Internal channel vents for posterior complete crowns

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.

Crown behaviour during cementation

Complete seating of restorations during cementation is hindered by the need for excess cement to be expressed. It has been shown that postcementation seating is usually worse than precementation seating. Techniques have been developed to minimize this problem, including venting, die spacing and limiting cement placement, and these techniques are reviewed. The behaviour of the crown during cementation is considered, and consequences of crown cementation are discussed.

Marginal fidelity of four methods of swaged metal matrix crown fabrication

The swaged metal matrix provides a method for rapidly making a metal substructure for ceramic crowns. This study determined the vertical and horizontal marginal fidelity of swaged metal substrate crowns made with four methods. No significant difference in vertical or horizontal marginal fidelity was found for metal margin crowns formed with either a plastic spacer or a paint-on die spacer. The vertical marginal fidelity was significantly better in crowns made with a metal margin (37 microns) than in crowns made with a porcelain facial margin (62 microns), and the latter were significantly better than crowns made with a 360-degrees porcelain margin (86 microns). Crowns made with all four methods were overcontoured by 46 to 82 microns. The 360-degrees porcelain margin was technically more difficult and time-consuming to make.