Multilayer Super-Translucent Zirconia for Chairside Fabrication of a Monolithic Posterior Crown

Abstract

This case report describes the chairside fabrication of a monolithic posterior crown using a multilayer super-translucent zirconia material. According to the manufacturer's information, the newly introduced multilayer zirconia (4-YTZP) offers a unique combination of fracture strength (>850 MPa with speed-sintering) and improved optical properties, thus allowing a reduced minimum material thickness and optional temporary luting. By using up-to-date components of the CEREC system, including superfast dry-milling and a speed-sintering process, the fabrication of a monolithic zirconia crown is possible within an acceptable timeframe for the chairside workflow (60-75 min). The usage of a multilayer super-translucent material allows for the individualization of the restoration, typically in a single combined stain and glaze firing. However, it should be noted that clinical data for this type of restoration are still sparse. Therefore, manufacturer recommendations regarding indication, preparation, and cementation must be followed very strictly.

Figure 1

Zirconia materials of the first generation could only be used for veneered restorations, especially the molar region was prone to an increased risk for fractures of the veneering ceramics.

Figure 2

Transillumination of a zirconia crown of the fourth generation (CEREC MTL Zirconia, Dentsply Sirona).

Figure 3

Initial situation: endodontically treated first upper molar with an insufficient composite restoration.

Figure 4

Design of the preparation limit: shoulder with rounded inner angle (8951.314.017, Komet Dental, Lemgo, Germany).

Figure 5

Preparation of the occlusal surface (8899.314.027, Komet Dental, Lemgo, Germany).

Figure 6

Preparation for the intraoral scan. For increased lateral extrusion of the soft tissues, a layer of cotton is applied after a knitted retraction cord is placed. The cotton is removed immediately prior to oral scanning.

Figure 7

Analysis of preparation and determination of the preparation limit. The entire preparation limit is shown and can be detected automatically.

Figure 8

Virtual crown design (CEREC SW 5.2.2., Dentsply Sirona, Charlotte, USA). The occlusal contact points are reduced/built-up until they are depicted in turquoise. The design of the proximal contacts should be optimized to show light green areas.

Figure 9

Vertical positioning of the restoration to determine the desired color gradient and the fixation area of the restoration.

Figure 10

Milled restoration made of CEREC MTL Zirconia (Dentsply Sirona, Charlotte, USA). A diamond-coated separating disk is used to remove the retention pin.

Figure 11

(a) Individualization of the cervical part of the restoration (Dentsply Sirona Universal Stain, color: Body S1, Dentsply Sirona, Charlotte, USA). (b) Fissure characterization with Dentsply Sirona Universal Stain, color Mahogany. A manual endodontic instrument (ISO 015) is ideal for precise application.

Figure 12

Adjustment of proximal contact points with a diamond-coated polyurethane polishing instrument.

Figure 13

Prior to cementation, the internal surface of the crown is air-abraded with fine-particle-size alumina (<50 μm) at a pressure of 0.1–0.2 MPa.

Figure 14

The comparatively easy removal of excess cement after a short-time light polymerization (2-3 seconds) is a clinically relevant advantage of self-adhesive cements.

Figure 15

Occlusal view of the cemented monolithic zirconia crown.

Figure 16

Lateral view of the final restoration 2 weeks after final insertion.