U.S. patent application number 11/439327 was filed with the patent office on 2008-02-21 for dental prosthetic forming system.
Invention is credited to Giulio Benetti.
Application Number | 20080041548 11/439327 |
Document ID | / |
Family ID | 38988729 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080041548 |
Kind Code |
A1 |
Benetti; Giulio |
February 21, 2008 |
DENTAL PROSTHETIC FORMING SYSTEM
Abstract
A system for forming a dental prosthetic using the lost wax
method utilizes a unitary pattern assembly to create a unitary
cavity in a mold incorporating a dental prosthetic pattern cavity
portion, a reservoir cavity portion and at least one sprue. The
volume of the reservoir cavity portion is greater than the volume
of the dental prosthetic pattern cavity portion.
Inventors: |
Benetti; Giulio; (Glendale,
AZ) |
Correspondence
Address: |
THOMAS R. LAMPE;BIELEN, LAMPE & THOEMING
1390 WILLOW PASS ROAD, SUITE 1020
CONCORD
CA
94520
US
|
Family ID: |
38988729 |
Appl. No.: |
11/439327 |
Filed: |
May 23, 2006 |
Current U.S.
Class: |
164/34 ; 164/35;
164/359; 164/516 |
Current CPC
Class: |
B22C 9/08 20130101; B22C
9/04 20130101 |
Class at
Publication: |
164/034 ;
164/035; 164/516; 164/359 |
International
Class: |
B22C 9/04 20060101
B22C009/04; B22C 9/08 20060101 B22C009/08 |
Claims
1: A method of forming a dental prosthetic by direct casting, said
method comprising the steps of: forming a unitary cavity in a mold
of investment, said unitary cavity incorporating a dental
prosthetic pattern cavity portion, a double-ended elongated
reservoir cavity portion and at least one sprue leading from said
elongated reservoir cavity portion to said dental prosthetic
pattern cavity portion, said unitary cavity being wholly disposed
within said investment, and said mold of investment defining a
substantially straight passageway substantially orthogonally
disposed relative to said elongated reservoir cavity portion
directly leading from the elongated reservoir cavity portion from a
location between the ends thereof to the exterior of said mold
investment, said unitary cavity being completely surrounded by said
investment except at said substantially straight passageway;
introducing an amount of molten casting alloy into said elongated
reservoir cavity portion through said substantially straight
passageway directly to said elongated reservoir cavity portion;
causing said molten casting alloy introduced into said elongated
reservoir cavity portion to flow from said elongated reservoir
cavity portion through said at least one sprue into said dental
prosthetic pattern cavity portion, the amount of molten casting
alloy introduced into said elongated reservoir cavity portion being
sufficient to completely fill said dental prosthetic pattern cavity
portion and said at least one sprue and partially fill said
elongated reservoir cavity portion whereby a sufficient amount of
molten casting alloy will be contained in said elongated reservoir
cavity portion within the confines of said investment to be drawn
into said dental prosthetic pattern cavity portion through said at
least one sprue due to cooling of said molten casting alloy in said
dental prosthetic pattern cavity, and said amount of molten casting
alloy introduced into said elongated reservoir cavity portion being
insufficient to completely fill said elongated reservoir cavity
portion after said molten casting alloy fills said dental
prosthetic pattern cavity portion and said at least one sprue
whereby said molten casting alloy remaining in said elongated
cavity portion during drawing of the molten casting alloy into the
prosthetic pattern cavity portion does not reach said substantially
straight passageway and will not be drawn into said substantially
straight passageway upon cooling of said molten casting alloy; and
employing said investment to insulate and delay cooling of said
molten casting alloy in said elongated reservoir cavity portion to
promote replenishment of the molten casting alloy in the dental
prosthetic pattern cavity portion and at least one sprue from
molten casting alloy solely from said elongated reservoir cavity
portion to produce a well defined, accurate dental prosthetic
substantially free of internal voids.
2: The method according to claim 1 wherein said dental prosthetic
pattern cavity portion is elongated, with said elongated reservoir
cavity portion spaced from and extending lengthwise along said
dental prosthetic pattern cavity portion, a plurality of spaced
sprues being disposed between and interconnecting said dental
prosthetic pattern cavity portion and said elongated reservoir
cavity portion.
3: The method according to claim 1 wherein said molten casting
alloy is introduced into said elongated reservoir cavity portion
from said substantially straight passageway through an opening
spaced from said at least one sprue and connected with said
elongated reservoir cavity portion generally mid-way along the
length thereof.
4: The method according to claim 1 wherein during step of forming a
unitary cavity, the volume of said reservoir cavity portion is
formed larger than the volume of said dental prosthetic pattern
cavity portion.
5: The method according to claim 1 wherein during step of forming a
unitary cavity, the volume of said reservoir cavity portion is
formed larger than the combined volumes of said dental prosthetic
pattern cavity portion and said at least one sprue.
6: The method according to claim 1 wherein the step of forming a
unitary cavity in said mold comprises forming a first pattern
member formed of plastic and including a substantially straight,
elongated base for forming said substantially straight passageway
and an elongated reservoir pattern for forming said elongated
reservoir cavity portion, forming a second pattern member formed of
wax and including a dental prosthetic pattern and at least one
sprue, attaching said first pattern member and said second pattern
member to form a unitary pattern assembly, placing said unitary
pattern assembly in a container, while said unitary pattern
assembly is in said container filling said container with
investment in sufficient quantity to cover said elongated reservoir
pattern and said second pattern member, and after hardening of said
investment heating said investment to melt said first and second
pattern members to form said unitary cavity.
7: The method according to claim 6 wherein said at least one sprue
includes an elongated sprue bar attached to the elongated reservoir
pattern of said first pattern member during said step of attaching
said first and second pattern members, and said elongated sprue bar
being positioned to extend along said elongated reservoir
pattern.
8: The method according to claim 7 wherein said first and second
pattern members are attached together by coating said first and
second pattern members with wax.
9: The method according to claim 6 wherein said container includes
a container end defining an end opening, said base of said first
pattern member being positioned in said end opening with said
reservoir pattern being spaced from said container end prior to
placing said pattern assembly in the container.
10-14. (canceled)
Description
TECHNICAL FIELD
[0001] This invention relates to a method and a unitary pattern
assembly for casting dental prosthetics, such as crowns, bridges,
single units and the like, using the lost wax process.
BACKGROUND OF THE INVENTION
[0002] The lost wax method is a well known process for producing
castings of many types. The lost wax method is commonly used to
create castings for dental prosthetics.
[0003] As noted in U.S. Pat. No. 4,741,378, issued May 8, 1988, the
production of cast dental restorations and prosthetics involves the
production of a wax pattern configured to match the desired
restoration. This pattern is attached to a support commonly known
as a sprue and the sprue is, in turn, secured to a base member.
[0004] The sprue, base member and wax pattern are placed within the
container which is thereafter filled with investment. After the
investment has hardened, it is heated in order to melt the sprue
and wax pattern, the melted wax flowing out of the investment
through an opening created by the sprue and base, thereby leaving a
passage and cavity within the investment.
[0005] Molten alloys are then directed through the passageway
created by the sprue and into the casting cavity created by the wax
pattern. A centrifuge is customarily used to promote flow. As the
alloy solidifies, a casting is produced which is essentially a
duplicate of the original wax pattern.
[0006] As further noted in U.S. Pat. No. 4,741,378, a variety of
sprue assemblies have been developed. However, they have a number
of drawbacks. One problem encountered relates to the shrinkage of
the alloy as it cools. When the molten alloy filling the casting
cavity cools, shrinkage occurs. In order to avoid irregularities in
the final casting, there needs to be a source of molten alloy which
can be drawn into the pattern cavity as the contents cool. To
provide this source of molten alloy, sprue pins were formed with a
bulbous area at a point toward the tip so as to create a reservoir
of molten alloy within the investment. This reservoir is very small
and does not provide a large amount of molten alloy. The primary
reservoir for molten alloy lies outside the mold.
[0007] The sprue pin of U.S. Pat. No. 4,741,378 was devised to
improve the performance of prior art sprue pins, more particularly
by use of a hollow sprue pin having a bulbous extension about it
wherein the end of the sprue pin which attaches to the wax pattern
gradually decreases in external circumference toward the tip. It is
indicated that such an arrangement prevents formation of blockages
between the cavity and the relatively small reservoir provided by
the sprue pin.
[0008] One of the problems inherent in prior art arrangements is
waste of metal alloy used to form the casting. These alloys often
incorporate precious metals. Principally, but not exclusively, this
problem is a result of the use of externally disposed "buttons" or
reservoirs of alloy material during the casting operation. These
cool relatively quickly and material can stick to the mold,
producing blockages and otherwise interfere with proper
casting.
[0009] As will be seen below, the system of the present invention
utilizes a relatively large internal reservoir within the confines
of the investment. This not only reduces waste and saves labor, the
arrangement produces a casting which is well defined, accurate and
free of internal voids or other defects. Placement of the alloy
reservoir within the confines of the investment enables the alloy
therein to remain molten for a long period of time, promoting
replenishment of the alloy in the dental prosthetic casting to be
supplemented during cooling thereof over that long period of time.
There is no shrinkage, porosity or "suck back." This results in a
superior casting. The invention may be used to produce dental
prosthetic castings of virtually any shape and size.
DISCLOSURE OF INVENTION
[0010] The method of forming a dental prosthetic of the present
invention includes the step of forming a unitary cavity in a mold
of investment, the unitary cavity incorporating a dental prosthetic
pattern cavity portion, a reservoir cavity portion and at least one
sprue leading from the reservoir cavity portion to the dental
prosthetic pattern cavity portion, the unitary cavity being wholly
disposed within the investment.
[0011] A molten casting alloy is introduced into the reservoir
cavity portion.
[0012] The molten casting alloy flows from the reservoir cavity
portion through the at least one sprue into the dental prosthetic
pattern cavity portion, the amount of molten casting alloy
introduced into the reservoir cavity being sufficient to completely
fill the dental prosthetic pattern cavity portion and the at least
one sprue and at least partially fill the reservoir cavity portion.
A sufficient amount of molten casting alloy will be contained in
the reservoir cavity portion within the confines of the investment
to be drawn into the dental prosthetic pattern cavity portion
through the at least one sprue due to cooling of the molten casting
alloy in the dental prosthetic pattern cavity portion.
[0013] The volume of the reservoir cavity portion is formed larger
than the volume of the dental prosthetic pattern cavity
portion.
[0014] The invention also encompasses a unitary pattern assembly of
unique character for use in forming a unitary cavity in a mold
formed of investment. The unitary pattern assembly includes a first
pattern member formed of wax or plastic having a base and a
reservoir pattern.
[0015] The pattern assembly also incorporates a second pattern
member formed of wax or plastic including a dental prosthetic
pattern and at least one sprue.
[0016] The first and second pattern members are attached together
with the dental prosthetic pattern and the reservoir pattern being
spaced from one another and interconnected by the at least one
sprue. The volume of the reservoir pattern is greater than the
volume of the dental prosthetic pattern.
[0017] Other features, advantages and objects of the present
invention will become apparent with reference to the following
description and accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a perspective view of a pattern member of the
unitary pattern assembly of the invention incorporating a base and
reservoir pattern;
[0019] FIG. 2 is a top, plan view of the pattern member of FIG.
1;
[0020] FIG. 3 is a front, elevational view of the pattern member of
FIG. 1;
[0021] FIG. 4 is a perspective view of an alternative form of
pattern member including a base and reservoir pattern;
[0022] FIG. 5 is a top, plan view of the pattern member of FIG.
4;
[0023] FIG. 6 is a front, elevational view of the pattern member of
FIG. 4;
[0024] FIG. 7 is an exploded, perspective view illustrating the
pattern member of FIGS. 1-3 prior to insertion of the base thereof
into an end cap of a container and prior to attachment of a pattern
member including a dental prosthetic pattern and a plurality of
sprues to the pattern member incorporating the base and reservoir
pattern;
[0025] FIG. 8 is a front, elevational view showing the two pattern
members connected together and the base positioned in an opening or
hole of the container end cap;
[0026] FIG. 9 shows the end cap being applied to a container body
to position the unitary pattern assembly within the interior
thereof;
[0027] FIG. 10 shows investment being poured into the interior of
the container to completely cover the unitary pattern assembly;
[0028] FIG. 11 is a perspective view showing the mold being removed
from the container after hardening thereof;
[0029] FIG. 12 is an elevational, cross-sectional view of the mold
and illustrating diagrammatically by arrows the flow path of molten
alloy when introduced into the unitary cavity of the mold, as for
example by a centrifuge;
[0030] FIG. 13 is view similar to FIG. 12, but illustrating alloy
in the unitary cavity;
[0031] FIG. 14 is a perspective view showing the cavity broken away
to illustrate cavity configuration after casting removal;
[0032] FIG. 15 is a perspective view of the casting produced in the
mold; and
[0033] FIG. 16 is a view similar to FIG. 15, but illustrating the
casting produced when using the embodiment of the pattern member
shown in FIGS. 4-6.
MODES FOR CARRYING OUT THE INVENTION
[0034] Referring now to FIGS. 1-3 and 7-15, according to the
teachings of the present invention, a unitary pattern assembly 10
is illustrated (FIGS. 8-10) and designated by reference numeral 10.
The assembly is for use in forming a unitary cavity in a mold
formed of investment.
[0035] The unitary pattern assembly includes a pattern member 12
formed of wax or plastic including a base 14 and a reservoir
pattern 16.
[0036] Unitary pattern assembly 10 includes a second pattern member
18 also formed of wax or plastic. Pattern member 18 includes a
dental prosthetic pattern 20 (in this instance an assembly of four
crowns) and four sprues 22 and a sprue bar 24. The combined volume
of the sprue bar and reservoir pattern 16 is greater than the
volume of the dental prosthetic pattern and sprues.
[0037] The two pattern members 12, 18 are connected together as
shown in FIG. 8 to form the unitary pattern assembly 10. Various
means may be employed to accomplish this, including coating the
pattern members with wax.
[0038] The unitary pattern assembly is held by a container end or
cap 30, as shown in FIG. 8, more particularly the base 14 of
pattern member 18 is inserted in an end hole or recess 32. The cap
30 is then attached to the bottom of a generally cylindrical
container portion 34 (FIGS. 9-11). This positions the unitary
pattern assembly 10 within the interior of the container with the
base positioning the reservoir pattern inwardly of the cap.
[0039] Next, investment 40 is poured into the container interior as
shown in FIG. 10. Sufficient investment is poured into the
container to cover the reservoir pattern and the pattern member
18.
[0040] After the investment has hardened, the mold 42 comprising
the investment is removed from the container as shown in FIG. 11.
The mold is heated to melt the pattern members 12, 18 and form a
unitary cavity 48 as shown in FIGS. 12-14.
[0041] FIG. 12 designates by arrows the flow of molten casting
alloy into the unitary cavity 48. The alloy in its molten state
passes through an upper opening 50 into reservoir cavity portion 52
and thence through cavity sprues 54 into the dental prosthetic
pattern cavity portion 56. This is normally accomplished by a
centrifuge (not shown).
[0042] The amount of molten casting alloy introduced into the
reservoir cavity portion produced by melting of the combined sprue
bar and reservoir is sufficient to completely fill the dental
prosthetic pattern cavity portion and sprues 54. This continues
until the reservoir cavity portion 52 is at least partially filled
and until a sufficient amount of molten casting alloy is contained
in the reservoir cavity portion within the confines of the
investment to be drawn into the dental prosthetic pattern cavity
portion through the sprues due to cooling of the molten casting
alloy in the dental prosthetic pattern cavity portion.
[0043] The volume of the reservoir cavity portion is formed larger
than the combined volumes of the dental prosthetic pattern cavity
portion and the sprues.
[0044] FIG. 15 shows a casting 60 produced by the unitary cavity 48
of mold 42.
[0045] FIG. 16 shows an alternative form of casting 62 which is
produced when one employs the pattern member 12A shown in FIGS. 4-6
in conjunction with a similarly curved second pattern member (not
shown). It will be appreciated that the principles of the present
invention can be utilized to provide dental prosthetic castings of
virtually any shape, type and size and that a wide variety of
molten alloys may be utilized in the casting. The invention can be
used not only for fabrication of multiple crowns and bridges but
single units as well.
[0046] The castings produced are accurate in dimension, non-porous,
easy to clean and free of "suck back." Utilizing the teachings of
the present invention, less metal or alloy is utilized then when
using prior art approaches. There is virtually no waste.
* * * * *