Amalgam capsule

A capsule for dental amalgam comprises a reservoir portion which has an open end and which contains the silver or silver alloy powder component of the amalgam and a cap portion which has an open end which is meant for containing the liquid or mercury component of the amalgam. A preferably funnel-shaped partition is fixed to the cap portion for retaining the mercury component therein. An orifice is provided in the base of the funnel-shaped partition. The orifice is of a size to prevent leakage of the mercury when the capsule is exposed to accelerations which are below a threshold value and which are typical for storage and transport of the capsule. When the capsule is exposed to acceleration above this threshold value, for example, when the capsule is placed in an amalgamator for mixing the components with each other, the mercury is forced through the orifice and into the powder component. After the amalgam is prepared, the cap can be removed along with its partition to expose the amalgam which is immediately ready for use.

FIELD AND BACKGROUND OF THE INVENTION 
The present invention relates in general to apparatus for mixing dental 
amalgams and, in particular, to a new and useful capsule which effectively 
maintains a separation between a liquid component of the amalgam and a 
solid component thereof until the two components are mixed together to 
form the amalgam filling. 
Dental amalgam fillings are produced by mixing a liquid component, 
generally mercury, with a powder component, generally silver or silver 
alloy powder. The mixed amalgam filling is initially sufficiently fluid so 
that it can be metered into a tooth to be filled. After a certain period 
of time, however, the amalgam solidifies, whether it has been utilized or 
not. 
Since the amalgam has only a limited useful life after it has been mixed, 
capsules have been developed which maintain a separation between the 
liquid and powder components of the amalgam until the amalgam is to be 
mixed. The capsules are used in conjunction with an amalgamator which 
vibrates and/or accelerates the capsule to mix the components with each 
other. 
U.S. Pat. No. 4,450,958 to Prasad discloses a self activated dental capsule 
which maintains the separation between the liquid component and the powder 
component by confining the liquid component within a foil container. One 
portion of the foil container is fixed to the interior of the capsule. The 
loose powder component of the amalgam is housed within the capsule. By 
vibrating the capsule, the foil container is ruptured, releasing its 
liquid component which is then mixed with the powder component to form the 
amalgam. By holding the container against the interior of the capsule, 
damage to the container beyond its initial rupturing is avoided. This 
prevents pieces of the container from becoming admixed with the amalgam. 
U.S. Pat. No. 4,632,243 to Muhlbauer discloses a foil package for 
containing both the liquid and solid components of amalgam. The solid 
component of the amalgam is in the form of a compressed briquet and the 
rolls of the foil package are rupturable to release and intermix the 
liquid and solid components. The foil package is meant for use in 
conjunction with an outer capsule and a mixing apparatus which vibrates 
the capsule. Under vibration, the package ruptures, releasing and 
intermixing its components to form the amalgam. Before the amalgam is 
utilized, however, the ruptured package must be retrieved from the mixed 
amalgam. 
SUMMARY OF THE INVENTION 
The present invention is drawn to an amalgam capsule which maintains a 
secure separation between the liquid and powder components of the amalgam 
for storage and handling of the capsule. The capsule of the present 
invention has an interior space which is divided into compartments by a 
yielding partition which extends across the interior of the capsule. One 
compartment contains the liquid component, e.g., mercury, and the other 
compartment contains the powdered component, e.g., silver or silver alloy 
powder. The yielding partition is structured so that when the capsule is 
exposed to accelerations below a threshold value, no mercury will pass 
through the yielding partition. Normal accelerations that the capsule 
would experience during transport are all below the threshold value. The 
capsule is exposed to accelerations above the threshold value when the 
capsule is placed in an amalgamator which vibrates the capsule. 
To this end, the yielding partition is either provided with one or more 
orifices which are of such a small size that, when the capsule is exposed 
to accelerations below the threshold value, no mercury passes through the 
orifice. This is due to the natural surface tension of the mercury and its 
lack of affinity for most surfaces, in particular, plastic surfaces from 
which the capsule and partition are advantageously made. 
In accordance with another embodiment of the invention, the yielding 
partition may include tear lines which are ruptured by the inertia of the 
mercury when the capsule is exposed to accelerations above the threshold 
value. 
Accordingly, an object of the present invention is to provide a capsule for 
dental amalgam which comprises a capsule member defining a closed interior 
space and yielding partition means fixed to the capsule member and 
extending across the space to divide the space into a first compartment 
for a powder component of the amalgam and a second compartment for a 
liquid component of the amalgam, the yielding partition means retaining 
the liquid component in the second compartment when the capsule is exposed 
to acceleration below a threshold value and allowing the liquid to pass 
into the first compartment when the capsule is exposed to accelerations 
above the threshold value. 
A further object of the present invention is to provide a capsule for 
dental amalgam which is simple in design, rugged in construction and 
economical to manufacture. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its uses, reference 
is made to the accompanying drawings and descriptive manner in which the 
preferred embodiments of the invention are illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings in particular, the invention embodied in FIGS. 1 
and 2 comprises a capsule generally designated 10 for containing the 
components of dental amalgam. The capsule can be used in conventional 
mixing apparatus or amalgamators which vibrate the capsule to mix the 
components with each other and produce amalgam filling. 
As shown in FIGS. 1 and 2, capsule 10 comprises a first capsule portion or 
reservoir 12 which has a closed end for receiving the powder component 32 
of the amalgam and an open end 20. A second capsule portion or cap 14 
which has a connecting sleeve 16 can be slid onto the outer surface 18 
near the open end 20 of reservoir 12 to hermetically enclose the interior 
space of the capsule. Cap 14 has an upper closed end and a lower open end 
22 and defines an interior space for receiving a ball of mercury 34. 
Mercury 34 is confined in the space of cap 14 by a funnel-shaped yielding 
partition 26 which includes a lower orifice 36. Partition 26 is 
advantageously made of synthetic plastic material for which mercury has 
little or no affinity. Due to the natural surface tension of mercury, the 
mercury ball 34 tends to form an oval solid, as shown in FIG. 1 which sits 
in the upper portions of funnel-shaped partition 26. Under the normal 
accelerations that capsules are exposed to during transport and storage, 
there is no tendency for mercury 34 to drip through orifice 36. This is 
caused both by the tapering shape of partition 26, in a direction toward 
orifice 36, and also, the relatively small diameter of orifice 36. Orifice 
36 is advantageously from 0.001 to 0.1 mm in diameter. 
FIG. 1 also illustrates the possibility of utilizing an extremely thin, 
rupturable membrane 36a of material that spans orifice 36 to block any 
flow of air between the compartment containing the mercury 34 and the 
compartment containing the powder component 32. This membrane may be made 
of the same material as the rest of the funnel. Alternatively, the 
membrane may be made of lacquer or other easily rupturable material. As 
will be explained later in the specification, it is also advantageous to 
minimize the air space within the compartment containing the mercury 
component. This reduces the possible formation of mercury oxides and vapor 
in the open volume of the compartment. 
In accordance with the present invention, when capsule 10 is placed in an 
amalgamator or mixing machine and exposed to accelerations above a 
threshold value, mercury will be forced down funnel-shaped partition 26 
and through orifice 36. This effect is shown in FIG. 3, in connection with 
the second embodiment of the invention. 
The continued vibration of the capsule causes the mercury to mix with the 
powder and form the amalgam. 
After vibration and acceleration of capsule 10, in the amalgamator or 
mixing machine, cap 14 is removed to expose the now fully mixed amalgam in 
reservoir 12. 
Since the amalgam has only a limited useful life once it has been prepared, 
it is advantageous to present the amalgam to the dentist in a ready-to-use 
condition. To this end, funnel-shaped partition 26 has a flange 28 which 
is fixed against a step 24 in cap 14. This can be done by ultrasonic or 
other adhesion, or by inclusion of a connecting ring 30 which is slipped 
into sleeve 16 and fixed against flange 28. In this way, when cap 14 is 
removed, funnel-shaped partition 26 is also removed, relieving the dentist 
of having to retrieve any substance or packaging from the amalgam. 
Alternatively, partition 26 may simply be seated between the reservoir 12 
in cap 14 by the press fit between sleeve 16 and surface 18. With the 
capsule closed, the yielding partition 26 is thus fixed in position and 
effectively separates the mercury or liquid component from the dry powder 
component. This embodiment of the invention does, however, require the 
additional manipulative step of removing the partition 26 after cap 14 is 
removed. 
FIG. 3 shows a capsule 40 which has a reservoir 42 and a cap 44. Reservoir 
42 has an open end with a connecting flange 46 which engages around the 
surface of cap 44 to form a hermetic press fit seal. Yielding partition 48 
is fixed, for example, by welding or adhesive, to the lower edge of cap 
44. 
In both the embodiments of FIGS. 1 and 3, ridges or knurling 52 and 54 are 
provided, both on the reservoir and on the cap, to facilitate grasping and 
twisting of the reservoir and cap for removing the cap from the reservoir. 
Although a sliding press fit has been shown in the embodiments of FIGS. 1 
through 3 for connecting the reservoir to the cap, the cap may also be 
threaded to the reservoir with the cap carrying either the internal or the 
external threads. 
FIG. 4 shows a further embodiment of the invention which includes a 
reservoir 62 for containing the powder component of the amalgam and a cap 
64 for enclosing the liquid or mercury component of the amalgam. In the 
embodiment of FIG. 4, a separate connecting sleeve 66 is provided which 
incorporates the yielding partition shown at 66a. Sleeve 66 has an upper 
outer surface 66b which is slid into the interior of cap 64 and a lower 
outer surface 66c which is slid into the open end of reservoir 62. In one 
form of the invention, surface 66b is welded to the interior surface of 
cap 64 after mercury 68 has been placed in the cap. This forms a one piece 
cap structure which, when removed from reservoir 62, retains the partition 
66a. 
In an alternate form of the invention, both surfaces 66b and 66c are 
welded, advantageously using ultrasonic welding to surfaces of the 
respective cap 64 and reservoir 62. This produces a hermetically closed 
and sealed capsule. After the capsule has been vibrated to mix the liquid 
component with the powder component, the capsule is opened by cutting the 
capsule along and an indicating mark 70 to expose the now mixed amalgam. 
FIG. 5 shows a still further embodiment of the invention, wherein a cap 74 
can be hermetically press fit into a connecting sleeve 76 of a reservoir 
72 for containing the dry powder component of the amalgam. Cap 74 contains 
the ball of mercury or liquid component 78, which is retained in the cap 
by a yielding partition 80 which is in the form of a disk that is 
adhesively connected or welded to the lower rim of cap 74. 
In the embodiment of FIG. 5, it is particularly advantageous to construct 
cap 74 so as to have an interior volume which is only slightly greater 
than the volume of the liquid component 78. To this end, cap 74 might 
either be made smaller than shown in FIG. 5, or the partition 80 may be 
sealed to the interior of cap 74 at a position closer to the upper end of 
the cap. 
Another possibility is to increase the wall thickness of cap 74 so that 
with an outer dimension, as shown, the interior volume of the cap is 
reduced. 
As shown in FIGS. 6 through 9, tear lines can be provided in partition 80 
which are in the form of a membrane or foil. Tear lines may be triangular, 
as shown at 82 in FIG. 6, circular, as shown at 84 in FIG. 7, or in the 
form of a star as shown at 86 in FIG. 8. Any other pattern for tear lines 
may also be utilized as long as all parts of the membrane remain together 
and connected to the cap 74. It is essential that no pieces of the 
membrane fall into the mixed amalgam in the reservoir 72. 
As with the size of orifice 36 in the funnel-shaped partition 26, tear 
lines 82, 84 or 86, are selected so that they rupture when the capsule is 
exposed to an acceleration above the normal threshold value. 
Although tear lines are shown in the embodiments of FIGS. 6 through 8, 
these lines may be replaced by lines of perforations which either extend 
completely through the partition or are in the form of point weaknesses 
which leave a thin, rupturable membrane of material. 
Referring to FIG. 9, partition 80 includes a peripheral ring of 
perforations or weakened points which extend most or all of the way around 
the partition. In the version shown, the peripheral ring of perforations 
or weakening points 88 extend approximately three quarters of the way 
around partition 80. 
For the purpose of this application, the term "foil" is meant to include 
membranes or diaphragms made of plastic, ceramic, metal or any other 
material that has the appropriate strength and, where needed, the 
appropriate tear characteristics. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that the invention may be embodied 
otherwise without departing from such principles.