Replacement Therapy for the Prevention of Dental Disease

Certain laboratory-derived and naturally occurring oral bacteria are promising effector strains for the replacement therapy of dental infectious diseases. In the case of dental caries, several types of low-acid-producing mutants of Streptococcus mutans and a natural variant of S. salivarius have been found that are virtually non-cariogenic. Laboratory rats can be readily and persistently infected with these micro-organisms. Once infected, the animals become much more resistant to infection by wild-type (disease-causing) strains of S. mutans. Thus, in the laboratory rat, replacement therapy has proved successful in providing lifelong resistance to dental caries following a single application of an effector strain. Attempts to extend these findings to humans have required a search for effector strains that can both colonize well and, in addition, displace indigenous, wild-type strains of S. mutans. A mutant of a strain of S. mutans producing a bacteriocin-like molecule has been found that appears to be well-suited for this purpose. Replacement therapy may also find a practical application in the prevention and cure of certain periodontal diseases. Hydrogen peroxide-producing streptococci are invariably found in plaque taken from healthy gingiva; they are rarely found in samples from active disease sites of patients with juvenile or refractory periodontitis. In vitro, peroxide production by these streptococci inhibits the growth of Actinobacillus actinomycetemcomitans and several other presumed periodontal pathogens. Bacterial interactions of this sort have also been directly demonstrated to occur in vivo. Thus, natural inhibitors in plaque may be essential for maintenance of periodontal health. Patients lacking such inhibitors may be treated by replacement therapy to restore the composition of their plaque flora to one that is conducive to health.