ABSTRACT
When using the old-style zinc phosphate cements for luting, it was possible to vary the setting time to some degree. Chilling the slab to just above the dew point and adding the powder in small increments gave the clinician some degree of control over working and setting times. However, this theoretical advantage was offset to some extent by the fact that the viscosity was higher and the flow properties lower than those of the glass-ionomers, and also phosphate cements had an ‘elastic memory’. This meant that it was necessary to maintain positive pressure after completing placement to ensure that the appliance did not lift off the tooth before the cement was set. The best way of overcoming the problem was to vent the crown prior to placement, thus allowing the escape of excess cement from the occlusal surface of a well-fitting appliance.
