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 ICC above 0.90 for the assessment of dental caries, gingival bleeding, 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.
Variables (N=482)
|
n
|
%
|
Socio-demographic background
|
|
|
Sex
Boy
Girl
|
233
249
|
48.3%
51.7%
|
Father’s education level
Primary school level, ≤6 years
Secondary school level or above, > 6 years
|
271
211
|
56.2%
43.8%
|
Mother’s education level
Primary school level, ≤6 years
Secondary school level or above, > 6 years
|
282
200
|
58.5%
41.5%
|
Monthly pocket money
Less than 50RMB (~US$ 7)
More than 50RMB (~US$ 7)
|
325
157
|
67.4%
32.6%
|
Oral health-related behaviours
|
|
|
Toothbrushing frequency (daily)
Less than twice
Twice or above
|
315
167
|
65.4%
34.6%
|
Sugary snacking habits
No
Yes
|
335
147
|
69.5%
30.5%
|
Sour food snacking habits
No
Yes
|
360
122
|
74.7%
25.3%
|
RMB: Renminbi (Chinese Yuen); US$: U.S. Dollar.
Oral health status
Among the study children, 167 (34.6%) had dental caries experience. The girls had a higher dental caries prevalence rate than boys (42% vs. 27%, p<0.001, Table 2). The mean (standard deviation [SD]) DMFT score was calculated to be 0.63 (1.10). The majority (95.2%) of the mean DMFT score consisted of unrestored cavities with the mean DT score of 0.60 (SD:1.10). The mean (SD) MT score was 0.02 (0.13), and the mean (SD) FT score was 0.01 (0.16). First molars had the highest dental caries prevalence rate (58.8%), while canines were the least affected ones (0.4%). The prevalence rate for all incisors and premolars were lower than 10%.
Table 2. Prevalence of dental caries and gingival bleeding according to socio-demographic background and oral-health related behaviours.
Variables (N=482)
|
DMFT>0
(%)
|
p-value
|
Gingival bleeding
(%)
|
p-value
|
Socio-demographic background
|
|
|
|
|
Sex
Boy (233)
Girl (249)
|
27%
42%
|
<0.001*
|
88%
89%
|
0.791
|
Father’s education level
Primary school level, ≤6 years (271)
Secondary school level or above, > 6 years (211)
|
33%
37%
|
0.345
|
92%
83%
|
0.003*
|
Mother’s education level
Primary school level, ≤6 years (282)
Secondary school level or above, > 6 years (200)
|
33%
37%
|
0.361
|
93%
82%
|
<0.001*
|
Monthly pocket money
Less than 50RMB (~US$ 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
|
DMFT: decayed, missing and filled teeth; RMB: Renminbi (Chinese Yuen); US$: U.S. Dollar.
For gingival bleeding, 426 children (88.4%) had gingival bleeding by probing. No significant difference was found between boys and girls regarding the prevalence of gingival bleeding (Table 2). First molars presented the highest prevalence rate of gingival bleeding (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 gingival bleeding 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. 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.
Risk factors for dental caries and gingival bleeding
In the chi-square test of independent variables and the prevalence of dental caries, only sex had a p-value less than 0.10 (Table 2). 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 covariates 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.
Variables
|
Rank of median DMFT score
|
p-value
|
Socio-demographic background
|
|
|
Sex
Boy
Girl
|
223
257
|
0.001*
|
Father’s education level
Primary school level, ≤6 years
Secondary school level or above, > 6 years
|
239
245
|
0.553
|
Mother’s education level
Primary school level, ≤6 years
Secondary school level or above, > 6 years
|
237
248
|
0.336
|
Monthly pocket money
Less than 50RMB (~US$ 7)
More than 50RMB (~US$ 7)
|
237
252
|
0.180
|
Oral health-related behaviours
|
|
|
Toothbrushing frequency (daily)
Less than twice
Twice or above
|
240
245
|
0.662
|
Sugary snacking habits
No
Yes
|
234
258
|
0.041*
|
Sour food snacking habits
No
Yes
|
237
254
|
0.160
|
DMFT: decayed, missing and filled teeth; RMB: Renminbi (Chinese Yuen); US$: U.S. Dollar.
For gingival bleeding, five independent variables had a p-value less than 0.10 in the chi-square test of independent variables and gingival bleeding (Table 2). They were studied as covariates in the multivariate logistic regression model. In the final model, three variables were significantly related to the prevalence of gingival bleeding (Table 5). Children whose mothers had a lower education level and those who had less pocket money had a higher chance of having gingival bleeding (OR=2.51, p=0.003 and OR=3.75, p<0.001, respectively). Moreover, children who brushed their teeth less than twice daily had a higher chance of having gingival bleeding (OR=2.41, p=0.004).
Table 4. Dental caries risk factors of the 12-year-old Lisu children (Zero inflated negative binomial regression model, N =482).
Zero-inflated portion
(DMFT=0)
|
Effect modifiers
|
Odds ratio
(95% C.I)
|
p-value
|
Sex
Girl
Boy#
|
0.35 (0.15, 0.79)
|
0.012
|
Negative binomial portion (DMFT>0)
|
Effect modifiers
|
Incidence rate ratio (95% C.I)
|
p-value
|
Sugary snacking habits
Yes
No#
|
1.55 (1.14,2.11)
|
0.005
|
#Reference group.
DMFT: decayed, missing and filled teeth.
Table 5. Gingival bleeding risk factors of the 12-year-old Lisu children (Multivariate logistic regression model, N = 482).
Effect modifiers
|
Odds ratio
(95% C.I.)
|
p-value
|
Mother’s education level
Primary school level, ≤6 years
Secondary school level or above, > 6 years#
|
2.51 (1.32, 3.53)
|
0.003
|
Monthly pocket money
Less than 50RMB (~US$ 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.
RMB: Renminbi (Chinese Yuen); US$: U.S. Dollar.