Erling Johansen

Microstructure of Enamel and Dentin

The histology of enamel and dentin and the histopathology of these tissues have been worked out in detail with the aid of the light microscope, and much valuable information related to the problem of dental caries has resulted. However, direct observations on individual apatite crystallites of enamel and dentin and on single fibrils of the organic matrix of these tissues could not be made prior to the development of the electron microscope. With this new method of study, details on the ultrastructure of these basic morphological units and on their organization, both in sound and carious tissues are being revealed. These findings are leading to a better understanding of the manner in which enamel and dentin are altered in dental caries; also they are providing a basis for deductions on the mechanism of action of caries-preventive agents which affect tooth structure. In this presentation our recent electron-microscopic observations on both the inorganic and organic phases of the tissues will be summarized.*

A New Technique for Oral Examination of Rodents

U P TO the present, one of the most serious handicaps in the use of rodents in investigation of oral diseases has been the lack of an easy and dependable method for routine oral examinations of the live animals. The small size of the teeth and the surrounding soft tissues and the posterior location of the molars make observation with the naked eye of questionable accuracy. An oral examination can be performed under the dissection microscope if the animal is properly anesthetized. However, this procedure is time consuming and always carries the risk of premature sacrifice of the animal. The development of an easy and dependable method of examining living unanesthetized animals therefore seemed desirable. The technique about to be described is simple, quick, and noninjurious when proper experience is attained.

The Relation of Streptococci, Lactobacilli, and the General Oral and Fecal Flora to the Progression of Dental Caries in the Hamster

LACTOBACILLI, AND THE GENERAL ORAL AND FECAL FLORA TO THE PROGRESSION OF DENTAL CARIES IN THE HAMSTER MORRISON ROGOSA, ERLING JOHANSEN, AND MURRAY N. DISRAELY WITH THE ASSISTANCE OF ALFRED J. BEAMAN National Institute of Dental Research, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, Bethesda, Md., and University of Rochester, School of Medicine and Dentistry, Rochester, N. Y.

USE OF ANIMALS FOR THE EVALUATION OF CARIOSTATIC AGENTS

Dental caries was first produced experimentally in laboratory animals in the early 1920’s. This was achieved by McCollum and coworkers in nutritional studies using deficient diets fed to albino rats.’ Since that time, the rat has frequently been used in experimental caries research, and we now have considerable knowledge about dental caries in this animal. With success in the production of caries in the rat, a search was begun for other animal species suitable for dental caries studies. Dogs, rabbits, guinea pigs, and monkeys were tested with little success, but hamsters were found to be suitable for the purpose. As a consequence, most studies dealing with evaluation of cariostatic agents have been carried out on rats and hamsters. The potentials as well as some of the shortcomings of these rodents in the screening of caries-preventive agents will be considered in this presentation.