Method and apparatus for making a dental model mounted on a base plate

A method and apparatus for making a model of a set of teeth, in which each tooth is mounted on a holding pin (17) which is removably disposed in a base plate (15). For positioning of the holding pins, a datum plate (10) of transparent material is placed on the impression (5) of a jaw and the desired positions, of a respective holding pin for each tooth root, are marked. Then pins are inserted into a pre-perforated base plate (15) according to the markings, or a pre-perforated base plate of transparent material is used instead of the transparent datum plate (10), and is marked with desired pin positions on one side and provided with pins on its other side. The pins then penetrate molding material placed in the impression (5), and harden in place as the molding material hardens. The hardened molded material can then be sawed into separate parts.

The present invention relates generally to a method and apparatus for 
producing dental models with individually removable teeth, and more 
particularly to a labor-saving method and apparatus for positioning the 
respective pins which support each tooth in the model's base plate. 
BACKGROUND 
Dental models, in which the individual teeth can be removed, are needed for 
producing crowns, bridges, and tooth prostheses. In order to form such 
replacement parts to fit precisely into the model, the model parts must be 
made removable, which means that, after sawing apart the originally cast 
model, the model parts must each be mounted on a folded pin which fits 
into a base plate. Starting from the original jaw impression used to cast 
the model, the process of correctly positioning the holding pins, whose 
locations differ as widely as the positions of a particular tooth in 
different people's jaws, for the respective models, has heretofore been 
very labor-intensive. 
For mounting these pins, one has heretofore used so-called pin sets. These 
have an X-Y movable stage on whose upper side is disposed the receptacle 
containing the jaw impression, and whose lower side supports the base 
plate. A fixed datum or alignment or sounding shaft is located above the 
jaw impression and corresponds to a fixed drill located under the base 
plate and having a shank which is aligned with the shank of the sounding 
shaft. The X-Y movable stage is moved around in such a way that the 
sounding shaft is directed to the positions where one wishes to later 
place a pin for mounting a model part. Upon reaching the desred positions, 
the X-Y movable stage is depressed, so that the drill makes a 
corresponding hole in the base plate. This process must be painstakingly 
repeated a number of times corresponding to the number of removable parts 
needed in the model. Conventionally, each tooth root or removable part in 
the models requires two pins, so that the part can not rotate when mounted 
in the base plate. 
Finally, pins are inserted into the finished, perforated base plate, the 
jaw impression is filled with plaster or similar molding material, and the 
base plate with protruding pins is lowered onto the molding material, 
taking care that the base plate is exactly aligned, so that where the pins 
actually penetrate the plaster or other molding material is at the desired 
positions. 
The disadvantages of this conventional procedure are, first of all, that 
the pin sets are very expensive. Aside from that, during drilling it often 
happens that the stage moves or the base plate becomes canted, so that the 
relatively thin drilling bit breaks off. Beyond that, the required 
procedure with the conventional pin sets is relatively involved, and the 
precisely undertaken feeling-out of the positions for the pins sometimes 
comes to naught, because the alignment of the pin-equipped base plate over 
the jaw impression filled with molding material requires a very precise 
eye. Finally, the time required for the conventional procedure is very 
high. 
THE INVENTION 
Accordingly, it is an object of the invention to improve and simplify the 
method and apparatus conventionally used for positioning the pins on the 
base plate, so that the need for expensive machines is avoided, the 
worktime is substantially reduced, and the desired precision in pin 
positioning is achieved without the danger of disturbances during the work 
process. 
Briefly, a datum or sounding plate of transparent material is placed on the 
impression in such a way that the desired positions of the holding pins 
can be marked on the side of the datum plate remote from the impression, 
the base plate is pre-perforated with a field of closely spaced holes in 
the curved region over the jaw impression, the datum plate is flipped over 
in a guide means, the base plate is laid in the guide means against the 
side of the datum plate remote from the markings, and holding pins are 
inserted in the base plate corresponding to the markings on the datum 
plate. 
Due to the features of the present invention, it is possible to very 
quickly mark, on the preferably glass-clear datum plate, the positions at 
which the base plate should be provided with pins. Thereafter, the datum 
plate is simply flipped over, and, by means of a common guide means, the 
base plate is placed atop it in precise alignment. The base plate has been 
pre-perforated at the time of its manufacture with an array of holes. Upon 
looking through the holes, one can see the markings made on the datum 
plate and place in the base plate the corresponding pins. Since the pins 
must be inserted from the side of the base plate remote from the datum 
plate, the datum plate had to be first flipped over, so that a pin pattern 
mirror-reversed from the pattern of the filled-in impression does not 
result. 
In a variation of the method and apparatus of the invention, a transparent 
base plate is provided, having a field of closely spaced holes in the 
region of the impression. The base plate is laid over the impression in a 
guide means, and the desired positions of the pins are marked on the side 
of the base plate remote from the impression. The base plate is flipped 
over in the guide means, and holding pins are inserted on the side which 
was adjacent to the impression, i.e. the side opposite to the side bearing 
the markings. This is a further simplification from the embodiment first 
described, which featured both a base plate and a datum plate. Again, it 
is advantageous to make the base plate glass-clear and transparent, so 
that the desired positions of the pins can be marked on the side remote 
from the impression, and one can, by simply flipping over the base plate, 
see the positions where the pins should be inserted. In order to avoid the 
individual drilling of the holes, it is again advantageous to make the 
base plate pre-perforated with a field of holes, from which one can simply 
select the appropriate ones in accordance with the markings. 
Both versions of the invention are exceptionally simple and reliable in 
their operation. In particular, no additional machines are necessary for 
carrying them out. In view of the fact that the plates used are each 
guided with respect to the impression, there is no difficulty in correctly 
placing the finished base plate on the molding material in the impression. 
Errors and inaccuracies cannot occur. 
As for the marking of the pin positions, this can be accomplished by 
sticking marker pins in the corresponding holes in the datum plate which 
can be provided with a field of closely spaced/adjacent holes. The marking 
of the holding pin positions could also be done by making colored points 
or the like. 
In accordance with the first version of the invention, the apparatus 
adapted for practicing it can advantageously be formed as follows: a datum 
plate, similar to the base plate and made of transparent material, is 
placed on the impression. The datum plate has a filled of closely 
spaced/adjacent holes. The datum plate is held in proper registration over 
the impression by a guide means, and the base plate is held in proper 
registration over the impression by the same guide means. The base plate 
has, for the holding pins, a field of closely spaced/adjacent holes 
corresponding to that of the datum plate. The fields of holes of the datum 
plate and base plate are mirror-symmetric to an axis passing through the 
middle of the guide means. 
With reference to this apparatus, its simplicity and reliability of 
operation must once again be stressed. Also, there are no special costs 
since the datum plate can be used repeatedly and a base plate is 
conventionally needed anyway for construction of the model. As for the 
mirror symmetry of the fields of holes of the datum plate and base plate, 
this permits the holes of the two plates to always be aligned, whenever 
the two plates are disposed in the common guide means. 
With reference to the second version of the invention, the apparatus for 
practicing it is advantageously configured as follows: the base plate is 
of transparent material; it has for the pins a field of closely 
spaced/adjacent holes in the region of the impression; and it is held in 
its position on the impression in proper registration. Thus, all one 
requires is the already necessary base plate, in a correspondingly 
prepared state. The proper registration of the base plate on the 
impression is accomplished as follows: after the marking of the holding 
pin positions, the base plate is taken off the guide means in order to 
emplace the pins on the side of the plate adjacent to the impression; 
then, when the plate is re-seated in the guide means, it is returned to 
exactly the same position as when it was being marked, assuring that the 
now-emplaced pins are arranged exacly on the previously desired positions. 
In the apparatus for practicing the second version of the invention, it can 
be advantageous to form the holes for the pins as "blind holes" open to 
only one side of the plate. This is particularly recommended when the 
marking is under taken by means of color points. The configuration of the 
holes as blind holes thus avoids any running of the color or ink into the 
holes. In order to simplify handling, the plate can be formed, on the side 
opposite that having the blind holes, with corresponding depressions or 
recesses, in which the color points can be precisely put or other marking 
means fastened. 
For all of the above versions and embodiments, it can be advantageous for 
the holes and at least the longitudinal portions of the pins which fit 
into the holes, to have a common asymmetrical cross-section. This permits 
the use of only one pin for each tooth root, while the turning of the 
tooth root with respect to the base plate is nevertheless prevented. This 
not only cuts in half the work of marking the pin positions and emplacing 
the pins, it also saves half the pins and avoids the jamming which two 
pins of the same root may cause due to plaster expansion during hardening. 
This makes later handling easier. 
It is further advantageous to make the longitudinal, to-be-inserted 
portions of the pins conical, so that good seating of the pins in the base 
plate results. 
It is also advantageous to secure the jaw impression on a carrier plate 
which has an integral guide means. Such a guide means can be formed as a 
wall portion of the carrier plate projecting perpendicularly to the 
surface of the impression and having therein at least one guide slot for 
engagement with a matching guide tab of the datum plate and/or base plate. 
These features assure, in particular, that during the entire handling, the 
guidance for the plates is always the same and their relative position to 
the jaw impression is preserved, so that during handling no errors or 
inaccuracies can arise.

DETAILED DESCRIPTION 
FIG. 1 illustrates a generally rectangular carrier plate 1 with two 
orthogonally upwardly projecting wall portions 2 and 3 at opposite ends of 
the plate. An impression 5, of the teeth of an upper or lower jar, located 
in a receptacle 4, is fastened to the upper surface of the plate 1. The 
receptacle 4 abuts the wall portion 2 of the plate 1, and the handle 6 of 
the receptacle 4 is fixed to the plate 1 by a glob of silicone rubber 7. 
Alternatively, the handle 6 can be formed to engage a slot 8 in the wall 
portion 3 of the plate. 
The wall portion 2 is formed with two guide slots 9, which preferably 
extend perpendicularly to the upper surface of the impression 5. 
FIG. 2 is an enlarged plan or top view of the impression 5 of FIG. 1. A 
datum plate 10, preferably of transparent material, has been placed over 
the surface of the impression 5. Through the plate 10 one can see the 
contours 11 of the jaw impression. The plate 10 is provided, in the 
semi-circular region of the tooth impressions, with a field or array of 
closely spaced or adjacent holes 12. Further, the datum plate 10 is also 
provided with guide tabs 13, preferably T-shaped, which interfit securely 
with the guide slots 9 in wall portion 2 of carrier plate 1. 
The fact that the contours of the impression 5 can be seen through the 
datum plate 10 makes it possible to mark the locations at which a base 
plate 15 later can be provided with pins. For example, marker pins 16 
(FIG. 3) can be placed into holes 12 from the top, e.g. at the location 
identified by numeral 14 in FIG. 2. 
A datum plate 10 provided with marking pins at these locations has a pin 
configuration which is the mirror image of the pin configuration actually 
required for the base plate 15. In order to reverse this mirror image, the 
datum plate 10 is flipped over and re-inserted in the guide slots 9, as 
shown in FIG. 3. Into these same guide slots 9, a similarly formed base 
plate 15, also having a semi-circular field of holes, is placed, so that 
it rests on the side of the datum plate 10 remote from the marker pins 16. 
One can then place holding pins 17 into the holes 18 of base plate 15 
which are aligned with the marker pins 16 of datum plate 10. When one then 
removes both plates 10 and 15 from the guide slots 9, flips base plate 15 
over, and re-inserts it in slots 9, the positions of the holding pins 17 
with respect to the depressions in the impression 5 correspond exactly to 
the positions which were selected in FIG. 2 with the help of the datum 
plate 10. 
The base plate 15 may also comprise transparent material. This is not 
necessary, since one can see through the holes 18 in the base plate 15 the 
positions at which the corresponding holes 12 of the datum plate 10 have 
been closed by the insertion of marker pins 16. One can then insert 
holding pins 17 in the base plate 15 at corresponding positions. When one 
then flips over the base plate 15 thus prepared and puts it in position on 
top of the impression, with the help of the guide means 9, the positions 
of the pins 17 correspond exactly to the positions which were selected, as 
shown in FIG. 2, with the help of the datum plate 10. One can then fill 
the impression 5 with plaster and press the base plate 5, together with 
its pins 17, onto the plaster, so that the pins 17 dip into the plaster at 
the desired locations and become fixed there as the plaster hardens. This 
is illustrated in FIG. 4, in which the holes 18 of the base plate 15 are 
visible. Excess plaster, which runs out through the unused holes 18 as the 
base plate 15 is pressed down, is designated by reference numeral 19. 
FIG. 3 shows that the pins 16 fit into conically shaped holes 20 in the 
datum plate 10. Pins 17 fit into similar conically shaped holes in base 
plate 15. One can form the pins and holes with non-round but corresponding 
or matching cross-sections, so that the pins will not rotate in the holes, 
and each tooth of the model will be prevented from rotating on the base 
plate, even though only one pin per tooth is provided. 
FIG. 2 shows that one could insert pins in a base plate in the desired 
manner without using a datum plate as an intermediate element. For this 
purpose, one uses a base plate, of transparent material, corresponding to 
the plate 10, and having a field of holes 12. This plate is laid on the 
jaw impression 5 as shown in FIG. 2. The positions designated for later 
insertion of pins can be marked on the upper surface by insertion of 
corresponding pins or by making color markings on the plate. Now the plate 
is flipped over, so that pins can be placed on the other side. Thereafter, 
the impression 5 is filled with plaster or similar molding material and 
the plate is placed on top in the manner shown in FIG. 2, so that it acts 
as base plate and pins pressing into the plaster. Due to the conically 
formed pins and the matching, unround cross-sections of their holes, the 
advantage set forth above are achieved. 
Insofar as one wishes, when using a transparent plate as a base plate, to 
mark it with inked or colored points, it is advantageous to form the holes 
on the impression-adjacent side as blind holes, so that, upon marking, the 
ink or coloring cannot run into the holes. For precision of marking, 
depressions or recesses can be provided on the plate side to be marked, 
corresponding to the blind holes on the opposite side of the plate. 
As those skilled in the art will appreciate, various changes and 
modifications are possible within the scope of the inventive concept.