Posterior Zirconia Crown Cementation

A 67-year-old female patient presented to the office with distal recurrent decay associated with a previously placed restoration on tooth No. 20. The restoration was a failing porcelain-fused-to-metal (PFM) crown that was more than 20 years old. In addition to performing a visual examination, a periapical radiograph was taken to aid in the diagnosis and determine the extent of the decay. A treatment plan was presented to the patient that involved removing the failing PFM crown, debriding the secondary decay, and then replacing the crown with one made of zirconia (KATANA^™ Zirconia HTML, Kuraray Noritake Dental). After alternatives were discussed, the patient accepted the treatment plan. The benefits that a zirconia-based restoration can provide regarding strength were certainly a deciding factor in this particular case. The use of glass ceramics was an option, but zirconia was the preferred option, especially considering that the remaining tooth structure for cementation was primarily dentin.

First, the existing crown was removed using a crown removal bur (Great White^® Ultra [855-025], SS White). Once the decay was removed and the crown preparation was completed, a double-cord impression technique was utilized to ensure proper tissue management prior to taking the final digital scan with an intraoral scanner (TRIOS^®, 3Shape). The scan data was then sent electronically to the laboratory for fabrication of the final restoration. Next, the patient was fitted with a provisional restoration that was made of bis-acrylic temporary crown-and-bridge material (Integrity^®, Dentsply Sirona), and after marginal fit and occlusion were checked, it was temporarily cemented with a zinc oxide non-eugenol cement (Integrity TempGrip^®, Dentsply Sirona). Postoperative instructions were then verbally provided to the patient to ensure optimal care of the provisional during her time away from the office.

Two weeks later, the patient presented for a try-in of the final restoration, at which time a hemostat was used to remove the temporary crown (Figure 1). To completely remove the residual cement, pumice was used in a prophy cup to thoroughly clean the area (Figure 2). The try-in of the restoration entailed checking for marginal integrity, proper interproximal contacts, and an ideal occlusal relationship (Figure 3). Following this, all necessary adjustments were made utilizing a fine diamond football-shaped bur (285.5Z-TSZtech, Premier Dental).

There are three requirements for the intaglio surface when bonding zirconia restorations: air abrading, cleaning, and applying an MDP-based primer or cement.¹ Therefore, after the final restoration was tried in but prior to final cementation, the internal surface of the zirconia restoration was air abraded with 27-µm aluminum oxide for 3 to 5 seconds to ensure that it was fresh and properly conditioned (Figure 4). Alternatively, 50-µm aluminum oxide may also be used. A cleaning step is not needed if the air abrasion is performed after the try-in. Next, a self-adhesive resin cement (PANAVIA^™ SA Cement Universal, Kuraray Noritake) was dispensed directly into the treated restoration (Figure 5). This cement was chosen for its dual-monomer technology, which allows it to bond to virtually every dental material without the need for a separate primer.³ Its unique LCSi monomer provides the silane coupling agent necessary to adhere to glass ceramics and composite resin, and it also contains the original MDP monomer to facilitate the chemical interaction between zirconia and the tooth structure.⁴ This cement can save clinicians time by eliminating a step during cementation while still creating a strong bond. Once placed, the restoration was tack cured for 2 to 3 seconds using a monowave curing light (SmartLite^® Focus^®, Dentsply Sirona). After tack curing (or, alternatively, 2 to 4 minutes of self curing), the cement becomes gel-like, which makes thorough cleanup significantly faster and easier (Figure 6). The excess self-adhesive resin cement was then easily peeled away from the margins (Figure 7). After the excess cement was removed, the occlusion was checked, and final polishing was performed to complete the procedure (Figure 8).

This new universal adhesive cementation system was chosen for this treatment sequence because of its ease of use as well as its ability to provide predictable adhesion. The combination of the two monomers frees the practitioner from concerns about substrate conditioning, providing a powerful single-step bonding formula that can make cementation more efficient when compared with traditional multistep protocols.

Troy Schmedding, DDS
Accredited Member
American Academy of Cosmetic Dentistry

Private Practice
Walnut Creek, California