In part 1 of this epidemiological study, a survey was conducted for all senior citizens aged 70 and over who resided in a mountainous village in the mid-section of Hyogo Prefecture. It focused on the relationship among the number of existing teeth, life environment, health status, and activities of daily living; and the correlation between oral status and QOL was analyzed. The daily activities of individuals were compared between those having one or more teeth and others who were totally edentulous. Subsequently, it was found that for both males and females, the odds ratio was significantly high for the dentulous individuals, in comparison with edentulous individuals, to exhibit a behavior indicative of a better QOL (such as "opportunity for conversation with family members or others)", "regular physical activities", and "attend meetings or group outings"). The result of this survey indicates that the presence of teeth is very closely related to one's daily activities. It was concluded that preventing tooth loss is vital for maintaining the masticatory function; so to prevent tooth loss, periodontal disease must be averted.