Table 1 Statistical significance by demographic variables for dental caries, calculus and gingival bleeding among 12–15-year-old students (n = 3868). N (%)

Total

2326 (60.1%)

1542 (39.9%)

708 (18.3%)

3160 (81.7%)

2656 (68.7%)

1212 (31.3%)

Age group

 12 years

589 (62.7%)^a

351 (37.3%)^a

225 (23.9%)^a

715 (76.1%)^a

666 (70.9%)^a

274 (29.1%)^a

 13 years

582 (59.2%)^a,b

401 (40.8%)^a,b

175 (17.8%)^b

808 (82.2%)^b

666 (67.8%)^a,b

317 (32.2%)^a,b

 14 years

597 (61.9%)^a

368 (38.1%)^a

178 (18.4%)^b

787 (81.6%)^b

687 (71.2%)^a

278 (28.8%)^a

 15 years

558 (56.9%)^b

422 (43.1%)^b

130 (13.3%)^c

850 (86.7%)^c

637 (65.0%)^b

343 (35.0%)^b

Gender

 Male

1300 (66.9%)^a

642 (33.1%)^a

281 (14.5%)^a

1661 (85.5%)^a

1313 (67.6%)

629 (32.4%)

 Female

1026 (53.3%)^b

900 (46.7%)^b

427 (22.2%)^b

1499 (77.8%)^b

1343 (69.7%)

583 (30.3%)

Urban and rural

 Urban

1145 (59.2%)

790 (40.8%)

380 (19.6%)^a

1555 (80.4%)^a

1270 (65.6%)^a

665 (34.4%)^a

 Rural

1181 (61.1%)

752 (38.9%)

328 (17.0%)^b

1605 (83.0%)^b

1386 (71.7%)^b

547 (28.3%)^b

Region

 Shouguang Weifang

540 (56.4%)^a

418 (43.6%)^a

187 (19.5%)^a

771 (80.5%)^a

665 (69.4%)^a

293 (30.6%)^a

 Huancui, Weihai

550 (58.0%)^a

399 (42.0%)^a

168 (17.7%)^a

781 (82.3%)^a

588 (62.0%)^b

361 (38.0%)^b

 Hedong, Linyi

595 (60.3%)^a,b

391 (39.7%)^a,b

212 (21.5%)^b

774 (78.5%)^b

682 (69.2%)^a

304 (30.8%)^a

 Pingyi, Linyi

641 (65.7%)^b

334 (34.3%)^b

141 (14.5%)^c

834 (85.5%)^c

721 (73.9%)^c

254 (26.1%)^c

An only child or not?

 Yes

913 (62.7%)^a

542 (37.3%)^a

274 (18.8%)

1181 (81.2%)

997 (68.5%)

458 (31.5%)

 No

1413 (58.6%)^b

1000 (41.4%)^b

434 (18.0%)

1979 (82.0%)

1659 (68.8%)

754 (31.2%)

Father's education level

 Never go to school

10 (62.5%)

6 (37.5%)

3 (18.8%)

13 (81.3%)

9 (56.3%)

7 (43.8%)

 Elementary or junior high school

1476 (61.3%)

932 (38.7%)

425 (17.6%)

1983 (82.4%)

1646 (68.4%)

762 (31.6%)

 High school

318 (56.6%)

244 (43.4%)

112 (19.9%)

450 (80.1%)

374 (66.5%)

188 (33.5%)

 College or university

349 (59.9%)

234 (40.1%)

109 (18.7%)

474 (81.3%)

418 (71.7%)

165 (28.3%)

 No father or do not know

173 (57.9%)

126 (42.1%)

59 (19.7%)

240 (80.3%)

209 (69.9%)

90 (30.1%)

Mother’s education level

 Never go to school

103 (68.7%)^a

47 (31.3%)^a

29 (19.3%)

121 (80.7%)

103 (68.7%)

47 (31.3%)

 Elementary or junior high school

1545 (61.2%)^b

978 (38.8%)^b

446 (17.7%)

2077 (82.3%)

1728 (68.5%)

795 (31.5%)

 High school

197 (53%)^c

175 (47%)^c

74 (19.9%)

298 (80.1%)

247 (66.4%)

125 (33.6%)

 College or university

290 (59.1%)^c

201 (40.9%)^c

101 (20.6%)

390 (79.4%)

357 (72.7%)

134 (27.3%)

 No mother or do not know

191 (57.5%)^b,c

141 (42.5%)^b,c

58 (17.5%)

274 (82.5%)

221 (66.6%)

111 (33.4%)