Does oral dryness influence quality of life? Current perspectives in elderly dental care

Background. The oral condition can functionally, socially and psychologically influence the quality of life. Oral dryness often occurs in the elderly due to the presence of systemic diseases and medications, which favors the development of many lesions and complaints, including dental caries, candidiasis, retention of full removable denture, taste disturbance and it enforces a change in nutrition.

Extended human lifespan resulting from civilizational development along with decreased birth rate leads to an increase in the percentage of the elderly in comparison to younger people.This is the reason why, in recent years, the number of ageing members of society has been increasing, especially in highly developed countries. 1,2The ageing process of the human body is an inevitable phenomenon and it concerns all the organs.Changes related to the ageing process occurring in the oral cavity involve teeth, the periodontium, oral mucosa, bones of the jaws, temporomandibular joints, and salivary secretion.In elderly people, reduced salivary secretion (hyposalivation) is frequently observed; this condition leads to oral dryness (xerostomia).It is estimated that 25-30% of people aged 65 and over suffer from this condition and experience its symptoms. 3,4Data regarding stimulated salivary secretion among healthy elderly people does not indicate a significant and age-dependent reduction in secretion, but only an insignificant reduction in the secretion of seromucous glands (but not the serous gland, i.e. the parotid gland) in the conditions of minimal or prolonged stimulation.It has been observed that as people get older, the number of acini decreases, and the adipose and fibrous tissue increase.Small salivary glands also undergo these changes.However, reduction in the acinar part of the glands resulting from the ageing process does not significantly reduce the secretory function of the salivary glands.Therefore, it is currently assumed that the production of saliva and its composition does not change with age in healthy people.6][7] Taking medications is considered to be the most common cause of oral dryness, as most elderly people take at least one medication which negatively impacts salivary secretion. 8Medications that cause xerostomia include, among others, antihypertensive, anticholinergic, anti-reflux and cytotoxic medications, as well as diuretics, antidepressants and beta blockers. 4,6Furthermore, some common diseases at an older age may lead to the hypofunction of salivary glands (e.g., diabetes type 2, and rheumatoid arthritis).Other causes include radiotherapy in the form of external radiation applied as part of head and neck cancer treatment, which destroys the tissues of the salivary glands and leads to long-lasting xerostomia. 6,7educed salivary secretion implies numerous clinical consequences, such as increased susceptibility to caries and periodontal diseases, which may then result in tooth loss, reduced denture tolerance, increased risk of fungal infections and taste disorders.People suffering from oral dryness have problems with eating (especially dry food, such as crackers or biscuits), speaking, swallowing and wearing removable partial dentures (their retention, pain experienced when wearing the dentures), as well as with the tongue tending to stick against the palate.Patients often report halitosis, burning mouth syndrome and intolerance to spicy food, excessive mucus or food accumulation. 8Moreover, patients frequently complain about oral dryness experienced particularly at night, as this is the time of the lowest salivary secretion.Intensified difficulties in speaking and eating may deteriorate the quality of social interactions. 9ral health considerably affects the overall quality of life.It leads to a reduction in everyday activity and to lack of physical and/or mental wellbeing.Therefore, the notion of Health-related Quality of Life -HRQoL has been introduced.1][12][13] The relation between oral health and the quality of life can be determined by assessing to what extent oral health influences the quality of life through performing functions, such as chewing, biting, swallowing, speaking, as well as through mental wellbeing (satisfaction with dental aesthetics, self-esteem), physical wellbeing (comfort while eating and lack of discomfort or pain), and social wellbeing (feeling comfortable while speaking to others). 14One of the most commonly used assessment tools is the Oral Health Impact Profile (OHIP) scale that consists of 49 questions, or its shortened version, which consists of 14 questions (OHIP-14). 15,16

Objectives
The aim of the study was to determine the influence of oral dryness on the oral health-related quality of life among elderly people.

Recruitment and study duration
The study was conducted for 24 months (from January 2015 to December 2016) after obtaining consent of the Bioethics Committee of Wroclaw Medical University KB 420/2015.
The study involved 500 subjects of both genders (180 men and 320 women) at the age of ≥65 (mean age 74.4 ±7.4,age range 65-99) who were urban residents of Wrocław.Data on the total number of 65 and over subjects living in the city was derived from the Central Statistical Office (Demographic Yearbook of Poland 2015).A minimum sample size was calculated based on data concerning caries prevalence in this age group with the assumed significance level of 95% and with ±5% error tolerance.It turned out to be 383; therefore, the number of the examined subjects exceeded this figure.

Survey inclusion/exclusion criteria
The inclusion criteria for the study were the following: age of 65 and over, place of residence (citizens of Wrocław), able to communicate and a written consent to participate in the survey.
The exclusion criteria were lack of a written consent or mental disorders which would have made filling out the questionnaire impossible.
The participation in the survey was voluntary.The patients were enrolled based on information provided in press, on the radio and on the Internet, as well as in Senior Citizens Associations, at the University of the Third Age, church organizations, primary care outpatient clinics, pharmacies, and residential homes.

Sociomedical examination
The demographic and personal information, and medical history were obtained from the subjects.The data included the date of birth and gender, marital status, level of education, and amount of monthly income before the appointment; the patients were asked to provide written information about current and past diseases, as well as medications currently taken by them.Medical data comprised the type of past and present diseases and medicine taken.

Psychometric examination
Oral health-related quality of life was assessed with the use of the Oral Health Impact Profile-14 scale (OHIP-14). 16,17It consists of 14 questions related to problems which have occurred within the past month, and which are connected with teeth, oral cavity or wearing dentures.The problems include: 1) trouble with pronouncing words, 2) worsened taste, 3) pain, 4) discomfort while eating, 5) self-consciousness, 6) emotional tension, 7) unsatisfactory diet, 8) interrupted meals, 9) difficulty with relaxing, 10) embarrassments, 11) irritability, 12) inability to complete everyday tasks, 13) reduced satisfaction with life, ( 14) complete inability to function.The answers to the questions were categorized in accordance with the frequency of occurrence on a five-level scale ranging from never (score 0), hardly ever (score 1), occasionally (score 2), fairly often (score 3) to very often (score 4).Oral health-related quality of life is expressed as the sum of the score for the 14 questions (OHIP-14 sum, maximum 56 points).Furthermore, the 14 questions constitute 7 domains.The domains are related to functional limitations, pain (physical), psychological discomfort, physical disability, psychological disability, social disability and handicap (infirmity).The OHIP-14 scale has been validated for the Polish population. 17

Statistical analysis
Continuous variables were presented as mean values with standard deviation or, if not normally distributed, as median and range, while categorical variables were reported as percentages and numbers.As the empirical distributions of quantitative variables differed significantly from the theoretical normal distribution (they were skewed), they were transformed using the Box-Cox technique.Continuous variables were compared by t-test, while categorical variables were compared by χ 2 test or Fisher's exact test.An analysis of variance (ANOVA) was performed to compare the mean values of transformed value between the OHIP-14 domains.The significance of the relationship between the oral dryness and the predictors analyzed was verified using the Pearson chi-square test or the exact Fisher test.For each predictor, odds ratio adjusted by age and sex was calculated.Its significance was verified using the Mantel-Haenszel test.A two-tailed value of p < 0.05 was used to reject the null hypothesis.All statistical analyses were performed using STATISTICA v. 13 (StatSoft, Inc., Tulsa, USA).

Sociodemographic characteristics of the subjects
Most of the subjects lived with a family member (62.0%) and were independent (90.8%).Secondary education was completed by 51.0% of the subjects, primary education by 16.2%, and higher education by 32.8%.High monthly income per person was declared by 27.2%, medium income by 45.2%, and low income by 25.6%.The remaining 1.8% did not provide their answers.

The subjects' medical history
Only 14% of the subjects did not report the occurrence of a chronic systemic disease.Most often, there were two coexisting systemic disorders (27.0%).Over 60% of the subjects reported hypertension, and over 20% diabetes (Table 1).

Oral dryness
Oral dryness was found in 32.8% of the subjects of both genders (Table 1), including mild dryness in 29.6, moderate -in 3.0% and severe -in 0.2%.Among women, the condition was significantly more common than among men (36.9% vs 25.6%, p = 0.025).The most frequent symptoms included the mouth mirror tending to stick against buccal mucosa -26.6% (more often among women than men 30.6% vs 18.3%, p = 0.000) or against the tongue -22.2% (slightly more often in women than in men 25.3% vs 17.8%, p = 0.068); the least common symptoms were cervical caries involving >2 teeth -1.0% (0.6% in men and 1.3% in women, p = 0.779) and debris on palate or sticking to teeth 0.8% (1.1% in men, 0.6% in women, p = 0.622).

OHIP-14 scale
The total OHIP-14 score (sum) for all the subjects was 8.01 ±13.59 and it did not reveal a gender-related difference (7.20 ±12.90 in men and 8.50 ±14.00 in women, p = 0.280).

Regression analysis
Results of multiple regression between OHIP-14 domains (transformed) and the studied variables (Table 3) showed the correlation of domain 1 (functional limitation) and 5 (psychological disability) with oral dryness, domain 2 (pain) with number of medication, domain 3 (psychological discomfort) and 5 (psychological disability) and kidney diseases, and domain 4 (physical disability) with cardiac infarction (Table 3).
Gender, age over 70 years, the value of the OHIP-14 scale higher than 0, as well as some coexisting systemic diseases, such as hypertension, cardiac infarction, kidney disease and hypothyroidism, were independent predictors of oral dryness.It was noticed that women had almost as twice as high probability to suffer from oral dryness than men (OR = 1.70).A similar observation was made with regards to patients aged over 71 years who provided a positive answer to at least 1 question included in the OHIP-14 scale.Patients suffering from cardiac infarction were twice as prone to suffer from oral dryness as those who were not afflicted with the disease (OR = 2.04).Patients suffering from kidney disease were 3 times more likely to develop oral dryness than patients who did not have the disease (OR = 2.75).In subjects with hypothyroidism, oral dryness was over 2 times more likely to occur than in patients who did not suffer from the disease (OR = 2.17) (Table 4).

Discussion
Oral dryness resulting from reduced salivary secretion can be detected with the use of various methods: by asking about symptoms (e.g., the Fox's test), asking about some systemic diseases and medications taken, measuring the stimulated and unstimulated salivary flow (sialometry), physical examination, salivary glands imaging and biopsy, and analyzing biochemical components of the saliva and serum. 6,8During the clinical examination, there is an attempt to identify symptoms of oral dryness, including glassy appearance of oral mucosa, mirror sticking to buccal mucosa, dry, painful and lobulated tongue, sticky and frothy saliva, no saliva pooling in mouth floor, turbid saliva flowing out of the salivary duct, as well as enlarged and painful salivary glands.Reduced salivary secretion results in cervical caries, accumulation of food particles due to oral clearance reduction, candidiasis, and angular cheilitis.Among subjects wearing removable dentures, reduced retention or denture intolerance resulting from lower lubrication of the tissue base and the denture plate are observed.][21][22][23] In our study, oral dryness was clinically assessed with the use of the Challacombe Scale that includes 10 characteristic symptoms related to saliva shortage in the oral cavity. 17The Clinical Oral Dryness Score (CODS), which consists of a 10-point scale with each point representing a feature of dryness in the mouth, may, in accordance with the current state of knowledge, be used individually during routine clinical assessment to detect hyposalivation. 18verall, oral dryness was determined in 32.8% of the subjects and that included 29.6% of mild dryness, 3.0% of moderate dryness and 0.2% of severe dryness.5][26][27][28] Niklander et al. found the occurrence of xerostomia in among 13% of women and half that many in men (6.1%) at the age of 18-83 years with a mean age of 46 years. 29They observed the highest prevalence in subjects aged 68-77 years (33.3%),followed by patients aged 78-83 years (22.27%).
A study conducted in India revealed that 58.6% of the 55-75-year-old and older subjects perceived dryness of mouth. 30Among Korean subjects aged 55 years and over, the occurrence of at least 1 symptom of xerostomia was observed in 70.1% of the subjects, and in 25.8%, the observed symptoms were severe. 31At the age of 60 and over (average age of 67.5 years), reduced secretion of stimulated saliva was observed in 64% subjects from Saudi Arabia. 32ge-dependent occurrence of xerostomia was identified and it ranged from 5% in the group aged 18-25 years to 16% in the group aged 65-67 years, and to as much as 26% in the group aged 75 and over. 28alivary glands function can be injured by many systemic diseases based on different mechanisms with the resulting complication of oral dryness. 33Our data showed a significantly higher number of co-morbid diseases in the subjects with clinical symptoms of dry mouth.Elderly people suffering from chronic diseases are on longterm therapy using polypharmacy.Hundreds of medicines induce oral dryness; some of them can exert a synergistic effect on the salivary secretion.Hence, drug-induced dry mouth is one of the most common oral problems in elderly individuals. 34Our data showed a significantly higher mean number of administered medicines among the subjects presenting oral dryness symptoms compared to these with no symptoms.Similar observations were made by Bogucki et al., who identified a correlation between xerostomia, medication taken by patients, age, gender and past diseases. 35he total OHIP-14 score in the examined subjects aged 65 and over was 8.01 ±13.59 and it did reveal a significant difference related to the gender.Comparing the figure in the same age group of different populations, we noticed a slightly higher value (8.88) in Spain 36 , 2.8-fold higher (22.4) in Iran 37 and 2.7-fold lower (2.9) in the United Kingdom. 38In our study, a significantly higher total OHIP-14 score was found in the subjects with clinical symptoms of oral dryness, indicating a poorer quality of life related to oral health (OHRQoL).Similar conclusions were made by Locker, who conducted research among a group of 225 subjects in a long-term care setting (average age: 83 years) and who observed a major influence of xerostomia on the well-being and quality of life of the population. 39he finding was consistent with the study performed in subjects aged 18-75 years and over in whom the total OHIP-14 score was ca.50% higher (6.3 vs 3.5) in the patients with xerostomia determined by a response to one item: "How often does your mouth feel dry?" 28 Another study involving subjects aged 18-87 years also presented a significantly higher total OHIP-14 score in patients with xerostomia than in patients without xerostomia (20.1 vs 12.7). 29A Japanese study performed on the elderly (mean age 66.1) showed that higher values of the OHIP-14 score were related to the perception of dry mouth on eating and hyposalivation. 40Our results indicated a relationship between oral dryness and 2 OHIP-14 domains: functional limitation and psychological disability.The Chilean study, which revealed more reduced OHRQoL in a group of patients with xerostomia, concluded that the highest impact was detected for the domains of psychological discomfort, psychological incapacity and physical pain. 29wn data indicated that gender, age over 70 years, the value of the OHIP-14 scale higher than 0, as well as some coexisting systemic diseases were independent predictors of oral dryness.
Several limitations have to be considered in a discussion about the results of this study.Firstly, this study was conducted using a self-reported questionnaire to report data such as OHIP-14, which could lead to identification bias.However, some studies showed the use of this scale to be a valid and reliable method of screening for oral healthrelated quality of life.
Secondly, the use of survey data did not allow us to explain temporal relationships or to show inferences on causality.Thirdly, while analyzing the obtained results, it is essential to bear in mind a possible self-selection error of the study participants, i.e., the participants who joined the study were worried that they were having dental problems, or they were aware of their dental problems and were looking for help; also, there may have been those who refused to participate in the study due to dental fear.Moreover, another interfering factor resulted from the application of the exclusion criteria.Finally, excluding patients with a mental disorder might have constituted another interfering factor.

Conclusions
Individuals with oral dryness symptoms had poorer oral health-related quality of life having a higher mean of the total OHIP-14 score than their counterparts without any symptoms.The findings support the view that oral dryness negatively affects everyday life; therefore, there is a necessity to monitor oral dryness during the routine dental care as well as to ensure the cooperation of the dentist with general practitioner to diminish oral dryness severity caused by medication.

Table 2 .
Mean transformed values of OHIP-14 scale adjusted by sex and age in relation to oral dryness

Table 4 .
Results of chi-square test a -adjusted by gender and age; b -Fisher's exact test; c -adjusted by age.