Associations between Age, Oral Health-Related Quality of Life, and Oral and Swallowing Function among Psychiatric Inpatients in Japan : a cross-sectional study

Along with the ageing society, hospitalized psychiatric patients are also ageing in Japan. The purpose of this study was to investigate the associations between age, oral health-related quality of life (OHRQoL), and oral health, including oral and swallowing function, among psychiatric inpatients. The subjects included 165 psychiatric inpatients in two psychiatric hospitals in Japan. The General Oral Health Assessment Index (GOHAI) and the Eating Assessment Tool (EAT-10) were included in the questionnaire survey for the measurement of OHRQoL and swallowing function. A score ≥ 3 on the EAT-10 was dened as suspected dysphagia. Oral examinations and oral diadochokinesis (ODK) measurements for the tongue-lip motor function evaluation were conducted. A chi-squared test, the Mann-Whitney U test, and linear regression analysis were used for the analysis. (64.5%) The higher DMFT the lower tongue-lip and suspected dysphagia was signicantly associated with the higher age group. Tooth loss and suspected dysphagia were signicantly associated with low GOHAI scores. The EAT-10 score was signicantly correlated with the GOHAI score only after adjusting for age and sex 95% CI:-0.97, -0.64). GOHAI th percentile th percentile (p<0.05),


Abstract Background
Along with the ageing society, hospitalized psychiatric patients are also ageing in Japan. The purpose of this study was to investigate the associations between age, oral health-related quality of life (OHRQoL), and oral health, including oral and swallowing function, among psychiatric inpatients.

Methods
The subjects included 165 psychiatric inpatients in two psychiatric hospitals in Japan. The General Oral Health Assessment Index (GOHAI) and the Eating Assessment Tool (EAT-10) were included in the questionnaire survey for the measurement of OHRQoL and swallowing function. A score ≥3 on the EAT-10 was de ned as suspected dysphagia. Oral examinations and oral diadochokinesis (ODK) measurements for the tongue-lip motor function evaluation were conducted. A chi-squared test, the Mann-Whitney U test, and linear regression analysis were used for the analysis.

Results
A total of 100 (64.5%) psychiatric inpatients (49 males and 51 females) participated in this study. Their mean±SD age was 67.3±14.5. The higher DMFT index, the lower tongue-lip function, and suspected dysphagia was signi cantly associated with the higher age group. Tooth loss and suspected dysphagia were signi cantly associated with low GOHAI scores. The EAT-10 score was signi cantly correlated with the GOHAI score only after adjusting for age and sex (β=-0.725, 95% CI:-0.97, -0.64).

Conclusions
In hospitalized psychiatric patients, impaired oral health in the older subjects was more pronounced compared with that among general adults. Tooth loss and swallowing function were associated with OHRQoL. Therefore, oral care for the recovery of occlusal and swallowing functions may be needed to improve OHRQoL among psychiatric patients.

Background
The number of patients with psychiatric disorders is increasing worldwide. A report from the World Health Organization stated that the lifetime prevalence of psychiatric problems is approximately 20% to 35% [1,2]. A survey conducted in Japan by the Ministry of Health, Labour and Welfare in 2017 estimated that 513 thousand patients (252 thousand inpatients and 261 thousand outpatients) were diagnosed with psychiatric and behavioural disorders [3]. With respect to the age of the psychiatric inpatients, the majority were 40 years and over, and the percentage of inpatients aged 65 and over increased considerably from 28.5% in 1999 to 58.4% in 2017 [3,4].
Several original international studies [5][6][7][8][9][10][11][12][13][14] and one meta-analysis [15] reported that the oral health status of psychiatric patients was poor compared to that of the general population. Some previous studies have reported that ageing in the general population is associated with poor oral health, low oral health-related quality of life (OHRQoL) and a high prevalence of dysphagia [16,17]. Therefore, both psychiatric disorders and ageing in psychiatric patients may contribute not only to their poor oral health but also to decreased OHRQoL and an increased prevalence of dysphagia.
OHRQoL scales are used to assess a patient's condition or a change in oral status during the course of care and to integrate the perceptions and expectations of the patient. The General Oral Health Assessment Index Questionnaire (GOHAI) has been widely used to assess oral health in clinical and epidemiological studies [18]. The GOHAI assesses self-perceived oral health through 12 questions that explore the pain, discomfort, dysfunctions and psychosocial impacts associated with dental diseases [19]. The GOHAI can be selfadministered and is quick and easy to use. Several studies have reported that age, number of remaining teeth, regular dental check-ups, chewing function, and cognitive function were associated with GOHAI [20][21][22][23][24][25]. However, there are few studies regarding psychiatric patients' OHRQoL [26,27] and no studies regarding the associations between age, OHRQoL, and oral health, including oral and swallowing function, among psychiatric patients.
The purpose of this study was to investigate the associations between age, OHRQoL, and oral health, including oral and swallowing function, among psychiatric inpatients.

Design and sample
This study was a cross-sectional survey of psychiatric inpatients in two psychiatric hospitals in Fukuoka Prefecture, Japan. Fukuoka Prefecture is situated on the northern shore of the Japanese island Kyushu. Hospital A was a prefectural hospital and had 300 beds.
Hospital B was a medical corporation hospital and had 270 beds. The subjects were recruited in the chronic phase wards (4 wards in hospital A and 2 wards in hospital B). The total number of subjects was 155.

Questionnaire survey
The questionnaire consisted of the following 3 parts: socio-demographic data, the GOHAI questionnaire for the measurement of OHRQoL, and the 10-Item Eating Assessment Tool (EAT-10) for the measurement of swallowing function and suspected dysphagia.
Socio-demographic information included sex, age, length of hospitalization, last psychiatric diagnosis (according to the International Classi cation of Diseases 10th Revision: ICD-10), and drug use for psychiatric disorders.
The Japanese version of the GOHAI was used in the questionnaire and was composed of 12 items [28]. The 12 items assessed physical function (eating, talking and swallowing) in items 1, 2, 3 and 4 and psychosocial impacts (self-esteem, social withdrawal and worries about oral health) in items 6, 7, 9, 10 and 11. Items 5, 8 and 12 assessed pain and symptoms (use of drugs to relieve pain, discomfort) related to the presence of oral diseases. There are ve response categories with an associated score (l=always, 2=often, 3=sometimes, 4=seldom, and 5=never). The GOHAI score is computed by summing the scores of the 12 responses, and the highest score (60) indicates excellent oral health.
The Japanese version of the EAT-10 [29] was used to measure swallowing function and suspected dysphagia. The EAT-10 consists of ten items about the severity of oropharyngeal dysphagia. Each question is scored from 0 (no problem) to 4 (severe problem). An elevated EAT-10 score indicates severe dysphagia. Participants were divided into two groups: those with an EAT-10 score between 0 and 2 and those with an EAT-10 score between 3 and 40 because a score ≥ 3 was de ned as the prevalence of suspected dysphagia in previous studies [30,31].
The validity and reliability of the Japanese questionnaires were veri ed in previous studies [28,29]. Cronbach's alpha values for each domain ranged from 0.894 in the GOHAI to 0.942 in the EAT-10.

Oral examinations
The clinical examinations were conducted in the wards by one dentist whose profession was preventive dentistry and who had more than 20 years of experience with dental examinations for research. He examined the participants with a mirror, a probe and a transillumination lamp without the use of radiographs. The participants sat on a chair during the examination. The clinical assessment was recorded according to the WHO criteria [32]: severity of lifetime accumulated caries estimated with the decayed-missing-lled teeth (DMFT) index [number of decayed teeth (DT), missing teeth due to decay (MT), and lled teeth (FT)].

Oral diadochokinesis
Oral diadochokinesis (ODK) was used for the comprehensive measurement of the motor speed and dexterity of the tongue and lips.
ODK has been used in older Japanese populations [33,34]. After the oral examinations, the participants were instructed to say each of the syllables /pa/, /ta/, and /ka/ repeatedly for 5 seconds. Pronouncing the syllables /pa/, /ta/, and /ka/ involves the use of the front (lips), middle (tip and the tongue), and back of the mouth (posterior tongue), respectively. The number of respective syllables produced per second was determined using an automatic counter (Kenkokun Handy, Takei Scienti c Instruments Co., Ltd.) [35]. A diagnosis of decreased tongue-lip motor function was made when the number of /pa/, /ta/, or /ka/ syllables said per second was less than 6.
Data procedure Two investigators who were psychiatric nurses visited the hospitals to recruit and interview the subjects. The researchers selected the participants if they could understand the study explanation, answer the questionnaire, and participate in the oral examination and the measurement of the ODK. The socio-demographic information of the selected inpatients was retrieved from the institutional medical records. The participants were interviewed for the measurement of the GOHAI and EAT-10 by the two investigators. The questionnaire surveys were conducted in hospital A from June to July 2018 and in hospital B from November to December 2018. After the questionnaire survey, the oral examinations and the ODK measurements were conducted in August 2018 in hospital A and in September 2018 in hospital B.

Ethics
This study was approved by the Ethics Committee of Fukuoka Gakuen, Fukuoka, Japan (approved #366) and was performed in accordance with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. The study was explained, and written informed consent was obtained from the inpatients.

Data analysis
A chi-squared test was used to explore the differences in nominal variables between age groups or GOHAI groups. The Mann-Whitney U test was used to explore the differences in the ordinal variables between age groups or between GOHAI groups. Spearman's rank correlation was used to explore the correlations between OHRQoL, EAT-10, and other variables. Linear regression was used to identify relationships between OHRQoL and variables after adjusting for sex and age. Missing data were excluded from the analysis. The data were analysed at the 5% signi cance level. The statistical analyses were performed using the IBM SPSS Statistics software program (version 21.0; IBM Corporation, Armonk, NY, USA).

Results
A total of 100 psychiatric inpatients participated in this study. Sixty-ve psychiatric inpatients were not recruited because they could not understand the study explanation, answer the questionnaire, and participate in the oral examination and the measurement of the ODK.
The participation rate was 64.5%.
The majority of the participants (51.0%) were female ( Table 1). The mean±SD age was 67.3±14.5. The ages ranged from 32 to 94 years. The mean±SD of the duration of cumulated hospitalizations was 9.4±11.5 years. The majority (74.0%) of the duration was less than 10 years. The two most common psychiatric disorders were schizophrenia (F20-29 in ICD-10; 46.0%) and dementia (F00-09; were found in the type of psychiatric disorder, the number of MT, the number of FT, the DMFT, /pa/, /ta/, /ka/ and the EAT-10 score between age groups (p<0.05).
Insert Table 1 here Table 2 shows the comparisons of the nominal variables according to the 50 th percentile of the GOHAI. No signi cant differences were found in sex or the types of psychiatric disorder between the groups. However, 74% of the participants with low GOHAI scores (<50 th percentile) had suspected dysphagia, and a signi cant difference was found in the EAT-10 score between the low and high GOHAI groups (p<0.001).
Insert Table 2 here Table 3 shows the comparisons of the ordinal variables according to the percentiles (25 th , 50 th , and 75 th ) of the GOHAI score. No signi cant differences were found in the medians of the number of DT, the number of FT, the DMFT index, or the oral ODK scores between the low and high GOHAI groups in all three percentile categories. A signi cant difference was found in the median of the number of DT between the GOHAI score <25 th percentile group and the GOHAI score ≥25 th percentile group (p<0.05), and a signi cant difference was found in the medians of the EAT-10 score between the low and high GOHAI score groups in all three percentile categories (p<0.001).
Insert Table 3 here   Table 4 shows the correlations between OHRQoL, EAT-10, and other variables. Age, the length of hospitalization, the number of MT, the DMFT index, and the number of /Ka/ syllable repetitions per second were signi cantly correlated with the EAT-10 score. The number of MT and the EAT-10 score were signi cantly correlated with the GOHAI score (Spearman correlation coe cient=-0.218 in DT and -0.686 in EAT-10). After adjusting for sex and age, only the EAT-10 score was signi cantly correlated with the GOHAI score (β=-0.725, 95% con dence interval:-0.97, -0.64, and p<0.001).
Insert Table 4 here Table 5 shows the percentages of having swallowing problems and the medians of GOHAI score according to whether they had the problem in EAT-10 items. Approximately 20-40% inpatients had the problems regarding swallowing in the items. There were signi cant differences were found in GOHAI scores between having no problem and having the problem in all EAT-10 items.
Insert Table 5 here

Discussion
This report is the rst to investigate the associations between age, OHRQoL and oral health, including oral function, among psychiatric inpatients. The mean±SD of the GOHAI score was 49.7±7.9 in this study. A previous study in France reported that the mean±SD of the GOHAI score was 45.5±8.4 among schizophrenic patients and that the GOHAI score was lower than that of the general population [26].
A previous study in Japan reported that the mean GOHAI scores among general Japanese adults (20-69 years) ranged from 51.3 to 54.8 [16]. Therefore, the results of this study showed that the OHRQoL among Japanese psychiatric inpatients was lower than that among the general Japanese population, and the tendency was similar to that in other countries. With respect to oral health, the mean±SD of the numbers of DT and MT in the older age group (≥65 years) were 1.2±2.0 and 14.3±10.2, respectively. A Japanese national survey in 2016 reported that those in the general Japanese population (≥65 years) were 0.8 and 9.7, respectively [36]. Therefore, the oral health status of the psychiatric inpatients was poorer than that of the general Japanese population.
The results of this study showed that the number of syllable repetitions per second among the inpatients were nearly 3.0, which were much lower than the standard value. And the fewer repetitions were signi cantly associated with aging. Some previous studies reported that age, dementia, and antipsychotic medication were associated with reduced motor functions [37][38][39]. In addition, some subjects repeated slowly the syllables although they were instructed to do as quickly as possible. It might be di cult for them to repeat quickly the syllables as instructed due to the low cognitive function. Therefore, it is suggested that the factors of the low number of the repetitions among the psychiatric patients might be not only low tongue mortar function but also low cognitive functions in psychiatric diseases. Further studies are needed to evaluate accurately the ability of tongue motor function for psychiatric patients.
With respect to swallowing function, the inpatients had a high prevalence of suspected dysphagia and 20-40% had the swallowing problems. A previous study for elderly people reported that fewer number of tooth and impaired tongue motor function were associated with lower swallowing function [40][41]. Swallowing problems due to aging were more likely to develop in individuals with fewer teeth [40]. The number of teeth and tongue are important for forming a bolus with a viscosity and particle size suitable for swallowing without a delay in the initiation of swallowing [41]. Therefore, the low oral functions among the inpatients might impaired swallowing function and contribute to having their swallowing problems such as taking effort for swallowing solids or swallowing pain.
In addition to those swallowing problems, they had problems that they took extra efforts for swallowing liquid, pills, or sticky food.
Those problems were thought to be caused by swallowing function itself. A previous study reported that ligamentous laxity, reduced muscle tone in the pharynx and esophagus, and increased duration of swallowing were recognized as physiological changes due to aging [41]. Patients with Alzheimer's dementia tended to have an increased number of swallows for any given amount in their mouth, a longer duration of the swallow, and a longer period of apnea [42]. They developed reduced pharyngeal clearance, reduced upper esophageal opening, and penetration and/or aspiration as the disease progresses [43]. Moreover, some studies have reported that impaired swallowing functions are associated with the side effects of drugs [44][45][46]. Therefore, these factors such as aging, dementia, and psychiatric drug might affect the swallowing problems among the inpatients.
Suspected dysphagia was associated with a low GOHAI score at the bivariate level. In addition, only the EAT-10 score was correlated with the GOHAI score after adjusting for sex and age. Having swallowing problems were signi cantly associated with low OHRQoL. It was hypothesized that OHRQoL were signi cantly associated with poor oral health status among psychiatric patients. However, our study showed that their OHRQoL was associated with swallowing function more signi cantly than oral health status.
A higher number of MT was associated with a low GOHAI score at the bivariate level. Some previous studies reported that tooth loss was associated with OHRQoL in elderly people [47,48]. Tooth loss lowered diet quality [49] and contributed to the prevalence of dysphagia [50]. These factors might affect OHRQoL among psychiatric inpatients. It is suggested that the provision of oral care for the recovery of occlusal and swallowing function might be needed to improve OHRQoL.
Several limitations associated with this study warrant attention. First, the study included only 155 psychiatric inpatients in two psychiatric hospitals in Japan. The inpatients with acute diseases or severe physical conditions were excluded from the study. In addition, the participants were recruited based on whether they could understand the study explanation, answer the questionnaire, and participate in the programme. Therefore, selection bias occurred, and the subjects were not representative of all inpatients in the hospitals. However, it would be very di cult to obtain information for this study from psychiatric inpatients in severe conditions. Second, this study was a cross-sectional study. Cohort studies are needed to verify the associations between ageing and OHRQoL or ageing and oral health, including oral function. Third, suspected dysphagia were de ned from EAT-10 in the questionnaire survey without clinical diagnosis. However, a previous study showed that the sensitivity and speci city in the EAT-10 of the screening for oropharyngeal dysphagia with an optimal cut-off at the score 2 were 0.89 and 0.82, respectively and suggested that the discriminating ability of the EAT-10 questionnaire for the clinical screening of oropharyngeal dysphagia is very high and useful methods for detecting the patients [51]. Forth, a similar approach for investigating psychiatric patients' OHRQoL was used in French study [26]. Finally, other factors, such as chewing function [22], nutritional status [24], and cognitive function status [25], might be associated with OHRQoL.
Therefore, further studies are needed to adjust for those variables.

Conclusion
This report is the rst to investigate the associations between age, OHRQoL and oral health, including oral function, among psychiatric inpatients. The oral health, including oral function, of the participants in this study was poorer than that of the general Japanese population. A higher DMFT index, low ODK, and suspected dysphagia were signi cantly associated with age. Tooth loss and suspected dysphagia were associated with OHRQoL, and swallowing problems were main factors for lowering OHRQoL. Ageing and psychiatric disorders might contribute to poor oral health, low oral function, dysphagia, and low OHRQoL. Therefore, it is suggested that health professionals should recognize that not only oral care for the recovery of occlusal by dentists but also oral and swallowing function recovery trainings by multi-professionals might be needed to improve psychiatric inpatients' OHRQoL and QoL. Availability of data and materials The datasets generated and/or analyzed during the current study are not publicly available as the ethics approval was granted on the basis that only researchers involved in the study could access the de-identi ed data. Raw data have been stored securely at Fukuoka Nursing College.

Competing interests
The authors declare that they have no competing interests.

Funding
The study was supported by Grants-in Aid for Private University Research Branding Project and partially supported by JSPS KAKENHI Grant Number 17K12001. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Authors' contributions SH searched and reviewed the literature, analyzed the data, and wrote the manuscript. FN, YH, MK, and HA negotiated with the hospitals to conduct this study, collected data, and assisted in nding documents, issuing questionnaires, analyzing the data. KK and TN critically reviewed the manuscript and supervised the whole study process. All authors have read and approved the manuscript.