Tooth loss is caused by complex interactions among several risk factors.¹⁾ Clinical dental factors such as dental caries and periodontal status are linked directly,²⁾ and other factors, such as health behaviors and general health problems, are indirectly linked to tooth loss.³⁾ Tooth loss leads to a poor chewing ability,^4,5) which can alter dietary habits and the oral-health-related quality of life.⁶⁾ Demographic factors, such as age, sex, household income, educational status, smoking, alcohol drinking, and frequency of tooth brushing⁷⁾ have also been associated with tooth loss.⁸⁾ Sarcopenia, defined as a decreased muscle mass or function, is associated with the aging process,⁹⁾ as is tooth loss in many older individuals.

Many reports have demonstrated the associations between oral health status and systemic health. Tooth loss is an objective indicator of oral health. Chronic diseases such as coronary heart disease¹⁰⁾ and diabetes mellitus (DM)¹¹⁾ are well-known risk factors for tooth loss. Sarcopenia and tooth loss, which are common features in elderly individuals, might be accompanied by other risk factors such as DM. Although an accurate assessment of muscle mass requires expensive equipment and may therefore not be feasible in community settings, from a public health standpoint, it is important to perform careful assessment of the possible relationship between tooth loss and sarcopenia if either is to be managed appropriately. Therefore, the aim of this study was to investigate whether sarcopenia is associated with tooth loss.

The study population comprised 8,053 males and 10,729 females ≥18 years of age in whom muscle mass and oral health were assessed. Individuals who did not undergo either one of these assessments were excluded (n=7,549).

Table 1 lists the clinical characteristics of the study population. Among males, participants in the sarcopenia group were, on average, older than those in the non-low muscle mass group (55.1±0.3 vs. 46.5±0.2, p<0.001). They were also less educated [less than elementary school: 770 (27.4%) vs. 739 (13.9%); p<0.001], less likely to exercise regularly (1,457 [52.6%] vs. 3,083 [58.4%], p<0.001), and more likely to have a lower income (760 [27.4%] vs. 739 [13.9%], p<0.001) and a smaller total energy intake. Female participants in the sarcopenia group were, on average, older than those in the nonsarcopenia group (50.9±0.2 years vs. 45.8±0.3 years, p<0.001) as well as less more educated (less than elementary school: 909 [29.5%] vs. 1,596 [20.9%], p<0.001), less likely to exercise regularly (1,432 [46.4%] vs. 4,037 [52.8%], p<0.001), and more likely to have lower income (low income: 781 [25.4%] vs. 1,367 [17.9%], p<0.001). Table 2 shows the relationships among sarcopenia status and oral hygiene and self-care. Periodontitis (defined as a CPI≥3) was more prevalent in the sarcopenia group (males, 30.3%; females, 45.9%) than in the non-sarcopenia group (males, 18.3%; females, 17.3%). Additionally, only 22.7% of male participants in the sarcopenia group had seen a dentist in the last year. Despite these facts, 12.6% (good, 11.6%; very good, 1.0%) of male participants in the sarcopenia group stated that their oral health status was better than good. Male participants with sarcopenia were significantly less likely than those without sarcopenia to brush their teeth three or more times per day (8.0% vs. 21.1%, p<0.001). Male participants with sarcopenia were also significantly less likely than those without sarcopenia to use secondary oral health products. Among both male and female participants, the number of natural teeth was significantly lower in the sarcopenia group than in the nonsarcopenia group. The DMF (decayed + missing + filled teeth) index was also significantly higher in the sarcopenia group for both sexes (males: 7.0±0.1 vs. 5.7±0.1, p<0.001; females: 8.1±0.1 vs. 5.9±0.1, p<0.001). The adjusted odds ratio for sarcopenia in participants with <20 natural teeth was 1.96 (95% confidence interval [CI], 1.58–2.48) for males and 2.86 (95% CI, 2.31–3.56) for females compared to male and female participants with full dentition (Table 3).

Table 4 shows the results of a subgroup analysis of the adjusted odds ratios of sarcopenia vs. remaining teeth according to age group. The adjusted odds ratio for sarcopenia in participants with <20 natural teeth was 1.14 (95% CI, 1.10–1.97) in young and middle-aged (<65 years of age) male participants and 2.31 (95% CI, 2.07–3.26) in young and middle-aged (<65 years of age) female participants. The adjusted odds ratio for sarcopenia in participants with <20 natural teeth was 1.92 (95% CI, 1.49–2.66) in older (≥65 years of age) males and 2.63 (95% CI, 2.26–3.64) in older (≥65 years of age) females compared to older male and female participants with full dentition.

This study showed that sarcopenia was associated with tooth loss. Sarcopenia and tooth loss are common problems in the geriatric population. Because tooth loss often leads to decreased oral function such as compromised eating and chewing ability,^4,5) it eventually reduces muscle mass and thus the quality of life.⁶⁾ Thus, identifying the risk factors for tooth loss is important to establish a strategy for maintaining oral health.

Studies of the association between weight and tooth loss have reported inconsistent results. Some found an association between being underweight and poor oral health.¹⁷⁾ However, Elwood and Bates¹⁸⁾ found no differences in tooth loss by body weight, whereas in the series of Halling et al.,¹⁹⁾ individuals with 1–15 teeth tended to weigh more than those with >15 teeth. Some studies have investigated weight change and tooth loss; however, little research is available regarding sarcopenia and tooth loss.²⁰⁾ Low muscle mass may negatively affect both chewing capacity and oral muscle function. A Japanese study found that occlusal power was associated with handgrip strength, walking speed, and body muscle volume.²¹⁾ A recent longitudinal study²²⁾ reported that the loss of oral occlusion power was associated with a decline in leg muscle power. These results support our finding that low muscle mass is related to tooth loss. In a recent study,²³⁾ poor oral health, including tooth loss, was shown to be a predictor of future sarcopenia among community-dwelling older adults. Our study is cross-sectional; therefore, future studies should investigate whether sarcopenia affects tooth loss. Although the mechanism remains unclear, associations between tooth loss and low muscle mass may occur via inflammatory²⁴⁾ and nutritional pathways.²⁵⁾ Inflammatory cytokines activate many of the molecular pathways involved in skeletal muscle wasting, leading to an imbalance between protein synthesis and catabolism; this inflammation is a common feature of periodontitis. Tooth loss affects dietary quality and nutrient intake in a manner that may increase the risk for sarcopenia.

Most oral health studies have used periodontal indexes, such as dental probing, to assess dental status. However, the diagnosis of periodontal disease is subjective because of poor interexaminer reliability; thus, it is unclear whether periodontal indexes can objectively assess oral health status for research purposes. Oral health studies differ in their definitions of periodontitis, as well as in their methods for determining periodontal status and cutoffs for periodontal diseases.²⁶⁾ In our study, the kappa value for inter-examiner reliability was 0.89; however, in other studies it was generally between 0.7 and 0.8. Different definitions of dental status and different methods for determining periodontal status used in other studies limit comparisons of their results.^27,28) In contrast, the measurement of “number of teeth lost” is a reliable indicator of dental health status for both general health clinicians and patients. Therefore, we focused on the associations between low muscle mass and tooth loss instead of the periodontal index.

This study had several limitations. First, it was a cross-sectional study and longitudinal relationships between the identified factors could not be determined. Hence, we were unable to assess definitively the cause-and-effect relationships between low muscle mass and tooth loss. Second, our study participants were relatively healthy because individuals admitted to hospitals or nursing homes were not included; thus, low muscle mass may have been underestimated. Third, our study did not take into account dental implants, prostheses, and dentures; therefore, additional evidence on the relationship between tooth loss and low muscle mass is needed.

Despite these limitations, this study benefited from a large sample size and extensive data on potential confounders for sarcopenia and tooth loss, which allowed multiple statistical analyses. These showed that patients with sarcopenia are at increased risk for tooth loss, even in old age.

In conclusion, this cross-sectional study identified an association between tooth loss and sarcopenia.