The risk factors were poor dental hygiene (RR = 1.7; 95% CI = 1.4 - 2.1), worked as factory worker or office worker before retiring (RR = 1.3; 95% CI = 1.2 - 1.5), poor / near oor economic status (RR = 2.3; 95% CI = 1.8 - 3.0).