Evaluation of Oral Dryness and the Salivary-flow Rate in Patients with Oral Lichen Planus

2.1. Study Participants

Data were collected from 30 OLP patients and 30 controls who visited the Faculty of Dentistry at Srinakharinwirot University in Bangkok from 2020-2021. The study was approved by the Srinakharinwirot University Ethics Committee (no. SWUEC/E-464/2563). All the participants were informed and gave written consent prior to the beginning of the study. Fig. (1) shows the flow chart of the study protocol. In the OLP group, the inclusion criteria were: being 20 years or older; having a confirmed diagnosis of OLP by clinical and histopathologic presentations according to the World Health Organization (WHO) criteria [12]; had not used corticosteroids or stopped using topical corticosteroids and systemic corticosteroids for at least two weeks and four weeks prior to data collection, respectively. The controls included patients who had no oral lesions and were 20 years or older. The exclusion criteria for both groups were people who had diabetes mellitus, autoimmune diseases, graft-versus-host disease, chronic kidney disease, and/or had used medication-induced hyposalivation such as hypertensive drugs, antidepressants, anxiolytics, bronchodilators, and decongestants. People who had oral candidiasis, a history of head and neck radiation and smoking were also excluded.

The demographic and clinical data consisting of age, sex, systemic diseases, and current medications were collected from all participants.

2.2. Oral-dryness Symptom Assessment

Subjective feelings of oral dryness were evaluated by using the Xerostomia Inventory (XI). This questionnaire consisted of 11 items. Each participant was asked to rate each item from 0-5 (score 1 = never; 2 = hardly; 3 = occasionally; 4 = fairly often; and 5 = very often) [13]. The scores on the 11 items were added to create a total XI score ranging from 11 (no xerostomia) to 55 (extreme xerostomia). The Bother Index (BI) was also used to determine the severity of oral dryness. A self-rated score ranged from 0-10, with 0 representing no burden and 10 representing the most trouble [14].

2.3. Salivary-flow Measurement

One examiner conducted the collection of saliva (VA). The assessment was made between 9:00 a.m. and 12:00 p.m. to minimize the effects of the circadian rhythm. The participants were instructed to refrain from eating, drinking, brushing their teeth, and using mouthwash for 60 minutes prior to the salivary measurement. They were asked to sit upright, swallow once to clear the residual saliva in their mouth, and not to swallow during the test [15, 16].

Unstimulated whole saliva (UWS) and paraffin-chewing-stimulated whole saliva (SWS) were collected via spitting. The participants were instructed to collect saliva in their mouths and spit it into the pre-weighed container. For SWS, the participants were asked to chew a paraffin-size 5x5 cm² and expectorate into the pre-weighed container. After the collection, both the UWS and SWS containers were reweighed. The collected volume was deducted from the weight of the container prior to collection. The salivary-flow rates were calculated by dividing the collected volume (assuming 1 g. of saliva equals 1 ml.) by the collection time (min), and the results were presented in ml/min. Hyposalivation was defined when the UWS was valued at < 0.1 ml and SWS was valued at < 0.5 ml/min [8].

The Modified Schirmer test (MST) was also used to determine the unstimulated salivary-flow rate. The test strip was a 4-cm-long filter paper strip with a 1-mm scale interval from 5-35 mm along its length. The participants were asked to lean backward, swallow once to clear the residual saliva in their mouth, and not to swallow during the test. Moreover, they were asked to rest their tongue on their palate so the test strip would not touch their tongue. The test strip was held vertically with a cotton plier and the end of the strip was placed on the floor of the mouth on the right or left of the lingual frenum. When the strip contacted the moisture, the strip was wet and was recorded at 1, 2, and 3 minutes. The strip was removed for 2-3 seconds for reading [17]. The measurements ranged from 5-35 mm. When the measurement was less than 5 mm, 5 mm was recorded, and when it was higher than 35 mm, 35 mm was recorded [18]. Hyposalivation was assessed if the distance was < 25 mm at 3 min [17].

2.4. Oral Examination

One examiner did the oral examination for all the participants (VA). Clinical signs of reduced saliva secretion were evaluated using the clinical oral-dryness score (CODS). CODS is a 10-point scale in which each point represents a clinical feature of oral dryness [14, 19]. The total CODS was calculated by adding the scores from these features. A high total score specified more severe dryness.

Regarding OLP, the location, size, and duration of the oral lesions were recorded. The OLP severity was evaluated according to the Thongprasom score as follows: 0 = normal mucosa; 1 = lesions with only white striae; 2 = mixed keratotic and atrophic or erythematous lesions smaller than 1 cm²; 3 = mixed keratotic and atrophic or erythematous lesions larger than 1 cm²; 4 = erosive/ulcerative lesions smaller than 1 cm²; and 5 = erosive/ulcerative lesions larger than 1 cm² [20].

2.5. Statistical Analysis

The statistical analysis was done using SPSS software, Version 25 (SPSS Inc, Chicago, IL, USA) for Windows. The difference in mean age between the two groups was compared by using the independent t-test. Sex and systemic diseases were compared using the Chi-square. The XI score, BI score, CODS, and salivary-flow rates were not normally distributed. Thus, the Mann-Whitney U test was used for the comparisons. The correlation between the variables was calculated by using Spearman’s rank coefficient correlation. The statistical significance was defined as a p-value of < 0.05.

3.1. Demographic Data and Clinical Presentation of the Study Populations

The participants in each group consisted of 25 women (83.3%) and 5 men (16.7%). The mean age of the OLP group and control group were 54.37 ± 13.05 years old and 54.77 ± 13.73 years old, respectively. There was no statistically significant difference in age and sex between the two groups (p > 0.05) (Table 1). Eight (26.7%) of the 30 OLP patients had systemic diseases, including thyroid disease (6.67%), followed by allergic rhinitis (3.33%), migraines (3.33%), seizures (3.33%), gastroesophageal reflux disease (3.33%), thalassemia (3.33%), and benign prostatic hyperplasia (3.33%). Four patients were taking medications that consisted of propylthiouracil (n=2), lamotrigine (n=1), and folic acid (n=1). In the control group, four patients (13.33%) had systemic diseases, including dyslipidemia (6.67%), thyroid disease (3.33%), and arrhythmia (3.33%). Two patients were taking simvastatin and one person was taking propylthiouracil.

Most OLP patients presented with the atrophic form (80%), followed by the erosive form (20%). The OLP severity scores were 2 (26.7%), followed by 3 (53.3%), 4 (10%), and 5 (10%). Sixteen patients (53.3%) had oral lesions at multiple sites. The most common site was the buccal mucosa (93.3%), followed by the gingiva (60%), tongue (26.7%), lip (10%), soft palate (3.3%), and the floor of the mouth (3.3%). About 53.3% had oral lesions for 1-5 years, 40% for more than 5 years, and 6.7% for less than 1 year (Table 1).

3.2. Oral Dryness and Salivary Flow-rate Assessment

The mean XI score of the OLP and controls were 21.33 ± 6.69 and 17.70 ± 6.40, respectively. The mean BI score was 2.35 ± 2.25 in the OLP group and 1.18 ± 1.50 in the control group. Both the XI and BI scores among the OLP patients were statistically significantly higher than among the controls (p < 0.05) (Table 2).

The UWS was 0.58 ± 0.45 and 0.78 ± 0.53 ml/min in the OLP and controls, respectively. The SWS was 1.21 ± 0.63 ml/min in the OLP and 1.43 ± 1.04 ml/min in the controls. Using MST, the UWS in the OLP group was lower than among the controls at all time points. However, the two groups had no statistically significant differences in the UWS, SWS, and MST (p > 0.05) (Table 2).

Clinical signs of dry mouth based on CODS were found in 14 OLP patients (46.67%) and 9 controls (30%). The CODS ranged from 0-2 in both groups. The mean CODS in the OLP group and control group were 0.57 ± 0.68 and 0.37 ± 0.61, respectively. When compared to the controls, the OLP group had higher CODS, although this was not at a statistically significant rate (p > 0.05) (Table 3).

3.3. The Correlations among Oral dryness, the Salivary-flow Rate, and the OLP-severity Score in the OLP Group

There was no correlation between the salivary-flow rates (UWS and SWS) and the subjective patients’-reported oral-dryness scores (XI and BI) among the OLP patients. The MST at three minutes, which was found to have high sensitivity and high positive predictive value (17), also showed no association between the XI and BI scores. There was no correlation between the OLP severity score, subjective oral-dryness symptoms, and salivary-flow rates (Table 4). Interestingly, the XI and BI scores were significantly correlated with each other (r_s = 0.687, p < 0.001). The association between the UWS and SWS also showed a high positive correlation coefficient (r_s = 0.610, p < 0.001). Additionally, MST was associated with UWS (r_s = 0.647, p < 0.001) and SWS (r_s = 0.655, p < 0.001), respectively (Table 4).