Objectives: To explore the effect of demineralization using orthophosphoric acid and remineralization using different concentrated fluoride solutions on dentine hardness of maxillary premolars.
Methods: Thirty-four maxillary premolars free of caries were included in acrylic resin. The crowns were sliced in coronal and cervical parts and divided into 4 groups: a control group (G1) for teeth treated with physiological serum , a second group (G2) for teeth treated with 3 ppm fluoride solution , a third group (G3) for teeth treated with 750ppm fluoride solution and a fourth group (G4) for teeth treated with 1500ppm a fluoride solution. The four groups underwent 500 thermocycles (5 and 55 degrees C) before being processed with a solution of orthophosphoric acid 37% for 20 seconds and a second thermocycling. The dentin hardness measurements were performed on dentin surfaces using a " D- SHORE HARDNESS DUROMETER ". Three hardness measurements were realized: after the first thermocycling; after acid application and after the second thermocycling. The statistical analysis was performed by SPSS 17.0 and significant results were considered for p ≤ 0.05
Results: After the first thermocycling, dentin hardness increased significantly according to the fluoride solutions concentration. After acid application, dentin-hardness decreased according to the fluoride solutions concentration.-After reapplication of fluoride, dentin hardness continues to decrease according to the fluoride solution concentration.
Conclusions: The dentin hardness increases when the tooth is subjected to a fluoridated environment. However, acid treatment decreases dentin hardness of teeth initially treated with fluoride, even when processed to refluoridation.
Dentin, Hardness Tests, Sodium Fluoride, Phosphoric Acids