A 4‐year‐old Japanese boy was referred to Osaka University Dental Hospital because of severe mobility and pain of the right lower primary canine. The canine had severe bone loss and a pocket depth exceeding 5‐6 mm. The left lower canine showed slight mobility and moderate alveolar bone loss. The other primary teeth showed no pathogenic findings. The subgingival microflora from the right lower canine was dominated by gram‐negative rods, especially capnocytophaga and fusobacterium, while actinomyces sp. were the most common gram‐positive bacteria. While neutrophil functions of the patient were within the normal ranges of healthy subjects, some lymphocyte functions such as IL‐2 production and IgG and IgM syntheses were lower in the patient. 7 months after the extraction of the right lower primary canine, the patient complained of pain around the right lower primary lateral incisor. In 3‐4 weeks, the alveolar bone was lost rapidly and mobility of the lower anterior teeth increased significantly. The primary lateral incisor was extracted and the other primary teeth were treated by scaling and systemic and local administration of antibiotics. After treatment, the lower anterior teeth became less mobile and the gram‐positive cocci predominated.

Prevotella intermedia and fusobacterium nucleatum are associated with various forms of periodontal disease. The purpose of the present study was to infect the clinical isolates of these periodontopathic bacteria and to induce a significant loss of alveolar bone in specific pathogen-free (SPF) rats in the absence of ligatures. P. intermedia YKD8 and F. nucleatum YKZ5 were isolated from a prepubertal periodontitis patient, while P. gingivalis MWB13 was from a patient with juvenile periodontitis. At first, SPF Sprague-Dawley rats (70 days of age, male) were infected with A. viscosus Ny1R and subsequently superinfected with P. gingivalis MWB13, P. intermedia YKD8, or F. nucleatum YKZ5, respectively. The control group was infected with A. viscosus Ny1R alone. All rats were killed and periodontal bone levels were assessed morphometrically 135 days after the first infection with A. viscosus. P. intermedia YKD8 was recovered frequently from rats, with serum antibody levels remaining highly elevated throughout the experiment. Significant loss of alveolar bone was found in rats infected with P. intermedia YKD8, the virulence of which was equivalent to that of P. gingivalis MWB13. F. nucleatum YKZ5 also induced alveolar bone loss, but not significantly when compared with rats infected with A. viscosus Ny1R alone.