as used herein , &# 34 ; commercial - batch - size &# 34 ; is meant to denote an amount that , when proportioned into packaged units , a sufficient number of units is yielded to make the process of manufacturing and packaging economically feasible for commercial distribution . it should be noted that the determination of the &# 34 ; commercial - batch - size &# 34 ; must take into consideration factors other than economic factors , i . e ., design of equipment ; ability to control quality and consistency ; ability to control environmental conditions ( exposure to air and moisture ); ability to control sensitive steps in the process ( mixing times , cooling ); ability to handle the process in safety ; and the ability to maintain a balanced inventory of finished product so that a line of commercially attractive flavors and sizes can be made readily available . the present invention enables a solution to this in that there is provided a method which ( 1 ) produces a composition which may be sub - divided and properly packaged for home - care use under professional supervision , ( 2 ) is of a viscosity so as to permit its use with a toothbrush as an applicator , and ( 3 ) is stable as to its stannous fluoride content over extended periods of time , particularly when stored under normal conditions . further , the composition is of a quality and stability to equal the &# 34 ; laboratory produced compositions &# 34 ; used to clinically establish the efficacy and advantages of stannous fluoride topical fluoride treatment agents having known concentrations . thus , the invention provides a commercially available composition in terms of quality and stability that will enhance the value of a variety of clinical studies such as ( 1 ) the further documentation of the value of stannous fluoride as a topical fluoride treatment for the purpose of reducing the occurrence of dental caries , ( 2 ) the further clinical documentation of the value of stannous fluoride in the area of hypersensitivity treatment , and ( 3 ) the further clinical documentation of the value of stannous fluoride in the area of plaque control . the present inventive improvement of the earlier method of producing stable gels is predicated on the discovery that up to about an 80 %, by weight , reduction in the amount of hydroxyethylcellulose needed for the gel may be achieved by following the above described method . moreover , the reduction in the amount of hydroxyethylcellulose needed for the gel does not impair the desirable viscosity characteristics and stability of the gel . in addition , the time required to produce the commercial - scale - size batches has been greatly reduced owing to the fewer number of steps required for the improved method . the apparatus described in u . s . pat . no . 4 , 418 , 057 , the disclosure of which is incorporated herein by reference , may also be employed to carry out the method of the present invention . the percentages expressed herein are by weight and are based upon the weight of the final gel composition unless otherwise specified . glycerin ( 150 liters ) was added to the tank and heated to 180 ° c . stannous fluoride ( 17 . 2 kg ) was added and the contents stirred until completely dissolved . the resulting solution was dissolved into a tank containing 61 liters of glycerin and the mixture mixed until homogeneous . the mixture may be stored in a tightly covered container indefinitely at temperatures no less than about 25 ° c . glycerin ( 220 liters ) was measured into a compounding tank . the glycerin was heated and hydroxyethylcellulose ( 2 . 6 kg ) was added thereto with mixing . heating was continued until the temperature reached about 140 ° c . the solution was mixed for 30 minutes at 140 ° c . glycerin ( 160 liters ) was measured into a tank and 54 kg of the stannous fluoride solution of example 1 added thereto . the hydroxyethylcellulose solution was added to the stannous fluoride solution with mixing until temperature equilibrium was reached . one of the following batches of flavoring agent was intimately admixed with the solution ; grape - 2 kg ; raspberry / creme de menthe - 3 . 27 kg ; cinnamon / creme de menthe - 5 . 04 kg ; mixed fruit - 2 . 23 kg ; mint - 3 . 88 kg . finally , 225 kg of glycerin was added , thoroughly admixed therewith and the resulting gel packaged . glycerin ( 100 liters ) was added to a compounding tank and heated to 180 ° c . stannous fluoride ( 3 . 0 kg ) was added thereto and the solution mixed until completely dissolved ( 30 min .). an additional 100 liters of glycerin was admixed with the stannous fluoride solution . glycerin ( 150 liters ) was measured into a compounding tank and hydroxyethylcellulose ( 2 . 6 kg ) added thereto with mixing and heating to 140 ° c . until completely dissolved ( 30 min .). the hydroxyethylcellulose solution was added to the stannous fluoride solution with mixing . an additional 250 liters of glycerin was added and the resulting gel packaged .
a method of producing stable gels consisting essentially of from about 0 . 38 % to about 0 . 42 % of stannous fluoride , from about 0 . 25 % to about 0 . 45 % hydroxyethylallulose and the remainder anhydrous glycerin .