Effects of pharmacologic reductions in salivary flow on taste thresholds in man

Salivary buffering capacity is correlated with umami but not sour taste sensitivity in healthy adult Japanese subjects

OBJECTIVE

Saliva serves multiple important functions crucial for maintaining a healthy oral and systemic environment. Among them, the pH buffering effect, which is primarily mediated by bicarbonate ions, helps maintain oral homeostasis by neutralizing acidity from ingested foods. Therefore, higher buffering capacity, reflecting the ability to neutralize oral acidity, may influence taste sensitivity, especially for sour taste since it involves sensing H+ ions. This study aims to explore the relationship between salivary buffering capacity and taste sensitivities to the five basic tastes in healthy adult humans.

DESIGN

Eighty seven healthy adult students participated in this study. Resting saliva volume was measured using the spitting method. The liquid colorimetric test was used to assess salivary buffering capacity. The whole-mouth taste testing method was employed to determine the recognition threshold for each tastant (NaCl, sucrose, citric acid, quinine-HCl, monosodium glutamate).

RESULTS

Taste recognition thresholds for sour taste as well as sweet, salty, and bitter tastes showed no correlation with salivary buffering capacity. Interestingly, a negative relationship was observed between recognition threshold for umami taste and salivary buffering capacity. Furthermore, a positive correlation between salivary buffering capacity and resting saliva volume was observed.

CONCLUSIONS

Salivary buffering capacity primarily influences sensitivity to umami taste, but not sour and other tastes.

Neurolocalization of taste disorders

Neurolocalization of taste disorders requires a knowledge of the functional anatomy involved in mediating taste information from the peripheral mucosal surfaces through numerous peripheral cranial nerves to complex subcortical and cortical brain regions. Our understanding of this functional anatomy has advanced in recent years. Taste is an experience that is both innate and learned, and the "taste" experience involves the integration of information from other sensory modalities, such as olfaction and somatosensation. Normal taste perception is influenced by different neurophysiologic states, which involve endocrine function, emotions, and even attitudes and expectations toward eating. At its core, the normal effective ability to taste is a reflection of the proper function of many organ systems within the body and may be considered a marker for good health. Clinical taste disorders, on the other hand, involve the dysfunction of the normal neural taste pathways and/or aberrant influences on multisensory integration and cortical taste processing. The number of disease processes, which can adversely affect taste, are numerous and quite varied in their presentation. There may be contributory involvement of other organ systems within the body, and the appropriate management of taste disorders often requires a multidisciplinary approach to fully understand the disorder. Depending on the underlying cause, taste disorders can be effectively managed when identified. Treatments may include correcting underlying metabolic disturbances, eliminating infections, changing offending medications, replenishing nutritional deficiencies, operating on structural impairments, calming autoimmune processes, and even stabilizing electrochemical interactions.

Taste Loss and Recovery Following Radiation Therapy

Previous investigators have reported deficits in taste acuity in patients following radiation therapy for oropharyngeal cancer. In the present longitudinal study, 13 patients (mean age = 51.6 yrs) received conventional or hyperfractionated radiotherapy (63–76.8 Gy) for primary tumors of the oropharynx. One or both parotid glands and at least two-thirds of the tongue were included in the radiation field. Smell recognition and taste detection thresholds were determined at baseline, 1 month, 6 months, and 1 year post-radiation. Differences for smell recognition and the 4 taste qualities were assessed (independently) at the 4 time intervals, with a one-way ANOVA. Smell recognition was unaffected by radiation. There were significant elevations in thresholds for sweet (p < 0.005), salty (p < 0.005), bitter (p < 0.005), and sour (p< 0.001) during radiation therapy that were restored to baseline levels at 6 months and 1 year after radiation. This study demonstrated that radiation-induced taste deficits can be recovered by 6 months.

Management of a post-radiotherapy xerostomic patient--a case report

OBJECTIVE

The objective of the study was to fabricate complete denture with palatal reservoir filled with artificial saliva for a post radiotherapy edentulous patient.

BACKGROUND

Xerostomia is a subjective complaint rather than a disease. It is caused by irradiation, medication, Sjogren's syndrome & neurological factors such as stress. Radiotherapeutic treatment of head and neck cancer patients often causes long term dysfunction involving their salivary function, swallowing capabilities & taste. All three of these domains are affected by radiation- induced damage to the salivary glands. This in turn results in poor retention of complete denture, frequent trauma to alveolar ridge & other oral infections. All these events drastically affects quality of life of ageing patients.

MATERIAL AND METHOD

A complete denture in heat cure acrylic resin was fabricated in which a palatal reservoir was made on the palatal side.

RESULTS

Problems arising due to xerostomia were reduced to a great extent.

CONCLUSION

Prosthodontic management of Xerostomic patient include several techniques. This paper presents a case report of post radiotherapy edentulous patient in which complete denture with palatal reservoir filled with artificial saliva was fabricated.

Relationships of beta-blockers and anxiolytics intake and salivary secretion, masticatory performance and taste perception

OBJECTIVE

Assess the influence of salivary flow on physiological parameters of the stomatognathic system in patients who take beta-blockers or anxiolytic medications.

DESIGN

Sixty patients were divided into three groups based on the following criteria: Group 1, control (n=20; no use of medication); Group 2, use of antihypertensive beta-blockers (n=20); and Group 3, use of benzodiazepine anxiolytics (n=20). Salivary flow was assessed by determining stimulated and non-stimulated flow/minute. The quantification of the sense of taste was determined on a visual analogue scale (VAS) using solutions of 0.9% NaCl (salty), 50% sucrose (sweet), 20% unsweetened coffee (bitter) and 4.2% vinegar (sour). The DMFT index (number of decayed/missing/filled teeth) was determined by a calibrated examination, following the criteria of the World Health Organization (WHO). Masticatory performance was assessed with an Optosil comminution test and Rosim-Ramler equation.

RESULTS

The results did not reveal a significant correlation between salivary flow and masticatory performance (p>0.05). We observed significant decreased non-stimulated salivary flow for Group 2 (p=0.05) when compared to controls. However, taste perception was not influenced by salivary secretion amongst groups. Furthermore, we observed a significant negative correlation between non-stimulated salivary flow and DMFT in Group 1 (p=0.02; r=-0.52).

CONCLUSIONS

Patients under beta-blockers therapy presented reduced non-stimulated salivary flow when compared to controls, without influencing the sense of taste or masticatory performance. The use of anxiolytics did not affect salivary flow and taste perception in the studied sample.

Influence of oral characteristics and food products on masticatory function

Mastication is a complex process that involves activities of the facial muscles, the elevator and suprahyoidal muscles, and the tongue. These activities result in patterns of rhythmic mandibular movements, food manipulation, and the crushing of food between the teeth. Saliva facilitates mastication by moistening food particles, making a bolus, and assisting swallowing, whereas food consistency modifies masticatory forces, the mandibular jaw movements, the duration of the mastication cycle, and the number of cycles preceding the first swallow. Jaw elevator EMG activity research shows a clear relation between muscular activity and food properties. The teeth, masticatory muscles, and temporomandibular joints are also important because together they form the mechanism by which the food particles are fragmented. Hard and dry foods require more chewing cycles and a longer time in the mouth until swallowing for sufficient breakdown to take place and for enough saliva to be added to form a coherent bolus safe enough for swallowing. Product characteristics, the amount of saliva, dentition, and bite force affect the chewing performance. This study presents an update and synopsis of the effects of saliva, food, dentition, muscle force, and temporomandibular disorders on the masticatory process.

Taste preference and acceptance in thirsty and rehydrated [correction of dehydrated] rats

Experiments were designed to determine whether water deprivation affects taste preferences and/or taste acceptance. In experiment 1, both five- and two-bottle preference tests were performed in normally hydrated rats to permit the selection of five groups of rats showing the same taste preference for one of four prototypical tastes. Subsequently, in the same groups of rats, taste preferences were determined by a two-bottle test (experiment 2), and taste acceptance by a one-bottle test (experiment 3), following 12, 24, 36, and 48 h of water deprivation. After both 12 and 24 h of dehydration, during the first 10 min of the tests of experiment 2, all rats ingested greater volumes of either NaCl or sucrose solution than water, but more water than either HCl or quinine solution, and the differences were very significant (P<.0001). After 36 or 48 h of dehydration, the differences became very small and, in some cases, the P-values were at the lowest or borderline level of the significance, suggesting that dehydrated rats poorly discriminate the nature of the fluid drunk. During the 11-60 min interval, all rats preferred either sucrose or NaCl to water, but water to either HCl or quinine. Experiment 3 was performed to ascertain whether the need for fluid might overcome the palatability of solutions. All rats, dehydrated for 36 or 48 h, after 10 min of exposure, drank equal amounts of fluid, independent of its palatability. During the 11-20 and 21-60 min interval, the fluid intake of rats changed in accordance with the palatability of the solution available. In conclusion, severe thirst in rats may override the palatability of the solutions, and the thirst drive may be so strong that they do not reject fluids because body fluid balance would be severely compromised.

The influence of aging on oral health and consequences for taste and smell

Oral diseases that are commonly seen in older adults can impair chemosensory function. Many stomatological conditions are preventable and treatable, yet unmanaged, they can cause significant morbidity and a diminished quality of life. Importantly, many oral diseases are not necessarily an inevitable consequence of growing old, and are frequently attributed to systemic diseases and their treatment. Although gustation may undergo mild age-related decrements, olfaction declines dramatically with greater age. The oral-facial region is intimately involved in the sensations of taste and smell, and diseases affecting this region in an older person could adversely affect an already compromised chemosensory system. Older adults with impaired taste and/or smell should be thoroughly evaluated for oral and pharyngeal diseases. It is reasonable to expect that a healthy adult can grow older with good oral health and function, and can continue to experience the hedonic pleasures of taste and smell associated with eating and drinking.

Effects of extracellular pH, PCO2, and HCO3- on intracellular pH in isolated rat taste buds

We studied the effects of changing external pH (pHo), external bicarbonate concentration ([HCO3-]o), and PCO2 on taste receptor cell (TRC) intracellular pH (pHi) in taste bud fragments (TBFs) isolated from rat circumvallate and fungiform papillae with the pH-sensitive fluoroprobe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) using microfluorometric and imaging techniques. In N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solutions, TRC pHi responded rapidly and monotonically to changes in pHo between 6.5 and 8.0. The relationship between pHi and pHo was steep, with slopes varying between 0.8 and 1.2. Similarly, varying pHo by changing PCO2 at constant [HCO3-]o or changing [HCO3-]o at constant PCO2 led to rapid, monotonic changes in pHi. The relationship between pHi and pHo was once again steep, with slopes varying between 0.8 and 1.2. However, simultaneous changes in PCO2 and [HCO3-]o at constant pHo did not cause any significant changes in steady-state pHi. In imaging studies, single, isolated TRCs responded to changes in pHo, with parallel changes in pHi in the soma and apical process. In addition, changes in pHo induced parallel changes in pHi throughout TBFs. These data suggest that the steady-state TRC pHi is a function of pHo. Changes in TRC pHi may be involved in acid sensing, and salivary [HCO3-] may play a role in the maintainance of steady-state TRC pHi and in the neutralization of acid-induced changes in pHi.

Physiologic responses to sensory stimulation by food: nutritional implications

The importance of sensory factors (both the sensory properties of foods and sensory abilities of consumers) in food selection is widely accepted. Less recognized and understood are the effects of sensory stimulation on physiologic processes. Mere exposure to the sight, smell, taste, and textural attributes of foods elicits myriad digestive, endocrinologic, thermogenic. cardiovascular, and renal responses. The responses are rapid (generally occurring within minutes of sensory stimulation), small (relative to the magnitude achieved when food is actually being metabolized), and transient (returning to near-baseline levels within minutes). Nevertheless, they have been hypothesized to prime the body to better absorb and use ingested nutrients. They are termed preabsorptive or cephalic phase responses. This review summarizes current knowledge of stimuli that trigger cephalic phase responses and selected response features (eg, magnitude and type of enzymes or hormones released). Mechanisms by which cephalic phase responses may influence nutrient absorption and use are proposed. Current knowledge of the behavioral and physiologic importance of cephalic phase responses is limited, thereby hampering development of dietary recommendations for preventive or therapeutic interventions. Further study of several identified promising areas of application and other easily proposed situations may provide a basis for expanded medical nutrition therapy.

A pilot study comparing three salivary collection methods in an adult population with salivary gland hypofunction

The purpose of this pilot study was to compare the reliability of three collection methods (draining, chewing of gum base, and the Saxon test) for whole saliva using a sample of middle-aged and older ambulatory adults (n = 18) with proven salivary gland hypofunction. The results demonstrated high reliability (r values ranging from 0.91 to 0.80, p < 0.001) for all three methods. MANOVA analysis revealed significant (p < 0.001) differences in flow rates among the draining, chewing-stimulated, and Saxon methods.

Effects of hyposalivatory medications on saliva flow rates and dental caries in adults aged 65 and older

Institutionalized adults aged 65 or older often receive medications that have been associated with decreased saliva flow. Flow rates depressed by hyposalivatory medications are thought to increase susceptibility to dental caries. In this study, a cross-sectional comparison was made of stimulated whole saliva rates and coronal and root caries prevalence in a group of older adults, in a long-term care facility, taking hyposalivatory medications vs. a control group. No significant differences were found between the two groups in masticatory or gustatory stimulated flow rates or in mean decayed coronal or root surfaces.

Effects of age and removable artificial dentition on taste

Sodium chloride and sucrose gustatory recognition thresholds, suprathreshold taste intensity function, and sucrose suprathreshold taste preference in healthy adult males with removable artificial dentition were compared with persons having natural dentition. In addition, several inorganic salivary constituents were evaluated for their possible relationship with these modalities. The 75 participants studied were divided into two age and two dentition groups: less than 65 years versus 65 years and older; and natural dentition only versus either removable partial dentures or complete artificial dentition. Recognition threshold and suprathreshold psychophysical functions were assessed using aqueous solutions of sodium chloride and sucrose. Suprathreshold hedonic judgments were also determined for sucrose. Samples of stimulated parotid saliva were analyzed for sodium, potassium, and bicarbonate. As age increased, a statistically significant decrease was noted in the exponent of the psychophysical function for sodium chloride. A similar, but nonsignificant, trend was observed for sucrose, which was complicated by an interaction between age and dentition status. For sodium chloride, recognition thresholds tended to be higher for older persons with removable partial and complete dentures. However, no statistically significant effect was observed on the sucrose threshold or hedonic response as a result of dentition status. Analysis of several parotid saliva constituents showed no statistically significant effect caused by age or dentition status and correlations noted among the psychophysical measures appeared to be fortuitous.

Interaction of saliva and taste

In spite of the coexistence of saliva and taste in the oral cavity, an understanding of their interactions is still incomplete. Saliva has modulating effects on sour, salt, and the monosodium-glutamate-induced savory or umami taste. It has a diminishing effect on sour taste as a result of the buffering by salivary bicarbonate. It probably also contributes to the umami taste with endogenous salivary glutamate levels. Salt taste is detected only when above salivary sodium-chloride concentrations; thus saliva influences salt taste threshold levels. It also provides the ionic environment for taste cells, probably critical in signal transduction. Salivary flow rate and composition are influenced by the type of taste stimuli. In general, sour taste, elicited by citric acid or sour food, induces the highest flow rate and Na+ concentrations, while salt gives rise to high protein and Ca2+ concentrations. Stimulation with the four basic taste modalities (sour, sweet, salty, and bitter), however, does not increase the relative proportion of any of the salivary proteins. This review examines the literature on the interactions of saliva with taste, and the effect of taste on salivary composition. The possible role of the von Ebner's salivary glands and the role of saliva as a chemical cue are also discussed.

Functional and structural changes in parotid glands of alcoholic cirrhotic patients

The parotid gland function and structure was studied in 30 patients with biopsy-proven alcoholic cirrhosis and in 43 age- and sex-matched alcoholic and nonalcoholic control subjects. Mean simulated parotid saliva flow rate was significantly (p less than 0.05) lower in patients with alcoholic cirrhosis as compared with alcoholic and nonalcoholic control subjects. A similar reduction was observed in mean basal parotid saliva flow rate in patients with alcoholic cirrhosis that reached statistical significance (p less than 0.05) in comparison with nonalcoholic control subjects. In addition, the concentration of sodium, bicarbonate, and total proteins in stimulated parotid saliva was significantly (p less than 0.005) lower in patients with alcoholic cirrhosis as compared with the two groups of control subjects. Sialograms in 6 patients with alcoholic cirrhosis did not reveal any obstructive lesion in the primary parotid duct or its branches. Histology of salivary tissue revealed an increase in the interstromal fatty infiltration, edema, and fibrosis without evidence of inflammatory reaction in 5 patients as compared with the control subjects. These data provide evidence for marked parotid gland dysfunction in patients with alcoholic cirrhosis presumably due to metabolic derangement and altered parotid gland structure.

Hyposalivatory drug use, whole stimulated salivary flow, and mouth dryness in older, long-term care residents

Drug-induced hyposalivation has only been anecdotally related to various subjective and objective oral problems. The study described here of 157 residents of a long-term care facility reports data on whole masticatory-stimulated salivary flow rates, use of medications, and perceptions of symptoms associated with hyposalivation, including mouth and eye dryness, tooth sensitivity, chewing satisfaction, and taste and smell acuity. One hundred and twelve residents (71%) were taking one or more drugs that induced hyposalivation. Salivary flow rates were lower in persons who were taking such drugs, and lowest in persons who were taking such drugs for a protracted period. Flow was also lower in females than males, and lower in persons institutionalized for long periods than in persons institutionalized for short periods. Persons who were taking drugs that induce hyposalivation were institutionalized longer, used more medications, had more health problems, were dissatisfied with chewing, and had fewer teeth than persons who were not taking such drugs. Persons who reported having mouth dryness also reported eye dryness and were dissatisfied with their chewing ability. Perceived mouth dryness was not related to salivary flow.

Bacterial agglutinin activity in the saliva of human identical and fraternal twins

The major factor in human saliva responsible for the specific aggregation of oral streptococci is a high molecular-weight glycoprotein (agglutinin). To determine if the level of this glycoprotein in whole and parotid saliva was genetically determined, agglutinin activity for Streptococcus sanguis and Streptococcus mutans in saliva obtained from identical and fraternal twins was compared. Evidence for the heritability of agglutinin activity and also parotid flow rate and total protein was obtained. There was no evidence for a significant genetic contribution to salivary sodium concentration.

Salivary changes in solution pH: a source of individual differences in sour taste perception

The role of saliva in sour taste perception was investigated in a series of 4 experiments. In one pair of experiments, solution pH was measured before and after acetic, citric or hydrochloric acid solutions were mixed with saliva either normally in the oral cavity or after saliva was directly added to solutions. The results showed that large increases in solution pH occurred over a wide range of acid concentrations and that the changes in pH were related to individual salivary flow rates; greater increases in solution pH occurred among those individuals with higher flow rates. The other pair of experiments measured taste threshold and suprathreshold responses to different volumes of acids. The results demonstrated that individuals with high salivary flow rates were less sensitive to the taste of acids and that large volumes of acid were more easily perceived. The pattern of findings suggest that saliva-induced changes in solution pH are important in sour taste perception.

Prevalence of drugs causing hyposalivation in an institutionalized geriatric population

The types and numbers of drugs prescribed for nursing home residents were enumerated in order to determine the prevalence of drugs that cause hyposalivation. Drugs were coded as having a definite or probable hyposalivatory side effect, or as having no effect, and were also categorized by therapeutic action. The average number of drugs prescribed for each patient was approximately four. Approximately half of the institutionalized elderly received one or more drugs with a hyposalivatory side effect. The hyposalivatory drugs were mainly antipsychotics, antidepressants, antihistamines, and analgesics.

Short-term taste behavior and copper/vitamin B-6 nutriture in Long-Evans rats

The taste behavior of rats subjected to dietary depletions of copper and/or vitamin B-6 was tested. Weanling rats were fed casein-based methionine supplemented diets according to a 2 X 2 factorial design: -Cu/-vitamin B-6; -Cu/+vitamin B-6; +Cu/-vitamin B-6; +Cu/+vitamin B-6. Short-term (18 min) taste tests were conducted daily to assess the effects of the dietary treatment on taste stimuli intake behavior; body weight and ad lib food and water consumption were monitored during the study. These measures showed that dietary copper deficits had no apparent effect on growth, ingestive behavior or short-term intake of preferred taste stimuli but did cause a marginal depression in the short-term intake of quinine solution. In contrast, vitamin B-6 depleted rats reduced their ad lib consumption of food and water, failed to grow and exhibited elevated taste stimuli intake during short-term tests.

Effects of gustatory deafferentation on ingestion of taste solutions as seen by licking behavior in rats

The role of the taste nerves in licking behavior to various taste solutions was examined in rats. The study consisted of two experiments. In the electrophysiological experiment, the whole nerve recording of the anterior palatine nerve (PN) was performed to examine the response properties of this nerve to taste stimulation applied to the taste buds in the nasoincisal duct. When the moderate concentrations of solutions were used, the PN responded best to HCl, followed by sucrose and NaCl. Quinine hydrochloride elicited the smallest response. In the behavioral experiment, the number of licks/20 sec was measured for each of the test solutions such as 0.5 M sucrose, 0.01-1.0 M NaCl, 0.03 M HCl and 0.0005 M-0.01 M quinine in normal control and experimental rats. The experimental animals received bilateral deafferentation of the PN, chorda tympani (CT) and glossopharyngeal nerve (GN) alone or in various combinations. Rats without one of the 3 taste nerves still rejected the aversive HCl and quinine solutions. However, after lesions of both CT and GN, or all the 3 taste nerves, the rats showed a significant increase in the number of licks to these aversive solutions. These results suggest that taste aversion disappears after denervation of more than 80% of the total taste buds. The interlick interval, lick duration and the amount of intake per lick did not change significantly after sections of the taste nerves in any combinations.

Effect of transdermal scopolamine on salivation

The effect of transdermal scopolamine on salivary flow and composition was analyzed in 21 healthy volunteers. The flow rate of whole saliva was significantly lowered by transdermal scopolamine. Significant positive correlations were found between the placebo rate of flow and both the quantity and percentage decreases in response to transdermal scopolamine. The magnesium concentration was significantly increased during transdermal scopolamine administration, whereas the sodium, potassium, and calcium concentrations were not consistently altered. Accordingly, the magnesium secretion rate was unaltered, whereas sodium, potassium, and calcium secretion rates were significantly lowered by transdermal scopolamine administration.

A comparison of whole mouth resting and stimulated salivary measurement procedures

Methods for collection and stimulation of whole mouth saliva were compared. Resting salivary flow values were roughly equivalent for draining, spitting, suction, and swab collection techniques, but the swab technique was less reliable. Gustatory and masticatory stimuli induced significantly higher salivary flow compared to resting levels, but the between- and within-subject variances were also higher. Stimulation produced a fairly constant addition of saliva whether individual resting flow levels were low or high.