Nutrition and Oral Medicine (Nutrition and Health)

32 Part I / Nutrition and HealthHalf of all Americans aged 55 and older wore a partial or complete denture, whereas 60%of denture wearers reported one or more problems with their dentures (6).2.1. Masticatory AbilityResearch consistently has demonstrated that reduced chewing efficiency is associatedwith decreasing numbers of teeth, removable partial dentures as compared with a similarnumber of natural teeth, and complete dentures as compared with natural dentition (7). Theposition of natural teeth, the number of pairs of opposing tooth surfaces, and their functionare thought to be more accurate indicators of masticatory ability than the total number ofteeth in the mouth (8). Aging itself has little effect on chewing efficiency, but the reducedmuscle mass associated with aging may cause reduced oral motor function (9,10).2.1.1. NUMBER OF TEETHChanges in dentition can have a profound impact on eating, although perceived chewingefficiency with dental prostheses may be a more likely determinant of food acceptancethan measured function (11).Compiled evidence from the 1950s to the 2000s indicated that tooth loss affectsobjective measures of masticatory performance. Early studies implied a significantdecrease of masticatory efficiency in 75% of complete denture wearers compared todentate subjects. Later research indicated that losses in masticatory efficiency becauseof tooth loss were closer to 30 to 40%. However, the data suffer from differences inresearch methods, test food choices, and test populations (12).Masticatory ability is more a function of dentition status than of age (12). The BostonVeterans’ Administration Dental Longitudinal Study showed that dentate status was theprimary determinant of masticatory ability. The number of existing teeth affects masticatoryperformance and food selection (11,13–16). The presence of removable denturesand the possession of fewer than 20 teeth are both linked to reduced chewing ability.Chewing longer and swallowing larger food particles compensates for reduced chewingability (17). As adults age, they tend to increase the number of chewing strokes and chewlonger to prepare food for swallowing (15). Masticatory efficiency in wearers of a completedenture has been found to be approx 80% lower than in people with intact naturaldentition (18).The degree of dental impairment also determines chewing performance. When objectivemeasures of chewing ability were assessed, individuals with intact dentitions chewedthe best, followed in descending order by those with partially compromised dentitions(24–29 teeth) or compromised dentitions (20–26 teeth). People with one or two fulldentures had the poorest chewing performance (18).The Swallowing Threshold Test Index, an objective measure of chewing ability,assesses the number of chewing strokes required to reduce a hard food such as a rawcarrot to a small enough particle size for swallowing and is used as a gold standard. Whenfunctional feeding skills were measured in 79 healthy adults aged 60–97 yr, these skillswere not age dependent but were dependent on whether subjects wore full dentures (19).2.1.2. FUNCTIONAL TOOTH UNITSWhen Hatch et al. (20) tested a multivariate model of masticatory performance fordentate subjects, the number of functional tooth units and bite force were confirmed as