Periodontal Diseases in Children and Adolescents …
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limited to those of the collected area. Thus, we must carefully consider which specimens
match the purpose of studies prior to their initiation. In addition, the timing of collection of
the specimens is also important. We generally collect the specimens for the initial stage at the
second visit to our clinic, prior to giving detailed tooth brushing instructions, which enable us
to determine the natural bacterial profiles of each subject. The procedures for extraction of the
bacterial DNA are as follows. The subgingival dental plaque specimens
are collected in sterile
saline, which are centrifuged at 15000 rpm for 5 min to pellet the bacterial cells. Bacterial
genomic DNA is extracted from each pellet using a DNA isolation kit (Puregene, Gentra
Systems, Minneapolis, MN, USA). As for the saliva samples, expectorated whole saliva
collected from each patient is mixed with Chelex 100 (Bio-Rad Laboratories, Hercules, CA,
USA), which is then incubated at 56°C for 30 min, followed by boiling at 100°C for 10 min.
Each sample is then centrifuged at 15000 rpm for 20 min and the supernatants used as
templates for PCR assays.
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