Tripartite talk

Presented by Kuraray Noritake Dental Inc.

Highly translucent multi-layered zirconia developed by a proprietary material and manufacturing method from Japan

CURRENT STATUS AND FUTURE PROSPECTS OF ZIRCONIA RESTORATIONS

In this issue, we asked Markus B. Blatz, Professor at the University of Pennsylvania, USA, Aki Yoshida (Gnathos Dental Studio) and Naoki Hayashi (Ultimate Styles Dental Laboratory), both dental technicians active in the USA and international instructors for Kuraray Noritake Dental Inc., to give their views on zirconia restorations and their outlook for the future.

WITH THE INTRODUCTION OF ZIRCONIA, THE MAINSTREAM OF PROSTHETIC TREATMENT HAS SHIFTED FROM METAL CERAMICS¹ TO ZIRCONIA CERAMICS². WHAT CHANGES HAVE OCCURRED WITH THE INTRODUCTION OF ZIRCONIA?

Blatz: My mentor for my first Ph.D. in dental materials was in the group that developed lithium disilicate and glass-infiltrated alumina. Therefore, I have seen the evolution of dental ceramic materials, including zirconia, which is the subject of this presentation, up close and personal.

Early zirconia was white, opaque, and not as esthetic as today. However, there is no doubt that zirconia ceramics were much more esthetic than metal ceramics. At the same time, however, we often heard the opinion that bilayer zirconia ceramic restorations were problematic, and this provoked much discussion. We conducted a large study in collaboration with a Boston laboratory to compare more than 1,000 posterior porcelain-fused-to-metal crowns and 1,100 posterior porcelain-fused-to-zirconia crowns and found no difference in chipping or fracture rates after about seven years. This proves that bilayer zirconia ceramics are safe when used with the proper veneering materials and the proper sintering and cooling protocols. The fact that zirconia became established as it is today is a major change for dentistry in general.

Yoshida: I also switched from metal ceramics to zirconia ceramics, and now I don't use metal anymore. It used to take a lot of time and effort to invest and cast metal, observe it with a microscope, and fit it. Considering the recent rise in metal prices, it has also become more cost-effective. In addition, I am allergic to metal and have a skin rash every time I have a prosthetic processed, so the shift to zirconia ceramics as the mainstream prosthetic is a welcome change. Of course, the use of zirconia has also improved esthetics. The translucency of zirconia is the greatest advantage that metal does not have.

Hayashi: Yes, that's right. The big advantage of zirconia is that if the abutment is not strongly discolored, it no longer needs to be treated with an opaquer. It was not easy to control the reflection of light from the operative tooth when fabricating metal ceramics. In addition to the esthetic advantage, the prosthetic space can be thinner than that of metal ceramics.

1. Metal ceramics: Prosthetic made of metal frame with porcelain.
2. Zirconia ceramics: Prosthetic made of zirconia frame with porcelain.

THE YEAR 2023 MARKED THE 10^TH ANNIVERSARY OF THE FIRST MULTI-LAYERED ZIRCONIA – KATANA™ ZIRCONIA ML. SINCE THEN, HOW DO YOU THINK HIGHLY TRANSLUCENT MULTI-LAYERED ZIRCONIA HAS REVOLUTIONIZED PROSTHETIC DEVICE MANUFACTURING?

Yoshida: I feel the ability to extend the zirconia frame to the occlusal surface and the incisal edge is the greatest advantage of using highly translucent multilayered zirconia. This allows us to provide crowns of both esthetics and strength, even for patients with para function. I have also made a zirconia Maryland bridge using highly translucent multi-layered zirconia, and it is doing very well. There are some cases where it is not possible to use zirconia, but still, it is wonderful to have a wider range of options.

Blatz: Many people still have the impression that zirconia cannot be bonded to tooth structure, but resin cement can be used to bond zirconia to tooth structure after proper pretreatment. Clinical studies of resin-bonded zirconia bridges have shown very high success after 10 or 15 years. Currently, resin bonding is recommended for very thin, highly translucent zirconia, rather than cementation. However, it should be added that this requires the dentist and technician to understand the proper bonding technique for zirconia.

In addition, Kuraray Noritake Dental's multi-layered zirconia has revolutionized monolithic zirconia without the need for veneering porcelain. However, this has also resulted in the need for dental technicians to shift to a different approach: instead of building up the restoration as with veneering ceramics, esthetic features are created on the outer surface in each case.

Maxillary 6 anterior monolithic crowns (Markus B. Blatz)

Fig. 1a and b: Initial examination.

Fig. 1c: Simulation of final prosthetic restoration.

Fig. 1d: Completed prosthetic on model (monolithic crown using KATANA™ Zirconia STML).

Fig. 1e and f: Final restoration (Dr. Julian Conejo and Sean Han, CDT).

Two cases of Maryland bridge and laminate veneers and a mandibular canine single crown implant superstructure (Aki Yoshida)

Fig. 2a and b: Case 1: A case of a congenital defect of a lateral incisor was restored with a Maryland bridge. Since the proximal and distal width of the defect was greater than the central incisor, a non-prep veneer was fabricated on the central incisor to balance the proportions. KATANA™ Zirconia STML was used for the Maryland bridge. Note the harmony between the zirconia frame extended to the incisal edge and the transparency of the laminate veneers made of Super Porcelain EX-3™ on the central incisors. This case demonstrates the characteristics of zirconia, which combines strength and esthetics.

Fig. 3a to c: Case 2: A case of a screw-retained crown restoration of an implant placed in a mandibular canine tooth. Extension of the zirconia frame from the entire lingual side to the incisal margin prevents fracture of the porcelain by the screw access hole edges and canine guides. KATANA™ Zirconia STML provides natural transparency even when zirconia is exposed at the incisal edge.

Maxillary 4 Anterior teeth implant bridge (Naoki Hayashi)

Fig. 4a to f: Implant bridge of maxillary four anterior teeth using implants placed in the maxillary bilaterallateral incisors as abutments and maxillary bilateral central incisorsaspontics. The lingual side is fully backed with zirconia and the labial side is minimally layered with CERABIEN™ ZR.

Hayashi: Indeed, the highly translucent multilayered zirconia has expanded the possibilities of monolithic crowns. For patients with high occlusal forces, monolithic crowns are suitable in terms of strength, and with the use of highly translucent multilayered zirconia, it is possible to achieve a certain level of esthetics with monolithic crowns. In fact, some patients are happy with it. However, at least in the current situation, we believe that if patients and dentists want high-end esthetics, then porcelain buildup is necessary, and monolithic crowns are only an option.

Blatz: The variety of options available is the advantage of zirconia. The dentist and the technician can work together to provide the best possible outcome for the patient.

Yoshida: In terms of options, Kuraray Noritake Dental's zirconia can be sintered in a short time (approximately 90 minutes) in addition to the normal sintering time (7 hours) using a zirconia raw material and manufacturing method developed by Kuraray Noritake Dental, which is an advantage in that it can be used for immediate restorations, remanufacturing and other unexpected situations.

FINALLY, DO YOU HAVE A MESSAGE FOR THE NEW GENERATION OF DENTISTS AND DENTAL TECHNICIANS?

Blatz: I encourage my students and colleagues to always do their best. This leads to good results, makes you happy, and makes you feel satisfied with your life. Some people only try to get rich, but just accumulating wealth is never happiness. The second is to keep an open mind. Nowadays, we are inundated with information through social media.

Some of it is very stimulating and wonderful, but there is also a lot of it that is wrong. On the other hand, there are those who believe that everything one leader says must be done. I would like to tell them, "Make sure you get your information from reliable sources, and then choose reliable information for yourself. Dentistry is changing, so let's keep an open mind. The most important thing is that the patient is ultimately satisfied with the results.

Hayashi: I would like the future generation to learn more about tooth morphology, occlusion, and fit. Color is the essence of the quality of the final prosthetic device, but we need to learn tooth morphology, occlusion, and fit before we learn color. We are all about creating a prosthetic device that will function in the patient's mouth for the long term, and that is our goal. There will be new technologies and materials in the future, but their essence will never change. I hope that you will always remember what is important in your clinical practice. This is why basic knowledge of anatomy and function is necessary.

Yoshida: New technologies and materials will continue to emerge. But human teeth will not change. The most important thing is to provide the best possible care to the patient. I hope that you will accumulate such experiences, and that when you reach the end of your life, you will be able to say that you are glad you chose this profession.

Thank you very much for the meaningful discussion today.

Source: QDT Vol.49/2024 April
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Dentists:

Prof. Dr. Markus B. Blatz University of Pennsylvania School of Dental Medicine 240 S 40th St, Philadelphia, PA 19104, USA	Aki Yoshida, RDT Gnathos Dental Studio 56 Colpitts Rd, Weston, MA 02493, USA	Naoki Hayashi, RDT Ultimate Styles Dental Laboratory 23 Mauchly Suite 111, Irvine, CA 92618, USA

• 2024-08-08

KATANA Zirconia UTML View Product

KATANA Zirconia STML View Product

CERABIEN ZR View Product

Super Porcelain EX-3 View Product

KATANA Zirconia YML View Product

KATANA Zirconia HTML PLUS View Product