Dental infections such as tooth decay and periodontal disease are perhaps the most common bacterial infections in humans. Their non-life-threatening nature and theirubiqui-tousness have minimized their significance in overall human health. Yet the economic burden for the treatment of these dental infections can be staggering. In the United States the annual cost for the symptomatic treatment of dental infections in 1977 was over 11 billion dollars (69), and this had increased to about 24 billion dollars in 1984 (118). More than 90% of these costs are related to the restoration of teeth or tooth substance lost to dental decay (69). Despite the enor-mity of these dollar figures, they represent the cost for only those estimated 40 to 50% of the public who regularly visit the dentist and receive treatment (347). Put into this perspective, tooth decay and, to a lesser extent, periodontal infections are perhaps the most expensive infections that most individuals have to contend with during a lifetime. Dental infections are costly because the treatment is symptomatic and does not include a viable preventive approach based upon the control of the bacterial factors involved in both decay and periodontal disease. The prevail-ing opinion in clinical dentistry has been that the accumulation of bacterial communities on the tooth surfaces, in aggregates known as dental plaque, causes both decay and periodontal disease. This opinion results from the failure of 19th century dental scientists to identify within the plaques a microbial flora that was uniquely associated with dental pathology (25, 248). This led to the conclusion that dental infections were the result of bacterial overgrowth on the tooth surfaces and that therapy should accordingly be directed toward the prevention of this overgrowth. This concept of dental infections as being bacteriologically nonspecific offers no rationale for antimicrobial treatment other than the daily debridement of the tooth surfaces by modern versions of ancient implements, such as tooth-brushes, floss, and toothsticks. There is no convincing evidence that careful mechanical debridement by the patient has ever reduced the incidence of dental decay, although such procedures can reduce the amount of dental plaque and the level of gingivitis (inflammation of the gingiva or gums)