U.S. patent number 3,661,198 [Application Number 04/795,563] was granted by the patent office on 1972-05-09 for apparatus for making pontic cores.
Invention is credited to Roger A. Evenson.
United States Patent |
3,661,198 |
Evenson |
May 9, 1972 |
APPARATUS FOR MAKING PONTIC CORES
Abstract
This invention relates to the preparation of artificial teeth.
Significant reductions in weight and cost of pontics are achieved
by using a hollow metallic core filled with porcelain. The tooth
has a greater flexural strength because of the greater compressive
strength of the procelain filling in the metallic core. Vaporizable
forms for making the hollow metallic cores are provided in various
sizes in sheet form.
Inventors: |
Evenson; Roger A. (San Jose,
CA) |
Family
ID: |
25165836 |
Appl.
No.: |
04/795,563 |
Filed: |
January 31, 1969 |
Current U.S.
Class: |
164/246; 164/91;
249/62; 425/404; 164/34; 249/54; 425/117 |
Current CPC
Class: |
A61C
13/26 (20130101) |
Current International
Class: |
A61C
13/08 (20060101); A61C 13/00 (20060101); B22C
7/02 (20060101); B22C 7/00 (20060101); B22c
007/02 () |
Field of
Search: |
;164/246,36,35,132,369,34,138 ;18/DIG.11,DIG.12 ;249/61,54,62 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Baldwin; Robert D.
Assistant Examiner: Rising; V. K.
Claims
I claim:
1. A form for producing pontic cores for artificial replacement
teeth, comprising a vaporizable planar sheet having upstanding
therefrom a hollow form in the general shape of inwardly projected,
occlusal, lingual, buccal, mesial and distal faces of a human tooth
but not in the specific configuration of said faces and having an
outside surface smaller in all dimensions than at least the
occlusal, buccal, mesial, and distal faces of the replacement tooth
to serve as a subsurface tooth form, the thickness of said
upstanding form being at least 0.2 millimeters.
2. A form for producing pontic cores for artificial replacement
teeth comprising a vaporizable thermoplastic resin formed in the
general shape of the occlusal, lingual, buccal, mesial and distal
faces of the exposed portion of a human tooth and having an outside
surface smaller in all dimensions than at least the occlusal,
buccal, mesial and distal faces of the replacement tooth to serve
as a subsurface tooth form and having an enlarged portion on the
lingual face thereof extending downwardly toward the base thereof
from below the top of the crown and substantially half way
therearound to the mesial and distal faces.
3. Apparatus for producing pontic cores for artificial replacement
teeth, comprising a planar sheet of material vaporizable at
elevated temperature having a plurality of upstanding hollow forms
each in the general shape of inwardly projected occlusal, lingual,
buccal, mesial and distal faces of a human tooth but not in the
specific configuration of said faces and having outside dimensions
less than the outside dimensions of the desired pontic to be
produced therefrom, said sheet including forms of a plurality of
different sizes and different tooth configurations.
4. A form for producing pontic cores for artificial replacement
teeth comprising a vaporizable planar sheet having upstanding
therefrom a hollow form in the general shape of the occlusal,
lingual, buccal, mesial, and distal faces of a human tooth and
having an outside surface smaller in all dimensions than at least
the occlusal, buccal, mesial, and distal faces of the replacement
tooth to serve as a subsurface tooth form, the thickness of said
upstanding form being at least 0.2 millimeters and said form
including an enlarged portion on the lingual face thereof extending
downwardly toward the base thereof from below the top of the crown
and substantially half way therearound to the mesial and distal
faces.
5. Apparatus for producing pontic cores for artificial replacement
teeth, comprising a planar sheet of material vaporizable at
elevated temperature having a plurality of upstanding hollow forms
each in the general shape of the occlusal, lingual, buccal, mesial
and distal faces of a human tooth and having outside dimensions
less than the outside dimensions of the desired pontic to be
produced therefrom, said sheet including forms of a plurality of
different sizes and different tooth configurations and at least
certain of said forms including an enlarged portion on the lingual
face thereof extending downwardly toward the base thereof from
below the top of the crown and substantially half way therearound
to the mesial and distal faces.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to the manufacture of an
artificial tooth on a dental bridge or pontic. More particularly,
the invention relates to a method of forming a strong lightweight
pontic, the resulting pontic, and a form useful in manufacturing
the metallic core.
It has been known in the art to manufacture pontics having a base
metal structure adapted to rest on the alveolar ridge. These
metallic structures ordinarily are constructed from precious
metals, such as gold or platinum or alloys thereof. These metals
have the desirable properties of being inert to continued exposure
to bacteria, enzymes, acids and other chemicals commonly present in
the mouth. In order to improve the appearance of these metallic
structures and to more closely resemble natural teeth, it has been
known in the art to cover the metallic structures with porcelain.
It has been the practice to affix an opaque layer between the
metallic structure, usually dark in color, and then cover the
opaque layer with the translucent porcelain.
However, the prior structures have required considerable amounts of
precious metals which, at recent prices, raises the price of the
pontics so that it is not readily available to the total number of
persons requiring the same. Moreover, precious metals are extremely
dense and have a high thermal conductivity, so that an artificial
pontic with only a thin layer of porcelain covering has an
unnatural weight and also a high thermal conductivity between the
alveolar ridge and hot and cold substances taken orally. A further
disadvantage of the prior pontics has been the fact that the
previous metal has a lower compressive strength than porcelain. As
a result, the porcelain covering transmits the considerable
compressive forces upon the tooth to the metal which tends to flex.
This flexing of the underlying metal structure causes rupture in
the porcelain covering. Finally, the prior structures have had to
be built on an ad hoc basis to fit the precise tooth being
replaced. Manufacture of a pontic according to prior art was a time
consuming, laborious process and the resulting product was
expensive.
SUMMARY OF THE INVENTION
A hollow metal base structure is provided in which porcelain is
filled and over which the porcelain covering is placed. The hollow
metal core is made from a vaporizable form which evaporates upon
excessive heating of an investment casting formed thereabout.
It is an object of this invention to provide a pontic having lower
costs, lower weight and greater strength than prior art
pontics.
It is a further object of this invention to provide an improved
method of manufacturing pontics.
It is a further object of this invention to provide an improved
form for producing metallic cores to permit prefabrication and
prompt fabrication of pontics.
DESCRIPTION OF DRAWINGS
FIG. 1 is an elevational sectional view of a pontic according to
the present invention worn on an alveolar ridge;
FIG. 2 is a side elevational sectional view of a pontic in
accordance with the present invention supported in a bridge and is
taken along line 2--2 in FIG. 1;
FIG. 3 is a top perspective view of a hollow core pontic form in
accordance with the present invention;
FIG. 4 is a plan view of the structure shown in FIG. 3;
FIG. 5 is a cross-sectional view of the structure shown in FIG. 3
taken along line 5--5 in the direction of the arrow;
FIG. 6 is an elevational sectional view of a sheet containing a
number of hollow core plastic forms in accordance with the present
invention;
FIG. 7 is a flow sheet showing the formation of an artificial
pontic according to the present invention; and
FIG. 8 is a bottom view of a pontic during one step in the
manufacture thereof in accordance with the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
While the present invention has been described above as directed to
a pontic construction and method and apparatus for making same, it
will be appreciated that the structures and techniques described
are applicable for making other dental structures. However, for
purposes of illustration, the invention will be described with
reference to a preferred embodiment of the invention as shown in
the drawing.
Turning now to the drawing, with particular reference to FIG. 1,
there is shown a pontic 11 constructed in accordance with the
present invention and including a hollow, inverted cup-shaped,
metal, base structure 12 such as of a platinum-gold alloy having a
porcelain filling 13 therewithin and a porcelain coating 14 over
substantially all of the exterior surface. The pontic 11
illustrated has an exposed area of metal base structure on one side
thereof as preferred by some dentists. The pontic 11, as will be
described below, is designed to be positioned on the alveolar ridge
15.
Typically, to be supported over the alveolar ridge, the pontic is
cantelever supported from one side on another tooth or supported
from both sides in a bridge spanning a space between teeth. A
pontic 21 supported in a bridge 20 is illustrated in FIG. 2. As
illustrated, the pontic 21 includes a hollow, inverted cup-shaped,
metal base member 22 integrally formed with an abutment crown cover
32 and an abutment cover 42 on teeth A and B on either side of the
space for the pontic. The pontic 21 includes a porcelain filling 23
and a porcelain coating 24 which extends over the abutment cover 42
as a coating 44. While the cover abutment 32 for tooth A has been
shown as a full crown, this cover abutment could also include a
porcelain coating if so desired.
The method of making the pontic 21 as will be described below with
reference to FIG. 7 includes the use of hollow core pontic forms 51
illustrated in FIGS. 3-6. The forms 51 made of a vaporizable
material such as thermoplastic resin are formed generally in the
shape of the occlusal, lingual, buccal, mesial, and distal faces of
a tooth and typically of smaller overall dimensions than the pontic
to be formed. In accordance with the present invention, a large
variety of shapes and sizes for typical pontics to be made in
practice is vacuum formed on a mold in a single sheet 56 and
provided to the dental technician for selection of appropriate
forms 51 as desired. As illustrated, the preferred construction for
the form 51 includes an enlarged portion 52 extending substantially
half way around the form 51 extending downwardly from the top of
the crown 53 on the lingual face so that the enlarged portion 52
includes enlarged parts 54 and 55 on opposite mesial and distal
faces of the form adjacent to the teeth serving as a support for
the bridge.
Referring now to FIG. 7, there is shown a flow diagram of the steps
utilized in practicing the present invention. As indicated, the
dental technician first forms 61 a dentition replica in dental
plaster from the dentist's impression. Next, the abutment cover or
covers are formed 62 for the teeth or tooth to support the pontic,
and a hollow core pontic form 51 of appropriate size is selected 63
to fill the appropriate space. The abutment covers can either be
formed by hand out of dental wax as is conventional of from a
thermoplastic material formed onto the abutment supports. The
abutment covers and pontic forms are assembled and placed on the
dentition replica and joined together such as with dental wax and
then transferred with a sprue post to an investment molding
assembly wherein an investment molding is formed therearound 64
utilizing commercially available dental investments and investment
techniques.
When the investment molding has been formed and the sprue base
removed, the mold is heated 65 to elevated temperature, such as
1,300.degree. F., to vaporize the abutment covers and hollow pontic
form. Then with the investment mold defining the configuration of
the metal portion of the pontic and support structure to be formed
metal such as platinum-gold alloy is melted 66 such as with a torch
into the mold. A centrifugal casting machine can be utilized to aid
in the formation of the desired cast structure and the assembly
cooled 67 to harden the metal in the mold. The mold is then removed
68 from the casting and dental porcelain paste applied 69 to both
the interior of the hollow pontic portion and the exterior of those
surfaces desired coated therewith.
Since there is an unavoidable loss of porcelain volume during
firing and the tendency of porcelain shrinkage is toward the
greatest mass, it has been found that cross cuts 70 (See FIG. 8)
should be made in the porcelain and of such depth as to achieve the
effective division of the porcelain into separate quadrants
resulting upon firing in the shrinkage of porcelain away from the
cuts rather than away from the metal walls leaving an unfilled
space in the porcelain corresponding to the sectional lines. It has
been found that the porcelain within the hollow metal portion of
the pontic cut with a cross 70 to at least substantially 50 percent
of the depth of the porcelain does not separate from the metal
body.
Typically, porcelain is applied from an aqueous slurry of suitable
consistency, gradually accomplishing the porcelain buildup in
desired shape and mass in several stages with a firing after each
application and a final firing to accomplish porcelain
vitrification and suitable esthetic glaze. While continued desired
buildup of porcelain is being achieved on the exposed pontic
surface, voids at the cross 70 can be filled at the same time.
Pontics constructed in accordance with the present invention
sandwich the metal support structure thereof between a porcelain
covering and a porcelain filling avoiding flexing of the body that
would otherwise rupture the bond between the porcelain and the
body. Furthermore, it has been found that pontic structures formed
in accordance with this invention are as strong as or stronger than
structures with solid metal pontics.
With the present invention, there is a significant saving in metal
employed in the construction of a bridge span or a cantelever
pontic with the added advantage of reduced weight and a material
with a more desirable thermal conductivity resulting in greater
comfort to the patient. Also, by this method of this invention the
construction span or cantelever pontic is simplified and less
dependent on the skill of an individual technologist resulting in
increased uniformity and reliability of the finished product. It
has been discovered that thermoplastic forms of the type described
above and 0.3-0.5 millimeters produce sufficiently strong pontics
and pontic support structures. These forms should be at least 0.2
millimeters thick.
* * * * *