保健医療科学

2017Vol.66 No.5 p.545－552＜ Original ＞
Risk factors associated with early childhood caries in
18- to 23-month-old children in a Japanese city
Yoshimi Nakayama 1,2), Mitsuru Mori 3)
1）

Hokkaido Kushiro Public Health Center2）

Department of Public Health, Sapporo Medical University School of Medicine

3）

Hokkaido Chitose College of Rehabilitation

Abstract
Objectives: The aim of this cross-sectional study was to investigate factors associated with early childhood
caries (ECC) in 18- to 23-monath-old Japanese children.
Methods: Study subjects were 2,771 children aged 18 to 23 months. A self-administered questionnaire wascompleted by parents or guardians of the children. The survey contents included such things as sex, birthweight, the existence of smokers in the home, maternal smoking during pregnancy, nocturnal breastfeeding,snacking habits, parents sharing of utensils with child, and socio-economic status. We obtained the numberof decayed, missing, or filled teeth per person (dmft) via dental examination. Logistic regression analysis
was performed to estimate odds ratio of ECC.
Results: The average number of decayed, missing and filled teeth (dmft index) was 0.11. The prevalence ofdental caries was 3.2% (90/2771). Nocturnal breastfeeding habits were documented in 668 subjects (24.1%).
Environmental tobacco smoke (ETS) was reported for 1,704 children (61.5%). After excluding items of
multicollinearity, the results of multivariate analysis were as follows: the existence of smokers in the home,the number of smokers, nocturnal breastfeeding, breastfeeding more than or equal to 18 months, drinking
or eating sweets after dinner, and high birth weight were significantly associated with the risk of ECC.
Conclusions: This study suggests that ETS from family members, nocturnal breastfeeding, prolonged
breastfeeding, high birth weight, and snacking habits are correlated with ECC.
keywords: breastfeeding; environmental tobacco smoke; early childhood caries; birth weight(accepted for publication, 15th September 2017)

I．Introduction
Early childhood caries (ECC) is a common public healthproblem worldwide. ECC has been defined as “the presenceof one or more decayed (non-cavitated or cavitated lesions),
missing (due to caries), or filled tooth surfaces in any
primary tooth in a child 71 months of age or younger” [1].
The etiology of ECC is multifactorial. Heretofore, ECC
has been shown to result from the transmission of bacteria
from mother to child [2], daily habits such as oral hygiene
practice, snacking habits, and socio-economic status [3-7].
We previously reported a significant multivariableadjusted association between nocturnal breastfeeding andsnacking habits and dental caries in 18 to 23-month-old
infants both in the Tokachi area [8] and in the eastern Iburi
area [9]. In other previous studies, although the age ofsubjects was ≧ 2 years, nocturnal breastfeeding has been
identified as a risk factor for ECC [10-13]. Additionally,
ECC has been shown to be associated with prolonged
breastfeeding among children aged ≧ 2 years [12-17]. We
previously did not investigate the duration of breastfeeding.
However, the association between breastfeeding and ECC
is somewhat controversial. Several studies have observedthat the association between breastfeeding and ECC wasinsignificant among children aged ≧ 1 years [6,18-20], and
the World Health Organization (WHO) has recommended

Corresponding author: Yoshimi NAKAYAMA
Hokkaido Kushiro Public Health Center, 2-4-22 Shiroyama, Kushiro-shi,
Hokkaido 085-0826, Japan.
E-mail: nakayama.yoshimi@pref.hokkaido.lg.jp
Tel: 0154-65-5821 / Fax: 0166-65-5352

J. Natl. Inst. Public Health, 66 (5) : 2017545

Yoshimi Nakayama, Mitsuru Mori

II．Methods
1．Subjects
The study was conducted in one city in the eastern
Iburi region, located in the central part of Hokkaido, thenorthernmost island of Japan. The population of the city ofobservation in the eastern Iburi region was 173,317. The
total number of subjects aged 18 to 23 months from April
2014 to February 2016 was 2,828. Among them, 2,771(98.0%; 1,441 males and 1,330 females) received a dental
examination within the examination period of April 2014 to
February 2016. When children in Japan reach 18 months ofage, the municipality in which the family resides sponsors
a physical examination that includes a dental examination,measurement of height and weight, and an interview
survey with parents or guardians regarding the childʼshealth, in accordance with the Maternal and Child HealthAct. The reason that we selected this city in this study isthat it was the principal city of the area having numerous
ECC in Hokkaido. This study was approved by the EthicalCommittee of Sapporo Medical University on July 6, 2016.

1400

1285

1290

1200

Numb
ber of stu
udy subjeccts

that children be breastfed until 24 months of age [21].
We previously reported by multivariable analysis that
ECC was not significantly associated with environmental
tobacco smoke (ETS) from the family in 18 to 23-monthold Japanese children in the Tokachi area of Hokkaido in2006 [8] and in the eastern Iburi area of Hokkaido in 2012[9]. However, in most previous studies, although the ageof subjects was ≧ 3 years, it was suggested that children
exposed to ETS have an increased risk of dental caries inthe deciduous dentition [14,22-30]. Additionally, ECC has beenshown to be associated with maternal smoking during pregnancy
among children aged ≧ 2 years [5,6,14]. We previously did notinvestigate maternal smoking during pregnancy.
Previous studies [7,31-33] have shown that birth weight
was related to the increase of ECC. dos Santos Junior et al.
[7] reported that the prevalence of ECC was related to lowbirth weight among preschoolers aged from three to four
years. Conversely, Yokomichi et al. [32] reported that highbirth weight was associated with an increased risk of ECC
among 3-year-old Japanese children. However, there arefew studies on the association between birth weight andECC.
We aimed to identify risk factors associated with ECC in
18- to 23-month-old Japanese children by a cross-sectional
study.

1000
800
600
400

134

200
0

18months

19months

20months

24

21

17

21months

22months

23months

Figure11 Distributionof studyof
subjects
by agein monthsby age in months
FigureDistribution
study
subjects

examination. The questionnaire form was distributed toparents or guardians by mail beforehand and was collectedon the day of the examination. After the questionnaire
was completed, the data were checked by hygienists or
public health nurses. We did not fill in missing values, andthe data were not illogical. The dental examinations werecarried out at the examination site of the municipality by 68
dentists from local dental clinics with a dental mirror underartificial light. The dentists received adequate meetings
before performing the examination. They also were given
detailed criteria. We obtained dmft (number of decayed,
missing, and filled teeth per person) data from this dental
examination. We designed this survey contents in reference
to our previous studies [8,9]. The survey contents incommon with our previous study [9] were whether asmoker resides in the home, the number of smokers in thehome, nocturnal breastfeeding habits, snack times, drinking
or eating sweets after dinner, parents brushing their childʼsteeth daily, and the use of fluoride toothpaste. The added
contents in this survey contained items such as; sex, birthweight, socio-economic status, parents sharing of eatingutensils with the child, time of starting with baby food,
duration of breastfeeding, and application of 2% sodium
fluoride solution. ETS was defined as having at least one
smoker residing in the home and socio-economic status
was defined using the family residence tax (i.e. taxationof residence tax is high socio-economic status, no tax ofresidence tax is low socio-economic status). The response
rate of the survey was 98% (2771/2828). Figure 1 shows
the distribution of study subjects by age in months. Ninetythree % (2575/2771) of study subjects were 18- to 19-monthold children. Although the age of subjects was between 18
and 23 months, we did not obtain an accurate age in months
for each individual subject.
3．Analyses

2．Survey method
The self-administered questionnaire was completed
by the parents or guardians of the children before dental

546

The outcome variable was ECC. Risk factors for theprevalence of ECC were evaluated by univariate andmultivariate analysis using a logistic regression model.

J. Natl. Inst. Public Health, 66 (5) : 2017

Risk factors associated with early childhood caries in 18- to 23-month-old children in a Japanese city

III．Results
Figure 2 shows distribution of study subjects according
to dmft. No caries were observed 2681 infants. The
Table 1

3000

2681
2500

Number of stu
udy subjeccts

The odds ratios (ORs) and their 95% confidence intervals(CIs) were estimated with regard to risk factors for ECC.
Before the multivariate logistic regression analysis was
conducted, we evaluated multicollinearity among thevariables using Spearmanʼs rank correlation test. If r (thecorrelation coefficient) > 0.7, then we defined that there
is multicollinearity. The univariate analysis excluded thestudy subjects with missing values. The multivariate
analysis included all variables, after excluding items of
multicollinearity. The data used in multivariate analysis
contained only the study subjects without any missing
values. The χ2 test was used for the analyses of thecharacteristics of study subjects by dmft. Tests of statisticalsignificance were based on a two-sided P-value, and the
α-error was set at 5%. The SAS system (ver. 9.4; SAS
Institute, Cary, NC, USA) was employed for the analysis.

2000

1500

1000

500

0

dmft=053

37

1≦dmft≦3

4≦dmftFigure 2 Distribution of study subjects according to dmft
Figure2 Distribution of study subjects according to dmft

dmft index was 0.11 (standard deviation [SD] 0.71). The
prevalence of dental caries was 3.2% (90/2771). Table1
shows characteristics of study subjects by dmft. Nocturnal
breastfeeding habits were documented in 668 subjects(24.1%). ETS was reported for 1,704 children (61.5%).
High birth weight was reported for 29 children (1.0%). The
number of children in a family in the no residence tax groupwas 212 (7.7%).
Table 2 shows crude and adjusted ORs with 95% CI for

Characteristics of the study subjects by dmft

Variables
Sex：Male
FemaleApplication of 2% sodium fluoride solution： Yes
No
Unknown
Use of fluoride toothpaste：Everyday
Sometaimes or Never
Unknown
Drinking or eating sweets after dinner： NeverSometimes
Everyday
Unknown
Frequency of parents brushing child's teeth： Everyday
Sometimes or neverUnknown
Nocturnal breastfeeding：No
Yes
Unknown
Duration of breastfeeding：≦ 17 months≧ 18 months
Unknown
Time of starting with baby food：≦ 5 months
6 months≧ 7 months
Unknown
Snack times：Regular
Irregular
Unknown
Birth weight：＜ 2,500g
2,500g ～ 3,999g≧ 4,000g
Unknownmaternal smoking during pregnancy：No
Yes
Unknown
Smoker in family： Absence
Presence
Unknown
Number of smokers in family： No smoker
One smoker
Two smokers≧ Three smokers
Unknown
Residence tax： Taxation
No taxUnknown
Parental sharing of eating utensils with the child： Unshared
Common use
Unknowndmft：total number of decayed, missing or filled teeth*：χ２ test

dmft ≧ 1n(%)
56(62)
34(38)
22(24)
65(72)
3(3)24(27)
64(71)
2(2)36(40)
21(23)
30(33)
3(3)
66(73)
24(27)0(0)49(54)
40(44)
1(1)29(32)
45(50)
16(18)
33(37)
42(47)9(10)6(7)
30(33)
58(64)2(2)6(7)
76(84)3(3)5(6)
66(73)
24(27)0(0)14(16)
74(82)
2(2)
14(16)
37(41)
31(34)6(7)2(2)
58(64)
16(18)
16(18)
86(96)4(4)0(0)

J. Natl. Inst. Public Health, 66 (5) : 2017

dmft=0n(%)
1385(52)1296(48)566(21)2074(77)41(2)738(28)1915(71)28(1)1743(65)501(19)403(15)34(1)2267(85)386(14)28(1)2016(75)628(23)37(1)1406(52)689(26)586(22)1217(45)1031(38)308(11)125(5)
1465(55)1166(43)50(2)265(10)2306(86)
26(1)
84(3)
2352(88)283(10)46(2)1013(38)
1630(61)38(1)1013(38)1085(40)453(17)93(3)37(1)
2020(75)
196(7)
465(17)2591(97)
43(2)
47(2)

p-value*
0.049
0.391
0.911
<0.001

0.002<0.001<0.0010.204<0.001
0.059<0.001<0.001<0.001<0.001
0.044

547

Yoshimi Nakayama, Mitsuru Mori
ECC. In the univariate analysis, drinking or eating sweets
after dinner sometimes (OR 2.03; 95%CI, 1.17-3.51) or
everyday (OR 3.60; 95%CI, 2.19-5.92), parents brushing
their childʼs teeth less frequently (OR 2.14; 95%CI, 1.323.45), irregular snack times (OR 2.43; 95%CI, 1.55-3.80),
nocturnal breastfeeding (OR 2.62, 95%CI, 1.71-4.02),
breastfeeding more than or equal to 18 months (OR 3.17;
95%CI, 1.97-5.10), birth weight≧4,000g (OR 3.50; 95%CI,
1.04-11.82), maternal smoking during pregnancy (OR 3.02;
95%CI, 1.86-4.90), existence of smokers in the home (OR3.29; 95%CI, 1.85-5.85), the number of smokers in family(one smoker: OR 2.46; 95%CI, 1.33-4.59, two smokers: OR
4.95; 95%CI, 2.61-9.40, ≧three smokers: OR 4.67; 95%CI,
1.75-12.43, We used a trend test to investigate doseresponse relationship between number of smokers in thefamily and ECC. The result was significant (P<0.0001).),and no residence tax (OR 2.84; 95%CI, 1.60-5.04) weresignificantly associated with the odds ratio of ECC. Sex,use of fluoride toothpaste, application of 2% sodium
fluoride solution, time of starting with baby food, andparents sharing of eating utensils with the child were notsignificantly associated with ECC.
As shown in Table 2, the multivariate analysis included
sex, residence tax, application of 2% sodium fluoride
Table 2solution, use of fluoride toothpaste, drinking or eating
sweets after dinner, frequency of parents brushing childʼsteeth, duration of breastfeeding, time of starting withbaby food, snack time, birth weight, maternal smoking
during pregnancy, smoker in family and parental sharingof eating utensils with the child, after excluding items of
multicollinearity. The multivariate analysis included 1,719
infants. Application of 2% sodium fluoride solution (OR 0.44;
95%CI, 0.23-0.86), drinking or eating sweets after dinner
everyday (OR 3.58; 95%CI, 1.70-7.50), breastfeeding morethan or equal to 18 months (OR 3.37; 95%CI, 1.83-6.20),
birth weight≧4000g (OR 5.61; 95%CI, 1.14-27.69), andthe existence of smokers in the home (OR 3.18; 95%CI,
1.43-7.08) were significantly associated with the odds ratioof ECC in the multivariate analysis. Sex, use of fluoride
toothpaste, frequency of parents brushing childʼs teeth, timeof starting with baby food, snack times, maternal smoking
during pregnancy, residence tax, and parents sharingof eating utensils with the child were not significantly
associated with ECC.
Also, we conducted a multivariable analysis using
variables for nocturnal breastfeeding instead of variables forduration of breastfeeding. Nocturnal breastfeeding (OR 2.27;
95%CI, 1.32-3.91) was significantly associated with the

Crude and adjusted odd ratios (ORs), and 95% confidence intervals (CIs) of ECC for risk factors withlogistic regression analysis

Variables
Sex： Male
FemaleApplication of 2% sodium fluoride solution：Yes
No
Use of fluoride toothpaste： Everyday
Sometaimes or NeverDrinking or eating sweets after dinner：NeverSometimes
Everyday
Frequency of parents brushing child's teeth： Everyday
Sometimes or neverNocturnal breastfeeding：No
Yes
Duration of breastfeeding：≦ 17 months≧ 18 months
Time of starting with baby food：≦ 5 months
6 months≧ 7 months
Snack times：Regular
Irregular
Birth weight： ＜ 2,500g
2,500g ～ 3,999g≧ 4,000g
maternal smoking during pregnancy： No
Yes
Smoker in family： Absence
Presence
Number of smokers in family： No smoker
One smoker
Two smokers≧ Three smokers
Residence tax： Taxation
No taxParental sharing of eating utensils with the child： Unshared
Common use

Crude OR(95%CI)
1.00 (reference)
0.65 (0.42-1.00)
1.00 (reference)
0.81 (0.49-1.32)
1.00 (reference)
1.03 (0.64-1.66)
1.00 (reference)
2.03 (1.17-3.51)
3.60 (2.19-5.92)
1.00 (reference)
2.14 (1.32-3.45)
1.00 (reference)
2.62 (1.71-4.02)
1.00 (reference)
3.17 (1.97-5.10)
0.67 (0.42-1.06)
1.00 (reference)
0.72 (0.35-1.49)
1.00 (reference)
2.43 (1.55-3.80)
0.69(0.30-1.59)
1.00 (reference)
3.50 (1.04-11.82)
1.00 (reference)
3.02 (1.86-4.90)
1.00 (reference)
3.29 (1.85-5.85)
1.00 (reference)
2.46 (1.33-4.59)
4.95 (2.61-9.40)
4.67 (1.75-12.43)(P for trend, P<0.0001)
1.00 (reference)
2.84 (1.60-5.04)
1.00 (reference)
2.80 (0.98-7.98)

p-value
0.050
0.391
0.911
0.011
<0.001
0.002<0.001<0.001
0.085
0.373<0.001
0.382
0.044<0.001<0.001

Adjusted OR(95%CI)*
1.00 (reference)
0.63(0.34-1.16)
1.00 (reference)
0.44(0.23-0.86)
1.00 (reference)0.90(0.47-1.72)
1.00 (reference)
2.01(0.94-4.28)
3.58(1.70-7.50)
1.00 (reference)
0.87(0.36-2.09)
1.00 (reference)
3.37(1.83-6.20)
0.66(0.35-1.25)
1.00 (reference)
0.58(0.19-1.73)
1.00 (reference)
1.37(0.74-2.54)
0.26(0.04-1.96)
1.00 (reference)
5.61(1.14-27.69)
1.00 (reference)
1.31(0.53-3.21)
1.00 (reference)
3.18(1.43-7.08)

p-value
0.137
0.016
0.750
0.070
<0.0010.753<0.001
0.202
0.326
0.324
0.191
0.034
0.562
0.005

0.004
<0.001
0.002<0.0010.054

1.00 (reference)
1.74(0.74-4.14)
1.00 (reference)
2.52(0.52-12.10)

0.208
0.249

*：Adjustment for sex, residence tax, application of 2% sodium fluoride solution, use of fluoride toothpaste, time of starting with baby food, drinking or eating sweets after
dinner, frequency of parents brushing childʼs teeth, duration of breastfeeding, snack time, birth weight, maternal smoking during pregnancy, smoker in family and parental
sharing of eating utensils with the child

548

J. Natl. Inst. Public Health, 66 (5) : 2017

Risk factors associated with early childhood caries in 18- to 23-month-old children in a Japanese city
odds ratio of ECC (not shown in table).
Furthermore, we conducted a multivariable analysis
using variables for the number of smokers in a family
instead of variables for the existence of smokers in thehome. The number of smokers in a family (one smoker:
OR 2.89; 95%CI, 1.27-6.57, two smokers: OR 4.67; 95%CI,
1.74-12.53, ≧ three smokers: not calculated, P for trend,
P=0.0098) was significantly associated with the odds ratioof ECC (not shown in table).

IV．Discussion
By the Japan national data in 2015, the dmft index in
18- to 23-month-old Japanese children was 0.05 and theprevalence of dental caries was 1.8%. The caries data ofthese study subjects was poor compared to the national dataof ECC in Japan.
Distribution of these study subjects by dmft was about
the same as distribution of our previous study in theeastern Iburi area of Hokkaido in 2012 [9].
The present study found that ECC was significantly
associated with nocturnal breastfeeding between the ages of
18 and 23 months. Our results confirmed that those of ourprevious studies showed effects of nocturnal breastfeedingon dental caries between the ages of 18 and 23 months[8,9]. Saliva flow decreases markedly during sleeping hours,
which is thought to affect the mechanical self-cleansing andthe buffering capacity of saliva following fermentation ofcariogenic substrates [10]. Therefore, our results suggestthat nocturnal breastfeeding is likely to be a risk factor for
dental caries in 18- to 23- month-old Japanese children.
In this study, the prolonged breastfeeding was
significantly associated with ECC between the ages of 18
and 23 months in the multivariate analysis. Although our
results were similar to those of other previous studies
showing significantly association between prolonged
breastfeeding and ECC [12-17], the age of the subjects
in other previous studies was ≧ 2 years. Therefore,
our results were of particular value. In a longitudinal
investigation, a significant decline over time was observedin the levels of phosphate and calcium in breast milkthat help protect tooth enamel [34]. Bowen et al. [35]reported that human milk was significantly more cariogenic
than cowʼs milk, probably because of its lower mineralcontent and higher level of lactose. Hence, the prolonged
breastfeeding more than or equal to 18 months might
contribute to caries development.
In a multivariate analysis, the existence of smokers in
the home and the number of smokers in a family weresignificantly associated with the odds ratio of ECC.
However, our results differed from the results of ourprevious studies among 18- to 23-month-old Japanesechildren [8,9]. Although our results confirmed those ofother studies showing an effect of ETS exposure at homeon dental caries [14,22-30], the age of subjects in otherstudies was ≧ 3 years. We thought that the increase in a
proportion of ETS was conducive to this result (61.5% inthis study, 54.8% in Tokachi area [8], 59.2% in eastern Iburi
area [9]). In addition, a number of study subjects increased
from 1,317 in Tokachi area [8] and 1,675 in eastern Iburi
area [9] to 2,771 in this study. Regardless of the durationof ETS exposure, the present results might suggest thatchildren exposed to ETS have an increased risk of dental
caries in the deciduous dentition. Further study amongchildren under 2 years old is needed.
Causes that influenced ETS exposure at home onpediatric dental caries are considered to be as follows:First, Preston et al. [36] reported that ETS can reducethe concentrations of ascorbates in children, even when
the amount of exposure to ETS is minimal. Väänänen[37] reported that decreased vitamin C levels havebeen associated with the growth of cariogenic bacteria.
Lindemeyer et al. [38] reported that tobacco enhances thegrowth of cariogenic streptococci in vitro. ETS exposure
may increase cariogenic streptococci in the oral cavity of
infants. Secondly, Leory et al. [26] reported that children
raised by parents who smoked, brushed their teeth lessfrequently, received less help with tooth brushing, andconsumed more in between meals and nightly beverage
may have had poor oral hygiene and were more likely
to have dental caries. However, we found a relationshipbetween ETS exposure at home and ECC even after
controlling for oral hygiene and snacking habits in thisstudy. Third, ETS is known to increase inflammation of therespiratory tract, producing symptoms of various clinicalconditions, including allergic rhinitis, which frequently
causes mouth breathing and thus results in dry mouth andincreased caries susceptibility [23].
In this study, high birth weight was significantly
associated with ECC in the multivariate analysis. The
results of this study were in accordance with some previous
studies [32,33]. However, in other studies, the age of thesubjects was ≧3 years. Our study investigated 18- to -23month-old children. To our knowledge, there are no otherstudies similar to our own that have investigated children
under 2 years old. The mechanism underlying the formationof caries after exposure to intrauterine over-nutrition is
not yet understood. Hoegsberg et al. [39] reported that asubset of macrosomic infants have hyperinsulinemia. As
hyperinsulinemia causes an increased appetite, the primary
teeth of high birth weight children may be more frequently
exposed to cariogenic food and drink.

J. Natl. Inst. Public Health, 66 (5) : 2017549

Yoshimi Nakayama, Mitsuru MoriThis study found that ECC was not significantly
associated with parental sharing of eating utensils with thechild. Milgrom et al. [40] found no significant association
between maternal sharing of utensils and the presence ofwhite spot lesions or enamel cavitation in the offspring in
6- to 36-month-old children. Wakaguri et al. [41] reported
that multivariate logistic regression analysis did notshow any significant association between behaviour toprevent vertical transmission and caries experience in
3-year-old Japanese children. However, the association
between parental sharing of utensils with child and ECC iscontroversial. Cogulu et al. [41] reported that children withmaternal sharing of utensils trended to have higher rates ofcaries by longitudinal study. Further study among children
under 2 years old is needed.
In present study, frequent drinking or eating of sweets
after dinner was significantly associated with ECC. We
previously reported a significant multivariable-adjusted
association between frequent drinking or eating of sweets
after dinner and dental caries in 18 to 23-month-old
infants in the eastern Iburi area of Hokkaido in 2012 [9].
Subsequently, we obtained a similar result in one city ofeastern Iburi area of Hokkaido in this survey. Therefore,
our results suggest that frequent drinking or eating ofsweets after dinner is likely to be a risk factor for dental
caries in 18- to 23-month-old Japanese children.
In this study, children who experienced the applicationof a 2% sodium fluoride solution had more dental caries
compared to children who did not have the sodium fluoride
application. One city in the eastern Iburi area of Hokkaido
did not conduct a public service project for the applicationof a 2% sodium fluoride solution. Therefore, children might
receive the application of a 2% sodium fluoride solution atdental clinics when children had a dental caries.
There were some limitations to our study. First, thedata on dental caries used in the present study weregathered during routine examinations by dentists at
local dental clinics. The dentists were given detailed
criteria for performing the examination but were notspecifically trained so as to ensure standardization of their
examinations. Second, although the age of subjects was
between 18 and 23 months, we did not obtain an accurate
age in months for each individual subject. Incidence ofdental caries likely increases with age, so the age in months
has potential influence on the occurrence of dental caries
of infants. Third, because the sample size of dmft > 0 was
insufficient, some of the significant findings should be
carefully interpreted. Fourth, there were missing values
in this study. The largest rate of missing value was 21.7%.
However, there were no missing values in the outcome
variable.

550

In conclusion, this study suggests a significant associationof the existence of the smokers in the home, the number ofsmokers in the home, nocturnal breastfeeding, prolonged
breastfeeding, high birth weight, and snacking habits withthe prevalence of dental caries among 18- to 23-month-old
Japanese children after adjusting for potential confounders
such as socio-economic status. We need to highlight thatthese results are available for oral health guidance orhealth promotion planning such as efforts against passive
smoking for one city in the eastern Iburi region of Hokkaido
prefecture.

Acknowledgements
The authors claim no conflicts of interest.

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18 〜 23 ヶ月の小児におけるう蝕のリスク因子の検討
中山佳美 1,2），森満 3）1）北海道釧路保健所
2）札幌医科大学医学部公衆衛生学講座
3）北海道千歳リハビリテーション大学

抄録
目的：この研究の目的は，断面調査によって，日本の18～23ヶ月児の低年齢小児う蝕（ECC）と関連する要因を調査することである．
方法：研究対象者は，18～23ヶ月児の2,771人であった．質問調査は，保護者が回答した．調査項目は，性別，出生児体重，家庭内での喫煙者，妊娠中の母親の喫煙，夜間授乳，間食習慣，食具の共用，社会経済状況などであった．う蝕経験歯数（dmft）は，1歳6ヶ月児歯科健康診査から入手した．分析は，ロジスティック回帰分析を用いた．
結果：一人経験う蝕経験歯数（dmft index）は0.11本で，う蝕有病者率は3.2％であった．夜間授乳の習慣のある児は668人（24.1％）であった．環境たばこ煙（ETS）にさらされている児は1,704人（61.5％）であった．多変量解析の結果，う蝕と関連のあった要因は，家庭内喫煙者の存在，喫煙者人数，夜間
授乳，授乳期間が18ヶ月以上，夕食後の甘い飲み物やおやつの飲食，出生時体重が4000g以上であった．
結論：この研究は，夜間授乳，長期間の授乳，家族からの環境たばこ煙，出生時体重が高体重，間食習慣がう蝕と関連性があることを示している．今回の結果は，東胆振地域の市の歯科保健指導や受動喫煙対策に役立てられるだろう．
キーワード：授乳，環境たばこ煙，幼児う蝕，出生時体重552

J. Natl. Inst. Public Health, 66 (5) : 2017