Television programs such as "The Swan" and "Extreme Makeover" have brought cosmetic dentistry into the homes of millions of Americans, so it is no surprise that dental patients are becoming more concerned with the aesthetics of their dental work. In line with this trend, metal-free alternatives such as Zirconia (ZrO2) ceramic substrates are gaining in popularity for crown and bridgework. They offer superior aesthetics, as well as strength that is comparable, if not better than, traditional porcelain-fused-to-metal, or PFM, restorations. Preparation techniques for many all-ceramic systems are similar to traditional PFM crown and bridge techniques, so they are easy to incorporate into practice. Thus, clinicians are realizing benefits in both patient satisfaction and referrals.
The differences in appearance between traditional PFM restorations and all-ceramic crown and bridge systems are pronounced. Most people can recognize a PFM crown by the substructure that is often visible in the patient's mouth, appearing as a thin, gray line at the margin of the crown. All-ceramic crowns offer excellent marginal fit and eliminate gray margins.
In addition, PFM crowns do not transmit light through the crown, resulting in a somewhat dull tooth appearance. Zirconia ceramic substrates, on the other hand, allow for light transmission, so the entire tooth and the surrounding tissue are illuminated and lifelike in appearance. For example, Lava(tm) crowns and bridges, an all-ceramic system from 3M ESPE that uses computer-aided design/computer-aided manufacturing, or CAD/CAM, technology, offers colorable frameworks in eight different shades for natural color matching.
Tissue sensitivity can be a common issue with PFM crowns and bridges. Base-metal crowns contain nickel, which can cause an allergic reaction in many people, especially women. Restorations that use non-precious metals can sometimes result in gum tissue that is purplish in appearance, and some patients experience irritation and/or gingival recession. Alternatively, zirconia is a biocompatible material and has been used with great success in other medical applications, for example, hip replacements, for the past 20 years. Similarly, zirconia results in excellent tissue response when used in the mouth - gum tissue appears healthy and is pink in color. Further, the tissue does not pull away from the material, which can occur with traditional PFM restorations.
Strength was a concern for earlier alternatives to PFM restorations. In the past, when most glass-containing, high-strength ceramics on the market were subjected to masticatory forces, normal oral moisture led to subcritical crack propagation. Strength problems are no longer an issue with current zirconia-based, all-ceramic crown and bridge systems. These new materials deliver strength and durability that rival many PFM restorations. The system we use features a high-strength ceramic core material that measures 1,272 Mpa. The benefit is that less tooth structure needs to be removed during clinical preparation. At 0.5 mm, the Lava system can mill a thin, yet strong substructure.
While some dentists may shy away from using zirconia-based prosthetics because of initial financial concerns, a look into average fees for the different types of restorations and typical insurance reimbursement structures shows that cost should not be a barrier to all-ceramic systems. Based on the ADA procedure codes, the national average fee for a crown using porcelain-fused-to-base metal is $856 (code #2751); the fee for a porcelain-fused-to-noble metal crown is $888 (code #2752); and the fee for a porcelain-fused-to-high noble metal is $973 (code #2750). At $1,018 (code #2740), the average fee for a crown with porcelain fused to a ceramic substrate is not significantly higher. When insurance reimbursement is based on a percentage of the reasonable and customary fee in an area as defined by its zip code, the porcelain fused to a ceramic substrate will result in a larger reimbursement.
Other financial benefits of using all-ceramic materials for crown and bridgework include their accurate fit. The CAD/CAM technology used in our lab ensures an accurate fit the first time, virtually eliminating the need for costly remakes. Patient satisfaction with both the procedure and resulting aesthetics can have a significant impact on repeat business and increased patient referrals.
In the past, advancements in tech-nology required an investment in hardware and equipment by the dental laboratory, which limited accessibility for the dentist. This is changing. For example, our laboratory has become an Authorized Lava Milling Center, one of eight milling centers located across the country. This business model allows access for any doctor or laboratory to a high-quality crown and bridge system without expensive equipment investment.
Patients are becoming increasingly more demanding about the appearance of their smiles. All-ceramic crowns and bridges offer the high-appeal, aesthetic results patients desire without compromising strength and durability. When comparing appearance, tissue response, strength, cost considerations, and patient satisfaction, zirconia-based all-ceramic crowns and bridges offer a clear advantage in most cases over traditional PFM restorations.
As industry advances have continued to put new technology at dentists' disposal, both new and experienced dentists face an ongoing challenge. All involved must be knowledgeable about current procedures while keeping an eye on future trends.
Dr. Mike Malone, a former president of the American Academy of Cosmetic Dentistry who practices in Lafayette, La., has seen a variety of changes in the field during his 25 years in practice. Dr. Malone sees a continued trend toward metal-free dentistry.
"With the more frequent use of CAD/CAM systems for creating metal-free crowns and bridges, you will see more people move in that direction," Dr. Malone notes. "It is an aesthetic issue. There are two reasons people move away from metal. They either don't like the way it looks or some people have metal allergies or suspect they might be allergic to it.
"We have systems right now that work well for doing metal-free dentistry, but most of those systems are harder to do than more traditional dentistry," says Dr. Malone, "They cost more, take longer, and the training is more difficult. We will see improvements in metal-free systems to make them easier and more cost-effective. That is what I hope to see ... but we are starting to see that already.
"We already have stronger metal-free restorations versus what was available five or 10 years ago. Many of the procedures we use today are technique-sensitive. If performed ideally, excellent results can be obtained. But with some of these procedures, there is not much margin for error."
In addition to the move toward metal-free dentistry, Malone said there will be some impact on orthodontics as more people use invisible aligners for straightening teeth.
As current systems evolve, dental schools are faced with the task of staying on course with scientific progress so students are prepared for the working world.
"We have done a lot of revisions to the curriculum," says Dr. John Burgess, the assistant dean for clinical research at the LSU Health Sciences Center School of Dentistry.
"We have incorporated CAD/CAM as a senior elective. We have used sectional matrices and curing lights. We have to be at the cutting edge of technology and have students prepared to integrate with high-tech offices when they graduate.
"We continuously evaluate new technology. We have to find new techniques and have a partnership with research and industry. That partnership is critical for schools to remain viable."
When curriculum adjustments are made, those who oversee students' growth must be flexible and ready for the change.