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Social determinants of denture/bridge use: Japan gerontological evaluation study project cross-sectional study in older Japanese

  • Tatsuo Yamamoto1Email author,
  • Katsunori Kondo2, 3,
  • Jun Aida4,
  • Kayo Suzuki5,
  • Jimpei Misawa6,
  • Miyo Nakade7,
  • Shinya Fuchida1,
  • Yukio Hirata1 and
  • for the JAGES group
BMC Oral Health201414:63

https://doi.org/10.1186/1472-6831-14-63

Received: 29 January 2014

Accepted: 28 May 2014

Published: 3 June 2014

Abstract

Background

Studies suggest that using a denture/bridge may prevent disability in older people. However, not all older people with few remaining teeth use a denture/bridge. This cross-sectional study aimed to examine the social determinants which promote denture/bridge use among older Japanese.

Methods

A total of 54,388 (25,630 males and 28,758 females) community-dwelling individuals aged 65 or over, living independently, able to perform daily activities, and with 19 or fewer teeth. The dependent variable was denture/bridge use. Socio-demographics, number of teeth, present illness, social participation, social support, and social networks were used as individual-level independent variables. Data for social capital were aggregated and used as local district (n = 561 for males, n = 562 for females) -level independent variables. Number of dentists working in hospitals/clinics per population and population density were used as municipality (n = 28) -level independent variables. Three-level multilevel Poisson regression analysis was performed for each sex.

Results

High equivalent income, low number of teeth, present illness, and living in a municipality with high population density were significantly associated with denture/bridge use in both sexes in the fully adjusted models (p < 0.05). Denture/bridge use was significantly associated with high educational attainment in males and participating in social groups in females in the fully adjusted model (p < 0.05). No significant associations were observed between denture/bridge use and social capital.

Conclusions

Denture/bridge use was significantly associated with high economic status and present illness in both sexes, high educational attainment in males, and participation in social groups in females among community-dwelling older Japanese after adjusting for possible confounders.

Keywords

Social determinants Dental prosthesis Older people Cross-sectional study

Background

Fixed and removable prostheses are most commonly used to replace missing teeth with the aim of improving chewing ability, aesthetics and pronunciation. Recent studies have reported favorable effects of prosthodontic treatment on systemic health [14]. An intervention study showed that prosthodontic treatment improved the nutritional status of institutionalized older people [1]. Cohort studies have reported that older people who do not use dentures despite having few remaining teeth show a higher risk of dementia onset [2] and incident falls [3] after adjusting for possible confounders. Moreover, these studies showed no significant difference in dementia onset and incident falls between subjects having few teeth and using dentures and those having 20 or more teeth, suggesting that denture use may reduce the risk of dementia onset and incident falls in subjects having few teeth. Another cohort study showed that the use of dentures is associated with a decreased risk of mortality in edentulous older people [4].

Despite these favorable effects of dentures and bridges, not all persons who lose their teeth use a denture/bridge. In a 2011 Japanese national survey, approximately 29%, 19%, and 14% of the whole population aged 65–69, 70–74, and 75–79 did not use a denture/bridge, respectively [5]. A study from the UK reported that 25% and 15% of patients who were provided with partial dentures never or only occasionally wore dentures, respectively [6].

Denture/bridge use reflects access to dental care. Many factors have been reported to directly and indirectly influence utilization of dental services in older people. These factors can be divided into four main categories: socio-demographic factors, ill health-related factors, service-related factors, and attitude or subjective factors [7]. Socio-demographic factors include sex, age, education, and income [8, 9]. Ill health-related factors include number of teeth, general ill health, and functional limitations [10, 11]. Service-related factors include accessibility and insurance coverage [8, 9, 12]. Attitude or subjective factors include personal beliefs and satisfaction with dental visits [13, 14]. These factors may be associated with denture/bridge use.

Little is known about the factors associated with denture/bridge use. A study among older people in a Japanese municipality revealed an association between denture/bridge use and economic status [15]. An exploratory qualitative interview study from the UK reported differences in the attitudes of dentists and patients to the provision of removable partial dentures [16]. Dentists focused on restoration of physical function of the teeth, whereas patients focused on the social significance of oral rehabilitation.

It has previously been reported that access to medical care may be associated with social relationships and social capital [17]. However, the association between access to dental care and denture/bridge use and social relationships is unknown, although previous studies have suggested an association between dental health and social relationships [18, 19]. Individuals obtain health information through their connections with others, and it is possible that this may lead to denture/bridge use. Individuals with few teeth may need to wear denture/bridge to improve appearance or speech, which would help them interact in groups.

The purpose of this study was to examine the social determinants which promote denture/bridge use using cross-sectional data from community-dwelling older Japanese people. First, the association of denture/bridge use with known factors associated with access to dental care (socio-demographic factors, ill health-related factors, and service-related factors) was examined. Then, taking into account these factors, the association with denture/bridge use and social relationship factors was analyzed. In particular, multilevel (first level, individual; second level, local district; and third level, municipality) analysis was used because it is appropriate to assess contextual and individual determinants of health outcomes, which were not assessed in previous studies on factors associated with access to dental care and denture/bridge use [716].

Methods

Study population

Data from a cross-sectional study, which were collected as part of the Japan Gerontological Evaluation Study (JAGES) Project, were used for this on-going Japanese prospective cohort study. JAGES aims to conduct empirical studies from gerontological and social epidemiological perspectives. The sample was restricted to those who did not already have a physical or cognitive disability, defined by not receiving public long-term care insurance benefits, at baseline. From July 2010 to January 2012, a mail survey was conducted in a random sample of 169,215 community-dwelling individuals aged 65 years or over residing in 31 municipalities in 12 prefectures in Japan. Of the 112,123 respondents (response rate, 66.3%), 8,502 subjects were excluded due to a lack of age and sex information. Then, 5,851 subjects in three municipalities were excluded due to a lack of information on local district, social support, and/or general trust. After excluding 411 (lack of information of local district) and 4,525 (status of activities of daily living (ADL) was dependent or unknown) subjects, a total of 92,834 subjects aged 65 or older in 562 local districts in 28 municipalities were included in the present study. The JAGES protocol was reviewed and approved by the Ethics Committee on Research of Human Subjects at Nihon Fukushi University.

Outcome variables

Dental status was assessed using a self-administered questionnaire [20]. Respondents were asked to classify their dental status as having 20 or more, 10–19, 1–9 or 0 teeth. Data from all subjects, including those having 20 or more teeth, were used when local district-level social capital was calculated. However, subjects having 20 or more teeth were excluded when univariate and multilevel prevalence ratios (PRs) were calculated. Denture/bridge use was ascertained by asking, “Do you use a denture or bridge?” with possible answers dichotomized into yes and no.

Socio-demographic variables

Data on socio-demographics (sex, age, marital status, educational attainment, equivalent income) were obtained using a self-administered questionnaire. To adjust household income for household size, equivalent income was calculated by dividing the household income by the square root of the number of household members, and placed into one of seven categories (<500,000 yen, 500,000-999,999 yen, 1,000,000-1,499,999 yen, 1,500,000-1,999,999 yen, 2,000,000-2,999,999 yen, 3,000,000-3,999,999 yen, and ≥4,000,000 yen).

Ill health-related variables

Number of teeth and present illness were considered as ill health-related variables. Self-reported current medical treatment for cancer, heart disease, stroke, hypertension, diabetes, obesity, hyperlipidemia, osteoporosis, arthritis, trauma, respiratory disease, gastrointestinal disease, liver disease, mental illness, visual/hearing impairment, dysphagia, urinary disease, sleep disorder, or other conditions was used as the variable present illness, dichotomized into yes and no.

Service-related variables

Data on the number of dentists working in hospitals or clinics were obtained from the Survey of Physicians, Dentists and Pharmacists conducted by the Ministry of Health, Labour and Welfare, Japan in 2010. Data on population in 2010 and area of inhabitable land of each municipality were obtained from the National Population Census Survey conducted by the Ministry of Internal Affairs and Communications, Japan. Number of dentists working in hospitals or clinics per 100,000 people and population density were calculated for each municipality. The number of dentists working in hospitals or clinics per 100,000 people was categorized into four groups (lowest, low middle, high middle, or highest) based on 25th, 50th, and 75th percentiles. Population density was categorized into four groups (metropolitan, urban, semi-urban, or rural-agricultural).

Social relationship variables

General trust, norms of reciprocity, and attachment to place were assessed by asking “Generally speaking, would you say that most people can be trusted?”, “Would you say that most of the time people try to be helpful?”, and “Do you feel attached to the area you live?” with possible answers dichotomized into yes and no (including “depends”). For social participation, respondents were asked whether they belonged to industrial and trade associations, volunteer groups, older people’s clubs, sports groups or clubs, neighborhood associations or councils, or hobby clubs, with possible answers dichotomized into yes and no. The number of social groups was calculated for each subject.

Emotional and instrumental social support, both received and given, was evaluated by using the following questions: “Do you have someone who listens to your concerns and complaints?” (emotional social support received), “Do you listen to someone’s concerns and complaints?” (emotional social support given), “Do you have someone who looks after you when you are sick and have to stay in bed for a few days?” (instrumental social support received), and “Do you look after someone when he/she is sick and stays in bed for a few days?” (instrumental social support given), with possible answers dichotomized into yes and no.

Social network was measured by the question, “How often do you see your friends?” with the following possible answers: “almost every day”, “two or three times per week”, “once a week”, “once or twice per month”, “several times per year”, or “rarely”.

We created local district (n = 561 for males, n = 562 for females) -level social capital variables by aggregating the individual-level data on general trust, norms of reciprocity, attachment to place, social support (both emotional and instrumental received and given), number of social groups, and meeting friends (% of subjects meeting friends at least several times a year). General trust, norms of reciprocity, attachment to place, and social support were categorized as cognitive social capital. Number of social groups and meeting friends were categorized as structural social capital. Local districts were categorized into four groups (lowest, low middle, high middle, or highest) based on 25th, 50th, and 75th percentiles for each variable.

Analysis

The following analyses were conducted in subjects with 19 or fewer teeth (25,630 males and 28,758 females). First, univariate PRs and 95% confidence intervals (CIs) were calculated for each independent variable with denture/bridge use as the dependent variable in each sex. Because the percentage of people using a denture/bridge was high (males: 68.1%, females: 67.6%), adjusted odds ratio derived from the logistic regression could no longer approximate PR [21]. Therefore, multilevel Poisson regression model with random intercepts and fixed slopes was used separately for males and females to calculate multilevel PRs, taking into account variations in the outcomes between local districts and municipalities using MLwiN 2.28 (Centre for Multilevel Modelling, University of Bristol, Bristol, UK), with denture/bridge use as the dependent variable [22]. In model 1, socio-demographics (age, marital status, educational attainment, and equivalent income), health status (number of teeth and present illness) and municipality-level characteristics (number of dentists working in hospitals or clinics per 100,000 people and population density) were added. In models 2 and 3, number of social groups and frequency of meeting friends, both of which were significantly associated with denture/bridge use in the previous univariate analysis, were added to model 1, respectively. Moreover, to examine the association between each local district-level social capital variable and denture/bridge use after adjusting for socio-demographics, health status and municipality-level characteristics, each local district-level social capital variable was added to model 1. In the model, corresponding individual level variable was also added to avoid ecological fallacy.

Results

The percentages of males and females using a denture/bridge were 68.1% and 67.6%, respectively. Table 1 shows the PRs (95% CIs) for denture/bridge use according to individual-level variables. In both sexes, high equivalent income, low number of teeth, present illness, involvement in two or more kinds of social groups, and meeting friends 1–2 times per month were significantly associated with denture/bridge use. Age group, marital status, educational attainment, and instrumental social support given were associated with denture/bridge use in males.
Table 1

Association between denture/bridge use and individual-level characteristics in males and females

 

Males, n = 25630

Females, n = 28758

 

n

Denture/bridge users (%)

Univariate PR

n

Denture/bridge users (%)

Univariate PR

Characteristic

PR

95% CI

PR

95% CI

Socio-demographics

        

 Age group (years)

        

  65 - 69

6699

69.7

1.00

(reference)

6923

68.5

1.00

(reference)

  70 - 74

7081

68.1

0.98

(0.94-1.02)

7916

66.2

0.97

(0.93-1.01)

  75 - 79

6118

66.5

0.95

(0.92-0.99)a

6880

67.5

0.99

(0.95-1.03)

  80 - 84

3899

68.2

0.98

(0.93-1.03)

4443

68.2

1.00

(0.95-1.04)

  ≥ 85

1833

67.9

0.97

(0.92-1.04)

2596

69.3

1.01

(0.96-1.07)

 Marital status

        

  Married

21449

68.7

1.00

(reference)

15547

67.3

1.00

(reference)

  Separated/divorced

3216

65.9

0.96

(0.92-1.00)

11868

68.6

1.02

(0.99-1.05)

  Never married

441

60.5

0.88

(0.78-0.99)a

604

66.2

0.98

(0.89-1.09)

  Unknown/missing

524

63.9

0.93

(0.83-1.04)

739

59.8

0.89

(0.81-0.98)a

 Educational attainment (years)

        

  < 6

453

62.7

1.00

(reference)

1028

66.4

1.00

(reference)

  6 - 9

11161

62.6

1.00

(0.89-1.12)

13582

65.2

0.98

(0.91-1.06)

  10 - 12

7877

70.7

1.13

(1.00-1.27)a

9512

70.2

1.06

(0.98-1.14)

  ≥ 13

5048

77.4

1.23

(1.10-1.39)b

3171

70.7

1.06

(0.98-1.16)

  Missing

1091

66.0

1.05

(0.92-1.21)

1465

67.8

1.02

(0.93-1.12)

 Equivalent income (10000 yen)

       

  < 50

739

60.1

1.00

(reference)

1625

60.9

1.00

(reference)

  50 - 99

2192

59.6

0.99

(0.89-1.10)

3274

65.0

1.07

(0.99-1.15)

  100 - 149

3214

62.2

1.04

(0.93-1.15)

3151

66.4

1.09

(1.01-1.18)a

  150 - 200

5245

68.5

1.14

(1.03-1.26)b

4294

68.2

1.12

(1.04-1.20)b

  200 - 299

5452

71.6

1.19

(1.08-1.32)c

4768

71.5

1.18

(1.09-1.26)c

  300 - 399

3275

75.6

1.26

(1.14-1.39)c

2760

74.5

1.22

(1.13-1.32)c

  ≥ 400

2266

75.2

1.25

(1.13-1.39)c

2226

73.1

1.20

(1.11-1.30)c

  Missing

3247

62.8

1.05

(0.94-1.16)

6660

63.4

1.04

(0.97-1.12)

Health status

        

 Number of teeth

        

  10 - 19

10407

64.9

1.00

(reference)

11129

62.1

1.00

(reference)

  1 - 9

9786

73.5

1.13

(1.09-1.17)c

11565

73.7

1.19

(1.15-1.22)c

  0

5437

64.5

0.99

(0.95-1.04)

6064

66.4

1.07

(1.03-1.11)c

 Present illness

        

  No

6192

65.1

1.00

(reference)

6214

65.0

1.00

(reference)

  Yes

17602

69.2

1.06

(1.03-1.10)c

20081

68.2

1.05

(1.01-1.09)b

  Missing

1836

68.4

1.05

(0.99-1.12)

2463

69.7

1.07

(1.01-1.13)a

Social relationship

        

 General trust

        

  No

1075

64.6

1.00

(reference)

1273

64.8

1.00

(reference)

  Yes

23326

68.3

1.06

(0.98-1.14)

26111

67.8

1.05

(0.98-1.12)

  Missing

1229

68.1

1.05

(0.95-1.17)

1374

66.8

1.03

(0.94-1.13)

 Norms of reciprocity

        

  No

2237

66.5

1.00

(reference)

2517

66.9

1.00

(reference)

  Yes

22089

68.4

1.03

(0.98-1.08)

24635

67.8

1.01

(0.96-1.07)

  Missing

1304

66.9

1.01

(0.92-1.09)

1606

67.1

1.00

(0.93-1.08)

 Attachment to place

        

  No

1219

67.8

1.00

(reference)

1285

65.8

1.00

(reference)

  Yes

23754

68.2

1.01

(0.94-1.08)

26631

67.7

1.03

(0.96-1.10)

  Missing

657

67.0

0.99

(0.88-1.11)

842

68.1

1.03

(0.93-1.15)

 Emotional social support (received)

       

   No

1211

64.9

1.00

(reference)

727

64.1

1.00

(reference)

   Yes

11573

66.7

1.03

(0.96-1.10)

12619

65.7

1.03

(0.93-1.13)

   Missing

12846

69.8

1.07

(1.00-1.16)

15412

69.4

1.08

(0.99-1.19)

 Emotional social support (given)

       

   No

2225

65.0

1.00

(reference)

1112

64.2

1.00

(reference)

   Yes

13112

67.3

1.03

(0.98-1.09)

12703

65.8

1.02

(0.95-1.11)

   Missing

10293

70.0

1.08

(1.02-1.14)b

14943

69.5

1.08

(1.00-1.17)a

 Instrumental social support (received)

       

   No

1245

65.1

1.00

(reference)

1380

63.9

1.00

(reference)

   Yes

15949

67.7

1.04

(0.97-1.12)

16461

66.9

1.05

(0.98-1.12)

   Missing

8436

69.3

1.07

(0.99-1.15)

10917

69.3

1.08

(1.01-1.16)a

 Instrumental social support (given)

       

   No

2929

64.8

1.00

(reference)

3855

66.7

1.00

(reference)

   Yes

14467

68.2

1.05

(1.00-1.11)a

13287

66.6

1.00

(0.96-1.04)

   Missing

8234

69.1

1.07

(1.01-1.12)a

11616

69.1

1.04

(0.99-1.08)

 Number of social groups

        

   0

6074

66.4

1.00

(reference)

6693

66.5

1.00

(reference)

   1

4390

68.5

1.03

(0.99-1.08)

4551

69.9

1.05

(1.01-1.10)a

   2

3355

70.5

1.06

(1.01-1.12)a

3306

70.2

1.06

(1.00-1.11)a

   3 - 6

5207

71.1

1.07

(1.02-1.12)b

3871

70.2

1.06

(1.01-1.11)a

   Missing

6604

66.0

0.99

(0.95-1.04)

10337

65.6

0.99

(0.95-1.03)

 Frequency of meeting friends

        

  Rarely

2866

64.5

1.00

(reference)

1891

64.5

1.00

(reference)

  Several times a year

5163

69.5

1.08

(1.02-1.14)b

3127

68.7

1.07

(0.99-1.14)

  1 or 2 times/month

4986

69.7

1.08

(1.02-1.14)b

5225

69.1

1.07

(1.00-1.14)a

  Once/week

3595

69.1

1.07

(1.01-1.14)a

4965

68.2

1.06

(0.99-1.13)

  2 or 3 times/week

4304

67.6

1.05

(0.99-1.11)

6979

67.2

1.04

(0.98-1.11)

  Almost everyday

2930

68.2

1.06

(0.99-1.13)

4159

67.5

1.05

(0.98-1.12)

  Missing

1786

65.3

1.01

(0.94-1.09)

2412

65.8

1.02

(0.95-1.10)

PR, prevalence ratio; CI, confidence interval.

a, p < 0.05; b, p < 0.01; c, p < 0.001.

Table 2 shows the PRs (95% CIs) for denture/bridge use according to local district- and municipality-level variables. Local district-level emotional and instrumental social support received, meeting friends, and municipality-level population density were significantly associated with denture/bridge use in both sexes. Municipality-level number of dentists working in hospitals or clinics per population was associated with denture/bridge use in males, and emotional social support given in females.
Table 2

Association between denture/bridge use and local district- and municipality-level characteristics in males and females

 

Males

Females

 

n

Denture/bridge users (%)

Univariate PR

n

Denture/bridge users (%)

Univariate PR

Characteristic

PR

95% CI

PR

95% CI

Local district-level characteristics

        

  Cognitive social capital

        

  General trust (%)

        

   Lowest (<92.86)

85

68.6

1.00

(reference)

85

67.0

1.00

(reference)

   Low middle (92.86 - 97.00)

304

67.8

0.99

(0.93-1.05)

304

67.5

1.01

(0.95-1.07)

   High middle (97.01 - 99.99)

114

69.2

1.01

(0.94-1.08)

114

68.5

1.02

(0.96-1.09)

   Highest (100.00)

58

69.8

1.02

(0.91-1.13)

59

68.2

1.02

(0.92-1.13)

  Norms of reciprocity (%)

        

   Lowest (<84.91)

61

71.1

1.00

(reference)

61

68.0

1.00

(reference)

   Low middle (84.91 - 91.17)

250

69.3

0.98

(0.90-1.06)

250

68.8

1.01

(0.93-1.10)

   High middle (91.18 - 99.99)

237

67.0

0.94

(0.87-1.02)

234

66.7

0.98

(0.90-1.06)

   Highest (100.00)

13

71.6

1.01

(0.77-1.32)

14

69.7

1.02

(0.81-1.30)

  Attachment to place (%)

        

   Lowest (<91.03)

62

70.4

1.00

(reference)

63

68.3

1.00

(reference)

   Low middle (91.03 - 97.11)

379

68.4

0.97

(0.90-1.05)

379

67.9

0.99

(0.92-1.07)

   High middle (97.12 - 99.99)

84

66.4

0.94

(0.87-1.03)

84

66.3

0.97

(0.89-1.05)

   Highest (100.00)

36

66.7

0.95

(0.81-1.10)

36

70.3

1.03

(0.89-1.18)

  Emotional social support (received) (%)

        

   Lowest (<88.89)

142

71.9

1.00

(reference)

143

71.2

1.00

(reference)

   Low middle (88.89 - 92.85)

139

69.7

0.97

(0.92-1.02)

139

69.5

0.98

(0.93-1.03)

   High middle (92.86 - 95.44)

139

67.5

0.94

(0.89-0.99)a

139

67.5

0.95

(0.90-1.00)a

   Highest (≥95.45)

138

65.7

0.91

(0.86-0.97)b

138

64.3

0.90

(0.86-0.95)c

   Missing

3

45.6

0.63

(0.49-0.83)c

3

59.6

0.84

(0.69-1.01)

  Emotional social support (given) (%)

        

   Lowest (<85.71)

129

69.4

1.00

(reference)

130

70.4

1.00

(reference)

   Low middle (85.71 - 89.35)

151

69.0

0.99

(0.94-1.04)

151

67.8

0.96

(0.92-1.01)

   High middle (89.36 - 92.09)

140

66.9

0.96

(0.91-1.01)

140

66.3

0.94

(0.90-0.99)a

   Highest (≥92.10)

141

68.7

0.99

(0.94-1.04)

141

68.5

0.97

(0.92-1.03)

  Instrumental social support (received) (%)

       

   Lowest (<88.89)

148

71.2

1.00

(reference)

148

70.4

1.00

(reference)

   Low middle (88.89 - 92.26)

133

66.8

0.94

(0.89-0.99)a

133

66.7

0.95

(0.90-1.00)a

   High middle (92.27 - 94.81)

140

68.4

0.96

(0.91-1.01)

140

67.9

0.97

(0.92-1.01)

   Highest (≥94.82)

140

67.8

0.95

(0.90-1.00)

141

67.1

0.95

(0.91-1.00)

  Instrumental social support (given) (%)

        

   Lowest (<77.42)

140

67.9

1.00

(reference)

141

69.1

1.00

(reference)

   Low middle (77.42 - 81.87)

140

67.6

1.00

(0.95-1.05)

140

66.7

0.97

(0.92-1.01)

   High middle (81.88 - 85.41)

141

67.5

0.99

(0.95-1.04)

141

67.5

0.98

(0.93-1.02)

   Highest (≥85.42)

140

70.3

1.03

(0.98-1.09)

140

68.4

0.99

(0.94-1.04)

 Structural social capital

        

  Mean number of social groups

        

   Lowest (<1.280)

140

69.2

1.00

(reference)

141

70.4

1.00

(reference)

   Low middle (1.280 - 1.483)

141

69.4

1.00

(0.95-1.06)

141

69.2

0.98

(0.94-1.03)

   High middle (1.484 - 1.687)

139

68.1

0.98

(0.94-1.03)

139

67.7

0.96

(0.92-1.01)

   Highest (≥1.688)

141

67.0

0.97

(0.92-1.02)

141

65.6

0.93

(0.89-0.97)b

  Meeting friends (%)

        

   Lowest (<87.76)

136

69.8

1.00

(reference)

137

70.2

1.00

(reference)

   Low middle (87.76 - 91.00)

142

68.6

0.98

(0.93-1.04)

142

68.8

0.98

(0.93-1.03)

   High middle (91.01 - 93.32)

137

68.8

0.98

(0.93-1.04)

137

67.3

0.96

(0.91-1.01)

   Highest (≥93.33)

143

66.4

0.95

(0.90-1.00)

143

66.4

0.95

(0.90-1.00)a

   Missing

3

45.6

0.65

(0.50-0.85)b

3

59.6

0.85

(0.70-1.03)

Municipality-level characteristics

        

 Number of dentists per 100000 people

        

  Lowest (<47.29)

7

65.3

1.00

(reference)

7

65.7

1.00

(reference)

  Low middle (47.29 - 53.97)

7

66.4

1.02

(0.96-1.07)

7

67.5

1.03

(0.98-1.08)

  High middle (53.98 - 59.74)

7

67.7

1.04

(0.99-1.09)

7

67.4

1.03

(0.98-1.08)

  Highest (≥59.75)

7

70.1

1.07

(1.02-1.13)b

7

68.5

1.04

(1.00-1.09)

 Population density (/km2)

        

  Rural-agricultural (<1000)

2

64.4

1.00

(reference)

2

64.6

1.00

(reference)

  Semi-urban (1000–1499)

7

68.1

1.06

(1.02-1.10)b

7

68.4

1.06

(1.02-1.10)b

  Urban (1500–3999)

6

70.6

1.10

(1.05-1.14)c

6

68.5

1.06

(1.02-1.10)b

  Metropolitan (≥4000)

13

72.2

1.12

(1.08-1.17)c

13

72.0

1.12

(1.07-1.16)c

PR, prevalence ratio; CI, confidence interval.

n, number of local districts for local district-level characteristics and number of municipalities for municipality-level characteristics.

a, p < 0.05; b, p < 0.01; c, p < 0.001.

Table 3 shows the results of multilevel Poisson regression analyses. High educational attainment, high equivalent income, low number of teeth, present illness, and high population density were significantly associated with denture/bridge use in males (p < 0.05). High equivalent income, low number of teeth present, present illness, involvement in one or more social groups, and high population density were significantly associated with denture/bridge use in females (p < 0.05). In both the sexes, frequency of meeting friends was not significantly associated with denture/bridge use in model 3. Significance of the variables in model 1 did not change after adding the variable of frequency of meeting friends in both sexes.
Table 3

Multilevel prevalence ratios and 95% confidence intervals for denture/bridge use in males and females

 

Males

Females

 

Model 1

Model 2

Model 1

Model 2

 

PR

95% CI

PR

95% CI

PR

95% CI

PR

95% CI

Fixed effects

        

 Individual-level characteristics

        

  Age group (years) (reference 65–69)

        

   70 - 74

0.98

(0.94-1.02)

0.98

(0.94-1.02)

0.96

(0.92-1.00)a

0.96

(0.92-1.00)

   75 - 79

0.96

(0.92-1.00)

0.96

(0.92-1.00)

0.97

(0.93-1.01)

0.97

(0.93-1.02)

   80 - 84

0.98

(0.94-1.03)

0.99

(0.94-1.04)

0.98

(0.93-1.03)

0.99

(0.94-1.04)

   ≥ 85

0.99

(0.93-1.06)

1.00

(0.93-1.06)

0.99

(0.93-1.05)

1.00

(0.94-1.06)

  Marital status (reference married)

        

   Separated/divorced

0.97

(0.93-1.02)

0.97

(0.93-1.02)

1.02

(0.99-1.06)

1.02

(0.99-1.05)

   Never married

0.91

(0.80-1.03)

0.91

(0.81-1.03)

0.98

(0.89-1.08)

0.98

(0.89-1.08)

   Unknown/missing

1.00

(0.89-1.11)

1.00

(0.90-1.12)

0.93

(0.84-1.02)

0.93

(0.85-1.03)

  Educational attainment (years) (reference <6)

        

   6 - 9

0.97

(0.86-1.10)

0.97

(0.86-1.10)

0.99

(0.92-1.08)

0.99

(0.92-1.08)

   10 - 12

1.07

(0.95-1.21)

1.07

(0.95-1.21)

1.06

(0.98-1.15)

1.06

(0.97-1.15)

   ≥ 13

1.15

(1.02-1.30)a

1.15

(1.01-1.30)a

1.07

(0.98-1.17)

1.06

(0.97-1.16)

   Missing

1.00

(0.87-1.15)

1.00

(0.87-1.15)

1.02

(0.92-1.13)

1.02

(0.92-1.13)

  Equivalent income (10000 yen) (reference <50)

        

   50 - 99

0.99

(0.89-1.10)

0.99

(0.89-1.10)

1.06

(0.99-1.15)

1.06

(0.99-1.15)

   100 - 149

1.02

(0.92-1.13)

1.02

(0.92-1.13)

1.08

(1.00-1.17)a

1.08

(1.00-1.16)

   150 - 200

1.10

(0.99-1.21)

1.09

(0.99-1.21)

1.11

(1.03-1.20)b

1.10

(1.03-1.19)b

   200 - 299

1.14

(1.03-1.25)a

1.13

(1.02-1.25)a

1.16

(1.08-1.24)c

1.15

(1.07-1.23)c

   300 - 399

1.18

(1.07-1.31)b

1.18

(1.06-1.30)b

1.20

(1.12-1.30)c

1.19

(1.10-1.29)c

   ≥ 400

1.18

(1.06-1.31)b

1.17

(1.05-1.30)b

1.18

(1.09-1.27)c

1.17

(1.08-1.26)c

   Missing

1.04

(0.93-1.15)

1.03

(0.93-1.15)

1.03

(0.96-1.11)

1.03

(0.96-1.11)

  Number of teeth (reference 10–19)

        

   1 - 9

1.16

(1.13-1.20)c

1.16

(1.13-1.20)c

1.21

(1.17-1.25)c

1.21

(1.18-1.25)c

   0

1.05

(1.01-1.10)b

1.05

(1.01-1.10)a

1.12

(1.08-1.17)c

1.13

(1.08-1.17)c

  Present illness (reference no)

        

   Yes

1.06

(1.02-1.10)b

0.94

(0.91-0.98)b

1.05

(1.01-1.09)b

0.95

(0.92-0.99)b

   Missing

1.05

(0.99-1.12)

0.99

(0.94-1.05)

1.08

(1.02-1.14)b

1.03

(0.98-1.08)

  Number of social groups (reference 0)

        

   1

  

1.02

(0.97-1.07)

  

1.05

(1.01-1.10)a

   2

  

1.03

(0.98-1.09)

  

1.05

(1.00-1.11)a

   3 - 6

  

1.05

(1.00-1.10)

  

1.06

(1.01-1.11)a

   Missing

  

1.02

(0.97-1.06)

  

1.00

(0.97-1.04)

 Municipality-level characteristics

        

  Number of dentists per 100000

        

  people (reference lowest (<47.29))

   Low middle (47.29 - 53.97)

1.03

(0.98-1.09)

1.03

(0.98-1.09)

1.04

(0.99-1.10)

1.04

(0.99-1.10)

   High middle (53.98 - 59.74)

0.99

(0.94-1.05)

0.99

(0.94-1.05)

0.97

(0.92-1.03)

0.97

(0.92-1.03)

   Highest (≥59.75)

0.98

(0.93-1.04)

0.98

(0.93-1.04)

0.95

(0.89-1.00)

0.95

(0.89-1.00)

  Population density (reference rural-agricultural)

        

   Semi-urban

1.07

(1.02-1.12)b

1.07

(1.02-1.13)b

1.10

(1.04-1.15)c

1.10

(1.04-1.15)c

   Urban

1.10

(1.04-1.16)c

1.10

(1.05-1.16)c

1.11

(1.05-1.17)c

1.11

(1.05-1.17)c

   Metropolitan

1.12

(1.06-1.18)c

1.13

(1.07-1.19)c

1.17

(1.10-1.24)c

1.17

(1.10-1.25)c

 Intercept

0.52

(0.44-0.60)c

0.54

(0.46-0.63)c

0.50

(0.45-0.56)c

0.51

(0.46-0.58)c

Random effects

        

 Local district-level variance (SE)

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

 Municipality-level variance (SE)

0.000

0.000

0.000

0.000

0.000

0.000

0.000

0.000

Null model for males: Intercept, multilevel PR: 0.68 (0.66 - 0.69), p < 0.001, local district-level variance (SE): 0.000 (0.000), municipality-level variance (SE): 0.002 (0.001).

Null model for females: Intercept, multilevel PR: 0.67 (0.66 - 0.69), p < 0.001, local district-level variance (SE): 0.000 (0.000), municipality-level variance (SE): 0.002 (0.001).

PR, prevalence ratio; CI, confidence interval; SE, standard error.

a, p < 0.05; b, p < 0.01; c, p < 0.001.

All local district-level social capital variables were not associated with denture/bridge use.

Discussion

The results of the present study showed that factors independently associated with denture/bridge use in both sexes were equivalent income, number of teeth, present illness, and population density, all of which are known to be associated with access to dental care [7]. In particular, individual financial status was strongly associated with denture/bridge use in the present study, which is in agreement with findings of a study conducted in one municipality in Japan [15]. Studies have suggested that low socioeconomic status is one of the barriers to dental attendance and that such barriers appear to have negative effects on oral health [23, 24]. It is noteworthy that even in people with universal free access to dental services under the national healthcare insurance system in Japan, financial issues are a major factor affecting denture/bridge use.

Subjects presently having illness were more likely to use a denture/bridge in the present study. Systemic ill health and functional limitations have been reported as barriers to seeking dental health care [25]. The results of the present study do not corroborate these findings. However, this discrepancy can be explained as follows. First, all subjects in the present study were ADL independent; therefore, functional limitations were not barriers to seeking dental health care in the present study. Second, subjects presently having illness may be more likely to ask dentists as well as doctors to solve their health problems, because a study using dental and medical care insurance records of employees aged 20–39 years showed that individuals who consulted dentists tended to receive medical treatment more frequently [26].

Although both sexes shared the same factors associated with denture/bridge use, there were differences in factors associated with denture/bridge use between sexes. The results of the present study showed that females involved in one or more kinds of social groups were more likely to use a denture/bridge. These results agree with an interview study from the UK that showed that patients focused on the social significance of oral rehabilitation when defining the need for a removable partial denture [16].

High educational attainment was associated with denture/bridge use only in males. Few studies have reported gender difference in the association between educational attainment and oral health status and/or oral health behavior, probably because most of the studies analyzed the association including both sexes [810, 23, 24]. A study in a Japanese older population showed that males with the highest educational attainment showed healthier ageing and lower mortality compared to males with the lowest educational attainment; however, no such differences were seen among females [27]. These results suggest that educational attainment is associated with oral and systemic health in males, but not in females. Further studies that confirm the reproducibility of these findings are needed to explain the gender difference.

No social capital variables were associated with denture/bridge use. These results disagreed with those from a recent study that suggested that older people living in societies with rich social capital tend to have good oral health status, including having 20 or more teeth [18]. The results of the present study suggest that denture/bridge use was associated with personal factors, such as financial and social factors, but not social capital.

In contrast to social capital, high population density was associated with denture/bridge use in the present study. Because population density may be considered as surrogate information on socioeconomic status, it is possible that people living in richer areas tend to use denture/bridge.

The results of the present study show that target groups in which percentage of people using denture/bridge must be increased included people with low income and those living in the area with low population density. In addition, males with low educational attainment and females who do not have any social groups should be targeted. Taking this information into consideration, formulation of an intervention program for the target groups is recommended from the public health perspective.

The present study had a number of limitations. First, denture use was not distinguished from bridge use in the present study, which makes it difficult to interpret the results. A bridge is a fixed prosthesis and cannot be removed by patients; however, a denture can be removed by patients, and denture use is thus affected by patient compliance. To partially address this issue, we excluded subjects with 20 or more teeth and added number of teeth as a variable in the analyses.

Second, we did not obtain information regarding dental implants which is another type of dental prosthesis because dental implant is not covered by public health insurance in Japan. A recent national survey showed that 4.4%, 1.2% and 2.8% of the whole population aged 65–74, 75–84 and 85- had dental implants, respectively [5]. Additional studies adding information on dental implants are necessary to confirm the results of the present study in the future.

Third, the state of the denture such as stability and fit was unknown because this study was based on a self-administered questionnaire. Our previous study using a similar self-administered questionnaire showed that 13.7% of the participants with few teeth and dentures reported poorly fitted dentures [2]. Additional studies are needed to confirm the results of the present study using information on status of dentures.

Fourth, the measurements used were based on a self-administered questionnaire. Some forms of bias, such as social desirability bias [28], may have affected the results of the present study. Fifth, because this was a cross-sectional study, causal relationships are unclear.

Conclusions

Denture/bridge use was significantly associated with high economic status, present illness, and living in an area with high population density in both sexes among community-dwelling older Japanese having 19 or fewer teeth. Different factors were associated with denture/bridge use in males and females: high educational attainment in males and involvement in one or more social groups in females. Local district-level social capital was not associated with denture/bridge use.

Abbreviations

JAGES: 

Japan gerontological evaluation study

ADL: 

Activities of daily living

PR: 

Prevalence ratio

CI: 

Confidence interval.

Declarations

Acknowledgements

The present study used data from the Japan Gerontological Evaluation Study (JAGES). This study was supported in part by a grant of the Strategic Research Foundation Grant-aided Project for Private Universities from Ministry of Education, Culture, Sport, Science, and Technology, Japan (MEXT), 2009–2013 and Health Labour Sciences Research Grant, Comprehensive Research on Aging and Health (H24-Junkanki(Seisyu)-Ippan-007) from the Japanese Ministry of Health, Labour and Welfare (MHLW).

Authors’ Affiliations

(1)
Department of Dental Sociology, Kanagawa Dental University Graduate School of Dentistry
(2)
Center for Preventive Medical Science, Chiba University
(3)
Center for Well-being and Society, Nihon Fukushi University
(4)
Department of International and Community Oral Health, Tohoku University Graduate School of Dentistry
(5)
Department of Policy Studies, Aichi Gakuin University
(6)
Faculty of Sociology, Rikkyo University
(7)
Department of Nutrition, Faculty of Health and Nutrition, Tokaigakuen University

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  29. Pre-publication history

    1. The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1472-6831/14/63/prepub

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© Yamamoto et al.; licensee BioMed Central Ltd. 2014

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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