Distribution of dentists in the Greater Tokyo Area, Japan

Abstract

Introduction: Japan is considered to have an overabundance of dentists; however, there are scarce data on regional inequalities in the ratio of dentists to patients. We examined these inequalities in Japan’s Greater Tokyo Area – otherwise known as the Kanto region, and the world’s most populous metropolitan area – by subdividing it into small- and medium-sized medical care zones. Methods: We calculated the number of dentists per 100,000 population using the 2012 Survey of Physicians, Dentists, and Pharmacists for the three medical district tiers [primary medical care zones: municipalities (cities, towns, villages and special wards); secondary medical care zones: multiple adjacent municipalities; and tertiary care zones: prefectures]. We also estimated the influence of having a dental school in the district or an adjacent district on the number of dentists. Results: The number of dentists per 100,000 population was 79.2 across the whole Kanto region; the range for each type of medical care zone was as follows: 65.3–126.4 at the tertiary level; 38.0–929.6 at the secondary level; and 0–3,087.6 at the primary level. The median Gini coefficient among tertiary medical care zones was 0.16 (range 0.11–0.36). The median number of dentists per 100,000 population was 273.8 in primary medical care zones that had a dental school, 79.9 in adjacent zones, and 59.6 in other zones. Conclusions: We identified significant inequalities in the number of dentists among the medical care zones, and the presence of a dental school had a major influence on this number.

INTRODUCTION

Ensuring an appropriate number of dentists is a major issue in medical policy planning. In 1955, the number of dentists per 100,000 population in Japan was only 34.8. Following the Japanese economic recovery beginning in the early 1950s, the government held a Cabinet meeting in 1969 to address the shortage of dentists, ultimately deciding that there should be at least 50 dentists per 100,000 population throughout the country. This goal was successfully achieved within a decade by establishing a number of new dental schools. However, these measures led to an unintended surplus of dentists, which by 1982 the Cabinet had resolved to reduce. In 1986, a 20% reduction in the number of dentists was set as a goal and, in 1998, the Ministry of Health, Labour and Welfare (MHLW) pursued a further 10% reduction¹.

By 2012, there were 81.0 dentists per 100,000 population in Japan – a 2.3-fold increase from the 1955 figure, and representing a 38% surplus from the goal proposed by the government. Furthermore, it exceeded the 2012 mean of 63.6 dentists per 100,000 population in other Organisation for Economic Cooperation and Development (OECD) countries² by 22% (see Data S1 and S2)3., 4.. In Japan, 85.4% of dentists are private practitioners, and 11.7% are hospitalists⁵.

Despite this national surplus, there is evidence of regional inequalities, with some areas possessing an insufficient number of dentists. However, these data have not been fully delineated. Regional disparities in the number of dentists have been discussed only in terms of the mean values among the total Japanese population or in the 47 prefectural units comprising the ‘tertiary medical care zones’6., 7., 8.. Because dental patients tend to visit their nearest available dental clinic, tertiary medical care zones are too large to accurately determine patients’ level of accessibility to dentists in their area, thereby obscuring the undersupply in smaller zones. Therefore, an investigation of the number of dentists in smaller municipality units (i.e. primary and secondary medical care zones) is needed.

The population of Tokyo and its surrounding area (the Greater Tokyo Area, also known as the Kanto region) accounts for more than a third of the total Japanese population. This area is considered the political, economic and cultural centre of Japan. Tokyo alone has a population of more than 12 million⁹, of which 9.8 million live in the central special wards; by contrast, the population of the Greater Tokyo Area (which has an area of roughly 28,000 km²) is nearly 37 million. Between 1990 and 2014, the Greater Tokyo Area was named the world’s most populous metropolitan region, and it is expected to remain so until 2030¹⁰. Therefore, we chose this area as a representative case to investigate the distribution and inequalities in the number of dentists. In this study, we surveyed the distribution of dentist number by subdividing the Greater Tokyo Area into primary and secondary medical care zones. We also evaluated whether the presence of a dental school in a primary medical care zone or an adjacent zone affected dentist numbers. We hypothesised that the analyses of the number of dentists in the medical care zones would identify the unrecognised magnitude of inequalities and their contributing factors.

METHODS

Data sources

A ‘medical care zone’ refers to an administrative division used in Japan to determine the adequate distribution of medical resources and comprehensively promote medical care in accordance with an area’s particular medical needs. These zones are divided into primary, secondary and tertiary levels11., 12., 13.. A primary medical care zone, while not explicitly defined in the Medical Service Act, covers healthcare services that are familiar to and readily accessible to local residents. They encompass municipalities such as cities, towns, villages and special wards. Secondary medical care zones are defined in the Medical Service Act as an integrated area for the provision of inpatient care; in other words, they are areas wherein general healthcare (ranging from health promotion to disease prevention and hospitalisation) is provided, and they span multiple municipalities. A tertiary medical care zone, also defined in the Act, encompasses an entire prefecture of Japan.

Municipalities in Japan are classified according to their population size. Since April 2016, the Greater Tokyo Area has five designated cities with more than 500,000 inhabitants each, nine core cities and 14 special cities with more than 200,000 inhabitants each, 23 special wards within Tokyo without considering population size, and 257 other cities with more than 50,000 inhabitants each5., 14..

The Greater Tokyo Area has eight dental schools: Tokyo Dental College, Nihon University School of Dentistry, The Nippon Dental University School of Life Dentistry at Tokyo, Nihon University School of Dentistry, Showa University School of Dentistry, Kanagawa Dental University, Tsurumi University School of Dental Medicine, and Tokyo Medical and Dental University. We retrieved the location and number of dentists working at each dental school from its website as of 30 July 2015.

Measures

We retrieved population and household data from the Basic Resident Register of 2011 demographic surveys and from a file created by the Ministry of Internal Affairs and Communication concerning the number of dentists, types of business, and areas of employment in each medical care zone and municipality3., 4., 15., 16.. The number of dentists per 100,000 population was calculated for each medical care zone and displayed on a map using colour scales according to density¹⁷. We could not directly obtain data on the secondary medical care zones; therefore, the figures were calculated based on the municipalities and primary medical care zones within each secondary medical care zone.

The hospitals affiliated with each dental school were plotted onto a map of the secondary medical care zones. The number of dentists per 100,000 population was then calculated for each primary and secondary medical care zone with a dental school as well as the neighbouring zones. If two contiguous medical care zones both had dental schools, they were not counted as a neighbouring zone. The influence of a dental school on the number of dentists in neighbouring zones was calculated by dividing the number of dentists in the neighbouring zone by that in the dental school zone. We also calculated the number of dentists per 100,000 population of zones other than those with dental schools or that were adjacent to zones with schools by subtracting the number of dentists who worked at a dental school from the total number of dentists in a primary medical care zone.

Additionally, to assess the influence of the mobilisation of workers and students by the highly developed transport network in Tokyo, we analysed the relationship between daytime population and the number of dentists in the 14 commercial districts and the 39 non-commercial districts in Tokyo. The daytime population was derived from data from the Government of Tokyo¹⁸, and the number of dentists per 100,000 per daytime population was calculated for commercial districts and non-commercial districts, respectively.

Analytical approach

To evaluate the geographical inequalities in dental care availability, the Gini coefficient for each tertiary medical care zone in Japan was calculated using the numbers from the primary care zones in order to provide a comparison with values in the Greater Tokyo Area. To calculate the Gini coefficient, all regions were ranked in terms of their dentist-to-population ratio, and the cumulative proportion of dentists and the population of each region were plotted on a coordinate plane. The plotted line formed the Lorenz curve, and the Gini coefficient is the area between the Lorenz curve and the 45° line, divided by the triangle under the 45° line. The Gini coefficient varies from 0 (complete equity) to 1 (complete inequity) according to the degree of variation in the dentist-to-population ratios among the zones. Figure S1 shows the Lorenz curve of Tokyo as an example, which is fitted to the cumulative proportion of dentist-to-population ratio in each municipality in Tokyo. For all analyses, we used R version 3.4.3.

RESULTS

Tertiary medical care zones

The number of dentists per 100,000 population among the tertiary medical care zones in the Greater Tokyo Area showed a considerable variation, ranging from a minimum of 65.2 to a maximum of 126.4 (median 62.9), which was comparable to the inequality among all 47 prefectures of Japan (where the median was 70.2 and the range 53.0–126.4). The number of dentists per 100,000 population for the southern coastal prefectures was 77.7 for Tokyo, 65.0 for Chiba and 62.8 for Kanagawa. In contrast, the northern interior prefectures tended to have fewer dentists: 63.7 for Saitama; 50.9 for Gunma; 55.8 for Tochigi; and 57.7 for Ibaraki (Table S1).

Across the whole country, the median Gini coefficient value for the tertiary medical care zones was 0.170 (range 0.074–0.355); in contrast, the median in the Greater Tokyo Area was 0.158 (range 0.112–0.355). Furthermore, in the Greater Tokyo Area, the Gini coefficients for dentists were smaller in prefectures without a dental school (0.112 for Tochigi, 0.131 for Gunma and 0.141 for Ibaraki) than in prefectures with dental schools (0.158 for Kanagawa, 0.159 for Saitama, 0.221 for Chiba and 0.355 for Tokyo).

Secondary and primary medical care zones and municipalities

The number of dentists per 100,000 population in secondary medical care zones showed a considerable variation, ranging from 38.0 to 929.6 (median 63.3; Figure 1; Table 1). Among the secondary medical care zones of the Greater Tokyo Area, the median numbers of dentists were 59.9 (range 38.0–109.4) in the northern regions and 77.2 (range 48.3–929.6) in the southern regions.

Figure 1.

Number of dentists per 100,000 population for secondary medical care zones in the Greater Tokyo Area. The number of dentists is shown with colour grades. Numbers 1–9 on the map denote the locations of dental schools.

Table 1.

The number of dentists per 100,000 population in the Greater Tokyo Area

	Secondary medical care zones	Primary medical care zones
Prefectures
Kanagawa	69.8 (48.3–106.7)	62.8 (22.3–223.1)
Chiba	65.0 (55.5–119.0)	65.0 (12.8–332.9)
Tokyo	90.1 (56.5–929.6)	77.8 (35.8–3,087.6)
Saitama	61.8 (47.9–109.4)	63.7 (0–345.0)
Gunma	53.0 (38.0–89.9)	50.9 (0–89.9)
Ibaraki	59.7 (47.3–68.2)	56.4 (28.4–93.7)
Tochigi	62.1 (52.0–66.5)	55.8 (27.1–109.3)
Type of cities
Designated cities (n = 5)	77.7 (59.2–119.0)
Core cities (n = 9)	75.7 (63.7–124.2)
Special cities (n = 14)	67.1 (53.9–93.7)
Tokyo special wards (n = 23)	112.4 (72.1–3,087.6)
Other municipalities (n = 257)	57.7 (0–154.5)

The median values are shown with the minimum and maximum values in the parentheses. The cities with more than 200,000 population are categorised as designated cities, core cities or special cities based on the administrative functions. Tokyo has 23 special wards. There are 257 other small cities in the Greater Tokyo Area.

Among the primary medical care zones (Figure 2 Table 1), the dentist number per 100,000 population ranged from a minimum of 0 in a mountainous rural region and a maximum of 3,087.6 in the central district of Tokyo (median 62.9).

Figure 2.

Number of dentists per 100,000 population for primary medical care zones in the Greater Tokyo Area. The number of dentists is shown with colour grades.

In the special wards of Tokyo, the number of dentists per 100,000 population was 112.4, which was substantially higher than that in other municipalities, at 57.7 (Table 1). The data for the five designated cities, nine core cities and 14 special cities are also shown in Table 1. The median number of dentists in larger cities was 80.3 (range 59.2–3,087.6), whereas that of smaller cities was 57.7 (range 0–154.5).

Zones with a dental school and neighbouring zones

Table 2 shows the data for zones with and without a dental school. Among the primary medical care zones, the median number of dentists per 100,000 population was 278.3 (range 124.3–3,087.6) in those with a dental school, 79.6 (range 64.5–345.6) in neighbouring zones, and 59.6 (range 0–154.4) in other zones. The mean incremental rate of the influence of zones with dental schools on neighbouring zones (compared with other zones) was 45.6% (range 11.2%–87.5%). The mean proportion of dentists working in an affiliated hospital of a dental school in primary medical care zones was 51.2%. The median number of dentists in zones with a dental school but who were not working in such schools was 85.5 (range 77.8–1,383.6) per 100,000 population. Among the secondary medical care zones, the median number of dentists per 100,000 population was 108.1 (range 66.5–929.6) in zones with a dental school and 70.3 (range 57.2–111.0) in neighbouring zones.

Table 2.

Incremental effects of dental schools in primary and secondary medical care zones

	The number of dentists per 100,000 population			Incremental effects
	Zones other than target zones, median	Target zones (A)	Surrounding zones (B)	B/A × 100 (%)
Primary medical care zones
Kanagawa prefecture	66.6
Showa University		223.7	95.7	42.8
Kanagawa Dental University		124.3	80.2	64.5
Chiba prefecture	63.9
Tokyo Dental College		332.9	75.3	22.6
Nihon University, School of Dentistry at Matsudo		154.5	72.1	46.7
Tokyo	74.2
The Nippon Dental University and Nihon University		3,087.6	307.6	10.0
Showa University		156.5	94.1	60.1
Tokyo Medical and Dental University		523.9	170.1	32.5
Saitama prefecture	62.9
Meikai University		345.0	76.1	22.1
Secondary medical care zones
Kanagawa prefecture	63.5
Showa University		82.7	73.8	89.2
Kanagawa Dental University		106.7	68.5	64.2
Chiba prefecture	59.5
Tokyo Dental College		119.0	58.0	48.7
Nihon University, School of Dentistry at Matsudo		87.7	61.7	70.4
Tokyo	85.1
The Nippon Dental University, Nihon University, and Tokyo Medical and Dental University		929.6	109.4	11.8
Showa University		155.2	120.8	77.8
Saitama prefecture
Meikai University	109.4	62.2	56.9

A target zone indicates a medical care zone with a dental university.

Influence of daytime population

In the commercial districts in Tokyo, the median number of dentists per 100,000 residential population was 162.2 (range 59.5–3,087.6), while the median number of dentists per 100,000 daytime population was 96.2 (range 64.4–184.7). Similarly, in the non-commercial districts in Tokyo, the median number of dentists per 100,000 residential population was 77.8 (35.8–523.9) and, per 100,000 daytime population, it was 83.5 (range 33.1–293.3).

DISCUSSION

The present study showed that, although the tertiary medical care zone of the Greater Tokyo Area had a relatively high dentist density by international standards (Data S3), there were significant disparities in density among the primary and secondary medical care zones. After mapping dentist density onto the primary and secondary medical care zones, a number of major geographic differences became apparent.

First, there was a north–south disparity in the Kanto region, with a tendency for zones in the north to see a shortage of dentists. Common features of the zones in this region include an absence of dental schools, being a considerable geographic distance from the concentrated areas of central Tokyo and being primarily mountainous.

Second, the number of dentists varied greatly among the primary medical care zones according to whether there were dental schools with affiliated hospitals in the zone or a neighbouring one. The number was noticeably higher in zones with a dental school than in areas without one. Notably, primary medical care zones containing multiple dental schools with affiliated hospitals showed a dramatically larger number of dentists. For example, the most central ward (Chiyoda) of Tokyo had two of the largest dental schools with affiliated hospitals, and nearly 3,087.6 dentists per 100,000 population (or roughly a single dentist for every 32 inhabitants). Primary medical care zones with hospitals affiliated with a dental school had a median dentist density of 278.3, whereas those where the central hospital had a small or no dental department had a median dentist density of 61.8 (indicating a 4.5-fold disparity).

A previous study in Toronto, Canada, showed that the number of dentists tended to be higher in districts with high-earning residents¹⁹. Another study, conducted in the UK, showed that the number of dentists was higher in more densely populated areas²⁰. In Iran, dentists tend to gather in larger cities because that is where they can access continuing education²¹. All these studies are consistent with our findings showing that the number of dentists is lower in small cities and rural areas, where there are few or no dental schools. These findings are also concordant with reports indicating that there were more dentists in highly populated prefectural capitals22., 23..

We also illustrated the bottom-up influence of primary medical care zones with a dental school on the density of dentists in adjacent zones: that is, 33 of 37 neighbouring primary medical care zones had larger densities compared with the median number in the Kanto region. In other words, when a primary medical care zone had a dental school, neighbouring zones tended to have a higher density compared with the prefectural median.

Just over half (51.2%) of dentists in primary medical care zones with dental schools worked in the affiliated hospitals of those schools. After excluding dentists that were enrolled in a dental school, all eight districts with dental schools still had dentist densities higher than the national median. Furthermore, the Gini coefficients of dentists were lower in prefectures without dental schools than in those with dental schools. Overall, the Gini coefficients between the whole country and the Greater Tokyo Area were similar. However, it should be noted that the tertiary medical care zone in Tokyo had a twofold higher Gini coefficient compared with the national coefficient, indicating a prominent maldistribution of dentists in the area. Considering that regional medical care is predominantly provided by individual practitioners, these primary medical care zones in central Tokyo appear to benefit from ample dental care resources.

Secondary medical care zones showed a similar trend to those of primary zones, with the exception of the central region of Saitama Prefecture (Figure 1 Table 1). In secondary zones with dental schools, the median density of dentists was 106.7, and all these zones had a higher density than the median of the Kanto region. This is consistent with a previous report by Ahmad and Quiñonez¹⁹. The median dentist density in the neighbouring zones to those with dental schools was 63.5, indicating a 1.7-fold disparity. The Greater Tokyo Area has 51 districts (including core or special cities and the Tokyo special wards; Table 1), which together had a median dentist density of 80.3; this is higher than the national standard, indicating that dentist densities are higher in metropolitan areas.

Of note, the influence of the mobilisation of workers and students by the highly developed transport networks in Tokyo was not negligible, as shown in the differences of the number of dentists between residential population and daytime population. In the commercial districts in Tokyo where many people gather from suburban areas via the transport networks, the number of dentists per daytime population showed a decrease compared with that per residential population, although the former was still higher (96.2) compared with the number (81.0) for the whole of Japan.

The present study has some implications for decision-making concerning the optimal allocation of dentists in major metropolitan areas. Relative to the Japanese government’s target index of 50 dentists per 100,000 population, the mean surplus in dentists was 31.7% in 201224., 25.. However, simply reducing the current number of dentists by 30% without correcting for regional disparities would produce many regions with a significant shortage of dentists. Namely in leading to a collapse in regional medical care. Namely, in underserved areas, local residents would not receive general dental care as well as emergency dental care sufficiently and continuously, because a shortage of dentists would impose an increased spatiotemporal and financial burden, even if the residents commute to an urban area.

It should also be noted that the Japanese population is rapidly aging²⁶. In 2013, the population aging rate in Japan was 25.1%, which was the highest rate worldwide and three times the global mean²⁶. In Japan, elderly people tend to make more dental visits compared with younger people²⁷. Therefore, a dentist shortage in aging districts would exacerbate problems with dental care, especially for elderly inhabitants. In addition, dentists in Japan are themselves getting older: in 2014, 51.7% of dentists were 50 years old or older, while only 25% were 39 years old or younger²⁴. Soon, the increased number of aged dentists might lead to deterioration in the delivery system for community dental healthcare. Thus, the anticipated rate of retirement of dentists should be considered.

In Japan, the roles of dentists must be changed. As a reference, efforts made in the USA should be considered. Immediately after World War II, the USA founded institutions encouraging collaborative care between physicians and dentists, thereby increasing the focus on systemic diseases as part of dental care²⁸. In a similar fashion, Japan might realize a new demand for more dentists by intensifying medical and dental collaboration. Moreover, to mitigate dentist density disparities among areas in the country, it might be effective to limit new entry to areas with an excess of dentists.

This study has several limitations. First, we focused on the Greater Tokyo Area and did not include other areas in Japan. Second, we did not analyse background factors related to the workplaces of dentists, such as salary or number of patients. Although further studies are necessary to mitigate the inequality of distributions of dentists, one of the most striking characteristics of the changing face of dental care in Japan is its rapidly ageing population. There will be various emerging needs for dental care among the elderly population, and such demands should be satisfied by not only considering the number of dentists but also by encouraging the adoption of new technology. Third, under dental law, it is mandatory for dentists to complete government surveys on the number of dentists, but we cannot determine if some dentists did not complete these surveys. Finally, our findings might not be fully applicable to other countries with different dental care systems.

In conclusion, there were significant disparities in the number of dentists relative to the population at the primary and secondary medical zone levels in the Kanto region of Japan. The presence or absence of a dental school was a major factor for these disparities. Although Japan has a relatively high density of dentists, a simple reduction policy might exacerbate their unequal distribution throughout the Greater Tokyo Area. Policymakers should prioritise introduction of countermeasures to alleviate this uneven distribution, such as financial incentives and subsidies to dentists who work in underserved areas.

Acknowledgement

This research was supported by the Medical Governance Research Institute.

Conflict of interest statement

Dr Tanimoto receives personal fees from MNES Inc., outside the submitted work. Other authors declare that they have no conflicts of interest.

SUPPORTING INFORMATION

Additional Supporting Information may be found in the online version of this article:

Figure S1. The Lorenz curve fitted to the cumulative proportion of dentists per 100,000 population in each municipality of Tokyo.

Table S1 The number of dentists per 100,000 population in the Greater Tokyo Area and all prefectures in Japan

Data S1. OECD means.

Data S2. Number of dentists in Japan and OECD countries.

Data S3. International comparison of dentists.