Predominant cultivable supragingival plaque in Chinese "rapid" and "slow" plaque formers

The aim of this study was to compare the predominant cultivable bacterial flora in supragingival plaque samples of Chinese "rapid" and "slow" plaque formers, using the experimental gingivitis model. 11 Chinese subjects (5 "rapid" and 6 "slow" plaque formers) were selected from 49 healthy young adults. The selection was based on the plaque index on the buccal surfaces of all the canines, premolars and 1st molars after 3-days without plaque control. The 11 subjects began a 14-day on oral hygiene period after prophylaxis. Plaque samples were collected on day 1, day 3, day 7 and day 14 from the buccal surface of upper right canine, 2nd premolar, 1st premolar and 1st molar, respectively. The samples were then dispensed into a tryptic soy broth, and cultured anaerobically to obtain pure isolates which were then identified by conventional means. Results showed similar trends in plaque development in the two groups; gram-positive bacteria were the predominant cultivable species ("rapid": 71-37%; "slow": 53-63%) and gram-negative species increased in proportion to the plaque age ("rapid": 9-47%, "slow": 13-28%). "Rapid" plaque formers showed a statistically significant higher percentage of gram-negative rods (38%) than the "slow" group (17%) in the 14-day samples. The difference in the proportions of other groups of bacteria between the "rapid" and "slow" plaque formers were also found to be statistically significant using the MANOVA test (p = 0.0162). Most of the cultivable gram-negative rods belonged to Fusobacterium and Capnocytophaga species. Besides the quantitative difference observed clinically, there seems to be a qualitative difference in the cultivable flora between subjects with different rates of plaque formation.