Background Art

Die models are commonly used in dental laboratories for a number of well-known dental fitting and fabri- cation purposes. Typically, a model is formed of a gypsum or epoxy material by casting from a negative impression mold of the teeth made in a dentist's office. The die model is then used to fabricate, size, and pre-fit dental appliances such as crowns, porcelain jacket crowns, indexed multiple crowns and the like. In order for these appliances to fit properly in the mouth, the model must accurately represent the structural condition of the teeth and must be free of flaws which often result due to the nature of the tooth prepara- tion, impression process and of the casting process. Further, dental models must often be modified to reflect the structural condition of the teeth which should exist at the time of fitting of an appliance even though such a condition did not exist at the time the impression mold was made. Exemplary of such flaws and conditions which must be corrected on the model are bubble voids which occur in the casting process, undercuts which occur usually in the tooth preparation process, and deep areas which often result on removal of decay and which are not filled in on the tooth prior to impression molding. These voids, undercuts, and deep areas must be filled in, blocked out, or based up as necessary in order to produce a

model of the tooth which is proper for seating or fitting a crown or other appliance on the model of the tooth without resistance. Once the model itself has been pro¬ perly prepared, operations such as the indexing of two or more dental crowns and subsequent transfer to a sol¬ der investment are often required. In some situations, the model itself must be unbreakable in order to index a bridge or precision partial abutment.

Disclosure of Invention The present invention contemplates the use of materials which allow rapid and efficient prepara¬ tion of a dental model and the performance of various operations on a prepared model. In particular, the invention provides an inexpensive material which re- quires no extraordinary use precautions, which requires no mixing or after-use clean-up, which* sets in a minimum of time to a hardened condition not susceptible to wax flow-through or adherence, and which does not exhibit an unacceptable degree of shrinkage. The methods according to the present invention involve the use of high viscosity cyanoacrylate compounds which are hardened through the use of an accelerator, particularly by the application of an atomized mist of an accelerator, whether or not in a volatile solvent, to the cyanoacrylate compound previously positioned on the model. Substantial savings of time and labor result through practice of the present methods, certain heretofore unobtainable advantages to be hereinafter described being realized according to the teaching of the present invention.

Brief Description of Drawings

Figure 1 is an idealized elevational view of a single tooth of a die model after preparation;

Figure 2 is an idealized elevational view of a single tooth of a die model wherein the tooth model has an undercut which is to be blocked out to cause the model tooth to conform to the configuration of the model tooth of Figure 1; Figure 3 is an idealized elevational view of a single tooth of a die model wherein the tooth model has undercut areas which represent areas on a tooth from which decay was removed, the undercut areas being necessarily blocked out on the model tooth to conform to the configuration of the model tooth of Figure 1;

Figure 4 is an idealized elevational view of a single tooth of a die model wherein the tooth model has a deep area which resulted from the removal of decay from the tooth from which the model was made, the deep area being based up on the tooth model in order that the nerve in the actual tooth will be insulated from a crown or other appliance made from the die model; Figure 5 is an idealized elevational view of a single tooth of a die model wherein the tooth model has a missing area which is to be filled in to cause the model tooth to conform to the con¬ figuration of the model tooth of Figure 1; Figure 6 is an idealized elevational view of a single tooth of a die model wherein the tooth model has a bubble void which is to be filled in;

Figure 7 is an idealized view of a series of indexed crowns which are bound together according to the invention prior to soldering;

Figure 8 is an idealized side elevational view of a single tooth of a die model illustrating the

blocking out of undercut areas below the margin of the model tooth;

Figure 9 is an idealized elevational view of a single tooth of a die model wherein an undercut area on the die model is blocked out below the height of contour in order to facilitate fabrication of dental appliances such as a removable partial clasp;

Figure 10 is an idealized elevational view in section illustrating the molding of an unbreakable die model tooth within a crown;

Figure 11 is an idealized perspective view illustrating the preferred application of a cyano¬ acrylate compound to a die model having a missing area; and Figure 12 is an idealized perspective view illustrating the application of an accelerator com¬ pound to a missing area which has been built up with the cyanoacrylate compound.

Best Mode of Carrying Out the Invention Several methods constituting the present in¬ vention particularly contemplate a new use of com¬ pounds previously used to bond structural elements together, the compounds being generally referred to as cyanoacrylates and including activators or accele- rators therefor which are typically classed as Lewis bases. Such materials are described inter alia in U. S. Patents 3,903,055; 3,992,515; 3,223,083; 3,264,249; 3,559,652; 3,839,065; 3,940,362; and 4,042,442, the disclosures of which are incorporated hereinto by reference. U. S. Patent 3,903,055 is exemplary in that the patent discloses the causation of accelerated setting of cyanoacrylate monomers and comonomers through the use of an amine catalyst, the catalysis typically polymerizing 2-cyanoacr lic

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acid. In particular, isobutyl cyanoacrylate is polymerized by N,N-dimethyl-p-toluidine to cement brackets to the teeth in a proposed "in-mouth" usage. The cyanoacrylates can further be thickened in a variety of ways, such as through addition of organic fillers as disclosed in U. S. Patents 2,794,788; 3,836,377; 3,692,752; and 4,102,945; or through addition of inorganic fillers as disclosed in U. S. Patents 3,663,501 and 3,607,542; the dislo- sures of these patents being incorporated hereinto by reference. Certain cyanoacrylate compositions are disclosed in U. S. Patent 3,625,930, the dis¬ closure of which is incorporated hereinto by re¬ ference, this patent disclosing inter alia the poly- irierization of methyl or ethyl esters of the cyano¬ acrylate by an aromatic amine which can be carried in a highly volatile acetone solvent.

Preferred accelerator compounds according to the invention include aromatic amines such as N,N- dimethyl-p-toluidine and the ho ologs thereof and phenylethylethanolamine and the homologs thereof. These accelerators can be carried by a volatile solvent such as triσhloroethane. Preferred base materials include ethyl cyanoacrylate, methyl cyano- acrylate, n-butyl cyanoacrylate and the like. The invention uses a high viscosity cyanoacrylate which remains positioned on the dental model at the loca¬ tion where placed, that is, the material does not readily flow. The cyanoacrylate, which is referred to as a "base" is typically placed on an area of the model through use of an applicator as will be de¬ scribed hereinafter to fill in, base-up or block out a flaw, the base cyanoacrylate then being contacted with an accelerator which immediately initiates cure or hardening of the base material. The base

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material typically hardens adequately for further use of the model within a period of two to three minutes. The accelerator is typically applied in the form of a fine, atomized mist from a squeeze bottle or similar applicator which allows ready control of the quantity of accelerator applied to the base and of the location of application of the accelerator. Since both the base and the accelera¬ tor can be dispensed directly from storage containers of the compounds onto the model, the necessity for mixing and cleaning is eliminated. The accelerator can be carried by a volatile solvent which assists in dispensing said accelerator, the solvent being vapo¬ rized almost instantaneously when dispensed from an applicator such as an aerosol container.-

Referring now to the drawings and particularly to Figure 1, a model of an ideal preparation on a tooth which is to receive a crown is shown generally at 1 . Both the tooth which is to ultimately re- ceive the crown and the model tooth 12 on a die model must have a desired design, such as is known and typically approved by the American Dental Association and the various state dental examiner's boards. The preparation on the model tooth 12 must have walls or sides 14 which are essentially parallel or nearly parallel as in a slightly upwardly tapering "tepee" or similar shape. The crown or other dental appli¬ ance can then be fitted or seated on the model tooth 12 without resistance. The fitted crown is thus subsequently precisely located on the actual tooth. The original outline of the tooth can be seen at 16 in phantom. In practice, dental models must be "prepared", that is, flaws which often occur due to errors or intentional omissions must be corrected on the dental model. These flaws range from voids

which occur in the casting of the model to undercuts and the like which can result from the manner of original tooth preparation.

As can be seen in .Figure 2 , an undercut at 18 on one of the walls 14 of the tooth 12 must be filled in or "based-up" so that a crown can seat or fit on the model tooth 12 without resistance. The walls 14 must be parallel or nearly so as aforesaid. The undercut 18 is based up by applying a high viscosity cyanoacrylate compound such as by the technique illustrated in Figure 11, an accelerator being then applied to the compound as illustrated in Figure 12 and as will be described in greater detail herein¬ after. The hardened cyanoacrylate readily adheres to the model tooth 12 and can be readily shaped if neces¬ sary by cutting such as with a sharp modeling knife. Referring now to Figures 3, 4 and 5, areas are seen on the model tooth 12 which usually result from the taking of an impression after removal of decay from an actual tooth but without filling of the resulting cavity. ■ It is to be understood that such a cavity can be conventionally filled by the dental practitioner prior to taking the impression from which a negative mold of the teeth is made. However, a cavity in the tooth is often left un¬ filled until after the impression is taken with the result that the model tooth 12 has undercut areas such as are seen at 20 in Figure 3, a deep area such as seen at 22 in Figure 4, or a missing area such as is seen at 24 in Figure 5. These areas 20, 22 or 24 must then be based-up or blocked out on the die model which is made from the impression mold. According to the present invention, the areas 20, 22 or 24 are filled in by deposition of the cyanoacrylate, such as ethyl cyanoacrylate, into or

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onto said areas in order to completely fill or build up the area to the desired contours, the cyanoacrylate then being sprayed with the accelera¬ tor, preferably in a fine, atomized mist, to cause rapid hardening of the cyanoacrylate. The model tooth 12 can then be worked with within a very short time as necessary.

Referring now to Figure 6, the model tooth 12 is seen to have been formed with a negative void or bubble 26 or other negative artifact which results from the casting process. The bubble 26 can be readily filled with the cyanoacrylate compound and contacted with the accelerator as described herein. Application of the cyanoacrylate compound can occur by a variety of techniques, including the deposition of the cyanoacrylate compound onto a blade or other sharp instrument and application to the bubble void. Such an application technique is particularly suited to small bubbles 26 which are too small to accommodate even a single drop of cyanaoacrylate compound from a drop-wise dispenser.

In Figure 7, an illustration is seen of the indexing of two or more dental crowns 28 on a die model. The dental crowns 28 must be indexed on the die model prior to soldering together of the crowns. When the crowns 28 are properly indexed on the die model, the crowns must rigidly stick together when transferred to the solder investment so that the relationship between the crowns will not change. The material used to hold the indexed crowns 28 together during this processing must exhibit a mini¬ mum of shrinkage and must adequately stick to the crowns. Further, once the* crowns are placed into the soldering investment, the material must burn off cleanly without leaving a residue which can

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act as an anti-flux to prevent the solder from bonding or welding the crowns together. In effect, the ma¬ terial must be a fluid which becomes solid within a reasonable time and which, when solidified, exhibits the characteristics thus noted. As seen in Figure 7, cyanoacrylate compound cement 30 is disposed between the crowns 28 and cured by contact with the accelera¬ tor as described herein, the crowns 28 are thus caused to rigidly adhere to each other within a matter of two or three minutes, the indexed and joined crowns being then soldered with complete burn off of the hardened compound and minimal shrinkage. According to a preferred method, the crowns 28 are placed on the die model for indexing and one application of accelera- tor is made to the crowns. The cyanoacrylate compound is then applied both between the crowns 28 which are to be joined and on top of the crowns. Accelerator is then again applied. A complete hardened cure occurs in less than five ^' minutes, a time saving previously unavailable to the dental technician.

Fabrication of a procelain jacket crown requires that a platinum foil be first adapted to a die model and then subsequently removed. As seen in Figure 8, model 32 used for such a fabrication process must not have undercut areas, such as at 34 below margin 36. Such undercut areas 34 must be blocked out prior to adaptation of the foil to the model 32 in order to prevent distortion of the foil on removal of said foil from the model. The cyanoacrylate compound according to the present invention will flow only to the margin angle shown at 38 and will stop at said angle without overflow due to the viscosity of the compound. Accordingly, little or no carving of the hardened cyanoacrylate is necessary. Figure 9 illustrates the blocking out of an

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undercut area 40 on a model 42 as one operation in the fabrication of a removable partial denture. The undercut area 40 below the height of contour where a clasp of the denture will be placed must be blocked out on the model 42 in order to control the depth or intensity of the retention of the clasp. When the cyanoacrylate compounds described herein are used to fill the undercut area 40, the compound flows to the height of contour at 44 and not over said height of contour due to the viscosity of the com¬ pounds. Misting of the compound with the accelera¬ tor as described herein results in an extremely rapid set of the compound and allows the technician to con¬ tinue with fabrication of the partial denture with a minimum of delay.

Referring now to Figure 1.0, a multiple layer unbreakable die model 46 is seen. The die model 46 is typically fabricated either after the crowns are re-indexed in the mouth and prior to soldering, or for the construction of a precision partial denture.

Cavity 48 of a crown 50 is lubricated with an oleagi¬ nous lubricant such as is known in the art and any undercuts (not shown) are blocked out. The cavity 48 is a negative mold of a previously prepared die model. The cavity 48 of the crown 50 is then pre¬ ferably sprayed with accelerator and a cyanoacrylate compound according to the invention is deposited within the cavity 48 of the crown 50 to a depth of approximately one-third the height of said cavity. The accelerator is then spread over the exposed surface of-this first layer of compound,* a second layer of cyanoacrylate compound being then deposited into the cavity over said first layer to a total depth of approximately two-thirds the height of the cavity. The accelerator is then sprayed over the

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exposed surface of the second layer of the cyano¬ acrylate compound to a desired height, and a sub¬ sequent spraying of this third layer of cyanoacrylate compound with accelerator. A mechanical retentive device 52 can be embedded in the third layer of cyanoacrylate compound prior to the final accelerator spray. The cyanoacrylate compound is layered with the accelerator in order to assure complete and rapid hardening of the relatively large bulk of material forming the unbreakable die model 46 thus produced.

The device 52 holds the die model 46 to an appropriate base (not shown) which is added later. By this technique, as well as by casting, unbreakable die models can be formed according to the invention. Unbreakable models so formed are particularly useful for indexing a bridge or precision partial abutment.

Referring now to Figures 11 and 12, a simplified illustration of physical techniques for applying the cyanoacrylate compound and the accelerator according to the invention can be seen. In Figures 11 and 12, the method of the invention is seen to be practiced in the build-up of the missing area of a crown pre¬ paration on a die model in order to 'form a more ideal shape to the model. The situation shown in Figures 11 and 12 is essentially that situation shown in Figure 5. As seen particularly in Figure 11, a mass 62 of the cyanoacrylate compound is applied to a missing area 54 of tooth model 56 through a small Teflon or polyethylene tube 58. The tube 58 can be connected to the tip of a squeezable storage bottle or similar storage container (not shown) from which the compound can be directly dispensed. The highly viscous cyanoacrylate compound can be controllably dispensed through the tube 58 'as small drops 60 which can be accurately located on the missing

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area 54 or similar area which is to be filled in, based-up, or blocked out. Any desired quantity of the compound can be dispensed. The compound can essentially be dispensed onto the area 54 in the conformation desired for the finished product, the tip of the tube 58 being useful to shape the compound if necessary. Other implements can, of course, be used to shape the fluid compound. Once the desired quantity of the compound is properly placed on the area 54, the accelerator is sprayed onto the mass 62 of the compound, preferably from an aerosol or atomizing container such as the container 64 shown in Figure 12. Only a relatively small amount of the accelerator is sprayed onto the cyanoacrylate compound mass 62, the quantity of accelerator being controllable such as by the use of the aerosol container 64 as aforesaid or by means of a similar pump spray. Only about 1% of the accelerator to the compound by relative weight percent is typically required to rapidly harden the mass 62. On application of the accelerator, the cyanoacrylate compound immediately begins to set or cure and becomes a hardened mass within two or three minutes. Once the surface of mass 62 begins to harden, the die model can be lubricated and wax applied for sculpting of a wax tooth over the die model 56 as required for further processing. The mass 62 may be cut and shaped after hardening and before other operations are performed. The wax used for performing such additional operations cannot melt into the hardened mass 62 nor does the wax adhere substantially to the hardened mass 62. When a crown is cast in gold or other alloy and the crown is finished or polished on the die model, the heat thereby generated cannot melt the hardened mass of cyanoacrylate compound, thereby eliminating a

number of vexing problems encountered in the prior art as described herein. When a large quantity of the cyanoacrylate compound is to be built up, the mass of cyanoacrylate compound can be built up in layers as described relative to Figure 10. Alternately, the accelerator can be sprayed first on the model surface which is to receive the cyanoacrylate compound and the exposed surface of the mass 62 sprayed once the mass 62 is completely deposited. The present invention further contemplates the addition of a dye to the cyanoacrylate compounds in order to color the base material for the purpose of providing contrast on the die model. Such a dye can be chosen from the well-known dye materials used to color cyanoacrylate compounds in other use environ¬ ments. In order to prevent degradation of the cyano¬ acrylate compounds , the dye can be supplied separately for mixing with said cyanoacrylate compounds immedi¬ ately before use. As a further use of the cyano-acrylate compounds according to the invention, orthodontic wires can be in¬ dexed o ^" a die model and bonded together with the cyano¬ acrylate base material and accelerator according to the methods previously described. The indexed wires can then be preferably soldered on the die model with advantages accruing to the present method in a similar manner as is described relative to Figure 7.

The methods of the present invention provide ad¬ vantages to the dental technician which have pre- viously been unavailable. In particular, the inven¬ tion provides methods for preparing and using a dental die model with a cyanoacrylate material which allows rapid filling of voids, basing-up of undercuts, build up of missing areas-, and indexing of crowns inter alia. Use of the cyanoacrylate material provides

substantial time savings and enables a less skilled technician to more rapidly and more assuredly produce a quality work product.

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