Received: 18 December 2019

| Revised: 12 March 2020 | Accepted: 28 March 2020

DOI: 10.1111/joor.12975

ORIGINAL ARTICLE

The factors related to decreases in masticatory performanceand masticatory function until swallowing using gummy jelly insubjects aged 20-79 years
Keitaro Ohno | Yuko Fujita
Division of Developmental Stomatognathic
Function Science, Department of Health
Promotion, Kyushu Dental University,
Kitakyushu City, Japan
Correspondence
Yuko Fujita, Division of Developmental
Stomatognathic Function Science,
Department of Health Promotion, Kyushu
Dental University, 2-6-1 Manazuru,
Kokurakita-ku, Kitakyushu 803-8580, Japan.
Email: y-fujita■kyu-dent.ac.jp
Funding information
Ministry of Education, Culture, Sports,
Science and Technology, Japan, Grant/Award Number: 17K1196717K11967| Yoma Ohno | Tomohiro Takeshima | Kenshi Maki
Abstract
Background: There is growing international interest in the prevention of decreased
oral function for managing oral health in older people.
Objective: The aims of the present study were to identify factors related to decreases
in masticatory performance and masticatory function until swallowing in subjects
aged 20-79 years old.
Methods: A total of 152 subjects, ranging in age from 20 to 79 years, were divided
into six groups according to their chronological age: 20-29, 30-39, 40-49, 50-59,
60-69 and 70-79 years. Grip strength, maximum occlusal force, maximum tongue
pressure, masticatory performance and swallowing threshold were measured in all
subjects. Masticatory performance and swallowing threshold were determined according to the concentration of dissolved glucose obtained from gummy jellies; decreased masticatory performance and decreased swallowing threshold were defined
as glucose concentrations in the lowest 20th percentile. A multivariate binary logistic
regression analysis was used to identify factors associated with decreased masticatory performance and decreased swallowing threshold. A self-administered lifestylequestionnaire was also completed.
Results: Logistic regression analyses revealed that factors related to decreased masticatory performance included use of more than one kind of medicine for treating
chronic diseases and removable denture use, while factors related to decreased swallowing threshold included eating between meals once or more per day, poorer mental
health and decreased saliva flow.
Conclusions: Different factors are related to decreased masticatory performanceand decreased swallowing threshold, although both of these phenomena are closely
associated with general health status.
KEYWORDS

adults, eating habit, general health, masticatory performance, swallowing threshold, tongue
pressure

The peer review history for this article is available at https://publo​ns.com/publo​n/10.1111/joor.12975

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,provided the original work is properly cited.
© 2020 The Authors. Journal of Oral Rehabilitation published by John Wiley & Sons Ltd.
J Oral Rehabil. 2020;00:1–11.	﻿

wileyonlinelibrary.com/journal/joor

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OHNO et al.

1 | I NTRO D U C TI O N

getting on/off the toilet, bathing, walking on level surfaces, ascending and descending stairs, dressing and control of bowel function and

There is increasing international interest in the identification of ap-

bladder, based on the assessment variables in the Barthel index11; (c)propriate strategies for management of age-related decline in oral

occlusal contact of either the natural teeth or artificial teeth includ-

health and prevention of decreased oral function in older people.1

ing removable dentures at the first molars; and (d) no current dental

In 2016, the Japanese Society of Gerodontology presented crite-

diseases or complications. The exclusion criteria included systemic

ria including decrease in tongue pressure, decrease in masticatory

disturbances causing swallowing impairments, obvious facial asym-

function and deterioration of swallowing function for diagnosis of

metry that could affect the recordings, soft tissue abnormalities,

oral hypofunction in older people.1 Recent studies have indicatedtemporomandibular joint dysfunction and irregularities in the form

that decreased tongue strength may be an important factor in nutri-or structure of the natural teeth.

tion-related sarcopenia. 2,3 Moreover, several studies have reported

A previous study reported that the mean masticatory perfor-that masticatory performance is closely related to hand grip strength

mance among adult patients was around 180 ± 30 mg/dL. If the truein adult subjects.4,5 These findings suggest that oral hypofunction

difference in the decreased function and normal means is 20 mg/

is linked to skeletal sarcopenia or poor general health status; simul-

dL,8 30 decreased function participants and 120 normal function

taneously, we hypothesised that decrease in masticatory function

participants were calculated to be required to reject the null hypoth-would be related to physical and mental health status as well as den-esis that the means of the decreased and normal groups are equaltal health status.

with a power of 0.9. The probability of a Type I error associated with

There are many studies on the factors related to the masticatory

the test of this null hypothesis was 0.05. To account for potential

performance including the number of residual teeth and occlusal

dropouts, we recruited 152 adults aged 20-79 years (76 males andforce.4-6 However, there have been fewer studies on factors related

76 females).

to the swallowing threshold than on masticatory performance; a

The subjects were divided into six groups according to theirstudy reported that subjects with shortened dental arches without

chronological age, with each group being further divided into two

occluding molars had higher number of chewing cycles and longer

subgroups according to gender (20s, 12 males and 15 females; 30s,

chewing time until swallowing test foods than the subjects with

12 males and 13 females; 40s, 15 males and 12 females; 50s, 13

complete dental arches.7 However, few studies have evaluated mas-

males and 12 females; 60s, 12 males and 12 females; and 70s, 12

ticatory performance and swallowing threshold simultaneously inmales and 12 females).

adult subjects. A recent study reported that better mental health
was associated with a higher swallowing threshold in subjects intheir 20s.8 These findings suggest that some people begin swallow-

2.2 | Anthropometry and dental examination

ing foods with less chewing at a relatively young age.
Earlier countermeasures could be implemented if lifestyle

Height and body weight were measured in the consultation room

factors, general health and oral health could be used to predictof the clinic. Height was measured to an accuracy of ±0.1 cm using

decreased masticatory performance and swallowing threshold, po-a portable digital stadiometer (AD-653; A&D), with the head in thetentially preventing nutrition-related sarcopenia.

Frankfort plane, while body weight was measured to an accuracy of

The aims of the present study were to determine changes in

0.1 kg.12

various oral functions according to age, as well as factors related

During the intra-oral examination, the number of functional

to decreased masticatory performance and decreased masticatory

teeth and total number of decayed, missing and filled teeth (DMFT)

function until swallowing in 20-79 years old.

were recorded, and the Community Periodontal Index (CPI) was recorded according to the criteria recommended by the World HealthOrganization.13

2 | M E TH O DS
2.1 | Participants

2.3 | QuestionnaireThis study was approved by the Human Investigation Committee of

The survey solicited the following information: demographic charac-

Kyushu Dental University (Kitakyushu, Fukuoka, Japan; Approvalteristics (sex and age), eating habits, physical activity, sleep, current

Number 16-27), and all subjects provided written informed consent

and past smoking habits, alcohol use, removable denture use andbefore participation. Subjects visited one private dental clinic in

use of medicines to treat for chronic diseases (including hyperten-

Japan for an oral examination, based on which the final study par-sion, arrhythmia, diabetes, hypercholesterolaemia, anaemia and oth-ticipants were selected. The inclusion criteria were as follows

9,10

: (a)

ers). Mental health was assessed using the 12-item General Healthnormal language comprehension; (b) ability to independently per-Questionnaire (GHQ-12; Japanese version). A higher score indicatedform activities of daily living (ADL), including feeding, sit to standpoorer mental health status. The validity and reliability of the GHQ-(chair to bed), personal grooming (washing, shaving and combing),

12 have been confirmed in a previous study.14

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OHNO et al.

2.4 | Hand grip strength

device (GLUCO SENSOR GS-II; GC Co. Ltd.) to measure masticatory
performance.8 A glucose concentration in the lowest 20th percen-

Hand grip strength was measured using a portable grip strength

tile was defined as decreased masticatory performance based on themeter (T-2288; TOEI LIGHT Co. Ltd.). Participants were asked toprevious studies regarding the criteria of sarcopenia.15-17

stand and hold a dynamometer in their hand with their arm parallelto the body, without squeezing the arm against the body. Hand grip
strength was measured, in kg, twice for each hand (alternately) witha 30-s interval between trials. The highest value from either the left

2.8 | Swallowing threshold and stimulated
salivary flow

or right hand was recorded as the grip strength.8
Following evaluation of masticatory performance, an assessment

2.5 | Maximum occlusal forceof swallowing threshold was performed using the gummy jellies(GLUCOLUMN, GC Co. Ltd.). The three variables related to swallowing (ie number of chewing cycles, chewing time and glucose con-

Maximum occlusal force was measured using a portable occlusal force

centration in the filtrate [ml/dl]), were assessed in all participants. In

meter (GM10; Nagano Keiki Co. Ltd.), which consisted of a strain gauge

the studies on dysphagia, "decreased swallowing threshold" meansin the centre of a biting element encased in a plastic tube. Participants

more sensitive to stimuli for swallowing.18,19 In this study, we de-were examined while relaxed in a sitting position, with the Frankfort

fined "decreased swallowing threshold" as the condition that foodplane horizontal. Participants were asked to place the element on theis swallowed with less chewing, and used the glucose concentration

maxillary first molar or second primary molar and bite it with maximal

obtained from chewed gummy jelly as the swallowing threshold justvoluntary muscular effort for approximately 3 s. Occlusal force wasbefore the participants determined that swallowing was possible.

measured in kilonewtons (kN) by a digital pressure gauge built into the

Each participant was instructed to chew a gummy jelly on their ha-element. The maximum bite force was measured on each side with abitual chewing side. Participants were then instructed to chew until

30-s interval between bite measurements. The larger of the values re-

feeling the desire to swallow, at which time they were instructed

corded on the left and right sides was considered to be the maximum

to stop chewing and signal to the examiner that they were ready tobite force and was used in subsequent analyses.8,9expel the gummy jelly. The examiner counted the number of chewing cycles, and the time from the onset of chewing to the moment

2.6 | Maximum tongue pressure

at which participants raised their hand was recorded using a stopwatch. The subsequent steps were the same as those used for theevaluation of masticatory performance.8

Maximum tongue pressure was measured using a tongue pressure ma-

Whole saliva was collected to evaluate the swallowing threshold.

nometer (JMS). Participants were examined while relaxed in a sitting

All filtrates with gummy jelly pieces removed were used to measureposition and were asked to place a balloon on the anterior part of their

the stimulated salivary flow, with the amount thereof calculated bypalate and close their lips, biting a hard ring with the upper and lower

deducting 10 mL from the total amount of filtrate. All saliva speci-

incisors. Then, they were asked to raise their tongues and compress

mens were collected between 10:00 am and 3:00 pm6 A glucose con-the balloon onto the palate with maximal voluntary muscular effort for

centration in the lowest 20th percentile was defined as decreased

approximately 7 s. The pressure was measured (in kilopascals) using aswallowing threshold based on previous studies regarding the crite-

digital voltmeter attached to the tongue pressure manometer.8,9

ria of sarcopenia.15-17

2.7 | Masticatory performance

2.9 | Reliability of measurements

Masticatory performance was assessed according to the concen-

All measurements were performed in duplicate, separated by a 30-s

tration of dissolved glucose obtained from a cylindrical-shaped

rest period, and the mean values were used in subsequent analyses.

gummy jelly consisting of 40% maltose, 10% sorbitol and 5% glu-

All examinations were performed by the same examiner. The datacose (GLUCOLUMN; GC Co. Ltd.). Before the experiments, partici-

were assessed in terms of intra-rater reliability using the intra-classpants were shown how to perform the masticatory movements andcorrelation coefficient (ICC; 0.800 ≤ ICC ≤ 1.000 corresponds tomouth-rinsing procedure to ensure that they would not swallow. The

high reliability). 20

participants were then instructed to chew the gummy jelly on theirhabitual chewing side (left, right or both) for 20s. After chewing, theparticipants were asked to take 10 mL of distilled water into their

2.10 | Data analysis

mouth and to spit out the gummy jelly, distilled water and saliva into
a filter cup. The glucose concentration in the filtrate (mg/dL) was

The Shapiro-Wilk test was used to determine the normality ofmeasured using a reliable, previously validated glucose-measuring

the data. All continuous data are expressed as mean ± standard

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OHNO et al.

TA B L E 1

Anthropometric parameters, dental examination results and GHQ-12 score by age group and sex
Community

Age

Sex

group

(n = 152)

Age (y)20s

M (n = 12)

30s
40s
50s
60s
70s

Periodontal

GHQ -12

Index

score

Body weight

Body mass

Number of

Height (m)(kg)

index (kg/m2)functional teeth

23.67 ± 3.52

1.66 ± 0.07‡

61.54 ± 7.18

22.55 ± 3.35

26.25 ± 1.91† ,‡4.00 ± 4.09† ,‡2.25 ± 0.97

2.92 ± 1.88

F (n = 15)

24.53 ± 2.53

1.56 ± 0.05*

46.47 ± 4.03*,†

19.05 ± 1.49*

27.93 ± 0.26*,† ,‡6.20 ± 4.18† ,‡1.60 ± 0.74† ,‡2.07 ± 1.10

M (n = 12)33.92 ± 3.78

1.68 ± 0.03‡

66.17 ± 6.03

2.00 ± 2.22

DMFT index

23.33 ± 2.02

27.42 ± 1.38† ,‡13.17 ± 5.18‡

2.75 ± 0.87

,†

† ,‡

12.38 ± 5.41‡

2.69 ± 0.85

2.15 ± 1.46

16.00 ± 5.44

2.93 ± 0.59

1.07 ± 1.03
1.83 ± 2.21

F (n = 13)

35.46 ± 2.79

1.56 ± 0.06*

48.62 ± 6.86*

19.90 ± 2.76*

27.46 ± 0.78

M (n = 15)

46.13 ± 2.17

1.68 ± 0.05‡

73.00 ± 13.55‡

25.91 ± 4.50

26.60 ± 1.72† ,‡F (n = 12)

44.58 ± 2.78

1.60 ± 0.05*,‡53.50 ± 6.61*

20.88 ± 2.06*

26.75 ± 1.76† ,‡17.58 ± 7.28

2.75 ± 0.87

M (n = 13)

54.15 ± 2.91

1.68 ± 0.08‡

65.46 ± 7.99

23.29 ± 2.21

26.08 ± 2.10† ,‡14.62 ± 4.61

2.85 ± 0.80

1.77 ± 1.24

F (n = 12)

55.08 ± 2.15

1.54 ± 0.03*,†53.83 ± 8.99*

22.59 ± 3.46

26.50 ± 1.17† ,‡18.83 ± 5.27*

3.00 ± 0.95

1.83 ± 1.19

M (n = 12)63.25 ± 2.22

1.71 ± 0.06

73.58 ± 13.02‡

25.19 ± 3.41

24.42 ± 2.57† ,‡19.92 ± 3.09

3.42 ± 0.51

2.25 ± 1.42

F (n = 12)65.50 ± 2.54

1.54 ± 0.04*

52.75 ± 5.58*

22.15 ± 2.09*

24.33 ± 2.64† ,‡17.25 ± 4.20

2.83 ± 0.58*

1.17 ± 0.72*

M (n = 12)74.92 ± 3.03

1.65 ± 0.06

63.92 ± 7.19

23.42 ± 1.75

18.92 ± 5.23

20.58 ± 3.48

3.50 ± 0.67

2.00 ± 1.35

F (n = 12)73.75 ± 2.80

1.50 ± 0.06*,†

52.67 ± 7.94*

23.39 ± 2.50

17.83 ± 6.83

23.25 ± 4.65

3.17 ± 0.72

1.42 ± 1.16

Note: Data are expressed as mean ± standard deviation. Differences between males and females within each group were assessed by a two-tailed ttest or the Mann-Whitney U test. Differences between males or females in their 70s and other groups were assessed by a Kruskal-Wallis test.
Abbreviations: DMFT, decayed, missing and filled teeth; F, female; GHQ, General Health Questionnaire; M, male.
*P < .05 vs group-matched males.
†

P < .05 vs 70s males.

‡

P < .05 vs 70s females.

deviation (SD). Mean values were compared between the twoof chewing cycles, chewing time, glucose concentration and stimu-

groups using a two-tailed t test or the Mann-Whitney U test. The

lated salivary flow until swallowing were all ≥0.83.

Kruskal-Wallis test was used for comparison of more than two

The anthropometric, dental examination and GHQ-12 data aregroups. The chi-squared test or Fisher's exact test was used asshown in Table 1 by age and sex. The number of functional teeth inappropriate to compare the normal masticatory performance and70- to 79-year-old males and females was significantly lower thandecreased masticatory performance (lowest 20%) groups, and thethat in the males and females in the other groups (all, P < .05). The

normal swallowing threshold and decreased swallowing threshold

DMFT index of females in their 70s was significantly lower than that(lowest 20%) groups, in terms of categorical variables. Binary lo-of males and females in their 20s and 30s (all, P < .05).

gistic regression analysis with the forward selection (conditional)

The mean scores for hand grip strength, maximum occlusal force,

method was used to identify factors predicting decreased masti-

maximum tongue pressure, masticatory performance and swallow-

catory performance and decreased swallowing threshold in eaching threshold are shown in Figure 1. Maximum occlusal force andgroup. Independent variables that were significant in the univari-maximum tongue pressure were significantly higher for males thanate analyses were included. Categorical variables were coded ap-

females within four groups (30s, 40s, 50s and 60s; all P < .05). No

propriately before being entered into the model. The adjusted

significant difference in masticatory performance was seen by age

odds ratios (ORs), and their 95% confidence intervals (CIs), wereor sex. Among males, the mean hand grip strength and maximum

calculated for the low masticatory performance and low swallow-

tongue pressure were highest in those in their 30s vs all other age

ing threshold groups. A P-value <.05 was considered to indicate

groups, and the difference between the 30s and 70s age groups was

statistical significance. All data were analysed using SPSS forsignificant (all, P < .05). Among females, the mean hand grip strength,

Windows software (version 23.0; IBM Japan).

maximum occlusal force and maximum tongue pressure were highest in those in their 20s vs all other age groups. The glucose concen-

3 | R E S U LT S

tration until swallowing did not differ by age or sex.
Table 2 summarises the data on decreased masticatory performance and decreased swallowing threshold by demographic and

The ICCs for height, body weight, number of functional teeth, DMFT

health-related variables. Participants with decreased masticatory

index, CPI, GHQ-12 score, hand grip strength, maximum occlusal

performance were more likely to be older, to be former smokers,

force, maximum tongue pressure, masticatory performance, number

to take more than one medicine for chronic diseases and to use

F I G U R E 1 Comparison of hand grip strength, oral functions and stimulated salivary flow by age group and sex. Data are expressed
as mean ± standard deviation. M, male; F, female. (A) Hand grip strength; (B) maximum occlusal force; (C) maximum tongue pressure; (D)masticatory performance; (E) number of chewing cycle; (F) chewing time; (G) swallowing threshold; (H) stimulated salivary flow. Differences
between males and females within each group were assessed by a two-tailed t test or the Mann-Whitney U test. Differences between males
or females in their 70s and other groups were assessed by a Kruskal-Wallis test. *P < .05

OHNO et al.

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TA B L E 2variables

OHNO et al.

Decreased masticatory performance and decreased swallowing threshold according to demographic and health-related

Participants (n = 152)

Normalmasticatory
performance(%)

Decreased
masticatory
performance(%)χ2

P-value

Normalswallowing
threshold(%)

Decreasedswallowing
threshold (%)χ2

P-value

GenderFemale60 (49.6)

16 (51.6)

61 (50.0)

15 (50.0)Male

61 (50.4)

15 (49.4)

61 (50.0)

15 (50.0)—

1.000†—

1.000†

11.655

.040‡

—

.038†

11.478

.003‡

—

.280†

0.637

.727†

1.318

.517‡

0.443

.801‡

Age (y)20-29

24 (19.8)

3 (9.7)23 (18.9)

4 (13.3)

30-39

21 (17.4)

4 (12.9)20 (16.4)

5 (16.7)

40-49

25 (20.7)

2 (6.5)25 (20.5)

2 (6.7)50-59

22 (18.2)

3 (9.7)22 (18.0)

3 (10.0)

60-69

15 (12.4)

9 (29.0)

18 (14.8)

6 (20.0)

70-79

14 (11.6)

10 (32.3)

14 (11.5)

10 (33.3)

16.635.005‡

Eating between meals
Less than once a day

49 (40.5)

13 (41.9)

Once or more a day

72 (59.5)

18 (58.1)
0.021

55 (45.1)

7 (23.3)

67 (54.9)

23 (76.7).884‡

Physical activity
30 min or more a day

30 (24.8)

4 (12.9)30 (24.6)

Less than 30 min a day
None

20 (16.5)

5 (16.1)

25 (20.5)

0 (0.0)71 (58.7)

22 (71.0)

67 (54.9)

26 (86.7)

2.171

4 (13.3).338‡

Self-assessed sleep qualityGood

79 (65.3)

22 (71.0)

84 (68.9)

17 (56.7)

Poor

42 (34.7)

9 (29.0)38 (31.1)

13 (43.3)

0.357

.550‡

Alcohol drinking
Never

53 (43.8)

19 (61.3)

56 (45.9)

16 (53.3)

Less than three times
a week42 (34.7)

8 (25.8)

41 (34.4)

8 (26.7)

Three times or more
a week26 (21.5)

4 (12.9)24 (19.7)

6 (20.0)

2.998

.211‡

SmokingNever

94 (79.0)

19 (61.3)

93 (76.9)

20 (69.0)

Former5 (4.2)Current

20 (16.8)8 (25.8)9 (7.4)4 (13.8)

4 (12.9)19 (15.7)

5 (17.2)

14.503.001‡

Medicines for chronic diseases084 (69.4)

9 (29.0)76 (62.3)

17 (56.7)

1

34 (28.1)

19 (61.3)

41 (33.6)

12 (40.0)≥23 (2.5)3 (9.7)5 (4.1)1 (3.3)17.615<.0005‡(Continues)

| 7OHNO et al.

TA B L E 2(Continued)
Normalmasticatory
performance(%)

Decreased
masticatory
performance(%)

No

114 (94.2)

17 (54.8)

Yes

7 (5.8)14 (45.2)

Participants (n = 152)

χ2

P-value

Normalswallowing
threshold(%)

Decreasedswallowing
threshold (%)

108 (88.5)

23 (76.7)

14 (11.5)

7 (23.3)

χ2

P-value

Use of removable dentures—†

Fisher's exact test.

‡

chi-squared test.

<.0005†—.135†

removable dentures (P = .005, P = .001, P < .0005 and P < .0005,

For every point increase in the GHQ-12 score, the odds of a de-respectively).

creased swallowing threshold increased by a factor of 1.566

Participants with a decreased swallowing threshold were more

(P = .001, 95% CI = 1.165-2.104). In contrast, for every 0.1 mL

likely to be older, eat between meals once or more per day and haveincrease in the salivary flow before swallowing, the odds of aa low physical activity level (P = .040, P = .038 and P = .003, re-decreased swallowing threshold dropped by a factor of 0.282

spectively). Of the participants in this study, 28 took medicine for(P = .004, 95% CI = 0.137-0.582).

hypertension, 16 took medicine for arrhythmia, and 5 took medicine for diabetes or hypercholesterolaemia at fixed intervals (datanot shown). Additionally, as the results of Kruskal-Wallis test, there

4 | D I S CU S S I O N

were no significant differences in stimulated salivary flow according
to the number of regular medicines (data not shown).

In the present study, consistent differences in hand grip strength andTable 3 summarises the data on decreased masticatory perfor-maximum tongue pressure were observed by age group. These re-mance and decreased swallowing threshold by age, body weight,

sults are in agreement with previous studies. 21,22 Maximum tongue

dental and mental health status, and muscle strength. Regarding de-pressure significantly declined in males in their 70s, whereas pre-creased masticatory performance, the number of functional teeth,

vious studies showed that maximum tongue pressure significantly

CPI, hand grip strength, maximum occlusal force, maximum tongue

declined in the 60s. 21,23 The reason for this difference was that, inpressure and swallowing threshold in the decreased masticatory

our study, the mean height and body weight were highest in males in

performance group were significantly lower than those in the nor-

their 60s among all age groups, where a recent study reported thatmal masticatory performance group (all, P < .05). The mean age andmaximum tongue pressure was significantly associated with heightmean DMFT index in the decreased masticatory performance groupand body weight in young adults.9 In females, skeletal and oral mus-were significantly higher than those in the normal masticatory per-cle strength tended to decline earlier than in males; however, theformance group (both P < .05).

speed of decline tended to be slower than in males.

Regarding decreased swallowing threshold, the number of func-

Additionally, we found that masticatory performance andtional teeth, maximum occlusal force, masticatory performance,swallowing threshold did not obviously differ by sex or age, unlike

number of chewing cycles, chewing time and salivary flow in the

maximum occlusal force and maximum tongue pressure. It may bedecreased swallowing threshold group were significantly lower thanthat masticatory muscle function declines more slowly because of

those in the normal swallowing threshold group (all, P < .05). The

various factors, the presence of which might also have been associ-mean age, mean DMFT index and GHQ-12 scores in the decreased

ated with the ability of the elderly participants in our study to inde-swallowing threshold group were significantly higher than those inpendently perform ADL.

the normal swallowing threshold group (all, P < .05).

In the logistic regression analysis, the use of more than one med-

Table 4 shows the predictors of decreased masticatory perfor-

icine for treating chronic diseases was significantly associated withmance, as revealed by logistic regression. The use of more than one

decreased masticatory performance. Previous epidemiological stud-

medicine for treating chronic diseases (OR = 10.919, P = .008, 95%

ies reported that periodontitis and the number of lost teeth were

CI = 1.891-63.053) and use of removable dentures (OR = 10.198,

positively related to the prevalence of chronic diseases, including

P < .0005, 95% CI = 3.215-32.354) were both associated with higher

hypercholesterolaemia, hypertension and diabetes in adults, 24,25 as

odds of decreased masticatory performance.

well as the incidence of cardiovascular disease and coronary heart

Table 5 shows the predictors of decreased swallowing thresh-disease in middle-aged males. 26 In the present study, the number ofold, as revealed by logistic regression. Eating between meals once

functional teeth in the decreased masticatory performance groupor more a day (OR = 3.390, P = .021, 95% CI = 1.198-9.591) was

was significantly lower than that in the normal masticatory perfor-

associated with higher odds of a decreased swallowing threshold.

mance group, and the CPI in the decreased masticatory performance

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OHNO et al.

TA B L E 3 Decreased masticatory performance and decreased swallowing threshold according to age, body weight, dental and mental
health status, and muscle strengthAge (y)Normalmasticatory
performance(n = 121)

Decreased
masticatory
performance(n = 31)

Normal swallowing
threshold(n = 122)

Decreasedswallowing threshold(n = 30)46.65 ± 16.22

57.94 ± 18.66*

47.56 ± 16.42

54.63 ± 19.75†

Height (m)1.62 ± 0.08

1.59 ± 0.09

1.62 ± 0.08

1.60 ± 0.10

Body weight (kg)59.71 ± 12.72

57.58 ± 9.67

59.59 ± 12.18

58.03 ± 12.23

Body mass index (kg/m2)

22.61 ± 3.50

22.64 ± 2.68

22.62 ± 3.40

22.59 ± 3.13

Number of functional teeth (N)26.00 ± 3.20

21.84 ± 5.79*

25.73 ± 3.44

22.80 ± 5.92†

DMFT index

14.38 ± 7.23

18.03 ± 6.48*

14.53 ± 7.00

17.53 ± 7.68†

Community Periodontal Index

2.71 ± 0.94

3.10 ± 0.60*

2.74 ± 0.88

3.00 ± 0.95

GHQ-12 score (point)

1.88 ± 1.59

1.77 ± 1.06

1.65 ± 1.48

2.73 ± 1.23†

Hand grip strength (kg)33.83 ± 10.90

28.23 ± 8.21*

33.42 ± 10.68

29.71 ± 10.02

Maximum occlusal force (kN)

0.42 ± 0.15

0.32 ± 0.17*

0.42 ± 0.15

0.34 ± 0.18†

Maximum tongue pressure (kPa)

35.64 ± 7.71

30.36 ± 6.48*

35.03 ± 7.47

32.65 ± 8.71

Masticatory performance (mg/dL)

177.03 ± 36.22

98.71 ± 13.66*

170.87 ± 43.16

121.17 ± 31.90†

Number of chewing cycle (N)26.90 ± 10.01

26.45 ± 6.79

28.34 ± 9.40

20.57 ± 6.58†

Chewing time (s)19.41 ± 6.17

21.00 ± 5.55

20.89 ± 5.80

15.03 ± 4.75†

Swallowing threshold (mg/dL)

167.46 ± 47.09

119.55 ± 36.69*

173.53 ± 40.98

93.27 ± 12.85†

1.08 ± 0.80

0.92 ± 0.63

1.14 ± 0.76

0.66 ± 0.67†

Salivary flow (mL)

Note: Data are expressed as mean ± standard deviation. Differences between normal and low groups were assessed by a two-tailed t test or the
Mann-Whitney U test.
Abbreviations: DMFT, decayed, missing and filled teeth; GHQ, General Health Questionnaire; Swallowing threshold, glucose concentration on firstswallow.
*P < .05 vs normal masticatory performance group.
†

P < .05 vs normal swallowing threshold group.

group was significantly higher than that in the normal masticatory

performance. A previous study reported that maximum occlusal

performance group, although the differences were not statisticallyforce was higher in individuals with implant fixed dental prosthesis

significant in the logistic regression analysis. These findings suggest

than in those with removable dental prostheses. 27that poor tooth and periodontal health could be associated with theuse of more than one medicine for chronic diseases.

In the present study, removable denture use was not significantly
correlated with decreased swallowing threshold. These results sug-

In addition, the logistic regression analysis revealed that remov-

gest that longer chewing time and a larger number of chewing cy-

able denture use was closely correlated with decreased masticatory

cles until swallowing compensated for the reduction in masticatory

Independent variables

Category

Adjusted odds
ratio
(95% CI)

Number of regular medicines
for chronic diseases

0

1

—

0

1

2.466
(0.880-6.915)

.086

1

≥2

10.919(1.891-63.053)

.008

2

No

1

—

0

Yes

10.198(3.215-32.354)<.0005

1

Use of removable dentures

P-value

Score assigned

Note: Forward selection (conditional) method. −2 Log likelihood = 119.867. Hosmer and Lemeshow
test: χ2 = 0.210, P = .900. Cox-Snell R 2 = .200. Nagelkerke R 2 = .314.
Abbreviation: CI, confidence interval.

TA B L E 4 Predictors of decreased
masticatory performance based on logistic
regression analysis

| 9OHNO et al.

TA B L E 5 Predictors of decreased
swallowing threshold based on logistic
regression analysis

Adjusted odds ratio(95% CI)

P-value

Score
assigned

Less than once
a day

1

—

0

Once or morea day

3.390 (1.198-9.591)

.021

1

GHQ-12 score(per 1-point increase)

1.566 (1.165-2.104)

.001

—

Salivary flow(per 0.1-ml increase)0.282 (0.137-0.582)

.004

—

Independent variables

Category

Eating between meals

Note: Forward selection (conditional) method. −2 Log likelihood = 121.441. Hosmer and Lemeshow
test: χ2 = 9.239, P = .323. Cox-Snell R 2 = .177. Nagelkerke R 2 = .281.
Abbreviations: CI, confidence interval; GHQ, General Health Questionnaire.

performance associated with use of removable dentures. Therefore,

Thus, the factors related to decreased masticatory performance

we believe that removable denture use could be less likely to be as-

and decreased swallowing threshold were closely associated withsociated with decreased swallowing threshold.

not only oral health status but also general health status in subjects

The logistic regression analysis showed that eating between meals

aged 20-79 years.

once or more per day was significantly associated with a decreased

Our results showed that 9 out of 30 individuals with a decreased

swallowing threshold. Generally, when chewing food, sensation isswallowing threshold were aged below 40 years. It could be sug-transmitted from the baroreceptors in the periodontal ligament andgested that the habits of eating quickly and swallowing with lessthe muscle spindles in the masseter muscle to the trigeminal mes-

chewing, beginning at a young age, can cause choking and cough-encephalic nucleus (Me5). It has been reported that the histamine

ing fits, a decline in swallowing muscle strength and function, andnervous system receives projections from Me5, which activates theeven an increased risk of death from suffocation and aspiration. It

histamine nervous system and suppresses appetite via the satiety

is a natural providence that muscular strength declines with ageing;

28-30

These findings suggest that individuals swal-

however, we believe that decrease in swallowing threshold will belowing foods without chewing might not feel full or be able to obtainable to prevent by chewing foods sufficiently before swallowing anda feeling of satiety; we believe that this could explain the significantly

keeping good physical and mental health from young adulthood.

centre in animals.

higher prevalence of decreased swallowing threshold among those

The present study had several limitations. First, the number of

who reported eating between meals once or more a day in this study.

participants was small compared to previous epidemiological stud-

In addition, the logistic regression analysis showed that GHQ-12

ies. Among the patients who visited one dental clinic, the number ofscores were closely correlated with a decreased swallowing threshold.

patients who met all of the conditions we set was less likely as they

A previous study indicated that GHQ-12 scores can reflect anxiety,became older. Therefore, this study was performed with the minimum

31

The present results were con-required number of participants calculated by the power analysis. It

sistent with recent findings among 20- to 29-year-old young adults.8

may be that differences in oral function by age will be clearer in stud-

Additionally, another study reported a higher chewing frequency

ies with higher numbers of participants. Second, this study used a

per second after stress induction compared to resting conditions incross-sectional design, which precluded the determination of causal

depression and social dysfunction.

32

These findings suggest that a decreased swallowing

relationships between decreased masticatory performance and swal-

threshold may be related to anxiety, depression or personality charac-

lowing threshold with the variables included in the logistic regression

teristics rendering an individual more vulnerable to stress. In the pres-analyses. Longitudinal studies are needed to investigate the relative

ent study, the causal relationship could not be revealed, but anotherinfluence of factors associated with decreased masticatory perfor-

possibility is that feeding behaviours such as swallowing foods withmance and decreased swallowing threshold. Third, the questionnaire

less chewing may contribute to poor mental health status.

section on frequency of eating between meals did not capture theadult subjects.

In this study, stimulation of salivary flow until swallowing was

number or types of snacks, so we could not discuss the association be-also significantly associated with a decreased swallowing threshold.

tween eating between meals and decreased masticatory performance

In previous studies, age seemed to play an important role in unstim-in detail. Future studies should confirm the relationship between eat-ulated salivary flow rates,33 while stimulated saliva secretion rates

ing between meals and decreased masticatory performance.

were not significantly different between healthy old and young
adults.34,35 In the present study, there were no significant differences in stimulated salivary flow according to age or the number of

5 | CO N C LU S I O N S

regular medicines. We suggest that the reduced salivation of individuals with a decreased swallowing threshold was due to fewer chew-

In the present study, masticatory performance and swallow-

ing cycles and a shorter chewing time.

ing threshold did not clearly differ by sex or age, unlike maximum

10|

OHNO et al.

occlusal force and maximum tongue pressure. The factors related
to decreased masticatory performance included use of more than
one medicine for treating chronic diseases, and factors related to decreased swallowing threshold included poorer mental health state.
Different factors were related to decreased masticatory performance and decreased swallowing threshold, although both of these
phenomena were closely associated with general health status insubjects aged 20-79 years.
AC K N OW L E D G M E N T S
This work was supported by Grants-in-Aid from the Ministryof Education, Culture, Sports, Science and Technology, Japan(17K11967).
C O N FL I C T O F I N T E R E S T
The authors have no financial conflict interests to disclose.
AU T H O R C O N T R I B U T I O N S
KO and YF formulated the study design and drafted the whole manuscript. YO and TT analysed the data. KM supervised the data analysis. All authors read and approved the final manuscript.
ORCID
Yuko Fujita

https://orcid.org/0000-0002-5803-0742

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How to cite this article: Ohno K, Fujita Y, Ohno Y, TakeshimaT, Maki K. The factors related to decreases in masticatory
performance and masticatory function until swallowing using
gummy jelly in subjects aged 20-79 years. J Oral Rehabil.
2020;00:1–11. https://doi.org/10.1111/joor.12975