WO1999066856A1

WO1999066856A1 - Denture system

Info

Publication number: WO1999066856A1
Application number: PCT/US1999/014088
Authority: WO
Inventors: Richard Jacobs; Don Porteous; Eckart Mathias; Juan Cervantes
Original assignee: Cadco Dental Products, Inc.
Priority date: 1998-06-23
Filing date: 1999-06-22
Publication date: 1999-12-29
Also published as: WO1999066856B1; AU4707599A

Abstract

Denture product and forming system for denture products comprising tooth structure and a supporting base, including: a fluid, two-component thermosetting resin supply (70) having a mixer for mixing a resin reactive mixture from the components and an injection outlet (84) from the mixer; a denture mold (28) comprising a closed cavity (68) having an inlet for receiving delivery of the resin reactive mixture from the supply under injection pressure and at a predetermined cavity filling flow rate; and spaced from the inlet a vent (86, 88) adapted for venting gases from the cavity while blocking resin reactive mixture from emptying from the cavity at greater than a predetermined cavity emptying flow rate which is less than the cavity filling flow rate, so that the resin reactive mixture overfills the cavity and self-pressurizes to a pressure sufficient to block any incorporated gases in the resin reactive mixture from forming voids or bubbles during curing.

Description

Denture System Description

Background of the Invention 1. Field of the Invention

This invention relates to a system for the rapid production of dentures using improved manufacturing methods and apparatus and, preferably, carefully tailored urethane resin compositions to provide a unique combination of desirable properties. 2. Background Art In making a denture, an edentulous impression of the gums is taken from the patient and a stone model is made therefrom which replicates the lower or upper jaw structure and respective lingual or pallet area. The relationship between the stone model and new tooth structure is created in the lab by a technician who uses an articulator to position a selection of replacement teeth for partial embedment into what will eventually become a cast denture structure. The first approximation of the denture structure, however, is created by applying wax onto the stone model and then building the wax model up and around the roots and cervical areas of the teeth terminating at what will become the gingival margin of the denture.

The wax model becomes a means of temporarily holding the teeth in the stone model during the subsequent fabrication of an investment material, typically a silicone rubber, encapsulating the wax model of what will eventually become the exposed gum areas and replacement teeth. The investment and waxed-up model are backed by the dental stone in the flask. The upper portion of the flask contains the either the investment or stone model and the lower portion will contain the complementary portion. The separator line between the upper and lower portions of the flask intersects the wax portion of the model. Once the silicone rubber upper or lower mold portions are cast and cured, the mold is separated and the wax is removed. What remains is a void which contains the stone model residing within either the lower or upper flask form and the teeth embedded within the investment material or silicone rubber within the complementary mold form. The roots and cervical areas of the teeth remain protruded within the cavity. Particular attention is paid to removing any remaining wax from the base of the prosthetic teeth so chemical bonding of the teeth is proficient and thorough. Typically, artificial or prosthetic teeth are primarily acrylic, either of a poly methyl methacrylate (PMMA) or composition of a polyacrylate composition, and sometimes of a porcelain composition. Often times, a diatoric (undercut of the teeth) is provided for achieving retention of the denture material. These teeth are supported in a denture buy a mass of resin which is typically an acrylic or acrylate resin of pasty viscosity that is packed into a cavity around the supported teeth.

The state of the art for denture packing materials is a family of acrylate resins. Usually, the final composition is a mixture of a Part A component containing liquid acrylate monomers and oligomers which also contain amine promoters. A second Part B component comprises solid acrylate polymers which are ground into a fine powdery consistency and includes peroxide catalyst which is admixed or commutated between the grains of the powdery polymer. The catalyst can be alternatively placed in the Part A liquid monomer/oligomer component and the promoter alternatively placed in the Part B component. Whichever combination is selected, the objective is to maintain the peroxide catalyst and amine promoter in separate components to maintain stable mixtures while the components are stored on the shelf. Colorants and colored fibers are added to either the Part A or Part B components to achieve a life-like replication of the gum structure. Other methods can be used. For example, a pourable resin mixture can be used rather than the packable pasty materials. Pourable low viscosity compositions have flowability so bubbles and entrapped air are swept out ahead of the main stream of liquid before polymerization occurs. The promoter and catalyst components of the low viscosity compositions are mixed and then poured through a port into the mold void and the excess exits from a sprue passageway cut into the investment material and a vent. Heat is used to cure the compositions; this can be both an advantage and a disadvantage. On one hand, increased heat and reduced cure time is desired to provide for manufacturing efficiency, but curing at too high a temperature and at too fast a rate can induce internal stresses and distortions within the packed denture material. This can occur when the mixture gels at too high a peak exotherm temperature inducing the denture to undergo shrinkage during cool down to room temperature. Or curing too quickly can produce stresses due to variations in the heat history of the mixture as it is packed into the mold. The major advantage of flow grade materials is that a low modulus silicone investment material can be used to embed the teeth. In the transfer molding method, the mixture of the Part A and Part B ingredients can be purposely formulated to have a mastic high viscosity or a pourable low viscosity quality. When the Part A liquid component is mixed with the Part B powdery component, the mixture becomes promoted and polymerizes within a short period thereafter to achieve a highly mastic consistency. During a brief period of time, the mixture will maintain its thick mastic consistency. At that stage, the mixture can be placed into the mold cavity. The mastic high viscosity compositions are formulated that way purposely for producing displacement of entrapped air within the mass of material as it is packed into the mold. The high viscosity in combination with external pressure allows the technician to displace entrapped air around the base of the teeth and along the pallet area where considerable surface profile and under-cutting of mold surface exists. To achieve a thorough contact with all portions of the mold, particularly around the areas where the base of the teeth are protruding, the mixture is mechanically packed at high pressure to ensure that the voids are filled and air is expelled. The rate of cure and shrinkage are both a function of the thickness of mass that is cast at any one time. The packed casting is then placed in a warm oven or warm or hot water bath around 160 °F to drive the cure to completion at a sufficiently fast rate. After the denture components have been mixed, packed and cured, perhaps even in several steps, the casting is removed from the mold and ground as necessary for final fit and polished using a polishing powder. Summary of the Invention

Denture forming systems that rely on acrylates to support the prosthetic teeth require substantial polishing time after removal of the mold, making labor costs a major part of the entire cost of a denture. The diatorically-attached teeth sometimes separate from the denture material itself while in use. This detachment does not have to be a complete mechanical failure to be a problem, however. Even with slight separation, cracks open which breed the formation of bacteria that can create hygienic and unsightly darkening effects at the gingival margin. Weakly bonded teeth will require a diatoric, or undercut, for added strength. Acrylate dentures are easily breakable when dropped. The also have a permanent taste which is rather acrid. There is a need for a nonacrylic denture support for prosthetic teeth, but the improvement must at the same time use the traditional work-up techniques and provide the flexibility of design familiar to dentists and dental laboratories, to gain acceptance. In USP 4,024,637 to Colpitts a urethane denture was proposed comprising not only a base of urethane but urethane teeth. Standard artificial teeth are commercially available in the many hues and shapes required for the wide range of patients, and the industry appears unprepared to try new tooth materials with unknown suitability to the purpose or to vary their existing procedures. Thus the problem of improving on the state of the art is to develop improvements that fit the existing template of denture manufacture, but with better materials and better techniques adapted to the new materials.

It is an object of the invention to provide a nonacrylic denture forming system. It is a further object to provide a novel denture of any of numerous resin materials that are amenable to the improved manufacturing techniques disclosed herein. It is a further and highly specific object to provide a system for manufacturing a denture comprising a rapidly-building- viscosity two-part resin, preferably a particular, optimum urethane resin, packaged in side-by-side dual chambers of cartridges having an affixable static mixer tip tightly fitted to the injection port of the dental flask, with an opening usually on the labial side of the teeth. A further object is to provide a system in which moisture, entrapped air and bubbles are minimized or eliminated for perfect surface finish on the denture. A still further object is to provide an improved adhesion to the teeth by the denture base material. Yet another object provides a denture manufacturing system using a low pressure injection of a casting resin having the fluidity to fully contact all the contiguous areas of the mold surface and the viscosity to sweep away all air from the cavity surface which is otherwise naturally entrapped, and break down the occluded bubbles within the leading wave of the casting material. It is a further object to provide a process where the casting resin is internally pressurized due to a reduced size vent in relationship to the entry port, and the reactive resinous mixture supplied to the molding cavity is rapidly or slowly polymerized, using as needed an external pressure and fill volume sufficient to overcome the natural shrinkage during the polymerization process and which provides perfect replication of the edentulous and wax model areas, and provides a perfectly void-free and life-like appearance to the denture.

The preferred urethane materials herein obviate a number of the previously required, cumbersome processing steps involved in fabricating acrylic dentures. The additional adhesive strength of the invention denture compositions eliminates the need for a diatoric. The tight bond between the teeth and denture also prevents breeding of bacteria in that margin. Considerably less polishing is required during processing. In addition, the invention urethane dentures are more tolerable in the mouth, not having the problem of producing a bitterness or a sharp after- taste in certain mouth environments as is common with acrylates. In addition, the invention urethane materials are tough, having the ability to withstand breakage upon dropping onto a hard surface.

This invention, accordingly, provides a system for forming dentures comprising tooth structure and a supporting base, including: a fluid, two-component thermosetting resin supply generally closed to ambient air and pressurizable to an injection pressure, the resin supply having a mixer for mixing a resin reactive mixture from the components and an injection outlet from the mixer; a denture mold comprising a closed cavity in which the tooth structure is supported in its intended position in the denture with its roots exposed into the cavity, the mold cavity having an inlet for receiving delivery of the resin reactive mixture from the supply under the injection pressure and at a predetermined cavity filling flow rate for cure within the cavity in denture- forming relation; the resin reactive mixture tending to incorporate gases present in the cavity, and spaced from the inlet a vent adapted for venting the gases from the cavity while blocking resin reactive mixture from emptying from the cavity at greater than a predetermined cavity emptying flow rate, the cavity filling flow rate being greater than the cavity emptying flow rate, whereby the resin reactive mixture overfills the cavity and self-pressurizes to a pressure sufficient to block any incorporated gases in the resin reactive mixture from forming voids or bubbles therein during cure thereof visible in a denture comprising the resin reaction product of the resin reactive mixture cured to a solid in the shape of the mold cavity.

In this and like embodiments, the cavity comprises a wall in which the inlet and vent are formed, a tooth support structure within and surrounded by the cavity wall, the tooth support structure tending to be moisture containing, and including also coating the tooth support structure with a moisture barrier coating in advance of injection of the resin reactive mixture thereinto to block exposure of the resin reactive mixture to the tooth support structure moisture; selecting a thermosetting resin as the moisture barrier coating; selecting a two-component thermosetting urethane resin as the moisture barrier coating, mixing the components in reactive proportions, and applying the mixture to the tooth support structure in moisture barrier coating forming relation; selecting a two-component vinyl silane resin as the moisture barrier coating, mixing the components in reactive proportions, and applying the mixture to the tooth support structure in moisture barrier coating forming relation. Further the invention contemplates a system in which the resin supply injection outlet comprises a nozzle, the mold cavity inlet receiving the nozzle in sealing relation to receive the resin reactive mixture from the supply free of entrained ambient air in the resin reactive mixture; the resin supply mixer comprises a static mixer adapted to mix the resin components into the resin reactive mixture in advance of the injection outlet from the mixer, the injection outlet comprising a nozzle insertable into the mold cavity inlet for delivery of the resin reactive mixture into the mold cavity free of entrained ambient air; the supply includes first and second chambers containing respectively first and second side precursor components of a thermosetting resin, and a source of pressure for each of the chambers including a movable member adapted to drive each chamber-contained component from its chamber to the mixer; the source of chamber pressure includes a pressurized fluid supply selectively coupled to the chamber movable members for moving the members in precursor component driving relation from the chambers; the chambers comprise cylinders having movable pistons therein as the movable members, and a supply of pneumatic pressure to the pistons for expressing the precursor components from the cylinders, each of the cylinders having an outlet normally closed against ambient air, the outlets being openable for delivery of the precursor components, the precursor components further comprising a finely divided mineral filler in a viscosity increasing amount sufficient to block retreat of the precursor components farther into their cylinders upon opening the outlets in reaction to ambient air pressure causing the creation of bubbles in either precursor resin; the mineral filler comprises fumed silica; and, the fumed silica is present in an amount between about 0.1 and 10% by weight of the precursor component in the cylinder.

Further, the invention contemplates the foregoing system in which the denture resin comprises a urethane resin, such as the reaction product of a first precursor component comprising an isocyanato reagent, a second precursor component resin moiety comprising a poly ether, polyester, urea, urethane, castor oil, oxazole, oxazolidone, oxazolidinone, amide, imide, or imine moiety and a chain extender, said resin moiety and said chain extender each having separately active hydrogen, hydroxyl, amine, or amide functionality

In this and like embodiments, typically, the second precursor component resin moiety has a active hydrogen or hydroxyl functionality and a molecular weight above about 1000, and preferably second precursor component resin moiety has a molecular weight above about 5000. chain extender has a molecular weight below about 500, and a functionality of at least 3 or preferably 4, the chain extender comprises a tertiary amine having active hydrogen or hydroxyl functionality, e.g. the chain extender comprises a tertiary amine having the formula

R R l t

C - C - R

- R

in which at least one R=R1 and each remaining R is Rl or R2, and: in which:

Rl= -OH; -SH;

-N(CH2CH2OH)2;

-N(CH2CH3CH2OH)2;

-N(CH2CHCH3OH)2;

R2= -H;

-Me;

-Alkyl;

-OAlk;

-OMe; -Halogen;

-Aryl;

-Aroyl and cyclics of the above.

Preferably, the tertian- amine chain extender comprises ethylene diamine tetrapropoxylate. Alternative!}', the chain extender can comprises an alkylene oxide or ether adduct of a highly functional molecule, e.g. having a hydroxyl functionality between 4 and 12, and comprising pentaerythritol, sugar, starch or cellulose molecules, preferably pentaerythritol, and pentaerythritol adducted with ethylene and/ or propylene oxide and having a molecular weight of about 450. In a further embodiment, the highly functional molecule comprises a sucrose, fructose, or sorbitol molecule.

The system further contemplates the isocyanato reagent comprising an aliphatic isocyanate, preferably methylenedicyclohexane-4, 4 '-diisocyanate, or an aromatic isocyanate, preferably diphenylmethane diisocyanate. In these systems, typically the resin moiety comprises a polyether, polyester, urea, urethane, castor oil, oxazole, oxazolidone, oxazolidinone, amide, imide, or imine moiety having active hydrogen, hydroxyl, amine, or amide functionality and has a molecular weight above about 5000, and the chain extender comprises pentaerythritol molecule adducted with ethylene and/ or propylene oxide and having a molecular weight below about 500. Further, the resin moiety typically comprises a primary or secondary hydroxyl functional polyether polyol having an equivalent weight from about 20 to about 10,000 daltons, and a functionality of about 1 to about 20, such as a poly oxy-propylene oxide ether polyol having a functionality of from about 1 to about 3. The chain extender then typically comprises ethylene diamine tetrapropoxylate or the noted pentaerythritol and sugars adducted as described above

The invention further contemplates maintaining the supply resin components and the resin reactive mixture free of surface contact with ambient air before and during delivery thereof to the mold cavity; progressively increasing the viscosity of the resin reactive mixture in the mold cavity over a time period Tl, and driving air from the mold cavity by filling the mold cavity with increasing amounts of the increasing viscosity resin reactive mixture; maintaining the resin reactive mixture flowable over a time period T2, filling the mold cavity with the reactive mixture over a period T3, and maintaining the time period T2 greater than the time period T3; progressively increasing the viscosity of the resin reactive mixture over time period T2, and driving air from the mold cavity by filling the mold cavity with increasing amounts of the increasing viscosity resin reactive mixture.

The invention further contemplates in cases where the resin reaction mixture tends to shrink in size during cure, overfilling the cavity with pressurized resin reactive mixture sufficiently to compensate for the size shrinkage and completely fill the cavity in the cured condition of the resin. The invention further contemplates the resin reactive mixture being pressurized within the mold cavity to a pressure of from about 1 to about 40 psi, preferably 1 to 15 psi above ambient atmospheric pressure, the pressure being sufficient to block any incorporated gases in the mixture from forming voids or bubbles visible in a denture formed therefrom.

The invention further provides a denture forming apparatus comprising a mold cavity, artificial teeth, a support supporting the artificial teeth within the cavity, and a resin supply supplying a reactive resin mixture under injection pressure, the mold cavity having a resin reaction mixture injection inlet and spaced therefrom a vent, the vent being flow restricted relative to the inlet, whereby the resin reactive mixture is pressurized within the mold cavity.

In this and like embodiments there is further included a guide from the vent for guiding vented material from the mold cavity; a mixer and tip for mixing the resin reactive mixture and delivering the mixture to the mold cavity inlet, the tip being received within the inlet in sealing relation against air incursion into the mold cavity with the mixture; a pressure source pressuring the mixture for delivery into the mold cavity; the pressure source comprises a pneumatic pressure source.

In a further embodiment, the invention provides a denture formed by the foregoing system.

In a further embodiment, the invention provides a visible void- and bubble-free denture comprising one or more teeth and a resin support, the resin support comprising a urethane resin reaction product of an isocyanato reagent, a chain extender, and a tertiary amine formed under above atmospheric pressure conditions in a substantially closed mold cavity against a moisture- barrier-coated stone with the teeth embedded therein.

In a further embodiment, the invention provides a visible void- and bubble-free denture comprising one or more teeth and a resin support, the resin support comprising a urethane resin reaction product of an isocyanato reagent comprising diphenylmethane diisocyante, a chain extender comprising a poly oxy-propylene oxide ether polyol, and a tertiary amine comprising ethylene diamine tetrapropoxylate formed under above atmospheric pressure conditions in a substantially closed mold cavity against a moisture-barrier-coated stone with the teeth embedded therein.

In a further embodiment, the invention provides a method of restorative dentistry including taking an impression of a patient's gums, forming a visible void- and bubble-free denture comprising one or more teeth and a resin support, the resin support comprising a urethane resin reaction product of an isocyanato reagent comprising diphenylmethane diisocyante. a chain extender comprising a poly oxy-propylene oxide ether polyol, and a tertiary amine comprising ethylene diamine tetrapropoxylate formed under above atmospheric pressure conditions in a substantially closed mold cavity against a moisture-barrier-coated stone with the teeth embedded therein, and fitting the patient with the denture. Brief Description of the Drawings

The invention will be further described in conjunction with the attached drawings in which:

Fig. 1 is a pictorial view of the dental impression tray being filled with impression material;

Fig. 2A is a pictorial view of the taking of a dental impression by inserting the impression material filled tray into the patient's mouth preparatory to fabricating a replacement denture for the patient;

Fig. 2B is a view of the removed impression tray with the gum impression; stone model material is being added;

Fig. 3 is an oblique view of the molded stone model after removal from the impression tray;

Fig. 4 is an oblique view of the stone model after addition of wax and teeth;

Fig. 5 is an exploded view of the denture forming flask of the invention with the stone model, wax and teeth assembly in place preparatory to forming the investment casting;

Fig. 6 is a pictorial view of the assembled dental flask being filled with investment material; Fig. 7 is a pictorial view of the stone model, wax and teeth assembly being removed from the opened flask, leaving the molded investment material;

Fig. 8 is a pictorial depiction of the removal with hot water of wax from the stone model and the teeth;

Fig. 9 is a pictorial view of the application of a release agent onto the wax-free stone model;

Fig. 10 is a pictorial view of the forming of the denture mold in the flask by superimposing the stone model over the investment casting into which the teeth have been placed, root side up defining a cavity for molding of the denture with the teeth embedded therein;

Fig. 11 is a pictorial view of the mechanically assisted denture resin injection into the flask containing the denture mold;

Fig. 12 is a pictorial view of a detail of the resin injection apparatus; Fig. 13 is a pictorial view of the denture resin-filled mold within the flask;

Fig. 14 is an oblique view of the resin in the flask undergoing thermal cure in a bath; Fig. 15 is an oblique view of the unfinished denture according to the invention; and, Fig. 16 is a view like Fig. 15 of the finished denture according to the invention. Detailed Description

The method and apparatus of the invention are broadly applicable to use with any resin formed by mixing reactive components through a common mix tip, but dental requirements may limit the suitability of some resins. The preferred materials herein two-part urethane resins. As a class, two-part urethane thermosetting compositions offer advantages over acrylates as a denture material. To produce a urethane denture having overall superior characteristics to acrylics the invention preferably uses particular urethane reactants for their mechanical and thermal resistance properties, for lack of toxicity, and to ensure optimum processing characteristics. The invention further provides method and apparatus for obtaining the above broad-based properties of a commercially acceptable denture material while minimizing the notorious side-reactions of urethanes with moisture and overcoming the problems of air-encapsulation of typical casting methods. With reference now to the Figures in detail, in Fig. 1 dental impression tray 10 is filled with dental impression material 12 from a dispenser 14 to a level sufficient to take the needed impression. In Fig. 2A the filled dental impression tray 10 is fitted into the patient's mouth and after taking the impression of the gums is withdrawn. In Fig. 2B, the impression tray 10, with the set impression material 12 now conformed into the convex image 16 of the gums is used to mold the stone model 18 by spatulating stone material 20 onto the image 16 to obtain a concave image 22 of the gums in the stone model as shown in Fig. 3. In Fig. 4, the stone model 18 is used to support wax 24 generally conforming to the concavity of the model. Teeth 26 are fitted to the model 18 and retained in position by the wax 24. In Fig. 5 the flask 28 is shown to comprise an upper plate 32 having an inlet port 33, a lower plate 34, a sidewall 36 that fits between the upper and lower plates, and a retainer 36 that fits around the assembled plates and sidewall to keep all parts together in fluid tight relation.

The stone model 18 assembled with the teeth 26 and the wax 24 is placed on the lower plate. Tubing 38 is inserted into the wax 24 at the labial portion 42 of the stone model 18. In addition, tubes 44. 46 are placed in the wax at the extreme ends of the model. Tubing 38 and tubes 44, 46 are used to define passageways for purposes to appear. It may, however, be noted that the several ports 36a, 36b and 36c in sidewall 36 are arranged to register with the locations of tubing 38 and tubes 44. 46. In Fig. 6 the investment material 48, typically a silicone resin but per se forming no part of this invention, is introduced through the upper plate port 33 into the cavity 52 defined by the flask 28 and the assembled stone model 18, wax 24 and teeth 26. The resin investment material 48 cures and the result is shown at 54 in Fig. 7. The material 48 is now a negative replica 56 of the stone model 18, wax 24 and teeth 26. The stone model 18, wax 24 and teeth 26 (now separated from the stone model) are removed from the opened flask 28 and cleansed of the wax by a hot water treatment in basket 58 submerged in a bath 62, Fig. 8, or by other suitable means.

With reference to Fig. 10, the teeth 26 are inserted in the conforming voids 64 defined in the investment material 48 with their roots protruding. A release agent 66 is applied to the stone model 18 as shown in Fig. 9. The release agent coated stone model 18 is returned to the flask 28 where with the investment material 48 and teeth 26 it defines a denture molding cavity 68. Injection of the denture molding material is from a dual chamber cartridge 70 (See Fig. 12) that can be a hand operation, see U.S. Patent 4,869,400, for example, or a machine- aided operation. One type of machine is shown at 72 in Fig. 11. There hydraulic or pneumatic powered rams, not shown, or other pressure devices, activated by foot pressure on switch 74, drive the pistons 76 in chambers 78, 82 to force the reactive resin components (hereinafter described) from the chambers in precisely metered amounts through the mix tip 84 (a static mixer having a series of intersecting flights to mix, cut, mix and recut the advancing resin component mixture) and into the cavity 68. The amount and rate of filling of the reacting resin 72 is described in greater detail below, but Figs. 12 and 13 illustrate that the mix tip 84 is inserted into the cavity 68 within the assembled flask through port 36b and typically to the portion of the cavity 68 where the lingual part of the denture is to be created (Cf. Fig. 15) where the filling operation can proceed with maximum attention to the avoiding of unfilled areas, e.g. by changing the position of the mix tip within the cavity 68 during fill. The cavity 68 further includes outlet vents 86, 88 formed by tubing 44, 46 earlier, through which the denture resin 72 vents when the cavity is filled, or as preferred overfilled, as provided by having a greater inlet rate through mix tip 84 than the outlet vents 86, 88 to create and maintain a back-pressure for purposes elsewhere described herein relating to crushing air bubbles, filling all interstices within the cavity 68, and compensating for resin shrinkage during polymerization. The increase in viscosity, coupled with the increased pressure, militates against any incorporated or occluded gases being able to form a void or bubble within the reaction mass, and a void-free, bubble free denture 100 is obtained, any gas-produced voids or bubbles being too small to be detected by the eye, and thus invisible.

The fill process described is low pressure; the need to spatulate resins into the denture-defining cavity is avoided. The denture resin 72 filled cavity 68 within flask 28 is cured, in the air over a period of perhaps a day with the preferred urethane resins herein, or in hours in a hot water or other bath, as shown in Fig. 14. The molded denture resin 70 is removed after cure and appears as an unfinished denture 90 as shown in Fig. 15. The sprue 92 and any other imperfections are buffed away and the resin is polished as needed, although the preferred urethane resins herein are often satisfactory as molded without buffing to polish, to obtain the finished denture 100 firmly supporting teeth 26.

With further reference to the invention, certain other details will be explicated. The typical process for removing the wax from the stone model is to expose the stone to hot our boiling water until the wax is finally fully melted and desorbed from the cervical areas of the teeth. This process loads the stone with a substantial amount of water. Although the stone can be tamped dry of its moisture, it cannot be oven dried to such an extent that it no longer creates a moisture side-reaction with urethane casting materials if these are to be used as the denture resin. Therefore, the urethane is itself desirably made resistant to the moisture-side reactions that may create porosity on the casting surface. A combination of three steps has been found effective to achieving a perfect denture. First, the urethane composition is at substantially high viscosity before it is injected into the flask and before it contacts the moisture-laden stone. In the invention low-pressure injection process where two low viscosity liquids are dispensed from the side-by-side chambers in the cartridge, the liquids convert to high viscosity, preferably within the mixer tip. A urethane composition is selected which achieves a high viscosity within the mixer tip having typically up to 24 mixer elements. While being expressed into the cavity it will have achieved a mix viscosity sufficient to resist approximately 99% of its moisture side reaction capability.

Still, the moisture side-reaction condition may not thus be sufficiently retarded to make a 100% porosity-free casting against the stone surface. Therefore, and second, a thermosetting composition of some type is used as a barrier coat. The thermosetting composition can be a two- part composition or a 1-part composition. Two-part compositions are advantageous over 1-part compositions in that they can be cured within 15 to 30 minutes and will not to delay the manufacturing process. A two-part polymer barrier coat is applied to the stone model and cured. The barrier coat can be a two-part silicone, two-part silane, two-part urethane, two-part epoxy, two-part polyester, two-part acrylate or other thermosetting composition. A two-part urethane composition having a high hydrophobic content works well as a barrier coat. Silicones also work well.

One-part compositions are 1-part silicone sealants, 1-part urethane sealants, 1-part poly vinyl acetate or polyvinyl acetate/alcohol compositions such as Elmer's glue.

In addition to the barrier coat, a release agent is desired. The release agent applied in a third step serves as an additional moisture barrier and also provides the easy releasability of the denture casting from the stone model and substantially improves the aesthetics while reducing the polishing time.

The invention includes eliminating bubbles in the denture by creating a threshold of viscosity along with some minimum internal pressure. It is the combination of internal pressure and viscosity that allows the fluid to occlude air bubbles and sweeps them through the vent. A sufficient viscosity is chemically achieved by increasing the viscosity within the mixer tip by up to approximately a magnitude or more, i.e. up to 10 times, from about 2000 to 10,000 - 20,000 centipoises in each component or side or greater, and then creating an internal pressure by restricting the size of the vent in relationship to the inlet or entry port. Starting with low viscosity components and increasing the viscosity within the mixer tip by a magnitude or more allows the injection process to be low pressure yet achieves the ultimate purpose of removing entrapped air or stopping the moisture side-reaction from creating surface porosity. The internal pressure is raised to a necessary level by the natural flow rate of the casting mixture as it is pneumatically expressed into the mold cavity, e.g. from 1 to 40 psi over atmospheric, or preferably up to about 15 psi. over atmospheric, or two atmospheres. A pressure rise occurs because the sprue or inlet passageway is larger than the outlet or vent opening, in cross section, generally, and more specifically in flow rate permitted through the respective openings. For example, an inlet of 1/8 to 3/8 inch and a smaller outlet or vent of 1/16 to % inch, respectively. This pattern of larger inlet and smaller vent sizes allows sufficient flow for filling the mold cavity within the working time of the liquid or fluid reactive resin mixture yet creates sufficient resistance to flow within the cavity to force the high viscosity liquid to penetrate the air pockets, break them into small bubbles and carry them in the stream to the vent. Perfectly bubble-free castings can be made time-after-time with perfect void-free surfaces with a combination of elevated viscosity, e.g. up to about 25,000 centipoises and the increased internal pressure. The pressure should be maintained and increased over the 30 to 60 second fill time of the mold cavity, and not allowed to drop. Sweeping fingers of material flowing between the interstices of the teeth will allow entrapment of air at the leading edges of these streams and bubbles to remain entrapped on the surface of the denture casting if the pressure is not maintained to break the bubbles arising from the entrapment.

Natural forces cause shrinkage to occur as isocyanate monomers and prepolymers react with the base materials in the composition. In the process, each molecule's inter-molecular distance is reduced to an inter-atomic distance as each bond is formed. This bond can be a chain-adduction or cross-linking. Without any compensation, the casting will contract away from the sides of the mold cavity as these microscopic bond length reductions create shrinkage on the macroscopic scale. However, the invention low pressure injection system, where the pressures can range from as low as 1 psi to 25 psi up to 40 psi where the mold and stone materials will resist effects of the increased pressure, provides a compensating factor to alleviate or eliminate shrinkage and naturally induce the casting to remain conformed to the cavity walls during cure. Shrinkage occurs at the air-cure surface in the sprue or vent.

The morphological structure of the urethane casting material is advantageous in a denture. A denture must be resistant to deformational forces of the mouth and jaw during chewing and from chemical forces of destruction of the mouth environment. A critical factor for ensuring the use and longevity of the denture is the ability of the denture structure to resist deformation under heat. Usually the upper limit of human tolerance is somewhere around 150°F.

In formulating the preferred dentures of the invention, urethane compositions are desirably selected leading to a particular morphological structure for achieving a high modulus, rigidity and resistance to deformation at the extreme temperatures sometimes found in the mouth. The construction of the structure will take into consideration the limitations of certain monomers, oligomers and prepolymer starting materials because of their immediate leaching effects and. particularly, because of their latent toxicological properties after degradation of the denture and potential leaching of breakdown materials in the mouth environment and body. Given these potential concerns, the selection of isocyanates, polyols and amine-functional materials will be limited to those materials that are safe within the mouth environment. Part A Denture Component

The selection of aromatic isocyanates is preferred over aliphatic isocyanates because they offer essentially benign oral, respiratory and dermatological properties when converted into their respective end-product urethanes. The benign properties of fully cured urethanes derive from the parent aromatic isocyanate. Aromatic isocyanates can be assured of forming urea, urethane, allophanate or substituted urea linkages that are benign materials. These benign properties are a function of being easily and fully polymerized even in less than perfect mixing and curing conditions.

Diphenyl methane diisocyanates, as a subgroup group of the larger class of aromatic isocyanates, are preferable over other classes of aromatic isocyanates such as toluene diisocyanates and naphthalene diisocyanates as distinguishing groups. Diphenylmethane diisocyanates, as a group, offer a combination low vapor pressure during processing of the denture and low residual toxicity when converted to the final urethane product.

On the other hand aliphatic isocyanates, which might be preferable because of other properties, can remain in a semi-cured or un-cured condition when reacted with polyols and even when reacted with amines or other active hydrogen groups. Therefore, laboratory preparation of polyurethanes or polyureas from aliphatic isocyanates becomes more problematical from the toxicity standpoint in the mouth.

Therefore, in formulating a thermosetting polyurethane for use in the mouth as a denture, it is be preferable to select diphenylmethane diisocyanate monomer and prepolymers for the Side A or Part A component. Aliphatic isocyanates can be used, however, provided an efficient curing method is followed. Hardness of Denture Materials:

Diphenylmethane diisocyanates can produce hard materials on the order of 60 to 90 Shore D hardness when reacted with hydroxyl-functional, amine-functional or other active hydrogen functional oligomers by formulating with a high concentration of isocyanate monomers or polymeric monomers (polymerics) or monomers in a quasi-prepolymer or full prepolymer composition to produce a sufficiently high concentration of urethane or urea connecting groups within the cured polymer chain. A high level of isocyanate in the Side A or Part A component is effective because it is the urethane or urea group, in association with its attached aromatic urethane substituent, which is a primary contributor to hardness of the final material. This high level of isocyanate (measured as NCO) is desirably in the range of from 5 to 30 percent of the overall Part A/Part B material and is usually contained within the Part A component. The NCO, or isocyanato reagent, however, can also be partially contained within the Part B component as a pre-reacted polyurethane or polyurea adduct which is hydroxyl-terminated or amine-terminated. Fully-Reacted Active Hydrogens in the Final Casting

Also important to the longevity of the denture is to formulate with a sufficient number of isocyanate groups to react with all of the active hydrogen groups of the Part B component so that the number of chemical equivalents of isocyanates are at least equal (stoichiometric) to the total number of equivalents of active hydrogen groups or even exceeding the total number of active hydrogen group by perhaps 5 to 10 percent. The first purpose of providing at least a stoichiometric amount of isocyanate in the denture material is that any excess of active hydrogen groups will be prone to being degraded by moisture, a conditions which might tended to reduce stability in the mouth environment. Secondly, formulating to exact stoichiometric equivalency of active hydrogen groups can allow some active hydrogen groups to remain unreacted at the microscopic level just because of statistical variation and mixing inefficiency. Formulating with the isocyanate equivalents at 5 to 10 percent in excess of the active hydrogen equivalents provides some better assurance that essentially all of the active hydrogen groups are going to be reacted with isocyanates to produce urethane or urea connecting groups.

It is the nature of isocyanate reactants that if they are in chemical-equivalent excess to active hydrogen groups of the initial reactants, the reaction products themselves, urethanes and ureas, will contain active hydrogen groups which are also reactive to a lesser, yet sufficient, extent to produce strong enough bonds of allophanates and substituted ureas, respectively. These branched groups are less prone to degradation in water environments than hydroxyl or amine groups and produce an extra measure of chemical stability. Withstanding Deformation. Particularly in a Heat Environment

Polyureas have better heat stability than polyurethanes. The extra heat stability found in urea structures is derived from a nitrogen residing in the position adjacent to the isocyanate monomer, oligomer or polymer (RNCO), once it is reacted, where an oxygen group is attached to the RNCO of a corresponding urethane structure. The placement of nitrogen atoms in urea structure provides two advantages over an oxygen atom of urethane structure. Thus, the nitrogen is capable of producing more electron withdrawing on the carbamide carbonyl group, so that the urea structure is more polarized. The polarized, substituted urea bonds are less capable of internal bond rotation than corresponding urethane structures under deformation loads, particularly when at an elevated temperature. Also, the urea structure, being polarized, is more capable of producing hydrogen bonding, particularly with neighboring urea groups. The accumulation of hydrogen bonds among the urea groups in high concentration adds considerable secondary forces to the overall morphological structure creating a stronger, tougher structure and having greater resistance to deformation, particularly under elevated temperature conditions. Part B Denture Component

For producing heat-stable polyurea materials an aromatic amine might typically be selected for reaction with the diphenyl methane diisocyanate Part A composition. Aromatic substituted urea moieties are known for producing strong, tough and heat-stable urea materials. It is, however, out of the question to select any aromatic amine for use in the mouth unless its toxicological properties are fully understood and found to be benign.

Alternatively, aliphatic amines having amine functionality that would contribute to heat stability can be chosen. However, aliphatic amines are extremely fast-reacting with diphenylmethane diisocyanates and difficult to incorporate into the final composition at a sufficiently high concentration to be effective for providing heat stability. Also, the toxicity of aliphatic amines is of a concern, and a full knowledge of any selection of materials in this group would also require considerable study before being used in the mouth as a denture material. In lieu of these amines, hydroxyl-functional polyols reactants that are less desirable from the heat stability standpoint, can be used, such as the primary or secondary hydroxyl-functional polyols having an equivalent weight as low as 20 daltons up to 10,000 daltons. The functionality can be from 1 to 20, but polyols with a functionality of 3 produce both chain extension and cross-linking while also having low viscosity and being easily processable. The selection of polyols can be within a class of poly ethers, hydroxyl-functional, amine-function, amide-functional, active-hydrogen functional polyesters (derived from organic acids or dimer acids), castor oils, and other compounds that are non-hydroxyl-bearing but having similar reactivity properties thereto, such ureas, urethanes, cyclic urethanes, oxazoles, oxazolidones, oxazolidinones, amides, imides, imines and the like. Regarding the selection of polyols based on functionality, it is desirable to select a polyol having a high functionality if the sole purpose is to have a denture which resists deformation under load. However, highly functional polyols, oligomers or resins, by their nature of being branched, have high viscosities. Processing is also an important consideration, so some compromise is necessary between formulating with highly functional polyols for deformation resistance and a low functional polyols for easy mixing.

The selection of essentially hydrophobic materials is also a benefit for developing a Part A component/Part B component mixture that is less prone to moisture side-reactions and produces a denture material having resistance to moisture-caused degradation in the mouth.

Although polyester-based polyols might otherwise be desirable for the preparation of high strength dentures, the polyester materials can have the drawback of being prone to hydrolysis in moisture conditions. In the invention denture system, polyether polyols provide the best combination of low viscosity, reactivity, cure rate, hardness, toughness and chemical resistance, and are preferred.

Structure Limitations

The selection of certain polyether polyols produces urethane polymer backbone structure and secondary structure that are prone to deformation and heat softening. What is obtained is a denture structure which lacks a particularly necessary characteristic for good performance in the mouth — that is, resistance to deformation in a warm or hot environment.

The most severe type of environment for urethane compositions in the mouth is warm drinks in the temperature range from 120 °F to 150 °F intermittently. Under these conditions, heat softening of the compositions can be encountered, particularly if followed by chewing on warm or hot foods. This has been a limitation on some acrylate-based dentures, as well.

Polyether polyols include poly oxy-ethylene oxide ether polyols, poly tetramethylene oxide polyols and poly oxy alkylene oxide ether polyols. Among these the poly oxy alkylene oxide ether polyols are preferred as they contain pendent alkyl groups within each alkylene oxide group. Since the alkyl group provides some bulkiness, it will want to reside in a skewed position with respect to the adjacent bulky methylene group (within the chain as seen with Newman projections) of the polymer. This skewed conformational relationship causes the carbon atoms in the chain to twist, forcing the chain into a randomly helicized structure with a clockwise or counter-clockwise twist. The randomly helicized structure is capable of being deformed until it is finally stretched to its full pleated sheet form. The fact that there are many residual conformations available for deformation allows this family of polyethers to contribute strongly to the deformation of the polymer chain, once such forces are introduced. Preferably, herein poly oxy-propylene oxide ethers are selected from the family of polyoxy alkylene oxide ether polyols because the methyl group of the propylene moiety provides enough bulk to create sufficient hydrophobic properties. Selecting more bulky pendent groups can produce wasted side chain bulk resulting only in more secondary forces and less primary forces associated with chain extension and cross-linking.

Heat Stability

Heat stability is in dentures is a combination of properties:

1. Having a sufficiently high glass transition temperature so that the denture material exists in its glassy state within the major range of temperature conditions in the mouth.

2. If the denture material undergoes a transformation to its rubbery state while undergoing an extreme temperature excursion in the mouth, the rubbery properties of the denture will still provide sufficiently high elastic modulus to resist distortion and deformation under chewing loads. 3. The denture material should have a low hysteresis if it is temporarily deformed, even at higher temperature conditions of the mouth. Glass Transition

The essentially monophasic mass of denture material in its glassy state will undergo a radical softening if it reaches its glass transition temperature upon heating. At this temperature, the mass of denture material will make a transition to a rubbery state. The glass transition can act as if it is a secondary thermodynamic parameter, but it also has a time dependence not characteristic of a thermodynamic parameter. While the material undergoes this transition, besides softening, it undergoes other physical property changes such as changes in density, heat capacity and coefficient of expansion. These properties can be a measure of glass transition temperature. Although this transition is not well understood from the structural standpoint, it is generally associated with the ability of bonds being heated to a temperature where internal bond vibrations allow "barriers to rotation" to be overcome — producing many more new conformational states. Such randomized states are available when the body of the material resides in some meta-stable ordered state, upon deformation. The rubbery character (bounce back) of the polymer is derived from the many more statistically random states that are available, once the deformation force is removed. High Modulus of Elasticity in the Rubbery State

Assume that the denture material has made the undesirable transition into its rubbery state. When this occurs, it is essential that the rubbery polymer still have resistance to deformation. This resistance to deformation can be measured as the modulus of elasticity of its rubbery state. The modulus of elasticity in its rubbery state can be increased by providing certain structural restrictions to bond rotation. Reduction in Hysteresis

It is desirable to reduce the hysteresis of the rubbery mass once it is being deformed. The reduction of hysteresis is associated with returning the mechanical energy to the surroundings once it has been imparted to the denture mass. This characteristic is optimized in the preferred denture composition. Urethane Structure Having Stability to Deformation Under Elevated Heat Conditions:

Without resorting to the use for dentures of urea materials that have problematical toxicological side-effects, in accordance with the invention it has been found that a particular group of tertiary amines defined herein (see Formula 1), can be incorporated into the backbone of the polymer structure of the Side B or Part B component, allowing the polymer structure to have hydroxyl functionality rather than amine functionality, and producing a polyurethane denture material instead of a polyurea denture material. After reacting the Part A and Part B components, a urethane denture material is obtained having exceptional resistance to deformation, particularly under elevated heat conditions. In this way the helicized poly oxy- propylene oxide ether groups and tetrahedral structure (from tetrafunctional carbon such as from pentaerythritol-based polyols or multi-functional carbon such as from sorbitol- or sucrose-based polyols) are supplanted by hydroxyl-functional tertiary amines.

There are limits to use of these tertiary amine structures in order to: 1. Keep the total number of equivalents in the Part B component below the number of equivalents of diphenylmethane diisocyanate from the Part A component; and.

2. Maintain the level on any selected tertiary amine polyols sufficiently low- based on its viscosity contribution. Tertiary amine structures in the invention denture composition produce pyramidal structures within the polymer backbone. There are two particular advantages of pyramidal structure:

1. The pyramidal structure itself creates resistance to conformational changes from the forces of deformation. The pyramidal structure is tri-functional and, therefore, cross-linked to other polymer structure.

That is, in order for this structure to conform to an imposed deformation, it must "envelope'^" or "oil-can^*', that is turn inside-out to take on its mirror image. This conformational change requires considerable energy and, thus, the polymer resists deformation. 2. The lone pairs of these tertian' nitrogens create hydrogen bonding. The hydrogen bond is itself a weak secondary bond, but the accumulation of these weak bonds into the polymer backbone provides extra strength, extra resistance to deformation and extra resistance to deformation at elevated temperature conditions. Comparison of Pyramidal Structure of Tertiary Amine Polyols to Helicized Structure of Polyether Polyols

Using Newman projections, in an end-on view along the axis of the carbon-oxygen bond of the polyether polyol chain, it is seen that the one methylene group attached and adjacent to the polyether polyol ether oxygen provides only a partial anchor to oxygen substituent. Consequently, a deformational force can cause both displacement and rotation to the oxygen group when applied. The lack of anchoring of the oxygen groups translates into substantial lack of resistance to deformation from an applied deformational forces.

Similarly, in an end-on view along the axis of the carbon-nitrogen bond of the tertiary amine polyol chain, it is seen that the two methylene groups attached and adjacent to the tertiary amine groups, which are themselves attached to atoms in the polyol chain, provide two anchors to the amine group. Therefore, the amine group will resist both rotation and displacement from its position when deformed. The anchoring of the chains through each tertiary amine group provides substantial anchoring of the polymer due to deformation. The tertiary amine lone electron pair can also provide resistance to deformation upon being displaced. Since hydrogen bonds are readily broken and reformed, the secondary forces of hydrogen bonding contribute to the resistance of deformation as each bond is reformed.

Oxygen, having a 108-degree bond angle and no side substituents, is prone to "buckling." Its lack of resistance to deformation (conversely its tendency to buckle) is seen looking along the axis of the polyether polyol chain. A force exerted from the side of the chain (impinging into the page on oxygen) will cause the oxygen ether bond to buckle around the attached adjacent carbons. Buckling can occur even though the carbon centers do not have to be displaced and they are only slight torqued or deformed from their original orientations. Again, the summation of these deformation processes at ether bonds can result in an overall substantial macroscopic deformation from an outside force. Polyether Polyol Carbon-Nitrogen Bonds of the Chain:

Primary structure can be achieve by placing a tertiary nitrogen into the chain to prevent buckling. If an impinging force is placed on nitrogen (into the page on nitrogen), the pyramidal structure imposed within the chain structure cannot buckle. It is extremely resistant to deformation, and only under extreme force, would it deform the only way that it could which is to "oil-can" — that is, turn inside out and become deformed into its mirror image.

Although the relationship of tertiary amine structure (contained within the polyol chain) to the glass transition temperature is less well understood, the lack of mobility that the tertiary amine structure imparts to the polymer chain increases the glass transition temperature. An increase of modulus would also be expected if any transition to the rubbery state in encountered. Secondary Hydrogen Bonding Forces to Primary Structure:

The pyramidal structure of aliphatic tertiary amines contains an electron pair within each nitrogen group in the chain that is capable of producing a hydrogen bond with associated chain structure. Although the hydrogen bond itself is not particularly strong (having on the order of 5 kcals per mole of activation energy toward bond breaking), its high concentration can have a substantial effect on the overall stability of the denture material because of its high concentration in the denture mass. To elaborate, primary urethane structure (chain extension and cross-linking) is derived from the reaction of isocyanates with hydroxyl groups of polyols. Primary reactions are the primary means of creating polymerization and solidification of the liquid/liquid mixture into a solid mass. But once that mass is formed, its resistance to heat and deformation is improved by having pre-planned the secondary structure to create a high concentration of secondary forces. These forces are derived mainly from hydrogen bonding but can also be derived from ion-ion forces, ion-dipole forces, dipole-dipole forces and even from van der Walls forces. The more secondary forces imparted to the structure, the more likely the glass transition temperature will be increased and the more likely the flex modulus of the rubbery polymer will be increased if rubberiness is induced by external forces or heating. Reaction Rates

The reaction rate of the resin precursors is necessarily critically timed in this invention. Too fast a rate will produce a resin without filling the cavity. Too slow a rate of reaction will allow voids and bubbles to remain at a visible size as there will not be sufficient pressure from differential flow rates at inlet and outlet, and not sufficient increase in viscosity to block bubble formation by any entrapped air or gases.

Accordingly the chemistry of the resin precursors and the mechanics of the delivery system are correlated to provide full cavity fill, resin reaction mixture self-pressurization, and no voids visible in the denture product. This is accomplished by progressively increasing the viscosity of the resin reaction mixture in the mold cavity over a period of time that can be called Tl, the dwell time of the mixed resin precursors in the mold cavity, and driving air from the cavity by adding increasing amounts of resin to the cavity over the Tl period. In addition, a second timing relation is used. The resin reactive mixture is maintained flowable over a period of time T2, the fill time for the mold cavity is T3, and the period T2 is greater than T3. Therefore, the flowability of the resin reaction mixture continues past the time to fill the mold cavity.

A further benefit of the invention is the compensation for normal shrinkage in the resin mass as intermolecular distances change to interatomic distances with reaction and cure. A surplus of resin reactants in the cavity not only pressurizes the cavity contents but supplies added reactants to keep the cavity full in the face of reaction-induced shrinkage.

In addition the reactants in their cartridges are formulated to avoid shrink-back if pressure is let up to avoid sucking in air, as by the use of fumed silicas and like viscosity adjuvants. Example 1 :

A quasi-prepolymer solution was prepared where 94.4 grams of diphenyl methane diisocyanate (Isonate 2143-L from Dow Chemical Company) was added to a mixing vessel, and 5.66 grams of a 150 equivalent molecular weight polyol (Multranol 4012 from Mobay Chemical Company) was added. The mixture was stirred and the solution was heated to 150 to 170 °F for 30 minutes. While heating, 1.00 grams of fumed silica (CABOSIL TS-530 from Cabot Corporation) was added along with 0.1 grams of flow control agent (Fluorad FC430 from 3M Company). The mixture was then vacuumed at a reduced pressure of 5 mm or less until all bubbling stopped. This composition was then packaged into one cavity of a 6-fluid-ounce dual cartridge (PEC Duramix 6-ounce type). The cartridge was sealed by inserting a piston and all entrapped air was expelled.

A polyol solution was prepared in a suitable vessel where there was added 81.9 grams of a 150 equivalent weight polyol (Multranol 4012 from Mobay Chemical Company). Then 18.1 grams of ethylene diamine tetrapropoxylate (Quadrol from BASF Wyandotte Division) was added and blended in. A color concentrate was added at 1.0 grams, a fumed silica (Aerosil R- 972 from Degussa) was added at 0.76 grams, a fumed silica (CABOSIL TS-530) was added at 0.76 grams, 1/8 -inch red fibers were added at 0.30 grams, a flow control agent (Fluorad FC430 from 3M Company) was added at 0.02 grams and a defoaming agent (DEE FO G/O) was added at 0.01 percent by weight. This blend was heated with to 212 °F and vacuumed at a reduced pressure of less than 5 millimeters of mercury until bubbling stopped. The mixture was cooled down and packaged into the other side of the dual cartridge. The two sides of the cartridge were equalized.

The flask and cavity were prepared using a lost wax process. The stone model was waxed with a paraffin wax solution to create a release. The paraffin wax solution having the following composition was prepared from supersaturated solution of paraffin wax in 100 part of mineral spirits. 0.1 parts of defoamer Dee Fo G/O ( Ultra Additives, Inc.), 0.1 part of surfactant of Fluorad FC 430 (3M). Then to this mixture of 100 parts there was added 15.00 part of Red Base Plate Wax (Cadco Dental Products). The 15 parts of wax was completely dissolved in solution by heating to 50 degrees C, the filtered hot through stainless mesh of 300 mesh. Then material was kept in a container at roughly 30 degrees C and maintained at 30 degrees C to keep the wax melted. The solution was then sprayed onto the stone and briefly dried in the fume hood for 15 minutes. This step was repeated once more. A heat lamp was also used for drying. The stone is placed in the mold, and the casing and metal plate is affixed and clamped.

A low modulus dental silicone was used as the investment material. The mold surface and the surfaces of the teeth were cleaned thoroughly of all residues using isopropyl alcohol. An entry port into and a reduced size exit port from the molding cavity was established.

The dual cartridge was placed in a dispenser and the blind end tip cut off to allow injection of the Part A/Part B components from their chambers into the molding cavity. As the blind end is cut off, the mixture, formulated with silica as noted above does not suck back into the cartridge to create a bubble. This is important because that bubble can be come critically entrapped in the mixture. The levels of fumed silica in the Part A and Part B components were adjusted to provide this feature and the prevention of suck-back of the liquid is expressly prevented by use of the silica in both Part A and Part B of the composition. A Duramix 4901 static mixer (having a '/4-inch diameter and 22-elements in line) was selected and attached to the dispenser using a bayonet '/.-twist. Upon squeezing the trigger of the dispenser, a slight amount of both Part A and Part B components was dispensed onto a pad to ensure the delivery was proper and discarded. Upon squeeze of the trigger again, the liquid materials traversed the mixer tip entirely bubble free and fully mixed. With the mold tilted at approximately 45 degrees and with teeth facing downward, the Duramix mixer tip was inserted into the inlet port of the flask approximately 1 inch inside, and gradually withdrawn as the trigger was squeezed and as material filled the flask. The mixture entered the cavity and flowed along one side of the void to the bottom and then exited the top of the mold and finally exited the port. The time allowed for filling was approximately 45 seconds. During the filling process, the mixture achieved additional viscosity in the mold and in the vent stem. The material gelled and was allowed to stand for 15 minutes at room temperature. The casting was placed in a 200°F oven and cured for 15 minutes.

After 15 minutes, the denture casting was sufficiently cured for the mold to be removed from the oven. The mold was cooled to room temperature for one hour. The mold was then separated from the denture. Upon separation, the denture was removed from the stone model and the denture was extracted from the silicone mold. The stone model was broken away from the casting. Substantial porosity resulted on the denture casting where it was contiguous to the stone surface. The denture was then inspected for having sufficient bonding to the teeth by pressing first against the incisors with the fingertips. The casting had a full fill around the base of the teeth. Some teeth popped away from the cast material. It was found that some teeth had adequate adhesion and some teeth did not. An evaluation of the denture casting shows that the mixture apparently had a tendency to roll rather than to flow as it was poured into the entry port. The process of rolling incorporated bubbles that appeared within the casting. It appeared that there was considerable entrapment of air around the base of the teeth. It also appeared that some other process than simply pouring-in-place would be necessary to eliminate incorporated air. Having selected the reaction materials from as class of diphenyl methane diisocyanates, hydroxyl-functional tertiary amines and polyols of Example 1, which provided excellent physical properties. The next consideration was to develop a process which achieved the following: 1) Provide for the structural bonding of the teeth; 2) Control the moisture side-reaction; 3) Eliminate the voids at the surface of the denture which were emanating from entrapped air; 4) Create dimensional stability for replication; and 5) Create a life-like denture which has a good fit, good feel and good aesthetics.

Example 2:

The denture formula and process of Example 1 was used with the following exception: This time, the acrylic teeth were brushed with a methyl methacrylate solution using a soft paintbrush. The solution was allowed to dry for 30 minutes and the mold assembled as in Example 1. The other preparative steps of Example 1 were followed and the casting was repeated. This time, the urethane mixture adhered thoroughly against the acrylic teeth. The casting had the remaining flaws of severe porosity from moisture side reaction, severe voids from air entrapment, and less than perfect fit. The fibers were also irregularly distributed.

Example 3 :

The manual system was changed to a pneumatic system. A Duramix 6-ounce dual dispenser was used in lieu of the 4900 Manual dispenser to dispense the same formula of Example 2 and using the tooth-preparation procedures and other procedures of Example 2.

The casting was improved only in the disbursement of fibers. The fibers were arranged within the casting in a life-like random distribution. Example 4:

The casting formula of Example 3 was used and the casting was processed as in Example 3. However, instead of using a 200 F oven, the flask was submersed in a 160 F water bath for 30 minutes. After removing the casting, it appeared that this curing process was easily tolerated by the casting. The casting re-fit the stone model.

Example 5 :

A quasi-prepolymer solution was prepared wherein 94.4 grams of diphenyl methane diisocyanate (Isonate 2143-L from Dow Chemical Company) was added to a mixing vessel, and 5.66 grams of a 150 equivalent molecular weight polyol (Multranol 4012 from Mobay Chemical Company) was added. The mixture was stirred and the solution was heated to 150 to 170 °F for 30 minutes. While heating, a fumed silica, 4.00 grams of CABOSIL TS-530 was added along with 0.1 grams flow control agent, Fluorad FC430. The mixture was then vacuumed at a reduced pressure of 5 mm or less until all bubbling stopped. This composition was then packaged into one cavity of a 6-fluid-ounce dual cartridge (PEC Duramix 6-ounce type). The cartridge was sealed by inserting a piston and all entrapped air was expelled.

A polyol solution was prepared in a suitable vessel where there was added 81.9 grams of a 150 equivalent weight polyol (Multranol 4012 from Mobay Chemical Company). Then 15.0 grams of ethylene diamine tetrapropoxylate (Quadrol from BASF Wyandotte Division) was added and blended in. Then m-xylene diamine (from Mitsubishi Chemical Company) was added at 2.5 %. A color concentrate was added at 1.4 grams, a fumed silica (Aerosil R-972 from Degussa) was added at 1.14 grams, a fumed silica (CABOSIL TS530 from Cabot Corporation) was added at 0.38 grams, 1/8 -inch red fibers were added at 0.40 grams, a flow control agent (Fluorad FC430 from 3M Company) was added at 0.2 grams and a defoaming agent (DEE FO G/O. Ultra Additives, Inc.), was added at 0.01, and bismuth naphthenate catalyst (Coscat 83 from Cosan Chemical) was added at 0.1 percent by weight. This blend was heated with to 212 °F and vacuumed at a reduced pressure of less than 5 millimeters of mercury until bubbling stopped. The mixture was cooled down and packaged into the other side of the dual cartridge. The two sides of the cartridge were equalized. A mixer tip was attached to the cartridge. The 6-ounce cartridge was placed in a Duramix 4901 pneumatic dispenser. The flask and cavity were prepared using a lost wax process. The stone model was waxed with a paraffin wax to create a release. A low modulus dental silicone was used as the investment material. A sprue and vent the same diameter as the entry port was prepared and the exit port was established the same elevation as the entry port. Trigger was pneumatically squeezed and the liquids were mixed and dispensed into the cavity within 45 seconds until material existed the vent. The material gelled and was allowed to stand for 15 minutes at room temperature. The casting was placed in a 160 °F water bath for and cured for 30 minutes.

Upon removal from the oven the silicone investment material was removed from the casting. The stone model was broken away from the casting. Most of the porosity was removed from the casting where it contacted the dental stone. A substantial amount of the entrapped air was reduced from the casting. The acrylic teeth were not broken away from the denture casting.

The fibers were aesthetically distributed in the casting.

An evaluation the denture casting showed that the viscosity-building mixture apparently had a substantially reduced tendency to roll rather than to flow as it was poured into the entry port. The process of flowing rather than rolling reduced the air entrapment and incorporated bubbles that appeared within the casting. It appeared that there was considerably less entrapment of air around the base of the teeth. It also appeared that improvements needed to be made to reduce all of the moisture side-reaction and air entrapment.

Example 6:

The casting formula of Example 4 was used. The flask and cavity were prepared as in Example 4. However, the sprue passageway and vent port were cut to a 1/8 diameter.

Trigger was pneumatically squeezed and the liquids were mixed and dispensed into the cavity within 45 seconds until material existed the vent. The material gelled and allowed to stand for 15 minutes at room temperature. The casting was placed in a 200 °F oven and cured for 60 minutes.

Upon removal from the oven the silicone investment material was removed from the casting. The stone model was broken away from the casting. All of the entrapped air was removed from the casting. Most of the porosity was removed from the casting where it contacted the dental stone. The acrylic teeth were not broken away from the denture casting. The fibers were aesthetically distributed in the casting. It also appeared that improvements needed to be made to reduce all of the moisture side-reaction and air entrapment.

Example 7:

The casting formula of Example 6 was used. The flask and cavity were prepared as in Example 6. The stone was boiled, as before, and allowed to be tamped dry as it cooled. A two- part solution of a hydrophobic urethane was prepared as follows:

Barrier Coating, Part A, Step 1 : 28.00 grams of methylenedicyclohexane-4,4'-diisocyanate were placed into a vessel, followed by 62.00 grams of 2400 MW, di-functional, hydroxyl- terminated polybutadiene resin (R45HT, Elf Atochem). Both materials were mixed and heated to 310° F (154.4° C) for 1 hour to make a quasi-prepolymer.

Step 2: Once the Step 1 pre-polymer reaction was completed and the prepolymer cooled to room temperature, 10.00 grams of methylenedicyclohexane-4,4' -diisocyanate (Desmodur W, Mobay Chemical), and 1.00 grams of A187 silane (Union Carbide) were added. The mixture was blended thoroughly and then degassed at 5mm Hg reduced pressure for approximately 15 minutes until bubbles disappeared. The resulting polymer Part A was packaged in a container. Then 10 grams were placed in a vessel and diluted with methylene chloride. The mixture was placed in a dropper bottle.

Barrier Coating. Part B. Step 1 : 83.00 grams of 2800 MW, di-functional, hydroxyl-terminated polybutadiene resin (R45HT, Elf Atochem, North America) were weighed into a cup, followed by 15.0 grams of diethyltoluene diamine (Ethacure 100, Ethyl Corporation), 0.200 grams of Fluorad FC430 (3M Company) and 0.125 grams of Coscat 83 (Cosan Chemical). The mixture was mixed and heated at 212 degrees F (100° C) for 15 minutes to de- water the system, degassed at 5 mm Hg reduced pressure until bubbles disappeared and packaged in a container. Then 10 grams were placed in a vessel and diluted with methylene chloride. The mixture was placed in a dropper bottle.

The dropper bottle material of Part A was drawn into the dropper and dispensed in to a cup. The dropper bottle material of Part B was equally drawn into the dropper and dispensed into the cup. A short aired brush was used the mix the two material together and then the mixture was painted onto the stone model. All of the surfaces were carefully covered and then the stone was placed under an incandescent lamp for 15 minutes to cure. The cure polymer served as a barrier coating. After curing, a solution of paraffin wax was applied to the barrier coating and that solution was dried for 15 minutes under the incandescent lamp. The flask was assembled.

The casing material was processed as in previous examples. Upon removal from the oven the silicone investment material was removed from the casting. The stone model was broken away from the casting. Nearly all of the porosity was removed from the casting where it contacted the dental stone. All of the entrapped air was removed from the casting. The acrylic teeth were not broken away from the denture casting. The fibers were aesthetically distributed in the casting. It appeared that a slight improvement needed to be made to reduce all of the moisture side-reaction and air entrapment.

Example 8:

The casting formula of Example 6 was used. The flask and cavity were prepared as in Example 6 including the application of a barrier coat. However, instead of using a wax solution as in Example 6, a surfactant solution was used as a release agent. The surfactant solution was applied to the stone model and allowed to dry after application for 15 minutes under the incandescent lamp.

Trigger was pneumatically squeezed and the liquids were mixed and dispensed into the cavity within 45 seconds until material existed the vent. The material gelled and allowed to stand for 15 minutes at room temperature. The casting was placed in a 200 °F oven and cured for 60 minutes. Upon removal from the oven the silicone investment material was removed from the casting. The stone model was easily separated from the casting. All of the porosity was eliminated from the casting where it contacted the dental stone. All of the entrapped air was removed from the casting. The acrylic teeth were fully and structurally attached to the denture casting. The fibers were aesthetically distributed in the casting. The denture was of such a quality that it could have been used without polishing. The casting perfectly re-fit the stone model. It was essentially a perfect denture casting! Example 9:

Example 8 is duplicated substituting a silicone barrier resin for the urethane barrier resin of that example. The silicone was the reaction product of a vinyl silane with a silane. A good barrier coating was obtained and a perfect denture as well. Example 10:

A quasi-prepolymer solution was prepared where 94.4 grams of diphenyl methane diisocyanate (Isonate 2143-L from Dow Chemical Company) was added to a mixing vessel, and 4.0 grams of a polyol (Multranol 3901 from Mobay Chemical Company) was added. The mixture was stirred and the solution was heated to 150 to 170 °F for 30 minutes. While heating, 4.0 grams of fumed silica (CABOSIL TS-530 from Cabot Corporation) was added along with 0.1 gram of flow control agent (Fluorad FC430 from 3M Company). The mixture was then vacuumed at a reduced pressure of 5 mm or less until all bubbling stopped. This composition was then packaged into one cavity of a 6-fluid-ounce dual cartridge (PEC Duramix 6-ounce type). The cartridge was sealed by inserting a piston and all entrapped air was expelled.

A polyol solution was prepared in a suitable vessel where there was added 94 grams of a tetrafunctional polypropylene oxide adduct of pentaerythritol (Pluracol TP440) and 1.745 grams of m-xylene diamine. A color concentrate was added at 1.35 grams. A firmed silica (Aerosil R- 202 from Degussa) was added at 0.1.140 grams, and a second fumed silica (CABOSIL TS-530) was added at 0.76 grams. One-eighth-inch red fibers were added at 0.40 grams, catalyst (Coscat 83) was added at 0.10 gram along with and a flow control agent (Fluorad FC430 from 3M Company) at 0.210 grams and a defoaming agent (DEE FO G/O) at 0.01 gram. This blend was heated with to 212 °F and vacuumed at a reduced pressure of less than 5 millimeters of mercury until bubbling stopped. The mixture was cooled down and packaged into the other side of the dual cartridge. The two sides of the cartridge were equalized.

After dispensing as described in Example 1 , the denture is perfect in terms of strength and appearance. Example 11 :

A quasi-prepolymer solution was prepared where 94.4 grams of diphenyl methane diisocyanate (Isonate 2143-L from Dow Chemical Company) was added to a mixing vessel, and 4.00 grams of a 2000 equivalent molecular weight polyol (Multranol 3901 from Mobay Chemical Company) was added. The mixture was stirred and the solution was heated to 150 to 170 °F for 30 minutes. While heating, 4.00 grams of fumed silica (CABOSIL TS-530 from Cabot Corporation) was added along with 0.1 grams of flow control agent (Fluorad FC430 from 3M Company). The mixture was then vacuumed at a reduced pressure of 5 mm or less until all bubbling stopped. This composition was then packaged into one cavity of a 6-fluid-ounce dual cartridge (PEC Duramix 6-ounce type). The cartridge was sealed by inserting a piston and all entrapped air was expelled.

A polyol solution was prepared in a suitable vessel where there was added 69.9 grams of a 150 equivalent weight polyol (Multranol 4012 from Mobay Chemical Company) and 10 grams of a 2000 equivalent weight second polyol (Multranol 3901). Then 15 grams of ethylene diamine tetrapropoxylate (Quadrol from BASF Wyandotte Division) and 1.78 grams of m- xylene diamine were added and blended in. A color concentrate was added at 1.350 grams, a fumed silica (Aerosil R-202 from Degussa) at 0.76 grams, a second fumed silica (CABOSIL TS-530) at 0.76 grams, 1/8 -inch red fibers at 0.40 grams, a flow control agent (Fluorad FC430 from 3M Company) at 0.210 grams, and a defoaming agent (DEE FO G/O) at 0.01 percent by weight were all added along with catalyst (Coscat 83) at 0.060 gram. This blend was heated with to 212 °F and vacuumed at a reduced pressure of less than 5 millimeters of mercury until bubbling stopped. The mixture was cooled down and packaged into the other side of the dual cartridge. The two sides of the cartridge were equalized. After dispensing in the denture molding cavity as above described, useful dentures are realized.

The invention thus provides a nonacrylic denture forming system and novel dentures of any of numerous resin materials that are amenable to the improved manufacturing techniques disclosed herein. In particular the invention provides a system for manufacturing a denture comprising a rapidly-building-viscosity two-part resin, preferably a particular, optimum urethane resin, packaged in side-by-side dual chambers of cartridges having an affixable static mixer tip. In the invention system moisture, entrapped air and bubbles are minimized or eliminated for perfect surface finish on the denture through the use of a low pressure injection of a casting resin having the fluidity to fully contact all the contiguous areas of the mold surface and the viscosity to sweep away all air from the cavity surface which is otherwise naturally entrapped, and break down the occluded bubbles within the leading wave of the casting material. The casting resin is internally pressurized due to a reduced size vent in relationship to the entry port, and the reactive resinous mixture supplied to the molding cavity is rapidly or slowly polymerized, using as needed an external pressure and fill volume sufficient to overcome the natural shrinkage during the polymerization process to provide perfect replication of the edentulous and wax model areas, and a perfectly void-free and life-like appearance to the denture and superior physical properties through the use of the preferred urethane resin materials described.

Claims

We claim:

1. System for forming dentures comprising tooth structure and a supporting base, including: a fluid, two-component thermosetting resin supply generally closed to ambient air and pressurizable to an injection pressure, said resin supply having a mixer for mixing a resin reactive mixture from said components and an injection outlet from said mixer; a denture mold comprising a closed cavity in which said tooth structure is supported in its intended position in the denture with its roots exposed into the cavity, said mold cavity having an inlet for receiving delivery of said resin reactive mixture from said supply under said injection pressure and at a predetermined cavity filling flow rate for cure within said cavity in denture-forming relation; said resin reactive mixture tending to incorporate gases present in said cavity, and spaced from said inlet a vent adapted for venting said gases from said cavity while blocking resin reactive mixture from emptying from said cavity at greater than a predetermined cavity emptying flow rate, said cavity filling flow rate being greater than said cavity emptying flow rate, whereby said resin reactive mixture overfills said cavity and self-pressurizes to a pressure sufficient to block any incorporated gases in said resin reactive mixture from forming voids or bubbles therein during cure thereof visible in a denture comprising the resin reaction product of said resin reactive mixture cured to a solid in the shape of said mold cavity.

2. The system according to claim 1, in which said cavity comprises a wall in which said inlet and vent are formed, a tooth support structure within and surrounded by said cavity wall, said tooth support structure tending to be moisture containing, and including also coating said tooth support structure with a moisture barrier coating in advance of injection of said resin reactive mixture thereinto to block exposure of said resin reactive mixture to said tooth support structure moisture.

3. The system according to claim 2, including also selecting a thermosetting resin as said moisture barrier coating.

4. The system according to claim 3, including also selecting a two-component thermosetting urethane resin as said moisture barrier coating, mixing said components in reactive proportions, and applying the mixture to said tooth support structure in moisture barrier coating forming relation.

5. The system according to claim 3, including also selecting a two-component vinyl silane resin as said moisture barrier coating, mixing said components in reactive proportions, and applying the mixture to said tooth support structure in moisture barrier coating forming relation.

6. The system according to claim 1, in which said resin supply injection outlet comprises a nozzle, said mold cavity inlet receiving said resin reactive mixture from said supply free of entrained ambient air in said resin reactive mixture.

7. The system according to claim 1, in which said resin supply mixer comprises a static mixer adapted to mix said resin components into said resin reactive mixture in advance of said injection outlet from said mixer, said injection outlet comprising a nozzle insertable into said mold cavity inlet for delivery of said resin reactive mixture into said mold cavity free of entrained ambient air.

8. The system according to claim 1, in which said supply includes first and second chambers containing respectively first and second side precursor components of a thermosetting resin, and a source of pressure for each of said chambers including a movable member adapted to drive each chamber-contained component from its chambers to said mixer.

9. The system according to claim 8, in which said source of chamber pressure includes a pressurized fluid supply selectively coupled to said chamber movable members for moving said members in precursor component driving relation from said chambers.

10. The system according to claim 8, in which said chambers comprise cylinders having movable pistons therein as said movable members, and a supply of pressure to said pistons for expressing said precursor components from said cylinders, each of said cylinders having an outlet normally closed against ambient air, said outlets being openable for delivery of said precursor components, said precursor components further comprising a finely divided mineral filler in a viscosity increasing amount sufficient to block retreat of said precursor components farther into their cylinders upon opening said outlets in reaction to ambient air pressure causing the creation of bubbles in either precursor resin..

11. The system according to claim 10, in which said mineral filler comprises fumed silica.

12. The system according to claim 11, in which said fumed silica is present in an amount between about 0.1 and 10% by weight of the precursor component in said cylinder.

13. System for forming dentures comprising tooth structure and a supporting base, including: a fluid, two-component urethane resin supply generally closed to ambient air and pressurizable to an injection pressure, said resin supply having a mixer for mixing a resin reactive mixture from said components and an injection outlet from said mixer; a denture mold comprising a closed cavity in which said tooth structure is supported in its intended position in the denture with its roots exposed into the cavity, said mold cavity having an inlet for receiving delivery of said resin reactive mixture from said supply under said injection pressure and at a predetermined cavity filling flow rate for cure within said cavity in denture-forming relation; said resin reactive mixture tending to incorporate gases present in said cavity, and spaced from said inlet a vent adapted for venting said gases from said cavity while blocking resin reactive mixture from emptying from said cavity at greater than a predetermined cavity emptying flow rate, said cavity filling flow rate being greater than said cavity emptying flow rate, whereby said resin reactive mixture overfills said cavity and self-pressurizes to a pressure sufficient to block any incorporated gases in said resin reactive mixture from forming voids or bubbles therein during cure thereof visible in a denture comprising the resin reaction product of said resin reactive mixture cured to a solid in the shape of said mold cavity.

14. The system according to claim 13, in which said urethane resin is the reaction product of a first precursor component comprising an isocyanato reagent, a second precursor component resin moiety comprising a polyether, polyester, urea, urethane, castor oil, oxazole, oxazolidone, oxazolidinone, amide, imide, or imine moiety and a chain extender, said resin moiety and said chain extender each having separately active hydrogen, hydroxyl, amine, or amide functionality

15. The system according to claim 14, in which said second precursor component resin moiety has a active hydrogen or hydroxyl functionality and a molecular weight above about 1000.

16. The system according to claim 14, in which said second precursor component resin moiety has a molecular weight above about 5000.

17. The system according to claim 14, in which said chain extender has a molecular weight below about 500, and a functionality of at least 3.

18. The system according to claim 17, in which said chain extender has a functionality of at least 4.

19. The system according to claim 18, in which said chain extender comprises a tertiary amine having active hydrogen or hydroxyl functionality.

20. The system according to claim 19 in which said chain extender comprises a tertiary amine having the formula

R R

C - - C - - R

,R R / R R

- C - C -N

R R v

\ ^R R

C - - C - - R

R R

in which at least one R=R1 and each remaining R is Rl or R2, and: in which: Rl= -OH;

-SH;

-N(CH2CH2OH)2;

-N(CH2CH3CH2OH)2;

-N(CH2CHCH3OH)2;

R2= -H;

-Me; ΓÇó

-Alkyl;

-OAlk; -OMe;

-Halogen;

-Aryl;

-Aroyl and cyclics of the above

21. The system according to claim 20 in which said tertiary amine comprises ethylene diamine tetrapropoxylate.

22. The system according to claim 18, in which said chain extender comprises an alkylene oxide or ether adduct of a highly functional molecule.

23. The system according to claim 22, in which said highly functional molecule has a hydroxyl functionality between 4 and 12.

24. The system according to claim 23, in which said highly functional molecule comprises pentaerythritol, sugar, starch or cellulose molecules.

25. The system according to claim 24, in which said highly functional molecule comprises pentaeiythritol.

26. The system according to claim 25, in which said pentaerythritol molecule is adducted with ethylene and or propylene oxide.

27. The system according to claim 26, in which said adducted pentaerythritol molecule has a molecular weight of about 450.

28. The system according to claim 24, in which said highly functional molecule comprises a sucrose, fructose, or sorbitol molecule.

29. The system according to claim 14, in which said isocyanato reagent comprises an aliphatic isocyanate.

30. The system according to claim 29, in which said aliphatic isocyanate comprises methylenedicyclohexane-4, 4 ' -diisocyanate

31. The system according to claim 14, in which said first isocyanato reagent comprises an aromatic isocyanate.

32. The system according to claim 31, in which said aromatic isocyanate comprises diphenylmethane diisocyanate.

33. The system according to claim 32, in which said resin moiety comprises a polyether, polyester, urea, urethane, castor oil, oxazole, oxazolidone, oxazolidinone, amide, imide, or imine moiety having active hydrogen, hydroxyl, amine, or amide functionality and a molecular weight above about 5000.

34. The system according to claim 33, in which said chain extender comprises pentaerythritol molecule adducted with ethylene and/ or propylene oxide and having a molecular weight below about 500.

35. The system according to claim 33, in which said resin moiety comprises a primary or secondan' hydroxyl functional polyether polyol having an equivalent weight from about 20 to about 10.000 daltons, and a functionality of about 1 to about 20.

36. The system according to claim 35, in which said polyether polyol comprises a poly oxy-propylene oxide ether polyol.

37. The system according to claim 35, in which said polyether polyol has a functionality of from about 1 to about 3.

38. The system according to claim 35, in which said chain extender comprises ethylene diamine tetrapropoxylate.

39. The system according to claim 1, including also maintaining said supply resin components and said resin reactive mixture free of surface contact with ambient air before and during delivery thereof to said mold cavity.

40. The denture forming system according to claim 1, including also progressively increasing the viscosity of said resin reactive mixture in said mold cavity over a time period Tl, and driving air from said mold cavity by filling said mold cavity with increasing amounts of said increasing viscosity resin reactive mixture.

41. The system according to claim 1, including also maintaining said resin reactive mixture flowable over a time period T2, filling said mold cavity with said reactive mixture over a period T3, and maintaining said time period T2 greater than said time period T3.

42. The system according to claim 41, including also progressively increasing the viscosity of said resin reactive mixture over time period T2, and driving air from said mold cavity by filling said mold cavity with increasing amounts of said increasing viscosity resin reactive mixture.

43. The system according to claim 1, in which said resin reaction mixture tends to shrink in size during cure, and including also overfilling said cavity with pressurized resin reactive mixture sufficiently to compensate for said size shrinkage and completely fill said cavity in the cured condition of said resin.

44. The system according to claim 1 in which the resin reactive mixture is pressurized within said mold cavity to a pressure of from about 1 to about 40 psi above ambient atmospheric pressure, said pressure being sufficient to block any incorporated gases in said mixture from forming voids or bubbles visible in a denture formed therefrom.

45. Denture forming apparatus comprising a mold cavity, artificial teeth, a support supporting said artificial teeth within said cavity, and a resin supply supplying a reactive resin mixture under injection pressure, said mold cavity having a resin reaction mixture injection inlet and spaced therefrom a vent, said vent being flow-restricted relative to said inlet, whereby said resin reactive mixture is pressurized within said mold cavity.

46. Denture forming apparatus according to claim 45, including also a mixer and tip for mixing said resin reactive mixture and delivering said mixture to said mold cavity inlet, said tip being received within said mold cavity in sealing relation against air incursion into said mold cavity with said mixture.

47. Denture forming apparatus according to claim 45, including also a pressure source pressuring said mixture for delivery into said mold cavity.

48. Denture forming apparatus according to claim 47, in which said pressure source comprises a pneumatic pressure source.

49. A denture formed by the system of claim 1.

50. A visible void- and bubble-free denture comprising one or more teeth and a resin support, said resin support comprising a urethane resin reaction product of an isocyanato reagent, a resin moiety and a chain extender formed under above atmospheric pressure conditions in a substantially closed mold cavity against a moisture-barrier-coated stone with said teeth supported therein.

51. A visible void- and bubble-free denture comprising one or more teeth and a resin support, said resin support comprising a urethane resin reaction product of an isocyanato reagent comprising diphenylmethane diisocyanate, a resin moiety comprising a poly oxy-propylene oxide ether polyol and a chain extender comprising a tertiary amine or a pentaerythritol adduct with an alkylene oxide, formed under above atmospheric pressure conditions in a substantially closed mold cavity against a moisture-barrier-coated stone with said teeth embedded therein.

52. A method of restorative dentistry including taking an impression of a patient's gums, forming a visible void- and bubble-free denture comprising one or more teeth and a resin support, said resin support comprising a urethane resin reaction product of an isocyanato reagent comprising diphenylmethane diisocyanate, a resin moiety comprising a poly oxy-propylene oxide ether polyol. and a chain extender comprising tertiary amine or a pentaerythritol adduct with an alkylene oxide formed under above atmospheric pressure conditions in a substantially closed mold cavity against a moisture-barrier-coated stone with said teeth embedded therein, and fitting said patient with said denture.