THE ACTION OF INDIVIDUAL BACTERIAL STRAINS ON HUMAN TEETH UNDER IN VITRO CONDITIONS

¹ The University of Alabama, Dental School and Medical College, Departments of Biochemistry and Bacteriology, Birmingham, Ala.

Eight strains of microorganisms of the type occurring in the mouth were found to destroy human teeth extensively in less than 25 weeks, when subjected to the conditions of the artificial mouth. These organisms were Lactobacillus casei (2 strains), Streptococcus salivarius (2 strains), Streptococcus faecalis, Micrococcus pyogenes var. aureus, Micrococcus pyogenes var. albus, and Clostridium perfringens. One other microorganism, Neisseria catarrhalis, was tested and found to be without action.

These microorganisms exhibited marked differences in their ability to attack the various tissues of teeth. One strain of L. casei exhibited intensive decalcifying action; it had only a moderate ability to destroy decalcified dentinal matrix, but it destroyed external enamel surfaces readily. The other extreme of action was shown by C. perfringens, which destroyed calcified and decalcified dentinal matrix, without any obvious signs of decalcification. Other organisms showed actions intermediate between the extremes. Some destroyed dentin more rapidly than enamel and produced undercutting of enamel. A pigmentation of dentin seemed to be associated with a rate of dentinal decalcification greater than that of matrix destruction.

A restriction of the bacterial factor in dental caries to lactobacilli species seems an unwarranted oversimplification, but lactobacilli may be "indicator" microorganisms useful for showing the existence of conditions which permit rapid decalcification. The observed ability of a number of oral bacteria to destroy teeth rapidly, under in vitro conditions, suggests that many types of bacteria may participate in the carious process. The variable action of the several types of microorganisms on the different tissues of teeth indicates that carious lesions in different anatomical locations may have diverse etiologies, arising from the actions of many types of microorganisms acting singly, jointly, or consecutively.