Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to improved apparatus and
methods for making dental prosthetic devices. In particular, it
relates to an improved design for a dental dowel pin unit and an
improved method, using this apparatus, for preparing dies of
patient's teeth.
Conventional dental techniques for the making of dental
crowns, inlays, bridges and prosthetic devices of this nature
usually involve making a model of the patientls mouth, or at least
the teeth and gums in that region of the mouth requiring the repair
work. Such models are usually made by preparing a tray containing
a mouldable malleable material (hereinafter referred to as impression
material3 which is then pressed on to the teeth and gums in the
patient's mouth so as to ~orm a female impression thereof in the
impression material. By pouring a hardenable matexial, commonly
~eferred to as die stone, into this female impression, an exact
reproduction of the shape of the patient's teeth and gums is formed.
A dental technician then has an exact model of the patient's teéth
on which to do whatever technical work is needed to effect repairs
or prepare prosthetic devices. The technician's work commonly
requires that the individual tooth die be separated so that they
can be worked on individually and therefore techniques have been
devised by which the model of the patient's mouth can be cut into
individual tooth dies~ This, however, requires some manner by
which they can be replaced in their proper orientation and position
in the model. The technique commonly used is to insert a dowel pin
at approximately the central axis of each individual tooth when the
die stone is hardening leaving the top part of the dowel pin
protruding from the die stone. Later a second material, generally
known as the base material which is commonly a plaster or some
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such similar material, is poured over the die stone to cover
the protruding ends of the dowel pins. Thus when the individual
tooth segments are cut away and removed, they have protruding
therefrom a dowel pin which can be replaced in a corresponding
recess in the base material to reposition and orient the tooth
in its original relationship to other parts of the model.
Past experience has found difficulties with this
technique since constant removal and replacement creates wear
on the dowel pin or its recess in the base material which
eventually creates a loose and inadequate positioning of the
tooth model. Dirt and dust in the base recess will often affect
the repositioning. Furthermore, the positioning of the dowel
pins in the die stone often creates difficulty since it is
highly desirable that the dowel pins be substantially centered
on the vertical axis of the tooth models and that the pins be
oriented substantially parallel to each other so as to allow
the individual tooth dies to be separated and removed from the
mouth model. Manual placement of the dowel pins is considered
a clumsy, inexact and painstaking method. Other techniques
in which the dowel pins are positioned by support structures
attached to the edges of the impression material have been found
to be similarly inefficient and imprecise, partly because the
contours of the impression are so irregular.
It is the purpose of this invention to provide an
apparatus and method for production of dental models in which
dowel pins can be simply and efficiently placed so as to provide
a firm and precise replacement and orientation of the individual
tooth dies.
I have found that dental procedures of this nature are
improved by use of a dowel pin unit of my invention and an improved
method employing this apparatus. I have accordingly conceived a
lo~s3ss
dowel pin unit for use in maXing dental models comprising a dowel
pin having a tapered longitudinal section wider at the lower end
and narrower at the top end, and having asym.~etrical cross-section.
The dowel pin is enclosed in a jacket of plastic, or some such
material, ribbed on its outer surfa~e to form a structural bonding
with the surrounding die stone or base material, as the case may be~
At about middle of the dowel pin unit is a flat planar floater member
extending outwardly from the jacket approximately perpendicular to
the axis of the pin. The lower end of the pin is structurally fixed
within the jacket by an engaging notch and lug assembly and the
upper end of the pin is removably held within the jacket by an
engageable ball and socket assembly. The foregoing apparatus allows
a dental technician to employ the following method.
Having a female impression o~ the patient's mouth,
the technician may then fill the impression with die stone material
and insert the lower end of a pin unit, as described above, into
the individual tooth model while the die stone is soft using the
floater to position the pin unit in proper location and orientatio~
the floater being adapted to rest at the surface of the die stone
material. When the die stone material has hardene~, the upper
end of the pin unit will be protrudin~ and this can be embedded
in a base material by pouring the base material on top of the
die stone, this latter'step being taken after the jacket surround-
ing the pin has been severed or weakened just above the floater.
When the base hardens the individual tooth die can be separated
by cutting the die stone material on either side of the tooth die
and the tooth die can be removed by pulling the tapered dowel pin
out of the portion of the jacket embedded in'~the base (by overcoming
the resistance of the ball and socket). The lower end of the jacket
will, of course, remain embedded in the base material and provide
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a firm resilient and precise socket into which the dowel pin can be
re-inserted to replace the tooth die in its proper position and
orientation.
A better understanding of the improved apparatus can
be gleaned from a detailed description of one embodiment with
reference to the enclosed drawings in which:
Figure 1 is a vertical cross-section of a tray
containing an impression of a tooth filled
with die stone material incorporating a
dowel pin unit of the present invention;
Figure 2 is a horizontal cross-section of a dowel
pin unit in accordance with this invention;
and
Figure 3 illustrates a typical model of a patient's
mouth showing a removable tooth die.
The cross-section of Figure 1 illustrates a stage
in the making of a dental model using my improved dowel pin unit.
The tray 2 holds a quantity of impression material 4 which has
been pressed over the appropriate portion o~ a patient's mouth
to form a female impression of the patient's tooth (or teeth) and
gums as represented by the impression profile 6, the lower end of
which at 8 represents the configuration of the patientls tooth,
while the upper portion represents the configuration of the gums
at the base o~ the teeth.
Thus the technician is provided with an exact negative
reproduction of the shape of the relevant portion of the patient's
mouth, especially the teeth involved.
In order to perform the necessary prosthetic work,
the technician will produce an exact model of the patient's teeth
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and gums by filling the negative impression with a fluid (but
hardenable) material 10 known as die stone which, upon harden-
ing, will produce a tough resilient model of the patient's
teeth on which the technician can work.
Since the technician will want to work on an
individual tooth die, it is desirable to separate the individual
die from the rest of the model of the mouth and frequently during
his work will want to remove and replace the tooth to its
original position and orientation with respect to the rest of
the model. To facili~ate this, the model is provided with one
or more dowel pins such as illustrated at 12, the lower end of
which is embedded in th~ die stone of the tooth and the upper
half of which protrudes above the die stone where it is later
embedded in a base material 14 which is poured over the die stone
when the latter has hardened.
Conventionally, a dowel pin of previous design would
be inserted either before the die stone was poured into the
impression or after pouring but before the die stone had hardened.
Previous techniques for positioning dowel pins involved wire or
other supporting devices which could be struck into the sides of
the impression material or otherwise supported on the impression
or tray to maintain the dowel pin in position while the die stone
hardened. In the past, repeated removal and replacement of the
individual tooth die, by withdrawing the dowel pin from its
location in the base material and replacement thereof r developed
inaccuracies because of wearing of the base material or the
dowel pin itself or the inclusion of dirt or dust from the sides
of the base material and other foreign material in the dowel pin
recess in the ba~e~ For instance fine particles resulting from
the wear on constant replacement and removal of the dowel pin
would cause material to build up in the recess of the base
material preventing proper snug
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replacement of the dowel pin.
Figure 1 illustrates an improved design for a dowel
pin unit in which the dowel pin 12 is encased in a jacket 16 of
suitable material such as plastic, which has a series of ridges
18 (or other similar irregularities) about its outer surface so
as to provide a firm structural bond with the surrounding die stone
or base material in which it is encased.
Located approximately mi~way along the dowel pin unit
and extending outwardly from the outer surface of the jacket is a
floater 20 which is a flat horizontal planar element surrounding
and extending out from the jacket 16 and adapted to lie, as
illustrated in Figure 1, along the upper surface of the die stone
material. In the usual case, as illustrated in Figure 1, this
floater is positioned perpendicular to the long axis of the dowel
pin but in certain cases might be set at an angle less than 90
thereto ~epending on the t~pe of model and the work being performed
thereon.
~ ocated in the lower half of the dowel pin 12 is a
notch 22, which may or may not extend around the entire circumference
of the pin, and a corresponding lug 24 on the inner surface of the
jacket located and dimensioned so as to engage snugly in the notch
22. This provides a firm tight engagement and structural bond
between the lower end of the dowel pin and the jacket surrounding
it. In the upper portion of the dowel pin is a pair of sockets
26 in the form of indentations in-the wall of the pin in a generally
curved configuration of approximately the shape of a portion of a
sphere. Correspondingly the jacket at the same location has on
its inner surface a projecting ball portion 28 which engages
snugly into the corresponding socket 26.
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As can be seen in Figure 1, the dowel pin and its
jacket are generally tapered from a wider portion embedded in the
die stone to a narrower portion in the base material so as to
facilitate removal of the pin from the base material when the
technician is working on the model.
Figure 2 illustrates a corss-sectional view of the
dowel pin unit including the dowel pin 12, the surrounding jacket
16 and the sockets 26. The cross-sectional shape illustrated and
considered desirable is approximately a sector shape having two
straight sides subtenaed by a curved third side. This configuration
allows for easy replacement of the dowel pin within its recess
in the proper orientation and avoids the possibility of error in
replacing it in the wrong orientation.
The dowel pin also has an anchor 30 which is dove-
tailed in cross-section so as to anchor the pin firmly in the die
stone matçrial surrounding it.
The top end of the jacket covering the top end of
the dowel pin is substantially thinner, almost in the nature of
a membran~,--at 32-to allow for access to the top of the dowel pin
for purposes described later.
Thus with the use of this dowel pin unit, a technician
having an impression provided by known methods somewhat in the
nature of that illustrated in Figure 1, can proceed to fill the
impression with die stone material to approximately the level
illustrated, place the model on a vibrator to remove voids and --
level the fluid die stone, and then while the die stone is still
soft, position a dowel pin unit as illustrated approximately
co-axial with each individual tooth impression, inserting the
broad end of the pin until the floater 20 rests along the top
surface of the die stone material, as seen in Figure 1.
,
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Although the eLement 20 i9 re~erred to as a floater
it should be understood that it9 function does not depend purely
on floatation in the sense that it provides buoyancy by virtue of
its lighter specific gravity. To a large extent it may function
by virtue of its broad area combined with the thick viscosity of
the die stone fluid to maintain the orientation of the dowel pin
unit.
The die stone material is then allowed to harden to
substantial firmness thereby firmly embedding the lower end of
the dowel pin unit therein.
After the die stone has hardened, the jacket of the
dowel pin unit (being of plastic or other such material) can be
severed around the circumference oX the pin at approximately the
level of the top of the floater 20 so as to allow separation of
the upper and lower halves of the jacket at a later stage in the
pxocedure. Alternatively, the dowel pin unit might be fabricated
with an indentation or weakness around its circumference just above
the level of the floater which would allow separation of the two
halves by exerting sufficient force.
A base is then formed by pouring base material 14
(plaster or some such similar material) on top of the die stone so
as to substantially encase the upper end of the dowel pin and
jacket. The tip of the dowel pin unit may be allowed to protrude
from the top of the base although this is not necessary.
In accordance with conventional practice, it is
preferable to coat the upper surface of the die stone material
with a non-adhesive material to form a "separation coating" so
that in subsequent operation the die stone material may be lifted
and separated from the base material.
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When the die stone and base material are hardened,
tray 2 and impression material 4 can be removed leaving a model
of the patient's teeth, such as seen in Figure 3.
In order to remove a single tooth die a vertical cut
is made on each side of the tooth, as at 34 and 36 respectively,
in Figure 3, which cuts penetrate down to the line of interface
between the die stone and the base m~terial. Because of the non-
adhesive layer between those two materials they will separate
at the plane of contact. By exercising some force the tooth die
may be removed by pulling it out of the base with sufficient force
to pull the narrow upper end of the dowel pin 12 out of its jacket,
overcoming the resistance of the ball and socket engagement.
Thus the individual tooth 8 with its attached dowel pin 12 is
available for further work by the technician. The individual
tooth die may then be replaced in the model by re-inserting the
end of the dowel pin 12 into the end of the jacket which remains
embedded in the base material, as-seen at 38 in Figure 3.
This e~bedded portion of the jacket provides a tough
I resilient-recess which-will be léss subjec-t-to-wear from numerous- - -
I~ 20 movements of the tooth die. ~ecuase of the asymmetric (by which
is meant it does not have an axis of symmetry though it may be
- symmetrical about a chosen plane) cross-section the pin can
only be inserted in one orientation. Furthermore, because of the
ball and socket engagement the individual tooth member can be
held firmly in the base material without accidentally falling out.
As shown in Figure 1, the narrow end of the dowel pin
and jacket can be left protruding from the base material but if it
is not, the base material may be ground down until the upper end is
exposed. A small punch or other rod-lik~ instrument can be placed
against the narrow end of-t~e dowel pin 12 and tapped so a~ to
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lO~;9;~S5
assist disengaging the dowel pin from its jacket to remove the
individual tooth model.
An a~ditional advantage to this invention may be
achieved by using dowel pin units having a jacket of different
colours of plastic. This would facilitate matching individual
tooth dies back into their respective position by co-ordinating
the colour of the floater and the other saparated part of the
jacket embedded in the base material.
It may also be considered desirable to further
anchor the floater to the die stone material by dove-tailed
protrusions on the undeside of the floater, such as seen at
40 in Figure 1.
Although the notch and-lug 22 and 24 are shown
substantially spaced from the level of the floater, they might
be located closer to that mid point, as might the ball and socket
assembly-26 and 28,- as may be dictated by design considerations.
Thus a dowel pin unit, as disclosed, can be used
after the die;~stone material has been poured in liquid form into
the impression,-is=vibrated-and begins to harden. The broad end
of the dowel pin is inserted into the die stone down to the point
where the floater rests on the upper surface of the die stone
- material. The viscosity or thickness of the die stone material as
it is hardening combined with the broad area of the floater will
tend to keep the dowel pin unit in its upright position approx-
imately coincident with the vertical axis of the individual tooth.
Where several such pins are inserted, they will tend to be
substantially parallel which is important to facilitate removal
of the dies and other work by the dental technician. Unlike
previous methods, it is not so dependent on the technician being
able to estimate the parallelism o~ the pins nor is the position
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of the pin dependent on some auxiliary supporting device resting
on the generally irregular outline of the impression mould.
Although a variety of materials might be used, it
is considered advantageous that the pin be a strong material such
as metal although it might be a strong plastic, and the jacket
a firm, resilient, but not hard, plastic material. Since the
lower end of the pin will be withdrawn from the lower end of the
jacket it is desirable that the two materials be chosen or
otherwise adapted to permit easy parting during the processes
described above.
Various modifications and variations to the fore-
going structure and method could be improvised without departing
from the inventive concept herein.
