By PhD. M. Inokoshi.

INTRODUCTION

Kuraray Noritake Dental Inc. is a manufacturer with a long history and wealth of experience in the field of producing dental materials, including bonds, cements and ceramics. The all-ceramic restorations market, including that for zirconia products, has been growing rapidly around the world since the beginning of the 2000’s. In response to this trend, we have established an integrated production system that can be used to manufacture a wide range of dental zirconia products in-house, from powder to discs.

When we develop new zirconia products, we carefully analyze the characteristics of dental zirconia that are actually demanded by users in the clinical setting and, based on the results of our analysis, we craft new products with these clinically needed characteristics. In our first efforts we focused on developing a dental zirconia that would have a natural tooth color after sintering. We launched “KATANA™ Zirconia”, our first dental zirconia product to span all the VITA^* Classical A1-D4 shade Guide, in 2007. Following in 2013, using our original manufacturing method, we developed and launched “KATANA™ Zirconia” ML (Multi-Layered), a multi-layered zirconia product that produces smooth color gradations like those of natural teeth, avoiding sharp color transition between layers. Then, in 2015, we also released “KATANA™ Zirconia” UTML (Ultra Translucent Multi-Layered) and STML (Super Translucent Multi- Layered). These are highly translucent, multi-layered zirconia products that became other versions of our multi-layered zirconia family. We are one of the pioneering manufacturers of dental zirconia, and as such, we promise ourselves that we will keep on delivering excellent highly-esthetic dental zirconia products to the dental market now and into the future.

^*VITA is a trademark of VITA Zahnfabrik, Bad Sackingen, Germany.

Recent advancements in dental technology have made it possible to use zirconia as a prosthetic material across a wide variety of dental applications, from large-sized implants where great mechanical strength is required, to treatment in the anterior region, where esthetics are of the utmost importance. The material characteristics needed, however, differ from one treated case to another. Many dental zirconia suppliers respond to these therapeutic requirements by offering various types of dental zirconia that feature different levels of mechanical and esthetic properties. This requires dentists and dental technologists in clinical settings to select, from a wide range, the type of zirconia that will be more better appropriate to treat the case they are facing at any given moment. This means it is necessary for each clinic to keep in stock many types of dental zirconia materials with different characteristics, in order to meet the requirements of the wide variety of possible case parameters.

Several dental material manufacturers have responded to these circumstances by offering dental zirconia disc products that have combinations of multiple layers with different levels of translucency and mechanical strength. They claim these products make materials available that can be used to fabricate a wide range of restorations. These products, however, can have serious shortcomings. Some require laborious manufacturing work, tailored to the fabrication of the particular restoration. Others do not include the required high-strength zirconia layer that makes it possible to fabricate a bridge. These products, therefore, may provide no assurance of providing the mechanical strength recommended by ISO for the manufacture of certain restorations. A market need arose for dental zirconia products that could be used easily and safely for the fabrication of a wide range of restorations.

In response to this need, at Kuraray Noritake Dental Inc., we have developed and released “KATANA™ Zirconia” YML(YML), a new type of dental zirconia material that provides the blend of excellent performance variables provided by the “KATANA™ Zirconia” Multi-Layered series. With its well-balanced performance, the YML can be indicated for the fabrication of a wide range of restorations, from large sized ones requiring great mechanical strength to anterior crowns that require a high level of translucency In this paper, we would like to describe YML’s features and the technology behind it. We will also present comparative data collected by Masanao Inokoshi, a professor in the Department of Gerodontology and Oral Rehabilitation at Tokyo Medical and Dental University, Graduate School of Medical and Dental Sciences, on YML and a similar product from the competition.

FEATURES OF THIS PRODUCT AND THE TECHNOLOGY BEHIND IT

Short sintering time

YML can be baked satisfactorily in a short period of time, thanks to our innovative technology. In addition to the conventional sintering schedule of about 7 hours, and even the 90-minute schedule, we have also made it possible to shorten the sintering time further, to a remarkable 54 minutes^*.

^*The material is removed from the furnace at 800°C / 1472°F. Up to 3-unit bridges.

Excellent translucency and great mechanical strength

A YML disc consists of four layers: one Enamel and three Body layers. The top Enamel layer (35% of the total thickness: 750 MPa^*1) is composed of the same zirconia material as “KATANA™ Zirconia” STML, which is highly acclaimed for its excellent translucency. The three Body layers ((1): 1,000 MPa^*1, (2): 1,100 MPa^*1 and (3): 1,100 MPa^*1) that lie below the Enamel layer are made from a new type of zirconia material. Body layer (1) is an intermediate layer that has the desirable translucence of STML. It includes, however, a well-balanced combination of translucency and mechanical strength suitable for the treatment of cases, such as those requiring bridges, which demand these notable characteristics. Body layers (2) and (3) provide the high level of mechanical strength of “KATANA™ Zirconia” HTML suitable for the fabrication of large-sized restorations, along with an improved level of translucency. With its well-balanced combination of translucency and mechanical properties, provided by taking advantage of multiple zirconia ceramics, YML is a product that meets the demand for highly esthetic products. It is suitable for the fabrication of the whole range of restorations, from single crowns to bridges.

^*1 : According to ISO 6872: 2015, three-point bending test.

Multi-layer gradation

Kuraray Noritake Dental Inc. released our first multi-layered zirconia product in 2013. Subsequently, the company launched zirconia products very much appreciated for their smooth transition of color gradation, much like that of natural teeth. We use our own innovative pressing method to manufacture YML. It smooths the change of colors between layers, which provides the desirable feature of a very smooth and natural color transition.

Reduced deformation after sintering

In general, dental zirconia shrinks during the sintering process by about 20 percent in 2 dimensions (50 percent in volume). If shrinkage cannot be controlled adequately, it becomes difficult to fabricate restorations that fit precisely into complicated abutments or margin lines. The shrinkage of zirconia materials varies subtly from one production lot to another, even when the same raw material is used. We appropriate raw material control such as raw material crushing etc., using different sintering shrinkage rates for different production lots. In view of the fact that the sintering shrinkage of zirconia materials requires delicate control, it is not hard to understand that shrinkage control is even more difficult when different zirconia materials are combined into one disc. If the shrinkage rates of the layers of a zirconia disc differ, the restoration will necessarily be deformed during shrinkage. Many users voiced particular concerns about dimensional stability when they were asked about using zirconia discs (which require high precision) for the fabrication of implants. Kuraray Noritake Dental Inc. has an integrated production system that is used to manufacture zirconia products in-house, from the design and manufacture of zirconia powder as a raw material to final products, thus making it possible for us to control the shrinkage rate of zirconia with great accuracy. For this reason, we are able to use zirconia materials with stably controlled shrinkage rates to manufacture YML, even though it consists of multilayers made up of different zirconia materials. This minimizes deformation of restorations after shrinkage.

RESULTS OF A VERIFICATION OF THE PHYSICAL PROPERTIES OF YML AND A REVIEW OF ITS CLINICAL ADVANTAGES

To verify the physical properties of YML, the translucence, mechanical strength and crystalline structure of YML and ZirCAD Prime (Ivoclar Vivadent) were analyzed and compared with one another at the Tokyo Medical and Dental University. Among the physical properties examined, this paper focuses especially on data on the translucency and mechanical strength of each product.

Data on translucency:

Different alphabets indicate a definite difference between groups.

Data Courtesy of PhD. Masanao Inokoshi, Tokyo Medical and Dental University.

The translucency of ZirCAD Prime was significantly higher than that of YML, when a comparison was made at the Enamel layer. This is probably because Prime contains almost no pigment in the Enamel layer, in order to bring out the brightness (whiteness) of the zirconia itself. By contrast, YML contains some pigment, so the product can deliver an optimal level of brightness in the clinical setting. That is, it seems that the addition of pigments leads to a difference in translucency between YML and Prime.

Data collected at Kuraray Noritake Dental on the relative translucency of YML and Prime

Total light transmittance (%) (Illuminant: D65; test specimens with a diameter of 30 mm, and a thickness of 1 mm) Raw material in YML’s Enamel layer (no coloring agent): 49% Prime’s Enamel layer: 49%.

Regarding the layers lying beneath the Enamel, such as the Transition and Body layers, YML was found to be more translucent than Prime. It can be concluded that YML is sufficiently translucent even beneath the layers lying beyond the Enamel layer. This makes it possible to fabricate prostheses with natural tooth colors, when used in combination with an Enamel layer that is suitably adjusted to provide the optimum color.

Mechanical strength data as results of four-point bending test:

Different alphabets indicate a definite difference between groups.

Data Courtesy of PhD. Masanao Inokoshi, Tokyo Medical and Dental University.

The Enamel layer of YML had a significantly greater bending strength than that of Prime. On the other hand, when the bending strength of the Body layers was compared, Prime’s Body layer was the strongest. The three YML Body layers ((1), (2) and (3)) had bending strength values of more than 850 MPa^*2, and there were no significant differences in bending strength among Prime’s Body layer and YML’s Body layers ((1), (2) and (3)).

The results revealed that while YML has small differences in bending strength among the Enamel layer and the three Body layers, Prime has clearly different levels of bending strength between the Body layer and the other two layers. YML’s Body layers (including the intermediate layer) have such a high level of mechanical strength that it is quite feasible to use it to fabricate highly reliable prostheses.

^*2 : According to ISO 6872: 2015, four-point bending test.

LAYERED DESIGN CONCEPT

The guide for fabricating large restorations using YML states the requirement that at least 50% of the connector cross-section should be positioned in the bottom (lower part) of the disc. This means that generally you can meet the requirement of the guide by positioning the restoration at the center of the disc’s four layers. Guides or advices of restoration fabrication for using zirconia discs available in the market may sometimes be complicated to position the restoration as specified in the guide or to position the piece as specified by the guide, which makes it difficult to fabricate a highly esthetic restoration that makes use of the Enamel layer’s better translucency.

When we developed YML, Kuraray Noritake Dental kept in mind that the fabrication guide must be practical, as well as easy. That’s why YML was designed with a sufficiently thick Enamel layer that permits a high level of esthetics for any type of restoration that might be fabricated.

CONCLUSION

“KATANA™ Zirconia” YML is our new zirconia disc product, which features a well-balanced combination of mechanical strength and esthetics. It has been developed by using our innovative zirconia manufacturing technology, as well as bringing together the essence of the development and production technology of multi-layered zirconia discs. We hope YML will be one of the options of choice for zirconia materials available to dentists and dental technologists who need to use multiple zirconia materials for various applications or who have concerns about the mechanical strength and esthetic properties of the zirconia materials they are currently using.

YML LINEUP

Case by Keisuke Ihara, RDT, Yohei Sato, DMD, PhD and Tsurumi University School of Dental Medicine.

MINIMAL CUT-BACK DESIGN

Accommodate esthetics and function, achieves natural color and surface texture due to thin porcelain layer.

Step 1.  Teeth preparation.

Step 2.  Inner crowns were placed on the abutments.

Step 3.  Zirconia Frame (KATANA Zirconia HTML A1) cut-back designed for incisal frame.

Step 4.  Application of Cerabien™ ZR (CZR) for making base color and firing.

Step 5.  Application of Internal Stain and firing.

Step 6.  The final restoration and inner crown parts.

Step 7.  Post-operative view.

How did experts think about the effectiveness of MDP through the years? You can read about it below.

“In particular, primers and composite cements that contain 10-methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) resulted in a relatively high bond strength and durability.”

N. Nagaoka et al: “Chemical interaction mechanism of 10-MDP with zirconia” Nature, Sci Rep. 2017; 7: 45563.

“For most zirconia-bonding techniques, the use of an “MDP-containing primer” also appeared to have a positive effect.”

B. van Meerbeek et al: “Meta-analyis of Bonding Effectiveness to Zirconia Ceramics” J. Dent. Res. 93(4), 2014, 329-334.

“Based on the direct interaction of the phosphate-ester group of MDP with the metal oxides at the zirconia surface, a relatively favourable bonding effectiveness was recorded.”

B. van Meerbeek et al: “Durable bonding to mechanically and/or chemically pre-treated dental zirconia”, J. Dent. 41 (2013) 170-179.

“Clinical data provide strong evidence that air-abrasion at a moderate pressure in combination with using phosphate monomer containing primers and/or luting resins provide long-term durable bonding to glass-infiltrated alumina and zirconia ceramic under the humid and stressful oral conditions.”

M. Kern: “Bonding to oxide ceramics-laboratory testing versus clinical outcome”, Dent. Mater. Vol. 31 (1), 2016, 8–14.

“A high and reliable resin bond to alumina and zirconia ceramics was also achieved with airborne particle abrasion and by using a phosphate monomer (MDP) containing resin composite luting cement.”

M. Özcan et al: “Effect of surface conditioning methods on the bond strength of luting cements to ceramics”, Dent. Mat. 19, 2003, 725-732.

“In the present study, the use of the MDP-containing bonding/silane agent resulted in significantly higher bond strengths before and after long-term storage and thermal cycling with two types of resin luting agents.”

M.B. Blatz et al: “In vitro evaluation of shear bond strengths of resin to densely-sintered highpurity zirconium-oxide ceramic after long-term storage and thermal cycling”, J. Prosth. Dent. 91, 2004, 356-362.

“Dental zirconia can no longer be considered unbondable to tooth tissue (…) This also indicates that Al2O3 sandblasting is best followed by a chemical pre-treatment with an MDP containing primer.”

M. Inokoshi et al: “Meta-analysis of Bonding Effectiveness to Zirconia Ceramics”, J. Dent. Res. 93(4): 329-334, 2014.

“Airborne-particle abrasion of zirconia surface is one of the most-investigated methods, provides good bond strength to zirconia when combined with phosphate ester monomer.”

M. Ferrari et al: “Effect of surface pre-treatments on the zirconia ceramic–resin cement microtensile bond strength”, Dent. Mat. 27, 2011, 1024-1030.

“The data of the present work confirm the assumption of another study [13], that MDP bonds chemically to zirconia ceramic.”

C.H.F. Hämmerle et al: “Effect of thermocycling on bond strength of luting cements to zirconia ceramic”, Dent. Mat. 22, 2006, 195-200.

“An acidic adhesive monomer such as MDP shows chemical bonding to zirconia-based ceramics. The phosphate ester group of the acidic monomer results in chemical bonding to metal oxides (MxOy, oxidized surface of base-metal alloys), zirconia-based ceramics and other ceramics.”

J.M. Powers et al: “Guide to Zirconia Bonding Essentials”, New York, NY: Kuraray America Inc, 2009, 1-13.

Multiple porcelain layering with Internal Stain technique

In 2015, Kuraray Noritake Dental Inc. launched the new KATANA Zirconia UTML and STML. With this outstanding multi-layered zirconia you can reach high level of esthetic in less steps than usual working steps of layering porcelain technique. Just mill and sinter. Due to great properties of this new material, you will get a high esthetic and natural like result. On the other hand, there are many works existing in clinical situation that only professional handmade can achieve the highest esthetic level. Multiple porcelain layering and Internal Stain technique have bigger possibility sometime to show beyond natural.

Fig. 1. Pre-operative photo.

Fig. 2. After preparation.

Fig. 3. Checking the fit of Zirconia Frameworks on model.

Fig. 4. After 1st baking of OB as washbake.

Fig. 5. After wash-baking, using with Internal Stain A+ on the margin area to make a natural cervical color from Zirconia.

Fig. 6. Applying Opacious Body (OBA1) considering with mamelon structure. And apply Body A2B to make high chrome area on cervical area.

Fig. 7. After baking Opacious Body (OBA1).

Fig. 8. After applying Body porcelain (A2B), using wit Cut-Back method to make a space for applying Enamel & Luster porcelains.

Fig. 9. Applying Enamel porcelain (E2) and Luster Porcelain (T Blue) for explaining translucent gradation on the edge of mamelon.

Fig. 10. Applying E2 for making White-band and LT1 for making incisal edge. Considering of porcelain shrinkage after baking, apply 13% bigger than final shape.

Fig. 11. After baking.

Fig. 12. Internal Stain application Applying A+ for cervical color and White for make white spots on incisal area.

Fig. 13. Applying E2 on Cervical area and LT1 for covering surface. And using with E2 on the edge of incisal to make Hallow Effect.

Fig. 14. After baking and morphological correction. Then self-glazing.

Fig. 15. End result.

Fig. 16. Post-operative photo.

Courtesy: Kanare Technical Center in Japan

Case by Sung Bin Im, MDC, CDT and Sergio R Arias, DDS, MS

MINIMAL CUT-BACK DESIGN

KATANA multi-layered zirconia allows me to achieve great esthetic and functional outcomes on high risk patients.

Step 1. Titanium Abutments (#7, 9) were placed on the solid model.

Step 2. Zirconia Frame (KATANA Zirconia HT10) cut-back designed to minic anatomical dentin structure and incisal frame.

 
Step 3. Application and firing of Cerabien™ ZR (CZR) to achieve target shade and incisal effect.

Step 4. Completion of Internal Stain firing.

Step 5. Completion of Luster and Clear Cervical layering.

Step 6. Surface detail check.

Step 7. Post-operative view.

Virtual Kick-Off KATANA Zirconia Symposium

Lecture 1 of 3, Prof. Dr. Beuer
Watch how Prof. Dr. Beuer explains his experience with the new material. Two in one: Combining High Strength and High Translucent Zirconia.

Lecture 2 of 3, MDT Rondoni + MDT Rossi
Watch the recording of the KATANA Zirconia YML Online Symposium on July 3rd 2021, the second lecture plus hand-on which details the experience of MDT Rondoni and MDT Rossi with this new material.

Lecture 3 of 3 + Q&A, MDT Nondas Vlachopoulos
Mister Vlachopoulos deepdives in to a full procedure executed with the new material and demonstrates how liquid ceramics compliment the material establishing a very high-end aesthetic result.

Virtual Kick-Off KATANA Zirconia Symposium

Lecture 1 of 3, Prof. Dr. Beuer
Watch how Prof. Dr. Beuer explains his experience with the new material. Two in one: Combining High Strength and High Translucent Zirconia.

Lecture 2 of 3, MDT Rondoni + MDT Rossi
Watch the recording of the KATANA Zirconia YML Online Symposium on July 3rd 2021, the second lecture plus hand-on which details the experience of MDT Rondoni and MDT Rossi with this new material.

Lecture 3 of 3 + Q&A, MDT Nondas Vlachopoulos
Mister Vlachopoulos deepdives in to a full procedure executed with the new material and demonstrates how liquid ceramics compliment the material establishing a very high-end aesthetic result.

Case by Dr. Shoji Kato of Takanawa Dental Office, Japan

1. After preparing the abutments

An anterior bridge made of crown and bridge resin has become dislodged. The abutments are vital teeth.

2. Prosthesis

A PFZ bridge with a frame fabricated using KATANA™ Zirconia HT12.

3. Application of Try-in Paste

Evaluate the shade of the cement before cementation.

4. Try-in

After checking the cement’s shade, rinse the prosthesis and tooth surface with water to remove Try-in Paste.

5. Pretreatment of the prosthesis (A)

Sandblast the prosthesis (at 0.3 to 0.4 MPa), clean with an ultrasonic cleaner for 2 minutes, then dry.

6. Pretreatment of the prosthesis (B)

Apply CLEARFIL™ CERAMIC PRIMER PLUS and blow dry with air.

7. Pretreatment of the abutments (C)

Apply Tooth Primer, allow it to react for 20 seconds, then blow dry with air.

8. Application of Paste

Use Universal.

9. Placement of the prosthesis

After placement, remove excess cement using a piece of gauze, a small brush, etc.

10. Light-curing

Light-cure the entire surface of the prosthesis, including the margins.

11. Final polymerization

Make sure the prosthesis is left in place, unmoved, for 3 minutes.

The KATANA™ Zirconia family of multi-layered CAD/CAM blanks has a new member: KATANA™ Zirconia YML (yttria multi-layered). Based on Kuraray Noritake Dental Inc. (KND) proprietary multi-layer technology, this new material offers multiple layers with different levels of chroma and translucency PLUS different concentrations of yttria in a single blank. We talked to two experts from Kuraray Noritake Dental’s Research & Development Department in Japan, Atsushi Matsumoto and Yuta Tajima, about the new product and its specific features.

Mr. Matsumoto, Mr. Tajima, KND already offers a broad range of zirconia materials covering virtually every indication. Why did you decide to start developing yet another dental zirconia?

The KATANA™ Zirconia series has indeed received high praise and great feedback from the market. Users particularly appreciate the remarkably high strength of HTML, the well-balanced aesthetic and strength properties of STML, and also the high translucency of UTML. Although there has been a large increase of zirconia materials in the dental market recently, we have received many requests from our customers for a more universal material that offers the excellent properties of all variants of KATANA™ Zirconia in one product. This product should allow them to fabricate all kinds of restorations from a single disc, from single crowns to full bridges, while maintaining high aesthetic and mechanical properties for both anterior and posterior restorations. As the developer of the KATANA™ Zirconia series, the invention of KATANA™ Zirconia YML is our response to these desires expressed by our customers.

What is the main difference between KATANA™ Zirconia YML and the other available products of the KATANA™ Zirconia Multi-Layered Series?

All layers of KATANA™ Zirconia UTML, STML and HTML are produced from the same basic powder composition and therefore offer the same strength throughout the whole blank. Depending on the case specific requirements, users need to select the most suitable type of material, either a high-strength zirconia or a highly translucent variant. KATANA™ Zirconia YML is an all-in-one zirconia suitable for all cases: It consists of a high-translucency enamel layer, an intermediate layer offering well-balanced strength, translucency and colour, and a high-strength body layer. The raw materials used for this product are developed and produced by KND exclusively for YML. This is another milestone in advanced product development KATANA™ Zirconia.

We have received many requests from our customers
for a more universal material.

In general, the currently available zirconia materials with an integrated strength gradient do not have a very positive image in the eyes of many dental technicians and specialists, due to the fact that in the incisal area, the materials seem to be insufficiently strengthened. This can lead to fractures when it comes to long-span restorations, especially if they are inadequately positioned within the blank. How carefully did KND focus on these problems and how did they try to solve them in order to stand out from the competition?

The current yttria-based multi-layer products on the market are facing complicated limitations in connector position in large cases, such as full-arch restorations, due to the lack of an ideal combination of aesthetics and strength. To overcome this challenge, KND developed well-balanced raw materials of high strength and high aesthetics, and by including these raw materials in the intermediate layer between the enamel and body layers. The result is that even for long-span restorations, it is very simple to position the connectors thanks to its excellent balance between high strength and high aesthetic properties. Due to these unique attributes incorporated in our new product, the risk of deformation and breakage is avoided.

Another problem is the often clearly visible line between the different layers containing different amounts of yttrium oxide, which can be seen at a more detailed inspection after sintering. How did you address this issue?

At KND, we achieved both, adequate translucency gradation and invisible transition lines, even for zirconia layers with different yttria content. This has been accomplished thanks to our multi-layer zirconia manufacturing technology refined over many years, which includes mixing the appropriate amount of each layer's boundary to intentionally avoid transition lines. In addition, the newly developed interlayer raw materials and a newly designed sintering schedule were the keys to success.

How is it possible to have a sintering protocol that works for different zirconia components within the KATANA™ Zirconia YML blank and allows for the shortest sintering times ever?

The amount of shrinkage during sintering is determined by different factors such as the number and quantity of additives (yttria, alumina etc.) it contains. If the shrinkage ratio of each layer is different, transition lines are likely to appear between the layers, which might produce tensions in the material structure. The newly developed raw material for KATANA™ Zirconia YML enables us to control and unify the shrinkage ratio for all layers, even for raw materials with different yttria contents.

The use of proprietary raw materials produced in-house with excellent properties suitable for high-speed sintering was the main precondition that allowed for the development KND’s high-speed sintering schedule (54 min for restorations up to 3-unit bridges), which is available for all products of the KATANA™ Zirconia multi-layered series. This option improves the efficiency of the dental technician’s work and simplifies the workflow.

Are there any differences in milling and adjusting KATANA™ Zirconia YML compared to competitor products?

All KATANA™ Zirconia products from KND have an appropriate hardness with less chipping during the milling process thanks to the raw materials manufactured and refined in-house. Also, after the sintering procedure, it offers excellent chipping resistance, especially during very challenging marginal adjustments.

Is there anything else that sets KATANA™ Zirconia YML apart from other products with an integrated strength gradient?

Yes, KATANA™ Zirconia YML offers reduced sintering deformation, thanks to in-house developed raw materials, based on proprietary technology to control shrinkage rate. Moreover, we offer a wide range of shades (14), which is another important aspect (apart from the material’s well-balanced aesthetic properties and absence of transition lines) for the creation of lifelike restorations. Finally, since three out of four layers meet the conditions for an ISO class 5 classification, there are few restrictions on the design variation of the prosthesis.

Why should a dental technician consider using KATANA™ Zirconia YML instead of any other dental zirconia (in your opinion)?

Atsushi Matsumoto:

It is now possible for dental technicians to produce strong and aesthetic restorations with just one material, KATANA™ Zirconia YML. This allows for a reduced inventory, while working time is significantly shortened due to the possibility of high-speed sintering.

Yuta Tajima:

To my mind, the most convincing properties are excellent firing accuracy due to well-balanced material properties across all layers, the wide range of shades available and the great design flexibility even when designing long-span bridges. Last but not least, the trusted quality of the KATANA™ brand and the label “Made in Japan” are reasons to opt for this new product.

All blanks from the KATANA™ Zirconia Series stand out from other dental zirconia materials due to their particularly fine-grained, densely pressed microstructure, which is the basis for a superior surface quality, edge stability and the resulting accuracy of fit. What is the secret behind this exceptionally high blank quality?

Since we do not know the correlation between marginal stability properties (chipping, etc.) and material compositions, structures etc., it is very difficult to answer this question. It may depend on the structures of the zirconia crystals, the raw material itself, the correct strength level after pre-sintering or any other minor factor during the manufacturing process of the disc. All these factors together, of course, are important.

We are using pigments developed by KND, which have an excellent colour stability without fading even after the final sintering procedure.

Even if the restoration margins have been milled to a very thin profile, they still show smooth margins without any chipping.

A clear advantage of the KATANA™ Zirconia series, much praised by KND's Key Opinion Leaders, is its colour stability and shade match to the "VITA classical shade guide". Can you explain the importance of an in-house conducted addition of additives and color pigments in form of metal oxides to satisfy the user and distinguish KATANA™ Zirconia from competitors’ products?

We are using pigments developed by KND, which have an excellent colour stability without fading even after the final sintering procedure. The particle size is appropriately controlled. In addition, our professional "colour mixing" staff, reflecting the opinions of clinically experienced dental technicians both inside and outside the company, have achieved a pigment mixture that shows only a slight change in shade even in cases with different thicknesses.

What is your vision with regard to future developments in dental zirconia?

Since the introduction of zirconia on the dental market, many significant material advances have been achieved. Today, there are high-strength, low light-transmitting zirconia materials up to high light- transmitting, low strength zirconia materials available on the market. Furthermore, there are now also high light-transmitting, low strength zirconia materials in mixed systems (YML series) offered. Our foremost goal is to develop the ultimate zirconia in near future, combining both high strength and high light transmission, which breaks the general expectation of a compromise between strength and translucency within zirconia materials.

By Univ.-Prof. Dr. Florian Beuer MME

There is still some confusion among dental practitioners about how to cement zirconia restorations. In general, all types of cements – adhesive or self-adhesive resin cements and conventional cements – are compatible with all types of zirconia. The actual choice should be based on the restoration design (retentive or non-retentive), the translucency of the zirconia and the clinical situation (feasibility of working field isolation).

When to use which type of cement

The use of adhesive resin cements is mandatory whenever the highest possible bond strength is required. This is the case with one-wing Maryland bridges and other types of restorations lacking micromechanical retention, and with two-piece implant abutments.

In some other situations where retention is not an issue, adhesive or self-adhesive resin cements may have a beneficial effect. The major reason is their more esthetic appearance compared to conventional cements, which offers advantages whenever a highly translucent restorative material is used (e.g. KATANA Zirconia UTML). An important precondition for adhesive luting, however, is a dry working field. Consequently, conventional cements are preferable in the context of placing crowns, bridges and other types of restorations with retentive designs whenever opaque zirconia framework materials are used and / or it is difficult to ensure a dry working field.

How to pre-treat the tooth and the restoration

The highest bond strength of adhesive resin cements to zirconia is obtained after sandblasting with alumina (particle size max. 50 µm, pressure approx. 1 bar). Hence, this procedure is highly recommended. Subsequent steps may be different depending on the cement system employed and should be carried out according to the manufacturer’s instructions for use. On the side of the tooth, enamel etching is important independent of the products used.

Which products to use

In each of the cement classes, there are many different products to choose from. My recommendation is to select a proven and easy-to-use luting material. Among those products achieving the same high bond strength, the solution requiring the fewest application steps seems preferable as it reduces the risk of application errors. At Charité – University Medicine Berlin, we count on PANAVIA cements, which are based on many years of expertise in developing products for adhesive luting of zirconia.

Dentist:

PROF. DR. FLORIAN BEUER

Professor and Chair, Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Charité – Universitätsmedizin Berlin, Germany.