Masticatory Process

Eating replaces the body’s nutrients, thereby facilitating the maintenance of body composition. Mastication is the first step in this process and prepares the bolus of food for the alimentary tract. Yet the process of eating is more complex than the act of mastication. The process of converting the food into a bolus to be swallowed is associated with the release of molecules from the food that stimulates the olfactory and taste receptors, enhancing enjoyment of the food experience. This process is, however, highly dependent on a functioning dentition, which is an integral part of a healthy mouth, which in turn influences diet and nut rition. The presence of prostheses, or more simply the number and distribution of teeth, influences the ease of chewing and the pleasure derived from different foods. Older adults with fewer teeth than their younger counterparts rely on some form of dental prosthesis to aid mastication. These changes in dentition, in turn, are associated with masticatory efficiency and ability.¹ Nevertheless, patients can and do function well with a less-than-complete dentition. This is the concept of the “shortened dental arch” proposed in the early 1980s²: Dental resources preserve a dentition that provides adequate functional arrangement. This concept is a widely adopted treatment strategy.³ When there are fewer than 21 remaining teeth, however, there is an increasing reliance on removable prostheses,⁴ although masticatory efficiency with fewer teeth will be reduced even with a prosthesis.

Although teeth may not be a prerequisite for digestion, at least in the young,⁵ a reduced tooth number can make mastication more difficult and lead to the avoidance of specific foods that require rigorous chewing. As the tooth count decreases, patients are more likely to practice forms of food avoidance or dietary restriction. In particular they tend to avoid hard and tough foods that are diffcult to chew; this has been well described in patients with oral impairment.^6-8 An impaired dentition in geriatric patients also may render food digestion more complicated, because they may have reduced gastric secretion, intestinal mobility, and changes in absorption patterns. Such changes in food selection patterns can cause patients to favor more highly processed foods at the expense of harder, coarser, and more diffcult-tochew foods. This change in food selection also may lead to a dietary deficiency with regard to vitamins, minerals, fber, and proteins and may lead to calorific compensation of a diet higher in fats and cholesterol. Indeed, even edentulous health care professionals have been shown to eat fewer vegetables and less dietary fiber than those with 25 teeth or more.⁹ Some dietary changes have been directly associated with colon cancer, cardiovascular disease, and stroke. For example, it has been hypothesized that a reduction of I g of dietary fiber could result in a 4% increase in the risk of myocardial infarction, ¹⁰ and an elevation of I mmol/L of homocysteine (associated with low vitamins B₁₂, B₆, and folate) could lead to a 10% increase in card i ovascular disease.¹¹

Nutrient Intake and Dentition

Changes in the ability to eat food also are apparent in nutrition intake. Edentulous individuals living independently have been shown to have a lower nutrient intake compared with dentate adults.¹² Those with 21 or more teeth consumed more of most nutrients, especially the nonstarch polysaccharides (dietary fiber), while edentulous adults consumed less nonstarch polysaccharides, protein, calcium, nonheme iron, niacin, and vitamin C. It also was found that mean daily intake of nutrients and total caloric intake correspondingly increased with the number of teeth.¹³ In older patients, a greater number of occluding pairs of teeth was associated with higher consumption of intrinsic and milk sugars in addition to more nonstarch polysaccharides compared with dentate adults.^6,12 Nonstarch polysaccharide levels also have been shown to be lower in edentate adults than in dentate adults^9-14; these same levels are reduced in patients who have difficulty chewing.¹⁵ This is reflected in the Survey Europe on Nutrition in the Elderly: Concerted Action study, which investigated the dentition and dietary intake of the elderly in 12 European cities and the state of Connecticut in the United States. Edentulous patients were found to have more chewing difficulties; lower intakes of carbohydrates and vitamin B₆; and a trend toward reduced vitamins B₁ and C, fiber, calcium, and iron intake compared with dentate adults.¹⁶

Blood-derived values of key nutrients also appear to be influenced by oral health status. Data from the National Diet and Nutrition Survey (NDNS) conducted in elderly men and women from Great Britain showed that, even after controlling for confounding variables, plasma ascorbate and retinol were significantly associated with dental status. Furthermore, the relationship between ascorbate and tooth number was statistically significant. There also was a trend toward higher levels of most nutrients in dentate individuals. These findings are consistent with the results of the dietary intake of these populations.¹³

The effect of these findings perhaps is more clearly seen in the frail elderly. In a study reviewing the relationship between the oral and systemic health of institutionalized subjects, those with compromised oral function had both a significantly lower body mass index (BMI) and low serum albumin concentration.¹⁷ The presence of less than six occluding pairs of teeth was a strong predictor of malnutrition as determined by these parameters. A 6-year longitudinal study of the institutionalized elderly showed a greater decline in physical ability and higher mortality rates in edentulous subjects without dentures compared to patients with 20 or more teeth.¹⁸