Note: Descriptions are shown in the official language in which they were submitted.
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AN ARTIFICIAL TOOTH AND A PROCESS FOR MAKING AN
ARTIFICIAL TOOTH
Background of the Invention
The present invention relates to an artificial tooth and a process for
making an artificial tooth.
It is known to use polymerizable material in the dental practice
which is hardenable into its finished condition by light or thermal
polymerization thereof as well as, in some instances, by the application
of pressure thereto. In order to undertake a light hardening process, the
light must have an undisturbed access to the mass to be polymerized,
whereby it has become conventional to provide transparent molds far the
prostheses themselves. A solution of this type is disclosed in DE-OS 36
10 683. In this disclosed tooth prosthesis, an especially polymerizable
mass is used for the production of a form or mold piece which remains
white in color and which is comprised of, among other components,
urethane oligomers. A model forthe prosthesis is produced in connection
with the manufacture of such a prosthesis with the model having a
transparent mold overpiece. A disadvantage of this approach is,
however, the substantial effort required for the separate production of a
soft elastic mold component which is to be combined with a completely
hardened artificial or plastic material.
It has further already been suggested to produce an artificial tooth
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comprised entirely of light polymerizable material. Such artificial teeth
must be especially wear-resistant, so that the surface quality of the teeth
is measured against stringent standards. This process has not yet found
any acceptance in practice.
Artificial teeth are much more typically comprised of a ceramic
mass. A tooth produced in this manner is relatively hard and exhibits a
good surface quality. The tooth is also wear-resistant and is sufficient,
when produced with corresponding care and the use of corresponding
forming techniques, to satisfy today's aesthetic demands. A certain
disadvantage of teeth produced of ceramic sinter masses is that these
teeth have a surface which is harder than the natural tooth bloom. Thus,
those surfaces of teeth in the mouth of the patient which are in opposition
to the artificial tooth are placed under relatively strong demands. On the
other hand, artificial or composite material teeth have the advantage that
they are, at least, somewhat softer than natural teeth. Artificial teeth, i.e.
teeth of polymeric material, have, in contrast to ceramic teeth, certain
advantages, whereby a reduced wearing away of the oppositional
surtaces relative to the inserted artificial teeth is one of these advantages.
Plastic or artificial material is, on the other hand, less resistant to
pressure and is correspondingly more susceptible to wear than ceramic
so that, in the production of such artificial teeth, care must be paid to
ensure that the potentially achievable material properties are optimized.
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In order to produce an artificial tooth which is particularly resistant
to wear and that is hard, selected plastic or artificial material is used such
as, typically, a methyl methacrylate derivative. Evaluations have shown
that the manner of the polymerization, and the care exercised in
performing such polymerization, is a decisive factor in determining the
surface quality and the surface hardness of the artificial tooth produced
by this process. In this connection, an artificial tooth is typically
polymerized under comparatively high pressure at a correspondingly
increased or raised temperature.
In order to meet the aesthetic demands of the present day dental
practice, differing or varying layers are used - namely, a transparent
layer, which is intended to simulate the natural tooth bloom, and an
opaque layer, which is intended to simulate the tooth bone. These layers
are each produced under a corresponding pressure and corresponding
temperature in connection with their polymerization and each forms a
respective shell-shaped body. In connection with this approach, care
must be taken that a secure connection between the layers is ensured so
that the artificial tooth does not come apart into its individual components.
This process is, however, one which requires substantial effort in
that a multitude of molds andlor mold inserts must be used which must
be regularly cooled in an alternating manner and must also be regularly
heated or warmed in an alternating manner. A further problem lies in the
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fact that the artificial material is subjected to a multiple - for example,
four-fold - heating up beyond its melting point and is then subjected to
an intensive cooling off, all of which leads to a deterioration or negative
impact on its material properties. On the other hand, it is practically not
possible to heat and put under pressure only that sole layer which is to
be completely hardened for the reason that the layer lies in close
relationship to the neighboring layer unless completely separate forms or
molds are used. In spite of these disadvantages, there have been
heretofore no alternative approaches for optimizing the production of
artificial teeth.
Summary of the Present Invention
The present invention offers a solution to the challenge of
providing an artificial tooth whose production can be accomplished by a
simpler and more rapid production process while nonetheless having
improved surface quality precisely in the cutting region of the artificial
tooth.
The process of the present invention for producing an artificial
tooth surprisingly permits the production of such a tooth with at least a
homogeneous or uniform quality. Instead of the tooth undergoing a
pressure and, in particular, a temperature cycle during its production, a
multiple light polymerization process is performed and, indeed, is
performed by passage of the polymerizing light through mold pieces
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which, in accordance with the present invention, permit the passage of
such light therethrough. The artificial tooth of the present invention is
characterized throughout in that it is comprised of layers and the layers
are intensively connected with one another. The artificial tooth is formed
completely of light polymerizable material, whereby the cutting mass is
more transparent than the tooth bone mass. This produces several
particular effects which are exploited optimally in connection with the
present invention.
Firstly, the cutting mass is more transparent than the tooth bone
mass so that, during the light irradiation of the later-applied tooth bone
mass, the light passage capability of the light through the cutting mass is
particularly good. Those masses which are more difficult for light to reach
can thus be irradiated in an improved manner, which thus permits a
compensation to be realized so that neither the light output nor the length
of time of irradiation for effecting the hardening of the tooth bone mass
need be especially high.
On the other hand, the cutting mass is particularly intensively
irradiated with light beams precisely on its surfaces adjacent the mold.
This contributes to ensuring that these surfaces attain a particular
hardness and display an improved surface quality.
Moreover, the light polymerization process provides the possibility
to accommodate or tailor the intensity of the connection between the
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individual layers or masses in accordance with the requirements at hand.
Thus, an artificial tooth of the present invention can be produced which
is only fully or completely polymerized after the completion of all of the
light polymerization steps. The border layers or interfaces between the
individual masses remain, at least initially during the performance of this
process, still soft and contact-friendly, so that the intensive
interconnection in accordance with the present invention is automatically
produced.
It is to be understood that the manner and type of irradiation can
be accommodated to a wide range of requirements. For example, in
connection with one advantageous embodiment of the present invention,
the irradiation for the cutting masses is short and intensive - thus, for
example, accomplished with only a relatively short stand off distance from
the irradiation source - and the irradiation of the tooth bone or additional
masses is correspondingly less intensive and longer. Also, the frequency
and the periods of irradiation can be accommodated to the requirements,
whereby it is also possible to use a pulsed irradiation. In connection with
the types of light to be used, any desired suitable types of irradiation can
be used - that is, electromagnetic waves in those areas in which such
polymerization by such irradiation is possible and, in particular, ultraviolet
light.
In accordance with the present invention, it is particularly
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advantageous if the one after another overlying border surfaces are
formed such that material injection or pouring projections remain. These
projections contribute, in any event, to an interlocking and even further
improved anchoring or interconnection of the layers to one another. At
the same time, the misalignment or offset positions of the injection
projections at these locations contribute to a separation line-free
production of the cutting surfaces. The cutting masses can surround the
tooth in a full-surface manner, without requiring follow-up work to achieve
this result and the corresponding negative influence on the surface quality
resulting from such follow-up work.
In total, the present invention offers a surprisingly good surface
hardness and total quality for the artificial tooth produced in accordance
with the present invention, whereby, however, the production time is
drastically shortened in comparison to the heretofore conventional
production processes.
The process of the present invention preferably uses building
forms, which are, in accordance with an advantageous embodiment of
the process of the present invention, formed to permit the passage of light
therethrough. The cutting building form permits the cutting mass to be
pre-hardened separately in the desired configuration in the mold, in that
the light irradiation in accordance with the present invention is performed.
Following the light irradiation of the cutting mass, there occurs in the
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course of the light polymerization a certain hardness gradient, which is
exploited in accordance with the present invention in that the light
polymerization is ended or stopped following the passage of a
predetermined period of time so that the backside of the cutting area -
that is, the border surface of the cutting mass with the tooth bone mass
- is not yet completely hardened, while the remainder of the cutting mass
is, however, completely hardened.
In this semi-finished condition, the building form is removed and
replaced by a new building form, the tooth bone building form, which
permits the filling of the tooth bone mass. After the filling of the tooth
bone mass, the light polymerization is resumed, whereby not only the
border surface of the cutting mass relative to the tooth bone mass is
brought to a complete hardened condition but also the tooth bone mass
as well is polymerized to a complete hardened condition with the
exception, as desired, of its backside region which, in accordance with an
advantageous embodiment of the present invention, still remains to be
brought into contact with a base mass. The base mass is more opaque
than the tooth bone mass and, in a third step, is polymerized by a light
polymerization process in a corresponding manner.
In accordance with one modification of the process of the present
invention, different layers are polymerized such as, for example, a
forward or front cutting area and, in connection with the tooth bone mass,
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a neck and back cutting area. It is to be understood that, to this extent,
the color imparted to the masses which are so deployed can be
accommodated to a wide range of requirements - that is, such colors
can be accommodated to the desired aesthetic overall qualities.
S In accordance with the present invention, it is particularly
advantageous that a seamless encircling cutting area can be produced.
The building forms used in connection with the present invention permit
the formation of the cutting mass in an encircling manner by injection of
the cutting mass into the correspondingly thin gap between the mold and
the cutting mass building form. To improve the injection quality, it can be
provided, in connection with this approach, that more than a single
injection dose is used such as, for example, four injection doses
distributed around the gap circumference.
The cutting mass thus produced has a substantially bucket-shaped
body whose wall thickness is dependent upon the dimensioning of the
inner surface of the mold. The mold separation follows - with further
regard to the perspective of the cutting mass as a bucket - along the
bucket edge so that, in any event, it is not coincidental with the outer
cutting mass surface and, correspondingly, to this extent, no quality
encroachments need be feared.
Also, the openings for the release passage of air during the
production of the cutting mass can be configured on the portion of the
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surface turned toward the tooth bone mass and these release air
openings require no follow-up work. Instead, these interruptions of the
smooth surfaces result in an improvement of the interconnecting
capability of the interlocking connections.
It is to be understood that the further transition points - that is,
especially, transition points between a base mass and a tooth bone mass
- can be configured in a corresponding manner. In accordance with the
present invention, it is particularly advantageous if the artificial material
- that is, the tooth bone mass as well as the cutting mass - is an
inorganic or organic-filled light and heat hardenable monomer. In
particular, different methacrylate connections are suitable for this task.
The filler percent composition can preferably be in the range between 45
and 65%. The filler composition includes a monomer having a very
reduced viscosity such that it is injectable via a thin needle or the like. On
the other hand, in connection with a filler material of this type, the
shrinkage of such material in connection with the hardening thereof is
substantially small and this is especially so if glass particles or pyragens
and/or collapsed silica or silicic acid is used as the filler material. The
core or kernel size should preferably be between 0.7 and 20 microns,
whereby a kernel size of less than 5 microns promotes the polishing
receptiveness of the cutting mass surface. Basically, organic filling
materials should be considered which promote the polishing
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receptiveness, whereby, for example, very fine cross-linked polymers can
be used.
Brief Description of the Drawing
The object and advantages of the present invention will appear
more clearly from the following specification in conjunction with the
accompanying schematic drawing, in which:
The sole figure of the drawing shows an artificial tooth
produced in accordance with the present invention, the
artificial tooth being shown in cross-section.
Detailed Description of the Preferred Embodiment
As seen in the sole figure of the drawing, an artificial tooth 10 is
comprised entirely of a light polymerizable material. In the embodiment
illustrated, the artificial tooth is configured of three surfaces, whereby a
base surface 12 extends from a base mass 14 and forms the base of the
tooth. A tooth bone mass 16 is formed on the base mass 14 and the
tooth bone mass 16 is covered by a cutting mass 18.
The masses exhibit, as viewed in a direction from top to bottom --
that is, from the base mass toward the cutting mass - increasing
transparency.
The masses are produced in a layered and sequential manner
commencing with the cutting mass 18, thereafter, the tooth bone mass
16, and, finally, the base mass 14. In accordance with the production
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thereof by injection molding, the masses each include injection
projections, whereby the cutting mass illustrated in the sole figure of the
drawing includes three injection projections 20, 22, and 24; the tooth
bone mass includes two injection projections 26 and 28; and the base
mass includes one injection projection 30. The injection projections 20,
22, 24, 26, 2$, and 30 each extend respectively into the respective
neighboring mass and are surrounded thereby. In this manner, the
interconnection between the neighboring masses is intensified.
The base mass 14 is provided on its base surtace 12 with a
recognition or indicia field 32 which permits an indicia to be applied by
pressing of the indicia onto the indicia field 32 during the production
process or by applying a marking in a conventional manner by a
corresponding pouring insert.
In the illustrated embodiment of the artificial tooth of the present
invention, the tooth bone mass includes from its border surface 34 with
the cutting mass 16 outward a substantially smooth or flat surface. In
view of the fact that the surface 36 of the cutting mass 18 is strongly
structurally accommodated and conformed to the (not illustrated) mold,
there arises an uneven or non-uniform layer thickness of the cutting mass
18 on the tooth bone mass 16. This configuration permits the
appearance of the artificial tooth to even more closely resemble that of a
natural tooth.
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There follows hereafter a description of the production of an
artificial tooth in accordance with the present invention.
The mold is initially provided with a first building form, the cutting
mass building form. The surface of the building form corresponds to, and
shapes the configuration of, the surface of the tooth bone mass 16 along
its border surface 34. Thus there is formed a seamless and surrounding
gap between the mold and the cutting mass building form or forms.
This gap is then filled with the cutting mass in monomer form and,
in fact, is filled via the injection projections 20, 22, and 24. Additionally,
air release openings are provided in the building forms (these openings
are not shown) and these openings, in any event, leave tracks in the
border surface 34. As soon as the filling of the cutting mass 18, with its
good flowing capabilities and not yet polymerized properties, has been
completed, the light polymerization is performed and this is accomplished
by irradiation of the cutting mass 18 by a light source 40. The light
irradiation passes through the light passage permitting mold, whereby it
is advantageous to maintain the material thickness of the mold in as
substantially uniform a manner as possible in order to promote the
uniformity of the intensity of the irradiation from all sides. Additionally, a
reflector 42 is provided which promotes uniform irradiation of the cutting
mass and whose diameter is considerably larger than the diameter of the
artificial tooth 10 such as, for example, three times larger.
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The irradiation of the cutting mass by the schematically shown light
source 40 is pertormed for a predetermined time.
Following the period of irradiation, the cutting mass 18 is hardened
but is not, however, hardened fully through. In particular, on the portion
S of its surface facing away from the light source, the cutting mass is still
somewhat soft but not so soft that portions of the cutting mass 18 would
remain hanging on the cutting mass building forms during the pulling out
or removal of the cutting mass building forms.
After the removal of the cutting mass building forms, a new
building form is inserted whose surtace corresponds to the border surtace
44 between the tooth bone mass 16 and the base mass 14. Tooth bone
mass 16 is injected via the injection projections 26 and 28 into the hollow
space which is formed between the separation surtace 34 and the tooth
bone mass building forms.
Following the filling of the building forms with the tooth bone mass,
which is accomplished under the typical injection molding pressure, the
partially or semi-finished artificial tooth is then subjected to another light
polymerization process. The length and intensity of the irradiation can be
accommodated to the strength of the material which is to be polymerized
so that the light irradiation for effecting the hardening of the tooth bone
mass can be selected to be a larger irradiation than the light irradiation
for effecting the hardening of the cutting mass 18.
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The light irradiation is accomplished, in any event, by passage of
the light through the cutting mass 18. Due to the fact that the cutting
mass 18 is particularly translucent and permits the unimpeded passage
therethrough of light, the irradiation of the tooth bone mass 18 is anly
slightly dampened, or not dampened at all, by the passage of the light
through the cutting mass 18. A side effect of this second light irradiation
lies in the fact that the cutting mass is, particularly in the region of its
border surface 34, now completely hardened through.
The light hardening of the tooth bone mass 16 is performed to an
extent such that the tooth bone mass 16 is form stable without, however,
its border surface 44, which borders on the base mass 14, having been
brought to its complete hardness.
After the removal of the tooth bone mass building forms, a base
mass building form is inserted whose surface corresponds to the base
surface 12. The intermediate space which is thereby formed between the
base mass building forms and the border surface 44 is then filled with the
base mass, whereby an injection projection 30 is used.
Following the completion of the filling of the base mass, the light
source 40 is again actuated and a through hardening of those regions of
the tooth bone mass which neighbor the border surtace 44 as well as the
base mass 14 is undertaken.
While the light hardening somewhat warms the artificial tooth 10,
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this warming is not so strong as to burden or restrict the polymerization
of the newly-introduced mass - that is, the base mass 14 added after the
hardening of the tooth bone mass 16. After the completion of these
individual steps, which comprise the process ofthe present invention, the
now-completely light polymerized artificial tooth 10 is removed from the
mold and, thereafter, the base mass building forms are removed.
Subsequently, the hardness of the artificial tooth is increased by a hot air
treatment. This can be performed, for example, in an automatic manner
in that the removed artificial tooth can be conveyed through a hot air
station by a transport belt. Thereafter, as required, a surface treatment
such as a polishing of the surface 36 can be undertaken and also,
corresponding molding techniques can be performed, if these are
desired.
It is to be understood that a plurality of such artificial teeth can be
produced simultaneously and can accordingly be completed with a high
throughput. The finishing of such artificial teeth can also readily be made
automatic. It is to be understood that the form or mold for the material
which is deployed can be accommodated to the wavelength of the
irradiating light. If, for example, a light irradiation is to be performed not
with visible light but, rather, with UV light, then the mold material must be
configured to permit passage therethrough of ultraviolet or UV light. In
one modification of the present invention, the process of the present
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25199-234
invention can also be implemented for producing cutting shells. This permits a
blunted or cut-down tooth of a patient to be used as the mold, whereby it is
to be
understood that the term "artificial tooth" also encompasses such shells or
partial
teeth.
s An evaluation of the artificial tooth produced in accordance with the
present invention revealed that the desired finished hardness is particularly
good.
Also the interconnectivity is surprisingly good. A mass difference of less
than
0.08 mm was detected so that, in total, in particular with a view towards
drastic
reduction of the cycle time, the present invention considerably improves the
to production cycle time.
In a further embodiment, a building block is comprised of a material
not permitting the passage of light therethrough. The use of such a building
block
enables a screening against light hardening at the desired positions, if
necessary.
After removal of the building block a complete hardening can then be achieved.
is The present invention is, of course, in no way restricted to the
specific disclosure of the specification and drawings, but also encompasses
any
modifications within the scope of the appended claims.
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