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Effect of neutralization and hydrofluoric acid precipitates ultrasonic remotion on fracture strenght of ceramic crowns


The aims of this study will be to assess two hypotheses: a) if the neutralization with sodium bicarbonate associated with hydrofluoric acid precipitates ultrasonic remotion increases the fracture resistance of ceramic crowns and b) if there are relation between cement film thickness and the fracture resistance of ceramic crowns. Forty third maxillary molars will be selected and will receive a conventional full preparation for ceramic crown. A digital scanning of the preparation will make standardized all-ceramic crowns. The same crowns will be randomly divided in different groups according with surface treatments (n=10). The cementation will be simulated with fluid condensation silicon for cement thickness evaluation. The surface treatment will be done as follow: group I: hydrofluoric acid (HF), group II: HF + neutralization, group III: HF + ultrasonic bath, group IV: HF + neutralization + ultrasonic bath. After that crowns will be cemented with dual cure resin cement. The specimens will be submitted to fracture strength test through a compressive load (Kgf) applied in the center of occlusal surface parallel to the specimen long axis, with a crosshead speed of 1 mm/min until the fracture. The crown fragments will be collected and evaluated in SEM for fracture mechanism characterization. The achieved fracture strength numeric values will be submitted to statistical analysis compatible with the results. (AU)

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