Comparison of Retentive Strengths Among Four Different Prefabricated Primary Posterior Zirconia Crowns

Purpose: To assess retentive strengths of four commercially available posterior primary prefabricated zirconia crowns using a novel epoxy-resin block anchorage system.

Method: 60 extracted human teeth were mounted in epoxy resin blocks compatible with the Instron E3000, and prepared with a single standard prep design. Cheng Crowns (N=15), Kinder Krowns (N=15), NuSmile (N=15), and EZ-Pedo (N=15) were cemented using automix glass ionomer cement. Following thermocycling 5000 cycles from 5º to 55º C, crown retentive strengths were determined and statistically analyzed using one-way ANOVA with LSD post hoc test (P <0.05). Cement failure pattern was also recorded.

Results: Mean retentive strengths: Cheng Crowns 397.4±178.7 N, Kinder Krowns 158.2±58.9 N, NuSmile 183.5±55.5 N, and EZ-Pedo 482.5±87.4 N. EZ-Pedo had the most significant retentive strength, followed by Cheng Crowns (P<0.05). NuSmile and Kinder Krowns followed with no statistical significance between the two.

Conclusion: Retentive strengths among the four prefabricated zirconia crowns are significantly different. EZ-Pedo and Cheng Crowns have statistically significantly greater retentive strength than Kinder Krowns and NuSmile. EZ-Pedo and Cheng Crowns show greater adhesive failure to the tooth, whereas Kinder Krowns and NuSmile show greater adhesive failure to the crown.