429 Too Many Requests

Superior bond strength and consistently predictable results from one universal cement – PANAVIA™ V5 is nothing less than astonishing. It’s suitable for all indications, irrespective of restoration type or materials to be bonded. Simply pre-treat the tooth with PANAVIA V5 Tooth Primer, then prime the restoration with CLEARFIL CERAMIC PRIMER PLUS and cement. That’s all there is to it.  

Check out this video demonstrating PANAVIA V5 cementation workflow of zirconia crowns.

What is the story behind the development of Clearfil Universal Bond Quick Flip-Top Cap?

With this video, we will walk you through the story behind its development.

Users of dental zirconia are really spoilt for choice these days. Countless manufacturers offer zirconia materials that differ in their mechanical and optical properties and indication range. What is not apparent at first sight is that the available products also differ with respect to the quality of the CAD/CAM blanks offered. Blank quality is highly dependent on the quality of the raw materials and is affected by different aspects during raw material processing, pressing and pre-sintering. This has a huge impact on the surface quality, edge stability, fit and processing requirements of milled restorations.

Raw material production

Pre-shaded dental zirconia typically consists of metal oxides, including zirconium oxide, yttrium oxide and aluminium oxide, as well as additives like binders and colour pigments or ions. Most manufacturers of dental zirconia obtain pre-fabricated powder from an external industry partner, the most popular option being Tosoh Corporation. In contrast, Kuraray Noritake Dental relies on an end-to-end in-house process. This includes the production and addition of the components forming the company’s innovative multilayer technology for a polychromatic blank structure and – in the case of "KATANA™ Zirconia" YML – additional translucency and flexural strength gradation.

At Kuraray Noritake Dental, the powder is produced in-house.

Since more powder production steps are carried out in-house, the company is given full control over the quality of the raw materials, their grain size and the purity of the formulation. It also allows for a precise alignment of the mechanical and optical product properties to achieve a smooth transition from one layer to the next. The result is a seamless colour structure and outstanding match of the shades in the polychromatic blanks to the colours of the VITA classical A1–D4 shade guide.

In those materials combining different yttria concentrations in a single blank, additional in-house alignment measures may be taken. In the case of "KATANA™ Zirconia" YML, a completely new raw material was developed to deliver a uniform shrinkage ratio and harmonized coefficients of thermal expansion across the blank und thus bring flexural strength gradation to perfection.

Properties of zirconia restorations that are affected by the powder quality and composition include translucency and shade appearance, flexural strength, ageing behaviour and sintering performance.

Blank pressing

Zirconia discs and blocks used for CAD/CAM processing are usually produced by uniaxial and isostatic pressing. In the uniaxial compaction process, pressure is applied to the powder from one direction (uniaxial) or two directions (biaxial), whereas the isostatic compaction process involves virtually equal pressure applied from all sides. Hence, isostatic pressing typically results in a more uniform density distribution throughout the blank and a higher material homogeneity. These factors are prerequisites for a predictable processing and sintering behaviour and affect the fit of the final restoration. For optimal mechanical and optical properties of the zirconia material, it is essential to avoid large porosities, air pockets and impurities caused by airborne particles that are trapped during pressing.

At Kuraray Noritake Dental, a unique and extremely meticulous pressing process achieves a uniform pressure distribution and low risk of contamination by airborne particles. This specific procedure reduces gravitation forces and contributes to having as high as possible density of zirconia material. All the high-level preparation processes from raw material production to pressing are responsible for the high edge stability and surface quality of restorations milled from "KATANA™ Zirconia".”

Pre-sintering

The pre-sintering procedure is necessary in that it gives the pressed blanks the required stability to be machinable with milling tools. The selected temperature profile and duration of the pre-sintering cycle determine the material’s strength and processing properties and have an impact on the final sintering process.

The unique pre-sintering procedure carried out in the production facilities of Kuraray Noritake Dental results in blanks that are stable in their pre-sintered state. Although more stable, pre-sintered "KATANA™ Zirconia" is machinable with common diamond-coated milling tools without any increased risk of breakage or higher tool wear.

Fast sintering for the laboratory

The unique procedure has a positive impact on the surface smoothness after milling and can significantly shorten sintering times. In the dental laboratory, the sintering times may be reduced to 54 minutes* for single-tooth restorations and bridges of up to three units – an interesting option for rush cases and remakes.

*The material is removed from the furnace at 800 °C.

“KATANA™ Zirconia” YML speed sintered (90-minute sintering schedule), whereas the discs of competitors were sintered using typical overnight sintering schedules suitable for the particular material. Even with 90-minute sintering, KATANA™ Zirconia YML displays superior optical properties when compared to major competitors.

Uniform sintering schedules are offered for the whole "KATANA™ Zirconia" Multi-Layered Series.

Overview of the recommended sintering protocols.

Fast sintering for chairside

Using the "KATANA™ Zirconia" block with Dentsply Sirona’s CEREC system, it is possible to sinter single crowns up to three-unit bridges in 18–30 minutes without compromising the mechanical or optical properties.

The “KATANA™ Zirconia” block displays superior optical properties after 18 minutes of sintering compared with representatives of major competitors’ raw material after 30-minute and 60-minute sintering programs designed by Kuraray Noritake Dental based on the manufacturer’s recommendations.

Unique “KATANA™ Zirconia” properties

Together, these efforts taken by Kuraray Noritake Dental to produce dental zirconia of high quality make all the difference. The "KATANA™ Zirconia" series— "KATANA™ Zirconia" Yttria Multi Layered (YML), Ultra Translucent Multi Layered (UTML), Super Translucent Multi Layered (STML), High Translucent Multi Layered Plus (HTML Plus) and KATANA™ Zirconia High Translucent Mono Layered (HT)—have a homogeneous, high-density structure with low porosity and a high level of purity. In addition, "KATANA™ Zirconia" YML offers a seamless structure without transition lines despite flexural strength gradation. All these properties optimise the performance of the blanks during machining.

SEM images of non-polished “KATANA™ Zirconia” and a competitor’s material at 33× magnification. The four images of each material show the surface structure at different areas of a molar crown. In all areas, the surface of the restoration made of the competitor’s material is rougher and shows more porosity than the surface of the “KATANA™ Zirconia” crown directly after milling, according to Dr Josef Kunkela’s research results. One of the contributing factors to this result is the more densely pressed blanks with smaller grain sizes of “KATANA™ Zirconia”. (Courtesy of Kunkela Research Academy by Dr Josef Kunkela).

Surface roughness

An optimised processing behaviour leads to regular restoration margins, smooth surfaces and a precise fit of the restorations. The latter is due to the fact that the milling behaviour and volumetric shrinkage during final sintering are highly predictable, so that a user designing a 20 μm cement gap will get what he or she desires. Owing to the great control over optical properties and outstanding match to the VITA classical A1–D4 shades, "KATANA™ Zirconia" is considered to be one of the most aesthetic dental zirconia options available on the market.

Exellent marginal fit

SEM images revealing the fit of restorations made of two different materials (lithium disilicate and “KATANA™ Zirconia” Block STML) on a tooth abutment. The “KATANA™ Zirconia” restoration shows a more regular margin and more precise fit (with a cement gap of 19–21 μm) than the lithium disilicate crown (cement gap 26–45 μm). (Courtesy of Kunkela Research Academy by Dr Josef Kunkela).

Extremely regular margins of a “KATANA™ Zirconia” crown after milling, which is also a result of the favourable material structure.

In order to ensure all the desired material properties, including aesthetics and strength, one thing is essential: the machining carried out in the dental laboratory – milling and sintering - needs to adhere to the recommended protocols. This means that the milling machine and furnace should be cleaned and calibrated on a regular basis, which provides the conditions for optimised zirconia processing from the powder to the final, true-to-life dental restoration.

Mathias Fernandez Y Lombardi

EU Scientific Manager
Dental Ceramics & CAD/CAM Materials
Kuraray Europe GmbH

2013
Successful completion of an apprenticeship as a dental technician at Seuthe dental laboratory in Plettenberg, Germany

2018
Successful completion of dental technology studies at the University of Osnabrück, Germany. Graduation as an engineer in dental technology

Since March 2018
Employee of Kuraray Europe GmbH

Simply Create the Panavia Smile

One predictable procedure for cementing your prosthetics reimagined. All your cementation appointments become a joy. Even if you need to cement precious veneers. It’s now possible thanks to the revolutionary PANAVIA™ V5.

This PANAVIA™ V5 video demonstrates the work flow for: 

- Laminate Veneer Cementation

By MDT Daniele Rondoni.

This clinical report reveals why you should start:

• using fewer ceramic elements
• choosing minimal ceramic layering
• opting for micro-cutback solutions

without missing the quality and value of your restorations.

Advances in materials development and computer-aided processing allow for more streamlined workflows and an improved collaboration between the dental office and laboratory. In order to benefit from the new options, however, it is important that dental technicians embrace their new responsibilities: they need to keep track of the latest changes and need to acquire profound knowledge of how to leverage the materials’ and technologies’ full potential. Being open for new approaches and restoration techniques is part of this game. In return for their efforts, they will be able to achieve unparalleled aesthetic accuracy in a more efficient procedure.

The evolution of dental zirconia is an excellent example for advances in the field of dental materials: many modern zirconia discs have multi-layered structures and natural tranlucencies. Offering top-level performance and high versatility, these variants are increasingly often the materials of choice for the production of high-quality restorations.

The "KATANA™ Zirconia" multi-layered series, for example, is composed of four multi-layered materials: "KATANA™ Zirconia" HTML PLUS with the highest flexural strength (1,150 MPa) and lowest translucency, "KATANA™ Zirconia" STML with medium strength (748 MPa) and a high translucency, and "KATANA™ Zirconia" UTML with a strength above the level of glass ceramics (557 MPa) and ultra-high translucency. The latest add-on in “KATANA™ Zirconia” portfolio is YML - multi-layered zirconia disc that offers both flexural-strength and translucency gradation. With this portfolio, it is possible to select the right material for every specific need (e.g., high-strength variant for multi-unit restorations, high-translucency variant for anterior crowns). Using the zirconia with a monolithic or minimal vestibular cut-back design and a small layer of porcelain enables us to reduce the wall thickness of the restorations (as compared to a traditional framework design and full porcelain layer). As a consequence, a less invasive tooth preparation is required.

In addition, the design meets the functional needs in terms of low abrasiveness and high toughness, while a sophisticated aesthetic outcome is achieved using micro-layering with the materials contained in the 4.4.1. kit. These can be a winning alternative to traditional ceramic multi-layer solutions, as revealed using the following case example that illustrates the use of the 4.1. technique.

Fig. 1. Digital impression.

Fig. 2. Digital impression taken with the temporary in place.

Fig. 3. Digital model of the prepared teeth imported into the CAD software.

Fig. 4. Digital model of the teeth with temporary imported into the CAD software.

Fig. 5. Designing of four zirconia crowns: Transparent view.

Fig. 6. Designing of four vestibular enamel cutback zirconia crowns.

Dentin structure with internal anatomy

In the present case, "KATANA™ Zirconia" STML, in the shade A2, was selected based on the desired appearance of the final restorations, the colour of the abutment teeth and the space available. The selected design was a minimal vestibular cutback, while the palatal zirconia was left untouched. To replicate the natural aesthetics, we opted for vestibular micro-layering with single luster porcelain and specific internal design of the mamelons.

In order to achieve the best possible aesthetics, it is fundamental to incorporate the internal anatomy into the pre-sintered vestibular surface, and to precisely follow the recommended sintering protocol. Only a flawless sintering procedure will lead to the ideal translucency and correct shade appearance. Following sintering, the surface should be treated with a sandblasting unit (aluminium oxide, particle size 50 μm, pressure 1 to 2 bar).

Fig. 7. Cross-sectional view for a check of the correct thickness.

Fig. 8. Crown made of "KATANA™ Zirconia" STML after sintering.

Fig. 9. Checking the fit of the crowns on the printed working model.

Fig. 10. ILS technique: colour map.

Fig. 11. Application of "CERABIEN™ ZR" Internal Stains.

INTERNAL STAIN ADVANTAGES

• Powder becomes gel and is always ready for use
• The real colours are revealed already before baking
• Optical effects are achieved simply and rapidly
• Excellent adhesion to zirconia is ensured

To improve the mimicry effect, we use the internal light stain technique on the zirconia surface. Incisal Blue one is applied around the mamelons, Mamelon Orange 2 directly on the mamelons for a natural effect. For a calibrated chromaticity, A+ may be added in the cervical area.

Fig. 12. Appearance of the internal stains on the surface after firing.

Fig. 13. Light dynamics after firing.

Fig. 14. Luster layer: Colour map.

Fig. 15. "CERABIEN™ ZR" Luster Porcelain LT1 applied in a micro layer.

Fig. 16. Layering with LT1.

The vestibular body and incisal morphology are completed by adding a single ceramic micro layer of CZR Luster Porcelain LT1.

Before finalizing the restorations, the zirconia surface and texture were optimized with a stone and rubber polishers.

Polishing of the palatal surface was accomplished with Pearl Surface Z diamond paste before a final self-glaze step in the furnace.

Fig. 17. Appearance of the minimal ceramic layer after a single firing procedure.

Fig. 18. Light dynamics after firing.

Fig. 19. Final crowns after mechanical polishing.

Fig. 20. Check on the elements will be carried out on the printed digital model.

Fig. 21. Final situation after cementation.

Fig. 22. Palatal view of the final situation.

Conclusion

Considering aesthetic requirements and case difficulty, today it is possible to adopt different 4.4.1. approaches. In combination with the present generation of multi-layered zirconia, they allow the modern technician to make the best use of digital means to solve complex cases in an easy, effective, and successful manner.

The 4.4.1. system is recommended because it is a selection of materials used in a number of combinations, which help us achieve aesthetically sophisticated outcomes in a feasible, flexible and repeatable way.

For more information about the 4.4.1. system, click here.

Dentist:

DANIELE RONDONI, MDT

• Graduating in 1979, Daniele Rondoni opened a laboratory in 1982, which is also the home of the AAT Community College he founded.
• Teacher and counsellor for the “Italian School for Dental Technicians”at the University of Chieti, University of Sienna and University of Rome Tor Vergata.
• EAED and IAED Active Member and a SICED Associate and O.L.
• International Instructor for Kuraray Noritake Dental products.
• Author of “Tecnica della Multistratificazione in ceramica” (Ceramic Multilayering Technique) and a lab manual about the use of composite materials, introducing his own method – the “Inverted Hardness Layering System”.

Article by Dr. Stefano Daniele.

During bonding procedures for metal-free fixed dental prostheses (FDPs), try-in with specific cement shade matching glycerine paste is necessary for choosing the correct shade of resin-based cement. During try-in, however, saliva and blood could contaminate the bonding surfaces of the ceramic and dental hard tissue. It is essential for the ceramic surface and dental hard-tissue surface to be perfectly clean of bacterial biofilm and other contaminants before adhesive application. Both the procedures ensure efficient bonding and long-term reliability of the adhesive fixed prosthetic intervention.

It is essential for the ceramic surface and dental hard-tissue surface to be perfectly clean.

Cleaning the ceramic bonding surface after try-in

Try-in of metal-free fixed dental prostheses (FDPs) is a key procedure for evaluating the fit of the finishing line of the dental preparation and, for very thin veneers, for matching the resin-based cement to be used to bond the ceramic restorations to the dental hard tissue. Aesthetic features—value in particular—of thin veneers depend on different factors, and one of the most important is the choice of shade of the resin-based cement used under the thin ceramic. To make this procedure easier and repeatable, many manufacturers provide glycerine pastes that have the same colours as those of the corresponding resin-based cements. This pre-bonding procedure of try-in of metal-free FDPs enables the selection of the most appropriate resin-based cement. Glycerine pastes are generally hydrophilic and can be rinsed from the ceramic bonding surface after try-in with an air–water spray, but some contaminants, such as saliva, blood and crevicular fluid, may remain on the surface, and this may affect the efficacy of the bond to the dental hard tissue. Sandblasting contaminated surfaces of metal-free FDPs may be the best choice for removing contaminants from bonding surfaces, but it is important to consider that not all dentists have sandblasting devices in their offices. To this end, Kuraray Noritake Dental launched KATANA™ Cleaner, a specific detergent for decontaminating the bonding surfaces of ceramics that is able to provide complete removal of contaminants from the bonding surfaces of metal-free FDPs after the try-in procedure. A perfectly clean ceramic bonding surface is important for obtaining an effective micromechanical interlocking between glass-ceramic and cement, as well as for allowing the chemical bond reaction between a 10-MDP-based primer and the zirconia bonding surface.

A perfectly clean ceramic bonding surface is important for obtaining an effective micromechanical interlocking between glass-ceramic and cement.

Cleaning the dental hard-tissue bonding surface when sandblasting is not recommended

The dental hard-tissue bonding surface must be clean before bonding metal-free FDPs, and this procedures can be done by sandblasting with a ‘soft’ powder such as erythritol. The focus of this procedure would not be to create an additive retention rate for the ceramic surface, but instead to remove the bacterial biofilm from the dental hard-tissue surface before bonding. Actually, metal-free FDPs are designed to have supra gingival finishing lines. Supra gingival preparation is also important for permitting perfect isolation with a rubber dam. In clinical practice, often the finishing line may be (partly) sub gingival for specific reasons, for example in veneer preparation designed to close diastemas and cervical black triangles between anterior teeth. In those clinical cases, dental dam application may be difficult, and sandblasting dental hard tissue may pose too high a risk of periodontal tissue bleeding. Tissue bleeding near the cervical margin of the preparation before adhesive bonding procedures for metal-free FDPs may affect the seal between the restorative and preparation. These clinical situations indicate the use of cleaning agents rather than sandblasting to clean surfaces before bonding.

Limitations of conventional agents used to clean bonding surfaces

Most conventional cleaning agents are not effective cleaners of ceramic, including zirconia, surfaces of metal-free FDPs and dental hard-tissue surfaces when sandblasting is contra-indicated as described. The following is a short list of the limitations and adverse effects of the main detergents used in clinical practice before bonding procedures:

• Ethanol: It is not a very effective contaminant remover and is not able to remove saliva and blood proteins fully. Often ethanol fixates proteins rather than removing them.
• Sodium hypochlorite: It has good efficacy as a cleaner, including removal of saliva and blood proteins, but may have an adverse impact on bonding procedures owing to its oxidisation properties (free radicals released from a sodium hypochlorite reaction could result in interference with autopolymerisation and light polymerisation of resin monomers).¹
• Hydrogen peroxide: It does not have any contaminantremoving properties and, to a greater extent than sodium hypochlorite, could result in interference with free-radical polymerisation of resin-based materials used for adhesive procedures.
• Chlorhexidine: It does not have any adverse effect but also no capability of removing contaminants.

KATANA™ Cleaner and its specific features

KATANA™ Cleaner is a specific detergent solution for cleaning the surfaces of all kinds of prostheses, either metal based or metal free and for the adherent surfaces of dental hard tissue. KATANA™ Cleaner is for both extra-oral and intra-oral use. The chemical composition of KATANA™ Cleaner includes 10-MDP and a 10-MDP triethanolamine (TEA)-salt in an aqueous solution. 10-MDP-TEA is an emulsifier and surfactant compound able to solubilise many substances not soluble in water and to increase the wetting capacity of those. These chemical features of 10-MDP-TEA allow easier removal of contaminants from surfaces using water spray in order to obtain a clean surface. KATANA™ Cleaner is mainly targeting proteins; saliva, blood and the like. The 10-MDP-TEA-salt is amphiphilic. The non polair part enters the contamination forming micelles. the micelles are easy to rinse of with an air-water spray.

KATANA™ Cleaner is a powerful concentrated cleaner. It has a mild pH of 4,5 thus no adverse etching of the dental hard tissue. The presence of 10-MDP in the solution makes it compatible with all dental bonding agents. KATANA™ Cleaner is a purple-coloured solution, and this feature permits easy and accurate application on all surfaces to be cleaned. An easy flow chart follows that explains the use of KATANA™ Cleaner after try-in with glycerine paste before adhesive cementation of (metal-free) FDPs.

Fig. 1. Using KATANA™ Cleaner on the bonding surfaces of metal-free fixed dental prostheses and dental hard tissue after try-in and before bonding.

Fig. 2. Ceramic partial fixed dental prostheses (veneers) before the try-in.

Fig. 3. Glycerine paste used for the try-in.

Fig. 4. Veneer try-in.

Fig. 5. Use of KATANA™ Cleaner to remove remains of try-in gel and contaminants, such as saliva, from the bonding surfaces of the fixed dental prostheses.

CLINICAL CASE 1

Cleaning of "KATANA™ Zirconia" UTML FDPs after try-in using KATANA™ Cleaner

Fig. 6. "KATANA™ Zirconia" UTML fixed dental prostheses.

Fig. 7. Cleaning the fixed dental prostheses with KATANA™ Cleaner after the try-in.

Fig. 8. Tooth preparation cleaned with KATANA™ Cleaner before adhesive application and resin cementation.

Fig. 9. Fixed dental prostheses in situ at the recall appointment.

CLINICAL CASE 2

Tooth surface cleaning using KATANA™ Cleaner

Fig. 10. Ceramic partial fixed dental prostheses (veneers) before try-in and bonding procedures.

Fig. 11. Cleaning of the dental hard-tissue bonding surfaces in a clinical situation where sandblasting was not recommended owing to the high risk of periodontal soft-tissue bleeding.

Fig. 12. Bonded partial fixed dental prostheses at the recall appointment.

Fig. 13. Perioral aspect of the veneers during smiling.

Dentist:

DR STEFANO DANIELE

Dr Stefano Daniele received his dentistry degree from the University of Milan in Italy in 2001. He is in private practice in Milan and is an academic tutor in restorative dentistry in the Department of Biomedical, Surgical and Dental Sciences at the Faculty of Medicine of the University of Milan and is located at the San Paolo hospital in Milan. He was a visiting professor at the Università degli Studi del Piemonte Orientale “Amedeo Avogadro” in Novara in Italy, teaching restorative dentistry and dental materials until 2013.

Acknowledgements

Special thanks go to master dental technician Daniele Rondoni for the fabrication of the metal-free FDPs.

Reference

1. Lai SC, Mak YF, Cheung GS, Osorio R, Toledano M, Carvalho RM, Tay FR, Pashley DH. Reversal of compromised bonding to oxidized etched dentin. J Dent Res. 2001 Oct;80(10):1919–24. doi: 10.1177/00220345010800101101.

Innovation and workflow simplification made possible

In this edition of BOND, we're shining a spotlight on the innovation and workflow simplification made possible by high-quality products like our "KATANA™ Zirconia" range.

In an interview with Atsushi Matsumoto and Yuta Tajima about KATANA™ Zirconia YML these experts explain the benefits of this new material possessing different concentrations of yttria in a single blank, and highlight how its multi-layered nature allows practitioners to work with a nearly universal zirconia suitable for all cases.

Mathias Fernandez Lombardi has contributed an excellent article detailing the science behind "KATANA™ Zirconia", Kuraray Noritake Dental's brand new 4.4.1. kit is introduced and last, but certainly not least, Dr Stefano Daniele details his experiences with KATANA™ Cleaner.

Click here to read. Enjoy!

Start Reading: BOND | VOLUME 8 | 12/2021

Previous versions:

BOND | SPECIAL EDITION | 06/2021

BOND | VOLUME 7 | 10/2020

BY PETER SCHOUTEN

ZIRCONIA
CRYSTALLISATION

Zirconia is here to stay in dentistry. Since its introduction some two decades ago, the possibilities for use of zirconia have increased enormously. But how is this compound produced? What happens during sintering, what types are available, and how are the desired shape and shade of the final product achieved?

PSZ or Partially Stabilised Zirconia was the first of the zirconium oxides to be used in dentistry. This type of zirconia was stabilised using yttria, and is currently no longer in use. It consisted of a mix of monoclinic, tetragonal and cubic crystals. For many years, the so-called Y-TZP variety was used (yttria tetragonal stabilised zirconia polycrystal). This has outstanding flexural strength (> 1,000 MPa), however, a non aesthetic opaque white appearance. It consists for mostly of tetragonal crystals with a diameter of some hundreds of nanometres. Approximately 3 mol% yttria is added to keep the material stable at room temperature;
this variety is therefore sometimes described as 3Y zirconia. New varieties, such as cubic zirconia, were developed with the aim of improving the aesthetic
properties of the material. Cubic zirconia is characterised by high translucency but has a lower flexural strength. However, although the flexural strength of this type is considerably lower than that of the tetragonal version, it is nevertheless much higher than that of lithium disilicate. This form also contains a higher amount of yttria, ranging from 4 to more than 5 mol%.

CRYSTAL PHASES

We currently know of zircona crystals in three major shapes.

Monoclinic

Normally, zirconia exists only at room temperature in the monoclinic phase. Monoclinic zirconia has low strength and translucency.

Tetragonal
These zirconia crystals are metastable and only exist at room temperature after stabilisation, mainly by adding yttria.
Although tetragonal zirconia is strong, it has limited aesthetic properties.

Cubic
Cubic crystals are stable and provide improved translucency. Due to the addition of a higher percentage of yttria, cubic
zirconia work pieces are not as strong as tetragonal ones. On the other hand, they are highly aesthetic and therefore
suitable for monolithic restorations, even in the anterior zone.

CRYSTALLISATION PROCESS
Zircona is almost invariably offered as a partially sintered material. In this form it is always opaque white, and the true
colour and translucency is only apparent after sintering. During sintering, the material shrinks to its ultimate size; a
multitude of small crystals merg to form larger crystals, but although the crystals themselves increase in size, the total
volume decreases. This shrink factor is therefore taken into account in the software, so that the end product is not only
colourfast after sintering, but is also sizewise correct.

Small crystals merge into larger ones during the sintering process.

KATANA™ Multilayer HTML before (left) and after sintering.

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.

Interview with Mathias Fernandez Y Lombardi, EU Scientific Manager, Kuraray Europe GmbH

Kuraray Noritake Dental Inc. reinvented its original zirconia multi-layer technology by integrating newly developed raw materials with different yttria content into the proven multi-layer colour structure. The material that is based on this innovative technology, KATANA™ Zirconia YML, offers a well-balanced flexural strength, chroma and translucency gradation throughout the blank.

According to pilot users of the new zirconia discs, the greatest benefit of using KATANA™ Zirconia YML is in the true empowerment of the laboratory. We asked Kuraray Noritake’s EU Scientific Manager Dental Ceramics & CAD/CAM Materials, Mathias Fernandez Lombardi, to explain how the new material is able to positively affect work routines in the dental laboratory.

The greatest benefit of using KATANA™ Zirconia YML is in the true empowerment of the laboratory.

Mathias Fernandez Lombardi, who should consider working with KATANA™ Zirconia YML?

KATANA™ Zirconia YML is designed for laboratories and milling centres with a strong focus on simplification. With its strong body and highly translucent enamel layer, it offers exactly the properties required for an unlimited indication range. Being perfectly suited for the production of durable monolithic long-span posterior bridges and of highly aesthetic anterior crowns or partial restorations, KATANA™ Zirconia YML is a true all-rounder that eliminates the need for another zirconia or even ceramic CAD/CAM material. At the same time, it supports highly automated production procedures and requires minimal hand work.

What are the benefits of using a single material for every indication?

Several benefits are related to the use of a single, all-round material. It leads to a reduced number of blanks to be stored, which simplifies inventory management and minimizes the storage space needed. Moreover, it facilitates standardization of laboratory workflows. Using the same material every time means that there are no differences in the basic design and milling parameters like minimum wall thicknesses and connector strengths, in the sintering protocols and finishing options to be taken into account. Hence, errors are less likely to occur and routines are easily established. Finally, the risk of cross-contamination is eliminated when a single material is processed with the available equipment (milling machine, milling and finishing tools, and sintering furnace). Predictable outcomes and flawless aesthetics are usually the result.

What are the benefits related to the use of KATANA™ Zirconia YML as the only ceramic CAD/CAM material?

I guess that the most important argument is that aesthetic outcomes are easily and efficiently achieved with KATANA™ Zirconia YML for all kinds of restorations, even for long-span bridges. It is usually sufficient to produce monolithic restorations for the posterior region, which are just polished or glazed. Anterior restorations may be designed monolithically or with minimal cut-back, and the user may choose between CERABIEN™ ZR (CZR) FC Paste Stains and CZR Internal Stains plus glaze to obtain a natural look. Another benefit of KATANA™ Zirconia YML is its seamless multi-layer structure combined with an extraordinary blank quality.

Why is this seamless structure and high blank quality important for users?

The seamless multi-layer structure, that is a smooth transition from one layer to the next, is the precondition for structural integrity and flawless aesthetics. It ensures that the material is free of transition lines, offers accurate dimensions after sintering (due to uniform shrinkage) and shows a reliable long-term performance not compromised by internal tensions. In KATANA™ Zirconia YML, a completely homogeneous composition, with carefully aligned CTE-values and shrinkage ratios in all parts of the blank, is responsible for this benefit.

Aesthetic outcomes are easily and efficiently achieved with KATANA™ Zirconia YML for all kinds of restorations, even for long-span bridges.

For its development, Kuraray Noritake Dental leveraged its long-standing expertise in dental ceramics and the advantages of an end-to-end in-house blank production process, without which it would have been impossible to reach the requested quality level. Due to the fact that the material is so well aligned, it was even possible to develop a 54-minute sintering programme that produces equally good results as the proven 90-minute or 7-hour programmes and becomes the go-to option for all rush cases. With this feature, KATANA™ Zirconia YML becomes the “jack of all trades” material: It offers highest comfort and security like an SUV, but when it comes to speed, it is in no way inferior to a sports car.

The above sintering recommendations represent only a guideline; depending on each individual furnace and condition, some adjustments might be necessary. If the 54 or 90-minute sintering program is not programmable in your furnace, it is not possible to set the furnace according to one of these schedules. *The material is removed from the furnace at 8000C. A furnace with a configurable YML sintering program is required.

Users who have already tested ceramic materials with a strength gradient know that positioning of long-span restorations in the blank can be tricky. What are the rules to be respected when positioning a long-span bridge in a YML blank?

Positioning of restorations in KATANA™ Zirconia YML discs is extraordinarily easy. The reason is that the gap between the lowest flexural strength found in the enamel area and the highest flexural strength found in the lowest body layer is comparatively small. Moreover, the Body Layer 1 that is found adjacent to the enamel layer already offers a flexural strength that is higher than the 800 MPa requested for bridges with four or more units. Consequently, users are on the safe side whenever they place their long-span restorations in the middle of the blank. More specifically, half of the connector cross section needs to be in the lower half of the disc, which is quite different from other materials with strength gradation that allow for connector positioning in the body area only. KATANA™ Zirconia YML restorations with a maximum of three units may be positioned in any layer. In this context, the fact that the thickness of each layer increases proportionally with the height of the disc comes as a benefit: The enamel layer is large enough to exploit its aesthetic potential in single-unit or small bridge cases.

Positioning of long-span restorations in the middle of the disc.

What would you recommend dental technicians who would like to empower their laboratory or milling centre?

I can truly recommend testing KATANA™ Zirconia YML in the laboratory environment to see how it handles and to assess its potential. The exceptional blank quality and seamless integration of the different layers, the ease of positioning and processing efficiency are factors potential users need to experience in real life to understand what they mean for their daily work. Similarly, the aesthetic outcomes need to be assessed in the clinical environment for an authentic impression of the natural look and feel obtained. I am sure that KATANA™ Zirconia YML will be able to convince virtually everyone who wants to empower the laboratory with an easy-to-use, efficient universal zirconia solution that fits virtually every patient’s and every dentist’s needs! Kuraray Noritake Dental knows that dental technicians and practitioners are in need of products that support their striving for simplification, standardization and increased efficiency so urgently needed in present times. Therefore, our product innovations are all focused on delivering more performance with less effort. KATANA™ Zirconia YML is the latest addition to a whole series of materials pursuing this goal.

Minimum connector cross-sections are to be respected during the computer-aided design of KATANA™ Zirconia YML restorations.

Mathias Fernandez Y Lombardi

EU Scientific Manager
Dental Ceramics & CAD/CAM Materials
Kuraray Europe GmbH

2013
Successful completion of an apprenticeship as a dental technician at Seuthe dental laboratory in Plettenberg, Germany

2018
Successful completion of dental technology studies at the University of Osnabrück, Germany. Graduation as an engineer in dental technology

Since March 2018
Employee of Kuraray Europe GmbH