Fatigue Behavior of the Zinc-Phosphate Cement Layer

Purpose: Fatigue behavior of luting cement film between model fixed partial dentures (FPD) and their dies was investigated to gain a better understanding of the mechanical properties of zinc-phosphate cement. Materials and Methods: Fifty-six brass dies were made, half of them with grooves and half without grooves. A cantilever FPD for each die was cast in Au-Pd-Ag alloy. Four linear strain gauges were attached to the marginal portions of each retainer. The FPDs were cemented to the dies using zinc-phosphate cement. A fatigue test machine was used to cyclically load the specimens with 50 or 100 N for 5.5 3 105 cycles (1 Hz) in 37°C water. During the fatigue test, strain measurements were made after every 0.5 3 105 load cycles to discover if strain response was altered. After completion of the fatigue test, ultimate tensile strength of each specimen was measured and statistically analyzed by 2-way analysis of variance. Results: With or without grooves, strain responses were the same at every periodic strain measurement throughout the 50-N fatigue test. For the 100-N fatigue test, strain responses for the specimens without grooves were different before and after cyclic testing, but there was no difference for the specimens with grooves. There were no significant differences in tensile strength among the specimens after the fatigue tests. Conclusion: No fatigue fracture was observed in zinc-phosphate cement film after repetitive loading. Repetitive loading may improve stress transmission within the zinc-phosphate cement film.