the dental light - curing opaquer according to the invention contains the following components : ( a ) cross - linked bead polymerizate into which a coloured pigment is incorporated , and with the proviso that the quantity of ( a ) used is not completely soluble in the quantity of ( b ) used . the bead polymerizates used are preferably based on at least one ( meth ) acrylic acid ester . advantageous bead polymerizates ( a ) contain 1 to 40 , in particular 5 to 20 and particularly preferably 10 to 15 wt . % of incorporated coloured pigment , relative to the quantity of bead polymerizate . it has also proved to be advantageous that the bead polymerizate has a degree of cross - linking of 10 to 90 , in particular 20 to 80 and particularly preferably 40 to 60 %. typically , the bead polymerizate is present in the form of particles with an average particle size of 10 to 100 and in particular 12 to 30 μm , based on the number of particles . customary coloured pigments suitable for colouring dental materials can be used as coloured pigment . particularly preferred are ultramarine blue ; iron oxide pigments ; coloured pigments based on cobalt , aluminium , chromium , nickel and / or zinc oxides ; and / or organic coloured pigments . particularly preferred are red and yellow iron oxide pigments . black and white pigments , such as zro 2 or tio 2 , are not suitable according to the invention as coloured pigments and are therefore not covered by the term &# 34 ; coloured pigments &# 34 ;. known processes are employed to prepare the cross - linked bead polymerizate used in the opaquer . these are described for example in the patents ep - b - 11 190 , ep - b - 84 769 , ep - b - 11 735 , ep - b - 11 734 and u . s . pat . no . 4 , 500 , 658 already mentioned above and the literature quoted therein in each case . it is important that the polymerization takes place in the presence of the coloured pigment , so that the latter is incorporated in the resulting beads when polymerization is complete . furthermore , the light - curing opaquer according to the invention contains polymerizable polyfunctional monomer ( b ). coming into consideration for this purpose are polyfunctional ( meth ) acrylates used in dental materials . particularly advantageous are ethylene glycol dimethacrylate ( egdma ), triethylene glycol dimethacrylate ( tegdma ), hexanediol dimethacrylate , 2 , 2 - bis - 4 -( 3 - methacryloxy - 2 - hydroxy - propoxy )- phenylpropane ( bis - gma ), urethane dimethacrylates formed by reaction of 2 , 2 , 4 - trimethylhexamethylene diisocyanate with 2 - hydroxyethyl methacrylate , decanediol dimethacrylate ( d 3 ma ), butanediol dimethacrylate and the corresponding acrylates . the quantity of cross - linked bead polymerizate , provided with coloured pigment , that is used must not be completely soluble in the quantity of monomer that is used . an initial dissolution of the bead polymerizate in the polyfunctional monomer ( b ) and optionally present monofunctional monomer ( f ) is however possible . furthermore , it is undesired for the bead polymerizate to swell in the used monomers , since otherwise the viscosity of the opaquer would change too greatly . an increase in viscosity would mean , for example , that the opaquer composition could be pressed out only with great difficulty from the customarily used application syringes . for the opaquer according to the invention to allow a colour match to natural tooth material in a broad range , it usually also contains white pigment ( c1 ) and / or black pigment ( c2 ) in addition to the coloured pigment . zro 2 and / or tio 2 are preferably used as white pigment and carbon black pigment as black pigment . zro 2 is particularly preferred since it does not prevent through - hardening , even in very high quantities . furthermore , the opaquer according to the invention usually contains a photoinitiator ( d ) which catalyses the photopolymerization . in particular benzophenone and derivatives thereof as well as benzoin and derivatives thereof can be used for this purpose . other preferred photoinitiators are the α - diketones , such as 9 , 10 - phenanthrenequinone , diacetyl , furil , anisil , 4 , 4 &# 39 ;- dichlorobenzyl and 4 , 4 &# 39 ;- dialkoxybenzyl . camphor quinone is particularly preferably used . moreover , it is advantageous in many cases to use the photoinitiators together with reducing agents , for which purpose amines in particular , such as cyanoethylmethylaniline , dimethylaminoethyl methacrylate , triethylamine , triethanolamine , n , n - dimethylaniline , n - methyldiphenylamine , n , n - dimethyl - sym .- xylidene , n , n - 3 , 5 - tetramethylaniline and 4 - dimethylaminobenzoic acid ethyl ester come into consideration . inorganic fillers can also optionally be present in the opaquer . in particular precipitated or pyrogenic silicas with an average primary particle size of 5 to 100 nm and a bet surface area of 0 to 400 m 2 / g are used for this purpose . such materials are marketed by degussa under the name aerosil ® or by wacker under the name hdk ®. finally , the opaquer according to the invention can also contain polymerizable monofunctional ( meth ) acrylic acid esters , in particular methyl methacrylate ( mma ), hydroxyethyl methacrylate , tetrahydrofuryl methacrylate , cyclohexyl methacrylate , isobutyl methacrylate and the corresponding acrylates . the opaquer composition according to the invention is prepared in the usual manner , in particular by thoroughly mixing the used components . in particular , the procedure can be such that initially cross - linked bead polymerizate with an incorporated coloured pigment , for example red and yellow cross - linked bead polymerizates , are prepared . for this purpose , a premix of cross - linking agents with red or yellow colour pigments is mixed with methyl methacrylate , and peroxide is added to this mixture as a polymerization initiator . polyfunctional methacrylic acid esters , such as urethane dimethacrylates and triethylene glycol dimethacrylate , are typically used as cross - linking agents . the polymerization is then carried out in a known manner in an aqueous phase as a suspension polymerization . the obtained red or yellow bead polymerizates are separated off , dried and screened . there usually then follows a tempering stage in order to destroy any residual peroxide present . colour pastes are then prepared using the thus - prepared red and yellow bead polymerizates . to this end , polymerizable polyfunctional monomer ( b ) and optionally other components , such as photoinitiator ( d ) and inorganic filler ( e ), are mixed with the bead polymerizates . the mixture is then usually homogenized on a triple - roll mill , whereby light - curable red and yellow colour pastes are formed . in order to match the colour of these pastes to the required colour of a natural tooth , they are mixed with conventional white and / or black colour pastes . these conventional white and black colour pastes are obtained by homogenizing polymerizable polyfunctional monomer , photoinitiator and inorganic filler with black pigments or with white pigments , in particular zro 2 . the light - curing opaquer according to the invention is advantageously suitable for covering metal structures in dentistry . for this purpose , it is applied in particular to the metal structures of dental restorations , such as bridges or crowns , and cured , and then usually a veneer , in particular a plastic veneer , is applied in the usual manner to the metal structure provided with the opaquer , thereby forming an aesthetically pleasant dental restoration . it was surprisingly shown that , even with a high pigments content , in particular with zro 2 used as white pigment , and with a concomitant high covering power , the opaquer according to the invention can nevertheless be essentially completely cured with light . in contrast , conventional light - curing opaquers exhibit only a slight depth of through - hardening . furthermore , neither does the opaquer according to the invention tends to separation with formation of a filler - rich and a filler - poor phase , and therefore it is also suitable for extended storage . finally , the opaquer according to the invention also exhibits very good adhesion both to different metals which can form dental structures and to applied veneers . particularly advantageous quantities of the individual components of the opaquer according to the invention are given below , these being able to be chosen independently of one another : ( a ) 2 to 20 , in particular 2 to 15 and particularly preferably 3 to 12 wt . % of bead polymerizate with incorporated coloured pigment , ( b ) 20 to 70 , in particular 40 to 60 and particularly preferably 50 to 52 wt . % of polymerizable polyfunctional monomer , ( c1 ) 20 to 60 , in particular 25 to 50 and particularly preferably 30 to 45 wt . % of white pigment , ( c2 ) 0 to 0 . 1 , in particular 0 to 0 . 01 and particularly preferably 0 to 0 . 005 wt . % of black pigment , ( d ) 0 . 1 to 6 , in particular 0 . 5 to 4 . 5 and particularly preferably 1 to 3 wt . % of photoinitiator , ( e ) 0 to 20 , in particular 2 to 20 and particularly preferably 5 to 6 wt . % of inorganic filler , and / or ( f ) 1 to 6 , in particular 1 . 5 to 4 . 5 and particularly preferably 2 to 3 wt . % of polymerizable monofunctional ( meth ) acrylic acid esters . the invention is explained in more detail below with reference to examples . first of all , a base mixture having the composition below was prepared : ______________________________________base mixture______________________________________urethane dimethacrylate 3 . 0 gtegdma 0 . 530 gbutyl cresol 0 . 710 gsilica ( hdk h - 15 ) 0 . 350 gmethyl methacrylate 4 . 100 g______________________________________ this base mixture was mixed in each case separately with 1 . 1 g of a red iron oxide colour pigment ( siccotrans red ) and 1 . 1 g of a yellow iron oxide colour pigment ( siccotrans yellow ) respectively . red and yellow bead polymerizates were prepared in a reactor using these mixtures according to the methods of suspension polymerization , that is accompanied by stirring and heat . the grain size was controlled by the polymerization parameters , and in the case of the prepared bead polymers it was below 32 μm . the red and yellow bead polymerizates prepared in example 1 were used to prepare red and yellow opaquer colour pastes according to the invention . likewise , conventional white and black colour pastes were prepared . in each case , the individual components were mixed accompanied by stirring and homogenized in a triple - roll mill to form a paste . the individual red , yellow , white and black colour pastes had the following composition . ______________________________________ red yellow white black ( wt . %) ( wt . %) ( wt . %) ( wt . %) ______________________________________bis - gma 44 . 6 44 . 6 42 . 9 -- tegdma 5 5 5 -- hdk - 2000 3 . 5 3 . 5 5 -- bead polymer 40 . 0 40 . 0 -- -- zro . sub . 2 -- -- 40 . 0 -- camphor quinone 0 . 7 0 . 7 0 . 9 -- embo 1 . 0 1 . 0 1 . 0 -- decanediol dimethacrylate 5 . 2 5 . 2 5 . 2 -- carbon black pigment -- -- -- 30 ( microlith ) colophonian resin -- -- -- 70______________________________________ the abbreviations used have the following meanings : hdk15 microfine hydrophilic sio . sub . 2 , bet surface area 150 m . sup . 2 / g hdk2000 microfine hydrophobic sio . sub . 2 , bet surface area 170 m . sup . 2 / g embo pdimethylaminobenzoic acid ethyl ester different - coloured pasty opaquers were prepared using the colour pastes described in example 2 . the quantities of the individual colour pastes were varied in the ranges given below in order to achieve a broad colour adaptability . ______________________________________yellow colour paste 6 . 4 to 24 . 0 wt . % red colour paste 0 . 1 to 10 . 0 wt . % white colour paste 74 . 0 to 93 . 0 wt . % black colour paste 0 . 5 to 4 . 5 wt . % ______________________________________ in order to prepare the final opaquer , the individual colour pastes were weighed together and homogenized at high speed in an agitator . the obtained opaquers had a through - hardening depth which was clearly greater than that of comparable opaquers according to the state of the art . for comparison with conventional opaquers , a reddish opaquer according to the invention was prepared , the colour of which is close to the colour code 540 of the chromascop colour ring produced by ivoclar , liechtenstein . the white , red , yellow and black colour pastes described in example 2 were mixed to this end . a conventional opaquer of the same colour was prepared by mixing together white , red , yellow and black colour pastes to give a corresponding colour . the red and yellow colour pastes did not , however , contain any coloured bead polymerizates , but only the corresponding coloured pigments , namely iron oxide red and iron oxide yellow , were added . a thin layer of both opaquers was then brushed onto metal , this layer was polymerized in a light - curing apparatus , namely a spectramat from ivoclar , liechtenstein , for 2 minutes , a second , covering layer was applied and polymerization followed for a further 5 minutes in the light - curing apparatus . the opaquer layer was then scraped off with a probe . in the case of the opaquer according to the invention , the lower layer was hard throughout and completely polymerized , whereas the conventional opaquer containing no bead polymerizate with incorporated coloured pigment had a soft and unpolymerized lower layer .