Evaluation of protective factors in caries free preschool children: a case-control study

This was a case-control study evaluating the protective factors of dental caries-free in 528, 4–6-year-old children and their mothers selected from 22 randomly selected preschools that were enrolled in the study from April to December 2017 in Tehran/ Iran. The study was approved by the Ethics Committee of Tehran University of Medical Sciences (IR.TUMS.REC.1395.6070). The sample size was calculated using the EPI tools epidemiological calculator for case-control studies with a confidence level of 95%, and power of 0.8, and an equal number of cases and controls. For preschool selection, which could represent the whole city, the megacity of Tehran was divided into 22 strata according to the divisions of Tehran Municipality and the Ministry of Education. We actually applied the multi-stage cluster random sampling for preschool random selection. In fact, municipality districts were the stratum, and preschools in each stratum were clusters. We got a list of preschools in each district of Tehran Education Organization, and subsequently, one preschool (one cluster) was randomly selected in each stratum as a primary sampling unit and in each preschool, normal healthy 4–6-year-old children were included in the study by an oral examination. The healthy children were selected based on the children’s health report issued by a physician, which is accessible in children’s health files in the preschool office. The child would be placed in the case group if s/he was caries-free and would be placed in the control group if s/he had dental caries after obtaining informed consent from her/his mother. They were actually friends and neighbors controls. It was important to recruit 12 caries-free children and 12 controls in each preschool [13]. As we did not have enough cases in three preschools, we chose more controls.

In the next step, the mothers who were invited to the preschools were approached and the purposes of the study and interview were clearly explained to them and they were assured of the lack of side effects. After obtaining their approval for participation, they were requested to sign an informed consent form prior to enrollment. 27 mothers and their children were not willing to participate in the study; one mother and her child immigrated to another city, so the final sample size was 500 mothers and their preschool children. All mothers were motivated by offering preventive procedures such as professional dental cleaning, and educational sessions on proper oral hygiene measures, and the required dental treatment after the study.

The study was divided into two stages; stage 1 included the intra-oral examination of the children, and stage 2 was a mother questionnaire survey.

In stage 1, the children’s teeth were examined by an experienced and calibrated dentist (MP). The intra-rater reliability by Cohen’s kappa coefficient was 0.89 as an almost perfect agreement. The intraoral examination was conducted in accordance with the WHO standards, in an area well-lit with natural and headlamp using disposable plain dental mirrors, gauze wipes, and wooden tongue depressors [13]. The criteria for caries detection were cavities in the enamel and dentine. The children were examined in the sitting position on a chair in the preschool facing the window by the dentist. The children were divided into two groups. Participants in group 1 (cases) were caries-free children, which means that they did not have any decayed, missing, or filled primary teeth. A child was considered to be suffering from ECC when (s) he complied with the definition of the American Academy of Pediatric Dentistry (AAPD) defining ECC as the presence of one or more decayed, missing, or filled tooth surface in any primary tooth in a child of 71 months of age or younger [14]. These children who had AAPD criteria were categorized as group 2 (controls). As the cases and their controls were almost selected from the same preschool, they were approximately similar from the points of the calendar time of examination, and allocation, area of living, and overall health.

In stage 2, the mothers were interviewed by another dentist who was unaware of the results of the children’s oral examination performed by the first dentist. A standard and valid structured questionnaire was considered for the interviews [15]. The questionnaire was evaluated for content validity once more by a group of five experts of community oral health and epidemiology. The questions that were found to be confusing were revised and retested on 10 mothers to check the questionnaire’s stability. The questionnaire reliability was determined by the internal consistency of 0.80 based on Cronbach’s alpha coefficient. Temporal consistency was evaluated by the test- retest method for categorical variables by kappa of 0.84.

The responses were recorded in face-to-face interviews. In such a study the level of participants’ education might be different. Therefore, our method in completing the questionnaire was the interview for two reasons. The first reason was to improve the accuracy of answers and the second reason was to prevent missed data.

The questionnaire included three domains, sociodemographic factors, behavioral oral health measures, and feeding practices and dietary habits. Sociodemographic data included sex, age, the number of siblings, and the parents’ level of education.

Bangkok Declaration of the International Association of Peadiatrics Dentistry (IAPD) on Early Childhood Caries emphasizes that dental caries is determined by biological, behavioral, and psychosocial factors [16]. “ECC is a global dilemma, and with the exception of a multitude of risk factors like oral hygiene maintenance, its incidence is associated with additional factors, such as socioeconomic and education status” [17]. As it was established that education is an important socioeconomic variable in health-related studies, maternal and paternal education were originally assessed using seven categories that were there after dichotomized into < 12 vs. 12+ years of schooling or respectively non-university education and university education since these groups contained most participants.

In behavioral oral health measures, the mothers were asked about the frequency of dental brushing in their children. The answers were categorized as “no brushing and equal to or less than once/day”; these were children who brushed their teeth less than 2 times/day, and “more than once/day”; these included children who brushed their teeth 2 times/day [18]. They were specifically asked if brushing was performed at night or at a random time. They were asked if brushing was self-implemented or performed by the mother or others. Finally, the mothers were asked about any previous dental visit, whether it was early (at the child’s age of 1 year and before it) or late (after the child’s age of 1 year), and its cause.

We did not have a question about toothpaste containing fluoride because even if 4–6 year- old children applied toothpaste with 500 ppm fluoride, it should not act as a protective factor. Studies have shown that toothpaste containing less than 1000 ppm fluoride does not have an anti-caries effect [19].

Dietary and nutritional data included questions about the child’s history of night time and on-demand feeding. Information was collected about daily consumption of foods containing sugar referred to as “sugary foods”, sweets, and drinks, as well as fruit juices (the answers were categorized as 3 times or less and more than 3 times). According to Fejerscov in the book of Dental Caries; “A moderate caries increases for the individuals receiving sugary snacks 4 times daily” [20]. On the other hand, a normal diet frequency includes three main meals and two snack meals. As our study groups were children who need more meals and snacks that are usually sugary, so we decided to choose three times daily consumption as our cut of point.

Another question that mothers were asked about was related to Iron drop consumption for which mothers would answer “yes” or “no”. This question was actually included to clarify mothers’ misunderstanding about the Iron effect on dental caries that happens most of the time.

Both the questionnaire and oral examination forms were manually checked for the completion of the required information.

The collected data were entered into the SPSS software version 21 for statistical analysis (IBM Corp. Released 2012. IBM SPSS Statistics for Windows, Version 21.0. Armonk, NY: IBM Corp). Before starting the study, and during the stage of study design, we weighted all preschools from the point of the target populations in all districts by categorization of preschools on their population/area (density). We randomly chose one preschool from the same density preschools in each district. At the end, the sample included the weighted children.

We performed case-control pairing appropriately to avoid the effects of a confounding variable in sampling and, moreover we adjusted for potential confounders through mathematical modeling using regression method (logistic regression) in the analysis step.