[Microflora around the bracket by direct bonding system].

The purpose of the present study is to clarify the influence of microflora in plaque of the brackets edge by direct bonding system and the cause of caries that is induced around the bracket during orthodontic treatment. The subjects were selected from the patients undergoing direct bonded orthodontic treatment and from the non-orthodontic patients. They were divided into four groups: those having no orthodontic treatment (control group), those having no caries around the bracket (group A) and those having caries around the bracket (groups B and C). Sample plaques were collected from the initial tooth surface with control group, from the tooth surface around the bracket with group A, from the carious cavity around the bracket with group B and from the non-carious tooth surface around the bracket with group C. The isolation rates of microflora in dental plaque of the four groups were compared, and the following conclusions were obtained. 1. Group A had almost same level with control group as to the proportion of each bacterium examined by shape and gram stain of microbiota. Group B had higher level of gram positive cocci than the other groups. 2. Group A and control group had no difference as to the isolation rates of genera Streptococcus, Actinomyces and Lactobacillus. 3. Group A had low level of S. mutans, was the same as control group. 4. The isolation rate of each genus: 1) The isolation rate of genus Streptococcus was almost same in groups A, C and control group. Group B had higher than the other groups. 2) The isolation rate of genus Actinomyces was the highest in all groups. 3) The isolation rate of genus Lactobacillus was exceedingly low. 4) Groups B and C had significantly higher level of S. mutans group than group A and control group. Group B had significantly lower level of S. mitior than group A and control group. 5. All four groups showed high level of biotype I, and biotype IV was observed in groups B and C. Biotype I was identified as S. mutans serotype c, biotype IV was observed as S. sobrinus serotype d.