Influence of dental treatment on physical performance in community-dwelling elderly persons

Authors


Shingo Moriya, Department of Oral Health, National Institute of Public Health, 2-3-6 Minami, Wako-shi, Saitama 351-0197, Japan.
Tel.: +81 48 458 6282
Fax: +81 48 458 6288
E-mail: shyomi@niph.go.jp

Abstract

doi: 10.1111/j.1741-2358.2011.00563.x
Influence of dental treatment on physical performance in community-dwelling elderly persons

Objective:  The aim of the study was to investigate the influence of dental treatment on physical performance (muscle strength and balance function) among the elderly.

Background:  Oral conditions have been associated with physical performance. We hypothesised that improved oral conditions by dental treatment would lead to improved physical performance.

Methods:  A total of 154 persons aged 65 years or over were judged to be in need of dental treatment as a result of dental examination; of these, 121 persons underwent dental treatment. After 1 year, differences in each parameter of physical performance before and after the intervention were evaluated using the Wilcoxon signed rank sum test. The Spearman rank correlation coefficient was calculated to examine correlations between changes in self-assessed masticatory ability (masticatory ability) and each parameter of physical performance, and multivariate logistic regression analysis was performed using changes in each parameter of physical performance as the dependent variable and changes in masticatory ability as the principal independent variable.

Results:  Improved physical performance was not observed for the total study population with dental treatment; however, in subjects with improved masticatory ability, one-leg standing times with eyes open increased significantly. A significant correlation was established between changes in masticatory ability and each parameter of physical performance. These relationships were not found in those without dental treatment. A significant relationship was also established for one-leg standing time after adjusting for age, gender, dentition status and needs of dental treatments.

Conclusion:  Chewing ability may be a positive contributing factor to balance function among the elderly.

Introduction

Prolonged life expectancy in Japan has led to an increase in the number of elderly persons. In 2009, 22.7% of the total Japanese population was over the age of 65 years, and this proportion continues to grow1. Such growth stresses the importance of preventing decline in functioning in activities of daily living (ADLs) among the elderly, as this is considered to be a major component of quality of life. It has been shown that decline in functioning in ADLs is induced by functional impairment, frailty, the risk of falls and gait disturbances and that these factors are significantly influenced by parameters of physical performance such as muscle strength and balance function2–7.

A number of epidemiological studies have shown that physical performance is significantly associated with dental status, periodontal status and chewing ability among elderly persons8–11. Dental treatment has been shown to improve functioning in ADLs and prevent falls among the elderly12,13. These findings suggest that improvement in some oral conditions by dental treatment may positively influence physical performance parameters and subsequently lead to improvement in functioning in ADLs and prevention of falls.

Therefore, we investigated the causal relationships between oral conditions and physical performance among the elderly. We hypothesised that improvement in oral conditions by dental treatment would positively affect muscle strength and balance function among the elderly, thereby applying a community-based intervention strategy for dental treatment.

Materials and methods

A total of 294 individuals aged 65 years or over and living independently underwent a dental health examination sponsored by the public authority in a rural community (Iwanai) in Hokkaido, the northernmost prefecture of Japan. The examination was performed over 10 days from August to September 2006. Of these 294 persons, 174 (59.2%) were judged to be in need of dental treatment and were advised to undergo treatment as a result of the oral examination (the baseline survey). Consequently, 154 (88.5%) of these 174 persons participated in the follow-up survey, which was performed 1 year after the baseline survey. Of these 154 persons, 121 (78.6%) underwent dental treatment during the last year as advised, but the other 33 persons (21.4%) did not undergo any dental treatment. These 154 individuals were enrolled in this study. All persons were informed of the purpose and methods of the study and the routine that they informed us of significant changes in general health status during the follow-up period, and then they provided written informed consent to participate. Ethical approval for the study was obtained from the ethics committee of the Graduate School of Dental Medicine, Hokkaido University.

Subjects were interviewed based on questionnaires about self-assessed masticatory ability (masticatory ability), demographic factors such as gender and age, and general health status such as hypertension, diabetes, cardiac, cerebrovascular, respiratory, hepatic, renal and mental diseases (absence vs. presence). Information about whether the participants could live independently or dependently was obtained from the Long-Term Care Insurance System of Japan (LTCI)14, which was under control of the public authority.

Masticatory ability was assessed using the following question: ‘How do you rate your masticatory ability?’ Answers were classified into one of the following: ‘I can chew all kinds of food’ (good); ‘I can chew only slightly hard food’ (fair); or ‘I can chew only soft or pureed food’ (poor)10.

Intra-oral examination was performed by two dentists. The intra-examiner reliability of the two dentists was considered to be good, as they had worked together at the same dental hospital for more than 5 years and calibration was conducted to obtain close agreement in the assessment of dental status, periodontal status, crown and bridge prostheses and dentures prior to the survey. Periodontal status was evaluated using the WHO Community Periodontal Index of Treatment Needs (CPITN), and a person in need of periodontal treatment was defined as a person with a CPITN code 2 or above. Need for treatment with dentures was defined as the presence of pain when using dentures, poor retention and stability of dentures clinically and not using dentures regardless of having missing teeth in the pre-molar or molar regions. A person with ill-fitting crown and bridge prostheses was also defined as a person in need of treatment. The pattern of occluding pairs of natural teeth was classified into one of the three classes based on the presence or absence of occluding pairs of natural teeth, that is, (1) tooth contact in all of the bilateral pre-molar and molar regions (total support), (2) tooth contact at least in one region except (1) (partial support) or (3) an absence of tooth contact (lost support).

Handgrip strength (kg) and one-leg standing time with eyes open (s) were measured for the evaluation of muscle strength and static balance function, respectively. The single greatest value of handgrip strength was measured with the subject standing upright holding a hand dynamometer (Tanita, Ltd., Tokyo, Japan) in both hands. The maximum measurement of the right or the left hand was used for each subject. For one-leg standing time with eyes open, subjects were asked to stand on one leg with their eyes open and with arms stretched out, once on each foot until balance was lost, and the maximum measurement of the right or the left was used as the value for each subject.

The chi-squared test was used to compare distribution of participants according to each characteristic between those with and without dental treatment. The Wilcoxon signed rank test was used to examine changes in handgrip strength and one-leg standing time with eyes open between before and after the intervention. The Spearman rank correlation coefficients were used to examine correlations between changes in handgrip strength and one-leg standing time with eyes open, and those in masticatory ability. After significant correlations were identified, multivariate logistic regression analysis was performed with handgrip strength and one-leg standing time with eyes open (improved vs. unchanged or impaired) as dependent variables and changes in masticatory ability as the principal independent variable. These models presented the odds ratio (OR) and 95% confidence interval (CI) for the impairment and improvement in masticatory ability as compared with the unchanged status. Only p values smaller than 0.05 were defined as statistically significant. Statistical analysis was performed using the IBM SPSS statistical package (IBM SPSS PASW® Statistics Base 18.0, IBM Japan, Tokyo, Japan).

Results

Characteristics of the subject at the baseline survey are shown in Table 1. Although the participants had some chronic medical diseases, all of them were kept under good medical control and none of them were certificated for care-needs in the LTCI during the follow-up period. The percentage distribution by masticatory ability before and after the intervention is shown in Table 2. In the participants with dental treatment, the number of subjects with good masticatory ability did not change, but the number with fair masticatory ability increased, and the number with poor masticatory ability decreased. Percentage distributions by the type of changes in masticatory ability before and after the intervention are shown in Table 3. In the participants with dental treatment, 12 (9.9%), 91 (75.2%) and 18 (14.9%) subjects had impaired, unchanged and improved masticatory ability, respectively. In those individuals without dental treatment, 3 (9.1%), 28 (84.8%) and 2 (6.1%) subjects had impaired, unchanged and improved masticatory ability, respectively.

Table 1.   Characteristics of the subjects.
 Participants with dental treatment n = 121Participants without dental treatment n = 33 p-valuesa
n % n %
  1. achi-squared test.

  2. bDental caries or impairment of crown prosthesis.

Gender
 Female6049.61957.60.416
 Male6150.41442.4
Age (years)
 65–694133.91133.30.119
 70–743730.6412.1
 80–842924.01339.4
 >851411.6515.2
The pattern of occluding pairs of natural teeth
 Lost support4436.41957.60.038
 Partial support4436.4515.2
 Full support3327.3927.3
Self-assessed masticatory ability
 Good8166.92472.70.729
 Fair3024.8618.2
 Poor108.339.1
Need for dental treatment
 Periodontal disease
  Needed9376.92266.70.233
  Needless2830.11133.3
 Dentures
  Needed4436.41751.50.115
  Needless7763.61648.5
 Othersb
  Needed54.113.00.772
  Needless11695.93297.0
Chronic medical diseases
 Hypertension
  Absence7259.52060.60.909
  Presence4940.51339.4
 Diabetes
  Absence10990.13193.90.495
  Presence129.926.1
 Cardiac diseases
  Absence10385.13090.90.391
  Presence1814.939.1
 Cerebrovascular disease
  Absence11494.23297.00.527
  Presence75.813.0
 Respiratory diseases
  Absence11998.333100.00.457
  Presence21.700.0
 Hepatic disease
  Absence11998.33297.00.612
  Presence21.713.0
 Renal disease
  Absence12199.233100.00.600
  Presence10.800.0
 Mental disease
  Absence11998.33297.00.612
  Presence21.713.0
Table 2.   Percentage distribution of the participants by masticatory ability before and after intervention.
Masticatory abilityBeforeAfter
n % n %
Participants with dental treatment (n = 121)
 Good8166.98166.9
 Fair3024.83831.4
 Poor108.321.7
Participants without dental treatment (n = 33)
 Good2472.72369.7
 Fair618.2618.2
 Poor39.1412.1
Table 3.   Percentage distribution by the type of changes in masticatory ability before and after intervention.
Type of changes in masticatory abilityBeforeAfter n %
  1. The ratios of participants with needs of each dental treatment are shown as follows:

  2. aPeriodontal diseases (58.3%), dentures (58.3%) and others (8.1%).

  3. bPeriodontal diseases (84.6%), dentures (29.7%) and others (3.3%).

  4. cPeriodontal diseases (55.6%), dentures (66.7%) and others (5.6%).

  5. dPeriodontal diseases (66.7%), dentures (66.7%) and others (33.3%).

  6. ePeriodontal diseases (71.4%), dentures (46.3%) and others (0.0%).

  7. fPeriodontal diseases (0.0%), dentures (100.0%) and others (0.0%).

Participants with dental treatment (n = 121)
 Impaireda
  n = 12 (9.9%)
GoodFair119.1
FairPoor10.8
 Unchangedb
  n = 91 (75.2%)
GoodGood7057.9
FairFair2016.5
PoorPoor10.8
 Improvedc
  n = 18 (14.9%)
FairGood97.4
PoorGood32.5
PoorFair65.0
Participants without dental treatment (n = 33)
 Impairedd
  n = 3 (9.1%)
GoodFair13.0
GoodPoor13.0
FairPoor13.0
 Unchangede
  n = 28 (84.8%)
GoodGood2266.7
FairFair412.1
PoorPoor26.1
 Improvedf
  n = 2 (6.1%)
FairGood13.0
PoorFair13.0

Comparisons of handgrip strength and one-leg standing time with eyes open between before and after the intervention are shown in Table 4. Handgrip strength decreased significantly in the total subjects and those with impaired masticatory ability, but no significant changes were observed in those with unchanged and improved masticatory ability. The one-leg standing time with eyes open did not change significantly in the total subjects and those with impaired masticatory ability; it decreased significantly in subjects with unchanged masticatory ability, but increased significantly in those with improved masticatory ability. No statistically significant changes in physical performance were observed in those without dental treatment.

Table 4.   Comparisons of handgrip strength and one-leg standing time with eyes open between before and after intervention.
Masticatory ability n Handgrip strength (kg)One-leg standing time with eyes open (s)
Mean ± SD p-valuesaMean ± SD p-valuesa
BeforeAfterBeforeAfter
  1. a p-values were evaluated with the Wilcoxon signed rank sum test.

Participants with dental treatment (n = 121)
 Total12128.0 ± 7.527.4 ± 7.70.04733.0 ± 33.329.9 ± 34.40.106
 Impaired1224.7 ± 6.822.6 ± 6.90.00521.0 ± 27.415.7 ± 20.60.182
 Unchanged9129.3 ± 7.328.7 ± 7.70.06637.8 ± 34.632.1 ± 34.80.029
 Improved1823.4 ± 6.824.2 ± 5.90.11716.5 ± 21.228.1 ± 38.90.029
Participants without dental treatment (n = 33)
 Total3326.9 ± 7.726.4 ± 6.70.73430.7 ± 30.023.0 ± 27.40.088
 Impaired321.0 ± 8.523.8 ± 6.30.10914.9 ± 5.330.0 ± 32.40.285
 Unchanged2827.6 ± 7.626.6 ± 6.80.20529.8 ± 27.122.1 ± 28.40.066
 Improved226.0 ± 8.828.0 ± 8.50.15768.0 ± 73.525.0 ± 0.00.655

There were significant correlations between changes in masticatory ability and each parameter of physical performance before and after the intervention in those with dental treatment, but not in those without dental treatment (Table 5). Further multivariate logistic regression models were performed to examine the independent relationships between changes in masticatory ability and improvement in each parameter of physical performance in those with dental treatment (Table 6). In these models, improved masticatory ability was significantly related to improvement in one-leg standing time with eyes open (OR = 4.05, 95% CI = 1.25–13.16, = 0.020), but these relationships were not established for handgrip strength.

Table 5.   Correlations between changes in handgrip strength and one-leg standing time with eyes open, and those in masticatory ability.
 Changes in handgrip strength between before and after – intervention (kg)aChanges in one-leg standing time with eyes open between before and after intervention (S)b
r p-value r p-value
  1. r: Spearman rank correlation coefficient.

  2. aQ–P; P = handgrip strength (kg) before intervention, Q = those after intervention.

  3. b SR; R= one-leg standing time with eyes open (s) before intervention, S=those after intervention

  4. cY–X; X = Categories of masticatory ability before intervention, Y = categories of masticatory ability after intervention., Categories of masticatory ability were created as follows: Poor = 0, Fair = 1, Good = 2.

Participants with dental treatment (n = 121)
 Changes in masticatory abilityc0.300.0010.210.020
Participants without dental treatment (n = 33)
 Changes in masticatory abilityc−0.090.635−0.260.146
Table 6.   Multivariate logistic regression models for improvement in each parameter of physical performance in the participants with dental treatment (n = 121).
 Dependent variables
Improvement in handgrip strengthaImprovement in one-leg standing timeb
OR95% CI p-valuesOR95% CI p-values
  1. OR, odds ratio; CI, confidence interval.

  2. aImproved (n = 43, 35.5%) vs. unchanged (n = 15, 12.4%) or impaired (n = 63, 52.1%).

  3. bImproved (n = 45, 37.2%) vs. unchanged (n = 5, 4.1%) or impaired (n = 71, 58.7%).

  4. cThere were no persons with impaired masticatory ability among those with improved handgrip strength.

Gender
 Female1.00 (reference)  1.00 (reference)  
 Male0.870.36–2.100.7591.900.79–4.560.153
Age
 65–741.00 (reference)  1.00 (reference)  
 75–840.870.35–2.200.7790.780.33–1.880.587
Occluding pairs of natural teeth
 Lost support1.00 (reference)  1.00 (reference)  
 Partial support2.900.84–10.100.0931.710.53–5.480.368
 Full support5.021.15–21.900.0323.130.79–12.390.104
Need for dental treatment
 Periodontal disease
  Needless1.00 (reference)  1.00 (reference)  
  Needed0.840.23–3.000.7840.370.11–1.250.109
 Dentures
  Needless1.00 (reference)  1.00 (reference)  
  Needed3.260.98–10.750.0531.330.42–4.170.624
 Changes in masticatory ability
  Impaired0.00c  0.630.14–2.770.541
  Unchanged1.00 (reference)  1.00 (reference)  
  Improved2.440.75–7.930.1394.051.25–13.160.020

Discussion

The present study revealed the influence of changes in masticatory ability following dental treatment on parameters of physical performance among community-dwelling elderly persons as follows. First, balance function improved significantly in subjects with improved masticatory ability. Second, there was a significant correlation between changes in masticatory ability and balance function. Finally, improvement in masticatory ability was significantly related to that of balance function after adjusting for age, gender, dentition status and the need for dental treatment. In regard to muscle strength, a significant correlation was observed between changes in masticatory ability and handgrip strength, but no significant improvement in muscle strength was seen in subjects with improved masticatory ability.

Subjects with unchanged masticatory ability accounted for about three-quarters (75.2%) of the total participants, because in this group, the number of subjects with good masticatory ability was large (76.9%) and the number of those in need of treatment with dentures was small (29.7%) at baseline (before intervention). The impairment in masticatory ability of 9.9% of the subjects may be explained by the possibility that the subjects in need of treatment with dentures (58.3%) were not satisfied with the results of the dental treatment they received. The subjectivity of evaluation for mastication can influence the results obtained. Since self-assessed masticatory ability has been shown to reflect dental status, periodontal status and denture-related factors in community-dwelling elderly persons15, the self-assessed masticatory ability to evaluate change in mastication was used.

Handgrip strength decreased significantly in the total study population and those with impaired masticatory ability, and it tended to decrease in those with unchanged masticatory ability. This decline was thought to be mainly an age-related change. In those with improved masticatory ability, handgrip strength did not tend to decrease, and there was a significant positive correlation between changes in masticatory ability and handgrip strength. Therefore, it is possible that the improvement in masticatory ability may contribute to controlling the age-related decline in muscle strength. These findings are supported by previous studies that reported a significant positive relationship between perceived chewing ability and muscle strength of the body among the elderly10,11.

One-leg standing time with eyes open decreased significantly in subjects with unchanged masticatory ability after the intervention. Subjects with impaired masticatory ability only showed a decreasing tendency in one-leg standing time, probably because the number of participants (n = 12) was too small to reach significance. This decline was thought to be mainly an age-related change. The significant increase in one-leg standing time with eyes open among those with improved masticatory ability suggested that improvement in balance function was accompanied by improvement in masticatory ability. This suggestion was further confirmed by the findings in terms of the significant positive correlation and independent relationships between changes in masticatory ability and one-leg standing time with eyes open. The present findings are consistent with those of epidemiological studies on the relationships between chewing ability and balance function, as well as a clinical trial on the influence of improved dental functional occlusion on the occurrence of falls in elderly with dementia10,11,13.

According to the related literature, physical performance such as muscle strength and balance function can be influenced by a variety of factors including ageing, the presence of physical diseases (including neurological) and psychological status in older adults16–19. Although the participants enrolled had some chronic medical disease, all of them were kept under good medical control. They had no difficulties in activities of daily living and could live independently, as none of them were certificated for care-needs in the LTCI14 during the follow-up period. It has been shown that masticatory ability was significantly associated with physical performance such as muscle strength and balance function after adjusting for some demographic and general health status9–11. Therefore, improved masticatory ability may influence physical performance positively as shown in the present study.

The relationships between chewing ability and physical performance can be explained by several possible underlying mechanisms. First, it has been shown that chewing ability is significantly related to nutritional intake and nutritional status20–22 and that nutritional status is a significant contributing factor to physical performance, especially muscle strength23–25, thereby suggesting that chewing ability may positively influence physical performance. Second, muscle strength and balance function may be influenced by orofacial sensory inputs from the trigeminal nerve, that is, epithelial mechanoreceptors and periodontal mechanoreceptors, temporomandibular joint receptors, jaw-closing muscle spindles and Golgi tendon organs26–32. Therefore, it is possible that these peripheral orofacial sensory inputs influence motor-neural control of muscle strength in other parts of body as there may be associations between orofacial motor control mechanisms33,34 and associations between changes in dental occlusion and postural stability35,36.

In these experimental studies, modification of dental occlusion may influence physical performance in a short time33–36. In a clinical trial, elderly persons with dementia underwent denture treatment, and then they experienced decreased frequency of falls during the 1-year investigative period13.

The present study had a limitation that it was not designed as a randomised controlled trial. Nevertheless, to the best of our knowledge, the present study is the first to elucidate the influence of changes in chewing ability on parameters of physical performance among community-dwelling elderly persons. Further sophisticated study designs such as a randomised controlled trial are required to confirm the findings reported.

Conclusions

Our hypothesis that dental treatment might improve physical performance among the elderly was not confirmed in the present study. Nevertheless, in the subjects where masticatory ability was improved by dental treatment, one-leg standing time with eyes open significantly improved, suggesting that chewing ability may positively contribute to enhancing balance function among the elderly.

Acknowledgement

The present study was supported by grants from the 8020 Foundation in Japan. We are grateful to the public authorities in Iwanai, Hokkaido, Japan, for their assistance.

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