Dietary Links to Oral Disease

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Summary

Root Caries: In the elderly, there is an increased prevalence of exposure of the tooth roots into the oral environment. The exposed cementum and dentin is susceptible to decay, with many factors contributing towards the etiology of decay in this group. There have been a large number of variables associated with the development of root caries from both prevalence and incidence studies. As would be expected, subjects with periodontal disease have an increased level of root caries, however, the attack rate is greater for those with untreated periodontal disease compared with subjects after periodontal care. This perhaps reflects better hygiene in these subjects (older individuals who demonstrate a good standard of oral hygiene have few root caries lesions).

Many studies have investigated risk factors for root caries and it can be difficult to separate the real risk factors from their co-variables. Chronological age is probably of little significance per se in determining root caries activity but increased biological age, with associated medical/physical deterioration and disability, may be of much greater importance. For example, high levels of root caries have been reported in chronically ill institutionalized older adults, drug addicts, and individuals with altered salivary function either as a result of disease or its treatment. There is also a strong relationship between past root caries experience and the development of new lesions and a weaker association between coronal decay experience and root caries. Higher prevalence rates are seen in men compared with women and there are a number of social attitudinal variables that are associated in both a positive and a negative manner with root caries. The numbers of remaining teeth and active social participation are both negative predictors for root caries. Negative life events, low educational attainment, low income, recurrent chronic illness, infrequent oral hygiene, irregular dental visits, and smoking are all positive predictors of the level of disease activity.

Caries requires sugar, plaque, and a suitable environment if it is to develop and root caries is no different. Epidemiological studies have shown that root caries is strongly related to the frequency of sugar intake and this is a key risk factor for root surface decay. Dentin has a higher pH for demineralization then enamel so reductions in pH that occur with sugar intake will be maintained below the demineralizing threshold for a longer period of time on a dentin surface. Poor or infrequent hygiene is also associated with an increased risk of disease while a number of studies have shown that wearing a partial denture may also be important. The oral stagnation that results from wearing a partial denture can more than double the risk of root decay being present.

Oral Mucosa:Nutritional deficiency states in older people may result in alterations in oral mucosal integrity exacerbating age-associated changes in the structure of this tissue. The micronutrients most commonly associated with mucosal pathology include iron, vitamin B12 and folate. In addition to their effects on oral mucosa, such deficiency is also associated with candida albicans infection both intraorally and at the angles of the mouth (angular chilitis). Such deficiency states are more prevalent in older population groups.

Oral Candidiasis:A superficial mycosis that can present in a variety of clinical forms. The presence of Candida alone is not an indication of an infection since the yeast can be found as a commensal organism in about 40% of the population. Candidiasis is essentially an infection that occurs in the unhealthy and reflects changes in host defense and susceptibility rather than increased pathogenicity of the organism. Oral candidiasis has been associated with a variety of predisposing factors and that include high carbohydrate diets and iron or folate deficiencies. Angular chilitis presents as an inflammatory fissuring and maceration at the commissures of the lips due to bacteria and fungi colonization. The usual constellation of factors that contributes to the condition involves loss of vertical dimension, xerostomia, and riboflavin deficiency. Denture stomatitis (papillary hyperplasia) is also associated with the presence of Candidiasis and impaired host resistance in denture wearers. The condition m ay take on a "warty" appearance like a bunch of grapes or it may take on a fiery red appearance with associated ulceration and burning pain.

Recurrent Aphthous Ulcers: Characterized by large size, long duration, and recurrence. Etiologies include altered immune response, allergic response and nutritional deficiencies (iron, B6, B12).

Atrophic Glossitis: Painful burning tongue characterized by inflammation and defoliation. The loss of filiform papillae produces a painful erythematous and granular appearing tongue and eventual complete atrophy of papillae produces a smooth/bald tongue. The condition has been associated with vitamin B1, B2, B6, B12, or folic acid deficiency.

Impact of Oral Health on Systemic Health
Recently, there have been a number of studies relating oral health to systemic health, notably to atherosclerotic disease (both stroke and myocardial infarction) and to pneumonias in debilitated subjects. The prime focus for these studies has been the role of periodontal pathogens and their associated circulating inflammatory markers in the initiation and progression of the formation of atherosclerotic plaques and subsequent disease. However, there is also a significant body of evidence that associates dietary imbalance with a variety of systemic illnesses. Thus, poor oral health may indirectly impact on systemic health through disturbances in nutritional intake.

Oral Health and Nutrition in Older People
Mastication and swallowing are the initial steps in the digestive process and we rely on efficient oral function to optimize their effectiveness. Oral function in older individuals is influenced by two key variables, the number of remaining natural teeth, or indeed whether someone has any remaining teeth, and the quantity and quality of saliva present in the mouth to facilitate bolus formation and lubricate swallowing. Both of these variables are altered in older adults. Older people tend to have fewer natural teeth and there are higher rates of edentulism with increasing age. The pattern of edentulism is changing with projected reduction in edentulism throughout the industrialized world over the next 20 – 30 years. Nevertheless, there are substantial numbers of older people who still rely on dentures for oral function. Even among those who are dentate, there are high proportions that need to use either partial dentures or possibly a full denture in one jaw opposed by some natural teeth. The oral function of this group of people is often little better than those who rely on full dentures. Oral health status does not influence our ability to digest a modern diet (at least in younger people) but it does exert an influence through variation in food choice to adapt the diet to something that an individual with impaired chewing can tolerate.

Impact of Oral Health Status on Nutrition
Food is taken into the mouth and chewing along with the incorporation of salivary enzymes is an important component of the initiation of digestion of foods. The breaking up of foods and their conversion into a bolus to be swallowed is associated with the release of "tasteants" from the food enhancing our enjoyment of the things we eat. Hence, it would be reasonable to assume that the health status of the mouth might influence diet and nutrition.

The number and distribution of teeth influence the ease of chewing, as does the functional capacity of complete or partial dentures. Chewing with conventionally retained dentures can be likened to an oral juggling act where the prostheses are controlled by the actions of the oral musculature and the forces of adhesion and cohesion holding them in place against the edentulous mucosa. Obviously the food itself will act as a profound destabilizing influence in this process as forces are applied eccentrically to the dentures unless the bolus can be manipulated such that chewing occurs simultaneously on the right and left sides. These effects are only made worse in someone with impaired salivary output in whom denture stability and tolerance will also be reduced. Ill fitting dentures and the potential for associated lesions and pain are of particular concern for those individuals suffering from dementia or other conditions that may prevent them from articulating the cause for difficulty chewing food. It is common to notice rapid weight loss in institutionalized elderly patients after placement of new dentures that are not monitored for comfort and functional efficiency. Most often, ill fitting dentures can be confirmed through the presence of lesions at the borders of the prosthesis. This can be in the form of tissue overgrowth (epulis fissuratum) or ulceration (denture ulcers).

Masticatory Efficiency
The ability to break down foods into discrete portions by chewing to permit swallowing is usually assessed by measuring the size of test food samples that have been chewed for a specific number of chewing cycles. The subject then spits out the test food which is analyzed using a sieving method or, more recently, using image analysis techniques to determine how finely the food has been broken down. This approach has consistently shown reduced chewing efficiency with lesser numbers of teeth, with teeth and removable partial dentures compared to a similar number of natural teeth, and with complete dentures compared to a natural dentition. Aging alone has little effect on chewing efficiency, although there is some suggestion in the literature of reduced oral motor function in older people, probably relating to altered muscle bulk.

Masticatory Efficiency and Digestion
In the 1950's Farrell demonstrated that the ability to chew does not influence our ability to digest food with a modern diet, although his experiments were undertaken in healthy young individuals rather than in older people where the alterations in the form and function of the GI tract would not have an effect. Unfortunately Farrell's work has not been repeated in an older population.

Masticatory Efficiency and Food Choice
While it may be the case that digestion per se is not influenced by mastication, there is compelling evidence that food choice is affected by our ability to chew. As masticatory efficiency is reduced, people report increasing difficulty chewing foods and people thus affected choose not to eat foods that are difficult to chew. This is of particular importance for those foods that could be regarded as more difficult to chew, for example stringy foods like beef or steak, crunchy foods like raw carrot and dry solid food like crusty bread. People become handicapped by their dentition and as a consequence suffer impaired intakes of fruit and vegetables and some key nutrients. One area of particular concern is the level of non-starch polysaccharide (dietary fiber) intake that is markedly reduced in older people compared with the RDA (for example an intake of 11 g/day in edentulous elders compared with an RDA of 25 g/day). These links are supported with evidence from a number of large cross-sectional and longitudinal studies from Europe and the US. The outcomes are independent of the effects of age, gender, regional variation within a country and socio-economic group, although there are marked differences between countries. There are some data that contradict these associations and explain the variations in diet seen in edentulous subjects as being linked to the lifestyle of the subjects (who tend to come from poorer socio-economic groups) rather than edentulism per se. These studies have tended to use generic measures of dietary intake (for example the Healthy Eating Index or the Mini Nutritional Assessment) rather than assessing specific dietary intake. Even within the group of papers using generic measures of nutritional status, some have shown associations between edentulism and poorer dietary quality. Such contradictions will occur in most aspects of medical epidemiology, those studies that demonstrate a link between edentulism and food choice also show a strong social class bias in patterns of foods consumption. Nevertheless, the impact of edentulism remains significant within those studies even when appropriate allowance is made for the social variation in food consumption.

These nutrient intake data are also supported by the outcomes of 2 large scale cross-sectional studies linking oral health status to biochemical analyte levels for key nutrients. In both studies (the National Diet and Nutrition Surveys in the UK and the National Health and Nutrition Examination Survey III in the US), there were significant reductions in key micronutrients (vitamin C and retinol in the NDNS and vitamin C, folate and ß carotene in the NHANES) in edentulous subjects compared with those who have natural teeth.

The impact of the effect of masticatory efficiency on food selection is likely to be compounded by food preparation. There would be an increased risk of fresh foods being over-prepared (for example removal of the skin from fruits and vegetables) or over-cooked by a person with reduced chewing efficiency in an effort to make their consumption practical. A wide range of nutrients are affected by these actions, including food constituents that are thought to be important in terms of prevention of cancer and cardiovascular disease (e.g., non-starch polysaccharides or dietary fiber) and for cellular defense and combating the effects of aging (e.g., the anti-oxidant micronutrient vitamins C and E). This is a particular problem for edentulous subjects without dentures and in debilitated individuals.

Dietary Fiber and Fruit/Vegetable Consumption
Reduction in dietary fiber and in fruit/vegetable consumption is associated with increased risk of cardiovascular disease. The mechanisms for this interaction have not been fully clarified. However, they probably relate both to the lipid-lowering capabilities of soluble fiber and the effects of anti-oxidants from the fruit and vegetables. Indeed, several studies have demonstrated elevated serum lipid levels in patients with severe periodontal disease and compromised dentitions. There are strong associations between increased fruit and vegetable intake and reducing risk of esophageal, gastric and colorectal cancer. In addition there are some data which link fruit and vegetable consumption to prostate, cervical, pancreatic and bladder malignancy, although the direct associations are not as clear.

Micronutrients
There are a large number of dietary components that form an essential part of the cellular mechanisms for defense against oxidative damage to DNA. These anti-oxidants include the trace elements selenium, zinc and manganese, vitamins A, C and E and other plant-derived derived micronutrients (e.g., ß-carotene, luteine, lycopene and plant flavenoids). The importance of these compounds in maintaining homeostasis is becoming increasingly apparent. Links have been demonstrated between Vitamin C, tissue breakdown, and cardio-vascular disease/stroke in the elderly. There is also evidence linking Vitamin C to cataract formation. Vitamin E and lycopene intake have additionally been linked to cardiovascular disease risk. It is widely recognized that a significant proportion of elderly people who are admitted to hospitals are suffering from nutritional deficiencies and that adequate nutrient intake is an important determinant of recovery from illness. An individual's ability to respond to nutritional advice will be moderated by their oral health status. For example, an edentulous subject who has had a stroke resulting in paresis of the facial musculature will have considerable difficulty chewing foods because their ability to juggle a complete denture in function will be impaired.

Solutions
The most obvious strategy would be to replace the missing nutrient(s) with some form of dietary supplement. However, intervention studies with micronutrient supplementation have been unsuccessful for reducing the risk of either cancer or of cardiovascular disease. The alternatives to supplementation would be to encourage a healthier dietary pattern in our patients. This could be undertaken by dentists during the instructions for use of complete dentures by challenging the patient to explore new foods with their replacement prosthesis. Dietary support and advice should also be given to patients being converted to edentulism for the first time since using complete dentures as a tool for chewing food is a challenge that will often be met by the blender unless positive support and advice is forthcoming from the dental team. Specific patterns of nutritional support may be required for edentulous subjects during their recovery from illness and professional dental help may be required to help such patients cope with poorly fitting dentures to maximize their functional efficiency.

Summary
There are profound and complex interactions between nutrition and oral health as well as oral health and nutrition. These have the potential to result in both increased oral disease and life-threatening systemic illness. Appropriate care strategies to cope with this issue have yet to be fully defined, but simple nutrient supplementation is unlikely to be effective on its own.

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