2~1333 The invention relates to a new, polymerizable dental material with greater transparency and good polishability.
Dental materials, particularly tooth-filling materials, essentially comprise liquid, polymerizable binding agents and organic and/or inorganic fillers. Known from DE-OS 14 92 040 are, for example, tooth-filling compositions the color of which automatically ad~usts after hardening to the color of the natural tooth material. For this it is necessary that the refractive indices of binding agent and filler differ sllghtly. As fillers, glass beads with a particle size in the range of 18 to 40 microns and glass fibres with a particle size in the range of 0 . 4 mm length and 13 microns diameter are used. These are so-called macrofillers.
r)E-PS 24 03 211 discloses dental materials in which solely microfine, lnorganic fillers (microfLllers) based on silica are used, the particle size of which lies in the range of 10 - ~00 nanometers. Surprisingly, filling materials with good transparency and polishability and excellent physical properties are obtalned.
In order to facilitate the incorporation of larger quantities of fumed silica, or precipitated sillca ~reoared according to the wet-process, it has been proposed to modify these fillers, ~ mi~-~l ly or by heat-treatment, prlor to their incorporation. The BET surface is thus reduced (EP-PS 0 040 232, EP-OS 113 926~ .
DE-PS 27 05 220 proposes transparent dental materials with high compressive strength, in which a finely divided filler is used with such a grain distribution that 70 to 95 % of the particles display a grain size of 0 . 7 to 25 microns and 5 to 30 ~ of the particle~ a grain size of 0.2 to 0.7 microns.
Particles with a smaller diameter than 0.2 microns are also used at the most in small quantities. The-average grain size ~ 213~ 333 of the fine-particled fillers is given as 1 - 5 microns.
According to the examples, raw oc-quartz is heated and ground according to a certain method.
US-PS 4,220,582 describes filling materials with improved X-ray opacity. A filler mixture comprising a barium glass and amorphous silica is used, the content of BaO in the glass having to be at least 22 . 5 wt-% .
The fillers in DE-PS 32 47 800 are amorphous, spherlcal partlcles. They have a partlcle slze of 0.1 - 1 micron, the partlcles belng composed of silica and 0 . 01 - 20 mol-% of an oxide of at least one metal of C~roups I, II, III and IV of the periodic system and the cn~rnn!~nts bein~ chemically bonded to each other. These fillers are prepared from hydrolyzable compounds of silicon and the metals by reaction with ammonia, as is described in more detail in DE-PS 32 47 800. The refractive index of the fillers obtained ls reportedly ln the range of 1.35 to 1.70. The BET surface of the fillers can be reduced by calcination. Dental materials are ~uoted which contain such a filler, mixtures of the named fillers of mixtures or the fillers with a polymer filler.
US-PS 4, 503,169 describes X-ray opaque composites, which contain, as filler, special non-glass microparticles. These are prepared e.g. from an a~ueous SlO2/ZrO2 solution whlch is sub~ected to heat treatment. The refractive lndex can lnfluence the visual opacity of a composlte.
Finally, in EP-OS 238 025 X-ray opa~ue dental compositions are proposed which contaln certaln heavy metal fluorldes.
The transparency of the fully polymerized dental compositlons depends on the ratio o~ the refractive index of the fllllng bodles to the polymeric matrix. It can be further deduced from thls publlcatlon that tooth-fllllng composltlons prepared with glasses are less abrasion-stable vls-à-vls c[uartz, because of the low hardness of glass. It is not 2~31333 .

posslble to grin~ the glasses so finely that tooth-filling compositions polishable to a high gloss are also obtained.
Glasses which are so finely ground become opaque because of the grlnding processes necessary for this, whlch impairs the optical properties of the dental compositions.
From the prior art it emerges that, now as then, it is necessary to improve the properties of dental materials, particularly their transparency, while maintalning good pol ~ F:h;~h~ l ~ ty and not impairing the other physical properties such as e.g. high compresslve strength, low water absorption, high a~rasion resistance, good bending strength, X-ray opacity etc. Although the microfilled dental materials in DE-PS 24 03 211 pointed the way with regard to pol ~ Rh;~h~ l ~ ty and transparency, it has been shown that these materials stlll display certain disadvantages. Particularly, the incorporation of the fillers into the binding agent should be made easier, without time-consuming and labor-intensive pre-treatments of the inorganic filler being necessary, such as is quoted e.g. in EP-PS 40 232.
The present invention makes available a dental material with good transparency and polishability, as well as other good material properties, during the preparation of which the inorganic fillers are easily incorporable into the binding agent. The transl~arency is o~ decisive importance both for achieving as complete as possible a through-hardening of the material duriny photopolymerization and for the aesthetics of the f~n~hP~ product.
The sub~ ect of the invention is a novel dental material based on a polymerizable, ethylenically unsaturated monomer as binder, a catalyst for the cold-, hot and/or photopolymerization and 20 to 90 wt-% of an inorganic filler, comprising a mixture of:

2~ 33 ~A) amorphous, spherLcal particles comprising silica and up to 20 mol-% of an oxide of at least one element of Groups I, II, III and IV of the periodic system with a refractive index of 1. S0 to 1. 58 and with an average prlmary particle size of 0 .1 to 1. 0 microns, and (B) quartz, glass ceramiGs or glass powder or mixtures thereof with a refractive index of 1.50 to 1.58 and with an average particle size of 0.5 to 5 . 0 microns .
The term "dental material" is taken to mean tooth-filling materials, materials for inlays or onlays, dental cements, veneering materials for crowns and bridges, materials for dentures or other materials for prosthetic, preservative and preventive odontology.
In particular, the dantal material according to the invention is a composite, i, e . a tooth-filling material comprising inorganic fillers and at least one ethylenically unsaturated polymerizable binding agent and a suitable catalyst system.
It was surprlslngly found that by using binding agents known per se and a selected choice of inorganiG filler mixtures with quite specific physical properties, it is possible to make available a dental material which 2 ~ 3 3 . ~ .

displays unexpected physical properties. It i8 partlcularly surprising that the transparency and pol i Rh~h~ l i ty are very good .
As inorganic filler mixtures, mixtures of at least two different fillers are used. Inorganic filler (A) is an amorphous, spherical material based on silica, which additionally contains an oxide of at least one metal from Groups I, II, III and IV of the periodic system. Strontium and/or zirconium oxide are preferably used. The average primary particle size is in the range of 0 .1 to 1. 0 microns, particularly 0.15 to 0.5 microns. The refractive index of the lnorganic filler (A) is between 1. 50 and 1.58, particularly between 1.52 and 1.56. An especially preferred value is 1. 53 ~ 0 . 01. Filler mixtures are also possible, provided that they meet the parameters with regard to particle size and refractive index. Fillers of the (A) type are described in DE:-PS 32 47 800. The filler of type (A) can also be present as a mixture of sintered agglomerates with an average particle size of 1 to 30 microns .
The inorganic flller (B) of the filler mixture is quartz, glass ceramics or glass powder. Glasses are preferably used. The average primary particle size of the inorganLc filler (B) is to lie between 0.5 and 5.0 microns, particularly between 1. 0 and 2 . 0 microns and especially preferably between 1.0 and 1.5 microns, while the refrac-tive index is to display values between 1.50 and 1.58, particularly between 1.52 and 1.56. Filler mi~tures can also be used. Preferably used according to the invention are Ba-silicate glasses with an average grain size in the range of 1.1 to 1.3 microns, and Sr silicate glasses with an average grain size in the range of 1.1 to l . 3 microns, and also Li/Al silicate glasses with an average grain size of l . 0 to 1. 6 microns . Such powders are obtainable e . g . by 2~1333 fine-grindlng with an RS-ultrafine mill from Reimbold &
Strich, Cologne.
Other fillers ~C) can also be optionally added to achieve increased X-ray opacity; their average primary particle size should not exceed 5 . 0 microns . Such fillers are described e . g . in DE-OS 35 02 594 . An especially preferable filler (C) is ytterbium trifluoride.
For controlling viscosity, small quantities of microfine, fumed or wet-precipitated silica (filler (D) ) can be optionally incorporated into the dental material, subject however to a maximum of 5 wt-%, relative to the dental material .
The total filler quantity, comprising fillers (A), (B) and optionally (C) and (D) in the dental material according to the invention is, ~lPrPn~l~n~ on the intended use, between 20 and 90 wt-%. Preferably, the proportion by weight of filler (~) is 5 - 60 %, particularly 10 - 30 %, that of ~iller (B) 15 to 85 %, particularly 30 - 70 %, in each case relative to the total dental material.
The inorganic ~lllers are pre~erably sllanized. Suitable as adhesion promoter is e . g . ~-methacryloxypropyl trimethoxy silane. The quantity of adhesion promoter used depends on the type and BET surface of the filler.
Suitable as polymerizable organic binding agents are all binding agents usable for a dental material, particularly monofunctlonal or polyfunctional methacrylates which can be used alone or in mlxtures. Examples oi these compounds which are useful are methyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, tetraethylene glycol dimethacrylate, triethylene glycol dimethacrylate, diethylene gylcol dimethacrylate, ethylene glycol ~51333 dimethacrylate, polyethylene glycol dimethacrylate, bu-tanediol dimethacrylate, he-~An~rlinl dimethacrylate, n~ lol dimethacrylate, ~lo~ An~ l dimethacrylate, bisphenol-A-dimethacrylate, trimethylol propane trimethacrylate, 2,2-bis-4(3-methacryloxy-2-hydL~"Ly~ oxy)-phenylpropane (bis-GMA) and the reaction product3 f rom isocyanates, particularly di- and/or triisocyanates, and OH-group-containing methacrylates.
Examples of these are the reaction products of 1 mole hexamethylene dLisocyanate with 2 moles 2-hydroxyethylene methacrylate, o~ 1 mole tri(6-isocyanatohexyl)biuret wLth 3 moles 2-hydroxyethyl methacrylate and of 1 mole 2, 2, 4-trimethyl hexamethylene diisocyanate with 2 moles 2-l~ydL~)~syæ~hyl methacrylate, which hereinafter are referred to as urethane dLmethacrylates. The proportion of these mostly long-chain ~ ~ in the dental material ranges from lO and 80 wt-96.
DepPn-i~n~ on the type of the catalyst used, the dental material can be hot, cold or photo polymerizable. As catalysts for the hot-polymerization, the known peroxides such as dibenzoyl peroxide, dilauroyl peroxide, tert.-butylperoctoate or tert.-butylperbenzoate can be used, but ~,~'-a20-bis(isobutyroethyl ester), benzpinacol and 2,2'-dimethylbenzpinacol are also suita~le.
Usable as catalysts for the photopolymerLzation are e . g .
benzophenone and its derivatives, and benzoin and its derivatives. Other preferred photosensitizers are the ~-diketones such as 9,10-phenanthrene quinone, dlacetyl, furil, anisil, 4,4'-dichlorobenzil and 4,4~-dialkoxybenzil. Camphor quinone is especially preferred.
q~he use of photosensitizers together with a reducing agent is pref erred . ~xamples of reduclng agents are amines such as cyanoethyl methylAn~ l ine, dimethyl aminoethyl methacrylate, triethylamine, triethanolamine, N, N-3~3 dimethyl;ln~ 1 inP~ N-methyl dlphenylamine, N,N-dimethyl-sym. -xylidine and N, N-3, 5-tetramethylaniline and 4-dimethyl aminobenzoic acid ethyl ester.
Used a~ catalysts for the cold-polymerization are readical forming systems, e.g. benzoyl or lauroyl peroxide together with amines such as N,N-dimethyl-sym.-xylidine or N,N-dimethyl-p-toluidine. Dual-hardening system~ can also be used for catalysis, e.g. photoinitiators with amLnes and peroxides. As photocatalysts, mixtures comprising catalysts which are W-light-hardening and hardening in the range of vi~ible light are suitable.
The quantity of these catalysts in the dental material is usually betwcen 0 . 01 and 5 wt~
Fine-particled splinter or bead polymers, which can be homo- or copolymers of the already described vinyl compounds, can also be incorporated in the dental material. These homo- or copolymers can, for their part, be filled with the described inorganic filler~, also X-ray opaque ones. The dental material can also contain the usual pigmentation agents and stabilizers.
The dental material according to the invention prefernbly serves as tooth-filling material. Tooth-filling material6 are also prepared as two-component materials, which cold-harden after formulation. The composition is s1milar to that of the light-hardening materials, only instead of the photocatalyst6, e.g. benzoyl peroxide is incorporated into one paste, and e.g. N,N-dimethyl-p-toluidine into the other paste. By mixing roughly equal parts of the two pastes, a tooth-filling material is obtained which harden6 thoroughly in a few minutes.
If, in the case of the last-named materials, the amine is 205133~
.
g left out and as catalyst e.g. only benzoyl peroxide is used, a hot-hardenlng dental materlal is obtained which can be used for producing an inlay or dentures. For producing an inlay, an impression of the cavity is made in the mouth of the patient and 5 a plaster model is formed. The paste iB introduced into the cavity of the plaster model and the whole ls polymerized by heat in a pressure pot. The inlay is removed, processed and then cemented into the cavity in the mouth of the patient.
The invention relates not only to the dental material, but also 10 to finished parts made irom it, e.g. crowns, inlays etc. Thus the invention includes the use of the present dental materials as tooth-filling material, material for inlays or onlays, dental cement, veneering material for crowns and bridges, material for dentures or other material for prosthetic, preservative and 15 preve~tative dental treatment.
In the following, the invention will be illustrated in more detail with reference to examples. The comparative examples relate to dental materials which are not composed according to the lnvention, because they contain a greater proportion of 20 microfine fumed ~ilica instead of the flller component (A).
The fumed silica used, AEROS;!L oX 50 sil. from Degussa, is a fumed silica with an average primary particle size of 40 nanometers and a BET sur~ace of 50 ~ 15 m2/g, which is silanized.
Filler (A) used in the examples is one such as per DE-PS 32 47 25 800, i.e. an amorphous, spherical filler with an average primary particle size in the range of 0 .15 to 0 . 4 microns and a refractive index of approximately 1. 53 . The filler contains silica and 17 . 5 mol-% zirconium dioxide and is silanized.
The Ba-silicate glass used had an average graln size of 1. 2 30 microns and a refractive index of ca. 1. 53, the Li/Al silicate glass an average grain size of 1. 0 microns and a ~133~
_ 10 --refractlve index of approximately 1.538. The aforementioned gla3ses are inorganic fillers (B) for the purposes of the invention. The desired particle size was obtained by fine-grinding in a RS-ultrafine mill. The powders were silanized.
Filler (C) used in the examples was ytterbium trifluoride wLth an average primary particle size below 1 micron and a refractive index of approximately 1. 53 .
The f iller mixtures according to the inventLon were incorporated using usual methods, c.g. with the aid of a kneader or a three-roll mill.
Test pieces were made from the material3 of the examples and polished for 5 minutes with a rubber polisher. The surfaces were ~YAm~n~(i under a microscope.
Transparency was measured by using the method described in E~-OS 189 540. The through-hardening depth was de'c~rmin~-l Arrnrtlin~ to ISO 4049, the test pieces being illuminated with a commercLal light-hardening apparatus (Heliomat~D
from Vivadent) for 40 secondc~, provided a light catalyst was present.

r ComParative examPle 1 (Filler: finely ground silani~ed Ba glass, AEROSILa~ OX 50 sil . and ytterbium trif luoride ) .
16 g silanized AEROSIL~ OX 50, 15 g ytterbLum trifluoride and 51 g silanized Ba-silicate glass were incorporated into 18 g of a monomer mixture comprising 27 Wt-9~1 of a 2~51333 urethane prepolymer (reaction product from 1 mole trimethyl hl Lhylene dLisocyanate wLth 2 moles hydroxyethyl methacrylate), 42,2 wt-9~ bis-GNA, 30 wt-9~
trLethylene glycol dlmethacrylate, 0.3 wt-9~ camphor quinone and 0.5 wt-4 N,N-3,5-tetramethylaniline. A solid, ~~x~ll;qhle paste resulted, which was light-hardened.
Transparency: 27 96 pol ~ Rh~hi l i ty: good ComParative examPle 2 (Filler: finely ground ~ n~ 7~ Ba-glass and AEROSIL(~ OX
50 sil . ) 16 g silanized AEROSII~D OX 50 and 63 g silanized Ba-silicate glass were Lncorporated Lnto 21 g of the monomer mLxture described in example 1. A solid, modellable paste resulted, which was light-hardened.
Tran3parency: 31 9~
Polishability: good Comparative examPle 3 (Dual-hardening cement, filler: finely ground silanized Ba-glass and AEROSI~9 OX 50 sil. ) a) sasic paste:
7.5 g R~l Ini7~ AEROsIL3 OX 50, 10 g ytterbium trifluorLde and 51 g sil~ni7e~ Sr-silicate glass were Lncorporated Lnto 31. 5 g o~ a monomer mixture comprising 80 wt-96 of a urethane prepolymer (reaction product from 1 mole trimethylhf Lhylene diisocyanate with 2 moles hydroxyethyl methacrylate ), 1 8 . 7 wt- 9~ dorl~c~ n f 7i i o l 2~1333 dimethacrylate, 0.6 wt-% camphor quinone and 0.7 wt-% N,~-3,5-tetramethy]~n~ 1 in~. Additionally, small amounts of color pigment3 were added to obtain a tooth-like appearance. A viscous cement paste resulted.
b ) Catalyst pa3te:
7.5 g silanized AEROSILIID OX 50, 10 g ytterbium trifluoride and 51 g sl l~n~ Sr-silicate glass were incorporated into 31.5 g of a monomer mixture comprising 80 wt-% of a urethane prepolymer (reaction product from 1 mole trimethyl h~ thylene diisocyanate with 2 moles hydroxyethyl methacrylate~, 19.2 wt-% dodecanedLol dimethacrylate and O . 8 wt-% dibenzoyl peroxide . A viscous cement paste resulted.
Both pastes were mixed to form a dual-hardening (auto- and light-hardening) cement and then h~r~nf.~.
Transparency: 25 %
Polishability: good Through-hardening depth: 3.6 ~ 0.1 mm (steel mould, 40 sec. E~eliomat~) Example 4 15 g ytterbium trifluoride, lS g silanized ~iller (A) and 52 g .~ ni 7e~1 Ba-silicate glass were incorporated into 18 g of a monomer mixture ~ Rins 49 wt-% bis-G~A, 49 wt-%
dotl~ ~n~ l dimethacrylate, 2 wt-% dibenzoyl peroxide and 500 ppm MellQ. A solid, tran~lucent paste with good modellability resulted.
The dental material obtained was suitable as tooth-colored, hot-hardening inlay/onlay material.

~ 20al33~
_ 13 --Transparency: 4 4 %
pol i ~h~h~ 1 i ty: good Example 5 15 g ytterbium trifluoride, 16 g silanized filler (A) and 51 g silanized Ba-silicate gla3s were incorporated into 18 g of the monomer mixture described in comparative example 1. Addltionally, small amounts o~ color pigments were added to obtain a tooth-like appearance. A solid, translucent paste with good '^llAhllity resulted.
The dental material obtained was suitable as tooth-colored, light-hardening filling material for the molar area and as inlay/onlay material.
Transparency: 41 %
Poli ~hi~h~ 1 1 ty: good Bending strength: 139 i 11 MPa 20 Through-hardening depth: 4.4. ~ 0.1 mm (steel mould, 40 sec, }Ieliomat( D
Examp 1 e 6 25 17 g silanized filler (A) and 60 g silanized Li-Al-silicate glass were incorporated into 23 g of the monomer mixture described in comparative example 1. P.dditionally, small amounts of color pigments were added to obtain a tooth-like appearance. A solid, translucent paste with 30 good ~ hi 1 i ty resulted .
The dental material obtained was suitable as tooth-colored, light-hardening crown and bridge veneering material and as filling material for front teeth.
Transparency: 45 %

~Q~1333 _ 14 --Poli3hability: good ExamPle 7 15 g ytterbium trifluoride, 16 g silanized filler (A) and 50 g silanized Li-Al-silicate glass were incorporated into 19 g of the monomer mixture described in comparative example 1. Additionally, small amounts of color pigments were added to obtain a tooth-like appearance. A solid, translucent paste with good ,lf-17Ahi~ity resulted.
The dental material obtained was suitable as tooth-colored, light-hArlen~n~ filling material for front teeth.
Transparency: 44 %
Polishability: good ExamPle 8 a) Basic paste:
8.5 g sil~ni7~A filler (A), 10 g ytterbium trifluoride and 51 g silanized Ba-silicate glass were incorporated into 30 . 5 g of the monomer mixture described in comparative example 3 (basic paste). Additionally, small amounts of color pigments were added to obtaLn a tooth-like Arrl~ArAn~-e. A viscous cement paste reE~ulted.
b) Catalyst paste:
8.5 g silAni~ filler (A), 10 g ytterbiu~n trifluoride and 51 g silanized Ba-silicate glass were incorporated into 31. 5 g of the monomer mixture described in comparative example 3 ( catalyst paste ) . A viscous cement paste resulted.

~51333 . ~
_ 15 --Both pastes were mixed to form a dual-hardening (auto- and light-hardening), translucent cement.
Transparency: 42 9e Through-hardening depth: 4 . 8 + O .1 mm ( steel mould, 4 0 sec, Heliomat~8 )