Patented Mar. 11, 1941 2,234,383 UNITED STATES PATENT OFFICE 2,234,383 DENTAL, MPRESSION COMPOSITON Bennett Preble, Berkeley, Calif., assignor to Sur gident, Ltd., Los Angeles, Calif., a corporation of California. No Drawing. Application October 28, 1939, Serial No. 301836 9 Claims. (C. 18-4) This invention relates to reversible dental in filler materials as above described. A further pression materials and pertains more particularly object of the invention is to provide a modified to dental impression compositions of the hydro hydrocolloid gel in which the desired strength colloid type. This application is a continuation and toughness may be produced Without the aid 5 in-part of my allowed application Serial No. Of filler materials, and Which is further chair 207,311, filed May 11, 1938, allowed August 24, acterized by an improved development of “body' 1939, for “Dental impression composition.' as the gel passes through the Solidification range The principal object of the present invention is and enters the gel phase. to provide a hydrocolloid dental impression com A further object of the invention is to provide O position of high breaking strength and resistance a dental impression material of the character O to plastic deformation, and of advantageous set forth, having improved characteristics with characteristics with respect to the Setting of respect to the setting of gypsum plaster in con gypsum plaster brought in contact therewith in tact with the impression surfaces Wherefore im the reproduction of models. proved plaster casts may be obtained, having a The hydrocolloid dental impression composi Smooth, hard Surface Which is advantageous in 5 tions, of which the compositions of the present the reproduction of the detail and dimensions invention are types, are characterized by being of the subject. resilient solid gels at temperatures below normal There is a group of materials Which are known human body temperature, and capable of con to greatly increase the strength and toughness of version to a Sol condition at temperatures ad hydrocolloid gels formed With vegetable muci 20 jacent the boiling point of Water. The material lages, which mucilages usually have polymers of is reversible in nature, and Will gel when cooled derivatives of the hexose Sugars as their main to just below normal human body temperature constituents, such as agar-agar, Irish moss, or and may be reconverted into a fluid Sol and back Iceland moss, gels. Certain alkaline silicates again into the gel condition by repeated heating have been found to toughen these gels, as have and Cooling. The principal constituent em hydroxides of the alkali metals, but these par 25 ployed in Such impression compositions is a re ticular agents are disadvantageous in a dental Versible gel-forming hydrocolloid, such as agar impression composition inasmuch as the result agar, Irish moSS, or Iceland moss, which, when ing material is in general too strongly alkaline made up in water, Will furnish a gel which may to be used in a patient's mouth without discom be used to faithfully reproduce objects in dimen fort Or burning if sufficient of the agent is added 30 Sion, but such plain or simple gels have little to obtain a significant toughening effect. Borax strength and will fracture under the deformation (Sodium tetraborate decahydrate) has been customarily encountered in dental practice. For found effective in securing this desired increase this reason it is necessary to add some filler mate in Strength and toughness of Such hydrocolloid 3 5 lial to the agar-agar gel such as Waxes or the gels, but the presence of borax heretofore has like as are disclosed in U. S. Patent to Poller been found to prevent the proper setting of No. 1,672,776, or a reversible thermoplastic mate gypsum plasters, and at the same time a borax rial Such as is disclosed in U. S. patent to Har modified gel is caused to have a lesser resistance rison No. 2,021,059. to plastic deformation whereby the impressions O The principal effect of these filler materials produced With Such compositions undergo dis 40 is that of improving or modifying the solidifying tortion and permanent deformation when the characteristics (development of “body' or con Solidified or gelled impression is pulled from the sistency) of the material as it is cooled to the subject (for example, the teeth), wherefore the Solidifying temperature of the hydrocolloid base accuracy of reproduction is substantially lost. material, as more particularly described in the According to the present invention I incor above-mentioned Harrison patent. In general, porate in Such a hydrocolloid gel a borate-con the strength increase directly due to the addi taining compound, either ordinary borax or any tion of such fillers is rather small, wherefore other borate-containing compound, preferably While the SO-modified composition is preferable together with a plaster-hardening agent, whereby 50 to a plain agar composition, the strength of such both the desired strength characteristics and compositions is not materially increased over the behavior towards dental plaster are obtained, strength of simple agar-agar gels. Alkali-metal Sulphates, Such as potassium sul In VieW of the above, One of the important ob phate have heretofore been employed in con jects of the present invention is to provide a ventional hydrocolloids for the purpose of in dental impression composition of the hydro proving the behavior of such gels with respect colloid gel type, comprising a base consisting to dental plaster, as exemplified by U. S. Patent principally of a reversible hydrocolloid gel which No. 2,089,552, issued to Laurence E. Harrison, has a materially greater strength than simple but I have found that when the pH of the borate 80 agar-agar gels or agar-agar gels modified with containing hydrocolloid material is established 60 2 2,234,383 Within certain broad limits the presence of a ployed the above limit may be exceeded some plaster-hardening agent, particularly an alkali What without adversely affecting the plaster be metal Sulphate, is found not only to cause the havior of the gel. - gel to have a satisfactory behavior with respect For all practical purposes, I prefer to employ to plaster-Setting, but to cause the gel to have an alkali-metal sulphate in the proportion of at high strength characteristics, both as to ultimate least 1% based upon the total weight of the gel rupture and as to plastic deformation. composition, if the impression material is to be The effect of the alkali-metal sulphate is be used in the preparation of full or partial den lieved to be partly physical and partly chemical. tures and the like. Where the composition is It is known that high pH is detrimental to the to be employed in other uses, wherein but nomi O proper setting of gypsum plaster, and when an nal strength increase in the gel state is required alkali-metal sulphate is incorporated in the (as compared to plain agar-agar gels) the pro borate-containing gels a noticeable decrease in portion of both borate and alkali-metal sulphate pH is secured, which is of direct benefit as re ray be correspondingly reduced. For example, 5 gards behavior of the gel composition towards the incorporation of as little as .025% borax in 5 plaster. Many plaster-Set accelerators or an agar-agar gel showed a strength increase of "hardeners' are known however, and substan roughly 25% over a corresponding plain agar tially all inorganic Salts which increase the Solu agar gel, with a resulting pH of 7.9, and the bility of gypsum in Water Will contribute to the strength was further increased by the incor 20 improved behavior towards gypsum plaster of poration of 2% potassium sulphate in the com 20 the borate-containing gels of this invention. position, with a resultant pH of 7.65, and a Such accelerating or hardening agents as also slightly better plaster set was obtained. Where Serve to decrease the pH of the gel composition the borax content is raised to in the neighbor (Such as the alkali-metal sulphates, and potas hood of 0.75%, at least 3% K2SO4 is required in 25 sium Sulphate in particular) are of particular Order to Secure good plaster behavior. In gen 25 benefit. Satisfactory behavior towards plaster eral, a ratio of about 1:4 between the borate and is conventionally defined in the dental trade as alkali-metal sulphate contents has been found one which will cause or permit a standard (dental useful. grade) gypsum plaster to set hard against the AS far as is known, any chemical compound 30 mold within about one-half hour, and produce containing a borate radical is operative to . Se 30 a casting substantially free of a powdery surface. cure the desired toughening action, although by The broad pH range of the gel containing both Virtue of other properties, such as physiological a plaster-set accelerator and a borate compound properties which might prevent the use of the has been found to be in the neighborhood of pH gel composition for Oral impressions, some bo 6.8 to pH 8.5, although acceptable plaster be rate compounds would be objectionable. Among 35 havior may be obtained With borate-containing the borate-containing compounds which I have gels in a restricted pH range of from pH 7.9 to employed With complete success, may be listed: pH 8.2 in the absence of Such plaster-set ac barium borate, borax (sodium tetraborate deca Celerator. hydrate), boric acid, cadmium borate, calcium 40 The pH of the borate-containing dental hydro borate, chronic borate, ferric borate, ferrous bo 40 colloid may be established within the desired rate, magnesium borate, manganese borate, and range by adding to the gel composition a borate Zinc borate.