Influence of Dental Prostheses on Cognitive Functioning in Elderly Population: A Systematic Review.

AIM: The aim of the systematic review was to assess the influence of dental prostheses on cognitive functioning in elderly population.
MATERIALS AND METHODS: This systematic review was conducted according to the PRISMA guidelines. The initial electronic search was conducted using the following search databases: MEDLINE (PubMed), Cochrane Library, Google Scholar, and EMBASE. The search was limited to English language using the search items/keywords: "dental prostheses and cognitive functioning," "dental prostheses and brain function," "Tooth loss and cognitive loss," "mastication and prefrontal activity," and "prostheses on mental state." The search strategy was followed using the PICOS framework.
RESULTS: A total of 19 studies were selected according to the selection criteria. Out of 19 studies, 15 studies were included and 4 studies were excluded from the review.
CONCLUSION: With the available evidence in the literature, it can be concluded that dental prostheses have a very significant role in preventing the cognitive impairment and act as a protective factor in enhancing the cognitive function in patients with dementia-related diseases and neurodegenerative diseases. Copyright:

INTRODUCTION

Cognitive decline is most common in elderly aged population, leading to dementia and Alzheimer's related problems. Loss of teeth in humans causes decreased neurodegenerative cognitive function, and many authors have shown that chewing efficiency is directly related to the number of teeth present in the oral cavity.[1] In the literature, it has been proved that mastication is closely related to cerebral cortex activity and also mastication tends to increase the cerebral blood flow leading to increased oxygen levels in the prefrontal and hippocampus area. Thus, reduced mastication brings about a decline in the cognitive capacity function. Therefore, in older adults to increase their chewing efficiency, replacement of missing teeth by oral rehabilitation is done.[2] Oral rehabilitation by dental prostheses directly aids in the simulation of the chewing-related cortices in the prefrontal and parietal sensorimotor areas enhancing the cognitive capacity of an individual and thereby decreasing the probabilities of dementia or Alzheimer's disease in an individual.[34]

Oral health-related quality of life (OHRQoL) is a subjective assessment of an individual. Adults with decreased cognitive functions, dementia, Alzheimer's disease, and Parkinson's disease tend to have a greater impact on their quality of life (QoL). Tooth loss affects the esthetics, and rehabilitation with dental prostheses is done which aids in the enhancement of OHRQoL.[56]

In the literature, no review has been done on the topic, so it was necessary to evaluate the review on this topic which is relevant in the current scenario. This systematic review aim is to analyze the literature data and consolidate the information regarding the impact of dental prostheses on the cognitive functioning in elderly individuals.

MATERIALS AND METHODS

This systematic review was conducted according to the PRISMA guidelines, and the research methodology was followed based on the Cochrane Handbook for Systematic Reviews of Interventions. The systematic review has been registered with PROSPERO (Registration number 210522). The review was conducted from January 2020 to July 2020.

Search strategy

The review included articles from the year 2000–2019. The initial electronic search was conducted by two investigators independently using the following search databases: MEDLINE (PubMed), Cochrane Library, Google Scholar, and EMBASE. The search was limited to English language using the search items/keywords: “dental prostheses and cognitive functioning,” “dental prostheses and brain function,” “teeth loss and cognitive loss,” “mastication and prefrontal activity,” and “prostheses on mental state.” In addition to the electronic search, hand search was also done by reviewing the references in the included studies. The search strategy was followed using the PICOS framework [Table 1].

Table 1

PICO framework

Focused question: Is there any effect of dental prostheses on cognitive functioning in elderly population?

Population: Human subjects-elderly population/old-aged adults both male and female

Intervention: The use of dental prostheses to replace missing teeth in elderly population, thereby enhancing the chewing effect and cognitive capacity

Comparison: Role of prostheses in influencing cognitive capacity with individuals receiving no prosthetic replacement for missing teeth and with individuals with prosthetic replacements

Outcome: Effect of dental prostheses on enhancing the cognitive functioning of elderly individual

Study design: Prospective/case-control/cross-sectional/longitudinal studies

Inclusion criteria

Studies including patient group >60 years

Studies following under criteria such as interventional studies, human studies, questionnaire studies, and cohort studies

Studies involving patients falling under completely and partially edentulous category in the study group

Studies showing a relation between dental prostheses (fixed or removable) and cognitive functioning

Studies published only in English language.

Exclusion criteria

Studies which do not clearly state the need of dental prostheses for better cognitive functioning

Studies where the selected patient groups are <60 years in their selection criteria.

Screening and selection of studies

The screening and selection of the articles was done by two reviewers independently. Both the reviewers thoroughly discussed the selection criteria. Then, according to the inclusion and exclusion criteria, the reviewers screened the titles of the published records through electronic and hand search. Initially, the abstracts of all the articles were analyzed, and from the abstracts, the full text of the articles was selected and reviewed. Disagreement with the selection of the articles was sorted out by discussion. Cohen's kappa coefficient was used as a measure of agreement between the reviewers. The kappa score was 0.80 suggesting good interobserver agreement.

Data extraction and quality assessment

Data extraction was done based on the inclusion criteria by two reviewers independently. The studies were classified according to study design and outcome variables. Double checking was done by the reviewers.

The risk of bias in the articles included in this review was assessed according to the study verification checklist of the “Cohort of the Critical Appraisal Skills Programme”[7] [Table 2].

Table 2

Risk assessment of bias in articles (Cohort of Critical Appraisal Skills Programme)

	1	2	3	4	5a	5b	6	7	8	Quality assessment
Seraj et al.	+	+	+	+	+	+	+	+	+	High
Fanny et al.	+	+	+	+	−	−	+	+	+	Moderate
Klotz et al.	+	+	+	+	+	+	+	+	+	High
Narita et al.	+	+	+	+	+	+	+	+	+	High
Kamya et al.	+	+	+	+	−	−	+	+	+	Moderate
Reibero et al.	+	+	+	+	+	+	+	+	+	High
Yoshikama et al.	+	+	+	+	+	+	+	+	+	High
Banu et al.	+	+	+	+	+	+	+	+	+	High
Cerutti et al.	+	+	+	+	+	+	+	+	+	High
Hosoi et al.	+	+	+	+	−	−	+	+	+	Moderate
Seungkok et al.	+	+	+	+	−	−		+	+	Moderate
Okamoto	+	+	+	+	+	+	+	+	+	High
Shoi et al.	+	+	+	+	−	−	+	+	+	Moderate
Onozuka et al.	+	+	+	+	+	+	+	+	+	High
Campos et al.	+	+	+	+	+	+	+	+	+	High

1. Did the study address a clearly focused issue? 2. Were the subjects recruited in an acceptable way? 3. Was the exposure accurately measured to minimize bias? 4. Was the outcome accurately measured to minimize bias? 5a. Have the authors identified all important confounding factors? 5b. Have they taken account of the confounding factors in the design and/or analysis? 6. Do you believe the results? 7. Can the results be applied to the local population? 8. Do the results of this study fit with other available evidence?

RESULTS

Selection criteria were based on the PRISMA statement flowchart [Figure 1]. A total of 19 studies were selected according to the selection criteria. Out of 19 studies, 15 studies were included and 4 studies were excluded from the review. For all the included studies, the data were tabulated with information about the type of study, year of publication, duration of study, number of patients, study groups, statistical method used, outcome, and inference. The data in the included studies were further tabulated according to various outcomes [Tables 3–6].

Figure 1

PRISMA flowchart

Table 3

Dentition and chewing ability on cognitive functioning

Study author/year	Type of study	Duration	Sample size (number of patients)	Groups	Statistical method used	Outcome (mean and SD)	Inference
Seraj et al., 2017	Casecontrol	Not mentioned	50 (male=25, female=25)	Two groups  Group 1: low scoring SMMSE (n=31)  Group 2: Control group (n=19)	Independent t-test and Chi-square test	Number of teeth  G1=6.2  G2=9.7 Chewing ability  G1=9.2  G2=10.3	Group with low SMMSE scores had fewer number and teeth and impaired chewing ability, leading to decreased cognitive function
Fanny et al., 2013	Casecontrol	Not mentioned	51 (male=7, female=45)	Two groups  Group 1: Patients with dementia (n=29)  Group 2: Control (n=22)	Student t-test and Mann-Whitney U-test	Number of teeth  G1=4.9±8.3  G2=6.5±8.8 Chewing ability  G1=2.2  G2=2.9 Cognitive ability  G1=5.0±0.9  G2=5.5±0.6	Chewing efficiency is associated with cognitive functioning independent of number of teeth

SD: Standard deviation, SMMSE: Standardized mini-mental state examination

Table 6

Mastication and cognitive functioning

Study author/year	Type of study	Sample size (number of patients)	Groups	Statistical method used	Outcome (mean and SD)	Inference
Kim et al., 2020	Longitudinal study	7029 subjects (2987 men and 4042 women)	Single	T-test Chi-square test	Average MMSE scores for the impaired group and the normal group were 17.77±0.11 and 27.99±0.29, respectively	Mastication plays an important role in preventing cognitive decline
Campos et al., 2006	Cross-sectional study	32 G1-Elderly aged G2-Healthy control	Two groups G1=16 G2=16	Nonpaired t-test and Pearson’s correlation with α=0.05	Compared to controls, mild AD patients had decreased MP (P<0.01) and MMSE (P=0.01) MP showed a moderate negative correlation with MMSE (r=−0.69)	Mild AD was associated with impaired chewing function

SD: Standard deviation, MMSE: Mini-mental state examination

DISCUSSION

A projection shows by 2050 in low and middle income countries one in five persons are expected to attain age greater than 60 years. In India, the number of elderly people is expected to rise drastically due to increased life expectancy caused by newer technologies in the medical field. By 2100, in India, the number of elderly people will increase by one elderly for every three working-age populations. Studies show that persons with dementia are expected to double by 2030, and these would be seen mostly in developing countries like India.[8]

Cross-sectional studies have revealed that nutrition plays a major role in dental health and the importance of dental health in influencing the cognitive functioning.[9] Masticatory function is known to have an impact on the cardiac activity, and there are evidences of increased sympathetic stimulation and rise in oxygen levels in the prefrontal cortex and hippocampus area during chewing. A study conducted by Seraj et al. concludes that there is increased cognitive capacity and memory retrieval in elderly people having good chewing efficiency.[10]

Conventional denture prostheses and implant-supported prostheses significantly increase nutritional status and oral health perception in elderly people, thereby increasing their cognitive capacity.[11]

Various outcomes discussed in the included studies have shown the importance of dental prostheses on cognitive capacity of the individual. In this systematic review, a total of 15 studies were evaluated. The 15 studies had various outcomes, and these were categorized according:

Mastication and cognitive function.

Dentition and chewing ability on cognitive functioning

Two studies evaluated the importance of number of dentition and chewing ability on the cognitive functioning. Seraj et al.[10] concluded in the study that people with low Mini-Mental State Examination (MMSE) scores had fewer number and teeth and impaired chewing ability, leading to decreased cognitive function. Fanny et al.[12] expressed the role of chewing efficiency in enhancing the cognitive functioning of the patient. The author concluded that the presence of limited teeth makes the surface area of the total occlusal table to be less, thus a reason for impaired chewing efficiency.

Prostheses and chewing ability on cognitive functioning

Five studies have shown in their research work about the importance of prostheses and chewing ability on cognitive functioning. Klotz et al.[4] suggested that tooth loss is directly related to a decline in chewing efficiency, and besides tooth loss, dementia also contributes to the impaired chewing efficiency. Narita et al.[13] concluded in the study that wearing partial denture leads to increased activation of dorsal prefrontal cortex and also an increased MmEEG activity. These results suggested that wearing partial denture prostheses stimulates the masticatory muscles and also helps in preventing the cognitive decline.

Kamiya et al.[1] have shown that there was no difference in chewing efficiency between elderly subjects and younger controls when wearing dental prostheses and prefrontal activity was also improved in elderly adults wearing prostheses. Ribeiro et al.[5] concluded that rehabilitation with removable prostheses improved their oral health QoL and also their mental assessment values, thus suggesting the importance of prostheses and chewing function on cognitive capacity of an individual. Yoshikawa et al.[14] suggest the role of dental prostheses in liquid swallowing. They concluded that subjects with prostheses had better ability in liquid swallowing and thus increasing their chewing efficiency.

Prostheses and Brain functioning

Banu et al.[15] have shown in the study the importance of prostheses over two implant-supported mandibular overdentures, and they have concluded that the mental state of the subjects was improved by the prostheses; this was due the functional activity of the prostheses rather than the mere existence of the implants without any function. Cerutti-Kopplin et al.[16] related the quality of denture to their function on improving the cognitive status of the individual. In the study, it was observed that masticatory ability was impaired in subjects with low functional assessment values of dentures, leading to decreased mental examination scores.

Hosoi et al.[17] reviewed the importance of brain function activity and denture treatment. The author conducted Electro Encephalo Gram measurements for the subjects, and it was concluded that brain function activation was increased after chewing in individuals wearing partial dentures, thus suggesting that occlusal contact area and occlusal force play an important role in brain function.

Ki et al.[2] highlighted the importance of dental implants in improving the cognitive function of patients. The author suggested that oral rehabilitation with dental implants with biosignal monitoring had a significant role in preventing the cognitive decline.

Okamoto[18] evaluated the effect of chewing on brain function with and without occlusal support on implant prostheses. The author concluded that the EEG and mandibular kinesiograph values increased among the impaired region group after gum chewing and also increased brain function when the total occlusal support area was increased. Shoi et al.[19] highlighted the importance of posterior tooth replacement on brain function. The author concluded that individuals with shortened dental arch had decreased brain activity (middle frontal gyrus) on chewing than the patients who were replaced with posterior tooth replacement.

Mastication and cognitive function

Campos et al.[20] concluded that mild Alzheimer's disease had decreased masticatory performance and low MMSE values. The results suggested that decreased masticatory performance leads to lower brain memory stimulation.

Kim et al.[21] evaluated the relationship between mastication and cognitive function. The author suggested that the use of dentures plays a significant role in enhancing the mastication and the increased masticatory performance aids in preventing the cognitive decline.

CONCLUSION

Factors such as number of teeth present, total surface area of the occlusal table, and the masticatory efficiency correlate with the effect on prefrontal activity, leading to enhance cognitive function. Data analyzed in this systematic review suggested that dental prostheses have a very significant role in preventing the cognitive impairment and act as a protective factor in enhancing the cognitive function in patients with dementia-related diseases and neurodegenerative diseases.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Table 4

Prostheses and brain function/cognitive function

Study author/year	Type of study	Sample size (number of patients)	Groups	Statistical method used	Outcome (mean and SD)	Inference
Banu et al., 2015	Prospective study	10	Single	Wilcoxon signed and Freidman test	MMSE values  Eden patients=17.84  Cd patients=18.30 Implant over denture=23.80	Highlights the significance of prostheses
Cerutti et al., 2015	Cross-sectional study	117	Single	Independent t-test ANOVA Pearson correlation	MMSE for the total sample was 23.1±4.4	Benefit of dentures on cognitive status
Toshia Hosoi et al., 2011	Prospective study	38	Two groups Cd-18 RPD-20	EEG data by ESA-pro dimension	Increased occlusal contact in both	Prostheses enhance the brain activity
Seungkok et al., 2019	Cross-sectional study	1115	Single	ANOVA Chi-square test	Natural teeth 9.50±6.42 Mean MMSE 24.93±3.55	Dental implants as tooth replacements play role in preserving cognitive function
Okamato et al., 2011	Prospective study	24	Single	Wilcoxon test	Brain function in the impaired region showed significant improvement after gum chewing (P≤0.005)	Occlusal support by the implant prostheses has the potential to enhance brain function
Shoi et al., 2014	Casecontrol	11	Two groups G1-with RPD G2-SDA	ANOVA	Chewing ability was significantly lower in subjects with SDA (P≤0.005)	SDA affects brain activity due to decreased masticatory function

SD: Standard deviation, MMSE: Mini-mental state examination, RPD: Removable partial denture, SDA: Sabouraud dextrose agar

Table 5

Prostheses and chewing ability on cognitive functioning

Study author/year	Type of study	Sample size (number of patients)	Groups	Statistical method used	Outcome (Mean and SD)	Inference
Klotz et al., 2019	Interventional longitudinal study	146	Single group	Bivariate analysis	Chewing patients=0.590±0.25 (mean and SD)	Chewing efficiency was influenced by dementia
Narita et al., 2009	Pilot interventional study	3	-	Paired t-test, Kolmogorov-Smirnov test Wilcoxon signed, Mann-Whitney test	Significant activity of dorsal prefrontal cortex in R/L hemisphere Increased Masseter muscles electro myography activity	Partial denture influences in both mastication and prefrontal cortex activation
Kamiya et al., 2016	Casecontrol study	24	Two groups  G1-Edentulous (12)  G2-Young healthy (12)	Paired t-test, Wilcoxon signed, ANOVA, Kruskal-Wallis	Masticatory force  G1=81±11.7  G2=98.5±24 Occlusal forcey  G1=638.7±127  G2=1200.7±642.3 Masticatory muscle EMG activity Wearing denture=834±161 Young adults=669.2±71.5	Intrinsic prefrontal activation during chewing with denture prevents prefrontal depression
Reibero et al., 2006	Observational study	34	Two groups  G1=Patients with partial denture  G2=Patients without partial denture	Paired t-test Wilcoxon signed test	Masticatory efficiency  G1 Before=7 ± 9.8 After=13.9±13.2  G2 Before=13.2±11.3 After=23.9±17.2	Oral rehabilitation with partial denture enhances OHRQoL and mental status
Yoshikawa et al., 2006	Cross-sectional	32	Two groups  G1=Edentulous 13  G2=Dentulous 19	Chi-square test ANOVA	Evaluation of swallowing Oral time  G1=0.99±0.33  G2=1.05±0.31 Pharyngeal time  G1=0.79±0.17 G2=0.70±0.11	Liquid swallowing function of edentulous people is less effective when dentures are not worn

SD: Standard deviation, MMSE: Mini-mental state examination, OHRQoL: Oral health-related quality of life