Resistance to the Fracture of Pediatric Zirconia Crowns: In Vitro

Background: Early childhood caries (ECC) is the most common chronic infectious transmissible disease with 24% of prevalence in Mexico. Pediatric zirconia crowns are an esthetic alternative for the restoration of teeth affected by ECC because of their ability to withstand external forces and resist fractures. Townsend et al (2014) and Al Shobber & Alkhadra (2017) compared the resistance to fracture of different brands of crowns finding that there were differences between them. The commercially available pediatric zirconia crowns in Mexico are NuSmile®ZR Primary crowns (NuSmile, Houston, Tex. USA) therefore, the purpose of this study was to measure their fracture resistance.

Method:The fracture resistance of 18 first and second, upper and lower molars pediatric zirconia crowns of NuSmile®ZR, randomly selected, cemented with glass ionomer on extracted primary molars, previously storaged in cloramine 0.5%, prepared according to the manufacturer`s instructions, placed under the universal testing machine Shimadzu Corporation© model AG-IC 100Kn were measured. Force was applied at 90° with crosshead speed of 0.5 mm/min until they fractured. Maximum breaking loads were recorded. Data was then analyzed using software that measured the fracture resistance of the crowns in megapascals (mPa). Descriptive statistics and One-way Analysis of Variance (ANOVA) was used for intergroup comparisons. The confidence interval for the mean was calculated at 95% of confidence.

Results: The fracture resistance of zirconia crowns, according to the descriptive statistic, had a minimum of 8.527 mPa and a maximum of 20.289 mPa with a standard deviation of 3.539 mPa. In the analysis of variance was observed F=.497 showing did not statistically significant difference in force required to fracture between the trials crowns. Four zirconia crowns had fracture of the extracted primary molar.

Conclusion: The first and second upper and lower molars pediatric zirconia crowns, showed high fracture resistance even under intense pressure load.