The chemosensory functions of taste and smell play a vital role in human physiology. They determine the fla- vor and palatability of foods and beverages, the selec-

The chemosensory functions of taste and smell play a vital role in human physiology. They determine the flavor and palatability of foods and beverages, the selection of nutrients essential for life, and the warning of fire, toxic vapors, and spoiled foodstuffs. The hedonic role of chemosensation is experienced daily by everyone. Alterations in these pleasurable sensations have serious implications for the preservation of oral and systemic health, with dramatic effects on quality of life. Chemosensory disorders can be caused by a variety of oral conditions, upper respiratory tract problems, peripheral or central nervous system (CNS) pathologies, systemic complications, and other factors (aging, circadian variations, menses, and pregnancy). Many patients initially complain to their dentist of altered taste or smell. Unfortunately, it is difficult to diagnose many chemosensory disorders, and occasionally no effective treatment can be found. However, oral health practitioners can assess smell and taste function, identify and treat disorders with orofacial causes, and refer patients to other medical providers when appropriate. When eating, smell is first perceived through the nasal passages before food is placed into the mouth. Taste is then perceived when food comes in contact with taste receptors located throughout the mouth. A second smell perception occurs retronasally via the nasopharynx as the food bolus is chewed and swallowed. Trigeminal stimulation (pain, tactile, temperature) contributes to flavor perception throughout the eating process. Smell and taste disorders are common in the general population, although accurate epidemiologic information is lacking. In the 1970s, the consensus was that more than 2 million adults in the United States had a disorder of taste or smell. A large nonrandom survey conducted by the National Geographic Society in 1987 found that 1% of their 1.2 million respondents could not smell three or more of six odorants using a “scratch and sniff” test. A 1994 National Health Interview Survey given to 42,000 randomly selected households reported adjusted national estimates of a prevalence of 2.7 million (1.4%) adults with an olfactory problem and 1.1 million (0.6%) adults with a gustatory problem. When smell or taste problems were combined, 3.2 million (1.65%) adults indicated a chronic chemosensory problem. The prevalence rates increased exponentially with age, with nearly 40% of all problems (1.5 million) existing in adults aged 65 years or older. Before considering disorders of these special senses in detail, it would be advisable to define the terminology in this field of oral medicine. Smell is the perception of odor by the nose, whereas taste is the perception of salty, sweet, sour, or bitter by the tongue. Flavor is the combination of taste, smell, and trigeminal sensation. Halitosis is defined as bad breath, and can contribute to taste and smell changes. Alterations in taste and smell are defined with relative and absolute terms (Table 27–1). Oral sources of altered taste function are common and can be evaluated by a dentist. Trauma (burns, lacerations, local anesthesia, surgery, reflux), local antiplaque medicaments and drugs excreted into saliva, infections (periodontal, dentoalveolar, soft tissue), vesiculobullous conditions, removable prostheses, metallic dental restorations, and salivary dysfunction can directly or indirectly affect taste function. Oral Molecular and pathophysiologic