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Yaghooti Khorasani M, Irannezhad M. The prevalence of caries in the first permanent molars among students of 7 and 12 years of age in Rafsanjan, Iran, in 2009-2010. JOHE. 2017; 6 (1) :25-31
URL: http://johe.rums.ac.ir/article-1-229-en.html

Assistant Prof., Dept. of Endodontics, School of Dentistry, Rafsanjan University of Medical Sciences, Rafsanjan, Iran , m.yaghooti@yahoo.com
Keywords: Dental Caries [MeSH], Students [MeSH], DMF [MeSH], Iran [MeSH],
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The prevalence of caries in the first permanent molars among students of 7 and 12 years of age in Rafsanjan, Iran, in 2009-2010
 
Yaghooti Khorasani MM, DDS, MS1*, Irannezhad M, Dentistry Student2
 
1- Assistant Prof., Dept. of Endodontics, School of Dentistry, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. 
2- Dentistry Student, School of Dentistry, Rafsanjan University of Medical Sciences, Rafsanjan, Iran.
 
Abstract                                                                                           Received: February 2017, Accepted: May 2017
Background: Dental caries is the most prevalent oral disease among children. The first permanent molar has been introduced as an index for predicting caries activity, and determining dental and oral health status and the groups most vulnerable to caries. Thus, the aim of this study was to determine the prevalence of caries in the first permanent molars among students of 7 and 12 years of age in Rafsanjan, Iran, in 2009-2010.
Materials and Methods: This cross-sectional study was conducted on 360 students (girls and boys) in Rafsanjan. The participants were selected through multistage random sampling. Clinical examination for the diagnosis of caries was based on the World Health Organization (WHO) criteria. Data were collected through interviews and clinical examinations and analyzed using Mann-Whitney and chi-square tests.
Results: The total mean decayed, missing, and filled teeth (DMFT) index of the sample was 1.66 ± 1.47 (1.78 ± 1.51 in boys and 1.51 ± 1.42 in girls) (P = 0.081). Mean DMFT was 1.79 ± 1.33 and 1.52 ± 1.56 in the 12 years and 7 years age groups, respectively (P = 0.029). The decayed teeth (DT), missing teeth (MT), and filled teeth (FT) in this index were 52.21%, 40.96%, 6.82%, respectively. The prevalence of caries free (CF) among the students was 34.7% (31.28% in boys and 37.57% in girls). A statistically significant difference was observed among the students in terms of gender and age (P < 0.05); CF was 43.24% in the 7 years age group and 24.57% in the 12 years age group.
Conclusions: Considering the WHO criteria, the prevalence of caries and CF in the first permanent molars among students of 7 and 12 years of age in Rafsanjan was relatively favorable.
Keywords: Dental Caries, Students, DMF, Iran.
 
Introduction
Dental caries is one of the most common chronic microbial diseases in the world which can result in the destruction of the calcified tissue of the teeth (1). Caries are the most common in the first permanent molars due to their pits, fissures, and anatomical concavities which can contribute to microbial plaque build-up; they constitute approximately 95% of all dental caries. Caries activity varies significantly; therefore, the progression of each lesion cannot be accurately predicted (1-3). It is necessary to recognize that although the treatment of symptoms is important, lack of determination and treatment of the underlying cause results in disease persistence. Thus, dental caries prevention is an important responsibility of the profession of dentistry, and therefore, timely diagnosis can prevent more severe problems (4).
The most commonly used epidemiologic scale of caries and index for the determination of oral and dental health status in adults and adolescents is the decayed, missing, and filled teeth (DMFT) index. The DMFT index evaluates the number of decayed, missing, or filled permanent teeth (1, 5). The amount determined using this index is not representative of the real prevalence of dental caries in a community (6). Therefore, the percentage of caries free (CF) is used as a complementary criterion in epidemiologic studies. An individual with no decayed, missing, or restored teeth (DMFT index score of 0) is recognized as CF (7, 8). The prevalence of CF in the study by Sadeghi on 12 and 15-year-old students of Rafsanjan, Iran, was 38.2% and 20.6%, respectively (1). Sadeghi also reported a CF prevalence of 30.4% in a study in 2006 on students of 11-12 years of age in Rafsanjan (4). The health status of the first permanent molar is a disease-centered index related to dental caries and a suitable dental health index for children and adults (9). The first permanent molar was introduced as an index for the prediction of caries activity, determination of dental and oral health status, and determination of groups most vulnerable to caries by the World Health Organization (WHO) in 1994 (1, 10). Permanent teeth grow during the ages of 6 to 13. The first permanent molars have been introduced as dental occlusion keys. These teeth are considered as the guidance factor for the maxillary growth pattern; thus, any damage to them can endanger the dental-skeletal system. In addition, they are considered as an important factor in dental arch formation. The space for the growth of canines and permanent premolars is shaped by the mesial surface of the first permanent molars and distal surface of the permanent lateral incisors. Moreover, the growth of the second permanent molar is determined by the distal surface of first permanent molar. Thus, they determine the position of the posterior and anterior teeth (11, 12).
The first permanent molars are the main units of the chewing function; therefore, they have the largest crown and root width. This tooth also impacts the determination of vertical occlusion and lower face height (11, 12). These teeth have pits and fissures which are not completely joined at the base, and thus, the material in the dental plaque which remain in these areas are transferred to the dentin. Furthermore, the pits in the lingual surface of these teeth in the upper jaw and the pits of the Buccal region of lower molars are prone to the rapid progression of caries (11, 13).
In the permanent dental system, caries generally begin in the pits and fissures of the first molar (14). Hence, sufficient statistical data on the prevalence of caries in the first permanent molars in different areas are useful for planning preventive measures and the correct pattern for the distribution of treatment facilities in the country. Therefore, the present study was conducted with the aim to determine the prevalence of caries in the first permanent molars among students of 7 and 12 years of age in Rafsanjan.
 
Material and Methods
This cross-sectional study was conducted on 360 students of 7 years of age (first year of elementary school) and 12 years of age (first year of guidance school) in Rafsanjan in 2009-2010. The participants were selected through multistage sampling (stratified cluster sampling and simple random sampling) from approximately 40 elementary and guidance schools. Rafsanjan was divided into 4 regions (strata), and from each region, 1 public and 1 private school (both elementary and guidance schools) were selected. From each school (cluster), about 50% of students of 7 and 12 years of age were randomly selected. The sample volume was determined based on the prevalence of CF in the study by Sadeghi (4) and stratified sampling (n = 187). This amount was doubled in order to increase the accuracy of the study (n = 360).

On arrival at the schools, a short explanation was given to students before the examination to ensure their cooperation. The students completed a demographic characteristics form consisting of questions on age, gender, and parents’ occupation and education. Then, the DMFT index was determined. After drying the students’ teeth, oral examination was performed by a trained individual under torchlight (the torch was held by a colleague) using a mirror and periodontal probe through observation of decayed, missing, and filled first permanent molars. Oral examination was, respectively, conducted on the upper right, upper left, lower left, and lower right jaw and the results were recorded by a colleague (15). It must be noted that this study was performed by observing the examination criteria, obtaining the approval of the research committee of the School of Dentistry, Ministry of Education, and headmasters or headmistresses of the schools, and obtaining informed consents from the students’ parents. Moreover, the participants’ information remained confidential.
In clinical examination, a tooth without any sign of restored or non-restored caries was considered as a healthy tooth. The detection of dental caries is difficult in stages in which no cavity is visible. Therefore, chalky white stains, discolored areas or uneven surfaces, pits and fissure in which the probe was caught only briefly, the enamel wall surrounding them was not soft, and there was no empty space underneath the enamel, and any lesion the researcher was not certain of it being carious was considered as healthy (15).
Teeth with a lesion in the pit and fissure or on the smooth surface which had an empty space underneath the enamel and the surrounding was soft were considered as carious. Moreover, teeth with temporary dressings, previously restored but still carious teeth, and cracked teeth were also considered as carious. Based on the abovementioned criteria, each student’s status was evaluated and recorded in the questionnaire in accordance with the WHO forms (1). The collected data were entered into SPSS software (version 16, SPSS Inc., Chicago, IL, USA) and analyzed using statistical tests. Descriptive statistical methods (percentage, frequency, and mean), and the Mann-Whitney and chi-square tests were used to analyze the data. The significance level was considered as P < 0.05 in all tests. 
 
Results
The assessment of 360 students (170 girls and 190 boys) of 7 and 12 years of age in Rafsanjan showed that their mean age was 9.41 ± 2.50 years, 9.57 ± 2.50 years in girls and 9.30 ± 2.49 years in boys. The relative frequency distribution by gender in the 7-year-old students (185 individuals) was 105 (62.5%) boys and 80 (37.5%) girls, and in the 12-year-old students (175 individuals), was 85 boys and 90 girls.
 
Table 1: Mean and standard deviation of the DMFT index of the first permanent molars in students of 7 and 12 years of age in Rafsanjan distributed by gender
Gender DMFT
(Mean ± SD)
DT
N (%)
MT
N (%)
FT
N (%)
Total
N (%)
Girls 1.51 ± 1.42 95 (57.84) 61 (36.9) 9 (5.25) 165 (100)
Boys 1.78 ± 1.51 93 (47.88) 86 (44.09) 16 (8.02) 195 (100)
Total 1.66 ± 1.47 188 (52.21) 147 (40.96) 25 (6.82) 360 (100)
P-value 0.081 0.114 0.232 0.321  
DMFT: Decayed, Missing, or Filled Teeth Index; DT: Decayed teeth; MT: Missing teeth; FT: Filled teeth
As can be observed in the results presented in table 1, DMFT of the first permanent molars was higher in boys (1.78 ± 1.51) than girls (1.51 ± 1.42), but this difference was not significant. The rate of decayed teeth (DT) was higher in girls and the rate of missing teeth (MT) was higher in boys; however, these differences were not significant. The results of Mann-Whitney test showed that the DMFT index score and percentage of caries were significantly higher in the age group of 12 years compared to the age group of 7 years (Table 2).
 
Table 2: Mean and standard deviation of DMFT index of the first permanent molars in students of 7 and 12 years of age in Rafsanjan distributed by age
Age DMFT
(Mean ± SD)
DT
N (%)
MT
N (%)
FT
N (%)
Total
Nr (%)
7 years 1.52 ± 1.56 76 (40.95) 97 (52.38) 12 (6.66) 185 (100)
12 years 1.79 ± 1.33 107 (61.17) 56 (31.88) 12 (6.94) 175 (100)
Total 1.65 ± 1.44 188 (52.21) 147 (40.96) 25 (6.82) 360 (100)
P-value 0.029 0.000 0.059 0.231  
DMFT: Decayed, Missing, or Filled Teeth Index; DT: Decayed teeth; MT: Missing teeth; FT: Filled teeth
 
 
The DMFT of the first molar of the studied students was 1.66 ± 1.47 (Table 3). In the two age groups, DMFT was higher in boys than girls. The prevalence of DT in first permanent molars of the subjects was 52.21%. The prevalence of DT in both age groups was higher in girls compared to boys. The prevalence of MT among the participants was 40.96%; it was higher in 7 year-old boys compared to other age and gender groups. The prevalence of FT of the subjects was 6.82%; the highest prevalence was observed in 7-year-old boys (9.23%) and 12-year-old girls (7.01%), respectively.
 
Table 3: Mean and standard deviation of DMFT index of the first permanent molars of students distributed by age and gender
Index
Age
DMFT
(Mean ± SD)
DT
N (%)
MT
N (%)
FT
N (%)
Total
N (%)
P-value
7 years Girls 1.22 ± 1.44 40 (50) 38 (47.50) 2 (2.5) 80 (100) 0.031
Boys 1.76 ± 1.66 37 (35.38) 58 (55.38) 10 (9.23) 105 (100)
12 years Girls 1.78 ± 1.35 56 (62.83) 27 (30.15) 7 (7.01) 90 (100) 0.928
Boys 1.81 ± 1.32 51 (59.66) 28 (33.45) 6 (6.88) 85 (100)
Total 1.66 ± 1.47 188 (52.21) 147 (40.96) 25 (6.82) 360 (100)  
DMFT: Decayed, Missing, or Filled Teeth Index; DT: Decayed teeth; MT: Missing teeth; FT: Filled teeth
 
The total rate of CF of the students was 34.17%; it was higher in 7-year-old girls (50%) compared to 7-year-old boys and 12-year-old students (Table 4). Mann-Whitney test results showed significant differences between the age groups based on gender and age (P < 0.05).
In this study, 20% of subjects did not have their first permanent molars. The highest prevalence of CF was observed in 7-year-old girls and the lowest in 12-year-old boys (23.3%). The highest prevalence of caries (116 teeth; 38.2%) and tooth extraction (77 teeth; 28.6%) was related to the 36th molar. The highest rate of extraction of molars was observed in 7-year-old boys (125 teeth; 46.5%). In addition, the highest number of fillings was related to 46th molar (8 teeth; 36%). The highest rate of molar restoration was observed in 7-year-old boys (10 teeth; 40%).
Table 4: Relative frequency percentage of the caries free criterion in the first permanent molars of students of 7 and 12 years of age in Rafsanjan distributed by age and gender
CF Caries free index
(%)
Gender
Age
Girls Boys Total
7 years 50 38.1 43.24
12 years 25.9 23.3 24.57
Total 37.57 31.28 34.17
Pearson chi-square = 0.28                     P < 0.05
 
 
Discussion
Dental caries is one the main causes of the loss of teeth. Teeth can be preserved through adherence to health principles, diet control, preventive measures, and timely treatment if necessary (1, 16-18). The WHO has considered 6, 12, and 15 year age groups as target groups for the study of the prevalence of dental caries. The results of the present study showed that mean DMFT among students of 7 and 12 years of age in Rafsanjan was 1.66 ± 1.47. Mean DMFT was higher in 12 year-old students and in boys in both groups; however, no statistically significant difference was observed between 7-year-old boys and girls. Considering the goal of the WHO to reach a mean DMFT of 3 or less in 12-year-olds, the status of dental caries was favorable in the present study (10). Furthermore, the finding of the present study was in agreement with the results of the study by Sadeghi (1) The mean obtained in the present study was less than that found by Bayat (19) and the national mean for 12-year-old students (3.02) (10). There are very few documentary researches on first permanent molars; thus, periodic researches to evaluate dental and oral health programs are necessary.
In the present study, the prevalence of caries free in students of 7 and 12 years of age was 34.17%; its prevalence was 31.28% and 37.57% in boys and girls, respectively. The prevalence of CF in the study by Sadeghi in Rafsanjan was 37% in 12-year-old students (35% in girls and 41% in boys) and 20% in 15-year-old students (22.4% in girls and 17.8% in boys) (4). The results of the present study are not more favorable. Moreover, Sadeghi reported the prevalence of CF in students of 11-12 years of age in Rafsanjan in 2006 as 30% (26% in girls and 34% in boys) (1). The rate of CF in the study by Tomarian in Qom, Iran, was 10.7%, which was higher than that obtained in the present study (20). Considering the goals of the WHO in 2010, the obtained prevalence is low and must be promoted.
On the other hand, the DMFT index score and percentage of carious teeth was higher in the 12 year age group compared to the 7 year age group. This illustrates the necessity of planning to increase the awareness of individuals in the community regarding oral and dental health. More extensive education of parents and children through different methods regarding the importance of teeth and the necessity of maintaining teeth and its principles, encouraging individuals to undergo regular and periodic examinations (every 6 months) by a dentist and treatment if necessary, and preventive measures at different educational levels such as water fluoridation to drinking water and local fluoride therapy are essential. Some studies have reported very low concentrations of fluoride in drinking water in Iran. The best and most cost-effective method of providing individuals with fluoride supplementation is water fluoridation (21, 22). There are contradictory beliefs regarding the importance of fluoride in human health; however, the majority of studies with negative results have important limitations, and thus, their results cannot be entirely confirmed (23-25). According to the WHO, there is no basis for altering the public health policies concerning the use of fluoride in the prevention of dental caries and the best method for the provision of fluoride is water fluoridation (19).
 
Conclusion
Considering the WHO criteria, the prevalence and rate of CF in the first permanent molars among students of 7 and 12 years of age in Rafsanjan was relatively favorable, but attention to education with the objective of prevention and promotion of this index in ages higher than 7 years is necessary.
 
Acknowledgements
The authors wish to thank the Research Council of Rafsanjan University of Medical Sciences, and Mr. Hamidbakhshi and Dr. Baharlou for their assistance in the performance of this study. 
 
Conflict of interests: None declared.
 
References
  1. Sadeghi M. Prevalence of caries free in 12 and 15 year- old students of Rafsanjan city in 1998. Journal of Rafsanjan University of Medical Sciences 2002; 1(1):59-63.
  2. Xue Y, Lin W, Jie L, Qing D. Caries status of the first permanent molar among 7- to 9-year-old children in Tangshan city and their correlation. Hua Xi Kou Qiang Yi Xue Za Zhi 2015; 33(1):54-7.
  3. Wang JD, Chen X, Frencken J, Du MQ, Chen Zh. Dental caries and first permanent molar pit and fissure morphology in 7- to 8-year-old children in Wuhan, China. Int J Oral Sci 2012; 4(3):157-160.
  4. Sadeghi M. Prevalence and bilateral occurrence of first permanent molars caries in 12 year–old students. J Dent Res Dent Clin Dent Prospects 2007; 1(2):86-92.
  5. Ghandhari Motlagh M, Mahbobi M. An evaluation on DMFT and its effective factors among 12-year-old children of Soume-sara city (2003). J Islam Dent Assoc Iran 2003; 15(3):39-48.
  6. Ditmyer M, Dounis G, Mobley C,Schwarz E. Inequalities of caries experience in Nevada youth expressed by DMFT index vs. Significant Caries Index (SiC) over time. BMC Oral Health 2011; 11:12.
  7. Dabiran S, Braderan Nakhjavani Y, Khajehnasiri F, Eslambolichi A, Kighobadi M. Evaluation of DMFT index (number of permanent rotted teeth, lost due to caries and filled) and its effective factors in 12-year-old primary school students in Ghow Hesar, Shahr-e-Rei. Iran J Pediatr 2003; 13(Supplement).
  8. Mosavinasab M, Sheikhi F. Indication of caries free prevalence among 12 years old students in Izeh city. Journal of Research in Medical Sciences 2003; 8(3):113-4.
  9. Lee SH, Lee HS, Oh HW, Ju HJ, Park SY. The utility of dental health capacity of the first permanent molars as an oral health indicator among children and adolescents. Journal of Korean Academy of Oral Health 2015; 39(3):174-9.
  10. Javadinejad Sh, Karami M, Azizi HR. Caries prevalence in 12-year-old children of Isfahan city expressed by the significant caries index. Journal of Isfahan Dental School 2006; 2(2):13-7.
  11. Profit W, Fields H, Sarver D. Contemporary orthodontic. 5th ed. Maryland Heights, Missouri, United States: Mosby; 2012.
  12. Cağlaroğlu M, Kilic N, Erdem A. Effects of early unilateral first molar extraction on skeletal asymmetry. Am J Orthod Dentofacial Orthop 2008; 134(2):270-5.
  13. Wang JD, Chen X, Frencken J, Du MQ, Chen Z. Dental caries and first permanent molar pit and fissure morphology in 7- to 8-year-old children in Wuhan, China. Int J Oral Sci 2012; 4(3):157-60.
  14. Ahovuo-Saloranta A, Hiiri A, Nordblad A, Mäkelä M, Worthington HV. Pit and fissure sealants for preventing dental decay in the permanent teeth of children and adolescents. Cochrane Database Syst Rev 2008; 8(4):CD001830.
  15. World Health Organization. Oral health surveys, basic method, 4th ed. Geneva: World Health Organization; 1997.
  16. Ebrahimi M, Ajami B,  Sarraf Shirazi AR, Afzal Aghaee M, Rashidi S. Dental treatment  needs of permanent first molars in Mashhad schoolchildren. J Dent Res Dent Clin Dent Prospect 2010; 4(2):52-5.
  17. Ivančić Jokić N, Bakarčić D, Janković S, Malatestinić G, Dabo J, Majstorović M, et al. Dental caries experience in creation school children in Primorsko-Goranska county. Cent Eur J Public Health 2013; 21(1):39-42.
  18. Almasi A, Rahimiforoushani A, Eshraghian MR, Mohammad K, Pasdar Y, Tarrahi MJ, et al. Effect of nutritional habits on dental caries in permanent dentition among schoolchildren aged 10-12 years: a zero-in-flated generalized poisson regression model approach. Iran J Public Health 2016; 45(3):353-61.
  19. Bayat-Movahed S, Samadzadeh H, Ziyarati L, Memary N, Khosravi R, Sadr-Eshkevari PS. Oral health of Iranian children in 2004: a national pathfinder survey of dental caries and treatment needs. East Mediterr Health J 2011; 17(3):243-9.
  20. Toomarian L, Souri S, Farhadi H. Epidemiological evaluation of DMFT index in 12 – year – old students of Qom city in 2004. Journal of Dental School Shahid Beheshti University of Medical Sciences 2005; 4 (3):467-74.
  21. Taghipour N, Amini H, Mosaferi M, Yunesian M, Pourakbar M, Taghipour H. National and sub-national drinking water fluoride concentrations and prevalence of fluorosis and of decayed, missed, and filled teeth in Iran from 1990 to 2015: a systematic review. Environ Sci Pollut Res Int 2016; 23(6):5077-98.
  22. Ramezani G, Valaie N, Rakhshan V. The effect of water fluoride concentration on dental caries and fluorosis in five Iran provinces: a multi-center two-phase study. Dent Res J (Isfahan) 2015; 12(1):31-7.
  23. Richards D. Insufficient evidence that slow-release fluoride devices reduce caries. Evid Based Dent 2015; 16(2):45.
  24. Antonijevic E, Mandinic Z, Curcic M, Djukic-Cosic D, Milicevic N, Ivanovic M, et al. "Borderline" fluorotic region in Serbia: correlations among fluoride in drinking water, biomarkers of exposure and dental fluorosis in schoolchildren. Environ Geochem Health 2016; 38(3):885-96.
  25. Matloob MH. Dental caries in Iraqi 12-year-olds and background fluoride exposure. Community Dent Health 2015; 32(3):163-9.

 
 
 

*  Corresponding author: Mohammad Mahdi Yaghooti Khorasani, Dept. of Endodontics, School of Dentistry, Rafsanjan University of Medical Sciences, Rafsanjan, Iran.
E-mail: m.yaghooti@yahoo.com
Type of Study: original article | Subject: General

References
1. Sadeghi M. Prevalence of caries free in 12 and 15 year- old students of Rafsanjan city in 1998. Journal of Rafsanjan University of Medical Sciences 2002; 1(1):59-63. [Article]
2. Xue Y, Lin W, Jie L, Qing D. Caries status of the first permanent molar among 7- to 9-year-old children in Tangshan city and their correlation. Hua Xi Kou Qiang Yi Xue Za Zhi 2015; 33(1):54-7. [PubMed]
3. Wang JD, Chen X, Frencken J, Du MQ, Chen Zh. Dental caries and first permanent molar pit and fissure morphology in 7- to 8-year-old children in Wuhan, China. Int J Oral Sci 2012; 4(3):157-160. [PubMed]
4. Sadeghi M. Prevalence and bilateral occurrence of first permanent molars caries in 12 year–old students. J Dent Res Dent Clin Dent Prospects 2007; 1(2):86-92. [PubMed]
5. Ghandhari Motlagh M, Mahbobi M. An evaluation on DMFT and its effective factors among 12-year-old children of Soume-sara city (2003). J Islam Dent Assoc Iran 2003; 15(3):39-48.
6. Ditmyer M, Dounis G, Mobley C,Schwarz E. Inequalities of caries experience in Nevada youth expressed by DMFT index vs. Significant Caries Index (SiC) over time. BMC Oral Health 2011; 11:12. [DOI] [PubMed]
7. Dabiran S, Braderan Nakhjavani Y, Khajehnasiri F, Eslambolichi A, Kighobadi M. Evaluation of DMFT index (number of permanent rotted teeth, lost due to caries and filled) and its effective factors in 12-year-old primary school students in Ghow Hesar, Shahr-e-Rei. Iran J Pediatr 2003; 13(Supplement).
8. Mosavinasab M, Sheikhi F. Indication of caries free prevalence among 12 years old students in Izeh city. Journal of Research in Medical Sciences 2003; 8(3):113-4. [Article]
9. Lee SH, Lee HS, Oh HW, Ju HJ, Park SY. The utility of dental health capacity of the first permanent molars as an oral health indicator among children and adolescents. Journal of Korean Academy of Oral Health 2015; 39(3):174-9. [Article]
10. Javadinejad Sh, Karami M, Azizi HR. Caries prevalence in 12-year-old children of Isfahan city expressed by the significant caries index. Journal of Isfahan Dental School 2006; 2(2):13-7.
11. Profit W, Fields H, Sarver D. Contemporary orthodontic. 5th ed. Maryland Heights, Missouri, United States: Mosby; 2012. [Book]
12. Cağlaroğlu M, Kilic N, Erdem A. Effects of early unilateral first molar extraction on skeletal asymmetry. Am J Orthod Dentofacial Orthop 2008; 134(2):270-5. [PubMed]
13. Wang JD, Chen X, Frencken J, Du MQ, Chen Z. Dental caries and first permanent molar pit and fissure morphology in 7- to 8-year-old children in Wuhan, China. Int J Oral Sci 2012; 4(3):157-60. [PubMed]
14. Ahovuo-Saloranta A, Hiiri A, Nordblad A, Mäkelä M, Worthington HV. Pit and fissure sealants for preventing dental decay in the permanent teeth of children and adolescents. Cochrane Database Syst Rev 2008; 8(4):CD001830. [PubMed]
15. World Health Organization. Oral health surveys, basic method, 4th ed. Geneva: World Health Organization; 1997. [Book]
16. Ebrahimi M, Ajami B, Sarraf Shirazi AR, Afzal Aghaee M, Rashidi S. Dental treatment needs of permanent first molars in Mashhad schoolchildren. J Dent Res Dent Clin Dent Prospect 2010; 4(2):52-5. [PubMed]
17. Ivančić Jokić N, Bakarčić D, Janković S, Malatestinić G, Dabo J, Majstorović M, et al. Dental caries experience in creation school children in Primorsko-Goranska county. Cent Eur J Public Health 2013; 21(1):39-42. [Article]
18. Almasi A, Rahimiforoushani A, Eshraghian MR, Mohammad K, Pasdar Y, Tarrahi MJ, et al. Effect of nutritional habits on dental caries in permanent dentition among schoolchildren aged 10-12 years: a zero-in-flated generalized poisson regression model approach. Iran J Public Health 2016; 45(3):353-61. [PubMed]
19. Bayat-Movahed S, Samadzadeh H, Ziyarati L, Memary N, Khosravi R, Sadr-Eshkevari PS. Oral health of Iranian children in 2004: a national pathfinder survey of dental caries and treatment needs. East Mediterr Health J 2011; 17(3):243-9. [PubMed]
20. Toomarian L, Souri S, Farhadi H. Epidemiological evaluation of DMFT index in 12 – year – old students of Qom city in 2004. Journal of Dental School Shahid Beheshti University of Medical Sciences 2005; 4 (3):467-74. [Article]
21. Taghipour N, Amini H, Mosaferi M, Yunesian M, Pourakbar M, Taghipour H. National and sub-national drinking water fluoride concentrations and prevalence of fluorosis and of decayed, missed, and filled teeth in Iran from 1990 to 2015: a systematic review. Environ Sci Pollut Res Int 2016; 23(6):5077-98. [PubMed]
22. Ramezani G, Valaie N, Rakhshan V. The effect of water fluoride concentration on dental caries and fluorosis in five Iran provinces: a multi-center two-phase study. Dent Res J (Isfahan) 2015; 12(1):31-7. [PubMed]
23. Richards D. Insufficient evidence that slow-release fluoride devices reduce caries. Evid Based Dent 2015; 16(2):45. [PubMed]
24. Antonijevic E, Mandinic Z, Curcic M, Djukic-Cosic D, Milicevic N, Ivanovic M, et al. [Article]
25. Matloob MH. Dental caries in Iraqi 12-year-olds and background fluoride exposure. Community Dent Health 2015; 32(3):163-9. [PubMed]

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