REV. CHIM. (Bucharest) ♦ 63♦ No. 11 ♦ 2012 http://www.revistadechimie.ro 1120 Study Regarding the Resistance of Enamel and Dentine Affected by Dental Fluorosis to Demineralization Challenge SIMONA STOLERIU 1 *, GIANINA IOVAN 1 , GALINA PANCU 1 , ANDREI GEORGESCU 1 , ANDREI VICTOR SANDU 2 , SORIN ANDRIAN 1 1 „Grigore T. Popa” University of Medicine and Pharmacy of Iasi, Faculty of Dental Medicine, 16 Universitatii Str., 700115, Iaºi, Romania 2 „Gheorghe Asachi” Technical University of Iasi, Faculty of Materials Science and Engineering, 53A D. Mangeron Blvd., 700050, Iaºi, Romania The aim of the study was to assess the susceptibility of fluorotic enamel and dentine to acid challenge. 10 healthy teeth and 40 teeth having different degree of dental fluorosis according to Thylstup-Fejerskov classification splited in 4 groups were used in this study. The surface roughness of the enamel and dentine before and after the demineralization was calculated using AFM evaluation. The values were expressed by relative variation of roughness. The relative roughness for enamel and dentine increased with the increase of dental fluorosis severity. The results were analysed using ANOVA and post-hoc Bonferroni statistical tests. Significant statistical results were obtained when comparing the enamel roughness of the teeth having TF2, 3 and 4 and the teeth having TF0 and 1 and when comparing the dentine roughness indices for all study groups. The enamel of healthy and TF1 teeth was significantly more resistant to acid challenge when compared with the enamel of the teeth having superior severity of dental fluorosis. The susceptibility of the dentine to acid challenge increased with the increase of fluorosis severity. Keywords: enamel, dentine, acid challenge, dental fluorosis, AFM The use of fluoride in the prevention of carious dental lesions was one of the most remarkable successes of the public health programs. The control of exposure to fluoride in childhood is very important to maintain the fluoridation efficiency and to reduce the risk of dental fluorosis. Nowadays there is no common opinion regarding relation between fluorosis and cariogenic risk [1]. The carious process is initiated by bacterial biofilm [2, 3] produced on any hard surface exposed to adequate quantities of water and nutrients. The bacteria responsible of primary colonisation and the secondary microorganisms generate an extracellular matrix of polymers related to biofilm growing. The biofilm bacteria have an active metabolism causing pH variations. These fluctuations can cause mineral loss when pH decreases and mineral gain when pH increases [4, 5]. The cumulative result of these demineralization and remineralisation processes can be the mineral loss resulting in dissolution of hard dental tissues and carious lesions. The introduction of artificial carious models contributed significantly to the understanding of carious process kinetics. The development of subsurface lesion concept allowed the clarification of interactions between de- and remineralization processes. The atomic force microscopy is a valuable method for the study of demineralization processes and the effects of diverse solutions or oral environment factors on hard dental tissues. The aim of this study was to determine the resistance to demineralization of enamel and dentine affected by different degrees of dental fluorosis. Experimental part 10 healthy freshly extracted teeth and 40 teeth having different degrees of dental fluorosis splited in 4 groups according to Thylstup-Fejerskov classification (TF 1-4) were used in this study [6]. The teeth were sectioned in * email:stoleriu_simona@yahoo.com two halves to obtain the enamel and dentine samples. The samples were finished using silicon carbide discs (100, 600, 800, 1000, 1200, and 4000) under water cooling, and immersed in ultrasound bath for 4 minutes. The enamel and dentine samples were analyzed using atomic force microscopy (AFM) to determine surface roughness. A chemical model was used to induce structural changes similar with those induced by carious process. The enamel and dentine samples were immersed in acetic acid 0.05M (pH 5) for 16 h. The surface roughness of the enamel and dentine was calculated using AFM evaluation. The values were expressed by relative variation of roughness, using the formula ΔR= root mean squared roughness after demineralization - root mean squared roughness at baseline/root mean squared roughness at baseline. Results and discutions The values of relative roughness indices for the enamel samples varied between 6.18 and 6.37 for teeth with fluorosis TF 0; between 6.27 and 6.43 for teeth with fluorosis TF 1; between 6.32 and 6.48 for teeth with fluorosis TF 2; between 6.42 and 6.62 for teeth with fluorosis TF 3, and between 6,95 and 7.26 for teeth with fluorosis TF 4. The relative roughness for enamel increased with the increase of dental fluorosis severity. The values of relative roughness indices for dentine samples varied between 2.78 and 3 for teeth with fluorosis TF 0; between 2.96 and 3.21 for teeth with TF 1; between 3.18 and 3.26 for teeth with TF 2; between 3.32 and 3.38 for teeth with TF 3, and between 3.61 and 3.67 for teeth with TF 4. The relative roughness for dentine increased with the increase of dental fluorosis severity. The appearance of enamel before demineralization is presented in figures 1 (2 μm section) and 2 (10 μm section). In these figures can be observed the surface roughness and polynuclear crystals. The profile of 2 μm section proves