Oral dryness is extremely common in individuals who regularly take prescription or non-prescription medications. More than 400 common medications have xerostomic side-effects, with about 15–30% of the United States population affected by their usage. These drugs include the anti histamines, anti hypertensives, diuretics, and anti depressants. The perception of a dry mouth has been correlated with insufficient saliva production but this is not always the case. Hyposalivation has been defined as the clinical condition where the resting salivary flow rate is below about 0.1–0.2 ml/min; in contrast, the average normal resting flow rate is about 0.4 ml/min.

The oral mucosal site having the thinnest coat of saliva immediately after swallowing is the hard palate. The wetness of different oral mucosal surfaces varies substantially and follows a pattern that is basically related to the variable distribution and flow of saliva from the six major and numerous minor salivary glands. Niedermeier and Hüber (1989) found that the perception of oral dryness is related to the rate of secretion of minor palatal glands. The feeling of dryness was evident when the rate of that secretion was below about 3 ?l/cm²/min. These observations suggest that the sensation of a dry mouth is perceived when there is insufficient mucosal wetting, especially of the palate. Whether and at what level of general hyposalivation the mucosal wetness (hard palatal mucosa in particular) is affected is unknown.

Hence, we have now sought to determine: (i) whether the pattern of residual mucosal wetness in normal individuals also occurs in hypo salivators; (ii) what levels of mucosal wetness, especially of the palate, might result in the perception of oral dryness; and, (iii) whether mucosal wetness and the salivary variables of flow rate and pH are related. To do this, the mucosal wetness of different regions of the mouths of individuals with and without the perception of a dry mouth and with resting whole-saliva flow rates below and above 0.1 ml/min was measured along with their resting salivary flow rates and pH. Dryness perception and resting salivary flow rate were the two criteria used to divide participants into ‘dry mouth’ and ‘normal’.

Patients with the complaint of ‘dry mouth’ were solicited through local newspaper advertisement. Qualification for participation in the study required them to be taking medications (prescription or non-prescription) with known xerostomic side-effects. Two groups of 25 dry-mouth participants were selected who were between 22 and 77 yr of age. One group of 25 had a resting salivary flow rate of 0.1 ml/min or less; the other had a resting rate >0.1 ml/min. At the same time, 25 other patients who were taking no medications, had no perception of dry mouth, and had flow rates >1.0 ml/min, were recruited and matched with the dry mouth groups for both age and sex. All participants were instructed to abstain from oral hygiene for 12 h and from eating or drinking for 1 h before their examination. All patients were examined between 8:00 and 11:00 a.m. and completed an informed consent form before examination. A comprehensive medical history was then taken according to the format established by the ADA and recorded on the ADA Long Form (S-500, 1988; Chicago, IL). All positive responses were queried and recorded. A complete record of the medications taken by each patient in the dry-mouth groups was obtained, including dosage, frequency and indication (if known by the patient). Whether the medications were xerogenic was determined from the medication guide published by Sreebny and Schwartz (1986) and the Physician’s Desk Reference (1993; Medical Economics Data Production Co., Montvale, NJ). The categories of xerostomic medications taken are listed in Table 2.

After completion of the initial interview, each patient was seated in the dental chair and allowed to relax for a minimum of 5 min. They were then instructed in the technique of saliva collection as follows. Each participant initially swallowed and then tilted his or her head forward with the chin near the chest and was instructed to avoid any lip or tongue movements, talking, or swallowing. The saliva was allowed to pool in the front of the mouth for exactly 2 min without swallowing. It was then gently drooled into a 100-ml, extremely thin, 8-cm square, plastic weighing boat (Cole Parmer Instrument Co., Niles, IL) that had been weighed on an electronic balance (Model EK-120A, A and D Co., Ltd., Japan and Circuits and Systems, Inc., East Rockaway, NY). The 2-min collection of saliva was weighed and the value recorded. Patients were informed that there might be little or no saliva to spit out and that this should not be a cause for concern. The 2-min collection was repeated twice and then patients were asked to gently empty their mouths of any remaining saliva into the collection vessel. The final saliva mass was then recorded to within ±0.01 g. A clean cotton applicator was dipped into the saliva in the collection vessel and transferred to and gently spread over a pH test strip (Gallard–Schlesinger Industries, Carle Place, NY); the pH was then determined by comparison to a colour standard after 10 s. The pH range of the test strip was between 6.0 and 8.1.

After a rest of 5 min, the residual wetness of the 22 selected oral mucosal sites was determined in each participant. Sialopaper™ strips (No. 2 Whatman filter paper now available slightly larger from Ora Flow®, Box 219, Plainview, NY) were pressed against the mucosa at each site for 5 s. The volume of saliva collected on each strip was then measured with an electronic micro-moisture meter, the Periotron 6000® (formerly Pro-Flow®, now Ora Flow®). The instrument used was modified to permit measurement of volumes up to 2.0 ?l. (A new Periotron 8000® has been developed since, which permits volumes up to 3.0 ?l to be measured; Ora Flow®.) Mucosal sites sampled on the right- and left-hand sides were similar to those measured earlier and included: I, anterior palate about 4 mm lingual to each canine; II, posterior palate about 5 mm palatal to the second molars; III, anterior cheek about 5 mm from the commissure of the lip at the height of the occlusal plane; IV, posterior cheek opposite the first molar at the height of the occlusal plane; V, anterior of the dorsal surface of the tongue about 8 mm from the tip; VI, posterior of the dorsal surface of the tongue as posterior as possible; VII, mucosal surface of the upper lip opposite the upper lateral incisor; VIII, mucosal surface of the lower lip opposite the lower lateral incisor; IX, maxillary vestibule in the area of the canine; X, floor of the mouth adjacent to the orifice of Wharton’s duct; XI, lingual mucosa of the floor of the mouth opposite the mandibular canines.

The ages of the participants in the three groups are shown in Table 1; mean ages were similar, viz. 48.5, 49.2 and 44.0 yr for groups I, II and III, respectively. As in other studies, females out numbered males, possibly reflecting a greater prevalence of dry-mouth symptoms in females. The medications taken by groups I and II are given in Table 2.

Residual saliva thicknesses for the various oral mucosal sites measured in the three groups are shown in Table 3, Table 4 and Table 5 and in Fig. 1. Thicknesses in ?m were calculated by dividing the volumes of saliva in ml collected on each Sialopaper™ strip by 31.7, the area of these strips in mm². Right- and left-hand sides of the mouth showed essentially no differences in mucosal wetness, which confirmed the remarkable bilateral symmetry found by DiSabato-Mordarski and Kleinberg (1996). Mean residual saliva thicknesses ±SEM for groups I, II and III were 22.4±0.4, 27.8±1.3, and 41.8±1.8 ?m, respectively. Values ranged between 4.8±0.6 and 55.8±10.5 ?m in group I, between 7.5±1.1 and 82.6±9.4 ?m in group II, and between 15.9±1.1 and 90.0±12.0 ?m in group III. Oral mucosal wetness showed a characteristic and similar pattern in all three groups. Driest sites were in the hard palate, with its posterior part (posterior to the rugae) having a lower wetness than the anterior parts. The wettest of the areas measured were the posterior dorsum of the tongue and the floor of the mouth near the openings of Wharton’s ducts. This pattern was observed in all three groups but levels were almost uniformly lower in group I and highest in group III.