In the present study, MM was associated with tooth loss. However, this association was statistically significant only for severe tooth loss in adults with MM aged ≥ 65 years (Table 4), and in adults aged < 65 years (Table 5) for moderate tooth loss if they had ≥ 5 (MMG3) or 1 (MMG1) chronic condition, and for severe tooth loss if they were from MMG3, compared with subjects without chronic conditions (MMG0).

First of all, it is important to understand the epidemiological context of the Chilean population, where life expectancy has increased and geographical distribution has changed [22, 23]. This has led to inequities in access to and use of oral health care, which is a major challenge for older Chileans. Adequate access to oral health care is essential, as it provides opportunities for health promotion, disease prevention, early diagnosis and treatment to prevent tooth loss [20]. It is also important to understand that tooth loss is a multifactorial process related to social factors, access to healthcare services, smoking, diet, and general state of health [24].

This is the first study to analyze this relationship in Chile. There is limited evidence analyzing the association between MM and tooth loss, but our findings are consistent with previous studies in other populations. Bomfim et al. analyzed data from the 2019 National Health Survey of Brazil, which included 88,531 individuals aged 18 years and older. MM was the main exposure, categorized into two groups, having 2 or 3 comorbidities, based on 13 self-reported chronic diseases: hypertension, DM, depression, back problems, mental problems, asthma, arthritis, cancer, heart problems, stroke, chronic obstructive pulmonary disease, chronic kidney disease, and work-related musculoskeletal disorder. Tooth loss was the main outcome, and it was classified into functional dentition and severe tooth loss. They reported that Brazilian adults with MM have a higher chance of severe tooth loss and a lower chance of functional dentition [25]. Zhang et al. 2022 assessed the association between MM and tooth loss in U.S. adults. They performed a secondary data analysis using the US 2012 Behavioral Risk Factor Surveillance System (BRFSS), a national cross-sectional telephone survey studying health conditions and health behaviors, including 471,107 US adults. MM was a dichotomous variable that was defined as having at least two of eight self-reported chronic diseases: DM, heart disease, stroke, arthritis, cancer, COPD, kidney disease, and asthma. Tooth loss was grouped into four categories: zero tooth loss, 1 to 5 tooth loss, 6 or more tooth loss, and edentulous. They found that people with MM are more likely to be edentulous than those with 1 or no chronic disease [26].

We found that 54.9% of the Chilean population had MM. This prevalence is higher than those reported by Garin et al. for China (45.1%) and Ghana (48.3%), similar to India (57.9%), and lower than South Africa (63.4%) and Mexico (63.9%) [27]. When stratifying the population by age, 50.6% of adults aged < 65 and 82.4% of those aged ≥ 65 years had MM. These prevalences are higher than those found by Bomfim et al. in the Brazilian population, where 19.3% of adults aged < 60 years and 50.9% of those aged ≥ 60 years had 2 or more chronic diseases [25].

The mean number of remaining teeth for adults aged < 65 years was 24.3 ± 6.8, and for adults aged ≥ 65 years was 10.8 ± 9.2. In both groups, a higher mean number of remaining teeth was observed in individuals without MM compared to individuals with MM≥ 2 and MMG2/G3. No studies evaluating the association between MM and the mean number of remaining teeth were found to compare these results.

Among the biological plausibility to explain the association between MM and tooth loss, the main one is inflammation. Graves et al. propose that systemic diseases modify the host response to oral bacteria, leading to increased inflammation than under healthy conditions [28]. This effect has been explored in the interactions of DM with periodontal disease, where pro-inflammatory mediators lead to tissue inflammation and modification of the immune response, increasing the susceptibility of oral tissues to destruction [29]. Rheumatoid arthritis also modifies the oral microbiota, increasing the levels of cytokines in the periodontium and saliva, leading to increased periodontal destruction [26]. A second possible mechanism is linked to the effects of the medications consumed by individuals with MM. Ucuncu et al. mention that the utilization of inhaled medicines such as corticosteroids and ß-mimetics by individuals with asthma and COPD modify the oral environment, making it drier, more cariogenic and leading to tooth loss [30].

This study has strengths and limitations that should be recognized. First, the limitations are that the ENS 2016-17 is a cross-sectional study, which cannot determine the directionality of the association between MM and tooth loss. The evidence supports hypothesizing the bidirectionality between MM and tooth loss, but it should be investigated with cohort and longitudinal studies. Second, some of the chronic diseases that compose the MM variable are self-reported, so they are susceptible to bias at the time of the study or cognitive status. And finally, the presence of residual confounding due to unmeasured or unidentified confounding variables.

Despite those above, it is possible to mention the following as strengths. First, it is highlighted that the ENS 2016-17 was used, representing the distribution of diseases and their determinants in the Chilean population [31]. Second, tooth loss was the outcome measure, a complex indicator that reflects the accumulation of oral diseases during life, influenced by biological, social and cultural factors [32, 33]. Finally, even though there are different definitions of MM, two definitions were used, one widely accepted with a cut-off in two or more conditions [34], and one aligned with the objectives of MINSAL’s ECICEP, with population divided into four categories: High Risk, with ≥ 5 chronic conditions (G3); Moderate Risk, with 2 to 4 chronic conditions (G2); Mild Risk, with 1 chronic condition (G1); and No Risk, with no chronic conditions (G0).

ECICEP is the new way of organizing Chile’s health care and population care. Generates a classification of risk in different strata, which allows health teams to program their interventions for each group, improving the management of chronic conditions in the population [19]. In this context, in November 2023, MINSAL approved the first program for periodontal treatment for people with DM between 35 and 54 years of age based on the fact that incorporating periodontal treatments in patients with MM can contribute to reducing the levels of glycosylated hemoglobin in adults with DM [35]. The inclusion of a definition of MM aligned with the ECICEP allows these findings to be used for future public policies in Chile, as the already mentioned periodontal treatment program.