MESSRS. EDITORS—In No. 21, this Vol., SCIENTIFIC AMERICAN, my attention was specially attracted by the article headed " Tin versus Gold for leeth," in which testimony in favor of the former over gold was adduced. To this I also wish to add my testimony. In 1839 I had my teeth examined by a good dentist, who filled all the cavities (fifteen), with but one exception, with gold. This exceptional tooth was filled with tin, and was considered so much decayed that the use of gold was held to be extravagant, hence the employment of tin foil for the purpose. One of the teeth then filled with gold is now entirely gone, and several others have had their filling renewed, but the one filled with tin is as good as it was on the day the operation was performed. I am satisfied, both in regard to the durability and comfort experienced, by the use of tin, as a substitute for gold in filling teeth. I do not express an opinion as to the cause ; I merely relate my own experience. Tin is, undoubtedly, a superior non-conductor to gold, and perhaps its expansion by slight oxydation may tend to render it more durable, and at the same time fit more accurately in the cavity. D. S. HOWARD. Corpus Christi, Tex., April, 1858.