Oral Health Promotion under the 8020 Campaign in Japan—A Systematic Review

(1) Background: The aim of this study is to review the benefits of the 8020 Campaign since its inception. (2) Methods: We followed the PRISMA guideline and collected information regarding the 8020 Campaign through online database searches. (3) Results: Twenty-five studies met the inclusion criteria and were eligible for analysis. The main outcomes of the 25 included studies were reviewed. The quality evaluation demonstrated a range of studies showing a credible relationship between masticatory function, number of teeth, salivary secretion, frequent dental check-ups, and general health concerns. Due to the risk of bias, publication bias, and indirectness, 22 studies were considered that only had “fair” quality. (4) Conclusions: The 8020 Foundation funded several of the studies, and other research papers noted the 8020 Campaign in their papers, however there were no clear explanations for any direct relationship between their findings and the 8020 Campaign. As a result, evidence for the direct effectiveness and benefits assessment of the 8020 Campaign positive outcomes were compromised by confounding social and economic variables over the 30-year period. To fully elucidate how improvement in Japan’s oral health was directly related to the 8020 Campaign, a more informed and systematic explanation of the campaign’s structure and activities is required.


Introduction
Major oral diseases and non-communicable diseases (NCDs) are closely associated and shared common risk factors [1,2]. Untreated oral diseases, such as dental caries and periodontal disease, can lead to tooth loss. Oral diseases can also impact overall health conditions [3,4]. Based on the previous research, tooth loss is associated with various poor health conditions [5]. Most older adults experience significant tooth loss; this becomes a specific concern in the Western Pacific Region which has fastest growing aging population. Although Japan has a highest percentage of older adults aged 65 and above in the world, it showed the lowest tooth loss rate [6]. Universal health insurance was introduced in Japan in 1961 and covered most dental treatments [7]. To tackle the high prevalence of oral diseases, the Japanese government initiated the 8020 Campaign in 1989, aiming to create a healthy and long-living society by building public policies, creating supportive environments, developing personal skills, and reorienting health services [8].
The 8020 Campaign is a long-term national oral health promoting strategy [9]. The rationale for the 8020 Campaign was built on the premise that if people can keep at least 20 functioning teeth by 80 years of age, they have a better chance of remaining healthy because of their ability to chew effectively, eat a range of foods, and maintain good nutrition, thereby providing a positive influence on general health and well-being [8].
Prior to this, there was a high prevalence of dental caries, gingival and periodontal diseases, and tooth loss among Japanese citizens [8]. The oral health improvement has been monitored through the national health surveys conducted every 6 years since 1957. Results of these national surveys suggest that the oral health of the Japanese population has extensively improved since the introduction of the 8020 Campaign [10]. There have been numerous studies on the effectiveness and consequences of the 8020 Campaign, including the association between the campaign's efforts and general or oral health [11][12][13][14]. However, the consistency and extent of any direct link between the 8020 Campaign exposure and tooth loss, for example, are unknown. There has been no comprehensive systematic review of the Campaign's effectiveness. During the 30 years of the 8020 Campaign, Japanese society at large has also experienced changes in social, economic, and public health services as well as nursing care [15]. These changing social determinants and dynamics and the benefit of universal health insurance which enables people to receive dental care with a minimal copayment need to be identified and controlled for in studies evaluating the success of the 8020 Campaign on both oral and general health outcomes. The aim of this study therefore is to critically review the literature pertaining to the major benefits and outcomes of the 8020 Campaign. We hypothesized that the 8020 Campaign had positive impacts on improving oral health and health conditions of the Japanese population over the period of its implementation.

Eligibility Criteria
The inclusion criteria are (1) original primary research articles published in peerreviewed journals between January 1989 and January 2022 using English and Japanese language; (2) grey literature from reliable sources such as government documents or survey reports that contain a clear description of methods, results, and limitation of the studies; (3) articles addressing oral health-promoting activities under the strategy of the 8020 Campaign and their outcomes across generations and any health conditions; (4) population-based surveys, cross-sectional studies, cohort studies, case-control studies, and interventional studies; and (5) studies with a comparison/control group.
The excluded studies were: (1) outcomes not specifically related to the 8020 Campaign and oral health; (2) grey literature in other forms, such as conference abstracts, posters, theses, dissertations, and study protocols; (3) case reports, animal studies, commentaries, and editorials; (4) outcomes which were solely evaluated through self-reporting assessments; (5) studies lacking complete information; (6) studies in which the full-text articles were inaccessible.
We used the PECO/PICO criteria as follows: the population of interest (P) was Japanese people regardless of their age or conditions; exposures (E) or interventions (I) which were oral health-promoting activities related to the 8020 Campaign or the state of having 20 teeth at the age of 80 and over; there was no restriction regarding the characteristics of comparison groups within each included study (C); outcomes of interest (O) were any changes related to oral health or health conditions, health literacy, and health-related behaviors. The PECO/PICO information was extracted from the included studies.

Search Terms
The search terms included combinations of the following keywords using Boolean operators: "tooth", "teeth", "oral", "dental", "mouth" and "8020" for PubMed, Web of Science, and EMBASE (English) literature search, and "8020", "oral health", "8020 運動 (the 8020 Campaign)", " 口腔 (mouth)" for Google Scholar (Japanese and English), "8020" for Ichushi (Japanese) literature search. Grey literature from Google Scholar and the websites of the 8020 Foundation; the Ministry of Health, Labour, and Welfare; and the Japan Dental Association were also reviewed. Additionally, the reference lists of all included articles were checked for potentially relevant studies.

Search Strategy
According to the PRISMA guidelines, [16] we collected information regarding the 8020 Campaign through online database searches from a Japanese academic search interface (Ichushi), PubMed, Web of Science, Google Scholar and EMBASE. From the 2490 results obtained (by setting keywords, we screened by title and relevance), 501 articles that were published from January 1989 to January 2022 were identified. These databases were selected based on a recommendation for a minimum requirement to guarantee adequate and efficient coverage for literature searches in systematic reviews [17,18]. Details of search criteria and data extraction are mentioned in the Supplementary Material.

Risk of Bias and Quality Assessment
Risk of bias was assessed using GRADE 25 and NIH 26 Quality Assessment Tools and results of the assessment are presented in Supplementary Files (Tables S2-S7). A summary of quality assessment is presented in Table 1.

Data Extraction
The following data were extracted from the included articles: database source, year of publication, author, study design, number of subjects, population, exposure, intervention (related to the 8020 Campaign, number of teeth, oral health conditions, etc.), control or comparison group, outcome, major findings, and funding sources (The 8020 Foundation or other source). In terms of general health, outcomes included any systemic or general health condition related to number of teeth or quality of life [5]. Data extraction from English articles was independently performed by three reviewers (TZ, AR, and FC), while extraction of data from Japanese articles was carried out by the two Japanese reviewers (HO * and AT). Any ambiguities were resolved through discussion between reviewers or consultation with one of the principal investigators (ST and RK).

Data Synthesis
We did a narrative literature review and generated a summary of our findings. Using the NIH quality assessment tool, we prepared tables summarizing our findings from the articles and evaluated the study's methodological quality. There was no restriction in effect measures of the outcomes. Further analysis, such as sub-group and sensitivity analysis, could not be conducted.

Results
By searching Embase, PubMed, Google scholar, Ichushi (Japanese website), and grey literature, 875 studies resulted, as shown in Figure 1. A total of 25 studies met the inclusion criteria and were eligible for analysis after 827 were initially screened by title and abstract and 135 studies were screened by full text. The excluded studies are explained in detail in Supplementary Files (Table S1). The quality of the included articles (n = 25) were tested and shown in the Table 1, and the main outcomes of the included studies, in Table 2. Table 1 showed the result of quality evaluation. The quality evaluation demonstrated a range of studies showing a credible relationship between masticatory function, number of teeth, salivary secretion, frequent dental check-ups, and general health concerns. The risk of bias, publication bias, and indirectness of 22 studies meant that assessments of the Program were only of "fair" quality. Three articles reporting on occlusal force and oral flora, provided only a small amount of evidence to be considered reliable [11,12,30]. Out of the 22 studies with a "fair" quality assessment, 22 reported association between the number of teeth with positive oral health, such as masticatory function, occlusal force, salivary flow, and general health, such as physical condition and nutrition. This is consistent with previous studies that analyzed the relationship between number of teeth and general health [5]. However, since the study design for these articles are cross-sectional and did not consider the influence of confounding factors, some of them showed low strength of evidence (18 out of 22) and some (15 out of 22) were included in imprecision criteria. It can also be suspected that publication bias underpinned many articles, such as studies that are not published in reputable, refereed, international journals.

Quality Assessment Results
The poor-quality articles have been designated as having high risk of bias as they did not recruit control and comparison groups from the same population as the targeted population. There was no availability of information about confounding factors in these articles. Moreover, the methodology was not properly described, and structures were not properly designed. With the many gaps in these studies, and the many limitations encountered, it is not possible to draw strong conclusions from these reports on the effectiveness and benefits of the 8020 Campaign.

Oral Health Promotions for Children (0-14 Years Old)
The lists of oral health promotions programs can be found in Table 2. One study reported the effect of the "Tooth Passport" as an oral health promotion under the 8020 Cam-paign on dental caries in children [19]. The passport users had less of an increase in caries of their first molars, comparing to the ones who did not use the passport. Beginning to reinforce proper oral hygiene programs in childhood significantly reduced the number of decayed and filled teeth in later life [19].

Oral Health Promotions for Middle-Aged Adults (44-60 Years Old)
Four studies reported the outcomes of 8020 campaign related oral health promotion activities in middle-aged adults. Two studies reported the good impact of keeping more teeth to oral health. Individuals with more than 20 current teeth, have higher saliva secretion [20,21]. In addition, functional tooth evaluation and occlusal contact area were significantly associated with saliva secretion [20]. A study from Takemae et al. showed that better oral condition (the number of teeth, periodontal condition, the ability to chew with one's teeth or artificial teeth, and the satisfaction of total oral function) were comprehensively related to healthier life style and more frequent participation in social activities [21]. The direction of the association between oral condition and life style cannot be demonstrated as this was a cross-sectional study. The other two studies reported the effect of oral health promotion activities under 8020 Campaign. Morita et al. reported that individuals who attend professional tooth cleaning treatment for 6 years or longer have more teeth present [22], showing that regular professional tooth cleaning contributed to prolonged overall tooth life. A study from the 8020 Promotion Foundation reported that lifestyle and oral health care contributed to the mother's oral conditions. Compared to the National Data, the prevalence of decayed teeth among participants was similar. However, the prevalence of untreated decayed teeth was lower [23].

Oral Health Promotions for Older Adults (>60 Years Old)
A total of 14 studies reported the positive impact of keeping 20 or more teeth for older people. At the same time, 3 out of 14 studies reported oral health condition as the main outcome together with physical strength such as body mass index, bone mineral density, and grip strength [13,25,26]. The main findings reported that the oral and general health conditions of those with a high number of remaining functional teeth showed significantly more positive health conditions and physical state than those with fewer natural teeth [13,25,26]. In terms of masticatory function, the studies reported that older people with more teeth could masticate a wide variety of foods, [27,34] and had both greater occlusal force and higher bone mineral density [13,25]. The occlusal force of older individuals was not affected by aging if the population had 20 or more natural, functioning, teeth, that is, if they achieved 80:20 [11,30]. Oral function exercises were found to be strongly associated with saliva secretion and swallowing capacity [36]. Moreover, the greater number of retained functional teeth, the lower the microbial flora, resulting in better overall oral health [12]. Studies suggested that better dental and mastication ability had a favorable impact on physical well-being and function [14]. However, income and the number of natural teeth present were associated determinants for the utilization of dental health services. Individuals with poor economic conditions and fewer teeth were less likely to have frequent check-ups [24].    The mean number of decayed and filled teeth of study and control groups was evaluated.
-"Tooth passport" users had a lower increase in caries of their first molars. The mean number of decayed and filled teeth in the control group is significantly higher (p < 0.05) than in the tooth passport group for both sexes.
No funding/Japanese Better oral condition (the number of teeth, periodontal condition, the ability to chew with one 's teeth or the artificial teeth, and the satisfaction of total oral function) were comprehensively related to healthier life style and more frequent participation in social activities.
No funding/Japanese     The following were evaluated in study and control groups: Occlusal force, Occlusal area, Occlusal pressure -The occlusal force of 8020achievers was not significantly different from that of normal occlusal persons in their twenties, but the occlusal force was lower in 8020-achievers with 23 teeth or less.
No funding/Japanese    The following were evaluated in study and control groups: Self-reported anxiety evaluated by STAI-S, STA-T.
• Older women who reported good chewing ability and no problem with dentures had less anxiety.
No funding/Japanese  The following were evaluated in study and control groups: Self-reported health condition, Incidence of NCDs Visiting dental clinics annually for regular check-ups was associated with self-reported health conditions. People who visited dental clinics for regular check-ups evaluated their health conditions higher than those who did not.

8020
Promotion Foundation ¶ /Japanese ¶ Public sector § Private sector. (a) No detailed information about age was provided in the article (b) No detailed information about gender was provided in the article. (c) No detailed information on number of persons was provided in the article.

Discussion
This systematic review evaluated studies related to the activities of the 8020 Campaign since its introduction in 1989, i.e., its impact on oral health conditions, health behaviors, and general health issues. Overall, the 8020 Program was associated with a positive impact on oral diseases, oral health behaviors, and reducing the burden of oral conditions related to general health. The evaluation found "good" quality data on the association between having a complete dentition (28 teeth) and a decreased risk of overall mortality [32], which is consistent with other previous studies [38][39][40][41]. However, this study lacks a degree of external validity because of the selection bias that the study only invited 70-year-old people with 20 or more teeth to participate at baseline. Even though the 8020 Foundation financed some of the included studies and was acknowledged in the publications, there was no clear explanation for the direct link between the findings and the 8020 Campaign.
The main strength of our systematic review lies in the comprehensiveness of the search. Multiple databases were used to search for relevant studies in two languages, as well as the grey literature. It also had no restriction on age groups, allowing us to look at the impact of the 8020 Campaign on all generations. Quality assessment methods also employed a reliable tool proposed by the National Heart, Lungs, and Blood Institutes Evidence Quality Grading System and the National Institutes of Health Critical Appraisal tool [42]. Furthermore, we followed the guidelines of PRISMA. Moreover, to our knowledge, this study is the first to systematically review "the 8020 Campaign" related publications and objectively assess the campaign's outcome in English.
Nonetheless, there are several limitations to be considered. First, quality assessment lacked uniformity, as no limitations were imposed on outcomes. In addition, many of the studies included in this review were cross-sectional, reporting associations rather than causal relationships between exposure and outcome. The overall strength of the evidence is not strong enough as the only one cohort study in this review had 10-year study period. As a result, it is impossible to establish for certain if there is a true causal relationship with health benefits occurring within the Japanese population and the 8020 Campaign. Furthermore, most of included articles focused on oral health of older adults, and only two studies examined oral health in the younger generation. Because of this, we cannot conclude anything about younger generations from our study. Aside from that, we were unable to find any comprehensive methods that were utilized to evaluate the impact of the campaign. As a result, the literature reviewed did not allow a high-quality assessment of the 8020 Campaign's overall direct effectiveness on health improvements.
Despite the above limitations, findings and interpretations of this research have important implications. First, this study showed that the current evidence is insufficient to support promotion of oral health by the 8020 Campaign. It has been reported that the 8020 Campaign has been successful as the results of the Japanese national survey 2016 showed that more than half of the people aged 80 years retained 20 or more teeth. For this reason, the Japanese Society of Oral Health has proposed a new goal as "28 teeth for Lifetime", which should follow after the 8020 Campaign [43]. However, as indicated from this review, the outcomes of the 8020 Program achievements have not been well evaluated in terms of reliable evidence. The outcomes of the 8020 Campaign need further evaluation by longitudinal and interventional studies. Second, this study has indicated the importance of a future-oriented, lifelong approach [6] to oral health and general health. Although life-course orientation is recognized as important, there was only one study with children as a targeted population found in this systematic review, while the majority of included studies targeted older adult [19]. Early life exposures are important as they can influence an individual's future health development. As the evidence on life-course approach to oral health is still limited, more studies, especially in early life-stages, need to be conducted [44].
In Japan, the 8020 Campaign may have benefited not only the Japanese people of all generations but also the community at large. Many beneficial effects of oral and general health conditions, health literacy, and health-related behavior have been identified in this review. The studies explained that there was an increase in the oral health program budget since the 8020 Campaign was launched. This too may be a positive outcome associated with the Campaign. Budget and financial aspects were not discussed in our review; however, budgeting and planning are important to support the 8020 Campaign and its evolution. The unique benefits of the 8020 Campaign in terms of improving general health and oral health are difficult to separate from the integration of oral health into the broader health promotion framework in Japan. Both the 8020 Campaign and other health promotion activities across the studied time period have addressed common risk factors such as diet, hygiene, smoking, alcohol use, stress, and trauma [45]. Considering other campaigns in the world, the Pan American Health Organization (PAHO) has been trying to strengthen oral health services through its Oral Health Program, especially for the most vulnerable populations [46]. The FDI World Dental Federation has provided a roadmap regarding possible strategies for a healthy aging society [47]. It is necessary therefore to evaluate the actions and benefits of the 8020 Campaign systematically. As suggested by the WHO Regional Action Plan on Healthy Ageing [6], further research is needed to address the major benefit of the 8020 Campaign and any direct causality of having 20 or more teeth at the age of 80 to oral and general health by using well-designed longitudinal and interventional studies.

Conclusions
Given the complex nature of the integration of oral health promotion into a common risk factor approach across the prevention of many chronic health conditions affecting older people, the clear outcomes of the 8020 Campaign could not be determined. To disseminate how Japan promoted oral health through the 8020 Campaign, a more informative and systematic description regarding the structure and activities of the 8020 Campaign needs to be established, and a better designed evaluation of the outcomes of this campaign is urgently warranted.

Patents
The current study can be interpreted as a first step in assessing the benefits of the 8020 Campaign. It is crucial to understand the elements of effective public health policy [8], such as financial resources [48], the role of the 8020 Promotion Foundation, and human resource recruiting so that the achievements identified in Japan's 8020 Campaign toward promoting oral health may be applied in other cultures and countries [49]. Further research could also contribute to a deeper understanding of the significance of hand-to-hand collaboration between the government officials and professionals along with citizens' compliance in implementing oral health promotion programs in other regions [8]. Although the 8020 activities in children were only partially explained by research [19], it is also still preferable to initiate such a campaign as early as feasible. The key issue, integrated life-course oral health promotion in all generations, showed its effectiveness in preventing tooth loss in older generations. As the FDI World Dental Federation recommended in the roadmap for a healthy aging society [47], governments worldwide have been working to support better oral health for healthy aging. Since Japan is one of the countries with the highest older population, experiences from the 8020 Campaign could provide, an integrated, positive way, to healthy aging.  [50][51][52][53]. Institutional Review Board Statement: The study was approved by the Ethical Committee of Niigata University (2021-0230).

Informed Consent Statement: Not applicable.
Data Availability Statement: The data supporting this study's findings are available from the corresponding author upon reasonable request.