Preparation and Delivery of a Posterior Zirconia Crown
Durable, long-lasting restorations require a careful thought process
Paresh Patel, DDS and Apolinar Madrigal, DDS
Thanks to their durability and esthetics, posterior crowns fabricated from zirconia have become a go-to restorative solution.1-3 But the long-term success of a restoration hinges on more than just material selection.4,5 It is also dependent on the successful execution of clean, well-defined gingival margins; high-quality, easily readable impressions; and proper technique when cleaning and cementing the final restoration.6
A 37-year-old, male patient presented with a broken lithium disilicate crown on tooth No. 19 (Figure 1). Upon its removal and examination, it was determined that the material was not to blame, but rather the original tooth preparation. The original tooth preparation presented with approximately 0.9 mm of bulk around the prep, which, according to the manufacturer's instructions, is insufficient for bonding and cementation of the material.7
To approach this case using minimally invasive dentistry, tooth No. 19 was prepared with supragingival margins. This helps to make the margins cleansable and enhances the biomimetic design (Figure 2). Biomimetic design allows dental lab technicians to recreate the original tooth contours in situations where removal of the tooth past the original curvature is not desired.
Once the tooth was prepared, a mandibular full-arch impression was captured using a VPS impression material (Splash!Max, DenMat) and an impression tray (The Gripper®, DenMat) that was thinly painted with adhesive on the tray walls (Figure 3). Due to its hydrophilicity, Splash!Max easily seeps past the margins to capture a highly detailed, quality impression, and the material also offers maximum tear strength, dimensional accuracy, and high contrast colors to help eliminate guesswork by the lab technicians.
To ensure that the dental lab was fully versed in the needs of this case, a full-arch bite registration was also captured (Vanilla Bite™, DenMat). This medium viscosity VPS bite registration material is ideal for 1- to 2-unit cases, and with a Shore A hardness rating of 90, it diminishes the risk of error when mounting the models, which reduces the need to make bite adjustments when seating the final restoration.
The full-arch impression and bite registration were sent to the dental lab along with a prescription for a zirconia crown (LumiZir™, DenMat). This material was chosen primarily for its strength: because they are monolithic, LumiZir crowns possess a flexural strength of greater than 1,150 Mpa, while also being kind to the opposing dentition and offering lifelike esthetics. The completed zirconia crown was delivered, and the patient returned for fitting and cementation of the restoration (Figure 4).
First, the temporary was removed in preparation for cementation of the final restoration. The tooth surface was then cleaned with plain pumice to remove any temporary cement and biofilm. Next, the crown was cleaned using isopropyl alcohol, rinsed with water, and gently air-dried. Finally, the enamel was selectively etched (Etch ‘N' Seal®, DenMat), and three to five coats of bonding agent (Tenure® Uni-Bond®, DenMat) were applied and light cured for 10 seconds.
Because the lingual wall of the crown preparation did not need to be extended to the gingival margins, in keeping with biomimetic design, the authors used a bond enhancer (Dab-Eze® Tenure® S sponges, DenMat) to enhance the bond strength. These presoaked sponges contain HEMA, a hydrophyllic, orally acceptable methacrylate monomer that wets oral surfaces to provide greater penetration into dentin. A sponge was used to apply a thin layer of Tenure S to the tooth's surface, and then it was light cured for 10 seconds (Figure 5).
A dual-cure, resin-ionomer cement (Infinity® SE, DenMat) was chosen to cement the zirconia crown due to its ease of cleanup, high bond strength, and self-adhesive properties (Figure 6). By sealing the dentin tubules, Infinity SE is designed to minimize placement and postoperative sensitivity and deliver insoluble seals at the margins without microleakage.8Once the crown was seated, the excess material at the gingival margin was spot cured for a maximum of 1 to 2 seconds and then easily removed using a hand instrument (Figure 7). Although the cement was light cured for this case, it also offers a 4-minute, self-cure option.
The final, cemented posterior zirconia restoration demonstrates the results that can be achieved in a well-executed case and underscores the importance of using proper clinical technique for long-term restorative success (Figure 8).
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