Fracture strength of preformed zirconia crown and new custom-made zirconia crown for the restoration of deciduous molars: in vitro study

Purpose Preformed metal crown (PMC) were considered as the best method of restoring primary molars. In recent years, dentistry has seen the emergence of esthetic full-coverage restorative alternatives that gave better results but their ability to manipulate the size, shape, and fit is very limited. The milled zirconia crown is a new alternative for the restoration of deciduous teeth, but the mechanical properties of these restorations need to be tested. Aim To assess and compare the force required to fracture on two posterior pedodontics crowns: a prefabricated Zirconia crowns (PZC) (NuSmile Zr Zirconia (R)) and a new custom-made zirconia crown (also called Zirkid(C)) on a freshly extracted deciduous molars. Methods Thirty freshly extracted deciduous molars were selected and were randomized into two groups: (1) molars prepared to receive the PZC and (2) molars prepared to receive the milled zirconia crowns. All pediatric crowns were cemented with glass ionomer and the samples were placed in the thermocycling machine for thermal aging of 1000 cycles. Mechanical compression forces were applied using the Universal Testing Machine until fracture of the crowns. The force required to fracture were evaluated. Since variable was normally distributed with Kolmogorov-Smirnov test, Student t test was used for statistical comparison. Results This study showed that the mean fracture force was significantly elevated with zirconia crowns made with Zirkid(C) (2888.6 +/- 1060.2 N) compared to NuSmile Zr crowns (646.5 +/- 223.9 N) (p value < 0.001). Conclusion Considering the limitations of the present in vitro study, further in vitro and in vivo studies are required to support the use of Zirkid(C) in primary molar teeth restorations and to assess others mechanical properties.