1 INTRODUCTION

The effectiveness of non-surgical scaling and root planing (SRP) followed by periodontal maintenance in preventing periodontal disease, and ultimately tooth loss, has been documented in several longitudinal studies (Axelsson & Lindhe, 1981; Becker et al., 1979; L. Chambrone et al., 2010; L. A. Chambrone & Chambrone, 2006; Lindhe & Nyman, 1984; McGuire, 1991; Sparrow et al., 2020). At risk populations for periodontal disease include patients with cardiovascular disease, diabetes, or those who smoke (Bergström et al., 2000; Nguyen et al., 2015; Westfelt et al., 1996). Another at risk population may include patients with dry mouth though there is a paucity of information regarding the association between dry mouth induced by prescription medication and periodontal health.

Given that the intake of prescription medication, some with known side-effects that include dry mouth, it is important to determine whether such individuals undergoing periodontal maintenance experience similar benefits as patients without dry mouth (Turner & Ship, 2007). A lack of saliva – which may result from use of prescription medication - increases the adherence of plaque and bacteria, thus possibly contributing to an increased risk of periodontal disease (Gupta et al., 2006). Saliva plays an essential role in oral health and has other beneficial functions such as lubrication and protection of the oral cavity, removal and flushing of debris, mastication and digestion, as well as prevention of tooth erosion, abrasion and dental caries (Humphrey & Williamson, 2001). Additionally, dry mouth symptoms include mild oral discomfort, bad breath, cracked lips, sore throat, burning mouth, chelitis, dysgeusia, the inability to retain removable prostheses and can cause difficulty eating, which leads to higher consumption of poor nutrient foods such as soft breads, cookies, and soda (Guggenheimer & Moore, 2003; Meisel et al., 2012).

The main objective of this study was to determine if patients with or without dry mouth have the same clinical periodontal outcome (number of sites with probing depth ≥ 4 mm) when receiving regular periodontal maintenance at 1–5 years post-SRP. We hypothesized that patients who underwent routine periodontal maintenance appointments would have no difference in periodontal outcomes at 1–5 years post-SRP because of the frequent disruption of the biofilm and removal of plaque with regular periodontal maintenance, regardless of dry mouth status.

2 MATERIAL AND METHODS 2.1 Study population and design

This retrospective study took place at a periodontal specialty clinic in Fonthill, Ontario, Canada. Patients who had SRP within 1–5 years and who routinely visited the clinic for periodontal maintenance between July 2018 and October 2018 were invited to participate. One hundred twenty participants (convenience sample) were invited and 119 completed the study. One patient was referred for emergency treatment due to high blood pressure at the time of the periodontal maintenance appointment and thus clinical measures were not obtained (Figure 1). The presence or absence of dry mouth was measured at the “present-day” periodontal maintenance appointment by measuring unstimulated salivary flow rate. Also, the self-reported xerostomia inventory questionnaire and the Registered Dental Hygienist (RDH) dry mouth observation questionnaire were completed at this same time point (present-day).

Flow diagram of study participants

A patient with an unstimulated salivary flow rate less than 0.1 ml/min was categorized as having dry mouth. A patient with an unstimulated salivary flow rate of 0.1 ml/min or greater was considered to be without dry mouth. Patients were contacted 1 week prior to their scheduled periodontal maintenance appointment to confirm their appointment and invite them to the study. Patients who agreed were scheduled 15 min prior to their appointment. At the time of the appointment, patients provided written consent. The study protocol was approved by the human research ethics board at Brock University in St. Catharines, Ontario, Canada and registered with clinicaltrials.gov as NCT03649789.

2.2 Periodontal examination

Probing depth was measured at three time points, before SRP (pre-SRP), 8–12 weeks following SRP (post-SRP), and at the present-day periodontal maintenance appointment. Data pertaining to dry mouth status, including salivary flow rate and information from the questionnaires, were collected at the present-day appointment which took place between 1 and 5 years post-SRP. Probing depth at pre-SRP and post-SRP were collected from the patient's dental charting history and probing depth at present-day was collected at the time of saliva collection and completion of the questionnaires. Prior to measuring probing depth, the five hygienists were calibrated to use 25 N of pressure at six sites per tooth using a UNC15 Probe (Hu-Friedy). These sites included mesiobuccal, buccal, distobuccal, mesiolingual, lingual, and distolingual. Average probing depths were calculated to compare among the three time points: pre-SRP (1–5 years ago), post-SRP (8 weeks following pre-SRP) and present-day.

2.3 Saliva collection

Patients provided a timed 5-min unstimulated saliva sample to determine salivary flow rate. Patients were instructed to tilt their chin to their chest and allow for saliva to begin pooling at the front of their mouth. Following this, patients were instructed to guide their saliva through the Saliva Collection Aid, a straw-like attachment apparatus, into the 2 ml cryovial. The volume (ml) of saliva collected per minute was used to calculate the salivary flow rate. Salimetrics protocol suggested a maximum of 5 min allocated, however, some patients were able to fill the cryovial before 5 min. Thus, the salivary flow rate was the amount of saliva in the cryovial divided by the minutes a patient used to provide the sample. A flow rate of 0.1 ml saliva/min or greater was considered adequate salivary flow rate while a flow rate of less than 0.1 ml saliva/min was considered inadequate and a patient was categorized as having dry mouth (Guggenheimer & Moore, 2003).

2.4 Self-reported xerostomia inventory questionnaire

The Xerostomia Inventory was used as a self-report questionnaire by the patient (Thomson et al., 1999; Thomson & Williams, 2000) to identify possible comparisons between salivary flow rate and self-reported symptoms. At the beginning of their appointment, each patient completed this questionnaire prior to salivary flow rate collection. Each of the 11-item statement was scored as follows: “Never” = 1 point, “Hardly Ever” = 2 points, “Occasionally” = 3 points, “Fairly Often” = 4 points, “Very Often” = 5 points. Scores of 11 equate to no symptoms of dry mouth reported, score of 12–33 were categorized to patients reporting mild to moderate dry mouth symptoms, and lastly scores greater than 33 equate to severe dry mouth symptoms.

2.5 Registered dental hygienist dry mouth observation questionnaire

Following a patient's periodontal maintenance appointment, the RDH completed the RDH dry mouth observation questionnaire (Plemons et al., 2014) that includes questions about the patient's salivation volume and consistency, observable symptoms dry mouth and use of dry mouth aids - to assess the potential association between a patient's unstimulated salivary flow rate and dry mouth observations made by the RDH. A symptom score was calculated from the list of observable symptoms, with 1 observed symptom equating to 1 point for a possible total of 14 points.

2.6 Assessment of covariates

Patient height and weight were collected at the time of saliva collection to determine their body mass index (BMI; in kg/m2). Additionally, information about sex, age, and smoking status were obtained from the patient's updated medical history forms. These covariates were assessed as they have previously been found to be associated with periodontal disease. Specifically, a patient who has a higher BMI, is male and/or is a smoker, has a higher prevalence of periodontal disease (Al-Shammari et al., 2005; Al-Zahrani et al., 2003; Patel et al., 2012).

2.7 Statistical analysis

Probing depth and patient characteristics were analyzed by a repeated measures analysis of variance and independent t-test to determine if there were significant differences for continuous variables such as age, number of medications consumed, probing depth and plaque index between patients with or without dry mouth. Chi-square were performed to determine whether there is a significant difference between the expected and observed frequencies between patients with or without dry mouth for categorical variables such as sex, BMI, smoking status and type of medication. SPSS version 25 was used to analyze all statistical procedures (Armonk, New York). Statistical significance was defined as p < 0.05.

3 RESULTS 3.1 Patient characteristics

Figure 1 illustrates patient recruitment. Of the 120 patients, 85 patients were determined to have adequate salivary flow rates and were considered to be without dry mouth. Thirty-four patients were determined to have inadequate flow rate and were considered to be with dry mouth. One patient was excluded from present-day appointment due to high blood pressure. This patient's saliva was collected, medical and dental history was updated, and consent was obtained. However, prior to periodontal maintenance their blood pressure was taken and exceeded the safe blood pressure recommendation for elective dental care. Therefore, the patient was dismissed and referred to a medical doctor. Table 1 shows the characteristics and clinical outcomes of patients with or without dry mouth. Age in both groups was similar. There was no significant difference between the number of males and females with dry mouth (p > 0.05). In regard to BMI, more patients without dry mouth had normal BMI compared to patients without dry mouth (p < 0.05). However, more patients with dry mouth were overweight (p < 0.001). There was no significant difference in the number of obese patients between groups. There were also no significant differences in smoking status (current smoker, former smoker, or never smoked) between groups (Table 1). Patients with dry mouth were using more medications than patients without dry mouth (p < 0.05). The number of medications used was also associated with a decreased salivary flow (p < 0.001) (Figure 2). When medications were categorized based on health condition (mental health, cardiovascular, diabetes, and osteoporosis) no significant differences were found (p > 0.05). As anticholinergic drugs are a significant predictor of dry mouth symptoms (Herbison et al., 2003), use of such drugs was assessed according to dry mouth status. No significant relationship was found between patients with or without dry mouth and use of anticholinergic drugs.

TABLE 1. Characteristics of patients with or without dry mouth Patient characteristics Patients with dry mouth (n = 34) Patients without dry mouth (n = 85) p valueb,c Age, years 61.6 ± 8.7 (34–79) 61.6 ± 11.1 (33–90) p > 0.05b Sex, n (%) Males 13 (38.2) 43 (50) p > 0.05c Females 21 (61.8) 43 (50)   BMI Normal 17 (50.0) 61 (70.9) p < 0.05c Overweight 15 (44.1) 20 (23.3) p < 0.001c Obese 2 (5.9) 5 (5.8) p > 0.05c All 23.28 ± 4.00 (14.05–38.85) 22.6 ± 4.23 (14.05–38.85) p > 0.05b Smoking status, n (%) Current smoker 9 (26.5) 18 (20.9) p > 0.05c Former smoker 12 (35.3) 34 (39.5) p > 0.05c Never smoked 13 (38.2) 34 (39.5) p > 0.05c Medication use, n (%) 31 (91.2) 58 (67.4) p < 0.05c Mental Health 8 (23.5) 13 (15.1) p > 0.05c Cardiovascular 18 (52.9) 39 (45.3) p > 0.05c Diabetes 3 (8.8) 4 (4.7) p > 0.05c Osteoporosis 3 (8.8) 7 (8.1) p > 0.05c Number of Medications 3.8 ± 3.0 (0–11) 2.2 ± 2.4 (0–13) p > 0.05b Anticholinergic drugs,d n (%) 9 (26.5) 13 (15.1) p > 0.05c a Data are expressed as mean ± standard deviation, range as (lower and upper values) for continuous variables, and n (%) for categorical variables. b Independent samples t-test was used to analyze group significance for continuous variables. c Chi-squared test was used to analyze group significance for categorical variables. d Anticholinergic drugs treat a variety of conditions including chronic obstructive pulmonary disease, incontinence, gastrointestinal disorders, respiratory conditions, Parkinson's disease and mental health disorders.

Correlation between the salivary flow rate and the number of medications used

3.2 Average probing depth for patients with or without dry mouth

There were no significant differences in average probing depth at each of the three time points between groups (p > 0.05) (Table 2). However, as expected, probing depth at pre-SRP was significantly higher than probing depth at both post-SRP and present-day for both groups, regardless of dry mouth status (p < 0.05) (Table 2). There were no differences between groups (with dry mouth or without dry mouth) for number of sites ≥4 mm at pre-SRP, post-SRP or at the present-day (p > 0.05). For plaque index, there was no difference between groups (p > 0.05). Given the new classification scheme introduced in 2018, periodontal diagnoses were categorized into stages and grades and examined for associations of dry mouth status. There were no differences between groups for Stage II Grade A, Stage II Grade B, Stage II Grade C, Stage III Grade B, Stage III Grade C, Stage IV Grade B, and Stage IV Grade C (p > 0.05) (Table 2). A significant difference was found among patients with a periodontal diagnosis of Stage III Grade A and their dry mouth status. More patients without dry mouth were classified as Stage III Grade A than patients with dry mouth (p < 0.05). In terms of current periodontal status, a higher number of patients without dry mouth had a current stable periodontal status than patients with dry mouth (p < 0.05). There were no differences (p > 0.05) between dry mouth groups in terms of patients with unstable periodontal disease or periodontal disease that was in remission. The number of patients that alternated periodontal maintenance appointments between the general dentist's clinic and the periodontal clinic did not significantly differ (p > 0.05) between patients with or without dry mouth (Table 2).

TABLE 2. Outcomes of periodontal health in patients with or without dry mouth Patient characteristics and clinical outcomes Patients with dry mouth (n = 34) Patients without dry mouth (n = 85) p valueb,c Plaque Indexd 40.1 ± 21.1 (10–100) 39.6 ± 19.6 (10–100) p > 0.05b Pre-SRP PD, # of sites ≥ 4 mm 85.6 ± 34.7e (13–144) 92.6 ± 40.6e (9–183) p > 0.05b Post-SRP PD, # of sites ≥ 4 mm 17.03 ± 11.8 (1–52) 14.3 ± 13.8 (0–72) p > 0.05b Present-Day PD, # of sites ≥ 4 mm 16.5 ± 16.1 (0–69) 14.9 ± 13.7 (0–90) p > 0.05b Periodontal classification Stage II Grade A 3 (8.8) 2 (2.3) p > 0.05c Stage II Grade B 7 (20.6) 13 (15.1) p > 0.05c Stage II Grade C 0 (0) 1 (1.2) p > 0.05c Stage III Grade A 2 (5.9) 6 (7.0) p < 0.05c Stage III Grade B 13 (38.2) 39 (45.3) p > 0.05c Stage III Grade C 1 (2.9) 8 (9.3) p > 0.05c Stage IV Grade B 3 (8.8) 12 (14.0) p > 0.05c Stage IV Grade C 5 (14.7) 5 (5.8) p > 0.05c Current periodontal status In Remission 1 (2.9) 7 (8.1) p > 0.05c Stable 5 (14.7) 14 (16.3) p < 0.05c Unstable 28 (82.4) 65 (75.6) p > 0.05c Alternating Patient, n (%) 22 (64.7) 51 (59.3) p > 0.05c Non-Alternating Patient, n (%) 12 (35.3) 35 (40.7)   a Data are expressed as mean ± standard deviation, range as (lower and upper values) for continuous variables, and n (%) for categorical variables. b Independent samples t-test was used to analyze group significance for continuous variables. c Chi-squared test was used to analyze group significance for categorical variables. d O'Leary Plaque Index. e Pre-SRP PD was higher than post-SRP and present day SRP regardless of dry mouth status. 3.3 Self-reported xerostomia inventory questionnaire

There were no differences in dry mouth scores between patients with or without dry mouth (p > 0.05) (Table 3).

TABLE 3. Self-reported score for dry mouth symptoms in patients with or without dry mouth Dry mouth score (0–55) Patients with dry mouth (n = 34)b Patients without dry mouth (n = 85)b p valuec n (%) 0–11 (No dry mouth symptoms reported) 0 (0) 3 (3.5) 12–33 (Mild – Moderate Symptoms Reported) 29 (85.3) 79 (91.9) > 33 (Severe symptoms reported) 5 (14.7) 4 (4.7) Average score 26.97 ± 7.12 (14–44) 23.17 ± 7.34 (11–40) p > 0.05c a Data are expressed as mean ± standard deviation, range as (lower and upper values) for continuous variables, and n (%) for categorical variables. b Dry Mouth status was determined through salivary flow rate samples collected at the patient's present day sanative therapy appointment (patients with a salivary flow rate of <0.1 ml/min samples were classified as having dry mouth). c Independent samples t-test was used to analyze group significance. 3.4 RDH dry mouth observation questionnaire

There were significant differences in saliva volume, saliva consistency, and specific observable symptoms between patients with and without dry mouth (Table 4). The majority of patients without dry mouth were found to have a copious salivary volume and serous salivary consistency compared with patients with dry mouth (p < 0.001, p < 0.05). Patients with a dry mouth were more likely to have a slight or deficient salivary volume and a frothy salivary consistency than patients without dry mouth (p < 0.001, p < 0.05, p < 0.05). The number of patients with fissured tongue and tongue crenulations was higher among patients with dry mouth (p < 0.05, p < 0.05).

TABLE 4. Characteristics of patients with or without dry mouth using the registered dental hygienist dry mouth observation questionnaire Characteristics of patients Patients with dry mouth (n = 34)b Patients without dry mouth (n = 85)b p valuec,d Saliva volume n (%)       Copious 0 (0) 28 (32.6) p < 0.001c Adequate 19 (55.9) 50 (58.1) p > 0.05c Slight 12 (35.3) 8 (9.3) p < 0.001c Deficient in Volume 3 (8.8) 0 (0) p < 0.05c Saliva consistency n (%)       Serous 14 (41.2) 60 (69.8) p < 0.05c Sticky 15 (44.1) 24 (27.9) p > 0.05c Frothy 5 (14.7) 2 (2.3) p < 0.05