In Laos systematic information about the oral health situation is scarce. Regular data collection does not take place and the only national oral health survey was implemented back in 1991. The present study provides information on the oral health status for urban and semi-urban 12-year old schoolchildren in Vientiane. The survey includes important target groups where it is expected that the oral disease pattern would reflect the changing living conditions and adoption of modern lifestyles. The study focuses on two of the most common chronic oral diseases in this age group, i.e. dental caries and gingival problems. As living conditions, lifestyles, and morbidity profiles are markedly different in urban and rural areas of Laos, this survey cannot be seen as representative for the entire country. It has however most likely relevance to children in and around the larger urban settlements of Laos.
In many high-income countries, research can benefit from a number of conditions of importance to sampling of a study population. For example, established population registries provide an opportunity of probability sampling. Furthermore, longitudinal data bases make it possible in studies of health and illness directly to assess the disease risks (RR), while in cross-sectional surveys it is needed to estimate the risk in terms of the Odds Ratio. For example, in Denmark, 98% of the child population and young people up to the age of 18 are covered by the public dental service and a unique population database exists as the children are examined on a regular basis. In low-income countries, such as Laos, however, alternative ways are to be identified in order to select a relevant sample for a survey. The sample for the present study was drawn from a list of well-defined secondary schools and these settings provide for a public health relevant sample and a high number of study units of the age group of interest. Moreover, this selection method allows for the data to be acquired in a timely manner assuring a high response rate at the same time. Nevertheless several aspects should be born in mind when using this approach. Firstly, risk of selection bias is present if children in high numbers are not attending school. The non-attendees are likely to represent a deprived group of the target population with a behavioural and morbidity pattern fairly different from the general population. Secondly, in numerous low-income countries girls are frequently underrepresented in schools, which is definitely also the case for rural areas of Laos. However, the school-approach was justified for this study as enrolment rates are high for both sexes of urban and semi-urban children. Selection bias could still be a problem if children absent from school suffer from acute illness or they are absent for reasons making them different to their peers. It is worth noting that the response rate obtained was surprisingly high, maybe due to the fact that the examination team visited the schools over several days allowing children absent for only a short period to be included.
As for the clinical examination an attempt to avoid misclassification was made by training and calibration of the examiners and the standard of reliability set by WHO was achieved [14
]. Meanwhile, the field examination took place with daylight being the only source of light and dental caries may thus be somewhat underreported. As regards risk behaviours, potential information bias like over reporting in favour of socially accepted behaviour such as tooth brushing may occur while underreporting could be the case for less accepted behaviour such as consumption of sugars. Moreover, recall bias especially in regards to food consumption and dental visits may be considered as well.
The relatively low mean DMFT found in this study is in line with those figures found in neighbouring China [8
] and Thailand [7
]. Having in mind the steep increase in sugar consumption in Laos one would have expected a higher DMFT compared to the countrywide DMFT of 2.0 found in 1991. Such trend was however not observed in the present study probably because the sugars consumption regardless of the steep increase is relatively low. The general sugars consumption in Laos is still far below the 15-20 kg/year observed as a threshold for a significant level of dental caries in a population [18
]. It remains a challenge for Lao health authorities to preserve the consumption of sugars at a low level if caries is to be controlled effectively.
Sugars consumption is an important factor in the development of dental caries and the adverse effect is both related to the frequency and the amount of intake of free sugars [18
]. The frequent intake of soft drinks observed among Lao students may possibly reflect the hot climate combined with the easy access to soft drinks during school hours. The present study has shown that the risk of dental caries is relatively high for children consuming sugary drinks. Such situation is found in several other low-income countries; for example, in Burkina Faso recent studies by Varenne et al found similar association between soft drink consumption and dental caries [5
Having filled teeth was highly associated to urban location, having a literate mother, and having an advantaged socio-economic position while untreated decay was associated mainly to semi-urban location. These findings may indicate differences in access to health services and different levels of education on oral health. Significant variation in total caries was however only observed across socio-economic groups. Such differences may be related to the financial capacity of buying large amounts of sweets and snacks among the socio-economic advantaged groups.
A somewhat high number of children stated tooth brushing at least twice daily (unpublished report by the author). At the same time an extraordinary high prevalence of gingival bleeding was observed in the clinical investigation. This inconsistency could be explained by either over reporting of tooth brushing or simply reflecting a lack of tooth brushing skills. While the tooth brushing technique may be inadequate to the vast majority of the children, they may still gain some caries preventive effect of such practice when using toothpaste with appropriate level of fluoride. An over reporting of toothpaste use is likely and might explain the lack of difference in caries level between fluoride exposed and unexposed children. The low level of decay among frequent brushers could possibly mirror an effect of both mechanical brushing and fluoride effect.
The survey revealed a consistency between information on untreated dental caries and the subjective evaluation of own oral health. Similar findings have been reported from Brazil [19
]. As for other low-income countries [6
] untreated decay is the main contributor to the caries index in Lao children and does explain the various negative impacts on their quality of life. Due to the progressive development course of untreated caries the experience of pulp-involvement and pain is relatively common in spite of the harmlessly looking DMFT level. Untreated caries is highly associated with tooth ache and absenteeism is experienced significantly more frequent by socio-economic disadvantaged children compared to their better off peers. A socio-economic gradient among children in need for dental care does hereby have the potential to impact negatively on the learning capacity of the children and the health effect of education in general. Nevertheless, caries was found to be associated somewhat stronger to attitude level than to the knowledge level of the children.
The dominant dD-component reflects the lack of access to curative dental care in Laos and confirms this situation in most low income countries [1
]. A high caries level was found to be associated with a recent dental visit and this mirrors the pattern observed in low-resource communities where dental visits are often prompted by pain and discomfort rather than regular preventive attendance [7
]. The high mean of missing teeth among children with a history of dental visits might reflect either a radical treatment approach of the dentist or the fact that treatment is sought rather late by children leaving conditions of teeth beyond repair. Significantly less untreated caries would have been expected among the recently treated children but it appears that dental visits primarily are undertaken for pain relief rather than comprehensive treatment of the entire oral cavity.
Common risk factors may be responsible for associations between BMI and dental caries level and this assumption has been investigated in a number studies [25
]. The results have however been inconclusive for several countries and this is echoed by the present study. Reasons for the lack of associations not only between dental caries and BMI but also between BMI and several other general health variables might be rather complicated due to the multi causal nature of obesity on the one hand and a population with little disease variation on the other hand.