
More than 100,000 people took part in the seven year study. Gender, age, and health conditions were all considered when accepting the participants. One half of them had their teeth professionally scarped and cleaned at least once a year, the other half had no tooth scaling.
None of the participants had a history of heart attack or stroke at the beginning of the study. Weight, smoking, and race were not adjusted in this research as they were not included in the Taiwan National Health insurance data base – the source of the information for the analysis.