Plastic article or earthenware shaping or treating: apparatus – Means forming a mold; or flask – per se – Including ram type feed of molding material or means to...
Reexamination Certificate
1998-02-19
2001-02-13
Silbaugh, Jan H. (Department: 1732)
Plastic article or earthenware shaping or treating: apparatus
Means forming a mold; or flask, per se
Including ram type feed of molding material or means to...
C264S017000, C264S019000, C264S478000, C249S054000, C425S174400, C425S567000, C425SDIG001
Reexamination Certificate
active
06186761
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a molding system and method for making injection molded dental appliances such as dentures, retainers, prostheses and similar appliances. The invention also relates to a means for dispensing materials which may limit operator exposure to harmful chemicals.
SCOPE OF THE PRIOR ART
Conventional molded dental appliances and methods of making them are widely practiced by dental laboratories. Most molded dental appliances are constructed in a dental flask containing a mold, also called an investment, of the appliance to be formed. The investment is made of plaster or other investment material and is molded around a wax model of the desired appliance, a wax-up, which is embedded in the dental flask. The wax-up may include items such as retainer wires or artificial teeth. Once the investment has hardened, the wax is removed from the dental flask, creating a cavity in the investment of the shape of the desired appliance. The uncured appliance material is then introduced by hand or by conventional injection methods. In conventional methods of packing, approximately three to four tons of force is required in order to squeeze out excess appliance material. After packing, the material is cured in the flask by conventional means such as by conduction heating, thereby forming a dental appliance of the desired shape.
The use of conventional molding systems and methods poses several problems for the practitioner. Often, too much material is added to the investment cavity, resulting in overpacking of the flask. Also, the high pressures can cause distortion of metal frameworks. In addition, when applied to partial dentures, tooth movement frequently occurs, requiring time-consuming reconstruction. Additionally, the material may undergo shrinkage during curing. Overpacking, excess pressure and shrinkage can all result in inaccurately dimensioned dental appliances. In addition, opening and subsequent addition or subtraction of material to the dental flask can cause a variety of significant problems, including but not limited to nonuniform or incomplete curing, the entrapment of air bubbles within the appliance, dislodging of embedded items such as teeth or retaining wires, premature appliance fractures (due to nonuniform preparation of materials), and inaccurately dimensioned appliances.
In addition to the problems disclosed above, conventional methods of mixing the materials may expose the operator to potentially harmful fumes and chemicals. For instance, many dental appliances are created using resins, such as acrylic, urethane or epoxy resins. A number of these resins are currently believed to pose a risk of cancer to exposed persons, and all may be harmful if absorbed through the skin or lungs or ingested, or if fumes emitted from the resins are inhaled. For example, in a conventional acrylic resin preparation of the type generally used in dentistry, the resin material is prepared on a benchtop by combining a fine, loose powder polymer with a liquid monomer and mixing by hand with a small stick or spatula until uniform. The polymer powder readily disperses into the air, and may be inhaled by the operator or absorbed through the skin. The liquid monomer is volatile, and may be inhaled in its gaseous state. In addition, the possibility of spillage of the liquid monomer is a constant threat to the operator. Moreover, upon combination of the powder and the liquid, a chemical reaction causes the immediate release of fumes, which may also be harmful to the operator if inhaled. In another example, epoxy resins are generally formed from two or more thick liquid components which are hand mixed on a benchtop, the process of which also releases potentially harmful vapors. In addition, as with virtually all commercially available uncured resins, mixed but uncured acrylic or epoxy material may be harmful and irritating if contacted with skin.
Moreover, conventional molding systems further cause an economic disadvantage to operators in that the flasks and attendant equipment used for each type of material are different. For instance, traditional flasks and injector modules for forming heat-curable appliances are different than traditional flasks and injector modules used for forming microwave-curable appliances. Thus, operators must purchase entirely separate equipment if they are to have the desired freedom to use both types of materials.
Thus, there is a need for an improved dental injection molding system which minimizes inaccurately dimensioned appliances, which protects operators from exposure to potentially dangerous fumes and chemicals and which allows operators the freedom to use at least some of the same equipment with more than one type of material.
As will become apparent from a detailed reading of the description, the system of the invention offers significant advantages over the prior art systems described above, most significantly including a system for pressurized and continuous injection in a closed system even during curing, which greatly minimizes the risk of inaccurately formed or non-uniform appliances. In addition, the injection system of the invention can accommodate conduction heat and microwave curing, both under pressure and without pressure. Lastly, use of the dispensing system of the invention will minimize operator exposure to harmful fumes and chemicals, regardless of the chemistry used to make the material. Other objects and advantages of the present invention will become obvious to the reader and it is intended that these objects and advantages are within the scope of the present invention.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a pressurized dental injection molding system whereby material may be continuously pressurized in a mold up to the point of cure of the material.
It is a further object of the invention to provide a system for making injection molded dental appliances that can compensate for shrinkage or overfilling or underfilling.
It is also an object of the invention to provide a system for making injection molded dental appliances which at least partly vents the injector module and flask during injection.
It is yet another object of the present invention to provide an injection module for making injection molded dental appliances that may be used with both conduction heating and microwave curable material.
It is still another object of the present invention to provide a dispensing system that minimizes operator exposure to chemicals and vapors.
The invention includes a system and method for making injection molded dental appliance apparatuses having an injector module removably attached to a dental flask, a press and a controlled compression means, wherein the press and compression means introduce pressure into the dental flask and the injector module, which pressure may or may not be maintained during curing of the appliance. The invention also includes a system for dispensing dental appliance chemicals having at least one chemical dispensing apparatus and a bag; whereby a separate dispensing apparatus is used for each chemical and the chemicals are dispensed directly into the bag and mixed in the bag.
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781 “Flexural Properties of Compression an-
Parisius Wolf
Petkow Lothar
Robertson A. A.
Gardner Carton & Douglas
GC America, Inc.
Silbaugh Jan H.
Staicovici Stefan
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