The effect of mechanical fatigue and accelerated ageing on fracture resistance of glazed monolithic zirconia dental bridges

The fracture resistance of glazed four-unit posterior dental bridges after mechanical fatigue testing and artificial ageing was evaluated. Thirty identical monolithic bridges were fabricated from “translucent” zirconia and divided into three groups of ten. The first group was monotonically loaded to fracture; the second group was dynamically loaded in water (0-300 N, 106 cycles) prior to fracture, while the third group was first subjected to accelerated ageing (in a diluted acetic acid solution at 134 °C for 12 h), then to mechanical fatigue and finally monotonically loaded to fracture. Two tested bridges did not survive 106 cycles of dynamic loading, one in Group 2 and one in Group 3. Mean monotonic fracture loads (N) were: Group 1: 547.3 ± 66.3, Group 2 (n = 9): 465.2 ± 118.0, and Group 3 (n = 9): 408.8 ± 58.9. According to the fractographic analysis the glaze embrittlement during artificial ageing and the stress corrosion during fatigue loading are proposed to be responsible for the reduced fracture resistance.