by Gary M. Radz, DDS
The most common indirect restoration is the single unit posterior tooth. In today’s dental practice there are many materials and options available to restore a tooth that has been compromised from disease or trauma. As our population ages, we will continue to see posterior teeth that have old direct restorations that need to be replaced with a stronger indirect restoration.
Today we have so many options available, it can become confusing. However, all these options provide dentists with the ability to customize the material and the preparation design to provide patients with the best possible restorative choice. Many of these choices include tooth-colored restorations, which is a priority for many of our patients. It is important for dentists to be well versed in these options.
Certainly the gold standard of indirect dental materials is gold. Numerous polls confirm that when it comes to an indirect restoration in their own mouths, dentists frequently state they would choose gold. Gold is a durable material that allows for a minimal preparation design, has excellent marginal adaptation, and has excellent biocompatible properties.
Its drawback is color, and today’s patients demand tooth-colored options. Recently another obstacle has become an issue — the price of gold, which has skyrocketed above $1,500 per ounce, thus increasing the cost of the restorations from the lab to the dentist, which leads to a higher price for patients.
Given all of these factors, gold, sadly, is being used less often. For many years, porcelain-fused-to-metal (PFM) has been the most common indirect restoration for posterior teeth. It meets patient demands of the tooth-colored restoration, while providing dentists with the strength and fit they require in their restorations.
While a time proven material, PFM does have some limitations. While it has been the esthetic material of choice for many years, it has its challenges in its ability to create a final restoration that simulates a natural tooth. Certainly there are materials that allow ceramists to more closely replicate a natural tooth. A high noble metal substructure made of a gold substructure such as Captek provides excellent esthetics. The other drawback of PFM restorations is that dentists are limited to crown and bridge restorations. Inlays and onlays are not part of what PFM can do.
For many years dentistry was limited to full gold or PFM restorations. However, in the past two-plus decades, some new materials have entered the marketplace that provide more options, and more importantly to some, more esthetic options.
Indirect composite resin restorations became available in the ’80s. In these early years, BelleGlass (Kerr) was a market leader in these materials. Long-term studies on this material demonstrated that it was a viable restorative material. Dentists who used it found it very beneficial for inlays and onlays. Indirect composite demonstrated physical properties that in many ways came close to porcelain and it was typically less expensive for the lab to fabricate. Sadly, North American dentists have never fully embraced the concept or benefits of indirect composites, and the material has never gained much traction within the industry.
About the same time as the introduction of indirect resin systems was the development of some revolutionary all-ceramic systems that were strong enough to be approved for limited posterior use. The market leader for many years was Empress (Ivoclar), a pressed ceramic that consisted of a leucite-reinforced glass that was highly esthetic and very popular for anterior restorations. Many dentists also found that it was an excellent material for inlays, some onlays, and selected posterior crowns. Its strength prevented it from being a universal posterior material, but when used in the proper conditions, it provided for a highly esthetic posterior restoration. Empress and similar pressed ceramics enjoyed a good run through the ’90s and into the early 2000s as a popular posterior restorative material.
Around the turn of the century a new material arrived to the industry — zirconia. Zirconia is an extremely strong material that has the benefit of being white. When this material was introduced, a zirconia substructure was used to replace the traditional metal substructures used in PFM. Then traditional powder/liquid porcelains were used to create an esthetic restoration. Lava (3M) and Cercon (DENTSPLY) were the early market leaders in this category. The real excitement with these materials was that there was now a tooth-colored material that could be used for anterior and limited posterior bridges. These early zirconia restorations continue to show promise, and many dentists have incorporated these restorations into their practices.
During the past couple of years, we’ve seen the introduction of full zirconia crowns and bridges. From a block of zirconia, laboratories fabricate fully contoured zirconia restorations, and the dental industry is showing growing acceptance. Recent data supplied by Glidewell Laboratories (one of the largest dental labs in the U.S.) shows that the largest single type of restoration they are producing is the full zirconia restoration, even more than PFM restorations! Esthetics, strength, and cost are all certainly contributing factors to this impressive growth.
The last material of recent interest is the lithium disilicate material, and eMax (Ivoclar) is currently the only one available. This material has presented with esthetic properties approaching or equaling the leucite-reinforced glass materials, but with significantly better strength properties, and providing a high level of esthetic restoration for posterior restorations. This material has seen such wide acceptance that leucite-reinforced glass is quickly fading away. Recent Glidewell data shows that lithium disilicate is the third most popular restoration created in their lab (behind full zirconia and PFM). Lithium disilicate has demonstrated the potential to be an almost universal restorative material.
Inlays are probably one of the most underused restorations in dental practices today. Yet there are still indications for the use of inlays, and dentists should be mindful that they are an option. A great place for an inlay is a large Class II preparation where the proximal contact and/or contours are challenging. The ability to work on a model indirectly provides the opportunity to create more ideal anatomy. Gold, indirect composite, and lithium disilicate are all excellent options.
Onlays have grown in popularity in recent decades, as tooth-colored alternatives have become more available. Onlays are an excellent choice when a damaged tooth presents with a lot of healthy tooth structure remaining, but one or two cusps require full coverage. An onlay provides the opportunity to accomplish a more conservative restoration while strengthening a compromised tooth. Gold, indirect composite, and lithium disilicate are all material options for an onlay restoration.
The full coverage crown is easily the most common posterior indirect restoration. Literally millions of teeth have been restored functionally and esthetically using crowns. Crowns are versatile and predictable restorations that have withstood the test of time. The material used for a crown is dictated by intraoral conditions of the particular tooth, as well as consideration of the patients’ esthetic goals. Gold, PFM, zirconium core, full contour zirconium, and lithium disilicate are all options.
For many years bridges have been the standard option for restoring missing teeth. All the considerations and materials discussed here for crowns also apply to bridges.
In the past few decades, the wide acceptance and clinical success of implants have decreased the use of bridges as the restoration of choice for a missing tooth. Traditionally, PFM has been the material of choice for implant restorations. But zirconia products are now used more frequently, and in the most esthetically demanding situations, many practitioners now use lithium disilicate to optimize their esthetic results.
Lastly, no discussion of posterior indirect restorations would be complete without mentioning CAD/CAM technology. Whether using an in-office system or a lab-based system, CAD/CAM is here to stay and will continue to grow. The benefits of CAD/CAM are seen in the precision of the technology and the decreased labor costs. Whether using indirect composite, lithium disilicate, or zirconia, CAD/CAM systems produce esthetic posterior restorations.
It’s an exciting time in dentistry as technology continues to provide us with more and better options to offer our patients. Our challenge is to stay up-to-date with this technology and understand the indications and contraindications of each material so that we can consistently provide patients with the best that modern dentistry has to offer.
Reference: Christensen GJ, Indirect Restoration Use – A changing paradigm, JADA, 143(4), 398-400.
Gary Radz, DDS, maintains a private practice focusing on esthetic dentistry in downtown Denver. He serves as an associate clinical instructor at the University of Colorado School of Dental Medicine.
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