Dental News - Effects of professional oral care on oral infection in the elderly

Hidenobu Senpuku, Japan

Thu. 19. February 2009

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The population is ageing rapidly because of the prolonged life expectancy evident in most industrialised countries in the world. Accordingly, the number of bedridden elderly requiring systemic care in residential and nursing homes is increasing. Institutionalised, elderly individuals who need systemic care have poorer oral health than those who live independently at home.1–3 In particular, the oral hygiene of the bedridden elderly is often poor.6

Diminished oral health, in turn, may affect their quality of life.^4,5 Moreover, changes in microflora related to poor oral hygiene include an increase in the prevalence of bacteria, and may contribute to the development of pneumonia¹ as bacteria present in oropharyngeal flora are aspirated into the respiratory tract; therefore, their presence is a risk factor for the elderly and compromised hosts. As a reservoir for respiratory pathogens, dental plaque can be aspirated into the lungs and cause pneumonia.^7,8 Therefore, professional oral hygiene is considered important for controlling oral micro-organisms, including opportunistic pathogens on tooth and mucosal surfaces, and some studies have indicated that oral hygiene treatment of hospitalised elderly patients reduces the risk of nosocomial pneumonia.^5,9,10 Thus, professional oral care may be effective for reducing the numbers of dental and respiratory bacteria in elderly residents of long-term care facilities.

Tooth brushing, removing of dental calculus, and oral washing are useful cleaning procedures for decreasing oral microorganisms. However, it is important to note that following oral care treatment, oral micro-organisms are restored for a few hours and a certain amount are retained in the oral cavity. Healthy oral bacterial flora require a certain amount of oral commensal micro-organisms. Oral bacterial communities, known as biofilms, are characterised by species composition, surface or substratum composition, and the conditioning films that coat the surfaces on which they form.^11,12 The interactions between oral streptococci and other bacteria are potentially beneficial for one or more species present in the biofilm through aggregation.^13,14 Oral streptococci have been shown to compose between 60 per cent to 90 per cent of the supragingival plaque biomass in the first 24 hours of colonisation.^15,16 Oral streptococci are normal inhabitants of the human oral cavity, which play a role in resistance to colonisation by invading pathogens.^17,18 The presence of α-streptococci has been shown to have an inverse correlation with the presence of Pseudomonas aeruginosa and MRSA in the oral cavity.¹⁷ The growth of α-streptococci is associated inversely with the carriage of pathogenic bacterial species in the oral cavity.¹⁷ This indicates that humans required a certain amount of micro-organisms, to survive for the process of evolution in the oral cavity.

The use of anti-microbiological agents for oral hygiene

Dental caries and periodontal diseases are a large problem for the elderly, and are significantly associated with tooth loss.^19–21 Several species of bacteria, including Streptococcus mutans, Streptococcus sobrinus, Porphylomonas gingivalis, and Aggretibacter actinomycetemcomitans, are pathogens related to dental caries and periodontal disease in humans.^22–24 The prevention of these diseases requires the control of these pathogens, which exist in an oral biofilm known as dental plaque. The use of antimicrobial agents has been found to be helpful for the prevention of dental caries, periodontal diseases, and pneumonia. Chlorhexidine and povidone-iodine are potent antimicrobiological and chemical agents that reduce oral pathogens in the oral cavity. However, their clinical application is limited because they have a bitter taste and can stain teeth with frequent use. Moreover, they induce various adverse reactions, such as anaphylactic shock,^25,26 and may destroy the balance of normal and microbiological flora, including oral streptococci, which exist in high concentration in the elderly, because the agents have broad spectrum to anti-microbiological activity. Thus, it is important to use anti-microbiological agents that exhibit few or no side-effects and act on specific pathogens in the oral cavity.

Routine oral care in the institutionalised elderly

Regular and routine dental care may be effective in reducing the number of dental and respiratory bacteria in elderly residents of long-term care facilities. Although the effects of oral care have been reported, few studies have examined the bacterial differences of opportunistic pathogens in institutionalised, elderly subjects before and after receiving regular dental care provided by caregivers and dental hygienists. Kokubu et al. (in press) evaluated the effects of routine oral care on opportunistic pathogens at various points after admission to a nursing home.²⁷ Twenty-five elderly subjects living in a nursing home (mean age: 86.0 ± 10.4 years old) participated in the study. Caregivers and dental hygienists cleaned teeth, dentures, tongue, and mucosa after each meal using both routine and professional oral care techniques. Regular oral care was found to be effective in reducing infection by several species and strains of opportunistic pathogens on tooth surfaces and the oral environment without food residue over a long-term (six months; Fig. 1). Further, such care over a short term (one month) significantly reduced infection by opportunistic pathogens on mucosal surfaces in subjects without dentures, but not in those with dentures. The results indicate the importance of regular and routine oral care of hard and soft surfaces in the oral cavity for the prevention of fatal pneumonia and thus the improvement in quality of life in the institutionalised elderly.

Fig. 1: The effects of routine oral care on reduction of more than four kinds of species and strains of opportunistic pathogens. The proportions of elderly subjects with more than four species and strains of opportunistic pathogens detected on tooth, tongue, and/or oral mucosa surfaces at zero, one, four, and six months after entering the institution are shown. Asterisks denote significant differences in the chi-square test proportion of elderly subjects (P < 0.05, zero months versus one, four, or six months in each sample). Fig. 2: The number of MS in elderly subjects with and without oral mucosal care. Number of MS detected on tooth surfaces at zero, one, two, three, six, and 12 months after professional oral care with and without oral mucosal care are shown. The results are expressed as the mean ± standard deviations of the number (Log10/ml) of MS. Asterisks denote significant differences between zero month and other months in the Student’s t-test with the Bonferroni correction (one asterisk, P < 0.05).

Effects of oral mucosal care on oral microbiological infection

Professional oral care with mucosal care is an important practice for maintaining the oral health of the elderly.^5,28 However, little is known about how oral mucosal care controls oral pathogens in the oral cavity. In order to determine an optimum control strategy for oral pathogens, such as mutans streptococci (MS) and Candida spp., with which to maintain the oral health of the elderly, Nishiyama et al. (unpublished) examined the combined role of oral mucosal care and the physical effects of professional care, as well as the effects of mucosal care as a method of reducing MS and Candida spp. in the oral cavity during short and long care.²⁹ Fifty dependently living, institutionalised, elderly subjects (mean age: 76.1 ± 7.8 years) participated in the study. After treatment using professional oral care with or without mucosal care, a significant decrease in the number of MS was immediately shown after professional care with mucosal care and at one to 12 months in all samples, but not following professional care without mucosal care (Fig. 2). No significant difference in total streptococci and lactobacilli was found in any samples in groups with infection, and the ratio of MS to total streptococci was not significant. Inhibition of opportunistic infection with Candida spp. was also observed in cases where oral mucosal treatment was used. Thus, it can been deduced that mucosal care may be more effective in controlling the number of MS on the hard tissues, such as the tooth and tongue, and opportunistic pathogen infections, such as Candida spp., in the oral cavity following professional treatment. The data suggest that mucosal care is an important procedure for the prevention of dental caries and pneumonia.

Effects of systemic immunity on oral microbiological infection

It deteriorates not only systemic immunity, but also oral immunity because of the alternation of the oral environment, for example, a decrease in saliva volume and a change in saliva constituents. Alternation of the oral environment results in a lost of balance in commensal bacterial flora. Decreased immunity may result in infection by these micro-organisms, and because of this, surgical procedures are thought to increase the risk of infection. Individuals with either inherited or acquired immune deficiency are subject to an increased risk of dental disease.^30,31 Many of the protective immune responses of elderly people are impaired, which leads to an increased risk of oral bacterial infections.

Little is known about the interaction between the systemic and local immune response with regard to oral infections and oral diseases. Kamoda et al. (in press) conducted an epidemiological study of the independent elderly, to determine the relationship between activated natural killer (NK) cells and oral bacterial infections, such as dental caries and periodontal disease.³² Natural killer cells are instrumental in the innate immune response for the early production of interferon-gamma (IFN-γ) and other cytokines necessary for controlling bacterial, parasitic, and viral infections.^33,34 Reports show that products prepared from broth extracts of Gram-positive bacteria, such as streptococci, staphylococci, and lactobacilli, activate human NK cells.^35,36

One hundred independent elderly people aged 77 years old (53 males, 47 females) were examined. Blood samples were drawn and activated NK cells were evaluated using CD16, CD56, and CD69 monoclonal antibodies with flow cytometry. Human blood NK cells responsible for antibody-dependent, cell-mediated cytotoxity constitutively express CD56 antigen and CD16. In addition, NK cells express C-type lectin receptors, such as CD69, which is an early activation marker.³⁷ The majority of CD69+NK cells (CD16+CD56+) showed significant correlation with the isolation numbers of total streptococci (R = 0.409, P < 0.01; Fig. 3a), species numbers of opportunistic pathogens (R = –0.318, P < 0.01; Fig. 3b), numbers of decayed teeth (R = –0.223, P < 0.05), and the amount of bridge work (R = 0.219, P < 0.05). A high proportion of CD69+NK cells are associated with the incidence of dental caries, the number of opportunistic pathogens, and total streptococci in the oral cavity of the elderly. This suggests that determining the proportionate numbers of CD69+NK cells may be a useful indicator of oral infection in elderly subjects.

Figs. 3: The correlation between oral bacteria status and NK cells. Correlation rate (R) between CD69+NK cells and numbers of total streptococci (A) or species numbers of opportunistic pathogens (B) was analysed using the Pearson productmoment correlation coefficient.

Following daily professional oral care for a month, the activated CD69+NK cells were measured in the institutionalised elderly. The results showed that the proportion of activated CD69+NK cells was significantly elevated by the treatment in comparison with the primary data of activated CD69+NK cells (Fig. 4). Therefore, it can be deduced that regular professional oral care may stimulate systemic immunity in the institutionalised elderly. This may indirectly control infection by opportunistic pathogens and the balance of the microbiological community, as well as the physical removal of bacteria in the oral cavity. However, further studies are required to explain these mechanisms.

Effects of local immunity on oral pathogens following professional oral care

We examined the amino acid residues 361–386 of Streptococcus mutans surface protein antigen (PAc) and an important region associated with the interaction between S. mutans and salivary components.^38,39 The PAc(361–386) peptide has been shown to induce an antibody that inhibits the interactions of S. mutans with salivary components on tooth surfaces, which is considered important for the adherence of S. mutans to tooth surfaces. Low and high concentrations of the salivary IgA antibody (PPA) to the PAc(361–386) peptide were found to be positively and negatively correlated with the concentration of MS in saliva from human subjects, respectively. Therefore, salivary IgA is key to controlling oral pathogens. However, little is known about how salivary IgA controls MS colonisation and infection in the oral cavity or about the components present in saliva that are anti-microbiological agents. In order to determine the best dental caries prevention strategy for maintaining oral health of the elderly, we examined the combined role of the PPA during professional oral care and in the physical effects of professional care, as well as the effects of antibody function in reducing MS in the oral cavity during short- and long-term care.⁴⁰ Here we studied two groups of elderly patients with PPA present or absent in their saliva. Thirty-nine dependently living, institutionalised, elderly subjects (mean age: 75.9 ± 7.5 years) participated in the study.

Following professional oral care, the number of MS decreased significantly after six months in the saliva samples from the group without PPA in comparison with the primary data, whereas in the PPA detected group, a significant decrease in the number of MS was shown immediately after professional care of one month to 12 months in the saliva samples (Fig. 5). The measurement of PPA may be used for preventive instruction at chair side in a clinical office because it provides an effective evaluation of professional oral care to indicate elderly patients at risk of caries.

Fig. 4: The effects of professional oral care on CD69+NK cells. Amounts of CD69+NK cells in NK cells were detected in blood from elderly subjects (n = 8) after conventional oral care for a month, professional oral care for a month, and three months after professional oral care. The results are expressed as the mean ± standard deviations of the percentages of CD69+NK cells. Asterisks denote significant differences between control (primary data, one asterisk, P < 0.05) or data after conventional oral care (two asterisk, P < 0.05) and data after professional oral care in the Student’s t-test with the Bonferroni correction.

Conclusion

Healthy oral microflora are ensured by professional oral care with mucosal care, which may stimulate systemic immunological activity, promote local immunological activities to oral pathogens, and play a role in the physical removal of biofilm and micro-colonies formed by oral micro-organisms on teeth and tongue surfaces and mucosal epithelial cells attached to oral microorganisms. Systemic and local immunities with the support effects of professional treatment that removes biofilm may be more effective in controlling oral micro-organisms in the oral cavity than conventional care that does not completely remove the biofilm. Routine professional oral hygiene using safe anti-microbiological agents is necessary for a healthy environment in the oral cavity in the institutionalised elderly. The microflora, re-established by commensal bacteria, such as α-streptococci, after removing biofilm through routine professional treatment, provide a barrier to opportunistic pathogens. Therefore, routine professional oral care is considered to re-establish or sustain the healthy and non-pathogenic microflora in the oral cavity of elderly people.

Editorial note: A complete list of references is available from the publisher. This article was originally published in Dental Tribune Asia Pacific Vol. 6, No. 11, 2008.

Contact info

Dr Hidenobu Senpuku can be reached at hsenpuku@nih.go.jp.

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