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 understand ing of the mechanical properties of zinc-phosphate cement. Materials and Me thods: Fifty-six brass dies were made, half of them with grooves and half w ithout grooves. A cantilever FPD for each die was cast in Au-Pd-Ag alloy. F our linear strain gauges were attached to the marginal portions of each ret ainer. The FPDs were cemented to the dies using zinc-phosphate cement. A fa tigue test machine was used to cyclically load the specimens with 50 or 100 N for 5.5 x 10(5) cycles (1 Hz) in 37 degrees C water. During the fatigue test, strain measurements were made after every 0.5 x 10(5) load cycles to discover if strain response was altered. After completion of the fatigue te st, ultimate tensile strength of each specimen was measured and statistical ly analyzed by 2-way analysis of variance. Results: With or without grooves , strain responses were the same at every periodic strain measurement throu ghout the 50-N fatigue test. For the 100-N fatigue test, strain responses f or the specimens without grooves were different before and after cyclic tes ting, but there was no difference for the specimens with grooves. There wer e no significant differences in tensile strength among the specimens after the fatigue tests. Conclusion: No fatigue fracture was observed in zinc-pho sphate cement film after repetitive loading. Repetitive loading may improve stress transmission within the zinc-phosphate cement film.