Document ZJeGe3Vk2nEoqRX4v6Oa61nM0

ESTABLISHED 1866 Le i: S. Smit h & Sox Ma m'f a c t i k in o Co . De x t a l Pr o d u c t s 7335 PENN AVENUE PrrTSBniGH.PENXA.,U.S.A. June 12, 1934* Dr. Robert E. Kehoe, Kettering Laboratory, Department of Physiology, University of Cincinnati, Cincinnati, Ohio* Dear Doctor Kehoe: 7/a are distributors of a denture base material manu factured by the Carbide and Carbon Chemicals Corpor ation (a subsidiary of Union Carbide and Carbon) from the thermoplastic resin "Vinylite". This, as you may know, is a polymerized compound of vinyl chloride and vinyl acetate* Over a period of three years in actual use no toxic effect has been observed. An improvement is contemplated which will involve the incorporation of one per cent of lead stearate in the resin. Knowing the present-day suspicion of materials which contain lead, we do not care to proceed with this work until we hav9 a definite and authoritative opinion that this resin will have no harmful physiological ef fect. The writer sought the advice of Ur. 7/illiam P. Yant, Superintendent of the Pittsburgh Experiment Station of the U. S. Bureau of Mines. He suggested that you would probably be willing to undertake this investiga tion. It is difficult for us to understand how there can be any introduction of lead into the system of the wearer of dentures made from this material since vinylite is unacted upon by dilute acids and alkalies, and the water N 2467 Le e S. s mit h & So n Ma n u f a c t u r e s Co . Dr. R. E. Kehoe -2 / / .6 12 54 absorption at 37C. has been determined to be of the order of 0,25/ in 168 hours and not much more than this in a much longer time. Incidentally, the color of the resin Is known to remain constant in the mouth for at least two years. In any case, the amount of lead present in finished dentures is small. A full upper and lower set of den tures weighs not more than forty grams. Since lead stearate contains 26.8/ of lead as metal, the total content of lead in a very large set of dentures would be 107 mg. Mr. Yant stated shat a daily intake of as much as two milligrams of lead has been found to be harmless. At this rate, a set of dentures would have to disinte grate completely in approximately fifty-days in order to approach this lim'.t, and this of course is impos sible. 'YouId you, therefore, on the basis of your expert knowledge of this subject, be willihg to Estate definitely that such a material would be harmless. If not, will y-ou kindly let us know whether you will undertake whatever investigation you may deem neces sary and give us an approximate idea of its cost, and of the time required. Yours very truly, (ft E. E. Marbaker, Ph.D., Research Department. 1/ ... P.S. 7?e are sending you under separate cover a finished denture molded from resin containing lead stearate: and a blank similar to that from which the denture was made.