The present study was approved by the Research Ethics Committee of Golestan University of Medical Sciences (IR.GOUMS.1397.166) and performed entirely following the Declaration of Helsinki. All participants’ rights were protected. Informed consent was obtained from parents before the study. Moreover, the data were handled anonymously and confidentially in all stages of the study.
Study population and sampling
The sample size was calculated at 330 preschool children, based on a 0.05 Type I and 0.2 Type II error rate. Also, 20% was added to compensate for possible losses, giving a total sample of 350 preschool children.
This cross-sectional descriptive-analytical study was conducted among 350 children aged 3–6 years selected from about 6000 children registered in the licensed kindergartens of Gorgan. Hence, the list of licensed kindergartens in three municipality districts of Gorgan was prepared. Then, according to the number of children in each municipality district’s kindergartens, the number of children in each district was determined. Numerous kindergartens were selected randomly (allocating a number to each kindergarten and selecting random numbers).
Children aged 3–6 years whose parents could easily speak Persian were selected. Exclusion criteria were a history of systemic diseases or receiving specific medication. Parents who did not complete the questionnaires were also excluded.
In the first session, the aim of research was explained to kindergarten teachers. Then, demographic questionnaires were given to preschool educators and administrators as well as consent forms to be completed by parents. Demographic information included data on the child’s age, gender, ethnicity, birth order, and parental level of education.
Questionnaires and data collection
In the next session, the parents completed the Persian version of the Early Childhood Oral Health Impact Scale. The questionnaire consists of 13 questions, classified into two sections: “impact on children” and “impact on parents”. The first 9 questions of the questionnaire examine the impact of the children's oral health, including items such as eating, sleeping, and talking. The second section, “impact on parents”, has 4 questions in 2 subscales: parents’ concerns (2 questions) and parents’ functions (2 questions).
Response options included “never”, “hardly ever”, “occasionally”, “often”, “very often”, and “don't know” that received a score of 0 to 5, respectively. A score for the missing items was imputed as an average of the remaining items for each section. Overall, the total score of this index ranges from 0 to 52 with a higher total score indicating more oral health problems and less oral health-related quality of life.
Children’s oral examination
Clinical examinations were performed by the researcher to measure the dmft index (decayed, missed, and filled teeth) using dental examination tools (disposable dental mirror, dental explorer, sterile gauze, and mask) according to the World Health Organization criteria for the diagnosis of caries. Moreover, all of the oral examinations were performed by a single trained and calibrated researcher. Hence, only intra examiner reliability was determined. Thus the oral examination of 10 randomly selected subjects was repeated at two time points to determine intra examiner reliability. The Kappa coefficient value for intra examiner reliability was 0.87 which is interpreted as very good.
For clinical examination, the child was seated in a chair in front of a window, and a flashlight was used if there was insufficient light. Besides, another person previously trained by the project administrator recorded the codes for the dmft index in the oral health assessment forms (provided by the World Health Organization).
Data were analyzed by the SPSS software version 16 using mean, standard deviation, frequency, and percentage. Then the normality of the data was determined by the Shapiro–Wilk test. An Independent t-test was used for data with a normal distribution, and the Mann–Whitney test was used for data that did not have a normal distribution. P-values less than 0.05 were considered significant.