Porphyromonas gingivalis FimA fimbriae have been classified into 6 genotypes 
(types I-V and Ib) based on the diversity of the fimA genes encoding the 
fimbrial subunits. We investigated the prevalence of fimA genotype in Japanese 
children. Dental plaque specimens were obtained from 400 subjects (age; 2 to 15 
years), including 134 with healthy gingiva, 239 with gingivitis and 27 with 
periodontitis, and then analyzed by polymerase chain reaction. P. gingivalis was 
detected in 1.5%, 10.0% and 29.6% of these subjects, respectively. Significant 
differences were observed with regard to P. gingivalis infection among the 
groups [chi-squared analysis: gingivitis vs. healthy, P < 0.01, odds ratio (OR) 
= 7.4; periodontitis vs. healthy, P < 0.001, OR = 27.8]. In P. 
gingivalis-positive subjects with periodontitis, the most prevalent fimA types 
were type Ib/type II combination (37.5%) and type IV (37.5%), followed by type 
II (25.0%), while type IV (33.3%) and type II (29.2%) were most often detected 
in those with gingivitis. Our results suggest that the presence of P. gingivalis 
is associated with periodontal diseases, and that the type II, IV and Ib/II 
combination are the most common among fimA genotypes.