In vitro Study of the Effectiveness to Fractures of the Aesthetic Fixed Restorations Achieved from Zirconium and Alumina

A small percentage of the population is hypersensitive to dental alloys. For the last few decades, numerous approaches have been made to enhance the hardness of ceramics used in fixed prosthetic restorations. The aim of the research was to study, in vitro, the effectiveness to fracture tests of the aesthetic fixed restorations realized from zirconia and alumina. The experiment was conducted in a physics laboratory at the Polytechnic Institute of Bucharest for a 2 years period. For testing we used a total of 60 crowns manufactured as follows: 30 identical zirconia crowns, 30 identical alumina crowns, and for plating we used compatible ceramics. Each batch of 30 crowns was then divided in 3 groups of 10 crowns. Subsequently the crowns were cemented on resin models using zinc phosphate cement. After the setting of cement, the crowns were stored in distilled water at a temperature of 37°C. After two years, the first group of crowns was not subject to any treatment, the second group was subjected to a heat treatment in water bath at 55°C for 20 s each, and then, the 2 nd and 3 rd group of aesthetic crowns underwent cyclic preloading, between 30-300 N, at 1 Hz. The researches results showed that zirconia crowns were 3 times stronger and tougher than alumina crowns, and that the success rate in the zirconia crowns batch was 100%.