Abstract:
The invention provides a dental device comprising thermoplastic polyamide having a Charpy notched impact strength of at least 3.5 ft-lb/in 2 . Preferably the polyamide comprises at least 10 percent by weight of micro-crystals having a largest dimension less than 750 nanometers. Preferably the device is a Denture base, denture, partial denture, clasp, splint, or night guard. Preferably, the polyamide has an opacity of less than 30 percent. The invention provides a metal cartridge container containing particles of thermoplastic polyamide effectively free of pigment. The metal cartridge is used in a method of making a partial dental prosthesis having a substantially transparent clasp. First a substantially transparent thermoplastic is injected into a first portion of a mold cavity of a mold containing an artificial tooth, and then a substantially opaque thermoplastic injecting into a second portion of the mold cavity. The removable partial dental prosthesis formed includes an artificial tooth supported by a base integrally connected to a clasp, wherein the base includes pigment and is substantially opaque, and the clasp is substantially transparent and effectively without pigment.

Description:
[0001]    The invention relates to dental devices, denture products, kits, systems and methods therefor. The invention provides a dental device such as a denture base, clasp, denture and partial denture. The invention provides kits, systems and methods for molding dentures having clasps. The invention provides a semi-crystalline transparent clasp, and partial dentures having a transparent clasp. This invention provides removable partial denture having clasps composed of a transparent semi-crystalline polyamide formed by an injection molding.  
         BACKGROUND OF THE INVENTION  
         [0002]    Thermoplastic partial denture clasps have been fabricated with pigmented polyamide/copolymer, polyacetal, which have poor aesthetic properties, and transparent ‘amorphous’ polymer compounds, which results in poor physical properties and require laborious fabrication methods. Amorphous polyamides display a clear and colorless quality however; very high viscosities and poor physical/mechanical properties preclude their use as injection molded dental resins.  
           [0003]    Removable partial dental prostheses are employed to restore one or more, but not all, of the natural teeth of a patient. The primary objectives of a properly designed dental prosthesis include the preservation of remaining teeth, along with hard and soft oral tissue, the restoration of oral function, and the restoration of dental and facial aesthetics.  
           [0004]    Removable partial dental prostheses are commonly formed with a base or saddle which rests on the oral mucosa in an edentulous space and is coupled by connector means to one or more abutment teeth, that is, a tooth which abuts or is adjacent to the edentulous space.  
           [0005]    Perhaps one of the most common forms of partial dental prosthesis is the distal extension removable partial denture which is used to replace posterior teeth with artificial teeth on one or both sides of the mouth. Distal extensions are commonly secured to an abutment tooth by clasps, which are mounted on the abutment tooth to provide for stabilization and retention of the prosthesis, and a connector, which extends between the clasp and the base of the distal extension. The base or saddle of the distal extension rests on the alveolar ridge.  
           [0006]    Prefabricated clear and tooth colored thermoplastic clasps are described in U.S. Pat. No. 5,102,337. The prefabricated clasps are contoured by applying heat to the area which the technician wishes to shape and bend. Kulwiec et al. In U.S. Pat. No. 4,412,824 discloses removable partial dental prosthesis and method of forming and supporting the same.  
           [0007]    Prior art dental devices have low impact strength. These problems of the prior art are overcome by the present invention. The prior art does not disclose a dental device including thermoplastic polyamide having a Charpy notched impact strength of at least 3.5, or a dental device including polyamide having at least 10 percent by weight of micro-crystals having a largest dimension less than 750 nanometers, as provided by the present invention.  
         OBJECTS OF THE INVENTION  
         [0008]    It is an object of the invention to provide a dental device including thermoplastic polyamide having a Charpy notched impact strength of at least 3.5.  
           [0009]    It is an object of the invention to provide a dental device including polyamide having at least 10 percent by weight of micro-crystals having a largest dimension less than 750 nanometers.  
           [0010]    It is an object of the invention to provide a metal cartridge container containing particles of thermoplastic polyamide effectively free of pigment.  
           [0011]    It is an object of the invention to provide a method of making a partial dental prosthesis having a substantially transparent clasp, by injecting substantially transparent thermoplastic into a first portion of a mold cavity of a mold containing an artificial tooth, and injecting substantially opaque thermoplastic into a second portion of the mold cavity.  
           [0012]    It is an object of the invention to provide a removable partial dental prosthesis including an artificial tooth supported by a base integrally connected to a clasp, wherein the base includes pigment and is substantially opaque, and the clasp is substantially transparent and effectively without pigment.  
           [0013]    It is an object of the invention to provide a kit for making a denture, including: a package supporting a first cartridge enclosing pigment and first particles of thermoplastic and a second cartridge enclosing second particles of thermoplastic effectively free of pigment.  
           [0014]    It is an object of the present invention to provide a removable partial dental prosthesis which is capable of restoring oral function and dental and facial aesthetics without destruction of adjacent teeth and soft oral tissue.  
           [0015]    Another object of the present invention is to provide a method of supporting a removable partial dental prosthesis in the mouth and particularly on the alveolar ridge which greatly reduces stress on the ridge and abutment teeth.  
           [0016]    Still a further object of the present invention is to provide a method for the manufacture or formation of removable partial dentures which is adaptable to denture manufacturing techniques and yet includes structure providing enhanced performance of the prosthesis.  
           [0017]    Another object of the present invention is to provide a method for supporting a dental prosthesis which enhances the life of the remaining teeth in the mouth and which does not afford a habitat for decay and infection causing debris.  
           [0018]    It is also an object of the present invention to provide a dental prosthesis which is compact, relatively easy to manufacture, highly durable, and distributes and redirects localized stress forces.  
           [0019]    The removable dental prosthesis and method of the present invention have other objects and features of advantage which will become more apparent from and are set forth in the following description of the preferred embodiment and the accompanying drawings.  
           [0020]    Opacity as used herein refers to the percentage of impinging white light transmitted from a spectrophotometer through a 1 mm thick sample of material being tested.  
           [0021]    Charpy notched impact strength as used herein refers to Notched impact strength in foot-pounds/inch 2  (ft-lb/in 2 ) measured by ISO 179:1993  
         SUMMARY OF THE INVENTION  
         [0022]    The invention provides a metal cartridge container containing particles of thermoplastic polyamide effectively free of pigment. The metal cartridge is used in a method of making a partial dental prosthesis having a substantially transparent clasp. First a substantially transparent thermoplastic is injected into a first portion of a mold cavity of a mold containing an artificial tooth, and then a substantially opaque thermoplastic injecting into a second portion of the mold cavity. The removable partial dental prosthesis formed includes an artificial tooth supported by a base integrally connected to a clasp, wherein the base includes pigment and is substantially opaque, and the clasp is substantially transparent and effectively without pigment. The invention provides a dental device including thermoplastic polyamide having a Charpy notched impact strength of at least 3.5 ft-lb/in 2 . Preferably the polyamide comprises at least 10 percent by weight of micro-crystals having a largest dimension less than 750 nanometers, and has an opacity less than 50%. More preferably the polyamide comprises at least 20 percent by weight of micro-crystals having a largest dimension less than 750 nanometers, and has a Charpy notched impact strength of at least 4.5 ft-lb/in 2 , and an opacity less than 40%. Most preferably the polyamide comprises at least 30 percent by weight of micro-crystals having a largest dimension less than 750 nanometers, and has a Charpy notched impact strength of at least 5 and an opacity less than 30%. The polyamide beneficially may have a Charpy notched impact strength of at least 6, and more beneficially may have a Charpy notched impact strength of at least 7. Preferably the device is a denture, partial denture, clasp, splint, or night guard. Preferably the polyamide has an opacity of less than 30 percent. 
       
    
    
     DESCRIPTION OF THE DRAWING  
       [0023]    [0023]FIG. 1 is a cross-section side view of a cartridge container tube enclosing polyamide from a kit for making a partial denture in accordance with the present invention.  
         [0024]    [0024]FIG. 2 is an end view of the cartridge container tube shown in FIG. 1 in accordance with the present invention.  
         [0025]    [0025]FIG. 3 is a cross-section side view of a cartridge plug which is inserted into the plug end of the cartridge container tube in accordance with the present invention.  
         [0026]    [0026]FIG. 4 is an end view of the cartridge plug shown in FIG. 3 in accordance with the present invention.  
         [0027]    [0027]FIG. 5 is a cross-section side view of a cartridge container tube enclosing polyamide from a kit for making a partial denture in accordance with the present invention.  
         [0028]    [0028]FIG. 6 is an end view of the cartridge container tube shown in FIG. 5 in accordance with the present invention.  
         [0029]    [0029]FIG. 7 is a cross-section side view of a cartridge plug from a kit for making a partial denture in accordance with the present invention.  
         [0030]    [0030]FIG. 8 is an end view of the cartridge cap shown in FIG. 7 in accordance with the present invention.  
         [0031]    [0031]FIG. 9 is a view of an injection mold with sprues for use in accordance with the present invention.  
         [0032]    [0032]FIG. 10 is a schematic diagram of a system for making molded dental devices from polyamide enclosed in a cartridge container tube in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0033]    The invention is now described with more particular reference to FIGS.  1 - 10 . With more particular reference to FIGS.  1 - 4  is seen cartridge container  12  and cartridge plug  14  enclosing nylon pellets  16 . Plug  14  is inserted into plug end  18  of container  12 . During shipping and storage cartridge container  12  with cartridge plug  14  inserted plug end  18  encloses nylon pellets  16 . In use cartridge container  12 , cartridge plug  14  and nylon pellets  16  are heated to melt the nylon pellets  16  to form liquid nylon. The liquid nylon is pressed through burstable end  19  into a mold from cartridge container  12 .  
         [0034]    With more particular reference to FIGS.  5 - 8  is seen cartridge container  22  and cartridge plug  24  enclosing nylon pellets  26 . Plug  24  is inserted into plug end  28  of container  22 . During shipping and storage cartridge container  22  with cartridge plug  24  inserted plug end  28  encloses nylon pellets  26 . Cap  30  is supported by threaded nozzle  36 . Nozzle inner wall  38  encloses an output channel. In use cartridge container  22 , cartridge plug  24  and nylon pellets  26  are heated to melt the nylon pellets  26  to form liquid nylon. The liquid nylon is pressed through the output channel and burstable end  29  into a mold from cartridge container  22 .  
         [0035]    With more particular reference to FIGS.  9 - 10  is seen a mold  100  and a system  110  for making molded dental devices  200  from polyamide  26  enclosed in a cartridge container tube  22 . Polyamide  26  enclosed in a cartridge container tube  22  is heated in heater  112 . Cap  30  is removed from threaded nozzle  36 . Threaded nozzle  36  is positioned under ram  120  in guide  122  of press  114  to force burstable end  29  to open the output channel of nozzle inner wall  38  into mold  100  when pressure is applied to polyamide  26  enclosed in a cartridge container tube  22 . Mold  100  is supported by metal flask  102 . Mold  100  has molded artificial teeth  202 A and  202  supported therein and made of an acrylic interpenetrating polymer network (IPN). Ram  120  is moved down pressing cartridge plug  24  down. As Ram  120  moves down pressing cartridge plug  24  down cartridge container tube  22  is crushed and pressure is applied to heated polyamide  26  pushing polyamide  26  through passage  196 ,  197  and  198  into a mold cavity wall  199  enclosing a mold cavity within mold  100  to form dental device  200  having molded polyamide  26  and artificial teeth  202 . The mold cavity within mold  100  has the shape of dental device  200 . Mold  100  is removed from press  114  and metal flask  102 . From mold  100  is removed dental device  200  having molded polyamide  26 .  
         [0036]    The transparent polymer used in clasps made in accordance with the invention preferably consists of a permanently transparent, chemical and stress crack resistant, high impact strength, UV and visible light stable, low water sorption, dimensionally stable, highly water resistant, steam sterilizable, semi-crystalline polyamide resin. This resin is beneficially maintains excellent physical properties while remaining permanently clear and colorless. The transparent semi-crystalline polyamide is preferably injection molded using dental flask/stone investment, a compact heating oven together with a low pressure injection molding machine (less than 90 psi) to sequentially fabricate a partial denture containing a “clear” aesthetic clasp attached to a tissue shaded base resin. The base material consists of a pigmented version of the transparent semi-crystalline polyamide resulting in a monolithic prosthetic device. Sequential injection molding of ‘clear’ aesthetic clasps allows for precise replication of waxed clasp design with high-strength, durable thermoplastic resin. Preferably acetal resins are used in sequential injection molding to fabricate clasps. Preferably bases are made of an opaque/pigmented semi-crystalline acetal resin.  
       EXAMPLE 1  
       [0037]    23 grams of pellets of transparent crystalline nylon, Lucitone FRS crystalline nylon without pigment are poured into an aluminum container having a threaded end and then a cap is pressed onto the threaded end and supported by the threads on the threaded end of the container. The cylindrical container body is 1 inch in diameter and 3.5 inches in length. The cylindrical container body is 0.005 inch thick. The conical container end extends from the cylindrical container body and is 0.4 inch in length and has a cylindrical nozzle which is 0.375 inch in diameter. The burstable end of the nozzle is 0.4 inch thick. Transparent crystalline nylon Lucitone® FRS™ in the container is useful for injection molding to form temporary, flexible, and monomer free denture base. It is useful for the fabrication of complete or partial removable dentures as well as occlusal splints and night guards.  
       EXAMPLE 2  
       [0038]    23 grams of pellets of transparent crystalline nylon, Lucitone® FRS™ crystalline nylon are coated with red pigment. The nylon pellets are poured into an aluminum container having a threaded end and then a cap is pressed onto the threaded end and supported by the threads on the threaded end of the container. The cylindrical container body is 1 inch in diameter and 3.5 inches in length. The cylindrical container body is 0.005 inch thick. The conical container end extends from the cylindrical container body and is 0.4 inch in length and has a cylindrical nozzle which is 0.375 inch in diameter. The burstable end of the nozzle is 0.4 inch thick.  
         [0039]    Table 1 describes typical properties, of transparent crystalline nylon, Lucitone FRS used in EXAMPLES 1 and 2, and molding temperatures, and injection, heating and cooling times used in EXAMPLE 3.  
                   TABLE 1                           Type and Class (according to ADA   Type III, Class 1       Spec. 12)       Storage temperature for powder and liquid   60° F.-90° F. (16° C.-32° C.)       Dosage:   1 cartridge (23 g)       Processing Time /Temp. (To reach   18 minutes @ 575 F.       injectable stage)       Injection Time   &lt;1 minute       Material used to invest wax-up   Dental Stone       Cool time (prior to deflask)   5 minutes                  
 
       EXAMPLE 3  
       [0040]    A partial denture with a transparent clasp is prepared by:  
         [0041]    Investment and Spruing  
         [0042]    Soak a cast and wax up of a patients mount in water for 25 minutes prior to investing. Mix investment and embed the cast and wax-up in the lower half of a flask. Using wax sticks, D-shaped Success™ Sprue Wax Sticks (7 mm×180 mm, Item # 904584) injection sprues are built. On upper dentures, attach the sprue to the posterior border of the denture and make sure the sprue is sufficiently wide. For lower full dentures, attach the sprue to both lingual extensions as well as in the mid-line. Then embed the upper half of the flask.  
         [0043]    Wax Elimination and Separator Application  
         [0044]    The flask is placed in boiling water for a 4 to 6 minutes to soften the wax. The bolts on the flask are loosened and the Metal Flask Brackets are removed. The flask is opened and the Space Maintainer is removed. Then a boil out procedure is completed to form a clasp mold and the wax is discarded.  
         [0045]    The flask is placed in boiling water for a 4 to 6 minutes to soften the wax. The bolts on the flask are loosened and the Metal Flask Brackets are removed. The flask is opened and the Space Maintainer is removed. Then a boil out procedure is completed to form a partial denture mold and the wax is discarded.  
         [0046]    The molds are flushed with clean boiling water. Bevel the stone with a lab knife around the mouth of the sprue. The flask margin and cavities are checked to ensure that both flask halves fit together with intimate metal contact. A thin coat of Al-Cote® Separating Agent is applied to the model and the model is allowed to dry completely. Mechanical retention is added by grinding diatorics into the teeth. Thermoplastic Injection Insert is positioned on one side of the flask and the flask halves are placed under an infrared heat source.  
         [0047]    Clear Clasp Fabrication  
         [0048]    The clasp is waxed to full contour, slightly over building the body of the clasp. All excess model is trimmed away, leaving a small core with the clasp attached. Two clasps are fabricated. Investment and spruing are completed. Wax is eliminated. Clear transparent Lucitone® FRS™ crystalline nylon is Injected into the mold to form the clasps while heating.  
         [0049]    Heating and Injection  
         [0050]    After removing the cap from a cartridge, formed by following the procedure of EXAMPLE 1, the container of transparent Lucitone FRS crystalline nylon is placed in an injection sleeve to form an assembly. When the container of transparent Lucitone FRS crystalline nylon is placed in an injection sleeve the threaded end of the container is positioned in the injection sleeve to face away from the injection sleeve handle. A sleeve plug is placed into the remaining space in the heating sleeve. The assembly is inserted into a cartridge furnace (preheated to 575° F.) and a timer is set for 18 minutes. While heating the assembly in the furnace for 18 minutes, the flask halves are assembled and placed in front of the Success Injection System manufactured and sold by Dentsply. The sleeve assembly is removed from the furnace and positioned on top of the flask such that the threaded end of the container fits into the opening of a thermoplastic injection insert to form a combination. The combination is then slid into the Success Injection System and the piston is engaged to press the transparent Lucitone FRS crystalline nylon from the container into the clasp mold enclosed by the flask. Injection into the mold is complete within one (1) minute. Then the flask and sleeve assembly combination is removed from the Injection system. The heating sleeve is then twisted off of the flask and the used container is expelled from the heating sleeve using a knock out base and knock out rod. The injected flask is deflasked five minutes after injection. The clear clasps are finished to final contour with carbide burrs and the clasps are fitted to denture mold. After removing the cap from a cartridge, formed by following the procedure of EXAMPLE 2, the container of pigmented Lucitone FRS crystalline nylon is placed in an injection sleeve to form an assembly. When the container of pigmented Lucitone FRS crystalline nylon is placed in an injection sleeve the threaded end of the container is positioned in the injection sleeve to face away from the injection sleeve handle. A sleeve plug is placed into the remaining space in the heating sleeve. The assembly is inserted into a cartridge furnace (preheated to 575° F.) and a timer is set for 18 minutes. While heating the assembly in the furnace for 18 minutes, the flask halves are assembled and placed in front of the Success Injection System manufactured and sold by Dentsply. The sleeve assembly is removed from the furnace and positioned on top of the flask such that the threaded end of the container fits into the opening of a thermoplastic injection insert to form a combination. The combination is then slid into the Success Injection System and the piston is engaged to press the pigmented Lucitone FRS crystalline nylon from the container into a partial denture mold enclosed by the flask. Injection into the partial denture mold is complete within one (1) minute. Then the flask and sleeve assembly combination is removed from the Injection system. The heating sleeve is then twisted off of the flask and the used container is expelled from the heating sleeve using a knock out base and knock out rod. The injected flask is deflasked five minutes after injection.  
         [0051]    Finishing and Polishing - The flexible partial denture with a transparent clasp is finished using coarse pumice and polished using Tripoli ™ polishing compound and High Shine™ polishing compound.  
       EXAMPLE 4  
       [0052]    A full denture is prepared by:  
         [0053]    Investment and Spruing  
         [0054]    Soak a cast and wax up of a patients mount in water for 25 minutes prior to investing. Mix investment and embed the cast and wax-up in the lower half of a flask. Using wax sticks, D-shaped Success™ Sprue Wax Sticks (7 mm×180 mm, Item # 904584) injection sprues are built. On upper dentures, attach the sprue to the posterior border of the denture and make sure the sprue is sufficiently wide. For lower full dentures, attach the sprue to both lingual extensions as well as in the mid-line. Then embed the upper half of the flask.  
         [0055]    Wax Elimination and Separator Application  
         [0056]    The flask is placed in boiling water for a 4 to 6 minutes to soften the wax. The bolts on the flask are loosened and the Metal Flask Brackets are removed. The flask is opened and the Space Maintainer is removed. Then a boil out procedure is completed to form a clasp mold and the wax is discarded.  
         [0057]    The flask is placed in boiling water for a 4 to 6 minutes to soften the wax. The bolts on the flask are loosened and the Metal Flask Brackets are removed. The flask is opened and the Space Maintainer is removed. Then a boil out procedure is completed to form a full denture mold and the wax is discarded.  
         [0058]    The molds are flushed with clean boiling water. Bevel the stone with a lab knife around the mouth of the sprue. The flask margin and cavities are checked to ensure that both flask halves fit together with intimate metal contact. A thin coat of Al-Cote® Separating Agent is applied to the model and the model is allowed to dry completely. Mechanical retention is added by grinding diatorics into the teeth. Thermoplastic Injection Insert is positioned on one side of the flask and the flask halves are placed under an infrared heat source.  
         [0059]    After removing the cap from a cartridge, formed by following the procedure of EXAMPLE 2, the container of pigmented Lucitone FRS crystalline nylon is placed in an injection sleeve to form an assembly. When the container of pigmented Lucitone FRS crystalline nylon is placed in an injection sleeve the threaded end of the container is positioned in the injection sleeve to face away from the injection sleeve handle. A sleeve plug is placed into the remaining space in the heating sleeve. The assembly is inserted into a cartridge furnace (preheated to 575° F.) and a timer is set for 18 minutes. While heating the assembly in the furnace for 18 minutes, the flask halves are assembled and placed in front of the Success Injection System manufactured and sold by Dentsply. The sleeve assembly is removed from the furnace and positioned on top of the flask such that the threaded end of the container fits into the opening of a thermoplastic injection insert to form a combination. The combination is then slid into the Success Injection System and the piston is engaged to press the pigmented Lucitone FRS crystalline nylon from the container into adenture mold enclosed by the flask. Injection into the denture mold is complete within one (1) minute. Then the flask and sleeve assembly combination is removed from the Injection system. The heating sleeve is then twisted off of the flask and the used container is expelled from the heating sleeve using a knock out base and knock out rod. The injected flask is deflasked five minutes after injection.  
         [0060]    Finishing and Polishing - The flexible denture is finished using coarse pumice and polished using Tripoli™ polishing compound and High Shine™ polishing compound.  
         [0061]    TABLE 2 shows physical properties of the products of Examples 3 and 4 and. The products of Examples 3 and 4 have more than 50 percent greater Charpy notched impact strength than commercially marketed dental products.  
                           TABLE 2                                       Examples           Property   3 and 4                           Formulation   Microcrytalline               polyamide           Tensile strength (psi)   9000           Tensile Modulus (psi)   232000           Flexural Strength (psi)   9300           Flexural Modulus (psi)   200000           Charpy notched ft-lb/in 2     7.6           Charpy unnotched   No break           Specific Gravity   1.06           Melt point C.   248           Glass transition T g  C   155           Melt flow (g/10 min)   N/A           Water Absorption % 24 hrs   .45                      
 
         [0062]    It should be understood that while the present invention has been described in considerable detail with respect to certain specific embodiments thereof, it should not be considered limited to such embodiments but may be used in other ways without departure from the spirit of the invention and the scope of the appended claims.