In this cross-sectional study amongst a rural and urban population of south-central Ethiopia, six out of ten adults were found to have dental caries experience. This study is one of the few oral health research projects to have been carried out in the country and the first population-based oral health survey to be part of a large multi-disciplinary global health project providing an overview of adult oral health in the community and the most extensive in nature. This research has certain limitations which need to be acknowledged. First, it was conducted in a relatively ethnically homogenous population, which therefore cannot be considered nationally representative. Second, almost half (46.8%) of the study participants were from the urban area due to the accessibility challenge in some rural areas. Since a large proportion (80.0%) of the general population in the country is rural, this again needs to be recognised as unrepresentative of the national situation; however, it allowed comparison between the rural and urban settings and given the study findings whereby the differences between urban and rural settings were not significantly different in the adjusted logistic regression model, this may not be a major factor. Third, the people who stayed at home and were available to participate in the data collection might be different from those who were out engaging in work and other activities and thus possibly overrepresented. However, every effort was made to ensure that people who worked away from home were included in the study, although most men working in the fields might have been missed. Fourth, the questionnaire data were collected by face-to-face interview, which means participants may have given more socially desirable answers about their lifestyle and behaviours. None-the-less, given the very low level of education in this community, this was the most appropriate survey method. Fifth, the sample size was calculated based on surgical care needs; however as surgical care needs are less common than oral diseases, this provided a substantial sample for the oral health survey when compared with other national dental surveys (29), and our findings will provide a sound basis to inform future epidemiological studies in Ethiopia.
The magnitude of untreated obvious caries (clinically visible lesions representing demineralisation in the middle third of the dentine, and above indicated by the ICDAS 4 threshold) in the study participants was high; if the early and sub-clinical lesions were included, which would require optimal clinical and radiographic examinations (40), a higher value would result. These findings suggest an increasing burden of NCDs in general (41). Interestingly, a higher proportion of dental caries experience was observed in rural areas, unlike a previous study in Ethiopia which reported a higher prevalence of caries in urban areas (61.1%) (14). However, the odds of experiencing dental caries were almost the same for both locations in the adjusted logistic regression model. Although rural areas are generally suggested to have less access to cariogenic foods, this may be changing with the nutrition transition in Africa; in addition to the limited access to dental care and preventive services as compared to urban areas. Similar issues exist in both lower and higher income countries, whereby the rural population has more untreated caries (35, 42).
In the study participants, the odds of experiencing caries increased with age and the pattern of the condition is also cumulative throughout life by its nature (34). This finding mirrors the emerging result of the Dunedin longitudinal study (the 1972/3 birth cohort) of dental caries trajectory assessment in which the participants dental caries experience in the different categories of the trajectory increased with age (43). However, there was no significant difference between males and females in our study regarding their dental caries experience unlike previous studies in the UK (44), but it is similar with the recent global burden of oral health study findings (6, 45).
In this regression model, the odds of experiencing dental caries significantly reduced with increasing educational attainment of adults. Education, being one of the social determinants of health can also influence an individual’s position in the society and determine their income. This in turn influences the risk of one’s exposure to different diseases (25), including dental caries in adults (34).
Health behaviours, whilst important risk factors for oral disease (9), are less likely to be significant in our model. Amongst the health behaviours assessed in this survey, chewing Khat daily was associated with increased odds of dental caries experience when keeping other variables in the model constant. The association of the oral hygiene practice and sugar consumption was no longer present after the statistical adjustment. However, people who reported cleaning their teeth twice or more per day were those with a higher dental caries experience. This might be explained by the fact that those who already have problem tend to perceive severity of the disease and clean their teeth more (46), but do not appear to be using fluoride toothpaste (47). Khat chewing has been suggested to be associated with some oral conditions including periodontal diseases, attrition of the tooth surface and tooth discolouration, oral cancer and other mucosal diseases. According to Al-Maweri (2018), Khat itself is not cariogenic. However, it has a dehydrating effect on the oral mucosa and a bitter taste. Consequently, Khat chewers tend to consume a large quantity of non-alcoholic fluids, such as carbonated soft drinks, water, and coffee (usually sweetened). Some also supplement the leaves with refined sugar and it also increases the tendency to tobacco smoking (38). A cohort study of 98 Yemeni Khat chewers and 101 non-chewers, aged 18–35 years with early occlusal caries suggested a higher risk of dental caries progression in low-income Khat chewers as compared to the non-chewers, although the study follow-up was short (48).
Whilst dental attendance was generally uncommon, it was notable in those with dental caries experience in our study, only just over one-third had attended a dental service. However, those who had been to the service had seven times the odds of dental caries experience than those who never did. This might suggest that dental visit was perceived need driven and given the level of untreated diseases, care was probably limited to the offending lesion. In this regard, the main reasons for not attending dental services are generally multifactorial (39), and it can also be highlighted by the barriers of access related to the direct and indirect costs. A study of Jordanian adults on factors influencing access to dental care also reported the cost of treatment and perceived lack of treatment need, following lack of time as main reasons for not attending a dental care (49). However, our study participants did not highlight lack of time as a reason, but mainly distance to the dental service and cost of treatments. Another study among adult city-dwellers in Burkina Faso also highlighted cost of dental treatment as the main barrier to dental visits (50). Dental treatment is known to expose households to unpredictable and significant financial costs; recent research has shown, in low income households the larger portion of their disposable income could be used for dental treatment mainly in out-of-pocket payment situations (51). This could also be the case in Ethiopia, as out-of-pocket payment is the main method of funding healthcare (52).
According to our findings, half of the people with dental caries experience had missing teeth due to caries, and less than one percent had dental fillings. This indicates that tooth extraction is the most widely used treatment modality for dental caries in the area. This can be explained by late presentation with disease, due to challenges in access to care resulting in limited choice of treatment. However, socioeconomic conditions can also determine the access to preventive and restorative dental treatments (53), in addition to the inequity of healthcare services which is a challenge in most developing countries. However, the use of primary care services helped most industrialized countries to achieve greater equity so that people with greater health needs can get better access to services (54), albeit with less regularity. Reviews of oral health in the African region also suggested those challenges can be addressed by creating universal and equitable access to quality, affordable and appropriate oral health services (55).
This research provides important insights to dental caries experience in Ethiopia and provides pilot data to inform a nationally representative survey of oral health. This will help to inform appropriate workforce capacity building, through modelling future scenarios for dental service provision. It will be important to develop research informed feasible ways of addressing their oral healthcare needs of urban and rural populations to inform health policy on health promotion and healthcare services. Further research should also investigate oral health in relation to NCDs, together with the possible relationship of Khat and dental caries.