ORIGINAL Asgari ARTICLE et al
Assessing the Oral Health-related Quality of Life in Iranian Adolescents: Validity of the Persian Version of the Child Oral Health Impact Profile (COHIP) Imaneh Asgaria/Arezoo Ebn Ahmadyb/Hillary Broderc/Faezeh Eslamipourd/ Maureen Wilson-Gendersone
Purpose: To evaluate the psychometric properties of an oral-health related quality of life (OHRQoL) instrument for application in the population of Iranian adolescents and to assess the discriminate and convergent validity and reliability of the Persian version of the Child Oral Health Impact Profile (COHIP) in a representative sample of this population. Materials and Methods: Using multistage stratified sampling, 597 schoolchildren aged from 13 to 18 years living in the city of Isfahan were recruited to complete the Persian COHIP questionnaire. They were also examined for dental caries and malocclusion by two trained, calibrated examiners. Results: Overall COHIP scores ranged from 15 to 135 (mean ± SD: 103.6 ± 18). Sixty-six percent of the students experienced at least one frequent oral health-related impact over the past three months. The Cronbach alpha coefficient was 0.89 for the overall score. Discriminate validity was supported by the significant difference between COHIP scores in the caries-free group and the others (P = 0.01). In addition, the questionnaire was able to differentiate among the groups by various degrees of need for orthodontic treatment (P < 0.01). Convergent validity was confirmed by significant association between the quality of life scores, the self-perceived health and oral health ratings and the self-perceived treatment need (r = 0.36, 0.57, -0.40). Conclusion: The Persian COHIP demonstrated acceptable psychometric properties for the descriptive purposes. Some discrepancies observed between the clinical data and quality of life status were confirmed by the perceptual identity of such indices influenced by several overt and covert variables. Key words: adolescents, child oral health impact profile, construct validity, oral health-related quality of life Oral Health Prev Dent 2013;11:147-154 doi: 10.3290/j.ohpd.a29367
O
ver the past thirty years, confidence in the use of subjective indicators for oral health outcomes has increased. A number of investigators a
Public Health Dentist, Department of Community Oral Health, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
b
Assistant Professor, Preventive Dentistry Research Centre, Research Institute of Dental Sciences of Shahid Beheshti University of Medical Sciences, Tehran, Iran.
c
Professor, Department of Cariology and Comprehensive Care, New York University College of Dentistry, NY, USA.
d
Associate Professor, Oral Public Health Department, Dental School, Isfahan University of Medical Sciences, Isfahan, Iran.
e
Associate Professor, Department of Social and Behavioral Health, Virginia Commonwealth University School of Medicine, Richmond, VA, USA.
Correspondence: Dr. Arezoo Ebn Ahmady, Department of Community Oral Health, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Tel: +98-212-242-1813. Email: aebnahmady@ yahoo.com or
[email protected]
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Submitted for publication: 30.07.11; accepted for publication: 30.05.12
have developed and tested the performance of measures designed to assess the functional, social and psychological outcomes of oral conditions (Allen and Locker, 1997; Slade, 1997). Oral HealthRelated Quality of Life (OHRQoL) measures are suitable subjective indicators that provide information on the impacts of oral conditions on an individual’s life and the perceived need for dental care (Sheiham, 2007). Along with the growing interest in quality of life outcomes in the assessment of adolescents’ health, the field of oral health-related quality of life should also be particularly considered (Solans, 2008). Only a few studies in the literature have assessed the use of socio-dental indicators in youth populations and their applicability in developing countries (Åstrøm and Okullo, 2003; Brown and AlKhayal, 2006; Dorri et al, 2007; Barbosa et al,
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2009; Jabarifar et al, 2010). As nearly half of the Iranian population is under the age of twenty, governmental policies have given priority to children and adolescents as a target group for oral health care. A review of oral health studies on youths revealed that the mean value of the DMFT (Decayed, Missing and Filled Teeth) index of 15-year-old Iranians was 2.1 in 2004, and within this population, there was a poor level of oral hygiene as well as a 40% prevalence of untreated decayed teeth (Yazdani et al, 2008). This record had a mean (SD) of 4.8 (3.6) in schoolchildren aged 12 through 19 in Isfahan in 2008 (Eslamipour, 2011). The World Health Organization (WHO) Oral Health Programme published by Petersen (2009) emphasised that the link between oral health, general health and the quality of life among the general population in developing countries is largely unexplored. Therefore, studies regarding the psychosocial implications of oral health/illness and quality of life are an important focus of health service research in our country. Due to the rapid physical and mental growth and cognitive changes during childhood and adolescence, measuring OHRQoL using a unique questionnaire for all ages is not appropriate. As oral health is strongly age dependent (John et al, 2004), there has been a focus on developing age-specific instruments (Jokovic, 2002; Yusuf, 2006; Broder et al, 2007). Recently, different questionnaires have been developed for specific age categories, one of which is the Child Oral Health Impact Profile (COHIP). COHIP is a psychometrically sound instrument, intended to measure OHRQoL among school-aged children between 8 and 15 years old, who have varied oral health conditions, health systems and ethnic backgrounds. It includes positive as well as negative aspects of oral health. The COHIP is the result of a large, international research project supported by the National Institutes of Health (Broder, 2007) and claims to be applicable across different cultures. The original English and Dutch versions of this questionnaire were tested for validity and reliability (Broder et al, 2007; Geels et al, 2008). Such measures of patients’ perceived oral health are increasingly in demand for epidemiological and clinical studies in Iran, as they add a complementary outcome dimension to the traditional clinical indicators. The original COHIP inventory has recently (2007) been translated and validated in a convenience sample of 15- to 17-year-old students in Hamadan city, Iran (Ravaghi, 2011). To confirm the construct validity of the Persian questionnaire, a representative adequate sample of schoolchildren
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was essential in studying the discrimination ability of the instrument across different ranges of oral diseases and varied backgrounds. The confirmatory factor analysis of this questionnaire will be followed in another study by the present authors. The aim of this study was to assess the convergent and discriminate validity as well as reliability of the Persian Child Oral health Impact Profile in a representative sample of schoolchildren aged 13 to 18 years old. A description of the oral health-related quality of life status among this sample of Iranian adolescents was followed through the study as well.
MATERIALS AND METHODS The target population for this cross-sectional study includes adolescents aged 13 to 18 enrolled in public high schools in the city of Isfahan. The study was approved by the Human Research Ethics Committee of the Isfahan University of Medical Sciences and the Isfahan Bureau of Education. Data were collected using non-proportional, multi-stage stratified random sampling. The sample size of 560 was calculated to detect a difference of two units in the score of OHRQoL by 90% power at 5% significance and considered a 10% attrition rate. Regarding geographical subdivisions of the city, five strata were considered as the basis of random sampling. First, twenty schools (ten boys’ schools and ten girls’ schools) were randomly selected from the list of public schools that were registered by the Ministry of Education. The schools included both guidance schools and high schools, as our intentions were to separately evaluate both early and late adolescence. In each school, thirty students were invited to participate in the study. Thus, 600 students were initially selected to be in the study. After describing the purpose and process of the work, instructions were presented in the classroom and those children with parental consent were asked to complete the questionnaire and cooperate in an oral examination. The Persian COHIP forms were completed by the students independently (self-administered). Participants were asked to choose their answers in response to the statement that best described him/her in the past three months regarding teeth, mouth or face. The five alternatives were ‘never, almost never, sometimes, fairly often, almost all of the time.’ The Persian COHIP questionnaire consisted of 34 items forming 5 conceptually distinct subscales:
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oral health (OH, 10 items), functional well-being (FW, 6 items), social-emotional well-being (SE, 8 items), school environment (SC, 4 items) and selfimage (SI, 6 items). Additionally, there were three items on the subjects of self-rating health/oral health, which were scored from ‘excellent to very bad’, and perceived treatment need that was answered based on a five-point Likert scale that ranged from ‘strongly disagree’ to ‘strongly agree.’ A brief written definition of ‘health’ and ‘oral health’ was provided to ensure concept clarity. Subscale scores were calculated by summing up the responses of the items specific to the subscale. The overall COHIP score was computed by summing all the items scores, thus resulting in a response that ranged between 0 and 136. Considering the adaptation for age-specific issues, an available Persian version of COHIP (Ravaghi, 2011) was reviewed by two bilingual dentists and researchers. The revised questionnaire was pretested in a group of ten students, and problematic or unclear words were replaced with more understandable alternatives. Gender, year of birth and mother’s educational level were recorded for students’ demographic characteristics. Mothers’ levels of education were scored using a five-point scale as ‘illiterate, school without formal qualification, high school with diploma, undergraduate university level, postgraduate university level.’ All participants then underwent a subsequent clinical examination for normative treatment-need assessment. It was performed by two qualified dentists (PI and her assistant) who were trained and calibrated to achieve desirable agreement in the pilot study prior to the project. According to the intra-class correlation coefficient (ICC), inter-examiner reliability of 0.95 and 0.91 was achieved for both DMFT and the Dental Health Component (DHC) of the Index of Orthodontic Treatment Need (IOTN), respectively. The decayed, missing and filled teeth (dmft) and DMFT were determined according to the WHO criteria of basic methods of surveys (WHO, 1997). The DHC of the IOTN was recorded as grade 1 (no need) to grade 5 (very great need) according to the occlusal traits, which included overjet, reverse jet, overbite, open bite, crossbite, crowding, impeded eruption, defects of cleft lip and palate as well as occlusal class (Brook and Shaw, 1989). Discriminate validity of the measure was assessed by comparing the average COHIP scores among the groups by different levels of dental caries and malocclusion using the Mann-Whitney Uand Kruskal-Wallis non-parametric tests. Discrimi-
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nate validity was further explored by examining the association between COHIP scores and clinical severity with DMFT and DHC grades, using partial correlation controlling for covariates. Convergent validity was assessed by examining the correlation between the COHIP scores and the self health/oral health rating of perceived dental treatment need. Partial correlation was used to measure the strength of this association after adjusting for the covariates. The level of significance was set at 0.05. Internal consistency was quantified using Cronbach’s alpha for the COHIP questionnaire as well as each subscale.
RESULTS Descriptive statistics Out of 600 participants, those who did not provide signed consent forms (n = 3) were excluded. Twenty-seven of the students who had a history of orthodontic treatment were not included in the discrimination testing. Of 597 study participants (response rate 99%), 53% were female between the ages of 13 and 18 with a mean age of 14.9 ± 1.2 years. There were no cases of extensively incomplete questionnaires; however, any missing value was replaced by the mean score of the item. Thirty-eight percent (n = 226) of the students’ mothers had a high school education, while 7% (n = 43) were illiterate and 12% (n = 71) had university qualifications. The mean COHIP score was 103.6 ± 18 and half of the scores (median) were above 107. Descriptive statistics of the index of quality of life and its subscales regarding three covariates are shown in Table 1. The prevalence of students with more than one item rated ‘fairly often’ or ‘almost all the time’ was 66% on the OH subscale. After that, the SE, SI, FW and SC with 34%, 32%, 18% and 7% were the most prevalent subscales, respectively. Having tooth sensitivity, bleeding gums, food sticking, crooked or abnormal-sized or discoloured teeth comprise the most frequent complaints in the field of oral health. In terms of functional difficulty, about 7% of the population reported difficulty biting or chewing and cleaning their teeth. Being unhappy or sad (17%) and worried or anxious (16%) were the most frequent social-emotional impacts. Fewer than 3% of the students expressed a lack of attention or a tendency not to speak in class due to their dental problems. Nearly 54% were confident and
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63% felt that they were good looking due to their teeth, mouth and face. Although there was no apparent difference in the COHIP overall score in the two genders or in the early (13–15 years) and late (15–18 years) adolescents, the pattern of differences at the subscales was varied. Sixty-three percent of the participants (n = 369) rated their personal oral heath as excellent or good. While 50% (n = 294) of them perceived the need for dental treatment, 33% (n = 196) did not feel the need for treatment. The prevalence of good and excellent perceived health rating was 83% in the students. The Kolmogorov-Smirnov test showed that the distribution of COHIP scores was not normal and tended to be skewed toward higher OHRQoL (skewness = -1.09; kurtosis = 1.55), as were the subscales, thereby requiring the use of non-parametric tests of statistical significance. The results suggested high levels of internal consistency for the overall questionnaire. Cronbach’s alpha for the overall COHIP in the sample was 0.89. The alpha coefficient for SE was excellent (>0.8) and acceptable for the SI, FW and OH (>0.66), but moderate for the SC subscale (0.48). Excluding all of the instances with missing values (valid data = 506), the Guttmann split-half coefficient would be 0.83 and the reliability for the questionnaire still seemed to be excellent.
‘oral health’ and ‘functional well-being’ differed significantly in the students with three or more untreated decayed teeth compared with those having fewer than three decayed teeth (P < 0.05); the other conditions were not significant. Applying the correction of type I error for multiple comparisons, the results showed that COHIP scores and all of the subscales were not sensitive enough to reflect the changes of decayed tooth levels. The results of the discrimination ability of the COHIP are presented in Table 2. Using the Kruskal-Wallis test, mean COHIP scores for ‘social-emotional’ and ‘self-image’ differed significantly between groups (P < 0.01) with varied DHC grades. There was a distinct gradient in the average COHIP across the categories of malocclusion severity, whereas those in the ‘great need’ category had the lowest and those in the ‘no need’ category had the highest scores on the quality of life index. In addition, there was also a significant difference in the total score in regards to the group with ‘definite need’ (DHC grades of 4 or 5) for orthodontic treatment (prevalence 16.5%) and ‘no definite need’ (grades 1-3) (P < 0.05). The bivariate correlation test showed a rho of -0.08 between the COHIP score and both DMFT and DT indices (P < 0.05); however, there was a rho of -0.17 regarding the DHC grade (P < 0.001).
Convergent validity Discriminant validity One-fourth of the students (n = 154) who were caries free had higher COHIP total scores than students who had some caries experience (P = 0.01). The differences between mean COHIP scores in regard to four dental health severity groups including DMFT = 0, 1 ≤ DMFT ≤ 4, 4 < DMFT ≤ 7 and DMFT > 7 with the respective prevalences 26%, 52.2%, 15.5% and 6.3% were significant using the Kruskal-Wallis test (P = 0.027). Regarding the subscales, only the ‘self-image’ subscale showed a significant difference among these categories (P = 0.001). A missing tooth, considered a parameter of perilous condition, was seen in 55 students (9%) and only revealed a significant difference in the ‘school environment’ subscale by the MannWhitney test (P = 0.01). The overall score and its subscales were tested between groups according to the criteria of ‘having a decayed tooth’ by applying the cut-off points such as 0, 2, 3, 4 and 5 for numbers of decayed teeth. Only the results of the
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Approximately half of the school children expressed a need for dental treatment, but 32% did not perceive any need. Sixty-three percent rated their oral health at a good or excellent level. Spearman correlations between the overall COHIP score and perceived oral health and health ratings were statistically significant in the study population (P < 0.001); however, an inverse significant correlation was observed between the perceived need for dental treatment and the quality of life score. The coefficients of the correlations are presented in Table 3.
DISCUSSION This study reported the oral health-related quality of life status in adolescents attending secondary and high schools in Isfahan, the second most populous metropolitan area in Iran. Moreover, in a representative sample of this population, some aspects of the psychometric characteristics of the Persian COHIP version are presented. The Persian COHIP
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Table 1 Descriptive analysis of Child Oral Health Impact Profile (COHIP) and the subscales regarding the covariates of gender, age and mother’s education level in Iranian adolescents Gender Mean (SD)
Age Mean (SD)
Pvalue
Male
female
13–15y
15–18y
COHIP Total
103.7 (18)
103.6 0.94 (18)
104 (18)
102.9 (18)
Oral health (0–40)
27.6 (5.1)
27.7 (5.6)
0.77
28 (5.6)
27.1 (5.9)
Functional well-being (0–24)
20.9 (3.7)
21.9 (2.9)
0.00*
21.3 (3.6)
Social-emotional well-being (0–32)
25.8 (6.2)
25.6 (6.6)
0.64
School environment (0–16)
14.8 (1.8)
15.1 (1.5)
Self-image (0–24)
15.5 (4.9)
14.9 (5.1)
Mother’s education Mean (SD) High Elemen- school PostPtary with Under- graduPvalue Illiterate school diploma graduate ate value 0.5
103.1 (20)
102.5 (17.4)
103 (18.8)
110 (15.4)
101 0.05 (21.2)
0.06
28 (6.1)
27.4 (5.6)
27.3 (5.8)
29.4 (4.8)
28 (6.9)
0.16
21.6 (2.9)
0.2
21.1 (4.7)
21.1 (3.3)
21.6 (3.3)
22.2 (2.7)
20.3 (2.9)
0.11
25.9 (6.3)
25.4 (6.4)
0.4
25.6 (7)
25.2 (6.3)
25.8 (6.3)
27.3 (5.9)
26.4 0.22 (10.4)
0.046*
14.9 (1.7)
15.1 (1.4)
0.2
14.9 (1.9)
14.8 (1.7)
15 (1.6)
15.4 (1.1)
14 (2.5)
0.06
0.046*
15.1 (4.9)
14.8 (5.1)
0.4
14.5 (4.9)
14.8 (5.1)
14.9 (4.9)
16.7 (4.8)
14.6 (4.3)
0.08
*significant at P < 0.05.
Table 2 Discrimination of the Oral Health Related Quality of Life index in the groups with different caries indices and results of mean scores compared by the Mann-Whitney U-test Mean difference of COHIP score according to the different cut-off points of caries index
COHIP score Mean Rank
P-value
Caries free (n = 154) With caries (n = 443)
334.7 286.6
0.003**
No active decay (n = 255) Active decay (n = 342)
311.5 289.7
0.127
DMFT > 2 (median) (n = 284) DMFT ≤ 2 (n = 308)
310.9 286.3
0.08
DMFT > 1 (last 2/3 of distribution) DMFT ≤ 1(first 1/3 of distribution)
284.3 315.4
0.03*
Having missing teeth (n = 58) No missing teeth (n = 539)
302.6 265.6
0.12
**significant at P < 0.01, *significant at P < 0.05.
version was reliable and valid enough for descriptive studies of oral health-related quality of life among Iranian schoolchildren aged 13–18. Reliability and discriminate and convergent validity of the instrument were confirmed in a well-structured representative sample of the target group. The quality of life associated with the oral conditions among this sample of Iranian adolescents was generally good. However, the prevalence of hav-
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ing at least one frequent impact on their life was quite high (66%). The majority of the presented problems was in the field of ‘oral health,’ in which the most frequently reported items included tooth sensitivity, unpleasant tooth appearance, dry mouth and halitosis. As adolescence is a critical period of the caries-formation process in permanent teeth, the occurrence of demineralisation in this population can be expected (Moynihan and Petersen,
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Table 3 Spearman correlation coefficient* between self-perceived health, oral health, need for dental treatment and the COHIP (overall/subscales) adjusted for age, gender and mother’s education Perceived oral health
Perceived health rating
Perceived treatment need
0.57
0.36
-0.40
Oral health
0.41
0.26
-0.33
Functional well-being
0.36
0.31
-0.21
Social-emotional wellbeing
0.47
0.25
-0.34
School environment
0.24
0.16
-0.15
Self-image
0.58
0.35
-0.36
COHIP Total scale COHIP Subscales
* All correlations are significant at P < 0.001.
2004). After that, the social-emotional and self-image subscales with 34% and 32%, respectively, were the most prevalent subscales. In a study by Broder and Wilson-Genderson (2007), the OHRQoL score in a sample of American and Canadian adolescents aged 8 to 15 was somewhat lower than in this sample. The study by Dorri et al (2007) of the oral impacts that were carried out in a sample of Iranian adults living in Mashhad revealed that 65% of them have problems with their teeth. Despite the different age range and OHRQoL, the prevalence of oral problems was similar to this study. Other studies in Tanzanian adolescents with a mean age of 15 and 12-year-old Sudanese schoolchildren reported the prevalence of having at least one oral impact as 48% and 34%, respectively (Mbawalla et al, 2010; Nurelhuda et al, 2010). According to a few studies, oral conditions related to dental caries, such as toothache and sensitive teeth, were the main self-reported causes of impact on the quality of life in children in developing countries (Gherunpong et al, 2004; Bernabe et al, 2009). The original English version of the COHIP was previously tested for its reliability (Broder and Wilson-Genderson, 2007; Geels et al, 2008) and both the internal consistency and test-retest reliability were found to be excellent (Cronbach alpha = 0.91 and ICC = 0.84, respectively). The alpha reliability of the overall score of the Persian COHIP was nearer to the original study (0.89) but presented lower values in the subscales, especially the SC subscale (_ = 0.48). A similar condition was apparent in the community group sample of the Broder (2007) study (_ = 0.50). Furthermore, Geels et al (2008) reported that some of the subscales of the Dutch version showed an insufficient Cronbach alpha and
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some of the intercorrelations between the subscales were quite high. For the purpose of examining the construct validity of the questionnaire, it was hypothesised that students with better dental health status would have higher quality of life scores and vice versa. This hypothesis was supported by the malocclusion status and overall COHIP score, in which the assumed pattern in the mean COHIP was seen among the categories of malocclusion severity. Similar to our findings, Foster Page (2005) observed a distinct gradient in the mean of emotional and social well-being domains of the Child Perception Questionnaire (CPQ) when malocclusion was examined by the Dental Aesthetic Index. Many studies have found a relationship between malocclusion and quality of life (Vig, 2007; Barbosa and Gaviao, 2008; Mtaya, 2008; Liu et al, 2009). A review of the findings of the cross-sectional studies on the relationship between malocclusion and quality of life carried out by Liu et al (2009) indicated that the strength of this correlation ranged from 0.15 to 0.45. However, a few researchers such as Bernabe et al (2008, 2009) did not find a significant difference in the OHRQoL scores between the groups with and without orthodontic treatment need in both 12-year-old Thai schoolchildren and 16-yearolds in London applying generic child-OIDP and OHIP-14, respectively. The assumed hypothesis that dental health/diseases could be reflected in the OHRQoL index was not completely supported by the findings of our study. The COHIP instrument was only able to make a distinction with regard to the existence of caries experience. The quality of life of persons who have had caries was affected, compared to caries-free
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individuals. However, worsening dental problems, such as increased tooth decay or missing teeth, was not reflected in a worse quality of life. This finding is also consistent with previous results of the Broder and Wilson-Genderson study (2007), which demonstrated lower quality of life scores in the group of children with craniofacial anomalies, but neither the paediatric nor the orthodontic group differed significantly from the community sample in their scores. Similarly, Brown and Al-Khayal (2006) found a significant correlation only between the DMFT and the oral symptom subscale of CPQ, but not with other domains (functional limitations, emotional and social well-being) in 11- to 14-year-old Arabian children. These findings support the notion that OHRQoL is a heterogeneous construct that is influenced by the person’s experiences, beliefs, expectations and perceptions. Applied as a valid instrument to determine whether a physical condition affects one’s personal or social life to a threshold level, it will be able to displace the quality of life score. This threshold level is driven by a complex network of variables. Convergent validity of the Persian COHIP was moderately correlated with the self-perceived constructs. Although like the original questionnaire, the positive relationship between ‘perceived health rating’ and COHIP was limited, a more powerful association was found between the self-perceived ‘oral health rating’ and ‘treatment need.’ The correlation observed in the Persian version of COHIP was stronger than the correlation reported for CPQ score and oral health and health ratings (r = 0.23 and 0.4, respectively) (Jokovic et al, 2002). These findings suggest that age, gender and the level of the mother’s education as factors reflecting the social status of the child did not influence the person’s quality of life. Therefore, a qualitative study may be necessay to explore the driving factors of OHRQoL in adolescents in our population. Although there are extensive variables that affect the subjective perceptions, experiences and expectations of an adolescent, a lack of ‘oral health literacy’ is also a cofactor of observable discrepancies between dental health status and reported OHRQoL in this age group. As we intend to use the COHIP as an outcome measure in community trials, its evaluative properties and sensitivity to change also need to be assessed. Moreover, longitudinal studies are required to determine the instrument’s longitudinal construct validity, test-retest reliability, responsiveness and minimal clinically important differences.
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CONCLUSION The Persian COHIP demonstrated acceptable psychometric properties for the descriptive purposes. Some discrepancies observed between the clinical data and quality of life status were confirmed by the perceptual identity of such indices influenced by several overt and covert variables.
ACKNOWLEDGEMENTS Imaneh Asgari created this study, determined its design, conducted data collection in Isfahan, performed the statistical analyses and wrote the manuscript. Arezoo Ebn Ahmady and Hillary Broder supervised and participated in the design and implementation of the study and have contributed to the completion of the manuscript. Faezeh Eslamipour supervised and conducted the training and calibration phase in the field, and Maureen Wilson-Genderson assisted in the statistical analysis and manuscript revisions. All authors read and approved the final manuscript. This study was financially supported by the Iran Centre for Dental Research, Shahid Beheshti Medical University. We would like to thank all students who took their time to participate in this survey. The assistance from Dr. Farzanekhoo for the dental examination is highly appreciated.
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Oral Health & Preventive Dentistry
