Note: Descriptions are shown in the official language in which they were submitted.
CA 02355581 2001-08-20
Dental material containing a component which contracts
during thermal treatment
The invention relates to dental materials which, in addition
to a filler and a polymerizable matrix, contain a component
which contracts during thermal treatment.
~~ Dental materials based on plastics contain in general one or
more fillers in addition to a polymerizable matrix. The fillers
serve to reduce the polymerization shrinkage and to improve the
mechanical properties of the cured materials. Fibre composites
contain fibrous fillers such as fibre mats or fibre bundles,
which are impregnated with the organic polymer matrix. For
reasons of stability, ii; is advantageous to select the filler
content as high as possible. This has however the disadvantage
that the rigidity of the uncured material .is increased and thus
its shaping made difficult.
W095/08300 discloses a process for preparing dental
restorations from fibre composites in which fibre mats
saturated with polymer matrix are applied to a tooth cast,
matched to the cast in a vhermoforming process and then cured.
The frame obtained in tizi.s way can be further processed. e.g.
by applying facing matez-7a1..
EP 0 872 218 A2 discloses a process for preparing fibre-
reinforced dental restorations, in which the fibre content of
the uncured starting material is increased during deep-drawing
by expressing excess matrix material.. The process necessitates
the use of specially designed moulds.
The known deep-drawing processes have the disadvantage that the
compaction forces do not act homogenously on the material from
CA 02355581 2001-08-20
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all sides simultaneously and no uniform compaction of the
materials is achieved.
The object of the inveni:ion is the provision of dental material
which can be compacted uniformly without special auxiliary
agents.
This object is achieved by dental materials which, in addition
to f filler and a polymeri_zable matrix, contain a component which
contracts during thermal treatment. This component is also
called shrinkage material in the following.
Preferred components which contract during thermal treatment
are so-called shrink fi~_ms and shrink tubes i.e. plastics films
or plastics tubes which contract during heating. These are
mostly thermoplastics which are uni- or bi-dimensionally
stretched during the course of their production and then
contract again on heating.
Suitable shrink films and shrink tubes are commercially
available. In particular, shrinkage materials based on
polytetrafluoroethylene (PTFE), polyvinylidene fluorides, such
as vinylidene fluoride hexafluoropropylene, polyolefins, such
as polyethylene and radiation-cross-linked polyolefins,
2.'i polyethylene terephthalate (PETP), and polyvinyl chloride (PVC)
have proved themselves far the preparaticn of dental materials .
Single-layered materials are preferred.
The shrinkage temperature of these materials is normally in the
range from 80 to 330°C. Preferred materials are those which
contract in the temperature range from 80 to 160°C.
Materials preferred according to the invention have a shrinkage
rate in the range from 1.3:1 to 5:1. Materials with a shrinkage
3_'~ rate of 3.5:1 to 4.5:1 and in particular approximately 4:1 are
particularly preferred. Shrinkage rates are, if not otherwise
stated, measured at a temperature of 150°C.
CA 02355581 2001-08-20
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Materials which shrink only uni-dimensionally are preferred.
In the case of tubes, i~he shrinkage preferably takes place in
radial direction whilst the length of the tube remains
essentially unchanged. The shrinkage rate in radial direction
indicates the ratio of the internal diameter of the non-shrunk
tube to the internal diameter of the shrunk tube. At a
shrinkage rate of e.g. 4, the internal diameter before the
shrinkage is four times greater than afterwards.
Furthermore, transparent shrinkage materials are preferred, as
these permit a photochemical curing of the polymerizable
material and in addition allow the preparation of dental
restorations with a natural. appearance.
1.5 Polymerizable monomers, oligomers, polymers and prepolymers as
well as mixtures of these substances are suitable as poly-
merizable matrix. Preferred monomers are ionically and/or
radically polymerizable mono- or multi-functional monomers, in
particular mono(meth)acrylates, such as methyl-, ethyl-,
21) butyl-, benzyl-, furfu.ryl- or phenyl(meth)acrylate, multi-
functional acrylates and methacrylates such as for example
bisphenol-(A)-di(meth)acrylate, bis-GMA (an addition product
of methacrylic acid and i~isphenol-A-di glycidyl ether) , UDMA ( an
addition product of 2--hydroxyethyl methacrylate and 2,2,4-
2ti hexamethylene diisocyanate), di-, tri- and tetraethylene glycol
di(meth)acrylate, decanediol di(meth)acrylate, trimethylol-
propane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate
and butanediol di(meth)acrylate, 1,10-decanediol di(meth)-
acrylate or 1,12-dodecanediol di(meth)acrylate.
3 CI
Bisphenol-A-derivates ~;uch as bisphenol-A-glycidyl-dimeth-
acrylate (bis-GMA), urethane dimethacrylate (UDMA), triethylene
glycol dimethacrylate (TEDMA) and mixtures thereof are
preferred among the aromatic dimethacrylate resins.
Other preferred polymerizable materials are polycarbonate-
di(meth)acrylates, in particular the condensation product of
CA 02355581 2001-08-20
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a hydroxyalkyl methacrylate, preferably 2-hydroxyethyl
methacrylate, and a bis(chloroformate), preferably triethylene
glycol bis(chloroformate), polycarbonate-tri- or -tetra(meth)-
acrylates, urethane-di..-, tri-, tetra(meth)acrylates and
~~ mixtures thereof. MonomE=_rs of this type are described in DE 36
32 868 A1 and US 5,444,104.
According to the invention, resin based on bis-GMA can also
preferably be used which was modified by copolymerization with
materials having low molecular weight, such as bisphenol-
glycidyl dimethacrylate (BIS-MA), bisphenolethyl methacrylate
(BIS-EMA), bisphenol propylmethacrylate (BIS-PMA), ethylene
glycol dimethacrylate (EGDMA), diethylene glycol dimethacrylate
(DEGDMA), triethylene glycol dimethacrylate (TEGDMA), tri-
ethylene glycol methacrylate (TEGMA), methyl methacrylate
(MMA), and polyurethane fluoromethacrylate (PFUMA).
A polymerizable matrix based vn a mixture of bis-GMA, decane-
diol dimethacrylate (DDDMA), triethylene glycol dimethacrylate
(TEGDMA) and urethane dimethacrylate (UDMA) is particularly
preferred. A particularly preferred polymerizable matrix
contains 65 to 75 wt . - a bis-GMA, 10 to 20 wt . -% triethylene
glycol dimethacrylate and 5 to 15 wt.-o highly-dispersed
silicon dioxide (relative to the mass of the matrix without
fibrous fillers and without shrinkage material).
The matrix preferably contains thermal and/or photoinitiators
to ini~iate the radical polymerization.
Preferred initiators for the thermal curing are peroxides, such
as for example dibenzoy7_ peroxide, dilauryl peroxide, tert.-
butylperoctoate and tert.-butylperbenzoate as well as azo-
bisisobutyroethyl ester, benzpinacol and 2,2-dimethylbenz-
pinacol.
Preferred photcir.itiators are benzophenone and benzoin as well
as their derivatives, a-diketones and their derivatives, such
CA 02355581 2001-08-20
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as for example 9,10-pihenanthrenequinone, diacetyl and 4,4-
dichlorobenzil. Particularly preferred photoinitiators are
camphor quinone and 2,2-methoxy-2-phenyl-acetophenone and in
particular, combinations of a-diketones with amines as
reduction agents, such as for example N-cyanoethyl-N-methyl-
aniline, 4-(N,N-dimethylamino)-benzoic acid ester, N,N-
dimethylaminoethyl methacrylate, N,N-dimethylsym.-xylidine or
triethanolamine. In addition, acylphosphines, such as for
example 2,4,6-trimethylbenzoyldiphenyl- or bis-(2,6-dichloro-
benzoyl)-4-N-propylphenylphosphinic oxide, are suitable as
photoinitiators.
Organic and inorganic fibrous materials, in particular fibre
mats and/or uniaxially oriented fibre bundles, are preferred
lei as fillers. The fibre bundles can be wrapped or braided with
fibres to further increase the mechanical strength. The
material can contain one or more fibre bundles.
Preferred fibres are glass fibres, aramid fibres, carbon fibres
2f and polyethylene fibres. (PE-fibres) and their combinations.
Preferred particulate fillers are amorphous spherical materials
based on mixed oxides of Si02, ZrOZ and/or TiOZ (DE 40 29 230
Al), microfine fillers such as pyrogenic silica or preci-
pitation silica as well ,as macro- (particle size of 5 ~m to 200
25 um) or mini-fillers (particle size of 0.5 to 5 Eun), such as
quartz, glass ceramic or glass powder with an average particle
size of 0.5 um to 5 ~m as well as x-ray opaque filler, such as
ytterbium trifluoride.
30 Combinations of fibrous and particulate fillers are possible.
The mixtures can also contain further additives such as
colorants (pigments .and dyes), stabilizers, aromatic
substances, microbiocidal active ingredients, plasticizers
35 and/or UV absorbers.
CA 02355581 2001-08-20
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Suitable fibre compos it:es , i . a . combinations of organic matrix,
fibrous filler, optionally particulate filler, auxiliary agents
and additives are described in W095/08300.
Preferred fibre compo~~ites for use with shrinkage materials
contain 7 to 94 wt.-% fibrous filler and 6 to 93 wt.-%
polymerizable matrix. Particularly preferred are materials
which contain 28 to 82 wt.-% and in particular 35 to 65 wt.-%
fibrous fillers.
The proportion of non-fibrous fillers preferably lies in the
range from 0 to 30 wt.-%, in particular 2 to 15 wt.-% and
particularly preferred in the range from 3.5 to 5.5 wt.-%.
According to a quite particularly preferred version, the
material contains 3.5 t:o 5.5 wt.-% highly-dispersed silica as
additional filler.
Initiators and optionally accelerators are used preferably in
a quantity of 0.01 to 3.0 wt.-% each, particularly preferably
in a quantity of 0.05 1~0 1.0 wt.-% each relative to the mass
of matrix material. The overall quantity of catalysts and
stabilizers is preferably 0.3 to 0.5 wt.-% each based on the
overall mass of the fibre composite.
2'~ Ot'Zer additives, such as e.g. pigments, are normally used in
a quantity of less than 0.1 wt.-%.
Fibrous and non-fibrous inorganic tillers are preferably made
water-repellent before being incorporated into the matrix,
particularly preferably silanized, i.e. treated with an organic
silicon compound such a~> an aryloxysilane, alkoxysilane and/or
a halogensilane such as (meth)acryloylalkoxysilane.
All the percentages named above and in the following relate,
3~~ if not otherwise stated, to the mass of the fibre composite
without the shrinkage component.
CA 02355581 2001-08-20
The composition of particularly preferred fibre composites is
stated in the following by way of example (ail figures are in
wt.-%):
Component Material Material Material
No. 1 No. 2 No. 3
Bis-GMA 38.7 24.6 35.3
DDDMA 0.5 0.3 0.4
1() TEDMA 9.7 6.2 8.8
Highly-dispersed 5.5 3.5 5.0
silica
Catalysts and <_0.5 <_0.3 <_0.4
stabilizers
1-'i Pigments <_0.1 <_0.1 <_0.1
Glass fibres 45.0 65.0 50.0
2C According to a preferred version, the component which contracts
when exposed to heat is ahaped like a tube. This is filled with
filler, preferably a fibrous filler, and matrix. When the tube
is heated, its inner and outer diameter decreases, whereby the
fibres are uniformly compacted .in the matrix and excess matrix
25 material i.s expressed from the tube at the ends of the tubes.
With long tubes, the use of perforated tubes can be advan-
tageous in order to facilitate the escape of the matrix
material. This compaction leads to an increase in the fibre
content and thus the strength of the dental material.
In general, the fibre content can be increased one- to four-
fold. The degree of compaction can be so controlled via the
shrinkage ratio of the shrinkage material that the desired
mechanical properties are achieved.
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To determine the comp~action ratio, cross-sections of cured
composite material with and without shrinkage material are
produced and the ratio of the areas covered by fibres and
matrix material are ascertained in each case. The compaction
corresponds to the quotients from the area ratio of fibre to
matrix with shrinkage material and the area ratio of fibre to
matrix without shrinkage material. If only inorganic fibres are
used, such as e.g. glass fibres, the compaction or the fibre
content can also be ascertained via the ash content.
Figure 1 shows an electron microscope picture of a cross-
section through a rod-shaped composite material which was cured
without shrinkage material, Figure 2 the picture of a cross-
section through a second composite material which is contained
1.'~ in a shrink tube. In both cases, the section was cut per-
pendicular to the fibre direction and to the longitudinal axis
of the material. The compositions of the composite materials
before curing and compaction were identical and correspond in
both cases to material. no. 2 described above.
A visual comparison of the figures already shows that the fibre
density of the material with shrink tube is clearly higher than
the material without ahrink tube. In addition, the Latter
contains large air .inclusions.
2 ~i _
A measurement of the cross-section sur'aces without and with
shrink tube produced values of 4.44 mm~ (without taking the
large air inclusion into acccunt) and 2.81 mm-.
3G Figures 3 and 4 show parts of the same cross-sections at a
greater magnification. Fibres and matrix can be clearly
differentiated. In Figure 3 (material without shrink tube) , the
area occupied by the fibres is 3863 ~mz, the area of the matrix
4573 ~m~ and the overall area 8436 um2. The area ratio of
35 fibres to matrix is accordingly 0.84.
CA 02355581 2001-08-20
_ 9 _
In Figure 4 (material with shrink tube), the area occupied by
the fibres is 5385 ~mZ, the area of the matrix 3237 ~mZand the
total surface area 8622: ~mz. The surface area ratio of fibres
to matrix is 1.66. This results in a compaction of 1.66 . 0.84
- 1.98.
According to a further preferred version, uniaxially oriented
fibres are encased in a tube made from a woven or knitted fibre
fabric and this combination is then enclosed by a component
which contracts during thermal treatment . The compaction which
occurs during heating improves the orientation of the fibres
and thus the transverse tensile strength, compressive strength
and torsional strength of the rod.
1'.i Tube- or rod-shaped components are suitable in particular for
the production of fibre-reinforced dental bridge frames. The
spatial measurements of the components are matched to the
production of dental restorations. Rod-shaped materials with
a length of 10 to 160 mm and a diameter of 2 to 4 mm (measured
2C1 without shrinkage material) are preferred. The materials
preferably have a circular cross-section. They are
characterized in that the fibre bundle impregnated with organic
matrix can easily be processed from outside while dry and thus
by hand without risk of soiling and without the risk of
2~~ contaminating the fibre bundles.
The materials according to the invention are shaped for example
using casts, such as casts with detachable segments made from
plaster and then seated. In the process, the component, which
30 contracts during thermal treatment, shrinks and thus effects
a compact.ion of the dental material. The material is then
cured, preferably by radical polymerization.
The shrinkage material is preferably removed after polymeri-
35 nation and the remaining, cured composite material is processed
further, for example faced with suitable materials.
CA 02355581 2001-08-20
_
It is however also conceivable that the shrinkage material is
firmly bonded to the matrix via polymerizable groups during
polymerization.
5 The compaction of fibre composites can also be achieved by
using shrinkage strips. A strip of the material contracting
during thermal treatment is wrapped round the fibre composite,
optionally together with the cast and preferably after shaping,
and this is then heated. The strip shrinks and compacts the
10 wrapped material. Complicated structures can also be homo-
genously compacted by using shrinkage strips. After the
polymerization of the matrix, which can take place during or
after heating, the strips are removed from the dental
restoration and the lataer optionally further processed, for
lei example faced or crowned. In the case of shrinkage strips, the
overlapping points of the strips serve as outlets for the
monomer.
The strips preferably hacve a width of 5 to 100 mm, particularly
preferably 10 to 30 mm. 'The thickness of the strips is variable
and is typically about. 0.4 mm. The shrinkage rate of the
strips, measured :in longitudinal direction, is preferably 1.3:1
to 4:1.
For the further processing of the cured materials, e.g. for the
application of facing materials, it is generally necessary to
roughen the surface of the fibre composite. This step involves
additional outlay. For this reason, a so-called tsar-off fabric
is applied to the dental restoration first before the shrinkage
material. ~y tear-off fabrics are meant materials which can be
removed (torn of_fi from the cured fibre composite after
polymerization and in the process leave a clean rough surface
behind. The fibre composite can be further processed after the
tear-off fabric is removed without additional roughening of the
surface.
CA 02355581 2001-08-20
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According to a further version of the invention, caps of
shrinkage material are filled with polymerizable composite
material and then matched to a cast, such as for example a
tooth stump, by shrin~;age. Size and shape of the caps are
matched to the use with teeth and tooth stumps. The poly
merizable material is then cured, the shrinkage material is
optionally removed and t:he cured moulding is optionally further
processed, for example by applying facing material. In this
way, e.g. dental crowns and bridge piers can be prepared for
1~ permanent and temporary use.
The preparation of a crown is described in the following in
more detail. The tooth to be restored is ground to a stump in
a manner known per se. A negative mould is prepared from the
1!i stump with impression materials such as for example alginate,
polyether or silicon, a.nd this is then cast with a modelling
material such as plaslter or epoxy resin. In this way, a
positive cast is obtained which is insulated e.g. with an
alginate solution (in t:he case of a plaster cast), or a wax
20 solution (in the case oi= an epoxy cast). A small cap made from
a shrinkage material, which is filled with polymerizable
material, is then applied to the insulated cast stump. The cap
is fitted onto the stump in such a way that it covers this . The
cap is shrunk by heating and the polymerizable material matched
2~~ to the stump and simultaneously compacted. The material is then
cured by light or further heating and the cured material is
made into the finished crown according to the usual dentistry
methods, e.g. by applying a suitable facing material. For this,
the surface of the crown blank is optionally roughened and the
3C facing material applied to the roughened surface. As a rule,
the application takes d ace in two or more layers, each of the
individual. layers being cured after the application. After the
last layer has been applied, the crown is subjected to final
curing, polished, cleaned and fitted to the patient by the
35 dentist.
CA 02355581 2001-08-20
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To manufacture a bridge, filling cavities are distally or
mesially prepared by the dentist with suitable instruments in
a manner known per se in the two teeth adjacent to the gap in
the teeth and then a positive cast is made of the mouth
situation as described above and this is insulated. The
insulation prevents the frame material from sticking to the
cast. Then e.g. a rod-shaped, fibre-reinforced composite
material, which is preferably contained in a shrink tube, is
cut to a length which corresponds to the distance between the
two prepared cavities. This strand is then introduced into the
cavities so that it spans the gap between the teeth. To prevent
the strand deforming during heating, it can be fixed at both
ends , a . g . by curing matrix monomer which emerges there through
brief irradiation with an optical conductor. Alternatively or
Z5 simultaneously, the strand can be supported with silicon
material so that that it cannot bend downwards. Support is
required above all if large gaps ( larger than approx. 6 mm)
must be spanned. Subsequently, the material is heated to
shrinkage temperature by a heat source, e.g. by a hot-air
2~~ blower or an IR radiator. After shrinking, the strand is cured
with a light source, e.g. Heliolux or Targis Power, the shrink
tube is removed and the frame is faced with a facing material
in the usual way. To remove the shrink tube, this is preferably
cut open and then peeled off.
