Deformation of vented crowns with fluids of differing viscosities.

Venting of full crown restorations is an effective aid to seating during cementation. Vent hole repair complicates placement procedures and potentially disturbs the coronal integrity of the restoration. Cervical deformation of crowns during cementation was measured with circumferential strain gauges. Crowns were able to be vented occlusally, and two silicone fluids of widely differing viscosities were used. Venting significantly decreased the time to seat for both viscosities. It also decreased deformation of crowns cemented with low viscosity fluid, but increased deformation during cementation with high viscosity fluid. The values of deformation were nearing clinical significance for ceramic systems. Increased axial wall separation gave a similar decrease in seating times, but with no increase in deformation. The advisability of venting is questioned when high viscosity cements are used, and methods of increasing axial wall separation are recommended.