Background
Although the dental caries in children has generally declined in the past 50 years [
1], dental caries of children is still prevalent in many countries and disadvantaged communities and is regarded as global major public health problem [
2,
3]. Bagramian et al. performed a review of epidemiological data and found that caries prevalence among children has increased in many developed and developing countries in the past 10 years [
4]. Oral health is an essential part of general health [
5]. Tooth decay, if left untreated, will progress and infect the dental pulp, causing pain and forming dental abscess. Moreover, it can lead to severe local and systemic infections [
6]. This increase in dental caries signals a pending public health crisis to many communities.
Water fluoridation was implemented in Hong Kong in 1961 and the caries experience of children has reduced [
7]. An oral health education unit has been established to promote dental health and good oral health-related behaviours in the community. In addition, the School Dental Care Service (SCDS) was established in 1980 to provide basic curative treatments for children attending primary schools in Hong Kong [
8]. There is, however, no continuation of dental care when the children enter secondary school, and they have to seek private dentists for check-ups and dental care.
Dental erosion is tooth surface loss caused by chemical processes without bacterial involvement [
9]. The impacts of dental erosion include compromised aesthetics, dentinal hypersensitivity, and reduced chewing ability, all of which may lead to complicated treatment and high treatment costs if advanced erosion occurs [
10]. Dental treatment for dental erosion can be very complex and challenging and early diagnosis is therefore important. However, many child patients are not aware of the problem and clinicians may sometimes overlook or fail to detect early stage erosion because the patient often does not present symptoms [
11]. Dental erosion is becoming a public health concern because of its high prevalence in population surveys [
12,
13]. Newly erupted permanent teeth of children have immature enamel, which is more susceptible to acid attack by soft drinks. Certain drinks, such as sport/energy drinks, ‘healthy’ drinks, and soda, are popular among them [
14] but are also acidic and have fermentable sugars [
15]. Therefore, it is plausible that more children will be affected by dental erosion [
10]. A survey in Iceland reported 31% of 15-year-old teenagers had signs of erosion, and 5.5% of children had severe erosion on their teeth [
12]. Another study in Sweden found that 34% of 18–19 year old adults had at least one tooth with severe erosion extending to dentine [
13].
The Department of Health performed a population-based oral health survey among 5- and 12-year-old children in 2001 [
16]. The survey followed the World Health Organization (WHO) guidelines on dental caries assessment [
17], but there is no report on dental erosion. Currently, the literature on the distribution and epidemiology of dental erosion among Chinese young adults is scarce. A literature search found no related studies reported in English so far. In order to better understand the dental health of children in Hong Kong, an updated survey on a representative sample is warranted. The collected information would be useful to the dental profession and the government for planning dental services in Hong Kong. The objectives of this study were to first investigate dental caries, prevalence, and the distribution of dental erosion in 12-year-old children in Hong Kong and second, to investigate the risk factors for dental erosion and dental caries.
Results
A total of 704 children in 7 primary schools were invited to participate in this study. Of those, 104 failed to complete the consent form, questionnaire, or the oral examination procedure due to uncooperative behaviour or absence from school. Therefore, 600 children were examined. The response rate was 85% (600/704). Among the 600 children examined, 60 were in Hong Kong, 234 were in Kowloon, and 306 were in New Territory, and approximately half (n = 316, 53%) of them were boys (Table
1). Kappa values for assessment of caries status and dental erosion were 0.95 to 0.97 (0.95, 0.97, 0.97) and 0.75 to 0.80 (0.75, 0.77, 0.80), respectively.
Table 1
Caries status according to variables studied
Children examined (600) | 21% | |
Gender (600) | | |
Girls (284) | 73, 26% | 0.004 |
Boys (316) | 51,16% | |
Place of birth (577) | | |
Hong Kong (491) | 95, 19% | 0.185 |
Not in Hong Kong (86) | 22, 26% | |
Frequency of soft drinks (600) | | |
At least once every two days (120) | 34, 28% | 0.020 |
Less than once every two days (480) | 90, 19% | |
Frequency of citric tea/drinks containing lemon (600) | | |
At least once every two days (113) | 19, 17% | 0.262 |
Less than once every two days (487) | 105, 22% | |
Frequency of fruit juice (600) | | |
At least once every two days (115) | 27, 24% | 0.408 |
Less than once every two days (485) | 97, 20% | |
Frequency of chewing gum (600) | | |
At least once every two days (70) | 15, 21% | 0.867 |
Less than once every two days (530) | 109, 21% | |
Frequency of Vitamin C supplement drinks (600) | | |
At least once every two days (82) | 29, 35% | <0.001 |
Less than once every two days (518) | 95, 18% | |
Frequency of toothbrushing (600) | | |
At least once a day (144) | 34, 24% | 0.317 |
Twice or more (456) | 90, 20% | |
Care taker (598) | | |
Parents (501) | 109, 22% | 0.162 |
Others (97) | 15, 16% | |
Education of father (573) | | |
Primary or below (61) | 16, 26% | 0.579 |
Secondary (395) | 83, 21% | |
Tertiary or above (117) | 23, 20% | |
Education of mother (585) | | |
Primary or below (64) | 15, 23% | 0.848 |
Secondary (434) | 89, 21% | |
Tertiary or above (87) | 19, 22% | |
Parent’ dental knowledge (600) | | |
Low (53) | 9, 17% | 0.534 |
Middle (534) | 111, 21% | |
High (13) | 4, 31% | |
Erosion experience (600) | | |
No (150) | 27, 18% | 0.352 |
Yes (450) | 97, 22% | |
Dental caries status
The caries experience of the children in DMFT (±SD) was 0.34 ± 0.76. Approximately half of the score was contributed by untreated decayed teeth (mean DT = 0.16 ± 0.52). Girls had a higher DMFT than boys (0.45 ± 0.89 compared with 0.23 ± 0.61, p = 0.001). Girls also had more untreated decay teeth (DT) than boys (0.21 ± 0.62 compared with 0.11 ± 0.41, p = 0.013). The proportion of children with dental caries experience (DMFT > 0) was 21% (n = 124). Out of these 124 children, only 1% (n = 14) had DMFT equal to or higher than 3. Among all the children examined, only 1 missing tooth was found due to caries. Results of binary logistic regression showed that the prevalence of dental caries were significantly related to the habit of drinking soft drinks (OR: 1.952, 95% C.I: 1.193-3.194) and taking vitamin C supplements (OR: 2.157, 95% C.I: 1.301-3.172) (Table
2). The odds for girls having caries experience (DMFT > 0) were 1.751 times more than for boys. There is no collinearity of the frequencies of consuming soft drinks, fruit juice and vitamin C supplement because they were not significantly inter-correlated, adjusted for prevalence of dental caries. The final model obtained by backward stepwise binary regression was the same as that obtained from the forward stepwise procedure.
Table 2
Relationship between caries prevalence (DMFT > 0) and variables selected
Frequency of soft drinks | | | | |
At least once every 2 days | 34, 28% | 1.952 | 1.193 - 3.194 | 0.030 |
Less than once every 2 days#
| 90, 19% | | | |
Frequency of Vitamin C supplement drinks | | | |
At least once every 2 days | 29, 35% | 2.157 | 1.301 - 3.172 | 0.003 |
Less than once every 2 days#
| 95, 18% | | | |
Gender | | | | |
Girls | 73, 26% | 1.751 | 1.141 - 2.687 | 0.010 |
Boys#
| 51, 16% | | | |
(Constant) | | 0.149 | | <0.001 |
Dental erosion status
A quarter (25%, n = 150) of the children were found to be free from dental erosion (BEWE score = 6 for all 6 sextants). None of the children were found to have severe erosion (BEWE score = 3), and 9 (1.5%) of the children had teeth in 1 or 2 sextants with distinctive erosion (BEWE score = 2). The sum of the scores of the 6 sextants in each child ranged from 0 to 13, and the mean was 1.7 ± 1.6 (Table
3). The eroded sextant in each child ranged from 0 to 6, and the mean number of eroded sextants in each child was 1.6 ± 1.4. Gender and place of birth were statistically not associated with the BEWE scores (p > 0.05) (Table
3). However, children who took fruit juice at least once every 2 days and children with caries experience had significantly higher BEWE scores (Table
4).
Table 3
Erosion and variables studied
Children examined (600) | 1.7 ± 1.6 | |
Gender (600) | | |
Girls (284) | 1.8 ± 1.8 | 0.166 |
Boys (316) | 1.6 ± 1.4 | |
Place of birth (577) | | |
Hong Kong (491) | 1.7 ± 1.6 | 0.438 |
Not in Hong Kong (86) | 1.8 ± 1.7 | |
Frequency of soft drinks (600) | | |
At least once every two days (120) | 1.9 ± 2.1 | 0.110 |
Less than once every two days (480) | 1.6 ± 1.4 | |
Frequency of citric tea / drinks containing lemon (600) | | |
At least once every two days (113) | 1.8 ± 1.7 | 0.194 |
Less than once every two days (487) | 1.6 ± 1.5 | |
Frequency of fruit juice (600) | | |
At least once every two days (115) | 2.0 ± 1.7 | 0.015 |
Less than once every two days (485) | 1.6 ± 1.5 | |
Frequency of chewing gum (600) | | |
At least once every two days (70) | 2.0 ± 2.1 | 0.046 |
Less than once every two days (530) | 1.6 ± 1.5 | |
Frequency of Vitamin C supplement drinks (600) | | |
At least once every two days (82) | 2.0 ± 2.0 | 0.064 |
Less than once every two days (518) | 1.6 ± 1.4 | |
Frequency of toothbrushing (600) | | |
At least once a day (144) | 2.0 ± 1.9 | 0.017 |
Twice or more (456) | 1.6 ± 1.5 | |
Care taker (598) | | |
Parents (501) | 1.6 ± 1.6 | 0.233 |
Others (97) | 1.8 ± 1.6 | |
Education of father (573) | | |
Primary or below (61) | 1.9 ± 1.8 | 0.574 |
Secondary (395) | 1.6 ± 1.7 | |
Tertiary or above (117) | 1.7 ± 1.2 | |
Education of mother (585) | | |
Primary or below (64) | 1.8 ± 1.7 | 0.614 |
Secondary (434) | 1.7 ± 1.6 | |
Tertiary or above (87) | 1.2 ± 1.1 | |
Parent’ dental knowledge (600) | | |
Low (53) | 1.7 ± 1.5 | 0.665 |
Middle (534) | 1.7 ± 1.6 | |
High (13) | 1.3 ± 2.0 | |
Caries experience (600) | | |
No (476) | 1.5 ± 1.4 | 0.004 |
Yes (124) | 2.1 ± 2.1 | |
Table 4
Relationship between BEWE scores and the selected variables
Frequency of fruit juice | | | |
At least once every 2 days | 0.377 | 0.163 | 0.021 |
Less than once every 2 days#
| | | |
Caries experience | | | |
Yes | 0.591 | 0.161 | <0.001 |
No#
| | | |
(Constant) | 1.470 | 0.078 | <0.001 |
Discussion
A stratified cluster sampling technique was employed in this study. It is important to note that cluster sampling can increase the sampling error because children in the same strata can be similar and are less likely to be representative of the population. However, this technique is an efficient sampling method to obtain a representative sample from a population with non-overlapping classifications, and the factor classifying the population may be significant on the study parameter. In this study, 3 geographical regions in Hong Kong were chosen as the strata because the household income of the families living in different regions may be different [
21], and household income was found to be a significant factor on caries experience and dental erosion in some studies [
7,
22,
23]. Therefore, questions on household income, considered to be sensitive in Hong Kong culture, could be omitted. Apart from avoiding sensitive questions, oral health seminars on preventing caries and erosion were given to the children after the oral examination, which was welcomed by the schools as part of their health education in their regular syllabi. This could explain the high response rate of 85%.
Two common assessment methods for dental erosion were Visual Erosion Dental Examination (VEDE) [
24] and Basic Erosive Wear Examination (BEWE) [
25]. Studies reported that the intra- and inter-examiner agreement in both systems had acceptable levels of reliability [
20,
24]. The BEWE system was developed in 2007 following an international workshop on erosion indices [
20]. It was recognized that previous indices lacked validity, as they mostly measured general tooth wearing instead of erosive wear [
25]; still, there was no intention to distinguish erosive wear from other forms of wear in the BEWE system [
20]. The use of the BEWE diagnostic criteria and recording system is not free from error. Therefore, it is essential to point out that the wear examined in this study is not necessarily due to dental erosion. In addition, it does not differentiate between enamel and dentine because surfaces are scored irrespective of structure. Diagnosis of early erosive wear can be difficult, and the extent of wearing by attrition and abrasion can also be difficult to determine [
20].
Re-examination of the students was performed on the same day to minimize disturbance to the school. The 3 examiners examined about 85 students each day at a given school. Each examiner would examine about 28 students and were likely to remember the tooth statuses of the re-examined children. Since the examiners were trained and their intra-examiner agreements were high in the calibration exercise, intra-examiner agreement was not assessed in the main study. Moreover, there would be many re-examined children if intra- and inter-examinations for all 3 examiners were conducted. This study found a reasonable inter-examiner agreement on the BEWE score between the examiners. Another study reported that BEWE was a convenient index with adequate sensitivity and specificity, but possibly not sensitive enough to detect the severity of some erosive lesions [
26]. Currently, there is no consensus regarding which index possesses absolute superiority over any others. BEWE was found to be a convenient index. The tooth with highest BEWE score (or the most severely affected tooth) in a sextant was recorded. The examiners in this study spent approximately 2 minutes on each child for erosion assessment. However, it is important to note that the 6 upper anterior teeth can be all eroded with no other teeth affected, and this is recorded as 1 sextant having erosion; however, 2 sextants having erosion are recorded if only 2 teeth in 2 sextants are eroded. The count of the number of eroded teeth, rather than of the sextant, is more precise but takes more time in the clinical assessment. Measuring the highest BEWE score of the sextant rather than the number of eroded teeth is quick and simple to perform, but the results collected lack discriminatory power. In this study, only a few children had teeth with distinctive erosion (BEWE score = 2) and no children had a BEWE score equal to 3, reflecting that the cut-off points of the grading in BEWE might be too high in this sample. An index with lower threshold values may be more suitable in our sample [
27].
This study found that the caries experience in mean DMFT score dropped from 0.8 in 2001, to 0.3 in 2012. This may be because of water fluoridation at 0.5 ppm since 1988, as well as the comprehensive preventive dental services provided by the SDCS [
28]. All children enrolled in local primary schools in Hong Kong were entitled to receive oral examination and treatment by the SDCS with an annual fee of approximately US $3 paid by the parents or guardians of the child. The treatment was provided by dental therapists and included fluoride gel application, fissure sealants, restorations, and extraction. In our study, a large proportion of the children had fissure sealants on their molars, which was probably performed by the SDCS dental therapists. The current mean DMFT score in Hong Kong was also low when compared to nearby countries such as Cambodia [
29], China [
30], and Thailand [
31]. However, these studies had identified various associated factors on caries experience. Since water fluoridation and dental visit patterns in our samples were different from those in other countries, caution should be taken when oral health data are compared internationally.
The prevalence of dental erosion was higher in this study when compared to another study conducted earlier in southern China [
32]. The difference may be attributed to geographical and socioeconomic factors. In our study, the survey was performed in Hong Kong, a well-developed city where acidic food and beverages are easily available. Many people in Hong Kong frequently drink fruit juices, a habit that is considered as part of a healthy diet. In this study, frequent fruit juice consumption increased tooth wear, and this result disagreed with the study by Wang et al. [
31]. One should be cautious when interpreting this result, as a wide spectrum of erosive power existed within each category of beverages [
33]. This study also found children who had caries experience had higher BEWE scores than those who had no caries experience. It was plausible that children who had caries consumed more acidic food. Abu-Ghazaleh et al. [
34] reported increased prevalence of wear in males compared to females, but this study found no statistically significant association of erosion with gender.
The closed-ended questionnaire used in this study aimed for an overview of fruit juice consumption. Information such as the kind of fruit juices, acidity, and scale of frequency of consumption were not recorded. Some recent epidemiological studies on dental erosion did not consider the dependency and interaction terms among the factors investigated [
31,
35,
36]. Because of the complex interplay among the risk factors on dental erosion, qualitative exploratory studies on biological, dietary, lifestyle, and cultural factors are necessary. Moreover, a more in-depth analysis on the interaction among these factors could be carried out.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
SN and AMH: performed the dental examination, data entry, and analysis and prepared the manuscript. CH: performed the dental examination and supervised fieldworkers during the survey. ECM: provided training, checked data analysis, and revised the manuscript. All authors read and approved the final manuscript.