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Learn more: PMC Disclaimer | PMC Copyright Notice BMC Geriatr . 2026 Feb 2;26:493. doi: 10.1186/s12877-025-06962-x Search in PMC Search in PubMed View in NLM Catalog Add to search Decomposing socio-economic inequalities in edentulism among community-dwelling older adults in a socially diverse metropolitan by using the Erreygers concentration index Aydin Joudi Aydin Joudi 1 Departments of Community Oral Health, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran Find articles by Aydin Joudi 1 , Katayoun Sargeran Katayoun Sargeran 2 Research Center for Caries Prevention, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran 3 Departments of Community Oral Health, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Find articles by Katayoun Sargeran 2, 3 , Hossein Hessari Hossein Hessari 2 Research Center for Caries Prevention, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran 3 Departments of Community Oral Health, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Find articles by Hossein Hessari 2, 3, ✉ Author information Article notes Copyright and License information 1 Departments of Community Oral Health, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran 2 Research Center for Caries Prevention, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran 3 Departments of Community Oral Health, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran ✉ Corresponding author. Received 2025 Jun 2; Accepted 2025 Dec 29; Collection date 2026. © The Author(s) 2026 Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/ . PMC Copyright notice PMCID: PMC13067675 PMID: 41629794 Abstract Objectives Edentulism, the complete loss of natural teeth, profoundly affects the oral health and quality of life of older adults. Socio-economic disparities are a critical determinant of oral health outcomes. This study assessed and decomposed socio-economic inequalities in edentulism among community-dwelling older adults in Tehran in 2023. Materials and methods The analytical study was employed data from the Oral Health Utilization Survey. Participants aged ≥ 60 years ( N = 478) were selected using a stratified random sampling method. Data were collected using a validated questionnaire including socio-demographic variables, individuals’ oral health-related behaviors and oral health information, and outcome variable of edentulism. The Erreygers-corrected concentration index (ECI) was employed to demonstrate disparity and its gradient qualitatively and quantitatively. A decomposition approach based on logit model was used, and analysis was conducted by STATA 16. Results The participants’ mean age was 68.9 (SD = 6.4) years. Approximately 48.0% of the participants reported no dental care utilization. The ECI was − 0.23 (95% CI: -0.31 to -0.15), indicating a pro-poor concentration of edentulism. Key contributors included wealth status (72.08%), chewing difficulties (-17.30%), and halitosis (5.02%). Notably, older age, living alone, and lower socio-economic status were associated with higher odds of edentulism. Conclusion Edentulism among older adults in Tehran is disproportionately concentrated among socio-economically disadvantaged groups. Edentulism was highly contributed to age, living arrangements, socio-economic status, and difficulty while chewing. Targeted public health interventions addressing socio-economic disparities and oral health promotion are essential to improve equity in oral health outcomes for the aging population. Supplementary Information The online version contains supplementary material available at 10.1186/s12877-025-06962-x. Keywords: Inequality, Edentulism, Older adults, Socio-economic status, Erreygers concentration index Introduction Edentulism, the complete loss of natural teeth, is the cumulative endpoint of a lifetime of poor oral health [ 1 ]. Quality of life in edentulous people was extremely affected since they could not chew efficiently [ 2 ]. Likewise, communication and even a person’s social life will be compromised due to unclearly speaking and facial sagging [ 3 – 6 ]. Moreover, edentulism also affects health issues such as cardiovascular diseases and cognitive impairment [ 7 – 9 ]. Edentulism is regarded as a crucial and comprehensive determinant of oral health for the older adults, serving as an effective marker of a population’s dental status globally [ 10 ], and represents the ultimate stage of severe loss [ 11 ]. The older adults is estimated to reach 1.4 billion people in 2030 from 901 million in 2015, a 56% increase [ 12 ]. This rapid growth in the older adult population is consequently expected to increase the prevalence of edentulism, which is already recognized as a significant cause of disability due to oral disorders worldwide [ 11 ]. In Iran, the same concern, regarding an increase in the older adults group in society, has been raised. A recent survey carried out in 2015 by the National Statistics Center revealed the aging phenomenon throughout the state, with about 9.3% of the population aged above 60 years [ 12 ]. Obviously, aging is a physiological process in a person’s life span and can cause physiological alterations. However, some alterations are more observed with aging, such as gum recession, dentin hardening, and xerostomia. Moreover, non-compliance with adequate oral hygiene practice throughout the person’s life span causes more dental decay and severe loss of teeth at old age [ 12 , 13 ]. According to the World Health Organization (WHO) reports, about 30% of older adults over 65 have severe tooth loss in their oral cavity and experience edentulism globally. Consistently, edentulism affects 48.7% of the older adults in Iran [ 14 ]. A national survey conducted on oral health status in Iran, in 2012, showed that 42.8% of the older adults aged 65 to 74 experienced edentulism in Tehran province [ 14 ]. Edentulism has a significant association with sociodemographic characteristics [ 15 – 17 ], oral health-related behaviors [ 15 , 17 – 19 ], and self-assessed health status [ 20 , 21 ]. On the other hand, individuals’ socio-economic status (SES) significantly contributed to oral health-related behaviors and utilization of dental care [ 22 – 24 ]. The distribution of health should be need-oriented rather than being dependent on social advantage, addressed as health equality [ 25 ]. In both developed and developing societies, a socio-economic gradient was found in the distribution of edentulism [ 26 – 28 ]. There is scant research on quantifying and decomposing socio-economic inequality in edentulism. One of the most common methods for quantifying inequalities is the Concentration Index (CI) and the Concentration Curve (CC), and the decomposition approach helps to monitor and reveal the indicators of inequality [ 29 ]. Measuring edentulism among the older adults can be used in implementing action plans aimed at promoting oral health status throughout life. Hence, the aim of this study was to measure the decomposing socio-economic inequalities in edentulism among community-dwelling older adults in a socially diverse metropolitan of Tehran to specify the related contributing determinants, in 2023. Materials and methods Study design and sampling This cross-sectional study was conducted in the 22 districts of Tehran Metropolitan, Iran, between January 2023 and June 2023. It adopted a multistage, stratified, and randomized sampling method. The targeted community was subjects aged 60 and older (older adults). A telephone-based method was used in this study, since it offers low-cost, quick representative sampling, especially in vast areas like metropolises. Ethical approval was acquired from the Ethics Committee of Tehran University of Medical Sciences (IR.TUMS.DENTISTRY.REC.1400.182). We guaranteed the security of the subjects’ information and assured them that they could withdraw at any stage of the interview, as they wanted. In the previous study, the methods of the research were explained [ 30 ]. Sample selection and data collection Data used for analysis considered subjects aged equal to or older than 60 years ( N = 478). The informed verbal consent consisted of the criteria of informed consent, such as introducing the interviewer and the project manager organization, explaining the study’s objectives and its societal benefits, specifying the time required for answering the questions (15 to 20 min), describing types of questions, and assuring the participants that their information would be reported anonymously, without disclosing their identities. Prior to the interviews, in a comprehensive two-hour orientation meeting, 12 interviewers were trained, and the project objectives were clarified for them. To ensure the quality and accuracy of the data collection, two sessions were conducted to monitor interviews and feedbacks. An informed supervisor oversaw the process, and the project manager’s contact information was provided for immediate issue resolution, thereby maintaining the high standards of the study. Measurements A structured questionnaire was developed for this study (see Supplementary File A). To ensure content validity and relevance, the questionnaire was constructed by adapting items from previously validated national and international oral health surveys. This structured questionnaire is prepared in two sections: I) The socio-demographic section consisted of gender, age, education attainment level (less than high school diploma, diploma, and higher education degree), living arrangement status, dental insurance coverage (Yes/No), housing status (owned or rented), the area of the house in square meters, size of household (the number of the individuals living in one house), and district of residence. Based on the previous study [ 31 ], we categorized 22 districts of Tehran into four categories according to the quality of life and development of districts. II) Individuals’ oral health-related behavior and oral health information section included smoking habits (Non-smoker, Ex-smoker, and Active smoker), self-rated dental status (Poor/Very poor, Fair, Very good/good, and Excellent), Chronic experience of halitosis (Yes, No), difficulty while chewing (Yes, No). A binary outcome determinant- edentulism status was used regarding the number of teeth in the oral cavity. The edendulism was scored 1 for subjects without any natural teeth and 0 for the other participants. The questionnaire validity was validity were quantitatively assessed by a panel of twenty experts in Community Oral Health, Pediatric Dentistry, and Epidemiology from six major medical universities in Iran (Tehran, Shahid Beheshti, Mashhad, Tabriz, Kerman, and Isfahan Universities of Medical Sciences) using the Content Validity Index (CVI) and Content Validity Ratio (CVR). Questions that caused disagreement were modified until a consensus was reached. Furthermore, the reliability of the questionnaire was evaluated using the test-retest method on a sample of 20 non-participant Tehran residents, which demonstrated an agreement of over 90%. Data handling and statistical analysis Missing data were due to the participants’ refusal to answer some questions, which were not more than 5%, and were imputed by EM (Expectation Maximization) imputation. To ensure the study’s results are representative, the data were weighted. Socio-economic status measure In order to address the SES of the subjects, the Wealth Index (WI) was employed. Subjects were given scores based on neighborhood deprivation (the most developed, developed, less developed, need for action), housing status (owner, renter/others), and their apartment/house area in square meters per person (m2/p). Principal Components Analysis (PCA) was employed to generate a weight or factor score. Standardization of the scores of PCA to a standard normal distribution with a mean of zero and a standard deviation of one was made. A standardized score for indicators, which varies depending on the subject possession status of each indicator, was assigned to each participant. The scores were summed by the subjects, and the total score of the participant was used to rank the subjects. The sample was divided into tertiles, that is, three groups, each comprising 33% of the participants. The low group was assigned to the poor bracket, the next group to the fair bracket, followed by another group to the rich bracket. Data analysis Descriptive statistics were employed to present the distribution of subjects’ background and sociodemographic characteristics (the frequency with percent). Weighted data were employed in the descriptive, concentration index, and statistical decomposition analyses. It ensures the actual representativeness of the survey results. To measure the socio-economic inequality in edentulism, the Concentration Index (CI) was employed. The CI is considered as a relative extent of disparity and is also described as twice the area between the equality line (the 45-degree line) and the Concentration Curve (CC) [ 32 ]. CI is formulated as: Where CI is represented by C, the mean value of the outcome indicator is described by µ, h is the edentulism, and r describes the cumulative percentage that participants represent the subjects after ranking edentulism by the WI. The CI ranges between − 1 and 1 for an unbounded indicator. In bound indicators, the CI varies between µ − 1 to 1 − µ. Considering the bounded nature of the binary outcome indicator, a modified version of the CI, suggested by Erreygers, known as the Erreygers Concentration Index (ECI) [ 33 ]. In this study, the ECI with the Standard Error (SE) was employed: where Erreygers Concentration Index is represented by ECI, the generalized concentration index is described by CI (y), and µ is the mean value of the outcome health indicator. CC was employed to graphically display the edentulism disparity. The CC shows the cumulative percentage of edentulism on the y-axis against the cumulative percentage of subjects ranked by the WI on the x-axis. When perfect equality exists, and each subject, irrespective of the social advantage, has the same extent of edentulism, the CI is zero, and the CC lies on the line of equality (i.e., at a 45-degree line). In cases with a negative value for the CI, the CC lies above the equality line (i.e., a pro-poor condition). On the other hand, in cases with positive values for CI, the CC lies below the equality line (i.e., a pro-rich condition) [ 23 ]. Decomposing inequality Decomposition analysis was employed to measure the relevant contribution of various indicators to the socio-economic disparity in edentulism among the older adults [ 32 ]. A logit model was employed for the decomposition analysis of the EI and indicators associated with the inequality in edentulism. Variation of each indicator across WI ranks is shown by the contribution of each indicator [ 32 ]. The positive contribution represents that the indicator will increase the inequality in edentulism and vice versa. For decomposition, ECI can be described as follows: where x̄ k is the mean of the indicators evaluated in the decomposition analysis, (ꞵ m k is the marginal effect calculated on the sample means, C k is the concentration index of each indicator, and GCε is the generalized concentration index of the error term ε. Concentration indices are widely utilized to assess economic or health inequalities across diverse population groups. Traditional decomposition methods typically involve calculating the absolute contributions of determinants to the overall concentration index and expressing these as proportions. Alongside this approach, this study proposes another approach where each determinant’s contribution is normalized by its concentration index, thereby highlighting the relative importance of determinants within their specific distributional contexts. Multicollinearity was evaluated by the Variance Inflation Factor (VIF) test. The tolerance values as well as the VIF demonstrated no problems with multicollinearity, as the mean value of VIF was 1.35. To evaluate the robustness of the decomposition approach by changing reference groups, sensitivity analysis was used [ 34 ]. All statistical analyses were conducted by Stata 16 SE (Stata-Corp., College Station, TX). P < 0.05 was considered statistically significant. Results Background characteristics of the subjects A total of 478 community-dwelling older adults (equal to or older than 60 years) were investigated. The edentulism prevalence among older adults in Tehran metropolis was 25.7% (95% CI: 21.7 ˗ 29.7). The subjects’ mean age was 68.9 years (SD = 6.4). The response rate was 52.4%. The weighted edentulism proportion based on the background characteristics of subjects was presented in Table 1 . About half of the participants were women, and 40.9% had a university degree. A large proportion of subjects with edentulism lived with others (88.9%) and were non-smokers (87.5%). About 40% of participants perceived their oral health status as poor or very poor, while 27.0% assessed it as fair. Table 1. Sociodemographic characteristics of older adults, in Tehran metropolis, in 2023 ( N = 478) Explanatory variable Weighted Frequency n % Demographic and socio-economic characteristics Gender Female 244 51.1 Male 234 48.9 Age group Early older adults (60–74) 267 55.8 Late older adults (+ 75) 211 44.2 Educational attainment level Illiterate/Primary and High school 141 29.6 High school diploma 141 29.5 Higher Education degrees 196 40.9 Living arrangement Alone 53 11.1 With others 425 88.9 Smoking status Non-smoker 418 87.5 Ex-smoker 26 5.4 Active smoker 34 7.1 Dental insurance status Yes 125 26.1 No 353 73.9 Wealth index (SES) Mean (SD) 2.13(0.79) Oral health status Self-assessed oral health Excellent 18 3.7 Very Good/Good 134 28.1 Fair 132 27.5 Poor/Very poor 194 40.6 Difficulty while chewing Yes 250 52.3 No 228 47.7 Experience of halitosis Yes 112 23.4 No 366 76.6 Open in a new tab SD Standard Deviation, SES Socio-Economic Status The findings of the logistic regression models for the explanatory indicators of edentulism are presented in Table 2 . Early older subjects (60˗75) experienced an 83% lower odds of edentulism compared to the late older subjects (OR = 0.17, 95%CI:0.09 ˗ 0.29). The odds of edentulism significantly decreased by a factor of 0.35 among the subjects who lived with others (OR = 0.35, 95%CI:0.19 ˗ 0.65) compared to the others who lived alone. Subjects who assessed their oral health status as good/very good had 1.82 times higher odds of being edentulous compared to those who assessed their oral health as poor/very poor (OR = 1.82, 95%CI:1.01 ˗ 3.27). Table 2. Univariate and multivariate logistic regression models for older adults, in the Tehran metropolis, in 2023 ( N = 478) Exploratory variables Univariate Regression Multivariate Regression OR 95%CI OR 95%CI Demographic and socio-economic characteristics Gender (male Ref. ) Female 1.45 0.97, 216 1.02 0.62, 1.68 Age group (< 75 Ref. ) Early older adults (60–74) 0.15 0.10, 0.23 0.17 0.09, 0.29 Educational attainment level (Higher Education degrees Ref. ) Illiterate/Primary and High school 0.52 0.33, 0.80 0.62 0.19, 0.86 High school diploma 1.77 1.20, 2.59 1.58 0.95, 2.65 Living arrangement (Alone Ref. ) With others 0.38 0.23, 0.63 0.35 0.19, 0.65 Smoking status (Active smoker Ref. ) Non-smoker 0.61 0,36, 1.03 0.73 0.35, 1.53 Ex.smoker 1.35 0.61, 3.01 1.16 0.35, 3.86 Dental insurance status (No Ref. ) 1.24 0.82, 1.89 0.97 0.58, 1.63 Wealth index (SES) (WI3 = Low SES Ref. ) WI1 (High SES) 0.88 0.80, 1.02 0.42 0.25, 0.71 WI2 (Moderate SES) 0.27 0.17, 0.42 0.15 0.08, 0.28 Oral health status Self-assessed oral health (Poor/Very poor Ref. ) Excellent 0.83 0.54, 1.25 0.93 0.51, 1.70 Very good/Good 1.74 1.19, 2.55 1.82 1.01, 3.27 Fair 0.77 0.29, 2,04 0.57 0.16, 2.06 Difficulty while chewing (No Ref. ) Yes 1.79 1.24, 2.58 3.02 1.81, 5.03 Experience of halitosis (No Ref. ) Yes 3.94 2.24, 6.95 1.31 0.60, 2.86 Open in a new tab OR Odds Ratio, CIs Confidence Intervals, SES Socio-Economic Status Having difficulty while chewing was associated with the experience of edentulism. The odds of edentulism increased by a factor of 3.02 for those experiencing difficulty while chewing (95%CI:1.81 ˗ 5.03). The likelihood of edentulism decreased by 58% (OR = 0.42, 95%CI:0.24 ˗ 0.71) for people with high SES, compared to the subjects with low SES. Likewise, the likelihood of experiencing edentulism decreased by 85% (OR = 0.15, 95%CI:0.08 ˗ 0.28) for those with a middle SES. Socio-economic inequality in edentulism Table 3 shows the calculated ECI for edentulism equals − 0.23 (SE = 0.04). This illustrated that edentulism was disproportionately concentrated in the worse-off groups in society ( p < 0.001). Figure 1 depicts the CC of edentulism in Tehran metropolis. The CC represents the relationship between the cumulative proportion of subjects sorted by the WI on the horizontal axis and the cumulative proportion of edentulism on the vertical axis. The 45-degree diagonal line illustrates the perfect equality line. The present study showed that the CC lying above the perfect equality line determined a pro-poor (worse-off) inequality in edentulism. Table 3. Concentration index of inequality in edentulism by wealth index amongst older adults, in the Tehran metropolis, in 2023 ( N = 478) Edentulism Erreygers Concentration Index 95%CI P -value Socio-Economic Status −0.23 (−0.31˗ −0.15) < 0.001 Open in a new tab Fig. 1. Open in a new tab The Concentration Curve of edentulism by wealth index among subjects aged equal to or older than 60, in Tehran metropolis, in 2023 ( N = 478) Decomposition of the socio-economic-related inequality in edentulism Decomposing of ECI was conducted to determine how much of the calculated socio-economic-related inequality in edentulism was due to WI and other indicators. Table 4 illustrates the results of the decomposition model. The decomposition model represents the contribution of each indicator to the total socio-economic-related inequality in edentulism. Table 4. Decomposition of inequality in edentulism amongst older adults, in the Tehran metropolis, in 2023 ( N = 478) Exploratory variables ECI Elasticity Con. Per. Con. Per. Con. Demographic and socio-economic characteristics Gender (male Ref. ) Female −0.2422 −0.0366 0.0089 −3.88 −3.67 Age group (< 75 Ref. ) Early older adults (60–74) 0.0956 −0.5569 −0.0532 23.30 −55.64 Educational attainment level (Higher Education degrees Ref. ) Illiterate/Primary and High school −0.0216 −0.1007 0.0022 −0.95 −10.18 High school diploma 0.0858 0.0204 0.0017 −0.76 1.98 Living arrangement (Alone Ref. ) With others 0.1436 −0.1672 −0.0226 9.88 −15.74 Smoking status (Active smoker Ref. ) Non-smoker −0.0098 −0.1807 0.0018 −0.78 −18.37 Ex.smoker 0.0038 0.0116 0.0001 −0.02 2.63 Dental insurance status (No Ref. ) −0.0191 −0.0228 0.0004 −0.20 −2.09 Wealth index (SES) (WI3 = Low SES Ref. ) WI1 (High SES) −0.7681 0.2143 −0.1646 72.08 21.43 WI2 (Moderate SES) −0.1807 0.1860 −0.0336 14.71 18.59 Oral health status Self-assessed oral health (Poor/Very poor Ref. ) Excellent 0.0290 0.0591 0.0017 −0.75 5.86 Very good/Good −0.1686 0.0556 −0.0094 4.11 5.58 fair −0.0141 −0.0055 0.0001 −0.03 −0.71 Difficulty while chewing (No Ref. ) Yes 0.0965 0.4094 0.0395 −17.30 40.93 Experience of halitosis (No Ref. ) Yes −0.0538 0.2135 −0.0115 5.02 21.38 Residual term 0.0101 −4.43 Open in a new tab ECI Erreygers Concentration Indice, Con . Contribtions, Per. Con . Percentage Contributions, Ref Reference gruop, SES Socio-Economic Status To denote the change in the dependent determinant (socio-economic-related inequality in edentulism) associated with a one-unit change in the explanatory indicators, ‘Elasticity’, a unit-free measure of partial association was calculated. As mentioned in Table 4 , the elasticity for subjects’ halitosis status was 0.21, showing that a change in the subject’s halitosis status from non-experienced to experienced halitosis will cause a 5.02% change (increase) in socio-economic-related inequality in edentulism. One unit change in the experience of problems while chewing (17.30%) decreased the pro-poor socio-economic-related inequality in edentulism. To illustrate the distribution of the explanatory variables concerning WI, the ‘CI’ was presented. The CIs, for instance, showed that women, subjects with halitosis experience, and subjects without dental insurance had a higher likelihood of being concentrated among the lower socio-economic class. On the other hand, the likelihood of concentration on subjects without lonely arrangements, individuals with high school diplomas, and subjects who experienced difficulty while chewing were higher in the higher socio-economic class. Finally, the relative contribution of indicators to the total socio-economic inequality in edentulism was presented in the percentage contribution column. A positive value is a specific determinant that increases the identified socio-economic inequality. Conversely, a negative value shows that the rise of this value has an impact on decreasing the observed socio-economic inequality. This study showed that the socio-economic inequality in edentulism was largely driven by the wealth index. The contribution of the high SES group (WI1) alone was 72.08%, as presented by the adjusted percentage contribution of inequality, and 21.43% by the adjusted percentage contribution of inequality with the concentration index of each indicator. The total combined contribution of the socio-economic status variable (comprising both the moderate and high SES groups) was 86.79% (calculated as 72.08% + 14.71%). The subjects who experienced difficulty while chewing were responsible for − 17.30% of the socio-economic disparity, and 40.93% by the adjusted percentage contribution of inequality with the concentration index of each indicator. Subjects with halitosis contributed to the socio-economic inequality in edentulism, explaining 5.02% of the inequality, and 21.38% by the adjusted percentage contribution of inequality with the concentration index of each indicator. Indicators like educational attainment levels and smoking status represented a small percentage of the inequality. The residual component/error term of the decomposition equals 0.0101. Hence, the decomposition findings presented a well-specified model, i.e., the residual approach is proximate to zero. It is noteworthy that one finding from the multivariate logistic regression model (Table 2 ) appears counterintuitive: individuals who self-rated their oral health as “good/very good” had higher odds of being edentulous. This observation is addressed in the discussion section. Discussion This is one of the pioneer studies to identify and decompose socio-economic inequalities in edentulism among community-dwelling older adults in a socially diverse metropolitan to specify the related contributing determinants. The findings of this study illustrated that edentulism was more concentrated among the poor bracket of society. Gender, living arrangements, SES, and difficulty while chewing were the major contributors to the pro-poor socio-economic disparity in edentulism. Previous studies have shown the socio-economic inequality in oral disease and revealed that the subjects belonging to marginalized brackets suffer from the burden of dental diseases disproportionately [ 35 , 36 ]. Our results can help stakeholders address the inequality issue in society and be a valuable source for monitoring inequality in the scientific literature. This study revealed that edentulism is in favor of subjects from the worse-off brackets. However, this does not connote that edentulism is not found throughout the better-off subjects. Consistent with this finding, previous investigations have shown that intimately, poverty and health are related, and that good health conditions are unfairly less prevalent among the worse-off bracket than the better-off group [ 16 , 37 ]. This result could suggest that socio-economically disadvantaged subjects may not be able to acquire oral health-related information and beneficial knowledge, have less awareness about the importance of oral health, and underutilize oral health care [ 22 , 23 ]. Likewise, it was found that SES, as a whole, was the major indicator, contributing 86.79% to the observed inequality. This total contribution is derived from the sum of the contributions of its high (72.08%) and moderate (14.71%) levels of the socio-economic inequality in edentulism. SES could affect subjects’ edentulism through its influence on utilizing oral health care services. Previous literature has revealed that the rate of utilization of oral care was higher among economically privileged subjects [ 38 ]. Disparity in access to appropriate information and oral care providers is associated with the socio-economic gradient [ 24 ]. Moreover, inequality in SES may cause disparity in other health-related characteristics, such as an individual’s ability to pay for the indirect cost of utilization of care, such as transportation fees to the health facility and other opportunistic costs, and direct costs for the utilization of dental care services. This finding is consistent with Seerig et al. study demonstrated that tooth loss is associated with economic status, and greater tooth loss exists among lower economic status individuals [ 39 ]. Difficulty while chewing was another important indicator of socio-economic inequality. Obviously, one of the crucial functions of the stomatognathic system is chewing ability. Difficulty while chewing is a deterministic factor of oral dysfunction [ 40 ]. An investigation conducted by Cavalcante FT et al. in Florida demonstrated that 16% of adult subjects stated being dissatisfied with the ability to chew, which was associated with indicators like dental caries, periodontal disease, tooth mobility, and edentulism [ 40 ]. Furthermore, educational attainment level has been identified as a factor associated with dental care utilization patterns over time [ 41 ]. This association might be elucidated by the disparities in providing oral care near individuals’ residences, distances to travel to the dental care office, and difficulty in utilizing dental care services among impaired health. Likewise, denture use, edentulism, living arrangements, and social networks were associated with not utilizing dental care. Edentulous people may not prioritize dental care utilization. Not utilizing dental care may lead to a worse oral health status and even edentulism [ 21 ]. Although the education attainment level did not much contribute to the socio-economic inequality in edentulism among older adults, previous studies revealed that education attainment level was associated with tooth loss [ 37 , 42 ]. Educational attainment level is a critical indicator due to its effect on altering oral health-related behaviors [ 43 ]. On the other hand, this indicator also has an impact on preparing more employment opportunities, a much better economic status, and quality of life. Subjects older than 75 years showed a higher likelihood of edentulism as compared to those aged 60–75 years. This may result as a consequence of life and subjects’ advancing age. Advancing age can influence appropriate behaviors related to the prevention of oral diseases and consequently the loss of teeth. The increase in the loss of teeth with aging is a natural trend and a demonstration of the cumulative impact of appropriate behaviors related to the prevention related to dental caries and gingival disease throughout a person’s life. Motivating preventive behaviors enhances the maintenance of more teeth among older adults. The employment of epidemiological and bioethical knowledge could be a good method to support subjects who are unable to utilize dental care, as needed, and who are socio-economically vulnerable. In this study, the assessment of living arrangements showed that the lower likelihood of edentulism was associated with non-loneliness, occurring 65% more in subjects living alone. This result states that individuals who didn’t live alone utilize better dental care. This may be related to the importance of dental health in interpersonal and social networks, like marital relationships. A noteworthy finding was the positive association between self-rating oral health as “good/very good” and edentulism in the multivariate model. This seemingly counterintuitive result may be explained by factors such as response bias and psychological adaptation. Edentulous individuals who have well-functioning and aesthetically satisfactory complete dentures may report good oral health based on their current prosthetic function rather than the absence of their natural teeth. Additionally, edentulism can be perceived as a definitive solution to long-standing dental problems (e.g., pain, infection), leading to an improved overall self-assessment of oral health status post-treatment. This highlights the complexity of self-rated oral health measures, which encompass not only biological condition but also psychosocial adaptation and satisfaction with prosthetic rehabilitations. Ultimately, our findings call for targeted oral health promotion programs, especially in socio-economically disadvantaged districts of Tehran. Subsidized dental services and educational campaigns are essential to reduce these inequalities. Furthermore, this study introduced a divisive approach to decomposing the concentration index, where each determinant’s absolute contribution is normalized by its own concentration index. This method provides a nuanced understanding by not only quantifying how much a factor contributes, but also how its own distribution across the wealth spectrum influences that contribution, potentially revealing dynamics that conventional decomposition might overlook. Future research should explore the applicability of this approach across other health inequality contexts. In summary, this study highlights the pressing need to address socio-economic inequalities in oral health among the older adults in Tehran. By targeting key determinants such as financial status, social support, and oral functionality, public health interventions can contribute to healthier aging and greater equity in oral health outcomes. Limitations This study has some limitations that should be considered when interpreting the findings. First, its cross-sectional design precludes the establishment of causal relationships between socio-economic status and edentulism; longitudinal studies are needed to explore these dynamics over time. Second, the reliance on self-reported data for oral health status, behaviors, and edentulism is susceptible to recall and social desirability bias. Future research would benefit from incorporating objective clinical examinations to validate these measures. Third, the exclusion of individuals with severe health conditions, hearing impairments, or neurological problems may limit the representativeness of our sample and could lead to selection bias, as these groups might experience different oral health outcomes. Fourth, while we controlled for several key variables, residual confounding from unmeasured factors such as detailed dietary habits, access to preventive care, or cultural beliefs remains possible. Fifth, although we used a stratified random sampling method, the generalizability of our findings is primarily confined to the community-dwelling older adult population of Tehran and should be extrapolated to other regions or countries with caution. Finally, the telephone-based data collection method, while cost-effective, may have excluded older adults who are less comfortable with technology or do not own a telephone, potentially introducing coverage bias. Future studies could employ face-to-face interviews or other data collection strategies to enhance inclusivity. Despite these limitations, this study provides crucial first-of-its-kind evidence on the magnitude and drivers of socio-economic inequality in edentulism in Tehran, establishing a baseline for future research and informing targeted public health interventions. Conclusion This study revealed pronounced socio-economic inequality in edentulism among older adults in Tehran, which was disproportionately concentrated among the socio-economically disadvantaged. The key contributors to this disparity were financial status, difficulty chewing, and living alone. These findings underscore the necessity for targeted public health policies that address the underlying social determinants of oral health to reduce inequalities and promote healthier aging. Supplementary Information Supplementary Material 1. (26.2KB, docx) Acknowledgements The present study was funded and supported by the Research Centre for Caries Prevention, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran (Grant No. 1402-33-32-33). Abbreviations SES Socio-economic status ECI Erreygers concentration index Con Contribution CVI Content validity index CVR Content validity ratio CI Confidence interval OR Odds ratio PCA Principal components analysis WI Wealth index M Mean TUMS Tehran University of Medical Sciences SD Standard deviation Authors’ contributions HH, and AJ formulated the research concept and developed the primary framework of the study; KS contributed to the final manuscript; AJ, and HH participated in the collection and arrangement of relevant references; AJ, and HH were involved in data collection and analysis; AJ, and HH drafted and revised the manuscript; KS was involved in reviewing the manuscript. All authors have read and approved the final version of the manuscript. Funding This study was funded by the Research Centre for Caries Prevention, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran. Data availability The datasets employed and analyzed in the current study are not publicly available due to protecting the privacy of the individuals. However, non-identifiable data are available from the authors upon reasonable request. Declarations Ethics approval and consent to participate This study was conducted in accordance with the ethical principles set forth in the Declaration of Helsinki. Ethical approval was obtained from the Ethics Committee of Health Sciences, Tehran University of Medical Sciences (IR.TUMS.DENTISTRY.REC.1400.182). Informed verbal consent was secured from all participants via telephone prior to their participation in the survey. Consent for publication Not applicable. Competing interests The authors declare no competing interests. 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