Dental caries and related factors in the elderly of the Azar cohort population: A cross-sectional study
There are approximately one billion elderly individuals aged 60 and olderworldwide, a number projected to 1.4 billion by 2030 and 2.1 billion by 2050 . Aslife expectancy increases and people live longer, the prevalence of oral and dental issues is likely to rese . Oral health is crucial for the quality of life among elderly individuals . It influences social interactions, dietary choices, body weight, as well as the ability to eat and speak . In some cities in Iran and other countries, the oral health of elderly individuals is concerning, make it a significant public health issue that requires greater global attention . The factors influencing the oral health status of elderly individuals vary across different communities due to cultural, social, and economic disparities . Studies conducted in Brazil , Germany , and Italy  reported the DMFT scores for elderly individuals as 28.16, 26.4, and 13.8, respectively. A national dental survey conducted in Iran in 2013 indicated that the mean DMFT for elderly individuals was 25.71 . Additionally, studies in Isfahan , Tehran , and Yazd  reported DMFT score for elderly individuals as 20.5, 22, and 26.6, respectively. While some studies in Iran have explored the relationship between oral health status, quality of life, and demographic factors among elderly individuals , there is a lack of comprehensive research on the association of various factors with the DMFT index in this population. This study aims to evaluatedental cariesamong the elderly in Iran using the DMFT index and to examine its correlation with various factors based on data from the Azar cohort study. 

This research is a cross-sectional study based on baseline data collected from the Azar cohort study, which focuses on elderly aged 60 to 70 years. In the Azar cohort study conducted in 2014, 15,006 adults aged 35 to 70 years were selected from the permanent residents of Shabestar city in East Azerbaijan Province, northwest Iran. The Azar Cohort was part of the Prospective Epidemiological Research Studies in Iran (PERSIAN cohort), which aimed to assess the risk factors for noncommunicable diseases . Evaluators conducted interviews using predefined and validated research protocols, along with Persian cohort questionnaires . The objectives of the Azar cohort, the sampling method, the variables, and the data collection tools and methods have been detailed in previously published articles . At the time of enrollment, written informed consent was obtained from participants, or their legal guardian in the case of illiterate participants. Those who completed the informed consent process were included in the study, with the option to withdraw at any time and for any reason. To ensure anonymity, participants in the Azar cohort were assigned unique identification codes. In this cross-sectional study, data from all elderly individuals aged 60 to 70 years whitin the Azar cohort population (n = 2,629) were included without any exclusions. In the present stud, we analyzed data concerning, DMFT index, gender, age, marital status, level of education, socioeconomic status, history of chronic diseases, smoking habits, alcohol consumption, frequency of tooth brushing, and body mass index. The DMFT index which represents the total number of decayed, missing, and filled teeth, serves as the outcome variable for this study. It is classified as a quantitative discrete variable. A dental examination was conducted by a single skilled examiner using a headlight, intraoral mirror, and explorer in accordance with the World Health Organization (WHO) Oral Health Surveys Basic Methods  to record the DMFT index. The components of the DMFT index -D (decayed teeth), M (missing teeth), and F (filled teeth)- were analyzed separately. The data from the Azar cohort Questionnaires were extracted as follows: The frequency of tooth brushing was categorized into two groups: brushing at least once a day and brushing less frequently than once a day. Age, as a qualitative variable, was categorized into two groups: 60–64 years and 65–70 years. Gender was also examined as a qualitative variable, divided into two groups: men and women. Marital status was classified into two categories: unmarried and married. Socioeconomic status was assessed using the Wealth Score Index (WSI), which was calculated through Multiple Correspondence Analysis (MCA). The WSI for each participant was determined based on ownership of various durable assets (e.g., dishwasher, car, and television), household conditions (e.g., number of rooms, type of ownership), and educational attainment. Participantsof the study were classified into five WSI quintiles, ranging from the lowest (1st quintile) to the highest (5th quintile): very poor, poor, average, good, and very good. The level of education was categorized into four groups: illiterate, primary, diploma and university. The smoking was grouped into three categories: non-smoker, ex-smoker, and smoker. The Body mass index (BMI) was analyzed as a qualitative variable with four categories: <18.5, 18.5–24.9, 25–29.9, and ≥30 kg/m 2 . Alcohol consumption was classified as qualitative variable with two responses: Yes and No. Additionally, self-reported histories of chronic diseases were extracted from the Azar cohort data. This cross-sectional study received approval from the Ethics Committee of Tabriz University of Medical Sciences, Tabriz, Iran (IR.TBZMED.REC.1401.527). Statistical analysis Statistical analysis was conducted using SPSS version 16 software (IBM Company, Chicago, IL, USA). Asignificance level of p<0.05 was established. Following the normality test, which utilized skewness and kurtosis indices, t-tests and one-way ANOVA were applied to compare the mean DMFT and M values. The Mann‒Whitney U test and Kruskal‒Wallis test were used to compare the D and F values based on the specified variables. Negative binomial regression with a log link function was employed to adjust for the effects of all potential confounding variables. 

Statistical analysis was conducted using SPSS version 16 software (IBM Company, Chicago, IL, USA). Asignificance level of p<0.05 was established. Following the normality test, which utilized skewness and kurtosis indices, t-tests and one-way ANOVA were applied to compare the mean DMFT and M values. The Mann‒Whitney U test and Kruskal‒Wallis test were used to compare the D and F values based on the specified variables. Negative binomial regression with a log link function was employed to adjust for the effects of all potential confounding variables. 

In the present study, data collected from 2,629 elderly individuals aged 60 to 70 years in the Azar cohort study were analyzed to examine the relationship between the DMFT index and various factors. The average age of the participants was 64.15±2.91 years. Approximately 52% of the elderly participants were women. A high body mass index was reported in 76% of the elderly population. The frequencies of all variables are presented in . The mean (SD) DMFT score was 28.42±6. The means (SD) for the D, M,and F components were 1.28±3.42, 26.58±8.36, and 0.55±2.13, respectively. Approximately 70.8% of the elderly participants were completely edentulous, and 64.4% of them brushed their dentures at least once a day. Only 28% of the elderly individulas with natural teeth brushed their teeth at least once a day. The mean DMFT score and the number of missing teeth were significantly higher in individuals aged 65 to 70 years compared to those aged 60 to 64 years (P<0.001). Conversly, the mean number of filled teeth in the 60 to 64 age group was significantly greater than that in the 65 to 70 age group (P<0.001). additionally, women exhibited a higher DMFT and a greater number of missing teeth (P = 0.003, P<0.001) compared to men. However, the mean number of decayed teeth was significantly higher in men (P<0.001). The mean DMFT score and its components demonstrated a significant difference based on the level of education (P<0.001). The DMFT score was higher in the illiterate group compared to the elementary group (P = 0.01). Furthermore, DMFT was greater in the illiterate group than in both the diploma and university groups (P<0.001). The mean number of missing teeth was higher among individuals with lower education levels, while the mean number of filled teeth was greater among those with higher education levels. Individuals with very poor socioeconomic status exhibited a higher DMFT score than those with good or very good socioeconomic status (P<0.001). The mean DMFT score among smokers was significantly higher (P<0.001). Moreover, the mean DMFT score was significantly greater in elderly individuals with a lower BMI (P = 0.04). However, the DMFT score in the elderly did not show a significant difference based on alcohol consumption. A comparison of DMFT scores based on various factors is presented in . In the regression model, the relationship between DMFT and the examined variables (age, gender, marital status, level of education, WSI, chronic diseases (such as diabetes, hypertension, stroke, cardiovascular diseases, cancer, chronic obstructive pulmonary diseases), smoking, alcohol consumption and body mass index) was evaluated, and no significant relationship was found . 

The present study evaluated dental caries and associated factors in the elderly population of the Azar cohort. The results indicated a high prevalence of edentulism and a high DMFT score among elderly individuals. Although the Kruskal-Wallis test showed significant mean differences in DMFT based on certain variables, no significant relationship was found between DMFT and the variables considered in the multiple regression analysis. In the present study, the mean DMFT score for elderly individuals was 28.42. This finding is comparable to the study conducted by Meibodi et al. in Yazd city, which reported a mean DMFT score of 26.6 , as well as the research by Freitas et al. in Brazil in 2016 which found a score of 28.16 , and the study by Ziebolz et al. in Germany in 2017 which reported a mean DMFT of 26.4 for elderly individuals . However, other studies have yielded different results. According to the national dental survey conducted in Iran in 2013, the mean DMFT score for elderly individuals was 25.71 . Additionally, Tahani et al. in Isfahan  and Farokhnezhad Afshar et al. in Tehran  reported DMFT score of elderly individuals as 20.5 and 22, respectively. The discrepancies in these findings may be attributed to the varying settings of the studies. The participants in the Isfahan study were elderly individuals attending municipal centers, and those in Tehran were elderly individuals frequenting parks. Those who engage in outdoor activities or sports tend to be more active and healthier. In the present study, 70.8% of the elderly participants were edentulous. According to a national dental survey conducted in Iran, 50% of elderly individuals were reported to be edentulous . Freitas et al. (2016) reported that 50.8% of elderly individuals in Brazil were edentulous . The higher prevalence of edentulism in the Azar cohort may be attributed to cultural differences in the Azerbaijan province. In the current study, 69.30% of the elderly population had full dentures, which aligns with the findings of a national dental survey in Iran that reported a prevalence of 52% . Additionally, only 2.5% of the elderly had an unmet need for full dentures. In Iran, certain insurance plans cover full denture treatments, which may impact these statistics. In the present study, no significant relationship was observed in the regression analusis between DMFT index and increasing age among elderly individuals. This finding contrasts with the results of a study conducted in Yazd . The discrepancy may be attributed to the age range of the participants in Yazd, which was 61–102 years old. In the present study, consistent with the findings of Meibodi et al.(2016) in Yazd  and Angelis et al.(2015) in Italy , no significant relationship was observed between the DMFT index and gender. However, a study conducted by Andari et al. in Beirut in 2015 revealed a higher DMFT index among elderly women . This discrepancy may be attributed to cultural differences and the inclusion of participants from social organizations and primary healthcare centers in Beirut and its suburbs. In the current study, no association was found between DMFT index and educational level. This finding contrasts with the results reported by Andari et al. in Beirut, which indicated that highly educated elderly individuals had lower DMFT scores . This discrepancy may be attributed to adjustment for several confounding variables in our analysis. As shown in , a simple analysis revealed that the mean DMFT and its components exhibited a significant differences based on educational level. Additionally, the study conducted by Wang et al. in 2017 in China found that elderly individuals with low socioeconomic status experienced poor oral health , which is inconsistent with the results of the present study. These associations can be partly explained partly by factors such as diet, behavior, and awareness particularly in rural areas. Strengths and limitations As a strength point, the present study represents the first comprehensive assessment of DMFT index and its related factors in elderly individuals in northwestern Iran, utilizing a large sample size. Consequently, the results can be generalized to the population of northwestern Iran. However, it is important to note that a cross-sectional study design cannot establish causality, which is a limitation of this research. Additionally, the lack of data regarding periodontal status in the Azar cohort restricts the assessment of overall oral health status. Therefor, it is recommended that future studies considered both the DMFT index and the periodontal status. Another limitation is that, within the Azar cohort, only one individual had their DMFT index assessed through oral examination, and the cohort did not calculate the level of agreement for this assessment. 

As a strength point, the present study represents the first comprehensive assessment of DMFT index and its related factors in elderly individuals in northwestern Iran, utilizing a large sample size. Consequently, the results can be generalized to the population of northwestern Iran. However, it is important to note that a cross-sectional study design cannot establish causality, which is a limitation of this research. Additionally, the lack of data regarding periodontal status in the Azar cohort restricts the assessment of overall oral health status. Therefor, it is recommended that future studies considered both the DMFT index and the periodontal status. Another limitation is that, within the Azar cohort, only one individual had their DMFT index assessed through oral examination, and the cohort did not calculate the level of agreement for this assessment. 

The high prevalence of edentulism and the significant rate of missing teeth amongthe elderly population in the Azar cohort highlight the poor dental health status of older individuals. It is crucial to integrate oral health programs with general health initiatives. Public health policies aimed at improving oral health in adolescents and young adults should be implemented to help preserve a greater number of healthy, and natural teeth into old age. Enhancing access to dental services, including insurance coverage and the incorporation of dental care within the primary health care system, can be highly beneficial. 

S1 Checklist STROBE statement—checklist of items that should be included in reports of cross-sectional studies . (DOC) 

