Casting collar for dental impression tray

A method and apparatus for facilitating the formation of dental castings utilizing a dental impression tray. A collar assembly is provided which is substantially oval and forms an upstanding peripheral enclosure around the dental impression tray. A rod transversely spans across the oval member and is retained in notches at the upper edge of the oval member. The rods pass through spherical coupling members from which depend dowel pins which can enter into the negative impression and are used for retaining the teeth which are subsequently formed by a casting process.

BACKGROUND OF THE INVENTION 
This invention relates to dental equipment, and more particularly to a 
reusable collar for a dental impression tray. 
The use of dental castings for making teeth is well known in the art. 
Dentists and dental laboratories have numerous devices to utilize in the 
making of single teeth or bridges for replacement and reconstruction of 
damaged portions of the patient's mouth. The usual procedure involved 
requires the formation of a dental impression, or a negative, directly 
from the patient's mouth and using that negative to make a positive 
casting of the desired teeth or bridge. 
Dental impression trays are generally utilized for this purpose. The trays 
are designed to fit sections of the mouth and accordingly numerous trays 
are available for different sections of the mouth. A casting material is 
placed in the tray and the patient bites down into the casting material to 
make the impression. The impression tray is then removed and strick wax is 
rolled out from sheets and placed about the dental impression tray to 
build up a protective wall about the tray to retain the material poured in 
to make the positive impression. Numerous types of holding devices are 
also inserted through the walls of the strick wax to hold the dowel pins 
which extend downwardly into the cavity in the negative impression and 
which will provide the support posts for the teeth. Such items as bobby 
pins are frequently utilized for holding the dowel pins. 
Although this procedure has been widely accepted and utilized throughout 
the dental profession, much of it is quite primative, cumbersome and 
awkward. For example, the use of the red strick wax is exceedingly 
bothersome and time consuming. The wax must be cut from the sheets, fitted 
about the tray and molded to shape the particular dental tray. This is a 
most awkward part of the process. 
Additionally, there is no secure method of holding the dowel pins in proper 
position. The use of bobby pins, or other such implements which are 
regularly used, is a most imprecise positioning technique and often 
prevents the proper positioning of the dowel pins in the cavity of the 
(preparation) negative impression. This is especially a problem where a 
large bridge section must be formed and more than one pin must be utilized 
for the section. When trying to pull up on the dies pins to remove the 
(bridge wax up) positively formed piece, the bridge section may be damaged 
or may even crack if the pins are not both positioned properly in the same 
section. 
Although the use of the strick wax, the bobby pins, and other such 
primative devices present difficulties in use, nevertheless, they still 
continue to be used by the dental profession as well as by dental 
laboratories, mainly for lack of any improved and more precise devices for 
facilitating the formation of dental castings. 
BACKGROUND OF THE INVENTION 
It is accordingly an object of the present invention to provide improved 
methods and apparatus for forming dental castings which avoid the 
aforementioned problems of prior art devices. 
Yet another object of the present invention is to provide a reusable collar 
for a dental impression tray which will facilitate the formation of dental 
castings. 
Still another object of the present invention is to provide a preformed 
collar for a dental impression tray which includes support and positioning 
means for properly placing the dowel pins into cavities within the 
negative impression (preparation) held by the impression tray. 
Still a further object of the present invention is to provide a collar for 
enclosing the periphery of a dental impression tray which supports rods 
extending across its top from which depend dowel pins which can be used to 
hold the positively formed teeth. 
Another object of the present invention is to provide a collar, rod, and 
spherical coupling device for use in the formation of dental castings. 
Yet another object of the present invention is to provide a unique method 
of forming a dental casting which is easier to implement, less time 
consuming, and more accurate than prior art methods. 
Briefly, in accordance with the present invention, there is provided a 
collar for a dental impression tray which includes a preformed 
substantially oval member having a continuous thin outer wall. The oval 
member forms an upstanding peripheral enclosure surrounding a dental 
impression tray. The oval member has an open top and bottom. A plurality 
of notches are formed about the upper edge of the wall at its opposing 
ends for supporting depending dowel pins which are positioned to engage 
the teeth which are being cast in the tray. 
At least one rod spans across the longer dimension of the oval member and 
is securely retained within the opposite pairs of notches. A spherical 
coupling member is utilized for interconnecting the rod with the depending 
dowel pins. 
The invention further comprises a method forming the dental castings, 
comprising the steps of positioning a preformed oval collar about a dental 
tray having therein the dental impression. The oval collar is sealed to 
the dental tray at its bottom. Dowel pins are then depended from an 
elongated rod which extends across the top of the oval collar. The casting 
material can then be poured into the impression tray and the rest of the 
procedure for forming the teeth or dental bridge is carried out as in the 
prior art. 
The particular collar can be made of plastic material whereby it is 
reusable. By preshaping the plastic collar to conform to the particular 
trays utilized, a proper fit between the collar and the tray will be 
attained. Each time a tray is selected its appropriate collar is utilized 
with the tray. 
The aforementioned objects, features and advantages of the invention will, 
in part, be pointed out with particularity, and will, in part, become 
obvious from the following more detailed description of the invention, 
taken in conjunction with the accompanying drawings which form an integral 
part thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, and more specifically to FIGS. 1 and 7, the 
usual procedure in forming dental castings is to utilize a dental 
impression tray, shown generally at 10. The tray has a generally U-shaped 
wall 12 and is generally curved so as to fit a portion of the mouth. A 
laterally extending handle 14 is provided so that the dentist or 
technician can hold the tray while it is placed in the patient's mouth. 
Some type of casting material 16 is generally placed into the tray and the 
tray is then inserted into the patient's mouth. The patient bites down to 
form the cavities or impressions 18. The tray is then removed after the 
material has hardened so as to form a negative impression of the tooth 
section. 
The dental tray is then usually taken and subsequently utilized as a mold 
for making a positive impression of the teeth to be replaced or the bridge 
section. In order to make the positive impression, it is necessary to pour 
casting material such as epoxy or stone, etc., into the mold. However, the 
dental tray has walls that are not high enough to accommodate the casting 
material which must be poured into the tray. Therefore, the walls on the 
side of the impression tray are usually built up with a type of strick wax 
material. The strick wax material is usually red and comes in flat sheets 
with paper inbetween. A section is cut off and it is wrapped around the 
impression tray and then must be held together by means of some type of 
sealing wax such as sticky wax. The strick wax must be cut and shaped to 
suitably fit the particular impression tray. This is usually a difficult 
procedure. 
In the present invention, there is provided a preformed collar shown 
generally at 20. The collar is typically formed of plastic material and is 
substantially oval in shape, however the particular shape is bent so as to 
suitable fit the particular tray. Since there are approximately 12 
impression trays that are used for the entire mouth, there would be a 
similar number of collars, each adapted to fit a particular dental tray. 
However, since they are made out of plastic or other similar material, 
they can be easily cleaned and reused. Therefore, a set will be provided 
with each tray having its corresponding collar and each time the tray is 
used its associated collar will be utilized with it. 
The collar 20 is formed of thin walled material 22 having an open top and 
bottom. Notches 24 are formed downwardly from the upper edge of the end 
portions of the wall. As can best be seen in FIG. 9, the notches 24 are 
substantially shaped in D-fashion. Each notch includes a vertical side 
wall 26, a horizontal bottom wall 28, and an arrow shaped opposing side 
wall having the angular portions 30 and 32 meeting at the vertex 34. 
The notches formed at the opposing ends are substantially colinear with 
each other. Along the side walls, there are formed U-shaped grooves 36. 
The grooves on opposing side walls are colinearly positioned. Located 
within selected opposing pairs of the grooves is a support rib 38 which 
includes ends 40 which can tightly fit within the grooves and be held 
therein. The supporting ribs 38 also include D-shaped notches 42 which are 
again colinear with opposing pairs of notches at the opposite end walls. 
There is additionally provided a rod 44 having a D-shaped cross section as 
can best be seen in FIG. 9. The rod has its front end tapered so as to 
form a spear-like front edge 46. At its rear end, the rod has two 
downwardly facing projections 48, 50 so as to form an indentation therein 
52. 
There are also provided dowel pins 54. The dowel pin can best be seen in 
FIG. 10 as comprising an elongated member 56 which is tapered from a wide 
end 58 to a narrow end 60. One side face is flattened 62. Extending from 
the wide end face 58 is a cylindrical stem 64 having a knurled outer 
surface. 
There are also provide spherical coupling members shown generally at 66. 
These can be seen in more detail in FIGS. 12-14 as well as FIGS. 4-6. The 
spherical members have two non-intersecting orthogonal channels. Both 
channels are substantially D-shaped in cross section. A first horizontal 
channel 68 is D-shaped and is available for receiving therethrough the 
D-shaped rod 44, as shown in FIG. 6. A second, vertical D-shaped channel 
70 is available for receipt therethrough of the tapered end of the dowel 
pins 54 as shown in FIGS. 4 and 5. In order to insure that the dowel pins 
remain in place, an inwardly extending tab or finger 72 extends inwardly 
into the channel 70 to lock against the flat end 62 of the dowel pin 54. 
In utilizing the aforedescribed devices, after the dental impression tray 
is removed from the patient's mouth and the contents therein are permitted 
to harden, in the usual prior art manner, the collar 20 is placed about 
the dental tray 10, as shown in FIG. 2. The dental tray is then inverted 
and the bottom edge of the collar is sealed to the bottom of the dental 
tray by means of sticky wax 74. The wax can be applied by means of a tool 
such as a spatula 76. Such sealing at the bottom is well known in the art 
and has been used even in connection with the strick wax. However, in the 
prior art, since the strick wax had to be shaped, a great amount of such 
sealing wax was required and it was awkward to apply it. In the present 
situation, since the collar is preshaped to fit the particular impression 
tray, it is a rather easy matter to seal the bottom of the collar to the 
bottom of the impression tray. 
The rod assembly can then be put together. If the dowel pins have not been 
already inserted into the spherical coupling members 66, then the dowel 
pins are inserted with the tapered ends extending into the channel 
containing the inwardly extending tab, as shown in FIG. 4. The dowel pins 
are pushed as far as they can go so that they will be held securely in the 
spherical coupling members, as shown in FIG. 5. As many dowel pins as are 
needed can be prefixed in their respective coupling members. 
After the dowel pins have been assembled to their coupling members, the 
rod, with the spear end forward, is threaded through the other channel 68. 
The spherical members 66 can slide along the rod so as to vertically 
position them in the desired locations. The rod is then snapped into place 
across the top of the collar by selecting suitable notches. It will be 
noted that since the rod is D-shaped, and the corresponding notches are 
also substantially D-shaped, the rod will snap into place in the notch and 
will be securely held and prevented from rotation. 
At the same time, the rod is laterally positioned so that the downwardly 
depending projections 48, 50 span on either side of the collar wall 22 so 
that the wall is held within the formed depression 52 as shown in FIG. 7. 
This will prevent lateral sliding of the rod across the collar. 
If additional support is needed for the rod, the support ribs 38 can be 
placed in position before the rod is assembled. These will be placed in 
appropriate grooves 36 and span transversely across the oval shaped 
member. When inserted, the rod would also be snapped in the notches 42 
contained in these support ribs. 
Once assembled, the dowel pins will be downwardly depending at the desired 
location directly within the particular cavities 18 of the preparation 
which are needed for the formation of the teeth. The knurled ends 64 of 
the dowel pins will extend the proper distance into the cavity of the 
preparation so that they will support the teeth which are subsequently 
formed. Should the dowel pins not be exactly positioned as desired, they 
can be slightly slid along the rod 44 so that they will be accurately 
positioned. At the same time, the rod itself can be shifted by moving it 
into different pairs of notches so as to properly position it. 
By making the rod out of flexible plastic material, it can be bent into any 
desired shape so as to suitably position the dowel pins as needed. At the 
same time, the spherical coupling means can also be made out of plastic 
material so that it can also be cleaned and reused each time as can be the 
collar and rod. The dowel pins, as in the prior art, can be made of a 
metal material. 
Once assembled, as shown in FIGS. 7 and 8, the suitable type of casting 
material such as epoxy, can be poured into the mold and the positive 
impression will be formed. Typically, the use of epoxy to form the teeth 
and a subsequent stone material to retain the teeth will be utilized. 
There has been disclosed heretofore the best embodiments of the invention 
presently contemplated. However, it is to be understood that various 
changes and modifications may be made thereto without departing from the 
spirit of the invention.