Dental foil compression device

A dental foil compressing apparatus is constructed of two parts which engage to form a closed cavity. A viscous material is placed into the cavity so that engagement of the two parts causes a hydrostatic compressive force within the cavity to compress a foil against a dental model supported within the cavity. The dental model is placed near the parting line of the engagement of the two parts so as to be easily loaded and unloaded.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to compression tools, and more 
particularly to an improved dental compression apparatus for generating 
compression in the dental porcelain laminate foil technique. 
2. Description of Related Art 
Invention and use of dental foil compression devices is known in the 
medical arts such as the porcelain laminate foil technique. FIG. 4 shows a 
cross-sectional view of a well known, prior art tool for achieving 
compression of foils against dental models known as dies. Generally, the 
problem is how to compress a thin metallic foil against a plaster model of 
a tooth or other dental structure so that the foil is able to be impressed 
with the surface contour and roughness of the dental structure. In a later 
step in the process, the foil will be used as a base for building up a 
thin porcelain cap or other structure to be fitted over a tooth of a 
patient. Therefore, the foil must be energetically impressed on the model 
so as to capture its surface contour with fidelity. The apparatus shown in 
FIG. 4 is used to achieve such a result. A base portion 50 is a 
cylindrical fixture having a cavity machined within it. Inside the cavity 
is placed a dental model holder 30 with the model 60 within it. This is 
placed over a washer 40 at the bottom of the cavity. A viscous material 
such as a clay 20 is pressed into the cavity over the dental model 60. A 
pin 240 extending from the model 60 is used to position the model 60 at 
the center of the fixture, the pin being positioned within a hole 90 in 
the washer 40. Further viscous material 20 is pressed into a small cavity 
in a ram rod 10. The ram rod 10 is then forced into the base portion 50 
driving the viscous material 20 into compression and thereby driving the 
foil against the tooth of the model 60. One major problem with this 
approach is that the ram rod 10, because it enters the base portion, often 
damages the model 60. Another problem with this prior art approach is that 
when the ram rod 10 is removed from the base portion 50, it is not 
possible to easily remove the model 60. In order to facilitate its 
removal, a push rod 70 is usually provided. This rod 70 fits within a 
small diameter hole 80 in the base portion 50 and is able to push against 
the washer 40, dental model holder 30, model 60 and viscous material 20 to 
try to dislodge this entire group of items together. However, the washer 
40 often tends to bind within the base portion 50 so that it is difficult 
to remove the model 60. Even when the group is dislodged from the base 
portion 50, it is not easy to remove the model, in that when the washer 40 
has been separated from the dental model holder 30, the model is not 
easily grasped since it is embedded in the viscous material and is held 
tightly inside the holder 30. The sharp pin 240 (see FIG. 3) makes this 
approach to removal of the model even more difficult and problematic. 
There is a need for a more suitable fixture for accomplishing the same 
result as the prior art device of FIG. 4 but which is less complex, less 
expensive to fabricate, and which is easier to load and unload. 
The present invention fulfills these needs and provides further related 
advantages as described in the following summary. 
SUMMARY OF THE INVENTION 
The present invention is an improved apparatus and method for compressing a 
foil against a dental model. It has been found that by placing a 
significant amount of the viscous material both above as well as below the 
model, and by joining the fixtures roughly at the position which the model 
takes within the cavity, the disadvantages of the prior art device are 
overcome. The invention includes a first and a second fixtures which 
engage, one within the other, but the fixture holding the model is not 
entered by the opposing fixture. The apparatus includes only these two 
parts instead of the five parts necessary for the prior art device. The 
constructional details of the two parts make the device simple and 
inexpensive to fabricate, being made by simple lathe cutting operations. 
The constructional details also make for a device which is much easier to 
use. With the first of the two fixtures nearly filled with the viscous 
material, and with the model place on top of the material so that the 
model is in the mouth of the first fixture, viscous material within the 
second of the two fixtures is able to be brought over the dental model, 
thereby compressing the foil. When the second of the two fixtures is 
removed from the first, the model is easily grasped for removal from the 
first fixture. 
Thus it is an object of the present invention to provide an improved dental 
foil compressing apparatus. It is a further object to provide such an 
apparatus having only two easily fabricated parts. It is a further object 
of the present invention to provide such an apparatus that has the 
advantage of being easy to load and remove the workpiece, i.e., the dental 
model. It is a final object of the present invention to provide a method 
of use of the apparatus that is easier then that taught in the prior art. 
Other features and advantages of the present invention will become apparent 
from the following more detailed description, taken in conjunction with 
the accompanying drawings, which illustrate, by way of example, the 
principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The above described drawing figures illustrate a device for compressing a 
foil 210 against a dental model 60. The apparatus includes a first 
cylindrical walled fixture 100 defining a first cavity 100C with a 
conically shaped mouth 108. The apparatus further includes a second 
cylindrical walled fixture 110 defining a second cavity 110C. The two 
fixtures 100,110 are mutually engagable, the first fixture 100 sliding 
within the second fixture 110 with the outer surface 106 of the first 
fixture 100 moving past the inner surface 112 of the second fixture 110. 
When these fixtures are engaged, a viscous material 20 of a type and 
consistency well known in the dental arts, which is pressed within the 
cavities, is compressed. The dimensional tolerance between these two 
surfaces must be such as to allow air to escape from the cavities when the 
fixtures are engaging, but to not allow the viscous material to escape. It 
has been found, through experimentation, that the outside diameter 130 of 
the first fixture must not differ from the inside diameter 120 of the 
second fixture, by more than 0.005 inches and by less then 0.001 inches. 
If the viscous material is able to escape from the fixtures, then the 
ultimate compressive force is not delivered to the foil. This structural 
imperative is, therefore, the key to the successful operation of the 
device. With the fixtures 100, 110 fully engaged, the volume of the first 
and second cavities 100C, 110C is approximately equal to the volume of the 
first cavity 100C alone, i.e., the first fixture 100 fills the second 
cavity 110C. The first cavity 100C, except for the conically shaped mouth 
108, is filled with the viscous incompressible material 20 which is a well 
known dental clay. The foiled dental model 60 is held on, and supported 
by, a surface 21 of the viscous material 20 in the first fixture 100. In 
this position the dental model 60 is approximately enclosed within the 
mouth 108 of the first cavity 100. It is important that this mouth be 
conically shaped and have an acceptance angle of approximately 90 degrees. 
The second cavity also is filled with some of the viscous material 20, but 
only the distal, approximately one-half of the second cavity 110C is so 
filled. When the fixtures 100, 110 are forced energetically into mutual 
engagement, the force of engagement compacts the viscous material 20 
within the cavities 100C and 110C causing the foil 210 to compress against 
a model tooth 200 of the dental model 60. The conical shape and angle of 
the mouth of the first fixture 100 causes the viscous material to flow 
against the model 660 but cannot damage it. In order for the apparatus to 
achieve its objective it is preferably made of a rigid structural material 
such as steel. However any rigid structural material able to withstand the 
force of compression of the viscous material and which may be formed with 
close tolerances, may be used. 
In operation the invention method results in compressing the foil 210 onto 
the face of the tooth 200 of the dental model 60. The fixtures 100, 110 
are filled to the appropriate level with the viscous material 20. The 
tooth 200 is covered with the foil 210; usually a foil of a precious metal 
is used because such metallic foils can be made as a relatively thin 
sheet, providing an advantage in fine surface contour reproduction. The 
tooth 200 and foil 210 are then covered with a plastic film sheet 220 as 
an outer protective coating. The fixtures 100, 110 are then coupled and 
forced energetically into full mutual engagement so that the force of 
engagement compacts the viscous material within the cavities and 
importantly, against, and all around, the model 60. The fixtures are then 
separated by pulling them apart. The dental model 60 is easily reached and 
removed manually from the first fixture 100. The sharp pin 240 is not 
directed toward the mouth of the fixture 100. 
While the invention has been described with reference to at least one 
preferred embodiment, it is to be clearly understood by those skilled in 
the art that the invention is not limited thereto. Rather, the scope of 
the invention is to be interpreted only in conjunction with the appended 
claims.