Plastic and nonmetallic article shaping or treating: processes – With step of making mold or mold shaping – per se – Utilizing surface to be reproduced as an impression pattern
Reexamination Certificate
2001-08-31
2003-12-09
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With step of making mold or mold shaping, per se
Utilizing surface to be reproduced as an impression pattern
C264S220000, C264S313000, C264S319000
Reexamination Certificate
active
06660204
ABSTRACT:
TECHNICAL FIELD
This invention relates to custom prostheses, especially to custom breast prostheses. More particularly, the invention concerns providing and shaping an intermediate product used in prosthesis fabrication, namely, a casting form.
BACKGROUND
Post-mastectomy products include prefabricated breast forms, and custom breast prostheses. Custom prostheses are designed to conform to the chest wall of the patient, and thus provide a fit that looks and feels more natural as compared to non-custom products. Processes for fabricating custom breast prostheses are disclosed, for example, in U.S. Pat. No. 5,798,062 (Thielbar), U.S. patent application Ser. No. 08/955,535 filed Oct. 22, 1997, and U.S. patent application Ser. No. 09/174,199 filed Oct. 16, 1998 as a continuation-in-part of the ′535 application. These processes require applying paste material (e.g., a dental alginate) substantially over the entire chest area in combination with wet plaster bandages. Then, a positive cast must be made, typically by spreading gypsum plaster over the inside of the negative cast. A breast form is sculpted using modeling clay placed on the positive cast. The sculpted clay is removed very carefully. A back mold is formed by applying a plaster or other paste material to the negative cast, to form on the back mold a positive replication of the chest area to which the custom prosthesis will be applied. Then, the sculpted formed clay mold is positioned on the back mold, the resulting structure is surrounded by a wall, and plaster poured to create a front mold. The front and back molds, when joined together, form a chamber into which a silicone gel is injected to form the custom prosthesis.
The preceding mold-forming process is time-consuming, cumbersome and unpleasant to the patient. The intermediate stages between the initial negative cast and the back mold reduce the degree of accuracy to which the back mold can replicate the thoracic (chest) area. Accuracy is further reduced by the tendency of the alginate to shrink when it dries. The initial negative cast frequently is not used immediately, but rather shipped to a fabrication center for use in making the positive cast and the front mold. This gives rise to the need to pack the negative cast in damp material and provide special expedited shipping and handling in an attempt to reduce the rate and amount of shrink due to drying out.
A further problem arises from the manner in which the clay breast form is provided, i.e., by sculpting a mound of modeling clay placed on the positive cast. When sculpting the clay, the clinician relies on a visible image, e.g., photograph of a remaining breast (reverse image), or the profile of an unsupported remaining breast provided by an unsupported positive cast. The patient may not be present during sculpting. If present, she can not inspect the form in situ, but instead must attempt to envision the appearance of the completed prosthesis based tab on the modeling clay form as it rests upon the positive cast.
SUMMARY OF THE INVENTION
The present invention provides a process for fabricating a custom prosthesis, in which the task of creating the intermediate casting form is considerably simplified, and enables a shaping of the casting form, in situ.
The primary source of these advantages is a thin-walled cup-like shell, substantially inextensible but elastic in that it tends to assume the cup-like shape when not subject to an external stress. Further, however, light pressure applied to the shell readily alters its shape. This balance of flexibility and formability is a result of the material involved, the shape of the shell, and the wall thickness. One material found well suited for constructing the shell is a semi-transparent, flexible polyethylene-based sheet material, available from American Plastics of Fort Worth, Texas under the brand name American Flexilene. Shells used in the fabrication of breast prostheses can have wall thicknesses ranging from about 1 mm to about 4 mm, with shells corresponding to larger cup sizes having the thicker walls.
The casting form is made of an elastomer; more particularly, a high viscosity polyvinylsiloxane putty. The putty is provided initially in two parts, combined by hand mixing of the parts in a 1-to-1 ratio to provide a putty mixture or matrix. The mixture has a setting or curing time on the order of seven minutes, and a working time (during which the putty matrix can be readily shaped, i.e., after which the matrix is largely permanently unalterable) of about three and one-half minutes. The curing time can be reduced, if desired, by the application of heat, even the relatively slight heat resulting from holding a hand or other part of the body against the matrix.
The casting form is made by mixing the parts of the putty, then without delay, filling the shell with the putty mixture, preferably to an excess of the matrix. Then, the filled shell is placed in a bra, and the bra fitted onto the patient, thus to press the putty mixture gently but firmly against the chest wall. Additional gentle pressure may be desirable, to ensure complete contact of a “back wall” of the matrix against the chest. After such pressure, however, the bra alone adequately maintains the shell/matrix position.
During the working time, the elastomeric matrix is pliable, and thus susceptible to shaping by hand as it cures. The shell, although resilient as noted above, is compliant in the sense that it tends to conform to the shape of the matrix. Thus, as the putty mixture is manipulated by hand into a new shape, the shell tends to conform to that new shape.
Simultaneously, the shell influences the shape of the matrix, by attenuating localized irregularities. For example, poking a thumb or finger into the matrix body away from the shell would tend to form a depression similar in radius to the thumb or finger. By contrast, pressure from the thumb or finger, when applied to the matrix through the shell, results in a much shallower depression with a much larger radius. In this manner, the shell “biases” any shaping of the shell/matrix combination away from local irregularities, toward smoother curves having larger radii. Such smooth, gradual contours are preferred, and are readily achieved even by relatively less skilled providers, when the shell/matrix combination is used to make the casting form. When cured, the elastomer is sufficiently hard (Shore A hardness of 25) to reliably maintain the desired shape.
Use of the shell in combination with the elastomeric putty matrix considerably simplifies fabrication of the casting form. The process no longer requires the application of a dental alginate and wet plaster bandages to the chest to form a negative cast, nor is the subsequent positive cast required. There is no need to sculpt a breast form from modeling clay, or to place the resulting form over the chest wall at the area of the scar. There is no need to form a separate back mold of dental alginate or other paste material.
The shell/matrix combination results in a more accurate casting form. The alginate or other paste material used in the conventional process tends to shrink when it dries, giving rise to the need for maintaining alginate casts and forms damp, or suffer the consequences of shrinkage. The elastomeric putty used in combination with the shell does not shrink as it cures, and consequently provides a closer replication of the chest wall, accurately reproducing incision marks, scar tissue, and soft tissue folds. The cured matrix can be shipped to the fabrication center at the fitter's convenience. No expedited handling is required. The resulting prosthesis assumes a more conforming, more comfortable fit.
A salient feature of the present invention is the degree to which the patient can participate in the shaping of the casting form. The modeling clay breast form of the conventional process typically is constructed in the absence of the patient, based on measurements and photographs or other visual aids. In the present process, the shell/matrix combination is shaped in situ while
Clover, Jr. William M.
Hendrickson Anna M.
Faegre & Benson LLP
Kuhns Allan R.
Otto Bock Orthopedic Industry, Inc.
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