Dental compositions which can be prepared and worked by the action of oscillations and method for the preparation thereof

Curable compositions are described which contain a binder and a high propion of fillers having a mean grain size of <50 .mu.m. The filler proportion of the curable compositions is so high that they cannot be used for the intended purpose because of their high viscosity However, they can be liquefied by exposure to oscillation in the frequency range of 20 Hz to 20 MHz with an amplitude of 1 .mu.m to 5 mm so that they are workable and can be employed for the intended purpose.

DESCRIPTION 
The invention relates to dental compositions which can be made and worked 
by the action of oscillations and a method for the preparation thereof as 
well as the use of highly filled dental filling materials (filling 
composites) for cementing inlays, onlays, veneers and the like by means of 
high-frequency vibrations. Such compositions include in particular dental 
preparations, for example filling compositions, but also other 
compositions, such as adhesives and fillers. 
In many technical fields, for example in the field of dental compositions 
and adhesive compositions and fillers, highly filled viscous curable 
compositions are used to fill defects or join defective parts together. 
The durability of these restorations is governed essentially by the 
properties of the binders and fillers, the binders generally representing 
the weaker part. It has therefore been found that the compositions permit 
particularly durable and high-quality restorations whenever the filler 
content is very high. Thus, in dentistry, dental filling compositions 
having up to 85% by weight fillers are offered and dental cements usually 
have 50 to 60% by weight fillers. 
This incorporation of fillers is limited in particular by the viscosity 
setting which the user requires. Thus, for example, dental filling 
compositions must still be plastically formable enough for the dentist to 
be able to introduce them with suitable instruments, for example spatulas 
and ball point pluggers, into the cavity, for them to be liquefiable under 
pressure to such an extent that they can fill the cavity completely by 
flowing and for them to be still workable with the instruments in such a 
manner that the surface can be adapted to the natural situation. To mount 
inlays, onlays, veneers and the like, usually readily flowing cement 
compositions are used which as a rule have a low content of inorganic 
fillers. Such cement compositions harden either by ion reactions, for 
example socalled zinc phosphate or glass ionomer cements, or by 
polymerisation reactions, for example by radical polymerisation of 
methacrylic acid esters. 
These latter materials are used in particular when adequately transparent 
inlays, onlays and veneers are involved, for example of porcelain or 
resin. The standard materials preferably used for this purpose are 
photocurable materials, and in some cases an aftercuring is effected with 
a following redox process. 
European patent 0 325 266 describes for example dental materials which may 
also be used for cementing inlays, onlays and veneers and which are cured 
in two steps. For this purpose the compositions contain two different 
photoinitiators with different light absorptions. Although in this patent 
specification highly filled dental filling compositions are described, 
cement compositions which are made by this system usually have less than 
50% by weight fillers. 
The demands in the field of cementing materials and adhesives are even more 
stringent. Since here it is frequently necessary to fill minute gaps with 
the adhesives, elevated flowability under pressure is necessary. Usually, 
here film thicknesses &lt;25 .mu.m should be obtainable under low pressure. 
It was therefore hitherto not possible to prepare and use compositions 
which are so highly viscous and are thus filled with filling bodies to 
such an extent that they can still be acceptably employed by the user. 
Conventionally, most multicomponent preparations are mixed with a spatula 
on a support, for example a block. Thus, suitable volumes or volumes of 
the individual components predosed in the mixing ratio are placed on a 
block and subsequently mixed with a spatula. However, this procedure works 
hitherto only with relatively low viscosity or highly thixotropic 
materials which become liquefied by the mixing movement to such an extent 
that complete mixing is thereby ensured. With less thixotropic and very 
highly filled materials it is not possible to apply these shearing forces 
at all. 
It is further known to mix predosed multicomponent materials in capsules 
(e.g. EP 0 157 121). As a rule, this is a powder/liquid system, the 
powder, for example a glass ionomer cement powder, being stored in the 
capsule interior, and a liquid component which is injected by a special 
activator system before the mixing being stored in a pad attached 
outwardly to said container. These capsules are thereafter mixed under 
high-frequency oscillations with amplitudes &gt;5 mm in the capsule. The 
disadvantage of this system is however that the energy transfer is 
relatively poor and that in the mixing movements in the chamber a certain 
amount of air is frequently introduced as well. 
It is known from EP 0 232 733 to mix low-viscosity or medium-viscosity 
compositions (dental impression compositions or epoxy adhesives) 
homogeneously together by means of so-called static mixing elements. In 
this case the materials are pressed through a cannula into which a mixing 
spiral is inserted. U.S. Pat. No. 4,219,619 describes a vibrating dental 
instrument for inserting crowns and bridges. By relatively low-frequency 
vibration in the range of 20-100 Hz, in this case a usual low-viscosity 
cement is liquefied on inserting the crown by means of the transfer chain 
vibrator/bite registration/crown. Liquefication of high-viscosity 
compositions is not described here. The use of filling composites or 
composite cements is not described either. Moreover, the method requires a 
specific instrument which must be specially acquired by the dentist. 
Thus, hitherto no method was available with which multicomponent highly 
filled highly viscous compositions could be mixed uniformly at the user's 
(i.e. by hand or in a mixing capsule). 
The objective of the invention is to solve the aforementioned problems by 
making available to the user extremely highly filled and highly viscous 
compositions which can be prepared with novel preparation methods and can 
be applied with novel processes.

The essence of the invention is to be seen in that highly filled 
compositions, the viscosity of which is so high that they do not permit 
working with the usual methods, are liquefied by a vibration treatment so 
that they can be prepared, worked and employed in accordance with their 
purpose. 
The subject of the invention is curable compositions which contain a binder 
and a high proportion of fillers having a mean (weight average) grain size 
of &lt;50 .mu.m and are characterized in that their filler proportion is so 
high that they cannot be used for the intended purpose because of their 
high viscosity and that by the action of an oscillation in the frequency 
range of 20 Hz to 20 MHz with an amplitude of 1 .mu.m to 5 mm they can be 
liquefied so that they may be employed for the intended purpose. 
The subject of the invention is further a method for preparing the 
aforementioned compositions which is characterized in that the fillers are 
mixed with the binder under the action of an oscillation in the frequency 
range of 20 Hz to 20 MHz with an amplitude of 1 .mu.m to 5 mm. 
The subject of the invention is further a method for mixing multicomponent 
highly filled highly viscous compositions, the components being mixed 
between two workpieces by shearing movements, the method being 
characterized in that at least one of the workpieces is set into 
oscillation in the frequency range of 20 Hz to 20 MHz with an amplitude of 
1 .mu.m to 5 mm. 
The subject of the invention is further the use of highly filled dental 
filling materials for cementing inlays, onlays, veneers or the like by 
means of high-frequency vibrations. 
The vibration is preferably generated by means of an ultrasonic device. 
The frequency range according to the invention is preferably 50 Hz to 50 
kHz and in particular 100 Hz to 30 kHz. The preferred amplitudes are 20 
.mu.m to 2 mm and in particular 50 .mu.m to 1 mm. 
With the method according to the invention it is also possible for the 
first time to mix compositions having a viscosity which is so high that 
said compositions could not be mixed with known methods by the user (that 
is by hand or in a mixing capsule). Such compositions in multicomponent 
form are advantageous in particular whenever several different curing 
mechanisms are to be combined with each other. It is particularly 
advantageous in the field of photocuring in shaded regions. In such cases 
a second curing mechanism independent of the illumination source can be 
incorporated, for example a redox initiator system for methacrylates. Said 
system consists for example of peroxides, such as benzoyl peroxide, and 
activators, for example amines, in particular aromatic amines or other 
reduction agents such as barbituric acids, or their derivatives, or 
alternatively malonyl sulfonamides and their derivatives. 
For the dental compositions to be mixed according to the invention 
ethylenically unsaturated monomers or polymers may be used, for example 
monomeric and polymeric acrylates and methacrylates. In this connection 
attention is drawn to the compositions described in DE-OS 3,609,038, the 
X-ray-opaque fillers described therein possibly also being omitted. 
As ethylenically unsaturated monomers or polymers for dental compositions, 
particular attention is drawn for example to the monomeric and polymeric 
acrylates and in particular methacrylates. In the case of polymerisable 
dental compositions, in particular the long-chain monomers of U.S. Pat. 
No. 3,066,122 on the basis of bisphenol A and glycidyl methacrylate are 
used, or the derivatives thereof obtained by addition of isocyanates. Also 
particularly suitable are the acrylic or methacrylic acid esters of 
monohydric or preferably polyhydric alcohols, for example triethylene 
glycol dimethacrylate and the like. Also particularly suitable are the 
diacrylic and dimethacrylic acid esters of bishydroxymethyl 
tricyclo-(5.2.1.0.sup.2,6)-decane cited in DE-PS 2,816,823. It is also 
possible to use the reaction products of diisocyanates and 
hydroxyalkyl(meth)acrylates, as described for example in DE-OS 2,312,559. 
Of course, mixtures of suitable monomers or unsaturated polymers prepared 
therefrom may also be employed. 
As photoinitiators, all substances may be used which after irradiation by 
UV or visible light initiate polymerisation, for example benzoinalkyl 
ethers, benzil ketals, acylphosphine oxides or aliphatic and aromatic 
1,2-diketone compounds, for example camphor quinone, the 
photopolymerisation possibly being accelerated in a manner known per se by 
addition of activators, such as tertiary amines or organic phosphites. 
Suitable initiator systems for initiating the polymerisation via a redox 
mechanism are for example the systems peroxide/amine or 
peroxide/barbituric acid derivatives and the like. When using such 
initiator systems, it is expedient to prepare an initiator (e.g. peroxide) 
and a catalyst component (e.g. amine) separately. The two components are 
then homogeneously mixed together just before use. 
The method according to the invention can however also be advantageously 
employed for other multicomponent and high-viscosity compositions, such as 
for example for mixing high-viscosity impression compositions or dental 
cements, such as glass ionomer cements or zinc/phosphate cements. 
A new field of application is also opened up by the use of highly filled 
high viscosity compositions which hitherto could not be reasonably mixed 
in the area of multicomponent adhesives and fillers. 
However, methods of mixing dental preparations are preferred. 
It has been surprisingly found that by the use of high-frequency vibrations 
in the mounting of inlays, onlays and veneers, even highly viscous, highly 
filled compositions become so readily flowable that the wetting of the 
replacement and the remaining hard tooth substance is optimum and very 
small film thicknesses of the cementing composite can be obtained. 
High-frequency vibrations mean here vibrations of more than 200 Hz. 
Frequencies of more than 1 MHz are no longer suitable for the cementing. 
Preferably, high-frequency vibrations of more than 1000 Hz, preferably more 
than 5000 Hz, particularly preferably more than 10000 Hz, are employed. 
Expediently, the high frequency vibrations are applied for the cementing 
procedure with socalled "sonic scalers" and/or "ultrasonic scalers". Such 
devices have been in use for a long time in dental surgeries for removing 
tartar and filling excesses. When applying the ultrasonic vibrations, in 
addition a cooling is achieved simultaneously by supplying water. With the 
use according to the invention it is advantageous to turn off this water 
cooling and to act with the rounded scaler centre portion on the surface 
of the inlays, onlays or the veneers with low pressure so that said 
portion can sink into the cavity filled with composite. 
It is advantageous here to arrange an intermediate layer, for example 
paper, waxed paper or the like, between the ultrasonic device and for 
example the inlay surface, in order to avoid any damage to the inlay 
surface by entrance of energy of the ultrasonic device. This can also be 
done in a favourable embodiment by placing a plastic sleeve over the 
scaler centre portion. The use of highly elastic rubber-like materials, 
for example bite impression materials, is not suitable for this purpose 
because said materials no longer transmit the high-frequency vibrations 
but absorb them. 
The composite filling materials preferably contain the following 
components: 
a) 60-95, preferably 70-90,% by weight inorganic fillers; 
b) 4-39.99, preferably 9-29.9,% by weight ethylenically unsaturated 
polymerisable monomers and/or polymers; 
c) 0 01-3, preferably 0.1-2,% by weight photoinitiators; 
d) and possibly activators, initiators for the initiation of a redox 
polymerisation, as well as pigments, X-ray-opaque additives and/or 
thixotropy aids. 
The filling bodies preferably have a mean particle-size distribution &lt;20 
.mu.m and in particular &lt;5 .mu.m as well as an upper grain limit of 150, 
preferably 70 .mu.m and in particular &lt;25 .mu.m. It is particularly 
advantageous to use socalled hybrid composites containing 5-25% by weight 
fillers with a mean grain size of 0.02-0.06 .mu.m and 65-85% by weight 
fillers having a mean grain size of 1-5 .mu.m. Inorganic fillers may for 
example be quartz, ground glasses, silica gels and pyrogenic silicic acids 
or their granulates. The at least partial use of X-ray-opaque fillers is 
particularly preferred. These may firstly be X-ray-opaque glasses, that is 
glasses containing for example strontium, barium or lanthanum, or 
alternatively part of the fillers consists of an X-ray-opaque additive, 
for example yttrium fluoride, strontium hexafluorozirconate or fluorides 
of the rare earth metals. 
To improve the incorporation into the polymer matrix it is advantageous to 
hydrophobe the inorganic fillers. Usual hydrophobing agents are silanes, 
in particular trimethoxymethacryloyl oxypropylsilane. 
The filler proportion in the compositions to be mixed may for example be 60 
to 95% by weight, and for dental preparations filler proportions of 80 to 
95% by weight and for adhesives and filling compositions 60 to 80% by 
weight are of particular interest. 
To prepare the compositions according to the invention with high filler 
content, for example conventional kneading devices are employed to which 
an oscillation is applied in the frequency range of 20 Hz to 20 MHz with 
an amplitude of 1 .mu.m to 5 mm. By the oscillation applied the components 
are kept liquid during the preparation procedure to such an extent that an 
appreciably increased filler content results. After stopping the 
oscillation the material is then of such high viscosity that it can no 
longer be worked with the usual techniques. It can then be worked only by 
again applying in accordance with the invention an oscillation in the 
frequency range of 20 Hz to 20 MHz with an amplitude of 1 .mu.m to 5 mm. 
With the method according to the invention for the mixing the procedure is 
such that the shearing between two workpieces is transmitted to the 
components. This may for example be done in that a vibrating spatula is 
employed and as counter piece a block or glass plate is again present. The 
material liquefies under the vibrating motions of for example the spatula 
and can be correspondingly well mixed. An alternative however is to use a 
vibrating spoon-like body in which with a usual commercial stationary 
spatula the materials can be mixed. A vibrating plate with a usual 
commercial spatula is another possible system. It is also possible to set 
both workpieces, i.e. for example spatula and block, in vibration 
simultaneously. 
A further embodiment of the method according to the invention is the mixing 
in a dynamic or static mixer. The vibration can advantageously be applied 
either to the wall of the cannula or to the mixing spiral. It is possible 
then to mix together homogeneously even compositions which are so highly 
viscous that without vibration they cannot be pressed through said 
arrangement without destruction of the workpiece. This embodiment is 
particularly well suited to highly viscous dental impression compositions 
or adhesives or fillers. 
To generate vibrations, either a separate device can be employed which is 
set into the corresponding vibration by means of piezoelectric or 
electromagnetic motors, or an insert can be made for an existing appliance 
used by the dentist, for example ultrasonic scaler or electrical 
toothbrush, which fits onto the corresponding counter pieces and after 
activation can in turn transfer the vibrations to the material. The 
generation of vibrations in the field of the invention is known in the 
art. 
The advantages according to the invention are as follows: 
1. Possible use for high-viscosity multicomponent cementing materials 
analogous to DE-OS 4,032,505 which can however now contain a second curing 
mechanism. This makes curing in shaded zones possible. 
2. Air-bubble-free mixing is possible for the first time with 
multicomponent systems. With high-frequency vibrations in said range air 
bubbles may be completely removed from highly viscous materials. This 
positively influences the hardness of the material and in addition has the 
aesthetic advantage that the air bubbles would always be "visible" at the 
surface. 
3. Preparation of dental compositions with very high filler content which 
in the cured state thus have a particularly high permanent strength and 
resistance to abrasion. 
4. Minimizing of the polymerisation shrinkage, the thermal expansion and 
the abrasion by the increased filler proportion. 
The invention will be explained in detail hereinafter with the aid of 
examples. 
EXAMPLE 1 
From 70 parts by weight bisacryloxymethyltricyclo-(5.2.1.0.sup.2,6)-decane 
and 30 parts by weight 
2,2-bis-4-(3-methacryloxy-2-hydroxypropoxyphenyl)-propane as well as one 
part by weight p-chlorobenzoyl peroxide, a homogeneous solution 1 is 
mixed. 
With the same parts by weight monomer and 1 part by weight 
p-N,N-diethylaminotoluidine and 3 parts by weight N,N-dimethylaminoethyl 
methacrylate and 0.3 parts by weight camphor quinone a homogeneous 
solution 2 is mixed. 
21 parts by weight of the solution 1 are kneaded with 55 parts by weight 
silanised tooth-dyed quartz having a mean grain size of 1.5 .mu.m as well 
as 5 parts by weight silanised pyrogenic silicic acid having a mean grain 
size of 0.04 .mu.m and 19 parts by weight silanised yttrium fluoride 
having a mean grain size of 1 .mu.m to give a homogeneous paste 1 
(catalyst paste). 
21 parts by weight of the solution 2 are kneaded with the same parts by 
weight quartz, pyrogenic silicic acid and yttrium fluoride to give a 
homogeneous paste 2 (base paste). 
Catalyst and base paste cannot be mixed together homogeneously using 
conventional means such as spatula/block, mixing capsules or the like. 
0.5 g catalyst paste are placed with 0.5 g base paste into a spoon-like 
attachment for an electrical toothbrush. The material cannot be mixed with 
a commercially available plastic spatula and the viscosity is so high that 
even kneading no longer appears possible. After setting the electrical 
toothbrush into operation the spoon-like attachment oscillates with a 
frequency of 50 Hz and a deflection of 0.8 mm. In this condition the 
materials can instantaneously be mixed very easily and give a homogeneous 
mixed end product. Immediately after stopping the vibrations the mixed 
paste again has a high viscosity which makes it very easy to model the 
material. 
The paste has a working time of 7 1/2 minutes and sets within 15 minutes 
(23.degree. C.). The compressive strength of the hardened material after 
curing in darkness is 350 MPa and if the pressure-resistant body is also 
irradiated on both sides with a commercially available dental illumination 
unit (Elipar Visio, ESPE) for 20 sec., a compressive strength of 400 MPa 
is obtained. The surface hardness of the material is 240 MPa, after both 
dark curing and light curing. 
The above example shows that it is possible for the first time with the 
method according to the invention to obtain a mixing of base and catalyst 
paste and thus to arrive at a material which has both the high viscosity 
properties and excellent physical properties after mixing with the method 
according to the invention. After the mixing the material is absolutely 
free of bubbles, i.e. the air bubbles usually also mixed into thinly 
liquid cements are completely eliminated by the vibration. The vibrations 
introduced cause the viscosity to decrease by about a factor of 10, as can 
be shown with the aid of a film thickness measurement. If about 500 mg 
base paste is introduced between 2 glass plates and the latter loaded 
thereafter with a total load weight of 15 kp, after a measuring time of 3 
minutes a film thickness of 110 .mu.m is obtained. If the measurement is 
carried out as above but the glass plates are set in vibration with the 
aid of the electrical toothbrush set forth in the example, a film 
thickness of 10 .mu.m is obtained. This means that with the method 
according to the invention it is possible to employ for cementing purposes 
even pastes of such high strength that they normally have film thicknesses 
far above the required 25 .mu.m. The vibrations introduced reduce the film 
thickness by the factor 10 from 110 .mu.m to about 10 .mu.m. 
EXAMPLE 2 
The two pastes of example 1 are placed in equal volumes on a commercially 
available mixing block (with surface of waxed paper). Thereafter, with a 
spatula attached to a commercially available ultrasonic device (Cavitron, 
Dentsply Company) said pastes are mixed together. After switching on the 
ultrasonic device (frequency about 28 KHz, amplitude 0.05 mm) the 
materials can be easily mixed together and after the mixing no air bubbles 
at all can be seen. After switching off the ultrasonic device the mixed 
paste again immediately has the original high viscosity. The materials 
thus mixed have physical properties as described in example 1. 
EXAMPLE 3 
A premixture is kneaded from 70 parts by weight 
bisacryloxymethyltricyclo-(5.2.1..sup.2,6)-decane and 30 parts by weight 
2,2-bis-4-(3-methacryloxy-2-hydroxypropoxy)phenyl propane (bis-GMA), 7 
parts by weight silanised pyrogenic silicic acid, 0.3 parts by weight 
camphor quinone, 3 parts by weight N,N-dimethylaminomethyl methacrylate 
and 110 parts by weight yttrium fluoride as X-ray-opaque filler. 
5.96 g of this premixture are kneaded with as great as possible an amount 
of silanised quartz (mean grain size about .mu.m) pigmented to be similar 
to teeth. With a conventional planetary kneader, at the most 16 g filler 
can be kneaded in. However, if the kneader pot is placed on a vibrating 
plate oscillated with an amplitude of 0.5 mm and a frequency of 50 Hz, a 
further 6 g of the quartz can be kneaded in. Once the vibration has been 
switched off kneading is no longer possible and the material has a high 
viscosity and cannot be appreciably deformed under pressure. 
If however this paste is taken up with a vibrating spatula as is described 
in example 2, the material can be introduced by the user into a cavity, 
again without any problems, and in this manner an extremely highly filled 
composite with an extremely low thermal expansion, extremely low abrasion 
and low polymerisation shrinkage is obtained. In addition, the material 
can be excellently worked with vibrating instruments, and the solid 
consistency after stopping the vibration is particularly advantageous, and 
consequently excesses and edges can be perfectly shaped in the 
nonpolymerised state. 
EXAMPLE 4 
A homogeneous solution is mixed from 70 parts by weight 
bisacryloxymethyltricyclo-(5.2.1.0.sup.2,6)-decane and 30 parts by weight 
2,2-bis-4-(3-methylacryloxy-2-hydroxypropoxyphenyl)propane, 0.3 parts by 
weight camphor quinone and 3 parts by weight N,N-dimethylaminoethyl 
methacrylate. 
21 parts by weight of this solution are kneaded with 55 parts by weight 
silanised quartz dyed tooth colour having a mean particle-size 
distribution of 1.5 .mu.m and 5 parts by weight silanised pyrogenic 
silicic acid having a mean particle-size distribution of 0.04 .mu.m and 19 
parts by weight silanised yttrium fluoride having a mean particle-size 
distribution of 1 .mu.m to form a homogeneous paste. The paste has a 
highly viscous pasty consistency which "per se" is not suitable for 
cementing. 
An inlay cavity is completely filled with the composite paste made in this 
manner. Thereafter, the prefabricated composite inlay (made from the same 
composite paste material but already completely cured throughout) is 
pressed into the cavity filled with the paste. Then, with an "ultrasonic 
scaler" (10,000 Hz) (Cavitron, Firma Dentsply) and with the water cooling 
switched off, the inlay is lowered into the filled cavity with slight 
pressure on the inlay surface. Due to the ultrasonic vibration the 
composite paste liquefies to such an extent that all excesses bulge out of 
the cementing gap and the inlay is pressed into the cavity until complete 
fitting is achieved. The excesses are thereafter removed with a probe and 
dental silk, this also being very simple due to the high viscosity of the 
paste. Thereafter, the cement is completely polymerised with all round 
exposure for 60 sec. with a commercially available dental radiation device 
(Elipar, ESPE). Then, the cement surface and the inlay are polished. No 
transitions can be seen and the inlay fits excellently. 
If the method is carried out with the same material on the same inlay but 
without the action of ultrasonic vibration, the inlay cannot even be 
completely introduced into the cavity. Transitions from the tooth surface 
to the inlay are visible and can easily be detected with a probe. 
Measurement of the Film Thickness 
100 mg of the described composite are placed between a planar metal plate 
and a glass plate and uniformly distributed to a starting layer thickness 
of 500 .mu.m. Thereafter, with the surface of the centre portion of the 
aforementioned ultrasonic scaler a pressure of 0.5 kP in each case is 
applied to the upper side of the glass plate. The pressure is left for 10 
sec., firstly with the vibration switched on and then with no vibration. 
With the ultrasonic device switched on a film thickness of 10 .mu.m is 
obtained. When the ultrasonic unit is not switched on the film thickness 
is 400 .mu.m. Even by applying higher pressures (for example 10 kP) for 
longer times (for example 30 sec.) the film thickness does not go below 50 
.mu.m.