The effect of delayed placement of capsulated cements on crown seating

The effect of delayed seating of a crown onto a die was determined when using capsulated zinc phosphate and glass ionomer cements. The space between the crown and the die was varied up to 60 microns, and the commencement of seating was from 30 to 210 seconds after mixing ended. The zinc phosphate cement gave gradually increasing seating discrepancies with time, but providing 45 microns of space was present, the crown could be well seated up to 3 minutes after mixing. It is argued that this cement is particularly suitable for cementing burnishable inlays. The glass ionomer cement permitted reduced seating discrepancies compared with zinc phosphate cement when 45 microns of space was present, but gave poor results when the seating was delayed more than three minutes. The capsulated cements were clean and quick to use, and it is recommended that if there is a delay in seating, a new mix of cement should be prepared rather than attempting to complete cementation with an obviously setting cement.