Note: Descriptions are shown in the official language in which they were submitted.
CA 02355451 2001-08-20
Shaping Cap for Dental Pin Structures
The invention relates to shaping- caps for dental pin
structures as well as kits and processes for the
preparation of dental pin structures.
Anchorage pins are used to secure tooth restorations and to
reconstruct missing hard tooth substance. These are usually
inserted into the root canal and therefore also called root
pins. However, besides the intracanalicular anchorage, a
parapulpal anchorage is also usual.
The insertion of these pins into the root canal takes place
in three phases. In the first phase, the root canal is
prepared up to the apex with customary root canal
instruments. In the second phase, the coronal part of the
root is prepared with standardized drills. In the third
_. phase, the anchorage or root pin is inserted into the
prepared canal.
A so-called pin or stump structure is then modelled on the
anchorage pin. The structures can be built up directly in
the mouth of the patient with moldable materials such as
amalgam and composite and be ground into the correct shape.
However, they can also be prepared indirectly in the dental
laboratory using an impression of the prepared hard tooth
substance with the set pin. Lastly, this structure is
crowned or veneered.
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To manufacture pin structures from composite materials,
caps of flexible plastic material such as silicone or
polyethylene can be used as auxiliaries which allow easy
shaping of a standard stump. The cap is usually filled with
composite, pushed over the root pin and the composite is
then cured. The caps consist of soft, flexible material and
after curing can be easily removed from the cured composite
material. The stump structure is then worked on further.
The caps are obtainable for front _and back teeth in
different sizes. The composites used to prepare the
structures contain, besides a polymerizable matrix
material, usually particulate fillers. The load-bearing
capacity of the structures is limited.
The object of the invention is to provide shaping caps for
the preparation of dental pin structures with increased
strength.
This object is achieved by shaping caps which are suitable
as a permanent constituent of the pin structure.
The shaping caps consist of metal, preferably of ceramic or
plastic material, those plastic materials being preferred
which contain an organic matrix material and a filler,
preferably fibrous filler.
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Further preferred are tooth-coloured and in particular
transparent shaping caps, so that the polymerizable
material contained therein can be cured by light.
Particularly suited as matrix material are ionically and/or
radically polymerizable mono- or multifunctional monomers,
in particular mono(meth)acrylates such as methyl, ethyl,
butyl, benzyl, furfuryl, or phenyl(meth)acrylate,
multifunctional acrylates and methacrylates such as, for
example, bisphenol (A) di(meth)acrylate, decanediol
di(meth)acrylate, butanediol di(meth)acrylate, 1,10-
decanediol di(meth)acrylate and/or 1,12-dodecanediol
di(meth)acrylate.
Particularly preferred matrix materials are polycarbonate
di(meth)acrylates, in particular the condensation product
of a hydroxyalkyl methacrylate, preferably 2-hydroxyethyl
methacrylate, and a bis(chloroformate), preferably
triethylene glycolbis(chloroformate), polycarbonate tri- or
tetra(meth)acrylates, urethane di-, tri-, tetra
(meth)acrylates and mixtures of these. Monomers of this
type are described in DE 36 32 868 Al and US 5,444,104.
Further particularly preferred monomers are bis-GMA (an
addition product of methacrylic acid and bisphenol A-
diglycidyl ether), UDMA (an addition product of 2-
hydroxyethyl methacrylate and 2,2,4-hexamethylene
diisocyanate), di-, tri-, (TEGDMA) and tetraethylenA
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glycoldi(meth)acrylate, trimethylolpropane
tri(meth)acrylate and pentaerythritol tetra(meth)acrylate.
To initiate the radical polymerization, the polymerizable
component contains thermal and/or preferably
photoinitiators.
Preferred initiators for the thermal curing are peroxides,
such as for example dibenzoyl peroxide, dilauryl peroxide,
tert.-butyl peroctoate and tert.-butyl perbenzoate as well
as azobisisobutyro-ethylester, benzopinacol and 2,2-
dimethylbenzopinacol.
Preferred photoinitiators are benzophenone and benzoin as
well as their derivatives, a-diketones and their
derivatives such as for example, 9,10 phenanthrenequinone,
diacetyl and 4,4-dichlorobenzil. Particularly preferred
photoinitiators are camphorquinone and 2,2 methoxy-2-
phenyl-acetophenone and in particular combinations of a-
diketones with amines as reduction agent, such as for
example N-cyanoethyl-N-methylaniline, 4-(N,N-
dimethylamino)-benzoic acid ester, N,D1-dimethylaminoethyl
methacrylate, N,N-dimethylsym.-xylidine or triethanolamine.
In addition acylphosphines, such as for example 2,4,6-
trimethylbenzoyldiphenyl-or bis-(2,6-dichlorobenzoyl)-4-N-
propylphenyl phosphine oxide, are suitable as
photoinitiators.
CA 02355451 2001-08-20
Diaryliodonium or triarylsulphonium-salts, such as for
example triphenyl sulphonium-hexafluorophosphate and
hexafluoroantimonate, are particularly suitable for the
dual curing of radically and cationically polymerizable
systems.
Redox initiator combinations, such as for example
combinations of benzoyl or lauryl peroxide with N,N,-
dimethyl-sym.-xylidine or N,N-dimeth_yl-p-toluidine, are
used as initiators for a polymerization at room
temperature. Further suitable initiators and accelerators
are vitamin C and barbituric acid.
Besides polymerizable monomers and/or prepolymers, the
matrix material also preferably contains fillers. Organic
and inorganic fibrous materials, such as fibres, fibre mats
and/or fabrics are preferred as fillers. Preferred are
glass fibres, polyethylene fibres (Spectra, Dynema),
polyamide, in particular aramid fibres (Kevlar), and carbon
fibres, as well as mats and fabrics of these fibres.
The fibrous materials preferably have a fibre diameter of
< 0.25 mm, in particular 0.01 to 0.25 mm, and a ratio of
fibre length to fibre diameter of > 10: 1, in particular >
. 1 to 100 . 1 .
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So-called whiskers are also preferred as fibrous fillers.
These are microfibres with a length of preferably 10 to
200 um and a diameter of preferably 0.1 to 1 um.
Alternatively or additionally to the fibrous fillers, the
cap material can contain particulate fillers. Preferred
particulate fillers are precipitated or ground plastics
particles, preferably with a particle size of 0.02 to
100 um; hybrid fillers such as ground polymerisate from an
organic matrix with organic and/or inorganic fillers, the
ground polymerisate preferably having a particle size of
0.5 to 80 Vim; and/or inorganic fillers.
Particularly preferred particulate fillers are amorphous
spherical materials on the basis of mixed oxides of SiOZ,
ZrOZ and/or TiOZ (DE 40 29 230 Al), microfine fillers such
as pyrogenic silica or precipitation silica, spherical SiOZ
particles (precipitated particles) with a particle size of
200 to 700 nm as well as macro- (particle size of 5 ~m to
200 Eun) or minifillers (particle size of 0.5 to 5 Vim), such
as quartz, glass ceramic, or glass powders with an average
particle size of 0.5 ~m to 5 um as well as X-ray opaque
fillers such as ytterbium trifluoride.
The organic and in particular the inorganic fillers are
preferably provided with a suitable adhesion promoter, i.e.
silanized for example, in order to guarantee a firm bond
between fibre and matrix. Suitable silanes are known to the
CA 02355451 2001-08-20
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person skilled in the art. Preferred silanes are gamma-
methacryloxypropyl-trimethoxy silane (A-174) and gamma-
methacryloxypropyl-tris(2-methoxyethoxy) silane (A-175).
These silanes are particularly suitable when the matrix
material contains polymerizable (meth)acrylate groups.
Furthermore, the mixtures can contain further additives
such as colouring agents (pigments and dyestuffs),
stabilizers, aromatics, microbiocidal.active ingredients,
plasticizers and/or UV absorbers.
Particularly preferred cap materials are fibre-reinforced
plastics on the basis of urethane dimethacrylate which are
additionally reinforced with particulate inorganic filler,
preferably glass powder, such as for example materials with
the following composition:
Component Proportion (wt -%1
Urethane dimethacrylate 10 to 20 %
Glass fibres (silanized) 60 to 70 %
Glass powder (1 Elm, silanized) 15 to 20
Pyrogenic silica (Aerosil) 0.5 to 5 %
Catalyst 0.02 to 0.5
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Further preferred cap materials are fabrics impregnated
with organic binding agent such as for example:
Component Proportion (Wt -~1
Bis-GMA 33 to 43 ~, e.g. 38 0
Triethylene glycol
dimethacrylate 5 to 150 , e.g. 10
~
Highly dispersed SiOz 3 to 10 ~, e.g. 6 0
Catalysts and stabilizers 0.5 to 2 %, e.g. 0.5
Glass fibres (fabric, 8-ply) 40 to 50 ~, e.g.45.5 0
Furthermore, thermoplastics are preferred as cap materials,
in particular those with a glass-transition temperature
(Tg) of more than 40 °C, preferably more than 80 °C and in
particular more than 100 °C. Particularly preferred are
plastic materials with an elasticity modulus (E-modulus,
measured according to EN ISO 178) of more than 2000 MPa
(measured at room temperature), in particular more than
5000 MPa. Amongst the particularly preferred thermoplastics
are polymethyl methacrylate (PMMA, Tg = 105 °C, E-modulus
- 3300 MPa), polysulphone (Tg - 190 °C, E-module - 2700
MPa) and polycarbonate (TG = 145 °C, E-modulus = 2300 MPa).
Increasing the E-modulus of the plastic materials can be
achieved by the addition of fillers, in particular fibrous
fillers . For example, polysulphone, which is filled with 25
CA 02355451 2001-08-20
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_(
wt-~ of glass fibres has an E-modulus of 7200 MPa.
Consequently, thermoplastics which contain filler are
preferred, in particular thermoplastics containing fibrous
filler. The E-modulus can assume values of 25, 000 MPa or
even 50,000 MPa.
The matrix of the shaping caps can be in uncured, pre-cured
or fully-cured form. It is essential that the caps maintain
their shape. The use of a pre-cured, i.e. partially
polymerized, material is preferred.
The surface, in particular the inner surface, of the
shaping caps is provided with agents which guarantee a firm
bond between cap and cap filling material. Caps of uncured
or partially cured material contain polymerizable groups
which ensure a firm bond between cap and cap filling
material by chemical bonds after curing. When using a
fully-cured material, as well as in the case of metal and
ceramic caps, the surface of the caps is preferably
modified in such a way that it contains polymerizable
groups. Polymerizable groups can be applied to the cap
surface, for example, by silanizing the caps. In the case
of plastic caps it is advantageous if the plastic material
contains inorganic filler, for example, glass powder or
glass fibres, as silanizing agents react preferably with
filler particles or filler fibres present on the cap
surface. The above-named silanes are preferred as
silanizing agents.
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Preferred polymerizable groups are radically polymerizable
groups, in particular ethylenically unsaturated groups such
as vinyl, allyl, acryl, and methacryl groups.
To improve the adhesion between cap and cap filling
material, the caps can also be treated with a solvent or a
reactive thinner so that the cap material swells at its
surface. This variant is particularly suited to fully-cured
plastic caps. -
Furthermore, firm adhesion can be achieved: by mechanical
means. For example, the cap surface can be roughened by
sand-blasting to improve adhesion, or the surface can be
provided with retentions such as undercuts, grooves or
perforations.
Ceramic caps or caps from plastic materials which contain
inorganic fillers, are preferably roughened and silanized
'. to guarantee a firm bond between cap and cap filling
material.
To improve adhesion, metal caps are preferably treated with
phosphoric acid esters containing (meth)acrylate groups,
such as e.g. the product Targis Link from the firm Ivoclar.
The phosphoric acid groups of these esters react with the
metal surface or metallic oxides present on the surface,
accompanied by development of phosphate compounds, the
(meth)acrylate groups are polymerizable and can react with
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the cap filling material. Furthermore, a thin, glass-like
layer, a so-called SiOY-C layer, can be applied to the metal
surface, which can be silanized, e.g. with the silanes
mentioned above. To this end, the metal surface is treated
for example with the product Silocoater0 from the firm
Kulzer. Additionally, silicatic particles can be anchored
to the metal surface by sand-blasting with a special
blasting agent (Rocatacu, ESPE), these forming a thin
ceramic layer which can also be silani_zed.
To prepare pin or stump structures, the caps are filled
with a polymerizable material, preferably a polymerizable
composite material (cap filling material) and fitted onto
the prepared tooth or a model of it. Before filling, the
cap can, optionally, be cut to size by scissors. The
polymerizable material and, optionally, the cap is then
cured, preferably by photopolymerization. The material is
firmly bound to the cap.
Mixtures of the above-mentioned monomers, polymerization-
initiators and preferably fillers also are particularly
suited as cap-filling material, non-fibrous fillers being
preferred as fillers. Preferred are materials which contain
20 to 80 wt-o of one or more polymerizable monomers, 20 to
80 wt-o filler and 0.05 to 2 wt-~ polymerization initiator.
The cap material preferably contains an initiator for the
photopolymerization and can be cured by light. Particularly
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preferred cap-filling materials have the following
compositions:
Fine-particle hybrid
Component Proportion (wt-% 1
Bis-GMA 6 to 12 %, e.g. 8.7
%
Decanediol dimethacrylate 3 to 7 %_, e.g. 4.7
%
Urethane dimethacrylate 6 to 14 %, e.g. 9.0
Barium glass filler
(silanized) 60 to 85 %, e.g. 72.0%
Highly-dispersed SiOZ 3 to 7 %, e.g. 5.0
%
Catalysts and stabilizers 0.2 to 1 %, e.g. 0.6
%
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Microfilled composite
Component Proportion lwt-~1
Ethoxylated
bisphenol A dimethacrylate 36.0 to 68.0 ~, e.g. 53.2
Triethylene glycol
dimethacrylate 11.0 to 17.0 ~, e.g. 13.3
Antioxidants 0.002 to -0.020
e.g. butylated
hydroxytoluene 0.008 s
Curing agent 0.06 to 0.20
e.g. bornane-2,3-dione 0.12
Curing accelerator 0.05 to 0.20
e.g.
ethyl-4-dimethylaminobenzoate 0.12 0
Submicronic silanized SiOZ 15.0 to 55.0 %, e.g. 33.3 0
Aerosil with a particle size of 0.01 to 0.04 ~m and
e.g. an average particle size of 0.02 um is preferably
used as submicronic SiOZ.
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Macrofilled composite
Component Proportion (wt-of
Binding Agent
Bis-GMA 55 to 66 ,
0 e.g.
61.2
Bisphenol A dimethacrylate 5 to 0, e.g.6.8 0
9
TEGDMA 20 to 34_ , g. 26.9
a e.
Methacrylic acid 1.5 to 2.5 ~, e.g.2.0
Benzil 0.1 to 0.5 ~, e.g. 0.3
~
Camphorquinone 0.1 to 0.5 ~, e.g. 0.3
0
2-(N,N-dimethylamino)ethyl
methacrylate 2 to ~, e.g.2.5
3
The percentage data refer to the total mass of the
binding agent.
20 to 35 wt-o of the binding agent is mixed with 65 to
80 wt-o silanized Ba-A1 silicate glass as a filler to
the ready to use composite, e.g. 28 wt-~ of the
binding agent and 72 wt-o of the filler.
In the course of the polymerization, the shaping caps are
firmly bound to the polymerizable material and thus effect
a distinct increase in the strength of the root-pin
structure without the need for additional steps. Rather, the
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removal of the shaping caps used previously for shaping the
pin structures no longer applies. The cap serves as the
basic shape of the stump. This can, for example, be veneered
or crowned later.
In contrast to previous shaping caps, the shaping caps form
an integral part of the dental restoration, i.e. the caps
remain permanently in the restoration and assume a
supporting function there. The shaping caps consisting of
soft, flexible plastic material which were used previously
for the preparation of pin structures are unsuitable for
this purpose as they possess insufficient mechanical
strength. Additionally, these caps are so designed that they
can be easily removed again after curing of the cap-filling
material. The shaping caps according to the invention
preferably have an E-modulus of at least 2000 MPa,
particularly preferably 5000 MPa, in the cured state. Caps
with an E-modulus of 10,000 MPa to 50,000 MPa and in
particular of about 30,000 MPa (measured according to EN ISO
178 at room temperature, without cap-filling material) are
quite particularly preferred.
The shaping caps are adapted in shape and size for use in
dentistry. Caps which are matched to the shape and size of
the tooth to be treated, such as incisor, canine tooth,
premolar and molar are preferred. At their base, the caps
preferably have an oval cross-section with a diameter in
longitudinal direction of 6 to 11 mm and a diameter in
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1 ~1 -
transverse direction of 4 to 9 mm. The caps can for example
have an elliptical cross-section with a ratio of large to
small semiaxis of 1.22 to 1.68. The height of the caps is
preferably 6 to 10 mm.
The shaping caps according to the invention effect a
distinct increase in the strength of the whole root-pin
structure and protect this from excessive stress peaks. The
preparation of pin structures is additionally simplified
as, on the one hand, the removal of the shaping cap is not
required, while on the other hand, the use of standardized
shaping caps simplifies matching e.g. of the crown.
Shaping cap and polymerizable material can be marketed
separately or preferably together as a kit. According to a
particularly preferred version, shaping caps filled with
polymerizable material are marketed. The filling by the
dentist or dental technician which was previously necessary
is thus no longer required. Kits and shaping caps which
contain polymerizable material are preferably marketed in
packs which are impervious to oxygen and, where applicable,
light, in order to prevent a premature curing of the
material.
A further object of the invention are kits for the
preparation of dental pin structures which contain at least
one of the shaping caps described above, at least one
anchorage pin and polymerizable material. The anchorage
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pins can be made of metal, ceramic, or preferably fibre-
reinforced plastic. Furthermore, the kits can contain a
material for the veneering of the shaping caps. The kits
preferably contain a shaping cap on the basis of fibre-
reinforced plastic material and are thus suitable in
particular for the preparation of fibre-reinforced pin
structures.
Alternatively, the kits can contain crowns or crown blanks
which are preferably already matched to the size of the
shaping cap.
To prepare a tooth restoration such as for example a crown,
the tooth to be treated is first ground by the dentist and
then, in the manner described above, fitted with an
intracanicular or parapulpal anchorage pin. Then a suitable
shaping cap is selected, the cap is filled if necessary
with a polymerizable material, the filled shaping cap is
fitted onto the anchorage pin and the polymerizable
material is cured. This is thus firmly bound to the shaping
cap and the anchorage pin. The construct consisting of
anchorage pin, cap-filling material and shaping cap is
called a pin or stump structure.
Figure 1 shows a tooth root 1 with a root canal 2. A root
pin 3 is inserted into the root canal 2. A fibre-reinforced
shaping cap 4 which is filled with polymerizable material
is pushed over the root pin 3.
CA 02355451 2001-08-20
Either an impression of the thus-prepared tooth is then
taken and a positive model for the manufacture of the crown
in a dental laboratory is made or the tooth is treated
further directly in the mouth of the patient. In the first
case, the finished crown is secured to the prepared tooth
with a fixing composite. In the second case, either a
ready-made crown, matched to the shaping cap, is fitted
onto the prepared tooth and ground or a crown is shaped
through application of veneering material to the prepared
tooth. Ready-made crowns are particularly suitable for
temporary treatment of the tooth until the final crown is
finished.
Two shaping caps, which are fitted onto the teeth bordering
a tooth gap, can serve as the basis for a bridge.
The preparation of the dental restoration can also be
carried out in a dental laboratory by a dental technician
using a cast (ex vivo). For this purpose, an impression of
the tooth is taken after insertion of the root pin and then
a pcsitive cast prepared of the tooth to be restored. This
serves as a basis, for example, for the preparation of the
stump structure or of the complete restoration consisting
of stump structure and crown. The preparation of stump
structure or dental restoration takes place in the manner
described above. The stump construction or the complete
restoration is then fitted to the patient by the dentist.
