Effect of increasing cement space on cementation of artificial crowns.

In this study, the effect of cement space on cementation with an artificial crown and machined die was investigated. Spacing was varied in increments of 10 microns, and the dies were cemented in the crown by a force of 25 N with either zinc phosphate cement or a silicone fluid. Separation of the artificial crown and die was measured relative to complete seating without cement. A silicone fluid of 10.6 Pa seconds viscosity was used first with seating times from 168 seconds (SD 8.8 seconds) with no spacing to 2.1 seconds (SD 0.07 second) with 50 microns spacing. Unless 40 microns of spacing was used, the zinc phosphate cement did not allow the artificial crown to seat to less than 30 microns seating discrepancy, and it was suggested that particles in the cement caused this effect. The seating discrepancy ranged from 368 microns (SD 10 microns) without spacing to 29 microns (SD 1 micron) with 50 microns spacing. It was concluded that providing cement space substantially facilitated seating of crowns during cementation.