Method and apparatus for storing, mixing and delivering dental amalgam

An amalgam capsule includes two chambers separated by a piston detachably formed as a part of the capsule end cover. One compartment is formed in part by a resilient flange portion of the capsule which is deformable to provide communication of the chambers and to permit a mixing of the contents of the chambers in the larger of the chambers. Delivery of the mixed amalgam is accomplished by removing a cap from one end of the capsule to expose an aperture therein, and connecting the opposite cover end of the capsule to a syringe, the plunger of which detaches the piston from the capsule cover and drives the piston through the mixing chamber to eject the amalgam therefrom.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the preparation and delivery of 
dental amalgam and relates more particularly to a method and apparatus 
wherein the amalgam constituents are stored and mixed in, and delivered 
from, a sealed capsule. 
Dental amalgams conventionally include an alloy of various metals in 
powdered form which is mixed with mercury just prior to application to a 
prepared dental cavity. In early dentistry, the amalgam ingredients were 
mixed in an open vessel and the proportions were gauged by the viscosity 
of the mixture. As dental techniques improved, it was recognized that more 
careful attention to the proportions of the ingredients was desirable and 
systems were devised whereby the amalgam ingredients were prepackaged in 
capsules in the correct proportions. Transfer from prepackaged capsules to 
the mouth still involved the use of open vessels with the opportunity of 
contamination of the amalgam by foreign matter and bacteria, and 
contamination of the environment by spillage and vaporization of mercury. 
The belated recognition of the toxic nature of mercury vapors and the 
dangers inherent in any procedure which permit the exposure of the mercury 
or the amalgam to the atmosphere has resulted in the proposal of a number 
of systems for storing, mixing and dispensing the amalgam to minimize such 
exposure. 
In U.S. Pat. No. 1,774,258, for example, a capsule is provided having 
separate compartments within which the amalgam ingredients may be 
separately stored. When the amalgam is needed, the membrane separating the 
compartments is broken and the mixing of the ingredients is accomplished 
by placing the capsule in a mixing machine. For delivery to a patient, 
however, the amalgam must be placed in an open container for pickup by an 
amalgam applicator and hence this particular approach eliminates only a 
part of the problem, namely the proportioning of the ingredients and the 
isolation thereof from the atmosphere during storage and mixing. Other 
forms of capsules for storing and mixing of dental materials are shown in 
U.S. Pat. Nos. 2,527,991 and 3,638,918. 
Later developments recognized the desirability of dispensing the amalgam 
directly from the container in which it was mixed into the prepared dental 
cavity. Patents exemplifying such a system include U.S. Pat. Nos. 
3,368,592, 3,521,356, 3,724,077 and 3,828,434. In none of these 
arrangements, however, does it appear that the amalgam constituents are 
packaged and stored in the container in which the mixing takes place. 
More recent developments have attempted to combine the storage, mixing and 
delivery functions in the same container or capsule. For instance, in U.S. 
Pat. No. 3,760,503 the ingredients are brought together by the puncturing 
of the compartment holding one component by a spatula which is then 
rotated to mix the ingredients. When mixing is completed, the spatula is 
withdrawn and a plunger inserted to deliver the mixture from the opposite 
end of the container. 
U.S. Pat. No. 4,084,320, discloses a structurally complex capsule having 
rotatable and removeable end members which are rotated to provide 
communication of the mercury with the powder materials, again rotated to 
provide a mixing of the materials, and then removed and replaced by 
special spout and plunger elements for delivery of the amalgam. 
Although various types of capsule systems have been made commercially 
available, they have not, for various reasons, become popular, and 
dentists today are still to a large extent using techniques which involve 
the placement of the amalgam on an open surface for piecemeal transfer to 
the cavity in an amalgam carrier. Not only do such techniques permit the 
release of toxic mercury vapors, but they also permit contamination of the 
amalgam by exposure to contaminents on the surface, in the air, and 
especially in the amalgam carrier which is repeatedly exposed to the 
bacteria of different patients' mouths. 
BRIEF DESCRIPTION OF THE INVENTION 
The present invention provides an improved amalgam capsule and a method of 
storing, mixing and applying the amalgam by use of such a capsule which 
simplifies the procedures and structural components employed by the prior 
art. Specifically, the invention includes a capsule having two chambers 
which are separated by a piston detachably formed as a part of the capsule 
end cover. The compartment carrying the fluid ingredient such as mercury 
is formed in part by a flange portion of the capsule body which is 
deformable upon the application of an axial force to provide communication 
of the chambers and the flow of the mercury into the larger, central 
mixing chamber. Mixing is accomplished by placing the capsule in a 
conventional mixing machine. 
Delivery of the amalgam mixture is effected by removing a cap from one end 
of the capsule to expose an aperture therein, and connecting the opposite 
end of the capsule to a syringe, the plunger of which detaches the piston 
from the capsule cover and drives the piston through the mixing chamber to 
eject the amalgam therefrom. 
In the preferred embodiment, the flange portion of the capsule body forming 
a part of the fluid chamber is configured at an acute angle to the 
cylindrical chamber body wall, preferably about 45.degree., such that 
axial deformation of the capsule will cause the resilient flange to spring 
over center, thereby providing a positive and unmistakeable opening of the 
fluid chamber into the mixing chamber which assures that all of the 
mercury has an opportunity to pass into the mixing chamber. Upon release, 
the resilient flange returns the capsule to its storage condition, again 
sealing the chambers with all of the amalgam constituents in the mixing 
chamber. 
With the present capsule, the amalgam is not exposed to the ambient air 
until the mixed amalgam is delivered from the capsule directly to the 
prepared cavity and accordingly there is no opportunity for mercury vapors 
to escape into the atmosphere or contaminents to reach the amalgam or its 
constituents prior to delivery to the patient's teeth. 
It is accordingly a first object of the present invention to provide an 
improved amalgam capsule and method for storing, mixing and delivering a 
dental amalgam. 
Another object of the invention is to provide a capsule and method as 
described which will substantially eliminate the contamination of the air 
by release of vapors and the contamination of the amalgam by the exposure 
to equipment and airborne contaminents. 
An additional object of the invention is to provide a method and apparatus 
as described which prevents waste of the amalgam by eliminating spillage 
and by permitting delivery of all of the mixed amalgam to the prepared 
cavity. 
Still another object of the invention is to provide a method and apparatus 
as described wherein the amalgam carrier system is disposable, thus 
eliminating the need for amalgam carriers and amalgam wells, preventing 
transfer of disease and providing a consistent viscosity of the amalgam. 
A further object of the invention is to provide a method and apparatus as 
described wherein the communication of the capsule chambers is provided by 
an elastic deformation of a portion of the capsule and does not involve 
the puncturing, breaking or removal of internal capsule partitions. 
Another object of the invention is to provide a method and apparatus as 
described wherein the deformation of the capsule to provide communication 
of the capsule chambers is effected by a simple application of an axial 
elongating force to the capsule body to produce a substantial and 
unmistakeable snap-action elongation of the capsule. 
Still another object of the invention is to provide a method and apparatus 
as described wherein the condition of the capsule and its contents may be 
visually ascertained during any step of the method. 
An additional object of the invention is to provide an amalgam capsule 
which can be used with conventional mixing devices. 
Another object of the invention is to provide a method and apparatus as 
described which saves time, which can be economically put into practice 
and which greatly simplifies the preparation and application of dental 
amalgam. 
Additional objects and advantages of the invention will be more readily 
apparent from the following detailed description of a preferred embodiment 
thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings and particularly FIG. 1 thereof, the capsule 10 
of the present invention comprises a capsule body 12 which is essentially 
of a hollow elongated cylindrical shape. In the preferred embodiment, the 
capsule body 12 includes an inner cylindrical sleeve 14 of a rigid 
material, an an outer body member 16 of a resilient, relatively flexible 
material. 
The capsule body terminates at one end in a conical nozzle portion 18 
formed only by the resilient body member 16 for a purpose explained below. 
A circular aperture 20 at the end of the nozzle portion 18 coaxial with 
the cylindrical body is closed during the storage and mixing uses of the 
capsule by a cap 22. The cap is preferably made of an elastic material 
which provides an airtight seal of the aperture 20 but which can be 
readily removed to permit delivery of the amalgam through the aperture 
following the mixing thereof. An annular bead 24 on the capsule body 
member 16 cooperates with an annular groove 26 of the cap to provide a 
resilient attachment of the cap which can be released by a sufficient 
axial withdrawing force applied to the cap. To facilitate the cap removal, 
an annular shoulder 28 is provided around the cap periphery. 
At the end of the capsule body opposite the apertured end, the body 
includes an annular flange 30 extending from the outer body member 16. The 
flange 30 includes a thinwalled angled portion 32 extending from the end 
34 of the cylindrical portion of the body, the angled portion 32 forming 
preferably about a 45.degree. angle with respect to the cylindrical 
portion of the capsule body. The angled portion 32 thus forms an outwardly 
sloping frusto-conical surface in the normal storage position of the 
capsule. At the outer end of the angled portion 32, the flange continues 
in a short radial section 36 which in turn joins with an axial portion 38 
terminating in a shoulder portion 40. The portions 36, 38 and 40 of the 
flange are of a thicker wall section than the angled portion 32 and are 
thus somewhat less flexible. The end of the sleeve 14 and the adjacent end 
of the cylindrical portion of the body member 16 are of a beveled 
configuration and thus provide a conical seating surface 42 having an 
angle of approximately 45.degree. with respect to the axis of the capsule 
body portion. 
The capsule also includes a cover 44 having an annular peripheral groove 46 
permitting connection with the shoulder 40 of flange 30 in sealing 
relation by means of a suitable adhesive. The cover 44 includes an annular 
internal channel 48 which is disposed essentially opposite the angled 
portion 32 of the flange and forms in conjunction with the portions 32, 36 
and 38 of the flange a chamber 50 adapted for the storage of fluid 
material such as a ball 52 of mercury as illustrated in FIG. 1. The 
chamber 50 is sealed from the space within the cylindrical portion of the 
capsule by means of a detachable piston 54 which is formed as an integral 
part of the cover. A cylindrical bore 56 in the cover extends to the outer 
surface of the piston, the bore 56 having an outwardly flaring portion 58 
adjacent the outer end thereof. The piston 54 is joined to the main 
portion of the cover 44 by a narrow annular neck 60 which is defined on 
one side by the bore 56 and on the other side by a frusto-conical surface 
62 having an included angle smaller than that of the conical surface 42. 
The cover 44 is dimensioned such that the surfaces 62 and 42 will engage 
in tight sealing contact to prevent communication between the chamber 50 
and the interior of the cylindrical portion of the capsule. 
The closures provided by the piston 54 and the cap 22 at the opposite ends 
of the capsule body 12 defines therewithin a sealed mixing chamber 64 
within which a quantity of powdered amalgam ingredients 66 may be stored. 
The contents of the chamber 64 are securely sealed from the contents of 
chamber 50 by the piston 54 and the sealing engagement of the surfaces 42 
and 62. 
The capsule as illustrated in FIG. 1 with the mercury 52 sealed in chamber 
50 and the powder material 66 sealed in chamber 64 is in the form in which 
the capsule is delivered to dentists from a dental supply house. The 
capsules may be stored indefinitely prior to use and present no danger of 
contamination of the atmosphere since there are no orifices or gaps such 
as screw threads through which the mercury vapors can pass. Similarly, the 
amalgam ingredients are protected from contamination from the atmosphere 
since each capsule is hermetically sealed. Additional protection may of 
course be provided by appropriate sealing of shipping and storage 
containers bearing a number of the capsules. With the preferred use of 
transparent materials for the capsule, the condition of the capsule 
contents may be examined during storage. 
To prepare the amalgam, the capsule is resiliently deformed to permit 
communication between the chambers 50 and 64 and the passage of the 
mercury 52 into the chamber 64 for mixing with the powdered material 66. 
This is accomplished by simply grasping the cylindrical portion of the 
capsule body 12 in a vertical position in one hand and pulling axially 
upwardly on the outer portion of the flange 30 with the other hand to 
reverse the inclination of the frusto-conical surface formed by the angled 
flange portion 32 as shown in FIG. 2. The thin walled resilient nature of 
the portion 32 permits the elastic deformation shown and results in the 
separation of the surfaces 42 and 62, thereby providing a wide opening of 
the chamber 50. The reversal of the angled portion 32 of the flange as 
shown in FIG. 2 forms a funnel shaped surface serving to direct the entire 
contents of the chamber 50 downwardly into the chamber 64. 
Following the deformation step required to provide communication of the two 
chambers, the deforming force applied to the capsule is released and the 
capsule will then elastically recover to the condition shown in FIG. 1 
with the seal provided by the piston 54 and specifically the surfaces 42 
and 62 becoming reestablished. The capsule is then inserted in a standard 
commercial mixing machine known as an amalgamator as shown in FIG. 3. The 
amalgamator 82 includes a pair of opposed fingers 84a and 84b which are 
vibrated or oscillated at an extremely high rate for a short period of 
time to thoroughly mix the mercury with the powdered materials to form an 
extremely dense viscous amalgam which is then ready for delivery directly 
from the capsule to the prepared dental cavity. 
For delivery of the amalgam, the capsule is connected as shown in FIG. 4 
with a modified form of syringe 66 which is characterized by a connector 
68 having an annular flange 70 adapted to receive the cover end of the 
capsule. The connector is made of a resilient material and includes an 
annular bead 72 at the periphery of the flange 70 which cooperates with 
the shoulder 40 of the capsule flange 30 to secure the capsule to the 
connector. The syringe includes a flexible tubular body 74 attached to the 
connector 68 within which is slideably disposed a syringe rod 76 having an 
enlarged rod tip 78. The body 74 is connected at its end opposite the 
connector to a finger grip 79 through which the rod 76 extends to the 
actuating plunger 80. Aside from the connector 68 and the rod tip 78 which 
are designed to fit the capsule, the syringe is of a conventional 
construction. 
For application of the amalgam to a prepared cavity, the capsule containing 
the mixed amalgam is placed in the syringe by snapping the capsule into 
the resilient flange of the syringe. The cap 22 is then removed and the 
plunger 80 of the syringe is depressed to move the rod tip 78 against the 
piston and sever the piston 54 from the annular neck 60. The controlled 
depression of the plunger advances the piston through the mixing chamber 
64, engaging the amalgam and forcing the amalgam through the aperture 20 
in the quantity required. The amalgam may thus be applied directly from 
the capsule to the prepared tooth and is neither subjected to 
contamination by contact with the air or other surfaces prior to 
deposition in the cavity. By the same token there is no opportunity for 
vapors to pass from the amalgam into the air except as unavoidably occurs 
in the patient's mouth during the placement of the amalgam. Any unused 
amalgam which remains in the capsule may be safely disposed of by 
replacing the cap 22, thus sealing the amalgam in the mixing chamber 
beneath the tight fitting piston 54. 
Should the delivery of all of the amalgam be desired, the frusto-conical 
end 18 of the capsule body is sufficiently flexible to expand to the 
diameter of the piston, thereby allowing the piston to travel to the 
aperture 20 and thus eject all of the amalgam from the capsule. The 
capsule construction thus minimizes waste of the amalgam material which is 
quite expensive since the powdered metal alloy typically includes a 
precious metal. 
The syringe may be repeatedly used with successive capsules without danger 
of contaminating any of the amalgam since none of the syringe elements 
come in contact with the amalgam and without contaminating the syringe 
with mercury. 
The proportions of the mixing chamber have been found to have an important 
effect on the mixing action effected in the amalgamator as well as the 
ease with which the amalgam can be delivered from the chamber. In the 
preferred embodiment of the invention, the ratio of the length to the 
diameter of the mixing chamber is substantially 4:1 although an operable 
range of these proportions would be between 3:1 and 6:1. With a capsule 
having a mixing chamber diameter of 0.20 inches and a 4:1 ratio of chamber 
length to diameter, it has been found that 18 seconds mixing time will 
produce amalgam of satisfactory quality. The commonly used pestle for 
promoting mixing has not been found necessary with a properly proportioned 
mixing chamber and accordingly no provision therefore need be made. 
The capsule elements are preferably molded of a plastic material and 
transparent polyvinylchloride (PVC) has been found to be excellent for 
this purpose. In a preferred embodiment, the sleeve 14, cap 22 and cover 
44 are formed of a hard PVC for example of 94 Durometer hardness, while 
the body member 16 is formed of a relatively flexible PVC having a 80 
Durometer hardness. Other materials having similar properties should also 
prove suitable for carrying out the invention. It is preferred that the 
capsule be made of a transparent material so that the condition of the 
contents can be readily evaluated. 
Although the angle of the portion 32 of flange 30 is preferably an acute 
angle of 45.degree. to the capsule body portion, modified forms of the 
invention could be effected using angles ranging from 15 to 85 degrees. 
Although any angle within this range should provide adequate passage for 
the mercury, an angle which provide a substantial displacement of the 
capsule portions is preferred since it provides a tactile as well as 
visual confirmation of the opened condition of the capsule chambers. 
The filling of the capsule may be accomplished in several ways. In one 
method, the cap 22 may be secured to close the aperture 20 prior to the 
placement of the cover 44. In such case, the powdered material 66 and the 
mercury 52 are inserted from the top with the capsule in the attitude 
shown in FIG. 1, and the cover is then applied to separate the chambers 
and seal the capsule. 
Alternatively, with the cover initially secured in place and the capsule 
inverted from its attitude shown in FIGS. 1 and 2, the mercury may first 
be inserted in the chamber 50 by deforming the capsule to its open 
position shown in FIG. 2. Upon closure of chamber 50 and the 
reestablishing of the seal by the piston and surfaces 42 and 62, the 
powder may be inserted in the mixing chamber 64 and the cap 22 applied to 
seal the capsule. 
Manifestly, changes in details of construction can be effected by those 
skilled in the art without departing from the invention.