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Dental caries, Family size, Gender, Oral hygiene, Primary school, IntroductionDental caries is the most common preventable chronic childhood disease worldwide, which is an infectious and multifactorial disease [ 1,]. Primary teeth play an important role in meeting the nutritional and developmental needs of children. Moreover, dental caries can pose negative effects on children&apos,s growth, health status, quality of life, speech and communication and their ability to eat. Therefore, prevention of dental caries in children is very essential [ 2,- 4,]. The results of one study showed that 298 billion dollars annually is spent on direct dental costs worldwide, accounting for 4.6% of total health spending [ 5,]. The prevalence and severity of dental caries in children worldwide has decreased, especially in developed countries [ 6,], while the prevalence of dental caries in developing countries is increasing [ 7,]. The causes of dental caries may be due to poor socioeconomic status, cultural habits, failure to prevent oral disease, lack of fluoride in water, use of sugar products, and poor oral hygiene [ 8,- 9,].The DMFT index of permanent teeth and the dmft index for primary teeth that include decayed (D/d), missing (M/m) and filled (F/f) teeth are important indicators in assessing the health of children in each community [ 10,]. The dmft index in Iran is high compared to the World Health Organization standards [ 11,]. Moreover, according to the report of the Deputy of Health, caries index in Iran in the age group of 6 years has increased from 5 in 2006 to 5.7 in 2011 [ 12,]. This age group refers to the dentist less frequently than others do for regular periodic examinations. Caries also affects primary teeth far more than permanent teeth, which can be attributed to differences in enamel structure, oral hygiene and less preventive measures. In addition, having caries early in life is a predictor of the risk of caries in adulthood [ 13,- 15,].Numerous factors have been shown to be related to dmft index such as gender, tooth brushing, parents&,rsquo occupation, level of education, and family size [ 16,- 19,]. The study of Emamian et al. [ 18,], which was conducted on 5620 6- to 12-year-old students, indicated dental status of girls was poorer compared to boys. A study in Yasuj showed that the higher the socioeconomic status of the families, the lesser the dmft and DMFT indices in children [ 19,]. Frequent toothbrushing and dental flossing was shown to have a positive effect on dental health in studies by Ramezani et al. [ 20,] and Abdelhamid et al. [ 21,]. They reported that students who brushed their teeth twice a day or more and those who flossed (whose number was relatively low) had lower DMFT score in comparison with students who did no brush their teeth regularly and did not use dental floss [ 20,- 21,].Despite advances in science and technology, none of the introduced materials in dentistry is as ideal as normal tooth tissue. Thus, prevention is the best way to address the issue of tooth decay [ 22,]. To take oral disease preventive measures in each area, it is essential that the oral health status of that area be determined initially. Surveying children in schools is the most common way of collecting information in societies [ 23,]. Since the mean dmft index changes over time and it is needed to have access to new information for future planning, the evaluation of this index should be repeated. Hence, in this study, the index was measured in all first-grade primary school students of Rafsanjan urban area for the first time. The aim of this study, which is conducted to pave the way for future prevention programs, was to determine DMFT index of first permanent molars and dmft and the associated factors in all first-grade primary school students in urban area of Rafsanjan in 2018.Materials and MethodIn this cross-sectional study, out of a total of 2105 first-grade primary school students of Rafsanjan urban area, 2031 students were examined by census method after being approved in the Ethics Committee of Rafsanjan University of Medical Sciences (code, IR.RUMS.REC. 1398.064) and in collaboration with Rafsanjan primary schools and education management in 2018 (May-June).Accordingly, the overall goals of the project were communicated to the schools, and parents were informed of these goals during a meeting held by the school health educator. After obtaining written consent from them, the appropriate time for the examination was determined in collaboration with schools&,rsquo principals.Inclusion criteria included six to seven years of age, school attendance on examination day, child cooperation and parental consent, and exclusion criteria included children with enamel and dentin aplasia, amelogenesis imperfecta, dentinogenesis imperfecta, other dental genetic abnormalities, diseases and drugs that reduce salivary secretion (antihypertesives, antihistamines, antidepressants, antipsychotics, antiemetics, antispasmotics and anti-parkinsonian drugs) and the presence of orthodontic appliance [ 24,- 25,].The questionnaire used in this study consisted of three sections including 1) examination date and school name, 2) demographic and oral hygiene information (name, gender and date of birth, number of family members, birth rank, education and occupation of parents, use of dental floss and frequency of toothbrushing per day), and 3) dental status (in form of a chart). The reliability and validity of this questionnaire were confirmed in previous studies [ 26,- 27,]. In order to answer the questions related to students&,rsquo age, number of family members, birth rank and occupation and education of parents, the students&apos, health profile was used and the students themselves were asked about behavioral questions (brushing and flossing) however, teachers confirmed the accuracy of the answers based on information they had obtained from parents.Examination of teeth was done under natural light using a disposable dental mirror (Atlas, Tehran, Iran) and community periodontal index (CPI) probe (HU Friedy, Chicago, USA) and when necessary, flashlight and explorer were used. The criteria for decay, filling and loss of teeth were based on the standards defined by the World Health Organization so that teeth with damaged surfaces or pit and grooves, cavitated enamel and softened surfaces (felt by the probe) were considered as decayed. Any tooth that was dressed with one of the temporary fillings and any tooth, which was filled but had caries, was considered decayed. White spots were not considered as caries. Teeth that were not present only due to caries were considered missing and teeth that were not present due to orthodontics, accident, and so on were not included. A tooth with one or more surfaces that had permanent filling and no old or new caries was considered as filled. The first permanent molar tooth with intact sealant was considered healthy. Teeth with faulty sealants were considered decayed [ 12,].All examinations were performed by a dental student and another dental student was responsible for recording information and completing the questionnaire. The dental students received the necessary training in examinations and calculations prior to the examination under the supervision of a pediatric dentist and their reliability was confirmed before the main study. Data were categorized and coded for statistical analysis in SPSS version 21.Statistical analysis methodData were analyzed using SPSS software (version 21). Results were reported as ",mean&,plusmn standard deviation (SD)", for quantitative variables and as ",number (percentage)", for qualitative variables.Kolmogorov-Smirnov nonparametric test showed that frequency distribution of DMFT index of first permanent molars and dmft and their components met normal distribution (p&,gt 0.05). Leven&apos,s test for homogeneity of variances also indicated that the variance of DMFT index of first permanent molars and dmfts and their components across the studied groups (number of households, parental education, parental occupation and frequency of brushing days) did not significantly differ (p&,gt 0.05). Significance level was set at 0.05.Independent two-sample t-test was used to compare the mean DMFT index of first permanent molars and dmft and their components across students according to school type, gender, mother&apos,s occupation, and dental flossing. One-way ANOVA was applied to compare the mean DMFT index of first permanent molars and dmft and their components in students by number of family members, birth rank, parents&,rsquo educational level, father&apos,s occupation and frequency of toothbrushing per day. Tukey&apos,s multiple comparisons test was performed when a significance result took place in the one-way ANOVA test.ResultsIn this study, 2031 first-grade primary school students of Rafsanjan were studied. A total of 1836 (90.4%) of the students had decayed primary teeth, 955 (47.1%) of them had missed primary teeth, and 564 (27.8%) of them had filled primary teeth. A total of 364 (17.9%) of the students had decayed first permanent molars. Four (0.2%) and 18 (0.8%) students had permanent missed (M) and permanent filled (F) teeth, respectively. The mean of these two components was not included in the statistical analysis because of their low value. In examination of first permanent molars out of 2031 students, 11 (0.5%) had none of the first permanent molars and 1619 (79.7%) had four sound first permanent molars. Also 83 (4.1%) of students were caries free.The minimum amount of all parameters was zero and the maximum amounts of d, m, f, dmft, D and DMFT index of first permanent molars were 16,16, 8, 20, 4 and 4, respectively. The mean&,plusmn SD for these indices were 4.49&,plusmn 3.07, 1.16&,plusmn 1.77, 0.72&,plusmn 1.45, 6.37&,plusmn 3.40, 0.29&,plusmn 0.70 and 0.30&,plusmn 0.72, respectively.According to Table 1,, the independent two-sample t-test showed that the means of d, f, and dmft components in students of public schools were significantly higher than students of private schools (p&,lt 0.05), while the mean of component f in students of private schools was significantly higher than students in public schools (p= 0.006). The results also showed that the means of other components were not significantly different across the school type (p&,gt 0.05).School typePublic school (n=1613) Mean &,plusmn Standard DeviationPrivate school (n=418) Mean &,plusmn Standard Deviationp ValueIndexd4.59&,plusmn 3.054.13&,plusmn 2.940.006m1.19&,plusmn 1.761.03&,plusmn 1.820.109f0.67&,plusmn 1.400.91&,plusmn 1.590.006dmft6.45&,plusmn 3.426.07&,plusmn 3.330.045D60.29&,plusmn 0.720.28&,plusmn 0.650.803DMFT60.30&,plusmn 0.730.29&,plusmn 0.670.797d, decayed, m, missing, f, filled (for primary teeth) dmft, decayed, missing and filled teeth (for primary teeth) D6, decayed first permanent molar DMFT6, decayed, missing and filled first permanent molar |