Table 3 Multivariate logistic regression model for calculus (method: backward)

Age group

 12 years

1

NA

NA

 13 years

1.566

1.227–2

< 0.001

 14 years

1.366

1.074–1.736

0.011

 15 years

2.131

1.65–2.753

< 0.001

Region

 Shouguang, Weifang

1.236

0.972–1.573

0.084

 Huancui, Weihai

1.456

1.133–1.871

0.003

 Pingyi, Linyi

1.554

1.190–2.028

0.001

 Hedong, Linyi

1

NA

NA

Gender

 Male

1.57

1.307–1.886

< 0.001

 Female

1

NA

NA

Q5 frequency of brushing (n = 3356)

 ≥ 2/day

1

NA

NA

 1/day

1.421

1.158–1.742

0.001

 < 1/day

1.691

1.209–2.364

0.002

Q9a frequency of having sweets

 Seldom or never

1.75

1.161–2.639

0.008

 1–3/month

1.37

0.944–1.988

0.098

 1/week

1.318

0.951–1.827

0.097

 2–6/week

1.311

0.981–1.752

0.067

 1/day

1.1

0.8–1.512

0.557

 ≥ 2/day

1

NA

NA

Q16 whether visited a dentist

 Yes

1

NA

NA

 Never

1.249

1.037–1.504

0.019