Now that zirconia crowns have been available for more than a decade, dentists across the U.S. are prescribing these all-ceramic restorations, like BruxZir^® Zirconia, at an incredible rate. Of the millions of crowns made yearly at Glidewell, 81% are monolithic zirconia, whereas the previous restorative leader, the PFM, now only makes up 7% of restorative prescriptions.¹

So while it may seem a foregone conclusion that PFMs are an outmoded solution, there are many indications for which they’re not only appropriate but also superior to their monolithic counterparts. This blog post will outline the differences between zirconia crowns and PFM crowns, highlighting their strengths, weaknesses and ideal uses.

Zirconia crowns are dental restorations made from zirconium oxide, a ceramic material with qualities that afford the fabrication of high-strength, tooth-colored restorations. Zirconium oxide has been used in health care settings since the 1970s, and came into popular use in dentistry in the early 2000s, first as substructures for other ceramics and then later as full-contour crowns.

Glidewell offers two varieties of zirconia crowns: BruxZir Full-Strength Zirconia and BruxZir Esthetic Zirconia. The full-strength zirconia formulation is ideal for clinical situations that require the toughest of materials. And the esthetic variety is designed for cases that demand more of a true-to-life appearance and somewhat less toughness. Both formulations, and zirconia crowns in general, are the strongest tooth-colored solutions available to patients today.

PFM (porcelain fused to metal) crowns are bilayered restorations made by layering ceramic over a metal substructure. Traditionally, feldspathic porcelain was used for most PFMs, though today there are PFM options made with advanced ceramics — including Glidewell’s Obsidian^® Fused to Metal restorations, which are made with lithium silicate.

PFMs have been used in dentistry since the late 1950s. At that time, dentists had limited material options available for full-contour crowns, with crowns being either cast metal or fully porcelain.2 Because of their two-material composition, PFMs offer a happy medium between full-metal restorations and all-porcelain crowns. A PFM’s metal substructure adds strength and longevity, and its ceramic covering creates a tooth-colored appearance more widely accepted by patients. PFMs have evolved over the decades, with newer generations of metals and ceramics featuring both enhanced strength and appearance.

To summarize the above, the key differences between zirconia and PFM crowns are the number of layers and the composition of said layers. Zirconia crowns are made from a single high-strength material, while PFMs are made from two materials: metal and a layering ceramic. Ultimately, the material makeup significantly impacts the definitive performance of a restoration.

Take PFMs, for example. Historically, they have displayed high rates of chipping, fracturing and shearing off of the layering ceramic. There are two primary reasons behind these breakages. First, because the ceramic layer is so thin, the material is less durable. Second, there are a difference between the thermal expansion characteristics of the substructure metal and those of the layering ceramic, which means that the layers expand and contract at differing rates during manufacturing. This imparts imperfections and weaknesses into the finalized restorations, especially at the location where the ceramic and metal meet.

Zirconia crowns, on the other hand, are milled from a solid block of zirconia and sintered as fully shaped restorations. The monolithic nature of the material means that all areas of the restoration share the same material characteristics, eliminating the issues observed in PFMs. Moreover, zirconia imparts significant performance characteristics, having nearly 10 times the flexural strength of an average feldspathic layering ceramic.^3,4

However, while zirconia is substantially stronger than the ceramics used for PFM crowns, the monolithic material does have a weakness: Zirconia bridges with long spans in an area with limited vertical space may fracture over time, an issue arising due to the bridge connectors having small volume. At Glidewell, for these bridges, we typically recommend that dentists use PFM restorations because their metal substructure ensures a longer-lasting solution in those compact areas.

Zirconia is an extremely versatile material that can be used in virtually any indication, including crowns, bridges up to 16 units, veneers, inlays and onlays, screw-retained crowns and bridges, and full-arch implant prostheses. Zirconia best serves patients who require durable, affordable and high-performing restorations as well as patients who have metal allergies. And due to continuous zirconia material improvements, today’s zirconia restorations offer patient-pleasing esthetics and can be used to solve most of dentistry’s everyday restorative and cosmetic challenges.

With zirconia restorations taking over many of the common indications for which PFMs would traditionally be used, there are fewer indications today for which PFMs are ideal. Compared to zirconia crowns, PFMs have worse performance characteristics for most restorative scenarios in dentistry. However, there are specific indications in which they still represent the better material option, including bridge cases that lack the vertical height necessary for adequate zirconia connectors, cases where the restoration must match nearby PFMs, and the restoration of endodontically treated teeth with crown or root staining that would bleed dark shadows through all-ceramic restorations. 

Dentistry’s half-century workhorse, the PFM crown, still has an important role to play for the practitioner. But modern materials like zirconia crowns offer substantially enhanced performance and appearance characteristics for most indications, thanks to advances in materials sciences.