of crystal-free highly disperse silica such that the sum of the components of the mixture is 100% by weight.