This study invited 512 12-year-old Lisu children from nine primary schools to participate, and 482 children (48% boys) were successfully recruited. All invited schools agreed to participate. Thirty invited children were absent from their respective schools and did not return the parental consent forms. Thus, the response rate was 94%. Among the participating schools, seven were from the western region and two from the eastern region. The ratio of recruited children in the western region and the eastern region was 8:1 (430:52). The intra- and inter-examiners reliability were excellent with the intraclass correlation above 0.90 for the assessment of dental caries, gingivitis, tetracycline-stained teeth and dental fluorosis. The children’s background information and their oral health-related behaviours are presented in Table 1.
Table 1
Socio-demographic background and oral health-related behaviours of the study Lisu children (N = 482).
Variables | DMFT > 0 (%) | p-value | Gingivitis (%) | p-value |
Socio-demographic background | | | | |
Sex Boy (233) Girl (249) | 27% 42% | < 0.001* | 88% 89% | 0.791 |
Father’s education level Primary school level, ≤ 6 years (271) Secondary school level or above, > 6 years (211) | 33% 37% | 0.345 | 92% 83% | 0.003* |
Mother’s education level Primary school level, ≤ 6 years (282) Secondary school level or above, > 6 years (200) | 33% 37% | 0.361 | 93% 82% | < 0.001* |
Monthly pocket money Less than 50RMB (~ US$ 7) (325) More than 50RMB (~ US$ 7) (157) | 32% 39% | 0.120 | 94% 77% | < 0.001* |
Oral health-related behaviours | | | | |
Toothbrushing frequency (daily) Less than twice (315) Twice or above (167) | 34% 36% | 0.667 | 93% 80% | < 0.001* |
Sugary snacking habits No (335) Yes (147) | 33% 40% | 0.142 | 90% 85% | 0.129 |
Sour food snacking habits No (360) Yes (122) | 33% 39% | 0.298 | 90% 84% | 0.057 |
Oral health status
Among the study children, 167 (34.6%) had dental caries experience. The girls had a higher dental caries prevalence rate than boys (42% vs. 27%, p < 0.001). The mean (standard deviation [SD]) DMFT score was calculated to be 0.63 (1.10). The majority (95.2%) of the mean DMFT score consisted of unrestored cavities with the mean DT score of 0.60 (SD:1.10). The mean (SD) MT score was 0.02 (0.13), and the mean (SD) FT score was 0.01 (0.16). Dental caries prevalence rates according to different tooth locations are presented in Fig. 1. First molars had the highest dental caries prevalence rate (58.8%), while canines were the least affected ones (0.4%). The prevalence rate for all incisors and premolars were lower than 10%.
For gingivitis, 426 children (88.4%) had gingival bleeding by probing. No significant difference was found between boys and girls regarding the prevalence of gingivitis (Table 1). The prevalence rates of gingivitis according to different tooth locations are presented in Fig. 2. First molars presented the highest prevalence rate of gingivitis (65.3%) and canines had the lowest prevalence rate (24.3%). However, unlike that of dental caries, all four lower incisors presented high prevalence rates, meaning over 30%. This study found no relationship between gingivitis and dental caries (p = 0.438). None of the study children had dental fluorosis.
There were 53 children who were not cooperative during the dental erosion status assessment. Therefore, dental erosion was assessed for 429 children. All study children had dental erosion, but none of them had severe erosion (BEWE score = 3). Twenty-three children (5.4%) had at least one sextant that had distinct defect of the tooth surface (BEWE score = 2), and 428 children (99.8%) had at least one sextant with an initial loss of enamel surface texture (BEWE score = 1). The cumulative scores of all sextants ranged from 2 to 12. Only one child had no risk with the cumulative BEWE score equaled to two. Almost all children (n = 425, 99%) had low risk with the cumulative BEWE score between three and eight, while three were at medium risk with the score between 9 and 12. The mean (SD) of the cumulative BEWE score was calculated to be 6.1 (0.5) and no significant difference was found between boys and girls (p = 0.965) (Table 2). No other independent variables were found to be related to the mean cumulative BEWE scores. Almost all of the study children did not have tetracycline-stained teeth (99.3%). The three children (0.7%) who had tetracycline-stained teeth were all from the western region but in different cities/autonomous prefectures.
Table 2
Mean cumulative BEWE scores according to independent variables (N = 429).
Variables | Mean (SD) cumulative BEWE score | p-value |
Socio-demographic background | | |
Sex Boy (204) Girl (225) | 6.1 (0.5) 6.1 (0.5) | 0.965 |
Father’s education level Primary school level, ≤ 6 years (249) Secondary school level or above, > 6 years (180) | 6.1 (0.5) 6.0 (0.4) | 0.056 |
Mother’s education level Primary school level, ≤ 6 years (267) Secondary school level or above, > 6 years (162) | 6.1 (0.4) 6.0 (0.6) | 0.400 |
Monthly pocket money Less than 50RMB (~ US$ 7) (311) More than 50RMB (~ US$ 7) (118) | 6.1 (0.6) 6.0 (0.2) | 0.395 |
Oral health-related behaviours | | |
Toothbrushing frequency (daily) Twice or less (293) More than twice (136) | 6.1 (0.5) 6.1 (0.4) | 0.208 |
Sugary snacking habits No (309) Yes (120) | 6.1 (0.4) 6.1 (0.7) | 0.832 |
Sour food snacking habits Less than once (327) Once or above (102) | 6.1 (0.5) 6.1 (0.3) | 0.744 |
Oral health-related behaviours and risk factors for oral conditions
All questionnaires were returned, and missing data followed-up. A considerable number (35%) of the study children reported that they brushed their teeth less than twice daily. There were 70% of study children indicated they ate sugary snacks every day, and 74% stated they had sour food snacks daily. These children were considered to have sugary snacking habits, and sour food snacking habits. Besides, nearly half of the study children (48%) had never visited a dentist.
In the Chi-square test of independent variables and the prevalence of dental caries, only sex had a p-value less than 0.10. In the Mann-Whitney U test of independent variables and the mean rank of the median DMFT scores, sex and sugary snacking habits were found to have a p-value less than 0.10 (Table 3). These mentioned independent variables were studied as effect modifiers in the ZINB model. The results of the Voung test showed that the ZINB model is the best-fit model when compared to other count models (p < 0.05). In the final model, girls were found to have less chance to have no dental caries when compared to boys (Odds ratio [OR] = 0.35, p = 0.012). In the negative binomial portion of the model, children who had a sugary snacking habit presented higher DMFT scores compared to those who did not (Incidence risk ratio [IRR] = 1.55, p = 0.005).
Table 3
Mean rank of median DMFT scores and independent variables (N = 482).
Variables | Rank of median DMFT score | p-value |
Socio-demographic background | | |
Sex Boy (233) Girl (249) | 223 257 | 0.001* |
Father’s education level Primary school level, ≤ 6 years (271) Secondary school level or above, > 6 years (211) | 239 245 | 0.553 |
Mother’s education level Primary school level, ≤ 6 years (282) Secondary school level or above, > 6 years (200) | 237 248 | 0.336 |
Monthly pocket money Less than 50RMB (~ US$ 7) (325) More than 50RMB (~ US$ 7) (157) | 237 252 | 0.180 |
Oral health-related behaviours | | |
Toothbrushing frequency (daily) Less than twice (315) Twice or above (167) | 240 245 | 0.662 |
Sugary snacking habits No (335) Yes (147) | 234 258 | 0.041* |
Sour food snacking habits No (360) Yes (122) | 237 254 | 0.160 |
Table 4
Dental caries risk factors of the 12-year-old Lisu children (Zero inflated negative binomial regression model, N = 482).
Zero-inflated portion (DMFT = 0) | Effect modifiers | Odds ratio (95% C.I) | p-value |
Sex Girl Boy# | 0.35 (0.15, 0.79) | 0.012 |
Negative binomial portion (DMFT > 0) | Effect modifiers | Incidence rate ratio (95% C.I) | p-value |
Sugary snacking habits Yes No# | 1.55 (1.14,2.11) | 0.005 |
#Reference group. |
For gingivitis, five independent variables had a p-value less than 0.10 in the Chi-square test of independent variables and gingivitis (Table 1). They were studied as effect modifiers in the multivariate logistic regression model. In the final model, three effect modifiers were significantly related to the prevalence of gingivitis (Table 5). Children whose mothers had a lower education level and those who had less pocket money had a higher chance of having gingivitis (OR = 2.51, p = 0.003 and OR = 3.75, p < 0.001, respectively). Moreover, children who brushed their teeth less than twice daily had a higher chance of having gingivitis (OR = 2.41, p = 0.004).
Table 5
Gingivitis risk factors of the 12-year-old Lisu children (Multivariate logistic regression model, N = 482).
Effect modifiers | Odds ratio (95% C.I.) | p-value |
Mother’s education level Primary school level, ≤ 6 years Secondary school level or above, > 6 years# | 2.51 (1.32, 3.53) | 0.003 |
Monthly pocket money Less than 50RMB (~ US$ 7) More than 50RMB (~ US$ 7) # | 3.75 (2.05, 6.86) | <0.001 |
Toothbrushing frequency (daily) Less than twice Twice or above# | 2.41 (1.33, 4.39) | 0.004 |
#Reference group. |