Method of constructing dentures
US 2899712 A
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Description (OCR text may contain errors)
Aug. 18, 1959 c. C. sMlTH 2,899,712
METHOD OF CONSTRUCTING DENTURES Filed Feb. 2o, 195e 1N ENTOR.
METHOD F CONSTRUCTING DENTURES Clark C. Smith, Kansas City, Mo. Application February 20, 1956, Serial No. 566,413
s claims. (ci. 1sss.1)
This invention relates to prosthetic dentistry and more particularly to the manufacture of partial or complete dentures, the primary object being to alleviate problems incident to volumetric shrinkage resulting especially from employment of modern-day denture materials and making it virtually impossible to produce a well fitting appliance by commonly employed methods.
To a large extent, the dough from which dentures are universally made, consists wholly or in part of acrylic resin and during the curing of the dentures, such dough undergoes an appreciable volumetric shrinkage. Manifestly, such shrinkage occurs during polymerization and following the condensation thereof into a relatively hard solid structure.
By virtue of such shrinkage therefore, it is virtually impossible to expect that the nished appliance will conform in any accurate sense to the shape and configuration of the cast from which it is made and, therefore, cannot possibly fit the mouth of the user with any degree of accuracy. Such shrinkage occurs in virtually all directions, i.e., in thickness, length and breadth. Usually the denture is too narrow from ridge to ridge across the posterior and there is a notable linear shrinkage from the anterior to the posterior. However, the most notable error consists of a space between the denture and the cast, not only in the palate of the denture, but at the crest of the ridge due not only to the pulling away of the denture plate material from the cast, but from warpage by virtue of the fact that the volumetric shrinkage is permitted to take place uninhibited through conventional techniques.
It is the most important object of the present invention, therefore, to provide a method of manufacturing artificial dentures whichk contemplates the control of such volumetric shrinkage so as to reduce, if not eliminate, the extent of variance in the shape and dimensions of the denture plate material with respect to the cast or positive dental model from which the denture is made.
Another important object of the instant invention is to provide a method of manufacturing articial dentures that includes as one of the essential steps, the maintenance of pressure upon the denture plate material while the same is cured `so as to hold it firmly against the positive pattern and thereby cause the same to accurately take on the shaperand configuration of Vsuch pattern.
Another object of this invention is to provide in a method of manufacturing artificial dentures, a novel step which contemplates differential pressures on opposite sides of the denture plate material during curing thereof so that 'the same is caused to assume the shape and configuration of the cast and to maintain such shape and configuration throughout the time the same condenses into `a hard solid denture with the result that the latter accurately fits the mouth of the user and engages the tissues uniformly throughout the palate, gum area and the ridge crest.
A further object of the present invention is to provide a method of the aforementioned character that takes ite States atent 2,899,712 Y Patented Aug. 18, 1959 lCC advantage of the inherent porosity of investing materials used in the molding flask for passage of fluid pressure to the denture plate material during polymerization, whereby such pressureY controls the direction of volumetric shrinkage as and for the purposes aforementioned. l
A still further object of the instant invention is to provide a method of making artificial dentures having for its primary object the improvement of proper fit by sealing one of the mold `sections Within the flask from the other mold section with material impermeable to the passage of the fluid pressure medium so that there is a pressure differential within the flask which will con tinue until the denture plate material is firmly set and ready for removal from the positive cast.
Other objects include more detailed procedure in carrying yout the aforementioned primary objects and which include the utilization of the denture base material itself as a sealing medium between the flask sections and the mold sections; the way in -which there is presented a space between' land areas formed on the mold sections and between proximal edges of the flask sections into which the denture base material may flash; the manner of providing such spaces through a waxingv procedure constituting one of the steps of the method; the way in which the mold sections Aand the flask sections are held against separation during curing of the acrylic resin or the like by pressure 'imparted thereto that is greater than the fluid pressure that is directed to the denture; and many otherimportant steps in the method which will be made clear as the following specification progresses. l
In the drawing:
Figure l is a cross-sectionalview through a flask section and a mold section showing a separating medium applied as contemplated by the first stepof the method.
Fig. 2 is a cross-sectional View through another flask section and mold section showing. the separating medium applied according to said first step. Fig. 3 is a cross section similar to Fig. 2. showing the denture material packed in place pursuant tothe second step .of the method; and Fig. 4 isa cross-sectional view showing the step of compression of the flask sections as well as the steps of applying and maintaining iiuid pressure.
Those skilled in'this art are familiar with the initial steps commonlytemployedyinthe manufacture of articial dental appliances, and while the method of the instant invention will be hereinafter outlined in accordance with the procedures to be employed for the manufacture of complete dentures, it is understood that the principles thereof apply equally well to the production of partial dentures and other types of artificial restoration. v
Accordingly, `in the usual manner, a negative impression'v of the users mouth will be taken from which is produced a positive model, pattern or cast and which cast is designated by the numeral 10 in Figs. 1 and 4 of the drawing.
Any suitable material such as wax may be used in the shaping of a base plate (not shown) over the cast 10 whereupon artificial teeth are mounted on such base plate in the usualmanner. Normally, the dentist will then adjust the teeth within the base plate by a trial fit `within the mouth of the user and thereupon the permanent denture can be produced according to the steps about to be outlined.
The said base plate is then attached to the cast 10 in the u sual manner through use of a removable' substance such as wax and the cast 10 is invested within a suitable casting material presenting a mold section 12 within one section 14 of a flask broadly designated by the numeral 16. vIf desired, lthe last mentioned casting U step may precede .the Waxing of the base plate to the cast 10. Y
l After the investment forming the molding section 12 'has hardened, edge 18 of vflask ysection 14,l as well as land .area 20 of investment 12 adjacent 'the edge 18 and adjacent the base plate, .are covered `with a removable 'substance such as wax. The base plate, together with artificial teeth 122, are then invested vwithin a casting material presenting a second mold section 24 within flask 'section 26.
Following the hardening of the investment forming the mold section 24, the two sections 14 and 26 of flask 16, as well as the two mold sections 12 and 24, are separated and all of the wax forming Ythe base plate, as well as the Wax that was placed along :land area 20 and edge 18, are removed, leaving cast in its initial condition and 'leaving the teeth 22 firmly embedded within the mold section 24.
It'is advisable to thereupon coat Vthe mold `sections 12 and 24 with a conventionalseparati-ng vmedium to facilitate removal of the completed denture, such coatings 'being shown in Figs. l and 2 and designated by .the numerals 27 Vand 29 respectively. Thereupon, as shown in Fig. 3, the mold section 24 is packed with a polymeric denture base material 28 completely covering the teeth 22 partially embedded within-'the -investment forming Vthe mold section 24, following which vthe ask `sections .14 and 26 and the mold sections 12 and 24, are Vreassembled in the manner illustrated -in Fig. 4 and compressed tightly together in any suitable manner so as -to cause the denture base material to not only distribute evenly over the cast ,10, but to flash outwardly between the mold sections 12 and VZ4 and between the edges of the iiask sections 14 and 26. For clearness, coatings 27 and 29 have been omitted from Figs. 3 and 4.
In the apparatus chosen for illustration in Figure 4, head 30 of a conventional press, rests directly yupon the ask section 14 and the ask section 26 is retained by a stationary plate 32 having an upstanding tubular portion 34.
`It is to be noted that one end of the flask section 26 registers directly with the ytubular lportion 34 and is sealed with respect thereto through use of a `gasket 36. The fact that the denture base material liashes outwardly from the cast 10 therearound 'and between the mold sections 12 and 24, as well as between the flask ysections 14 Vand 26, presents a seal and inasmuch as such material is impermeable to the ow of most fluids, it is possible to produce a pressure differential on opposite Ysides of the denture 28. Any suitable fluid medium such as air, water or nitrogen by way of example only, may be direc'ted into the tubular portion 34 by way of supply pipe 38 coupled therewith.
It is to be pointed out that most-casting materials commonly employed for investment purposes, are sufciently porous in nature when hard, to permit passage of the fiuid medium therethrough so that it impinges `directly upon the teeth 22, as well as the denture material 28 in the manner illustrated by arrows in Fig. 4 Vof the -drawing. Manifestly, the pressure exerted upon the flask 16 by the head 30, must be greater than the pressure of the fluid medium chosen to carry out the principles of 'the method to positively prevent 'an-y separation of 'the flask sections 14 and 26 and the mold sections 12 and 24. Thus, as the pressure differential is produced, the denture base Vmaterial 28 will be forced firmly against the cast 10 into conformity with the shape and configuration thereof, and such pressure should be maintained throughout the polymerization or curing of the material from which `the denture 28 is made. Such maintenance of pressure upon the denture 28 controls the direction of volumetric shrinkage so that at the completion of the c uring step (which incidentally may or may not be carried out in the presence of heat, depending upon the Vnature of the plastic material employed in prodlldllg th@ denture 28) denture 28 will have remained in firm engagement with the cast 10 throughout its entire effective area. It is to be particularly noted that when the permanent completed denture is removed, it may be again placed upon the cast 10 and unlike dentures made in accordance with the conventional methods, it will iit the cast 10 perfectly and particularly there will be no gap or space along the palate thereof.
From the foregoing it is evident that no attempt is made to prevent volumetric shrinkage because such shrinl'- age must take place in order for the dough to condense into a hard solid. Instead, the direction of volumetric shrinkage is controlled and as the same takes place, the denture base material is not permitted to pull away from the cast te at any point, forcing the same to harden or cure precisely according to the shape and configuration of the cast upon which it is polymerized.
It is now evident that Ithe nature of the material from which the cast 10 is made 'and :the material used to invest such cast is of no consequence to the method as above described. `Such materials'may well be solid and impermeable to flow of uids therethrough lfor the iiuid pressure acting on the denture material 28 will normally hold the latter firmly against the cast during polymerization. However, it is preferred that the same be porous since there will be no tendency .for bubbles forming .between the denture and the cast, preventing the denture lfrom bearing accurately and flatly against the cast. Fluids forming the bubbles -will be 4readily forced through the porous materials forming fthe cast and the investment in which it is mounted.
Furthermore, if such materials are su'ficiently porous to permit passage of fluids, the 'denture may 'be held firmly against the cast vby -reducing the. ,pressure Within flask section `14 rather than raising the pressure in flask section 26. Still further, .good results -ican be attained by exerting pressure within `section 26 while simultaneously reducing the pressure or applying a vacuum in section 14. The porosity of the Vmaterials tlends the same to attainment of the pressure Vdifferentials above referred to and is therefore, to be preferred to use of solid materials.
It may be said that the denture material, together with the boundary therearound whichflashes .to a point where it is even forced slightly between the flask sections7 presents an impermeable membrane or diaphragm which can be termed a separator or divider forv making it possible to carry out the principal object of the invention, i.e., control of volumetric Ashrinkage as aforesaid.
In this respect therefore, it is unnecessary that such divider be made entirely from the denture material. Instead, prior to packing with vthe polymeric resin, the area between the mold sections may be coated with a shellac or other material capable'of blocking liow of material. Thereupon, packing may be carried out in a conventional manner by successive steps fof trial and removal until the correct lamount of denture material has filled the spaceprevi'ously occupied by the base '.plate.
Having thus described the invention what is claimed as new and desired tofbe secured by Letters Patent is:
l. A process for producing artificial dentures comprising the steps of placing a divider between a pair of mold sections, said divider'being substantially impermeable to flow of fiuid therethrough, yorle of said sections including an internal first denture cast and the other section having an internal second denture cast of porous substance, at least a portion of vsaid divider -being of uncured synthetic resin denture material and disposed between normally opposed segme-nts yof said casts; compressing the mold sections together under sufficient pressure to force said Vsegments of the lcasts into firm engagement with said material; effecting a fluid pressure through the substance defining ysaid second cast' of not greater force than said compression pressure; and maintaining said compression and fluid pressures during polymerization and curing of the synthetic resin material to control :the direction of volumetric shrinkage thereof and force the same into conformity with the configuration of said segment of the first cast.
2. A process for producing artificial dentures comprising the steps of placing a divider of uncured synthetic resin denture material between a pair of mold sections, said divider being substantially impermeable to flow of iiuids therethrough, one of said sections including an internal first denture cast and the other section having an internal second denture cast of porous substance, at least a portion of said divider being disposed between normally opposed segments of said casts; compressing the mold sections together under sufficient pressure to force said segments of the casts into rm engagement with said material; effecting a fluid pressure through the substance defining said second cast `of not greater force than said compression pressure; and maintaining said compression and fluid pressures during polymerization and curing of the synthetic resin material to control the direction of volumetric shrinkage thereof and force the same into conformity with the configuration of said segment of the first cast.
3. A process for producing artificial dentures comprising the steps of packing a quantity of uncured synthetic resin denture material between a pair of mold sections one of said sections including a peripheral edge surrounding an internal `first denture cast and the other. section having a peripheral edge surrounding an internal second denture cast of porous substance, at least a portion of said material being disposed between normally opposed segments of said cast; compressing the mold sections together under sufficient pressure to squeeze a portion of the material into the space between opposed peripheral edges of the sections and force said segments into firm engagement with `said material, the latter presenting a divider between the sections, substantially impermeable to How of fiuid therethrough; effecting a fluid pressure through the substance defining said second cast of not greater force than said compression pressure; and maintaining said compression and fluid pressure during polymerization and curing of the synthetic resin material to control the direction of volumetric shrinkage thereof and force the same into conformity with the conguration of said segment of the first cast.
4. A process as set forth in claim 3 wherein said segments of the first and `second denture casts and said peripheral edges of the mold sections are coated with a separating medium prior to packing of the material into said sections.
5. A process as set forth in claim 3 wherein said material is an acrylic resin,
' References Cited in the le of this patent UNITED STATES PATENTS 1,592,536 `ONei1 July 13, 1926 2,279,952 Pryor Apr. 14, 1942 2,314,378 Van Rossem Mar. 23, 1943 2,320,826 Mandel June 1, 1943 2,370,956 Harkom Mar. 6, 1945 2,414,093 Cole et al. Jan. 14, 1947 2,493,439 Braund Jan. 3, 1950 2,632,227 Steele et al Mar. 24, 1953 FOREIGN PATENTS 928,364 Germany May 3l, 1955