Prevalence of dental caries and associated factors among secondary school students in Kigali, Rwanda: a cross-sectional study
The prevalence of dental caries is a worldwide alarming health concern both in developed and low-income countries . It is estimated worldwide that 60 − 90% of the population is affected by dental caries . Adolescents experience dental pain and losing teeth due to dental caries. Frequent eating of sugary food and using acidic foods or drinks have been reported to be associated with dental caries . On the other hand, gender, poor oral hygiene behaviors, low socioeconomic status, and lack of access to dental care were also documented to be associated with dental caries . In developed countries, the incidence and prevalence of dental caries have reduced due to improved oral health care systems and programs that focus on prevention, such as the use of fluoride products, applications of fissure sealants, and improved oral hygiene practices . In some Latin America, the Middle East, and South Asian countries, dental caries are quite high . In low-income countries from Sub-Saharan and African countries, the prevalence of dental caries is increasing due to rapid economic growth and lifestyle changes. A high prevalence of dental caries left untreated among adolescents and was reported as the main cause of dental pain, school absenteeism, life-threatening dental infections, and discomfort was associated with untreated dental caries among adolescents . In Rwanda, a study reported that 90% of dental caries remain untreated attributed to low socioeconomic status, lack of dental visits, and poor oral health practices . Seeking dental care was only limited due to dental pain relief or teeth extraction . The current Rwanda national oral health survey revealed two-thirds (64.9%) of the population experienced dental caries with 54.3% of the population having untreated caries . Half of the participants who had dental caries were from the city of Kigali . Recent studies done on dental caries in the city of Kigali showed low oral health care services utilization among adolescents with a high prevalence of untreated dental caries . Dental caries were the main cause of dental pain, school absenteeism, life-threatening dental infections, and oral discomfort . In the city of Kigali, oral health care services are still limited and it is provided by both public and private health institutions. At public health centers, only basic oral care is provided and in some cases transferred to the district and referral hospitals. Dental caries is the main cause of searching for dental care. The main oral health care services are extractions. Private clinics are scarce and they are at a high cost . Like other Low-income countries, oral health care service in Rwanda is not taken as a priority with limited dental infrastructure . On the other hand, poor oral health practices, lack of fluoridated water, not using fluoridated toothpaste, inability to pay for dental care, and poor oral hygiene practices were reported . Determining the prevalence of dental caries in this age group is crucial due to the transition period of behavior during the adolescent stage. Since no similar study was done, this study aimed to determine the prevalence of dental caries and associated factors among secondary schools in Kigali, Rwanda.   Study design A quantitative analytical cross-sectional study was conducted from September 2023 up to January 2024 in the city of Kigali, the capital city of Rwanda. It was carried out in 42 secondary schools in both private and public schools. The observation of past caries experience and distributions of associated factors to dental caries in secondary school students were collected. Study setting This study was conducted in the City of Kigali, which is the capital of Rwanda and has 3 districts namely Gasabo, Kicukiro, and Nyarugenge. This city has both urban and rural areas. The study setting was chosen on the basis that the prevalence of dental caries in rural areas was extensively studied. Study population The present study focused on secondary school students aged 12 to 25 years old from both daytime private and public schools. Being a student in one of the selected schools from the city of Kigali was the criteria for inclusion in the study. On the other hand, having any mental problem was an exclusion criterion . According to 2019 Rwanda education statistics, a population of 62,408 students were enrolled in secondary schools in Kigali as a basis to calculate the sample size. This age range was desired for WHO classification and comparison for dental caries surveillance . Sample size determination The study sample used a proportions formula for calculating sample size . Rwanda’s oral health survey reported 55% of adolescents . Where n was the sample size, N was the total population (62408 students), p was the proportion of those who had dental caries (55.7%), q was the proportion of those who don’t have dental caries (44.3%), e: stands for marginal error (4%) and [12pt]{minimal} 				 				  				  				  				 				 				 				 				$$\:{Z}_{}^{2}$$ Stands for critical value which is 1.96 for a 95% confidence level [12pt]{minimal} 				 				  				  				  				 				 				 				 				$$}}^2pq}  {{e^2}(N - 1) + Z_{{}}^2pq}}  &  = {{62408{{(1.96)}^2}*0.557*0.443}  {(62408 - 1)*{{.04}^2} + {{(1.96)}^2}*0.557*0.443}}  &  = 586.887  587\,students } $$ A total of 646 students participated after adding 10% of the non-respondent rate.   A quantitative analytical cross-sectional study was conducted from September 2023 up to January 2024 in the city of Kigali, the capital city of Rwanda. It was carried out in 42 secondary schools in both private and public schools. The observation of past caries experience and distributions of associated factors to dental caries in secondary school students were collected.   This study was conducted in the City of Kigali, which is the capital of Rwanda and has 3 districts namely Gasabo, Kicukiro, and Nyarugenge. This city has both urban and rural areas. The study setting was chosen on the basis that the prevalence of dental caries in rural areas was extensively studied.   The present study focused on secondary school students aged 12 to 25 years old from both daytime private and public schools. Being a student in one of the selected schools from the city of Kigali was the criteria for inclusion in the study. On the other hand, having any mental problem was an exclusion criterion . According to 2019 Rwanda education statistics, a population of 62,408 students were enrolled in secondary schools in Kigali as a basis to calculate the sample size. This age range was desired for WHO classification and comparison for dental caries surveillance .   The study sample used a proportions formula for calculating sample size . Rwanda’s oral health survey reported 55% of adolescents . Where n was the sample size, N was the total population (62408 students), p was the proportion of those who had dental caries (55.7%), q was the proportion of those who don’t have dental caries (44.3%), e: stands for marginal error (4%) and [12pt]{minimal} 				 				  				  				  				 				 				 				 				$$\:{Z}_{}^{2}$$ Stands for critical value which is 1.96 for a 95% confidence level [12pt]{minimal} 				 				  				  				  				 				 				 				 				$$}}^2pq}  {{e^2}(N - 1) + Z_{{}}^2pq}}  &  = {{62408{{(1.96)}^2}*0.557*0.443}  {(62408 - 1)*{{.04}^2} + {{(1.96)}^2}*0.557*0.443}}  &  = 586.887  587\,students } $$ A total of 646 students participated after adding 10% of the non-respondent rate.   The total number of secondary schools in the city of Kigali was 117 schools. Gasabo district had 56 (45.2%), Kicukiro had 31 (26.4%) and Nyarugenge had 30 (25.6%) secondary schools. Based on proportional sampling, we have selected 26 schools from Gasabo, 8 schools from Kicukiro, and 8 schools from Nyarugenge district. Systematic random sampling was used to select study participants with class rosters. 298 (46%) students were taken from the Gasabo district, 180 (27.8%) students were taken from Kicukiro, and 168 (26%) students were taken from Nyarugenge. The interval was every 96th participant on the class roster. The first participant was chosen randomly between 1st and 96th participants. Data collection procedure and research instruments Face-to-face interviews and oral examinations were used to collect data. The researcher executed oral examinations on portable dental chairs at all schools. Data was collected by one research assistant who was a dentist and one recording assistant calibrated during the pilot study. During the training and pilot study, two dentists were trained by the principal investigator about the research tool and DMFT index. An acceptable inter-observer agreement, Cronbach’s alpha coefficient (0.80) was found, however, during data collection, only one dentist collected all the data. The assistant was sitting close enough to the examiner so that instructions and codes were recorded. The examiner also verified the data that was being recorded correctly. Dental caries were assessed based on clinical criteria by the WHO for performing an oral health survey . The questionnaire was adapted from a previous study  and translated into Kinyarwanda. Back-translation was used as a quality assurance method. Information regarding social demographics, risk behaviors, and oral hygiene practices was collected. Variables such as age, gender, socioeconomic status, school location, parent’s education level, oral hygiene measures, visits to the dentist, dietary habits, and resident area were collected. The socio-economic status was categorized into 4 categories. Before data collection, the consent form was sent to the parents and students tasked to ask about their families’ socioeconomic status to reduce bias. The frequency of taking sugary foods or drinks was categorised in a way that if the student used sugary foods three times or more as a high frequent intake of sugary foods or drinks Dental caries experience as an outcome variable was recorded through oral examination. An oral examination was conducted in class with disposable dental instruments such as Explorer, dental mirrors, facemasks, gloves, and headlamps were used during oral examination . Dental caries was assessed as WHO recommended for performing an oral health survey . Decayed (D), missing (M), and filled (F) teeth (T) index (DMFT) were recorded from each study participant. The criteria used were based on the WHO recommendation of how to conduct the basic oral survey . To detect carious tooth was based on visually detectable carious lesions in a pit or fissure, or a smooth tooth surface. A tooth that had a restoration but also decayed was classified as a carious tooth. On the other hand, visually detectable caries on the root surface of the tooth was recognized as a decayed tooth. Only missing due to caries was recorded. A very destroyed tooth up to the root was considered a missing tooth. A tooth with restoration without caries was considered a filled tooth. A dental explorer and dental mirror were used to detect decayed teeth likewise a filled tooth. Extracted tooth due to caries was considered as missing due to caries. Missing teeth due to other reasons was excluded . Data analysis Data were entered into an Excel sheet, which was exported into Statistical Package for Social Sciences (SPSS) version 25 for statistical analysis. Descriptive statistics such as frequency and mean of variables were computed to describe data. The DMFT index was classified for the identification of the caries severity index following WHO . DMFT of 0.0-1.1 = Very low, 1.2–2.6, low severity, 2.7–4.4 = Moderate, 4.5–6.5 = High. Social demographic characteristic such as social category was transformed into two categories (poor or rich). For the Rwandan system of classifying economic status, category 1 is very poor (citizens homeless and who cannot feed themselves without assistance) & category 2 is poor (citizens who pay for a house and work for others as hard laborers) are classified as poor, then category 3 is the middle-class (citizen who could pay for their needs and work as professional or owns a business) & category 4 is rich (citizen who are working as a government official, director level or owns massive businesses) . Parent’s education was categorized into 3 categories (no formal, secondary or less, and University level). Qualitative variables such as socioeconomic status and oral health behavior were presented as frequency distributions. Cross-tabulation tables with two independent t-tests and ANOVA tests (Kruskal-Wallis H test) were used for bivariate analysis to test the relationship between independent and dependent variables. Poisson regression analysis was used to assess the associated factors for DMFT. This model was suitable for evaluating count data, with the result variable representing the number of times an event occurs in a given unit of observation. The significance was set at P-value < 0.05 with their odd ratios and 95% confidence intervals.   Face-to-face interviews and oral examinations were used to collect data. The researcher executed oral examinations on portable dental chairs at all schools. Data was collected by one research assistant who was a dentist and one recording assistant calibrated during the pilot study. During the training and pilot study, two dentists were trained by the principal investigator about the research tool and DMFT index. An acceptable inter-observer agreement, Cronbach’s alpha coefficient (0.80) was found, however, during data collection, only one dentist collected all the data. The assistant was sitting close enough to the examiner so that instructions and codes were recorded. The examiner also verified the data that was being recorded correctly. Dental caries were assessed based on clinical criteria by the WHO for performing an oral health survey . The questionnaire was adapted from a previous study  and translated into Kinyarwanda. Back-translation was used as a quality assurance method. Information regarding social demographics, risk behaviors, and oral hygiene practices was collected. Variables such as age, gender, socioeconomic status, school location, parent’s education level, oral hygiene measures, visits to the dentist, dietary habits, and resident area were collected. The socio-economic status was categorized into 4 categories. Before data collection, the consent form was sent to the parents and students tasked to ask about their families’ socioeconomic status to reduce bias. The frequency of taking sugary foods or drinks was categorised in a way that if the student used sugary foods three times or more as a high frequent intake of sugary foods or drinks Dental caries experience as an outcome variable was recorded through oral examination. An oral examination was conducted in class with disposable dental instruments such as Explorer, dental mirrors, facemasks, gloves, and headlamps were used during oral examination . Dental caries was assessed as WHO recommended for performing an oral health survey . Decayed (D), missing (M), and filled (F) teeth (T) index (DMFT) were recorded from each study participant. The criteria used were based on the WHO recommendation of how to conduct the basic oral survey . To detect carious tooth was based on visually detectable carious lesions in a pit or fissure, or a smooth tooth surface. A tooth that had a restoration but also decayed was classified as a carious tooth. On the other hand, visually detectable caries on the root surface of the tooth was recognized as a decayed tooth. Only missing due to caries was recorded. A very destroyed tooth up to the root was considered a missing tooth. A tooth with restoration without caries was considered a filled tooth. A dental explorer and dental mirror were used to detect decayed teeth likewise a filled tooth. Extracted tooth due to caries was considered as missing due to caries. Missing teeth due to other reasons was excluded .   Data were entered into an Excel sheet, which was exported into Statistical Package for Social Sciences (SPSS) version 25 for statistical analysis. Descriptive statistics such as frequency and mean of variables were computed to describe data. The DMFT index was classified for the identification of the caries severity index following WHO . DMFT of 0.0-1.1 = Very low, 1.2–2.6, low severity, 2.7–4.4 = Moderate, 4.5–6.5 = High. Social demographic characteristic such as social category was transformed into two categories (poor or rich). For the Rwandan system of classifying economic status, category 1 is very poor (citizens homeless and who cannot feed themselves without assistance) & category 2 is poor (citizens who pay for a house and work for others as hard laborers) are classified as poor, then category 3 is the middle-class (citizen who could pay for their needs and work as professional or owns a business) & category 4 is rich (citizen who are working as a government official, director level or owns massive businesses) . Parent’s education was categorized into 3 categories (no formal, secondary or less, and University level). Qualitative variables such as socioeconomic status and oral health behavior were presented as frequency distributions. Cross-tabulation tables with two independent t-tests and ANOVA tests (Kruskal-Wallis H test) were used for bivariate analysis to test the relationship between independent and dependent variables. Poisson regression analysis was used to assess the associated factors for DMFT. This model was suitable for evaluating count data, with the result variable representing the number of times an event occurs in a given unit of observation. The significance was set at P-value < 0.05 with their odd ratios and 95% confidence intervals.   This study included 646 secondary school students. The response rate was 91.2%. Table shows the socio-economic demographic characteristics of the study participants. Female participants had 50.5% of the study sample whereas male participants were 49.5%. Most of the participants were aged from 15 to 19 years old comprising 442 (68.4%). Half of the participants were from rural areas 324 (50.2%). Regarding parental education, 357(55.3%) of the adolescents’ fathers and 366 (56.7%) of their mothers had attained secondary education. Most of the students came from families with moderate socioeconomic status 260 (40.2%). Table shows dental caries experience. The average DMFT score was 3.3 (SD = 3.9), with the decayed component accounting for 61.1% of the total population. The untreated dental caries component had a mean of 3.17 and SD of 3.7. Notably, 33 (5.1%) of students were missing teeth as a result of dental caries and 11 (1.7%) had teeth filled. K-test: Kruskal-Wallis H test **: significance Table shows the caries severity index, with the Kruskal-Wallis test used to test any differences in dental severity index by age, gender, residence, and social category. The test revealed significant differences in dental caries index by age ( P = 0.034) and by gender ( P < 0.001). Participants who were aged 15 to 19 years had a high decayed missing-filled teeth severity index of 140(70.0%) when compared to other age categories. Female participants had higher severe carious teeth 132 (66.0%) when compared to their male counterparts. Table Shows the distributions of oral health behavior related to dental caries among study participants. The proportion of students who reported using fluoridated toothpaste was 330 (51.1%). Only one-third of study participants 149 (23.1%) have visited a dentist in the past 12 months. Frequent sugary food consumption and regular teeth cleaning were 413 (63.9%) and 361 (55.9%), respectively Table summarizes the bivariate analysis results and Poisson regression analysis used to investigate the factors associated with dental caries experience (DMFT). Through bivariate analysis, gender, age, parent’s education levels, and visits to a dentist predicted dental caries experiences (DMFT). With Poisson regression analysis, females had a 1.5 higher likelihood of dental caries proportions than their male counterparts (AOR = 1.5, CI:1.4–1.6, P < 0.001). Being younger (12–14 years) was 40% less likely to have dental caries (AOR = 0.6, CI:0.5–0.7, P < 0.001), showing that DMFT increased in older participants. However, in the multiple comparison test, there were no significant differences in age groups. Residence and social category were also significant factors for dental caries. Belonging to low-income families was a 20% lower likelihood of proportions of dental caries when compared to participants from rich families (AOR = 0.8, CI:0.7–0.9, P < 0.001). On the other hand, participants who did not use sugary foods or drinks frequently had a 10% lower likelihood of dental caries (AOR = 0.9, CI:0.8–0.9, p < 0.001). However, DMFT was 1.2 higher among participants who did not use fluoridated toothpaste (AOR = 1.2, CI:1.1–1.1.3, P < 0.001), and 1.1 times higher proportions of dental caries among those from rural areas (AOR = 1.1, P < 0.001) when compared to their counterparts.   Table shows the caries severity index, with the Kruskal-Wallis test used to test any differences in dental severity index by age, gender, residence, and social category. The test revealed significant differences in dental caries index by age ( P = 0.034) and by gender ( P < 0.001). Participants who were aged 15 to 19 years had a high decayed missing-filled teeth severity index of 140(70.0%) when compared to other age categories. Female participants had higher severe carious teeth 132 (66.0%) when compared to their male counterparts. Table Shows the distributions of oral health behavior related to dental caries among study participants. The proportion of students who reported using fluoridated toothpaste was 330 (51.1%). Only one-third of study participants 149 (23.1%) have visited a dentist in the past 12 months. Frequent sugary food consumption and regular teeth cleaning were 413 (63.9%) and 361 (55.9%), respectively Table summarizes the bivariate analysis results and Poisson regression analysis used to investigate the factors associated with dental caries experience (DMFT). Through bivariate analysis, gender, age, parent’s education levels, and visits to a dentist predicted dental caries experiences (DMFT). With Poisson regression analysis, females had a 1.5 higher likelihood of dental caries proportions than their male counterparts (AOR = 1.5, CI:1.4–1.6, P < 0.001). Being younger (12–14 years) was 40% less likely to have dental caries (AOR = 0.6, CI:0.5–0.7, P < 0.001), showing that DMFT increased in older participants. However, in the multiple comparison test, there were no significant differences in age groups. Residence and social category were also significant factors for dental caries. Belonging to low-income families was a 20% lower likelihood of proportions of dental caries when compared to participants from rich families (AOR = 0.8, CI:0.7–0.9, P < 0.001). On the other hand, participants who did not use sugary foods or drinks frequently had a 10% lower likelihood of dental caries (AOR = 0.9, CI:0.8–0.9, p < 0.001). However, DMFT was 1.2 higher among participants who did not use fluoridated toothpaste (AOR = 1.2, CI:1.1–1.1.3, P < 0.001), and 1.1 times higher proportions of dental caries among those from rural areas (AOR = 1.1, P < 0.001) when compared to their counterparts.   This study aimed to determine the prevalence of dental caries and associated factors to dental caries among secondary students in the city of Kigali, Rwanda. The prevalence of dental caries was (61.1%) and mean DMFT was 3.3 (SD = 3.9). The current findings also showed a significant difference in DMFT among female and male participants. Female participants had a greater mean DMFT of 4.1 (SD = 4.2) than male students 2.6 (4.5). The age-related rise in DMFT was also found in the current results, presumably due to the period of exposure of permanent teeth to sugary food eating among older students when compared to younger students. In addition, the higher DMFT was 1.2 times among participants who did not use fluoridated toothpaste frequently. The current study findings were almost similar to another study done in Rwanda that found a prevalence of (64%)  and in Vietnam 68.9% . However, these findings were higher than the prevalence found in Indore district, India (47.2%) . On the other hand, this prevalence was lower when compared with other studies done in Kazakhstan(74%) , Russia (77.5%) ; Tanzania (91.5%) , and India (89.3%) . These differences might have been attributed to differences in socioeconomic status study, study setting, and oral health behavior among study participants. The current results showed higher DMFT when compared to other similar studies done in China (2.38) , Tanzania (0.59) , and Sudan(3.06) . It is also reported a higher DMFT when compared to the DMFT set by WHO, suggesting when it is greater than 3 classified as a high caries severity index. This difference might be attributed to a variety of factors such as socioeconomic conditions, availability of healthcare infrastructure, and cultural attitudes towards oral health. Countries with well-established public health systems and preventive care programs tend to report lower DMFT scores . In addition, the current study highlights participants who were coming from low socioeconomic status and participants who were not using sugary foods or drinks frequently, had a reduced proportion of dental caries. This might be the reason that the participants from rural areas do not frequently snack when compared to their urban counterparts. This was due to the low availability and accessibility of sugary foods and drinks in rural areas . When compared to other countries that improved the prevention of dental caries, dental caries experience has decreased significantly in developed countries due to the availability of healthcare systems, such as the United States and several European countries, owing to widespread access to preventive measures such as fluoridated water, regular dental check-ups, and health education programs. The application of these measures has made a substantial contribution to the overall improvement in oral health outcomes among developed-country populations . However, the current results showed few filled teeth and low proportions of participants who had fissure sealant placed on high-risk teeth. Another study done in Korea estimating the prevalence, severity, and dental caries distribution among secondary school children reported a decrease in DMFT indices in 2000 and 2012, with mean DMFT of 3.3, and 2.2 respectively, due to improved healthcare systems and the provision of fissure sealants on posterior teeth . The current study also reported that 76.9% did not visit a dentist in the past 12 months, and this is not the contrary in many low- to middle-income nations. The prevalence of dental caries was higher in these areas because of limited access to dental care services, insufficient infrastructure, a lack of preventative measures with excessive sugar intake, and a lack of oral hygiene practices . Poverty and a lack of knowledge, for example, have a substantial role in impeding effective oral health promotion in these countries . One limitation of the study was the method used to detect dental caries, which relied entirely on visual and tactile screening rather than radiographic pictures. This method most likely resulted in an underestimate of the true prevalence of dental caries. Furthermore, the study utilized a cross-sectional methodology, while appropriate for analyzing variable correlations, only focused on characteristics thought to be predisposed to dental caries. The testing did not detect the presence or absence of caries at any given period. As a result, a cohort study within the examined age range is required to gain a more thorough knowledge of the relationship between dental caries and the underlying causes of tooth decay. This would allow for a longitudinal investigation of the dynamic nature of dental caries development and its link. The third limitation was recall bias might have happened during data collection on variables such as social category, however, this was minimized through working with parents in reporting their social status.   The prevalence of dental caries among secondary school students aged 12 to 25 years old in Kigali, Rwanda was high. Factors that were associated with dental caries were gender, age, socioeconomic status, dental service utilization, frequent use of sugary foods or drinks, use of fluoridated toothpaste, and residence of students. This recommended the necessity of resolving inequities in access to oral healthcare and establishing community-based initiatives to improve oral health equality in secondary students in Kigali. This shows that early treatments and preventative strategies are needed for dental caries among Kigali secondary schools. These findings might be used for oral health surveillance and monitoring of dental caries among secondary students in Kigali, Rwanda.   