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 165.
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 identification of swallowing problems and the screening of suspected dysphagia.
Socio-demographic information included sex, age, length of hospitalization, last psychiatric diagnosis (according to the International Classification 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 five 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 identify swallowing problems and screen for suspected dysphagia. The EAT-10 consists of ten items regarding swallowing problems. Each question is scored from 0 (no problem) to 4 (severe problem). 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 defined as the prevalence of suspected dysphagia in previous studies [30, 31].
The validity and reliability of the Japanese questionnaires were verified 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-filled teeth (DMFT) index [number of decayed teeth (DT), missing teeth due to decay (MT), and filled 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 Scientific 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. Before the interviews, the subjects with acute psychiatric symptoms and moderate-severe dementia were excluded by the nurses and doctors in charge of them. Those who were initially eligible received an explanation of the study and were interviewed with the GOHAI and EAT-10; those who could not communicate their feelings and respond after a question was repeated twice were also excluded based on the judgement of the investigators and nurses in charge of them. The socio-demographic information of the selected inpatients was retrieved from the institutional medical records. The questionnaire surveys were administered and the socio-demographic information was confirmed 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% significance level. The statistical analyses were performed using the IBM SPSS Statistics software program (version 21.0; IBM Corporation, Armonk, NY, USA).