Compositions: coating or plastic – Coating or plastic compositions – Dental
Reexamination Certificate
2000-03-23
2002-03-05
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Dental
C106S778000, C106S772000, C106S782000, C106S785000, C106S783000, C106S787000, C206S063500, C433S214000, C433S213000
Reexamination Certificate
active
06352585
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a gypsum castings composition and casting method. More particularly, this invention relates to a gypsum casting composition which is particularly useful as a gypsum dental casting and to a method for producing gypsum dental or similar castings.
For the purpose of the present invention, gypsum and gypsum compositions are defined as materials that are chemically structured as or with calcium sulfates (CaSO
4
),calcium sulfate dehydrate, calcinated calcium sulfate, or calcium sulfate hemihydrate as a reactive, setting or hardening component. They that are supplied as dry powders and are intended to be mixed with water to a slurry consistency and react with the water to harden into a set mass, mold or casting.
Gypsum for use in the production of castings is traditionally supplied as a dry powder that is extremely hygroscopic.
Dry gypsum powders intended for use in making gypsum dental castings are traditionally supplied as packaged in paper or plastic bags or corrugated boxes or fiber pails etc. in weight volumes of 25, 50, or 100 pounds and sometimes lesser quantities. For example, in one of the more prevalent methods for making gypsum dental castings the gypsum work area is located adjacent to a sink. The gypsum powder is transferred from its bulk package container to a plaster bin where it is stored and may be readily available. The process of transfer requires lifting a heavy weight package and then a messy, dusty task of emptying the dry powder into a storage bin. This transfer of gypsum powder to the storage bin releases dust into the surrounding air and causes cleanup requirements throughout the office. The dust also settles and in time absorbs moisture from the air thereby setting and clogging vents, cabinets, latches, control panels, dials, door hinges, and all nearby mechanical and electrical appliances and components.
The storage bin is traditionally compartmented to accommodate 25 to 50 lbs. of dental plaster, 25 to 50 lbs. of dental stone, and 25 to 50 lbs of dental die stone. These are different types of calcium sulfate hemihydrate determined by the temperature and method of calcining by a manufacturer.
Each type offers a different degree of hardness or set expansion. The transfer process is repeated each time one type of gypsum is emptied and needs replenishment.
To make a gypsum dental casting, the cover to the bin is opened and a measure of gypsum is removed and placed into a container on a weight scale. The amount is adjusted to a pre-determined weight. A measure of liquid is then placed into a measuring beaker. Manufacturers recommend a suggested liquid/powder ratio to achieve a pre-determined specification for set time, controlled expansion and hardness. Excess or insufficient liquid in the mix may affect the physical properties of the set casting. In practice however, the gypsum worker routinely desires to alter the physical properties of set time, hardness or expansion. This is time consuming, requires additional items of preparation such as a scale and a beaker, and increases the amount of gypsum dust that is dispersed into the air and spilled onto and around the work area. Extra cleanup time is additionally required for each of the items in use and the general cleanup of the work area.
The weighed gypsum powder and measured liquid is then transferred to a stiff rubber or vinyl mixing bowl. Mixing bowls are the preferred vessels for the preparation of gypsum and consistently produce predictable results. For general and routine small batch mixes, a stiff bladed spatula is used for the required vigorous stirring of the gypsum until a creamy paste/slurry is achieved. For large batches, a mechanical mixer/bowl device is recommended. The manipulation and transfer of gypsum powder to the mixing bowl further releases dust into the surrounding air. In effect every time the gypsum bin is opened, every time gypsum is transferred to a weight scale and every time gypsum is transferred to a mixing vessel, the powder dust is released into the surrounding air.
When the gypsum powder and the water are mixed to a slurry they are poured into a mold and allowed to set. All of the items used in the preparation of the mix are soiled with gypsum paste and must then be washed. This is the reason that gypsum work areas are traditionally located adjacent to a sink. This then creates an additional problem. The constant washing of gypsum items causes gypsum to build up in the pipes, plumbing and drains of the sink. Most gypsum work area sinks must be equipped with plaster traps that require frequent cleaning or plumbing repairs.
When the gypsum casting is set and returned to its dehydrate the problems of handling are still not ended. When the dry gypsum powder is mixed with water and allowed to set into a casting, the resulting casting is physically a reconfiguration of the original gypsum as mined. Gypsum is well known to have a characteristically, dry, chalky surface. Handling of the finished castings by workers has an irritating effect on the skin of the gypsum workers causing a drying and chaffing. In effect, it is the surface of the gypsum dusting off, through handling. This chalky surface is also traditionally weak and scratches easily producing more dust.
Attempts to reduce the problem of dust by formulating gypsums with various chemical additives have been disclosed such as in U.S. Pat. Nos. 4,911,759, 4,670,053, 5,698,610, 4,909,847 and 4,543,372. There has been little if any improvements utilizing these methods. Dust and mess continue to be a problem. Mixing bowls and utensils still need to be washed and sinks continue to be clogged.
U.S. Pat. Nos. 5,709,467, 5,618,105, 5,465,833 and 5,052,554 disclose a method of mixing gypsum compositions in a disposable plastic bag that is flexible and allows the gypsum mix to be kneaded. The physical constraints of a flexible bag and the kneading method prevent the gypsum from being vigorously stirred or agitated, as is usually required for dental castings. In addition once the bag is filled, water added and kneaded, its jelly-like form is difficult to properly manipulate and to portion out the slurry by squeezing and continual readjustment with one hand while holding and vibrating a mold with the other hand. The larger the bag the more difficult it becomes. The bag mixing techniques additionally makes it difficult for a worker to use a spatula to scoop out a portion of the paste mix and place it onto or into specific areas for shaping or building such as when articulating upper and lower dental casts or filling a void. There is commercially available, gypsum that is packaged in small unit size foil bags. This supply method reduces to some degree the dust associated with transferring the dry powder from a bulk container to a gypsum bin.
This small unit packaging still produces dust to the immediate breathing hazard of the worker when it is emptied into a mixing bowl for preparation of the mix with liquid and has not eliminated the problems of washing utensils and clogging of the sinks, or the dusting off of the surface of the set gypsum.
U.S. Pat. Nos. 4,299,790, 3,958,997 and 3,989,220 disclose a shaker-mixer-molding assembly and a gypsum composition. These methods and compositions do not address or reduce the dusting problem associated with measuring, weighing and transferring a dry gypsum powder from a bulk packaging container or from a bulk storage container to a mixing vessel. Neither do they eliminate the need to wash the mixing vessel, measuring devices and mix utensils in preparation for the next mix. They are related to a performance composition and a speedy method of direct filling a specific mold that is attached by design to the mixing vessel, an object of which is a molding apparatus which is a principle part of the shaker-mixer assembly for matched attachment and pouring.
Similar to the shaker-mixer-mold device of U.S. Pat. Nos. 3,958,997 and 3,989,220 but without the attached mold, there is commercially available a pre-loaded syringe, containing an alginate compositi
Conte Robert F. I.
Koslow C. Melissa
Lee Mann Smith McWilliams Sweeney & Ohlson
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