Outcome variables
Self-rated health and number of remaining natural teeth were used as outcomes. Self-rated health was measured through the question ‘‘What is your current health status: excellent, good, fair, or poor?’’ For analysis purposes, this variable was dichotomized in the manner similar to that used by Ichida et al. (2009), Kim and Kawachi (2007) and Subramanian et al. (2001) as follows: (i) good (“excellent/good”) and (ii) poor (“fair/poor”). To obtain data on dental status, respondents were asked to classify their dental status as having 20 or more teeth, having 19 or less teeth with dentures, having 19 or less teeth without any dentures, having very few teeth with dentures, or having very few teeth without any dentures. Retention of a minimum of 20 functional natural teeth at ages of 65 years and over was an oral health goal specified by the WHO and Federation Dentaire Internationale “Global Goals for Oral Health in the year 2000” (Federation Dentaire Internationale, 1982). The goal for an acceptable level of oral health set by the Japan Dental Association was retention of a minimum of 20 functional teeth at the age of 80. Previous research indicated that older people with 20 or more teeth had better nutritional intake than people with 19 or less teeth (Yoshihara, Watanabe, Nishimuta, Hanada, & Miyazaki, 2005). Therefore, dental status was used as a dichoto- mous variable: (i) having 20 or more teeth and (ii) having 19 or less teeth.