Schools for students with special needs were excluded. The second stage of sampling comprised selection of 25% students from 6th, 7th, and 8th grades of the previously selected schools. The study population included 4086 students: 2272 from Amman, 1425 from Irbid, and 389 from Al-Karak. Selected students were given copies of the questionnaire prepared for this study with consent forms to Bcl-2 expression be signed by their parents or their legal guardians. Cover letters were also attached to the questionnaires to providing additional information about the aim of this project and asking parents to kindly allow their children to participate. Only those with written consent were

included in the study. The diagnostic criteria of DE for each surface were determined according to Smith and Knight ([19]) Tooth Wear Index (TWI)[19] as modified by Millward et al.[20]. TSA HDAC All surfaces of permanent teeth were examined for loss of enamel surface characteristics and/or exposure

of dentin or pulp. Participants were considered as having DE if they had at least one surface that exhibited signs of DE. Students who exhibited changes in dental structure, such as amelogenesis imperfecta, dentinogenesis imperfecta, hypoplasia, diffuse opacities, white spot lesions, tetracycline staining, and fluorosis, were excluded from the study. Excluded teeth also included partially erupted teeth, teeth with orthodontic bands or brackets, extensive restorations and crowns, fractured teeth, surfaces with composite restorations, and fissure sealants. The clinical examination was conducted with students sitting in an ordinary

chair in their class rooms using daylight Ergoloid supplemented with a head light. Teeth were dried with gauze and, when necessary, cotton rolls were used to remove debris. A full mouth examination for DE was performed using a mirror, and information was recorded on a prepared examination form by a research assistant. All examinations were carried out by a single examiner who was trained and calibrated by a university assistant professor of paediatric dentistry by examining 20 patients aged between 12 and 14 years who attended the Jordan University of Science and Technology dental clinics before the commencement of the study. There was a 98.4 percentage of agreement between the two examiners. To assess intraexaminer reliability during the study period, approximately 300 participants of the total sample were examined twice. Thus, for every 25 students examined, the first two students in that group were re-examined. The kappa value of intraexaminer reliability was 0.98. The study utilized a self-reported questionnaire that was an Arabic version of the questionnaire used in the National Diet and Nutrition Survey in the United Kingdom[21].