ヘルスサイエンス・ヘルスケア

Volume 11，No.2（2011）

ARTICLES

Number of missing teeth by birth year in a Japanese population

Masaki Kambara，Masako Uene

Abstract：The purpose of this study is to analyze the change of Missing teeth (MT) recorded in the Japanese
National Survey of Oral Health by birth year cohort. In the results of the birth year cohort, theMT showed to be decreasing year by year during about 50 years. It reveals that many teeth
remain in the mouth of the elderly.
It was suggested that MT have the possibility of index to estimate the oral health of the elderly
and the outcome of total oral health system through a life.
Key words : missing teeth (MT), birth year cohort, Japanese National Survey of Oral Healthtotal population as of September 2010 2）．

Introduction
Japan is unique among the super-aging societies

For such a super aging society, few studies haveworldwide due to its rise in average lifespan andbeen conducted on dental status in Japan3）． The

the rapid growth of its elderly population1）． The

correlation between lifespan and the number ofemergence of this super-aging society can beresidual teeth has been reported4，5）． The mostexplained by the decline in the birth rate due toimportant implication of these investigations for

fewer people getting married, as well as thefuture dentistry was that the more residual teeth,

extended average lifespan due to advances in thethe longer the lifespan. This significant evidence

field of medicine and better preservation of thereaffirms the value of dental care.

environment. The proportion of elderly in Japan is

The present study aimed to investigate the fre-

the highest in the world, with elderly persons 65

quency of missing teeth in Japanese society based

years or older estimated to comprise 23.1% of theon a birth year cohort analysis using Japanesenational survey data.

【著者連絡先】〒573-1121 大阪府枚方市楠葉花園町 8-1
大阪歯科大学口腔衛生学講座
神原正樹
TEL：072-864-3019 or 06-6943-4184
FAX：072-864-3119

Materials and Methods
Values for decayed missing filled teeth (DMFT),
decayed filled teeth (DFT), and missing teeth (MT)recorded in nine Japanese National Surveys6） conducted at 6-year intervals between 1957 and 2005
̶ 35 ̶

Number of missing teeth by birth year in a Japanese population

were used for the birth year cohort analysis. Sub-1988, and 1989-1994. MT in each group was evalu-

jects older than 5 years of age were divided into

ated to calculate the average value for each 6-year

age groups at 6-year intervals, and the values inperiod. Changes in MT and DFT in each birtheach age group recorded every 6 years in theyear group were analyzed.

National Survey were analyzed as a birth year
cohort. There were a total of 15 birth year groups:

Results

1905-1910, 1911-1916, 1917-1922, 1923-1928, 1929-

Changes in DMFT, DFT and MT in the results

1934, 1935-1940, 1941-1946, 1947-1952, 1953-1958,of the 2005 Japanese National Survey are shown in

1959-1964, 1965-1970, 1971-1976, 1977-1982, 1983-Fig. 1. DMFT increased with age. DFT tended toFig. 1

DMFT, DFT and MT with age in the results of Japanese national survey at 2005

Fig. 2

Change of MT with age as a function of birth year
̶ 36 ̶

ヘルスサイエンス・ヘルスケア

Volume 11，No.2（2011）

increase from 6 years of age to around 40 years ofyounger generation of Japanese had more remain-age, then decreased after 40 years of age. MTing teeth, though the older generation lost teeth

increased exponentially after 35 years of age. Thewith age.

association between DMFT, DFT, MT and age

The“8020 Campaign”, which aims for 20

was observed in every result of the past 10 Japan-

remaining teeth at 80 years of age, is currently

ese National Surveys.

being promoted in Japan. The Japanese National

Changes in MT revealed by the cohort analysis

Survey held in 2005 indicated that the number ofbased on birth year are shown in Fig. 2. MT

remaining teeth at 80 years of age was 10. The

increased with age from 40 to 80 years of age inresults of our study suggest that it should be pos-people born before 1945. The average number ofsible to achieve the goal of the 8020 Campaign in

MT was 20 in people born between 1907 and 1911,

the future.

and nearly 10 in those born between 1937 andWe attempted to estimate which generation

1941. MT decreased by 10 over the course of 40

would achieve this goal and approximately when.

years. However, MT did not decrease in people

Multinomial expressions (y = ax + bx2 + c; y: miss-born after 1945 compared to those born before

ing teeth, x: age) were calculated from the MT1945.

data for each generation. The estimation curve ina typical generation is shown in Fig. 3 ((1), people
Discussion

born around the 1910s; (2), 1950s; (3), 1960s). The

MT in the Japanese population showed a ten-values for a, b and c in the equation y = ax + bx2

dency to decrease in younger as compared to+ c for (1), (2), and (3) were: a, 2.789, 0.049, 0.111; b, -older generations in our analysis of the birth year

0.016, 0.001, -0.001; and c, -95.0, -0.7, -1.2, respective-cohort. It is generally considered, based on thely. MT in people born in the 1910s (around 100

results of cross-sectional surveys, that teeth areyears of age) increased exponentially with age

lost with age. However, it was clear that theafter 40 years of age. MT in people born in theFig. 3

Change of MT with age as a function of birth year
̶ 37 ̶

Number of missing teeth by birth year in a Japanese population

1950s (around 60 years of age) also increased grad-The reason for the observed decrease in MT

ually with age. However, MT in people born in theover the course of 50 years must be considered.

1960s (around 50 years of age) did not increase

Tooth loss is generally thought to be due to bothwith age like that in people born before the 1950s,

dental caries and periodontal disease. If dental

and these people had many remaining teeth. The

caries and periodontal disease are the main rea-

number of MT which estimated at age 80 in allsons for increasing MT, the prevalence of thesethree generations from the multinomial expression

diseases should also be expected to decrease. It isestimation curve were 21.8, 9 and 4.1, respectively.

clear that dental caries is decreasing, as DMFT at

It was predicted that the goal of the 8020 Cam-12 years of age is about 1. Also, it is believed that

paign could be achieved when the generation born

the periodontal condition of adults in Japan has

in the 1960s reaches 80 years of age, approximate-improved from past decades. However, epidemio-

ly 20 years from now. It is predicted that Japaneselogical data for factors such as caries are lacking.

elderly people will have a large number of remain-

Because caries and periodontal disease have risk

ing teeth in the future.

factors similar to those of non-communicable dis-Figure 4 summarizes the changes in MT and7）

eases (NCDs), the FDI (Federation of Dental Inter-

DFT as a function of birth year with age. DFTnational) has recommended the inclusion of thesetended to increase before 40 years of age andconditions as NCDs. Further investigations aredecrease after 40 years of age. However, MT

necessary regarding the association between MT

decreased throughout the 50 years of the Japanesereduction and the prevalence of periodontal dis-National Survey. DFT changed by 6 or 7, whileease or socioeconomic factors, including lifestyle, toMT showed a difference of about 20. DFT

determine the reason for the decrease in MT.

decreased after 40 years of age by increasing MT,

MT is considered to reflect the oral health sta-but MT did not change dynamic. MT comes totus of a population, from birth to the elderly.

show the final result in the human mouth fromTherefore, MT in the elderly population in Japanbirth to old age.

is expected to reveal the success or failure of theFig. 4

Change of DFT and MT with age as a function of birth year̶ 38 ̶ヘルスサイエンス・ヘルスケア

Volume 11，No.2（2011）

Japanese oral health system, which consists ofmaternal and child healthcare, oral health examinations in 1.6-year-old children, 3-year-old children,and school-age children, oral health examinations
in companies, and oral examinations at 40, 50, 60
and 70 years of age, as well as the effectiveness of
the Japanese dental insurance system. To determine the outcome of oral healthcare in terms ofMT, I think that for example, the MT rate shouldbe calculated.
It is suggested that MT may serve as an important dental index as Japan emerges as a world
leader in terms of average lifespan.
References
1）Annual Report on the Aging Society：2010
http://www8.cao.go.jp/kourei/whitepaper/indexw.html (December 1, 2011 Access)
2） Journal of Health and Welfare Statistics 2011/2012.

̶ 39 ̶

Health, Labour and Welfare Statistics Association.
2011,58;39.
3）Taura K, Sakamoto S, Sakamoto M, Douglass CW. Is“8020”an Attainable Goal? : Prediction of Future
Number of Remaining Teeth of Japanese Adults；
Based on Data From the Survey of Dental Diseases inJapan. J Dent Health 45,；28-34. 1995.
4） Fukai K, Takiguchi T, Ando Y, Aoyama H et al.
Dental health and 15-year Mortality in a cohort of community-residing older people. Geriatr Gerontol lnt. 7：341-347：2007．
5） Fukai K, Takiguchi T, Ando Y, Aoyama H et al.
Mortality rates of community-residing adults with andwithout dentures. Geriatr Gerontol Int 2008；8：152–159.
6） National Dental Surveys -Statistical tables of thedental diseases-（1957-2005）．2009, Oral Health Association of Japan.
7） Kambara M, Masako Uene. Changes of DFT as afunction of birth year in Japanese population. Health
Science and Health Care 10：40-44，2010．