Flexural Strength of Treated Zirconia Frameworks Under Simulated Oral Conditions

Objectives: Limited data exists regarding the stress-corrosion properties of treated yttrium-tetragonal-zirconia-polycrystalline (Y-TZP) fixed-partial denture frameworks. This study evaluated the latter, fabricated using KaVo Everest^¨CAD/CAM technology, cyclically loaded under simulated oral conditions.

Methods: Fifty-five rectangular frameworks (20x5x2mm) milled from partially-sintered zirconium oxide were randomly assigned to 11 treatment groups (n=5), labeled A-K, described below. All specimens were fully sintered at 1450°C. A 3-point bend test (20mm between supports, load applied in center) was used to fatigue and determine framework flexural strength. All groups except A, B were immersed in artificial saliva for 120hrs. All groups except A, C received cyclic load applied by universal loading machine; load magnitude varied 10-300N for 1,200,300 cycles at 15Hz, with sinusoidal duty cycle. All samples were statically loaded to failure(MPa).

Results: One-way ANOVA provided evidence of significant effect for type of groups on the flexural strength (p=0.0052). The Tukey's Kramer test showed group E mean flexural strength was statistically significantly greater than groups J, H, and G. Pair-wise comparisons indicated groups with no significant difference.¹

Group

Flexural Strength

Pair-wise Comparisons

E (AlO-abraded²/wet/cycled)

958.82±168.25
A

D (wet/cycled)

827.34±77.87
A      B

B (dry/cycled)

824.98±113.95
A      B

A (dry/no-cycle)[CONTROL]

799.88±91.18
A      B

F (LL1-stain³/wet/cycled)

799.08±50.19
A      B

K (GB-abraded⁴/wet/cycled)

792.02±92.86
A      B

I (LL4-stain³/wet/cycled)

788.73±75.96
A      B

C (wet/no-cycle)

766.39±125.84
A      B

J (LL5-stain³/wet/cycled)

726.56±55.71
         B

H (LL3-stain³/wet/cycled)

699.82±90.84
         B

G (LL2-stain³/wet/cycled)

659.83±105.33
         B

¹means with the same letter not significantly different (p>0.05)

² post-sintering-aluminum-oxide-abraded

³ stained pre-sintering

⁴ post-sintering-glass-bead-abraded

Conclusions: Aluminum-oxide-abrasion of sintered Y-TZP rectangular frameworks resulted in increased flexural strength over a simulated 1-year life cycle, indicating that Y-TZP-based fixed partial denture frameworks are not negatively affected by this form of post-sintering processing.

Supported by KaVo America and the University of Iowa, College of Dentistry.