A Method for Staining of Carious Lesions in Teeth. ∗

Abstract

In the study of experimental rat caries large numbers of animals must be employed to obtain significant statistical results. As a result the methods for examination of the molar teeth become very important. Some investigators have employed the very tedious method of preparing stained thin-sections by the ordinary technics. Others have attempted to reduce the time and expense by resorting to either gross inspection of the carious teeth or to rapid grinding and examination of ground sections. At the suggestion of Dr. B. F. Miller of the University of Chicago the author has developed a rapid, simple and precise method for the staining of carious areas in rat molars (and also in human teeth). Previously, 1 the author had developed a method for the demonstration of insoluble calcium salts in the tissues. It was found that this method cannot be applied to the study of teeth because the silver solution used in the techmc will not penetrate the dense dental tissues. Dentin will get a very superficial black coating but enamel is entirely unstained. However, the surprising observation was made that carious areas stained deep black. This can be explained by the greater permeability to the silver solution of the rarefied carious tissue. That the action of acid actually increases the permeability of enamel and dentin was proved by the following experiment: into healthy, extracted human teeth symmetrical holes were drilled, two into each. One of these holes was packed with cotton soaked in distilled water, the other with cotton soaked in 5 to 10% lactic acid. The holes were sealed with paraffin. The cotton plugs were changed twice daily. After 3 days the plugs were removed, the teeth washed in distilled water and stained according to the technic mentioned.