Predictors of Dental Caries Among Adults Attending Public Oral Health Facilities in Two Districts in KwaZulu-Natal, South Africa: A Cross Sectional study


 Background: Dental caries is the most common chronic oral condition affecting millions of people worldwide. There are several predictors of dental caries that include amongst others water source, fluoride use, smoking status, alcohol use, employment status, level of education, diet and socioeconomic status. Aim: The aim of this study was to determine the risk factors and or predictors associated with dental caries among adults attending dental clinics at public health facilities in eThekwini and uMgungundlovu districts in the KwaZulu-Natal (KZN) province of South AfricaSetting: The study took place at thirteen dental public health clinics in eThekwini and six from uMgungundlovu districts in KZN province, South AfricaMethods: An observational cross-sectional study was conducted over a 5-month period from November 2018 to the end of March 2019 with a sample of 4716 patients of all adults 18 years and above age groups. A clinical examination as well as a close-ended questionnaire on the diagnosis, basic demographics data, socioeconomic status (SES), as well as lifestyle-related questions such as smoking, alcohol use and dietary choices, was administered to all consenting participants. Bivariate analysis and multivariate analysis using logistical regression were used to measure the association.Results: Females participants OR 1.4 (95% CI 1.2-1.6) p < 0.001**, patients consuming an unhealthy diet OR1.2 (95% CI 1.2-1.6) p < 0.001** were more likely to develop dental caries. Patients Achieving more than secondary level education were OR 0.8 (95% CI 0.7-0.9) p = 0.02* less likely to develop dental caries. Despite showing a slightly increased odds ratio OR 1.25 (95% CI 0.93-1.67) p = 0.14, lack of access to water was not a statistically significant contributor to dental caries.Conclusion: This study showed that female sex, consumption of an unhealthy diet and lower than a secondary level of education were the predictors of dental caries. It is hoped that these findings will contribute in influencing dental public health policy planning to ensure that planning for dental services takes a more comprehensive approach that includes health promotion, primary prevention, secondary prevention and tertiary prevention at appropriate levels of the health system.


Background
Dental caries is the most common oral condition and remains a major problem in the adult population of both developing and industrialized countries 1 . More than 90% of dental caries remains untreated in third world countries 2 . A Cross-sectional study in 2000 which examined dental caries and nutritional status showed a predominantly downward trend in the prevalence of caries in South Africa, particularly in the 5-6 year and 35-44 age groups, despite this there is also evidence of increased sugar consumption 3 .
Findings from the 2001 South African Oral Health Survey showed that almost 60% of 6-year-old children had dental caries which was above the 50% target set by the Department of Health (DOH) 4 . Furthermore, 80% of all dental caries in children in South Africa went untreated 5 . Our unpublished study, which was carried out in two districts in KwaZulu-Natal (KZN), South Africa, reported an overall prevalence of dental caries among the population of health seekers visiting public dental facilities of 63% 6 .
Various demographic and behavioral risk factors such as diet, alcohol, smoking, socioeconomic status, water source, gender and education level that are associated with dental caries among adults have been evaluated by different investigators in different parts of the world. It is well established that demographic variables, diet, use of uorides, oral hygiene and access to health service are some of the predictors of dental caries 7,8 .
It is evident from the literature that age is associated with the type of dental caries. For example, a survey in the United States of America (US) found that 94% of adults showed evidence of past or present coronal caries whereas children tend to have more occlusal caries 9 .
There seem to be mixed ndings on the association between sex and dental caries. An oral health survey done in 2001 in Germany showed that women had more dental caries than men 10 . An oral health survey amongst the adults and the elderly in Hungary, in 2004, did not show any signi cant differences between men and women 11 . These ndings are consistent in literature.
A cross-sectional study which explored the association between parents' education status and tooth loss among Korean Elders found that a strong relationship between socioeconomic status (SES) and oral health 12 . Other authors have found that as SES increases, disease, illness, and their impacts decrease 13 .
In a large-scale epidemiological survey among the Southern Chinese, socio-economic factors had a considerable effect on dental caries status. Individuals who were unemployed, or had no income, had higher dental caries scores compared to the those employed and with a higher income 14 .
In another cross-sectional study in 2017 which sought to determine the association between SES and dental caries in elderly people in Sichuan Province, China, the burden associated with dental caries remained high in disadvantaged, poor and older populations 15 . In addition, a systematic review and meta-analysis study in 2015 which explored socioeconomic inequality and dental caries found that those with lower educational level or lower income, were most likely to have a higher risk of caries lesions 16 .
A 2019 systematic review and meta-analysis study reported a positive association between tobacco smoking and dental caries 17 . This nding was further reinforced in a Swedish prospective study which explored tobacco use and caries increment in young adults which reported that smoking had a relative risk of 1.5 of increasing dental caries over 3 years. This study further concluded that habitual smoking is a risk factor for caries in young adults 18 .
There seems to be mixed evidence regarding the association between alcohol use and dental caries. A cross sectional study conducted in India on alcohol dependency and oral health, reported that alcoholdependent subjects had slightly lower mean plaque and salivary pH, and a higher prevalence of dental caries, periodontitis and mucosal lesions, compared with nonalcoholic subjects 19 . Another study on the prevalence of dental caries in chronic alcoholics conducted in Eastern Europe reported no major differences in the prevalence of caries in alcoholics compared to the non-alcoholics group 20 . A 2015 study which explored smoking, alcohol use, socioeconomic background and oral health among young Finnish adults found that the consumption of alcohol was not associated with dental caries and periodontal disease 21 .
There is a plethora of evidence in the literature that points to an association between dental caries and type of diet. A cross-sectional study among young adults in 2004 in Turkey, found a strong association of dental caries with sugar consumption 22 . The 2014, National Health and Nutrition Examination Survey in the US reported a lower prevalence of dental caries among individuals following a Healthy Eating Index.
This nding supports the notion of a heathy diet contributing to lower dental caries 23 . This is supported by another study in the US which reported that dietary patterns were associated with the prevalence of dental caries. It further concluded that while food groups high in sugar were associated with the prevalence and severity of caries, associations were more apparent in the context of overall diet 24 .
Oral health services and public health facilities in KZN constantly experience huge challenges such as poor prioritization, under-funding, limited resource allocation, overcrowding and often patients presenting late to seek help with advanced disease. On the other hand, there are various patient factors known in public health literature such as genetic, environmental exposure and social that will impact irrespective of the patients acquiring a particular disease. It is thought that an understanding of some of the risk facts that patients are exposed to even before they seek help from public health facilities may assist in educating and mitigating these factors and improve patient's oral health condition.
In addition, the association of dental caries and risk factors has been widely reported in the literature, however, there is a paucity of data in KZN and South Africa. It is therefore imperative to identify the risk factors associated with dental caries among adults attending public oral health facilities in KZN, South Africa in order to contribute to knowledge about these risk factors and educate the public.
The present study aimed to determine the risk factors/predictors associated with dental caries among adults attending dental clinics at public health facilities in eThekwini and uMgungundlovu districts in KZN province over a 5-month period. The adults were chosen as the results of our previous study on the prevalence of common oral conditions demonstrated that the adults had a higher prevalence of dental caries compared to the other groups.

Methods
A cross-sectional study was conducted over a 5-month period from November 2018 to the end of March 2019 with a sample of 4716 adult patients of 18 years and above age groups who attended seven dental public health clinics in eThekwini and six in uMgungundlovu districts. These two districts were selected as when combined, they served more than 40% of the entire population of the province. These 2 districts also represented both urban and semi-urban parts of the province and the dental clinics themselves were a combination of ve primary health care facilities, one district hospital, three regional hospitals, two tertiary hospitals and one central hospital.

Sampling and sample size
The estimated combined population size for the two districts was approximately 4 million 25 . The aim was to recruit at least 10% (4000 participants) for this study, noting that almost 90% of the population use public dental facilities for their oral health needs. Adult patients of 18 years and older who attended the out-patient dental and maxillofacial department (between 7am-4pm) in the two districts as well as those who attend the inpatient dental and maxillofacial department in the facilities after hours, were included in the study. All patients had to sign informed consent in order to participate in the study.
Patients who did not provide informed consent and those attending outside the study period were excluded from the study.

Data collection
Every participant was requested to participate in an interviewer-administered questionnaire. Illiterate participants were assisted by quali ed dental assistants. The clinician, a quali ed dentist or dental therapist consulting the patients, completed a standardized questionnaire following an oral health assessment. The dental caries status was examined with a dental mirror and a probe in a dental chair.
The structured questionnaire contained sociodemographic characteristics, health-related behaviours and key sociodemographic variables.

Variables
The independent variable was dental caries. Dependent variables included socio-demographic factors such as age, gender, education level, employment status and the location of the facility. The following health-related behavioural variables were recorded for each participant: access to uoridated water supply; smoking habits, alcohol use and dietary status (healthy or unhealthy).

Data analysis
The collected data were captured and analyzed using descriptive statistics presented as means, graphs and proportions. This was conducted on Stata Statistical Program version 15 with the assistance of a biostatistician. Firstly, the statistics used included the median, interquartile range (IQR) and the Pearson Chi-Square Test to determine associations. Univariate association between the participants' characteristics and the outcome measure of dental caries were performed in order to assess the extent of the association. Finally, multivariate logistic regression analysis was used to estimate the associations between the presence of dental caries and the dependent variables as well as to adjust for the confounder variables. The adjusted Odds Ratios (AORs), p-value and Con dence intervals (CI) were calculated. A 95% con dence level was adhered to for all statistical tests. A p-value of less than 0.05 was considered statistically signi cant.

Study population
At the end of the 5 months study period 4716 participants had been recruited, which was greater than the 4000 calculated number of recruits needed ( Table 1). The participants' age ranged from 18-98 years. The mean age was37.1 years (SD 14.3). Of the participants, 2516 (53%) were males compared to 2200 (47%) females. Most of the participants 3625 (76.9%) had achieved higher than secondary level of education and 1090 (23.1%) had achieved less than a secondary level of education. Most of the participants 3063 (65%) were unemployed compared to 1651 (35%) who were employed. Nearly all, 95% participants had access to clean water compared to 5% who had no access to water at home. On the self-reporting questionnaire provided, 3301 (70%) of the participants reported themselves as consuming a healthy diet. A large percentage, 3483 (73.8%) reported that they did not consume alcohol and 3697 (78%) reported that they did not smoke.

Outcome of dental caries results
Descriptive epidemiology of patients with dental caries Sixty nine percent (3273) (Figure 1) of the sampled patients presented with dental caries whilst (1443) 31% presented with all other oral conditions which includes periodontal disease, trauma and tooth loss. Dental caries was slightly higher among the adult population of 18-32 age group at (1670) 70% compared to the greater than 33 years age groups at (1603) 69.0 %, however this marginal difference was not statistically signi cant. Males (1832; 72.8%) compared to females (1441; 65.5%) and participants who achieved less than secondary level of education (787; 72.2%) compared to those that achieved higher than secondary education (2486; 68.6 %), had a statistically signi cantly higher dental caries rates (Table 1).
Unemployed participant's (2158; 70.5%), participants who that had access to water (3092; 69.1%), participants that do not consume alcohol (2431; 70.0%) and those that consumed healthy diet (2258;68.4%) showed higher but not statistically signi cant rates of dental caries. However, participants that did not smoke (2595; 70.0%) showed statistically signi cant higher dental caries than those that smoked (678; 66.5%) ( Table 1)  Access to water showed a signi cant increased odd of developing dental caries OR 1.2 (95%CI 0.9-1.7) on bivariate analysis but was non-signi cant after multivariate analysis.

Discussion
This study provided a pro le of some of the socio-demographic predictors of dental caries among adults attending public oral health facilities in the eThekwini and uMgungundlovu districts in KwaZulu-Natal, South Africa, over a 5-month period. It is worth noting that there was enormous co-operation from both staff and patients involved in this study. This resulted in a high response rate of 4716 (which is 760 more patients than our minimum calculated sample size) patient's visits in 5 months. This will strengthen our study ndings and enable it to be generalizable.
After adjusting for confounders this study showed that, out of the eight initial risk factors associated with dental caries, only three risk factors i.e. an unhealthy diet, female and achieving less than secondary education emerged as the predictors of dental caries in this study. This is also supported by a myriad of studies undertaken in both developed and developing countries which showed a varying association between diet, alcohol use, gender differences and access to clean water and dental caries among adults.

Diet and dental caries
This study found that adults who consumed an unhealthy diet were OR 1.2 (95% CI 1.2-1.6) times more likely to have dental caries than those who consumed a healthy diet. There seems to be mixed evidence in the literature on this association. A cross-sectional study conducted in 2018 in Brazil to evaluate the association of the consumption of healthy and cariogenic foods with the prevalence of untreated dental caries showed that consumption of cariogenic foods as well as other factors such as brushing habits were strongly associated with dental caries 29 .
Another study in 2019, which examined the association of dental caries with dietary sugars in Australian adults also found that there was a strong positive association between dental caries and unhealthy diet 30 . However, when controlled for confounders where sugar consumption was identi ed as a key determinant, the statistical signi cance between dental caries and unhealthy diet disappeared 30 . It concluded that any analysis of the relationship between dental caries and diet must include detailed data about sugar and carbohydrate consumption 30 . The results of our study may need to be explored further in future studies as our study did not differentiate the details of a cariogenic diet. Our study interest was broadly on diet behaviour, and as such participants were asked to indicate whether they followed healthy or unhealthy diet practices in general.

Gender and dental caries
There is a plethora of evidence in the literature on the association between gender and dental caries. There seems to be consensus that females are more likely to develop dental caries than males. The present study found that females were OR 1.4 (95% CI 1.25-1.62) times more likely to have dental caries than males. In support of this nding, a Canary Islands study in 2006 which sought to explain gender differences in the prevalence of dental caries among the sexes found that females tend to typically exhibit higher prevalence rates than males. The explanation provided in the study was that the biochemical composition of saliva and overall saliva ow rate are modi ed in several important ways by hormonal uctuations during events such as puberty menstruation, and pregnancy, making the oral environment signi cantly more cariogenic for women than for men 31 .
A study in 2019, which examined the association between dental caries and dietary sugars in Australian adults, found that gender was one of the demographic factors that were positively associated with dental caries 30 . This nding is consistent with our study which also found a strong association between females and dental caries after adjusting for confounders in a multivariate analysis.
Another study which explored the sex differences in dental caries: clinical evidence, complex etiology also supported the studies above in that the etiology of dental caries is complex and impacts understanding of the sex difference in oral health. Both biological (genetics, hormones, and reproductive history) and anthropological (behavioural) factors such as culture-based division of labor and gender-based dietary preferences play a role. It also concluded that females had a higher risk of dental caries than males 32 .
This study concurred with our ndings that females were more likely to have dental caries than males.
Education level and dental caries There seems to be consensus in the literature on the association between education levels and dental caries. This study found that education levels were signi cantly associated with dental caries. Those who achieved higher than secondary education level at school were less likely to have dental caries OR 0.8 (95% CI 0.7-0.9) compared to those who had achieved less than secondary level of education. A 2005 cross-sectional study which explored international perspectives on socio-behavioural risk factors in dental caries, found that the effect of educational background on measures of dental caries was observed for all countries but was found to be particularly strong when the disease prevalence was high. This study further found that individuals from a high education background as well as other favorable socioeconomic circumstances were less likely to have dental caries 33 .
A systematic review in 2012 which explored socioeconomic indicators and dental caries in adults in Brazil also concluded that educational level was signi cantly associated with a greater occurrence of dental caries 34 . It found that schooling of the subject was the most frequently used socioeconomic indicator. Lower schooling was statistically associated with greater severity of dental caries in six out of nine multivariate analyses 34 . One study found that lower schooling was associated with lower severity of dental caries, two did not nd signi cant association and one did not nd association between schooling of the father and dental caries 34 . There may be various hypothesis to explaining the difference in education levels and dental caries. Our study did not explore these further however, one can assume that participants with higher levels of education are more likely to be aware and exercise a choice and affordability of the type of diet they consume thus decreasing the chances of consuming high calories diet exposing them to developing dental caries. The other possible theory is that a higher level of education enables access to general awareness and preventive measures against dental caries thus less likely to develop dental caries compared to the less educated. Our study nding is therefore consistent with the literature, however further studies are needed to explore the differences in educational levels and dental caries.

Access to water and dental caries
This study showed that despite showing a slightly increased odds ratio OR 1.25(95% CI 0.93-1.67) access to water was not statistically signi cant after both analysis. The results of the present study show that having no access to clean water had a negative effect on dental caries. The participants who had no access to clean water were 1.25 times more likely to have dental caries compared to those that do have access to clean water. There is a myriad of studies to support the link between quality of drinking water and dental caries. A public health report as far back as 1942, pointed to an inverse relationship between the uoride content of the public water supply and dental caries in continuously using such water throughout life 35 .
This nding is further supported by other studies that areas where the potable water supplies contain the uoride ion at optimum concentration of 0.17 mg/L at the source, the dental caries experience of those who ingest these water uorides, especially during the years of tooth development, is about 60% less than among areas with uoride-de cient water supplies 36 . Adults who have used such water supplies continuously enjoy the dental bene ts obtained during childhood 36 . Controlled water uoridation for the prevention of dental caries, involving the addition of uoride compounds in optimum concentration to uoride-de cient supplies, has been studied since 1940 in different areas 37 . These studies have demonstrated that dental caries can be effectively reduced through controlled water uoridation to the same extent as observed in areas where water contains the uoride at the source 37 .
Another Cochrane based systematic review in 2015, of data analyzed in studies conducted prior to 1975 to 2014 indicated that water uoridation is effective in reducing caries levels in both deciduous and permanent dentition 38 . It further found that the initiation of water uoridation results in a 35% reduction of caries in children and a 26% reduction in adults 38 . Although many studies acknowledge the bene cial effect of uoride in preventing dental caries, there is caution also on the effects of over uoridation, which was not of interest to this study.

Study Limitations
Although meticulousness and diligence were maintained to ensure the integrity and veracity of the study, the study has several limitations. The most critical of these is information bias. The questionnaire did not quantify any unit of measure in the alcohol consumption as a result, bias could have an impact in our results as most papers have reported alcohol consumed in some unit of measure rather than a generalized question irrespective of alcohol consumption. In addition, we did not conduct a detailed analysis of the participants' dietary history, detailed dietary type, as such our results were based on selfreported perception of diet as healthy or unhealthy. Both these limitations could mean underreporting or over reporting by the participants on their responses. Finally having access to municipal water supply was considered safe, clean drinking water that was uoridated.

Conclusions And Recommendations
This study showed that female sex, consumption of an unhealthy diet and lower than a secondary level of education were the predictors of dental caries. It is hoped that these ndings will contribute in in uencing dental public health policy planning to ensure that planning for dental services takes a more comprehensive approach that includes health promotion, primary prevention, secondary prevention and tertiary prevention at appropriate levels of the health system.
Policy makers need to consider the emphasis on issuing dietary guidelines about sugar consumption and oral health as part of education awareness drives. It is hoped that this study has contributed to providing knowledge in the province about the dental caries among adults attending public oral health facilities in the eThekwini and uMgungundlovu districts in KZN, South Africa.

Consent for publication
Written informed consent for publication of their clinical details and/or clinical images was obtained from the patient. A copy of the consent form is available for review by the Editor of this journal Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request Competing interests Figure 1 Combined prevalence of dental caries in the eThekwini and uMgungundlovu districts of KwaZulu-Natal, South Africa