Zirconia Framework

[Edilma Howard]

Thesite is secure.

The ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Materials and methods: Twenty six consecutive patients with at least one congenitally missing tooth in the maxilla or mandible were provided with 58 single unit Y-TZP RBBs. The cantilever RBBs were designed and milled using a CAD-CAM system to produce frameworks which were veneered using a glass-ceramic material and cemented with a self-etching dual-cure resin cement.

Results: Following a mean follow up period of 36.2 months (maximum 62.3 months, minimum 25.4 months), 48 restorations remain in service with a survival rate of 82.7%. One anterior retainer fracture was encountered and no fractures of the posterior framework or ceramic were noted within the time frame reported.

Conclusions: All ceramic Y-TZP RBBs replacing maxillary and mandibular teeth in the anterior and posterior areas demonstrated an 82.7% Kaplan Meier survival rate over 3 years, which was comparable to previously published survival rates for the non-perforated metal framework RBBs.

Clinical implications: Replacement of anterior or posterior teeth using single unit cantilevered RBBs using Y-TZP ceramics should be considered a viable restorative option with a high survival rate.

Objective: Zirconia ceramics for frameworks of fixed partial dentures can be color shaded to better match the shade of veneering porcelain. The aim of this study was to evaluate the effect of color shading the green-stage zirconia ceramic on some mechanical properties.

Material and methods: Zirconia disks (diameter 19 mm, thickness 0.8 mm) were divided into 10 groups of 10 disks each according to the color shade of the zirconia ceramic. The disks were shaded with the same color liquid using either the recommended shading time (3 s) or prolonged shading time (60 s). Nine control disks were tested without color. Composition of the color liquids was determined with EDX analysis. All the disks were sintered at 1500 degrees C and their biaxial flexural strength was measured dry and at room temperature. Surface Vickers microhardness was measured. Data were evaluated using ANOVA analysis.

Biomaterials in dentistry must address several requirements, which include biocompatibility, strength related to intended purpose, and esthetics. The history of dental prostheses reflects a progression from function to esthetics, with gold restorations largely being replaced by porcelain-fused-to-metal restorations from the 1970s to the 1990s. The introduction of all-ceramic restorations beginning in the 1980s initiated a continuous transition from metal-based ceramics to various multilayered and monolithic all-ceramic restorations.

The central issue for all-ceramic restorations has been balancing esthetics (color and translucency) with strength or function. Different materials have been used, and their esthetic value traditionally has been inversely related to their strength. The basis for this clinical paradox is the use of glass phase ceramics to impart translucency to dental ceramics and the use of relatively opaque crystalline ceramics to achieve strength.

The past decade of clinical research has provided some insight regarding the performance of zirconia prostheses. A systematic review by Raigdroski et al. looked at the survival and complications of zirconia fixed dental prostheses (FDP). He reported survival rates that ranged from 73.9% to 100% within 12 studies. Five studies reported 100% survival rates during the observation period. One study reported 73.9% survival of frameworks and the rest (six studies) had survival rates ranging between 88.2% and 96.6%. The common complication reported was chipping, and it was suggested that with the development of new layering porcelains, better clinical properties would be expected. (1)

In a second report, a 2010 systematic review on the performance of zirconia-based FDP evaluated not only the survival, but also the complication rates for this type of prosthesis up to five years. Three hundred and ten prostheses were included. The five-year survival rate for all FDP was 94.29%, and 76.41% of FDP were considered free of complications, with chipping being the most reported complication. (2) Very rarely do we see fractures within the zirconia framework itself. For example, the systematic review by Sailer et al. indicated that compared to chipping rates of 13.6%, framework fractures occurred only 6.5% of the time. (3) Observed fractures were reported most commonly in connectors of multiunit posterior restorations, and/or second molar abutments.

The systematic review of Larsson et al. in 2014 suggested that the success rate of tooth- and implant-supported zirconia-based crowns is similar and comparable to that of conventional porcelain-fused-to-metal crowns. (4) A recent laboratory study utilized indentation to induce chipping of monolithic zirconia and lithium disilicate materials. The results confirm that ceramic veneered-zirconia displayed high chipping and monolithic lithium disilicate resisted this chipping; monolithic zirconia was most resistant to this induced chipping behavior. (5)

As revealed in the aforementioned reviews concerning zirconia restoration performance, one of the early and prominent observations made regarding the clinical performance of zirconia-based all-ceramic restorations was chipping of the veneering porcelain from the zirconia frameworks. While many different investigators have suggested fundamental reasons for this phenomenon, the clinical response to chipping is a concern for layered zirconia restorations.

When used as a framework, zirconia has an inherent basic esthetic value, due to the fact that it is white and can be alternatively colored to mimic surrounding dentin. Further, it can be provided with high opacity to cover discolored teeth and implant components. (6) This can be advantageous to the technician who is trying to conceal a dark underlying tooth structure, a metal post, or the remainder of amalgam restorations left after initial preparation.

Zirconia framework-based restorations, when veneered with an appropriate ceramic layering system designed for zirconia, can result in exceptional esthetics and can achieve an imperceptible match to the surrounding dentition. The talented technician may develop appropriate color and optical properties of the restoration within the veneering ceramics. However, the past decade of investigation has revealed that chipping within the veneering ceramic or at the framework/veneer interface frustrates higher clinical success and survival of these restorations. Veneer chipping, not framework fracture, appears to be the weak link in zirconia-based restorations.

Research regarding zirconia as biomaterial began in the late 1960s. Helmer and Driskell published the first paper in 1969. (7) In 1988, Christel et al. offered the use of zirconia as an alternative to other materials used at the time to manufacture the ball heads for total hip replacements. (8) Zirconia is still used in this application and other medical prosthetics to this day. Implied was acceptable biocompatibility. Clark showed that zirconia was found to be better than other ceramic biomaterials in use circa 1990 because it possessed higher strength and hardness.

Zirconia offers an excellent option for the restoration of dental implant cases. With digital design and precision milling, screw-retained monolithic zirconia (with or without facial layering) restorations can be predictably fabricated.

The introduction of zirconia-based ceramics as a restorative dental material has generated much interest in the dental profession. The mechanical properties of zirconia are the highest ever reported for any ceramic used in prosthetic dentistry. The strength of zirconia has allowed the incorporation of high-strength all-ceramics into its use for posterior FDP. (14) High strength, coupled with the possible high esthetics that zirconia offers, allows the material to become a highly valuable option in our prosthetic armamentarium.

The basis for the valued strength displayed by zirconia is its unique crystalline structure and its behavior under loads. Zirconium dioxide (ZrO2), also known as zirconia, is a white crystalline oxide of the metal element zirconium. Its most naturally occurring form is the rare mineral baddeleyite, though zirconium metal used for dentistry is obtained from the zirconium-containing mineral ore called zircon. After being processed and purified, these powders can be further processed to produce somewhat porous bodies that can be CAD/CAM-milled with great precision. Once densely sintered, a polycrystalline ceramic material is produced which, unlike most other dental ceramics, contains no glass phase.

Over the last several years, many high-strength ceramics have been developed for the construction of metal-free restorations. (15) Several studies have evaluated different all-ceramic systems and offered conclusions on where these ceramic systems may be used with success in the oral environment. Luthy et al. measured average load-bearing capacities for several ceramic systems and found 518 N for alumina-based restorations, 282 N for lithium disilicate-based restorations, and 755 N for zirconium restorations. (16) Raigrodski et al. also analyzed several different all-ceramic systems and concluded that the all-ceramic systems he studied were only to be used in the anterior, for single-crown restorations, and possibly three-unit FPDs. He also concluded that because of the higher strength of zirconia, this material offers a wider area of restorative options in the oral cavity, including posterior single units and multiunit restorations. (15)

3a8082e126