Effect of Thermomechanical and Static Loading on the Load to Fracture of Metal-Ceramic, Monolithic, and Veneered Zirconia Posterior Fixed Partial Dentures

J Prosthodont. 2019 Feb;28(2):171-178. doi: 10.1111/jopr.13008. Epub 2019 Jan 1.

Abstract

Purpose: To evaluate the influence of static (not preloaded) and thermomechanical loading on the load to fracture of metal-ceramic, monolithic and veneered zirconia computer-aided design/computer-aided manufacturing (CAD/CAM) posterior fixed partial dentures (FPDs).

Materials and methods: One hundred standardized specimens with 2 abutments screwed onto a platform were prepared from stainless steel to receive a posterior 3-unit FPD with an intermediate pontic. Specimens were randomly divided into 5 groups (n = 20): Metal-ceramic (control group), Lava Zirconia system, Vita In-Ceram YZ, IPS e.max ZirCAD, and Lava Plus. Half of the specimens of each group (n = 10) underwent no preloading, and the other half were subjected to thermomechanical loading in a masticatory simulator, and then all FPDs were loaded until fracture using a universal testing machine at a 1 mm/min crosshead speed. The load to fracture of the veneering ceramic and the load to fracture of framework (total fracture) were recorded for each specimen. Data were statistically analyzed using 2-way ANOVA, Tukey's HSD post-hoc test, Student's t test, and Weibull statistics, α = 0.05.

Results: Significant differences were recorded between the metal-ceramic and veneered zirconia groups for the veneering ceramic load (p < 0.001; f = 36.62; f = 57.76) in no preloading and thermomechanical loading subgroups, respectively, but no differences were observed between the static and thermomechanical loading conditions. No differences were observed among the veneered zirconia groups. For the total load to fracture, significant differences were observed according to the material (p < 0.001; f = 500.8), between the metal-ceramic and Lava Plus group and the other zirconia groups in no preloading subgroup, and between metal-ceramic and the other groups (p < 0.001; f = 303.33) in thermomechanical loading subgroup. For the type of preloading, significant differences were observed (p = 0.02; f = 5.24) between the Lava Plus group and the other groups. Thermomechanical loading significantly decreased the fracture load of the Lava Plus group (p = 0.005). The Weibull statistics corroborated the results.

Conclusions: Monolithic zirconia restorations provided the highest load to fracture values among the zirconia groups tested; however, the results indicate that they must be used in the oral environment with caution, because their load to fracture was influenced by the aging simulation.

Keywords: Fixed partial dentures; fracture load; monolithic zirconia; thermomechanical load; veneered zirconia.

MeSH terms

  • Computer-Aided Design
  • Dental Abutments
  • Dental Materials / chemistry*
  • Dental Restoration Failure*
  • Dental Stress Analysis
  • Dental Veneers
  • Denture, Partial, Fixed*
  • Materials Testing
  • Metal Ceramic Alloys / chemistry*
  • Random Allocation
  • Stainless Steel / chemistry
  • Stress, Mechanical
  • Zirconium / chemistry*

Substances

  • Dental Materials
  • Metal Ceramic Alloys
  • Stainless Steel
  • Zirconium
  • zirconium oxide