Reliability of Y-TZP versus PdAg alloy supported 3-unit bridges

Objectives:

To compare reliability and failure modes of porcelain veneered three-unit bridges with frameworks of Zirconia versus Palladium-Silver alloy subjected to mouth-motion step-stress accelerated fatigue.

Methods:

Abutment replicas (Nobel Biocare) were embedded in orthodontic PMMA resin. Zirconia (LAVA Frame, 3M/ESPE) and PdAg alloy (Superior Plus, PdAg, Jensen Industries)frameworks, of similar design (n=21 each), were fabricated and veneered with the porcelain recommended by each manufacturer. The bridges of each material (n=3 each) were cemented, and Hertzian contact (WC sphere, r=3.18 mm) tested to obtain ultimate failure load permitting design of step-stress profiles. The remaining specimens of each group (n=18) were distributed across 3-step stress profiles (ratio 3:2:1), and mouth motion step-stress cyclically loaded on the pontic lingual slope of the buccal cusp (WC indenter r=3.18 mm), at 300 inclination (off-axis) to the long axis of the abutment.

Results:

PdAg failures included flexural cracking of the abutment and/or connector area, whereas for 3M-Lava, failures were predominantly chipping of buccal aspect of veneering porcelain at the pontic . Failures originated from the contact area, from the connector, and at abutment margins, or combinations. Multiple failure modes make Weibull stress level probability curves general Including all failure modes the reliability (2 side @ 90% confidence bounds) for a “mission” of 50K cycles at 200 N load was determined (Alta Pro, Reliasoft).

Table: Reliability for a representative mission of 50K cycles at 200 N load

Output Zirconia (LAVA) PdAg alloy (Jensen Ind)

Upper limit 0.93 0.99

Reliability 0.79 0.98

Lower Limit 0.45 0.93

Conclusion:

No difference in reliability was observed, although there is a trend to higher reliability for PdAg group. Failure modes differed between groups, being mainly chipping for Zr and flexural cracking at connector area for PdAg. Supported by 3M-ESPE, Jensen Industries, CAPES-Brazil and Marotta Dental Studio.