Determination of the caries free prevalence in 12 year-old students in Guidance schools in sirjan city in 1996

Caries ferr is  an epidemiologic index for prevalence of dental caries in a society and it means that persons who do not have any dental caries,in other words,that equal to DMF=0.to determine the prevalence of caries ferr in 12 year-old student in Guidance school in sirjan city,this study was carried out with the method of WHO index in 1996.on the bases of a pilot study the of sample size was determined to be 300 persons(150 girls and 150 boys).this sample was selected by stratified cluster sampling.after dental examination and filling the WHO forms,the obtained data were statistically analyzed and the results were as follows.34.7 percent of 12 year-old(boy and girl) adolsent were caries ferr.39.3 percent of boys and 30 percent of girls in this study were caries free.according to WHO index caries prevalence was 65.3% in 12-year-old adolesents in sirjan which is considered relatively low.