Ten-year tertile shift of middle-aged males by number of present teeth and sound teeth

Ten-year tertile shift of middle-aged males by number ofpresent teeth and sound teeth

Koichi Yoshino1），Kakuhiro Fukai2）
Tokyo Dental College，2）Fukai Institute of Health Science1）

Abstract： The purpose of this study was to ascertain the change in the ranking of participants by presentteeth (PT) and sound teeth (ST) by cohort analysis. Dental examinations on 89 males, aged 40 to49, were conducted by two calibrated dentists in 1992 and 2002. The data were serialized indescending order by the total number of PT and ST in the baseline data and were then divided
into tertiles. Using the data from ten years later, the same subjects were again divided into tertiles. Some of them moved up or down while some remained in the same tertile during the tenyear observation period. Of the 30 participants in the top tertile at baseline, 23 (23/30, 76.7%)
remained there during the ten-year period. Of the 30 participants in the middle tertile at baseline,
20 (20/30, 66.7%) remained. Of the 29 participants in the bottom tertile at baseline, 22 (22/29,75.9%) remained. Participants who had a given cumulative relative frequency of PT at baselinetended to remain in the same tertile ten years later. Numbers of PT and ST is related to future
numbers of PT and ST.
Key words : Percentile, Present teeth, Sound teeth, Adults

Introduction

tus compared to that of the general population.

Percentile curves of numbers of present teeth(PT) were developed by Osada et al.

1）

Osada2） also

introduced

smoothed

percentilein 1990. Per-curves for PT in 1999. They estimated percentile

centile curves are useful indicators because they

curves and values on the basis of the distribution

allow individual clients and patients to visibly rec-of numbers of missing teeth in 5,036 subjects aged

ognize and understand their own oral health sta-40-79. Primary data on subjects’missing teeth
was obtained from the National Report on the Survey of Dental Disease in 19873）.

【correspondence】
Koichi Yoshino
Department of Epidemiology and Public Health,Tokyo Dental College
1-2-2 Masago, Mihama-ku, Chiba 261-8502, Japan
Tel：+81-43-270-3746 Fax：+81-43-270-3748
Accepted for publication：30 November 2012

Yoshino et al. 4） introduced percentile curves ofpresent and sound teeth (ST) for use in providing
oral health instruction to office workers. Yoshinoet al. 5） also proposed percentile curves of PT in
smokers and non-smokers. The percentile curves
for PT are not only useful indicators in assessing
̶ 84 ̶ヘルスサイエンス・ヘルスケア

Volume 12，No.2（2012）

ST, decayed, and filled teeth. The data analyzed inthis study was from 89 males aged 40 to 49 who
participated in both dental examinations. This age
group was selected because tooth loss increases
after the age of 40 3）．There were also females whounderwent the regular dental examinations, butthere were few who underwent both dental examFigure 1 Model of shift of ranking during 10-year observation period
The curves are based on cross-sectional data.

inations in this study. For these reasons, females
and subjects 50 years old and over were excludedin this study.
In this study, completely and partially erupted

the population, but have also been used in oral

permanent teeth and fused teeth were counted ashealth instruction for office workers.

one tooth. In addition, supernumerary teeth, pon-Using percentile curves, patients can clearly see

tics of bridge prostheses, and implant-supported

how their own oral status compares with that ofsuperstructures were excluded from the number

their age group in the general population. Howev-of PT. Third molars were also excluded.

er, when percentile curves are calculated by sec-

The data were serialized in descending order bytional data, it is difficult to precisely predict thethe number of PT and, when the number of PTfuture PT of a given age group (Fig. 1). The pur-was the same, by the number of ST. Both thepose of this study was to ascertain the shift in thebaseline data and the data from ten years later

ranking of PT and ST by cohort analysis.

were then classified into tertiles. Some of the participants moved up or down while some stayed inMethods

the same tertile during the ten-year observation

The health insurance union of a bank in Kana-period (Fig. 2).

gawa has conducted an annual dental examination
for insured persons since 1961. The data analyzed

Statistical Analysis

in this study is from dental examinations conduct-

The comparison of PT and ST among tertile

ed by two calibrated dentists in 1992 and 2002.

groups was conducted with Tukey and Games-

The two dentists were calibrated before theHowell. The level of significance was set at 0.05.

examinations in order to standardize their diagnostic criteria. The diagnostic criteria of this study
were set in accordance with the National Reporton the Survey of Dental Disease of 1987 3）．There
were 5,113 (participation rate: 5,113/6,292=81.3%)
participants in 1992 and 3,277 (participation rate:
3,277/4,007=81.8%) in 2002. The reduced population size can mostly be attributed widespread
restructuring at the bank due to worsening economic conditions during the 10-year observation
period. The dentists recorded the number of PT,
̶ 85 ̶Figure 2 How to read Figure 3

Ten-year tertile shift of middle-aged males by number of present teeth and sound teeth

The data was analyzed using the computerized

the 29 participants ranked in the bottom third atstatistical package SPSS, version 15.0 (SPSS Japan,baseline, 22 (22/29, 75.9%) remained there while 7Inc., Tokyo, Japan).

(7/29, 24.1%) moved up to the middle tertile. Participants who were at a given baseline cumulative
Results

relative frequency of PT tended to remain in theFigure 3 shows the ten-year shift of adult denti-same tertile ten years later.

tion by tertile. Of the 30 participants ranked in theTable 1 shows the mean number of PT and ST

top third at baseline, 23 (23/30, 76.7%) remained infor each tertile. At baseline, the mean number ofthe same tertile, 3 (3/30, 10.0%) moved down toPT for each group was 28.0, 27.4, and 24.3, respec-

the middle tertile, and 4 (4/30, 13.3%) moved down

tively. Ten years later, the mean number of PT

to the bottom tertile during the ten-year period. Of

for each group was 27.3, 26.4, and 23.1. The mean

the 30 participants ranked in the middle third atdecrease in PT for each group was 0.7, 1.0, and 1.2,baseline, 20 (20/30, 66.7%) stayed there while 6

but the differences among the groups were not(6/30, 20.0%) moved up to the top tertile and 4significant.

(4/30, 13.3%) moved down to the bottom tertile. OfAt baseline, the mean number of ST for each

Figure 3 Ten-year shift of the subjects by tertile
Table 1 Mean number of PT and ST by tertile (n=89)

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ヘルスサイエンス・ヘルスケア

Volume 12，No.2（2012）group was 19.3, 13.8, and 11.6, respectively. Tenof these reports, namely that number of PT is ayears later, the mean number of ST for eachreliable predictor of individual future tooth loss

group was 16.2, 11.9, and 9.5. The mean decreaserisk.

in ST for each group was 3.1, 1.9, and 2.1, but theIn this study, there were no significant differ-differences among the groups were not significant.

ences in the mean number of teeth lost during theten-year period among the tertile groups. Howev-Discussion

er, this means that participants can not easily

In this study, percentage of participants whochange among tertile groups. Participants who

were changed among teritle groups was small rel-

were at a given baseline cumulative relative fre-atively. These results show that the ranking of PT

quency of PT tended to remain in the same tertile

and ST did not change much during the ten-year

ten years later. Numbers of PT and ST is related

period. Because loss of PT is caused by irre-to future numbers of PT and ST.

versible disease, as the number of PT decreases,
the likelihood of losing more teeth increases.

References

Yoshino et al. 6） performed a six-year generational

1） Osada H, Tazawa M, Takaesu Y (1990) Percentile
curves for the numbers of permanent teeth and theirsignificances. J Dent Health 40：319-324. (in Japanese)2） Osada H (1999) Percentile curves and values ofremaining teeth as indicators of oral health in the adult
population. Shikwa Gakuho 99：573-589. (in Japanese)
3）Dental Health Division of Health Policy Bureau Ministry of Health, Labour and Welfare Japan (1987)
Report on the survey of dental diseases.
4）Yoshino K, Matsukubo T, Takaesu Y (2000) Evaluation of remaining and sound teeth of office workers
with percentile parameters. J Dent Health 50： 40-51.
(in Japanese)5） Yoshino K, Osada H, Matsukubo T, Takaesu Y(2006) Percentile curves for present teeth in smokers
and non-smokers in an adult male population. Bull
Tokyo Dent Coll 47：51-55.
6） Yoshino K, Sakurai M, Muramastu Y, Tanabe Y,Kagami N, Sugihara N, Matsukubo T (2009) Estimatedtooth loss based on number of teeth present in Japanese adults using national dental surveys in 1999 and2005. J Dent Health 50：159-164. (in Japanese)
7） Eklund SA, Burt BA (1994) Risk factors for total
tooth loss in the United States：longitudinal analysis ofnational data. J Public Health Dent 54：5-14.
8）Yamamoto T, Tsuneishi M, Murakami C, WatanabeT (2007) Retrospective study on tooth loss duringmaintenance care in a university hospital. J Dent
Health 57：632-639. (in Japanese)cohort analysis in which they estimated future
tooth loss based on the number of PT. They foundthat the rate of tooth loss increased as the numberof PT decreased. Eklund et al. 7） reported thatamong baseline oral conditions related to total
tooth loss, the most convincing association camewith the number of remaining teeth. Those with 17 teeth at baseline were nearly 20 times more likely to become totally edentulous than those with 24
or more teeth, and this relative risk was unaffected by age. This means that younger people withfew teeth were just as likely to become edentulous
as older people with few teeth. In the multivariate
analyses, the number of remaining teeth at baseline stood out as a remarkably stable predictor ofedentulism, even when many other variables wereassessed simultaneously. Yamamoto et al. 8）reported retrospectively on tooth loss during maintenance at a university hospital. Patients who lost
teeth were older, showed a higher prevalence ofsevere periodontal disease and hypertension, andhad a lower number of PT at the start of themaintenance. Our results support the conclusions̶ 87 ̶