Design, setting, and eligibility criteria
The present study was an analytical cross-sectional study among 130 visually impaired adolescents in Tehran, Iran, conducted in December 2018. Pilot and data collection was done from December 2018 to January 2019. Inclusion criteria were being in the sixth to the tenth grade (aged 12–17 years) and having the parents’ consent. Children were excluded from the study if they were not cooperative, and/or had mental disabilities or were absent at the time of the study. In Iran, girls and boys study in separate schools. There are only three schools for visually impaired children in Tehran which visually impaired children of all districts or even other cities study in. One of these three schools was for girls located in the north of Tehran with 98 students (school 1). The two others were for boys (school 2 and 3): school 2 located in the center of Tehran with 53 students and school 3 located in the west of Tehran with 150 students. Of all three schools for visually impaired children in Tehran, total of 133 children aged 12–17 years were recruited (census), which all had parents’ consent and only three children (2%) were excluded (one student from each school) because they were absent during the research period. All the participants were cooperative, none of them had mental disabilities and none of them refuse to join the study. Thus the inclusion rate of the adolescents of these three schools was 98%. Ultimately 130 adolescents participated in this study. The participants in each school were as follow: school 1, for girls (n = 37); school 2, for boys (n = 25); school 3, for boys (n = 68).
Study variables and data collection
World Health Organization (WHO) oral health questionnaire for children [28], including oral health-related questions and general characteristics, was filled out through face to face interviews. For every participant, the questions were read one by one followed by the optional answers. If it was necessary, the interviewer repeated the items to understand well. For content validity of the questionnaire for visually impaired children, the questionnaire was filled out for 20 visually impaired children in the eleventh grade and we asked them if there is a need for any changes in the questions according to their special conditions. Finally, two oral health experts reviewed and confirmed the questionnaire validity. The questionnaire showed an acceptable validity with Cronbach alpha coefficient of more than 0.9.
Oral examinations were implemented to assess Decayed, Missing, and Filled Teeth (DMFT), the Simplified Oral Hygiene Index (OHI‑S), and Bleeding on Probing (BOP). The school children were examined with a headlamp, a disposable mouth mirror and explorer, a WHO periodontal probe, and disposable gloves and masks while they were sitting on a chair in a comfortable position.
General characteristics
The children’s age, gender, grade, the status of visual impairment, place of residence, and their fathers’ and mothers’ education were considered as the general characteristics.
According to the 11th revision of International Classification of Diseases (ICD-11), the severity of vision impairment is classified into six levels: mild vision impairment, moderate vision impairment, severe vision impairment, and three categories for blindness [29]. In this study, we categorized visual impairment status in two groups: “low vision” for moderate and severe vision impairment, and “blind” for blindness [8].
Fathers’ and mothers’ education data were collected according to the number of years they spent in school and university. Since after 12 years of education in school, people would get a high-school diploma in Iran, in the analysis, we categorized them into two groups: (1) <12 years (less than a high-school diploma); (2) ≥12 years (a high-school diploma or higher).
Oral health-related questions
Oral health-related questions included the following variables:
-
(a)
perceived dental health status (how would you
describe the
health of your teeth?),
-
(b)
perceived gingival health status (how would you describe the health of your gums?),
In both “a” and “b” the 7-point Likert scale responses were categorized into two groups: (1) satisfied (excellent, very good, and good); (2) not satisfied (average, poor, very poor, and don’t know) for the analysis.
-
(iii)
the frequency of tooth brushing (How often do you clean your teeth?) was dichotomized into (1) at least once a day; (2) less than once a day,
-
(iv)
using a toothbrush, toothpaste, and dental floss,
-
(v)
using fluoridated toothpaste (Do you use toothpaste that contains fluoride?) with three responses (1. yes; 2. no; 3. don’t know),
-
(vi)
dental visit frequency in the last 12 months (How often did you go to the dentist during the past 12 months?), which were coded as: (1) yes (for at least once); (2) no (not in the past 12 months),
-
(vii)
the reason for the dental visit in the last 12 months,
-
(viii)
medical conditions dichotomized into two groups: (1) healthy (if there were no other physical or psychological diseases along with visual impairment); (2) not healthy (if there were one or more other physical or psychological diseases along with visual impairment), and (i) dietary habits included 9 questions concerning the consumption of sugary snacks or drinks (fruits, biscuits, cakes, cream, soft drinks, jam and honey, gum with sugar, sweets and candy, milk with sugar, tea with sugar, and coffee with sugar).
In order to evaluate the association between frequency of sugar consumption and oral health status, the answers were scored as follows: several times a day = 6, every day = 5, several times a week = 4, once a week = 3, several times a month = 2, never = 1. Then the sum of the scores for these nine questions was calculated for each child. After that the scores changed into scale 0–100 [30]. Normality test of the scores showed normal distribution (Shapiro–Wilk test: P = 0.13). Because of normal distribution of sugar consumption score, mean and median values were very close to each other (mean = 33.69, median = 33.33). So, choosing each one as the cut-off point had the same result [31]. In this study, we considered the median score of sugar consumption as the cut-off point between the low and high sugar consumption [32]. Consequently, according to the median score of sugar consumption among 130 study participants, children were categorized into two groups: 1. low sugar consumption, 2. high sugar consumption. Participants scoring more than the median score were identified as having high sugar consumption while participants scoring less than or equal to the median score were considered to have low sugar consumption.
The calibration
Oral examinations were carried out by a single examiner. For intra-examiner calibration, 10 children from the 11th grade were examined. Between the two assessments of BOP, there was half an hour break time to resolve previous bleeding (Kappa = 1). The examiner also assessed debris index (DI) and calculus index (CI) for OHI-S. Due to the removal of the debris by the explorer during the first examination, it was not possible to assess DI again. Thus only for CI, intra-class correlation coefficient (ICC) was calculated (ICC = 1). The examiner was calibrated by the WHO Oral Health Surveys Basic Methods for DMFT assessment (33). ICC for DMFT was 0.90.
Clinical examinations
Caries experiences assessed through DMFT index were dichotomized into two groups (DMFT < 3, and DMFT ≥ 3) [20, 34]. Oral hygiene was assessed by OHI-S [35], which consisted of DI and CI. Six permanent tooth (3, 8, 14, 19, 24, and 30) surfaces were scored on a scale of 0 to 3. The mean scores indicated as DI and CI [35, 36]. The sum of DI and CI was defined as OHI-S, which was then categorized into two groups for analysis: (OHI-S ≤ 1.8, and OHI-S > 1.8). Since, in the present study, only 6.9% of the children had poor OHI-S (> 3), and none of them had poor CI (> 1.8), we dichotomized OHI-S based on the scoring for poor DI (> 1.8) [8].
To assess BOP, buccal and mediobuccal surfaces of all teeth in the first to the fourth quadrants were examined by the WHO periodontal probe. The presence of local or general bleeding was coded as yes, and the absence of bleeding was indicated as no [37].
Statistical analyses
The STATA software version 14 (Stata Corporation, College Station, TX, USA) was used for data analysis. Univariate regression test was applied to identify the association between independent variables and categorical outcomes. To consider cluster effect of schools, we used mixed effect model in which clusters entered as random effect in the model. Multiple logistic regression analysis was performed to identify which variables were associated with outcomes in the presence of other variables to indicate possible predictors. If the P value for the association of variables was less than 0.2 by testing with univariate, it was included in the multiple regression analysis [38, 39]. A P value < 0.05 was considered statistically significant.
Ethics statement
The Tehran University of Medical Sciences Ethics Committee approved the study (IR.TUMS.DENTISTRY.REC.1397.104). Before the study written informed consent was obtained from the parents. In addition, the children gave “assent” to be sure they were happy to participate in the study.