Study design and Population
This cross-sectional study was carried out among adults who are 18 to 65 years old between May and October 2016 in Tabriz. A population-based household survey was conducted in order to recruit a representative sample of adults from the community. Eligibility criteria are: a) living in the study area and being at home at the time of data collection and (b) not having a diagnosed of mental or cognitive disorder. Written informed consent was obtained from each participant.
Sampling and sample size
The sample size was calculated based on the level of oral health status in the adult population of Tabriz. To estimate the oral health status of 50% (edentulous) [9], with a 95% confidence and an error of 3%, the sample size was estimated to be 2310. The population of Tabriz was estimated to be 980,000 (aged 18 to 65 years) in 2016 [16]. The study population was sampled using a multi-stage cluster sampling design [17]. In the first sampling stage, four health care centers (HCCs) were randomly selected from 16 HCCs. In the next stage, 25% of street blocks in the area of HCCs were selected. Then, every 11th household of each block was identified for the recruitments of study participants. Finally, in each household eligible individuals were asked to participate in the study. In total, 690 people refused to participate in the study. Sampling in the blocks was continued to reach the required sample size specified for that block. Four trained researchers conducted the interviews. They were bilingual in Farsi and Turkish, female, between the ages of 23 and 30 years old. In this study, a total of 2310 respondents completed the survey (77% response rate).
Data Collection and questionnaire
The WHO’s oral health questionnaire (WHO’s OHQ) for adults was used for measuring oral health status and oral health behavior [17]. WHO’s OHQ consists of 16 variables. Four questions assessed the oral health status: (a) self-reported number of teeth present (0 = no natural teeth, 1 = 1 – 9 teeth, 2 = 10-19 teeth, 3 = 20 teeth or more), (b) experience of pain/discomfort from teeth and mouth (yes/no), (c) wearing of removable dentures (partial/full upper/full lower; yes/no), (d) self-assessment of status of teeth and gums (ranging from 1 = excellent to 6 = very poor). Three items assessed oral health related behaviors: (a) frequency of tooth cleaning (ranging from 1 = never to 6 = once a day), (b) use of aids/tools for oral hygiene (e.g., toothbrush, wooden toothpicks, thread; yes/no), and (c) use of toothpaste with and without fluoride (yes/no). Two questions are related to (a) dental visits (ranging from 1 = less than 6 months to 5 = 5 years or more) and (b) the reasons for the dental visit(s) (e.g. consultation/advise, treatment/follow-up treatment, pain or trouble with teeth, gums, or mouth). One question assessed the experience of reduced quality of life due to twelve oral problems (e.g., “difficulty in biting food,” “difficulty in chewing food,” or “felt embarrassed due to appearance of teeth”) (0 = don’t know, 1 = no, 2 = sometimes, 3 = fairly often, 4 = very often). One question examined the consumption of sugary foods and drinks: (a) eating fresh fruits, (b) biscuits and cream cakes, and (c) drinking tea with sugar with answer categories 1 = never/seldom, 2 = several times a month, 3 = once a week, 4 = several times a week, 5 = every day, and 6 = several times a day. One item assessed the use of tobacco with type (a)cigarettes, (b) pipe, (c) cigar, (d) chewing tobacco and (c) use of snuff tobacco, and frequency (1 = never/seldom, 2 = several times a month, 3 = once a week, 4 = several times a week, 5 = every day, and 6 = several times a day). The last question assessed the consumption of alcohol (usual number of drinks per day) during the past 30 days (ranging from 0 = less than 1 drink to 5 = 5 or more drinks). The remaining questions were socio-demographic questions about age (between 18 and 35, 36 and 50, and 51 and 65 years old) and gender (male or female).
The validity and reliability of the WHO’s OHQ was assessed based on standardized cross-cultural translation guidelines [18]. The English version of the WHO’s OHQ was translated into Persian. The translation was done by two independent native Persian translators. Both translators agreed on a common translation. Then, the questions were translated back from Persian to English by two professional translators. The translators and researchers checked and agreed on the final Persian version. Content validity was conducted in a pilot study of 20 individuals [19]. They were asked to give feedback on the scale for improvement. This process led to some changes in the wording of the scale. Thereafter, the Persian version of WHO’s OHQ was evaluated by an expert panel (three health educationists and two dentists). The Persian version of WHO’s OHQ had satisfactory validity among the pilot population.
Statistical Analysis
Statistical analyses were performed using the Statistical Package for Social Science (SPSS 18 for windows, SPSS Inc.® headquarters, Chicago, USA). Normality of data was analyzed by Kolmogorov-Smirnov tests. Discrete variables are presented with a number and a percentage. Chi-square analyses were used to test the difference between biochemical variables between two groups. Results were considered statistically significant at p < 0.05.