THE EFFECT OF DELAYED PLACEMENT OF CAPSULATED CEMENTS ON CROWN SEATING

The effect of delayed seating of a crown onto a die was determined whe n using capsulated zinc phosphate and glass ionomer cements. The space between the crown and the die was varied up to 60 mum, and the commen cement of seating was from 30 to 210 seconds after mixing ended. The z inc phosphate cement gave gradually increasing seating discrepancies w ith time, but providing 45 mum of space was present, the crown could b e well seated up to 3 minutes after mixing. It is argued that this cem ent is particularly suitable for cementing burnishable inlays. The gla ss ionomer cement permitted reduced seating discrepancies compared wit h zinc phosphate cement when 45 mum of space was present, but gave poo r results when the seating was delayed more than three minutes. The ca psulated cements were clean and quick to use, and it is recommended th at if there is a delay in seating, a new mix of cement shoud be prepar ed rather than attempting to complete cementation with an obviously se tting cement.