Tooth loss and dementia: An oro-neural connection. A cross-sectional study.

BACKGROUND: Recent cross-sectional studies have suggested that chronic inflammation resulting due to gingival and periodontal diseases may have potential reversible risk factors for dementia. Recently, cognition, memory deficit, and along with the behavioral defect have been considered as characteristics of dementia. Age is one of the main factors which is also known to be associated with dementia. The aim of the present study was to establish the correlation between tooth loss and diagnosis of cognitive impairment/dementia in elderly patients.
MATERIALS AND METHODS: A cross-sectional study, comprising of 300 patients (Age: 50-80 years), was conducted. For the assessment of cognitive impairment/dementia, Mini-Mental Status Examination (MMSE) was conducted. All the results were analyzed using the Chi-square and Kruskal-Wallis ANOVA test.
RESULTS: Number of teeth was found to be directly associated with MMSE. Less number of teeth was associated with lower MMSE score, irrespective of gender. The level of statistical significance was found to be P < 0.001. Factors, such as socioeconomic status, school education, and marital status, were found to have a statistically significant impact on the dementia scale.
CONCLUSION: The current study found a significant association between tooth loss and cognitive impairment. Along with age factors such as socioeconomic status, education, and marital status were also found to have a direct or indirect impact on dementia. More prospective studies and clinical trials are required to be conducted to confirm the observations of this study.

INTRODUCTION

Dementia is a multi-etiologic syndrome and is a chronic or repeated disorder of subliminal processes caused by brain disease or injury that Leads to memory disorders, personality changes, and impaired reasoning. It can manifest in different ways, by affecting different parts of the brain.[1] Normally, it impedes the person's memory and propensity to frame out everyday tasks. Speech and the individual's concept of time and orientation capacity are other so-called cognitive capacities that are adversely affected. The symptoms make it difficult for people with dementia to cope with life without support from those close to them.[2] Among various etiologic factors, the oral infection might be one of the causes for dementia.[3]

Following much surveillance, it has been initiated that “the wreckage of sensory receptors encompassing the teeth is linked to some of the dying neurons.”[4] Following brushing and dental treatment procedures, oral microbes and lipopolysaccharide (LPS) get systemic access through bacteremia and ensuing immune responses may lead to nerve cell death and possibly memory loss.[45] Serum level of inflammatory markers is found to be very high in patients having periodontal diseases. Increased number of Porphyromonas gingivalis in the oral cavity of patients suffering from periodontitis have been found to be associated with cognitive impairment.[67]

Earlier studies have suggested a link between poor oral health and dementia.[135] Those studies found P. gingivalis in the brain, which may play a role in the brain topology in Alzheimer's disease (AD). Vascular dysfunction[8] and inflammation[9] play a pivotal role in the development of dementia in general and particularly in AD.[10] In AD, β-amyloid deposition exacerbates vascular damage leading to neurodegenerative process and cognitive decline.[9] The amyloid peptide invades and attacks the brain cells causing its death and parts of the brain shrink resulting in cognition impairment. Furthermore, there exists a relationship between systemic inflammation and periodontal pathogens.[10] Systemic LPS as a result of local periodontal infection and inflammation affect the passage of regulatory proteins through the blood–brain barrier which subsequently results in inflammation of the brain.[11]

Periodontal diseases are common oral infections affecting more than 50% of the Indian population which if left untreated is responsible for tooth loss in most of the cases.[12] Taking this background information into consideration, we hypothesize tooth loss as a proxy measurement of periodontitis and dementia. To address Mini-Mental Status Examination (MMSE) score differences in respect of number of teeth, subject school education, participant gender, household income, marital status, and patient participation in social groups, and MMSE score-specific analysis was performed.

MATERIALS AND METHODS

Design, site, and sample size

This cross-sectional study was conducted between March 2017 to November 2017. Following approval of the Institutional Ethical Committee, 300 patients (185 males and 115 females) with a positive history of dementia were recruited from the Neurology Department of Kalinga Institute of Medical Sciences, Bhubaneswar (Odisha, India). Recruitment was done after taking the informed written consent from the accompanying relative of each participant, and a detailed explanation of the study procedure was given.

Sample selection

All participants were selected from among patients reported to the outpatient Department of Neurology who were examined and assessed by a neurologist. Dentate patients with more than 50 years of age were kept as study participants. Patients with a history of brain strokes, brain injury, any periodontal therapy in the last 6 months, Parkinsonism disease, multiple sclerosis, epilepsy, schizophrenia, any depressive illness or personality disorder, and consumption of drugs of abuse were excluded from the study.

Cognitive status was assessed with the MMSE as reported earlier by Folstein et al.,[13] which included a set of simple questionnaire as follows: (1) orientation, (2) short memory tasks (repeating three words without delay), (3) arithmetic tasks, (4) language use and comprehension, and (5) basic executive and motor skills. After neurologic examination, cases were classified accordingly: Scores above 24 (out of 30), between 20 and 24, between 10 and 19, and below 10 were considered normal, mild dementia, moderate dementia, and severe dementia, respectively.

Entire oral examination and counting of the teeth (except wisdom teeth) were performed by a registered periodontist. The analysis was restricted to dentate participants only; however, the prevalence of edentulism could not be ignored because of two reasons as follows: (1) selection bias occurs on the basis of absence or presence of teeth and (2) among patients without edentulism, higher attachment loss is related with higher degree of periodontal disease. However, considering edentulism is the result of periodontitis, patients with high clinical attachment loss were considered periodontally healthier than edentulous patients. Considering the fact that these selection and information biases are common among patients with high proportions of edentulism, the tooth number was analyzed and recorded, but not periodontitis, to minimize these biases.

Measurement of confounders

Based on the available literature, putative confounders were selected.[11] Age, gender, school education (<10, 10, >10 years), diabetes mellitus, hypertension (≥140/90 mm of Hg), smoking status (current smoker, former smoker, or nonsmoker), and total alcohol consumption during past weekend were noted during case history recording after patient recruitment. Questionnaire was used to record marital status of the participants, number of children, socioeconomic status (lower class, lower middle class, middle class, upper middle class, and upper class),[14] and social relations of participants. Social relations were assessed by social network index (SNI)[15] of the questionnaire, given by Berkman and Syme and modified by John et al.[16] This index was based on the following components: (1) marital status of participants (married, unmarried), (2) number of close friends and relatives, (3) religious service attendance, and (4) participation in social groups. The SNI index was developed to measure the degree of social integration by assessing various types of social ties. Participants were categorized into four levels of social ties, ranging from low ties (Level 1-socially isolated) to high (Level 4-socially integrated). Participation in social groups was related with participation into any groups such as social or workgroup, self-help group or charity group, religious connected group, or senior center group.

Statistical analysis

All characteristics were recorded, tabulated, and analyzed after completion of the study. The Pearson Chi-square and Kruskal–Wallis ANOVA tests were employed to evaluate the data. In both tests, P values < 0.05 were considered statistically significant, and all the statistical calculations were performed through the Statistical Package for Social Sciences (SPSS) for Windows (SPSS-1999, SPSS Inc., New York, USA, version 10.0).

RESULTS

Dementia scale distribution in males and females was statistically significant [Table 1]. Statistically highly significant difference was found when the dementia scale was compared with SNI [Table 2], socioeconomic status of the participants [Table 3], and school education [Table 4]. Participants who were socially integrated (Level 3 and Level 4) were found with less grade of dementia [Table 2]. A decreased number of teeth was associated with a higher grade of dementia [Table 5]. Statistically highly significant difference (P < 0.001) was found when the dementia scale was compared with number of teeth present in participants. A higher proportion of edentulism was also associated with higher grade of dementia [Table 5].

Table 1

Dementia scale distribution in males and females

Crosstab
Count
Dementia scale	Sex		Total
	Male	Female
Dementia scale
Severe dementia	29	17	46
Moderate dementia	94	77	171
Mild dementia	41	19	60
Normal	21	2	23
Total	185	115	300
Pearson χ2	12.955
P	0.005*

P (<0.05) significant; *significant

Table 2

Dementia scale and social network index

Dementia scale	SNI				Total
	Level 4	Level 3	Level 2	Level 1
Severe dementia, n (%)	0 (0.00)	0 (0.00)	0 (0.00)	1 (100.00)	1 (100.00)
Moderate dementia, n (%)	4 (8.70)	2 (4.30)	23 (50.00)	17 (37.00)	46 (100.00)
Mild dementia, n (%)	3 (1.62)	16 (8.55)	78 (41.71)	90 (48.12)	187 (100.00)
Normal, n (%)	0 (0.00)	11 (16.66)	14 (21.22)	41 (62.12)	66 (100.00)
Total, n (%)	7 (2.33)	29 (9.67)	115 (38.33)	149 (49.67)	300 (100.00)
Pearson χ2	38.750
P	0.001**

P (< 0.05) significant; **Highly significant; SNI – Social network index

Table 3

Dementia scale and socioeconomic status

Crosstab
Count
Dementia scale	Socioeconomic status					Total
	Lower class	Lower middle class	Middle class	Upper middle class	Upper class
Severe dementia	14	13	7	12	0	46
Moderate dementia	6	8	22	74	60	170
Mild dementia	1	3	2	12	42	60
Normal	3	1	2	0	18	23
Total	24	25	33	98	120	300
Pearson χ2	126.670
P	<0.001**

P (< 0.05) significant; **Highly significant

Table 4

Dementia scale and school education

Dementia scale	School education					Total
	<10 years	10 years	>10 years	Illiterate	10
Severe dementia	24	8	4	9	1	46
Moderate dementia	35	49	80	7	0	171
Mild dementia	5	15	38	2	0	60
Normal	2	7	14	0	0	23
Total	66	79	136	18	1	300
χ2	70.067
P	<0.001**

P (< 0.05) significant; **Highly significant

Table 5

Relation between the number of teeth and dementia scale

Variable	Dementia status				P
	Severe (n=46)	Moderate (n=171)	Mild (n=60)	Normal (n=23)
Number of teeth present	13.95±8.44	22.67±5.89	24.33±5.67	26.21±4.4	<0.001**
Proportion of edentulism	25.21±31.47	12.53±11.42	11.49±4.67	11.77±6.09	0.008

P (< 0.05) significant; **Highly significant; n – Number of cases

DISCUSSION

The current cross-sectional study established a significant association between tooth loss and cognitive impairment. Other parameters, such as household income of the participants, school education, SNI, and number of teeth present, were also found to be associated with cognitive impairment when compared with the dementia scale. The current study reveals that tooth loss may be either due to less school education for which participants were unaware about the importance of maintaining healthy oral hygiene or also may be due to stress-related problems as a result of modern lifestyle where people are less bothered about their oral hygiene which may lead to unhealthy oral cavity producing plaque deposition, gingival bleeding which subsequently leads to periodontitis. The result of our study was in accordance with the findings of Okamoto and et al.,[4] Grabe et al.,[11] and John et al.[16] where they found an association between periodontitis and tooth loss with the cognitive impairment in various case–control and cross-sectional studies. Consideration of number of tooth loss as a proxy of periodontal disease makes the present study different from the others.

Dental caries is one of the common reasons behind tooth loss during childhood and young adults, while periodontal diseases are considered the most common cause of tooth loss during middle-aged and in elderly patients. It has been estimated that periodontitis is responsible for 50% of all extraction in participants >40 years of age.[17] Participants where tooth loss happened because of the subsequent result of periodontal diseases, systemic damage may persist on slow progressing periodontal diseases even after the removal of clinical features of periodontal diseases. There is a very clear association found between tooth loss with a history of periodontal diseases and systemic inflammatory diseases.[11]

In various studies, low socioeconomic status which is related to education and social class regarding occupation or income has shown a significant association with cognitive impairment.[18] This is in accordance with our study result. In the present study, poor social network has been found with high grade of dementia. This finding is in accordance with the results of Fratiglioni et al.[19] and Ertel et al.[20] where they found that an extensive social network seems to keep secure from dementia. The association between tooth loss and cognitive impairment can also be explained considering the fact that dementia patients are very prone to develop poor oral health due to impaired possibilities of oral hygiene maintenance and irregular dental visits for oral prophylaxis.[21]

The clinical significance of our study is that as we know periodontitis is curable,[22] it is still highly prevalent and leaves 20%–30% of adult population at high risk of chronic inflammatory action. Since more teeth are saved from caries and because life expectancy has been extended, more teeth will be at high risk of periodontitis.[23] The treatment of periodontitis and retention of teeth could alleviate cognitive impairment.[17]

In the present study, tooth loss assessment was done cross-sectionally; hence, the exact cause of tooth loss remains unanswered in the current study. This was the limitation of the study. However, additional follow-up studies and clinical trials are required to confirm the observations of the present study. At the same time, special attention is to be given to those patients at risk for cognitive impairment, with regular dental follow-up and various preventive measures to prevent periodontitis should also be provided.

CONCLUSION

Periodontitis is the primary cause of tooth loss in adults above the age of 50 years. In the present study, we came across that participants diagnosed with severe dementia had tooth loss which reflects periodontal history. Within the limitation of the present study, periodontitis appears to be associated with cognitive impairment/dementia.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.