Changes of DFT as a function of birth year in the Japanese population

ARTICLES

Changes of DFT as a function of birth year in the Japanesepopulation

Masaki Kambara，Masako Uene

Abstract：The purpose of this study was to analyze the number of Decayed and Filled Teeth (DFT) recorded in the Japanese National Survey of Oral Health by birth year cohort.
The DFT values recorded in the nine Japanese National Surveys, which were conducted at sixyear intervals between 1957 and 2005.
Based on the birth year cohort, DFT with age could be divided into three groups: old generation,
middle generation and new generation.
It is suggested that we must think the different strategy for each generation.
Key words : DFT, Birth year cohort, National Survey of Oral Health, Japanese
1. Introduction

lish oral health-centered dentistry, which focuses

In recent years, the prevalence of dental caries

on people who have a sound oral cavity, instead ofhas declined, especially among young people. It istreatment-oriented dentistry.

expected that the number of decayed, missing andThis new outlook in dentistry has alreadyfilled teeth (DMFT) at the age of 12 years would

been applied in oral examination, especially inreach 1 in Japan. A mean DMFT of 1 at the age ofassessment of dental caries based on the Inter-12 years may indicate that most subjects have nonational Caries Detection and Assessment Sys-

experience of dental caries and not visited a dentaltem (ICDAS) 1，2）． The objective of oral examina-

office. As a result, they have little interest in oraltion has changed from the detection of oral dis-health and do not make the effort to perform oral

eases to estimation of oral health because of ancare. Therefore, it is urgently necessary to estab-increase in sound teeth. It is needed to rearrange
the results of dental caries followed by the WHO
criteria of dental caries. The purpose of this study【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

was to analyze the number of Decayed and Filled
Teeth (DFT) recorded in the Japanese National
Survey of Oral Health by birth year cohort.

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ヘルスサイエンス・ヘルスケア

Volume 10，No.2（2010）

2. Materials and Methodand age was the same as in the previous nine

The DFT values recorded in the nine JapaneseJapanese National Surveys on DMFT. However,National Surveys, which were conducted at six-DFT increased until the age of 45 years alongyear intervals between 1957 and 2005 3）， werewith increase of DMFT, and then showed aused for birth year cohort analysis. The subjects

decrease.

above 5 years old were divided into groups withFigure 2 shows the changes of DFT with age in

an interval of six years of age, and the values inthe previous nine Japanese National Surveys oneach age group recorded every six years in theDFT. All changes of DFT with age revealed theNational Survey were analyzed by birth year

same chevron transition. The result of 2005

cohort. There were a total of fifteen birth year

reached the highest value around the age of 40

groups: 1905-1910, 1911-1916, 1917-1922, 1923-1928,

years and then decreased. The highest value of

1929-1934, 1935-1940, 1941-1946, 1947-1952, 1953-

DFT increased from 8 in 1957 to 14 in 2005. The

1958, 1959-1964, 1965-1970, 1971-1976, 1977-1982,

change in DFT was nearly 6 and 7.

1983-1988, and 1989-1994. The DFT in each group

The results of DFT as a function of birth year

was evaluated to calculate the average value with-cohort are shown in Figure 3. In the subjects bornin six years. The change of DFT in each birth

before 1945, DFT showed a chevron transitionyear group was analyzed.

change with age in each national survey; it
increased until the age of 40 years, peaked and3. Resultsthen decreased. In the people born between 1946

Figure 1 shows the changes in DMFT and DFTand 1970, DFT was high compared to the DFTwith age based on the most recent results of thebefore 1945, reaching the highest value at 14 andJapanese National Survey conducted in 2005. It

then decreasing gradually. In the people born after

reveals that the linear correlation between DMFT

1970, the DFT was low followed by a low DFT at

Fig. 1

Changes in DMFT and DFT with age in the 2005 Japanese National Survey
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Changes of DFT as a function of birth year in the Japanese population

Fig. 2

Changes in DFT with age in each of the nine Japanese National Surveys of Oral HealthFig. 3

DFT in each age group as a function of birth year

the age of 12 years and this low value was main-does not heal naturally and is an accumulating dis-tained with age.

ease. However, we feel that the oral health of thegeneral population is improving each year. There4. Discussion

fore, it is unclear why the correlation remained

In general, it is thought that DMFT increases

the same in each national survey. As DMFT

linearly with age, mainly because dental caries

includes decayed, missing and filled teeth, this̶ 42 ̶ヘルスサイエンス・ヘルスケア

Volume 10，No.2（2010）

study aimed to elucidate the change of DFT using

value would be 2 or 3 in each sextant. It remainsbirth year cohort analysis.

to be determined which teeth and tooth surfaces

1） Cross sectional results of DFT in past nine

are more susceptible.

Japanese National surveys2）Results of birth year cohort analysis of DFT

The relationship between DFT and age appeared

Based on the birth year cohort, DFT with age

to be of chevron transition. It is assumed that thecould be divided into three groups: old generation,

increase of DFT until the age of 40 years reflected

middle generation and new generation.

4）

the increase in DMFT shown at 12 years of age .

（1） Old generation (people born between 1907

It means that the dental caries seen in a child isand1945; 95-62 years of age)carried on when he/she becomes an adult. On theThe change of DFT in this generation showed

other hand, the decrease in DFT after the age ofchevron transition which peaked at the age of 40

40 years may correlate to the increased number ofyears as in the cross-sectional results of eachmissing teeth. An epidemiological analysis of miss-national survey (Fig.4. 1). The DFT then increased

ing teeth has to be conducted to clarify this point.

with late birth year as shown in Fig.4, 2. ThisThe highest value of DFT in chevron transition atincrease over 40 years of age is bigger than under

the age of 40 years changed from 8 in 1957 to 14

40 years of age. The DFT before 1945 was low,in 2005, and the mean change was 6. This highwhich shows that the Japanese society was poor

value can be associated with the increased num-as a material civilization and the people led an

ber of missing teeth after 40 years of age. A meananti-caries life style.

DFT of 8 indicates that the DFT is 1.3 in each of（2） Middle generation (people born between

the six sextants and for a mean DFT of 14, theFig. 41946 and 1970; 63-33 years of age)

DFT in each age group as a function of birth year
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Changes of DFT as a function of birth year in the Japanese population

The increase of DFT in this generation before

It appears that in the 20th century, dentistry

40 years of age was remarkable and was the high-

was focused on treating the increased DFT in oldest recorded in Japanese history. This increase ofand middle generations. In future dentistry, theDFT indicates that dental caries is a result of thesound teeth, decayed teeth and filled teeth are

emerging civilization with introduction of westernretained; therefore, dentists must evaluate not only

culture, food styles, convenience stores, family

decayed teeth, but also the quality of teeth, root

restaurants, and the Japanese society has changed

caries, tooth wear, tooth stains and secondaryfrom a traditional society to a substrate-full society

caries. A new system to assess these changes ofwhich means that the Japanese can somehow

tooth quality must be introduced.

obtain anything anytime and anywhere. The highest value of DFT in this generation was 14 with aReferences

DFT of over 2 in each sextant. It is interesting1） Ismail AI, Sohm W, Tellez M, Amaya A, Sen A,Hasson H, Pitts NB. The International Caries Detection and Assessment System (ICDAS) : an integrated
system for measuring dental caries. Community Dent
Oral Epidemiol 35：170-178，2007.
2）New index alternative to the DMFT「The International Caries Detection and Assessment System(ICDAS)」Attempt of introduction into Japan．J Dent
Hlth 60：318-321，2010．
3） National Dental Surveys −Statistical tables of thedental diseases−（1957-2005）．2009, Oral Health Association of Japan.
4） Kambara M. Innovative changes of school dental
health. Journal of the Osaka Association of School Dentists 10：1-6，2006．

that the DFT does not exceed 14 and show evenhigher values. The incidence of dental caries ismore in specific areas, such as the pit and fissuresin molars and interdental areas.
The stable or slightly declining DFT after 40
years is supposed to be associated with thedecrease in the number of missing teeth. It indicates that many teeth are retained in the mouth.
An epidemiological study of the missing teeth isrequired.
（3） New generation (people born after 1971 ;above 32 years of age)
The DFT in this generation was low, and is
expected not to increase in the future. The goal of
future dentistry is to maintain this low value ofDFT.

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