FAQ
-
Q: What type of porcelain is used for the overlay materials for zirconia copings?
A: There are a number of zirconia-optimized porcelain systems available. Most zirconia ceramics have a coefficient of thermal expansion (CTE) of about 10. Make sure the overlay porcelain has a CTE close to 10. Do not use porcelain intended for PFM.
-
A: New veneering porcelains for zirconia are formulated to match the coefficient of thermal expansion of the zirconia and to bond to the zirconia coping. Some systems require an initial application of a wash layer.
-
A: Flexural properties of sintered zirconia specimens can be measured but this test is destructive in nature. It is crucial that the dental laboratory work with a reputable milling center.
-
A: Both techniques should produce adequate strength if the heating and cooling temperatures encountered during processing do not create adverse thermal gradients that cause residual stresses.
-
Q: Does the wiggle room of a milled restoration compromise the retention of a crown?
A: The better the fit, the better the retention. Highly retentive zirconia-based crowns can be cemented, whereas poorly fitting crowns should be bonded to tooth structure. Use a self-adhesive resin cement or bonded resin cement for cases with poor retention.