There are some instances where you need to bond a zirconia crown due inadequate mechanical retention. Such as when the preparation for a full crown does not have 4mm or more of near-parallel axial walls from the gingival margin to the occlusal table, and that retentive tooth preparation should have no more than 20 degrees lack of parallelism. Crowns for example second molars or onlay; or anterior teeth that the preparation of tooth to crown ratio is inadequate.
Since zirconia oxide contains no glass, it simply cannot be etched. However, there are still ways to bond to zirconia oxide, namely through the use of phosphates. Phosphates containing primers, such as Bisco’s Z Prime Plus and Ivoclar Monobond Plus, bond well to zirconia.
Ivoclar Vivadent research shows that zirconia oxide gets contaminated once the crown is tried in the mouth and comes in contact with saliva. It turns out that the phospholipids in saliva contain the same phosphate groups as the zirconia primers. Simply rinsing the saliva out of the crown does not remove phosphate groups that are bonded to the zirconia. So instead of cleaning the saliva out of the crowns as you did in the past with other crown and bridge materials, phosphoric acid on zirconia actually worsens the problem by flooding the inside of the crown with more phosphate groups than were present in the saliva. Since the salivary phosphate is bonded to the zirconia oxide in the crown, we need to flood the inside of the crown with a greater concentration of zirconia oxide. Placing Ivoclean (the only product available today) into the crown creates a concentration gradient, so the phosphates that were bonded to the crown become bonded to the zirconia oxide in the Ivoclean. After 20 seconds, the Ivoclean is simply rinsed away, creating a fresh bonding surface on the inside of the zirconia oxide crown for zirconia primers.
Ivoclean should be used on zirconia restorations, even if it looks like you have adequate retention. Cementing crowns into place after try-in knowing there is a contamination present could cause problems later.
STEPS FOR BONDING (Not Luting) ZIRCONIA CROWNS
Preparation of Tooth Dentin/Enamel
* All three procedures are successful if done well. Self-etch and selective-etch are the most predictable relative to production of postoperative tooth sensitivity. Total-etch can cause more postoperative sensitivity if not done well. If you are currently successful with the technique you're using, don't change.
*Self-adhesive resin cements have a lower incidence of sensitivity than adhesive or traditional crown and bridge cements. Marginal staining of self-adhesive resin cements has been reported to be lower than with traditional cements. A recent survey of clinical consultants of THE DENTAL ADVISOR indicated that self-adhesive resin cements were most commonly selected for cementation of high-strength (zirconia) all-ceramic restorations.