By Dinesh Sinha, BDS, PHD, Senior Technical and Marketing Manager Dental Division, Kuraray America, Inc.

Since the early 2000’s, the global all-ceramic restoration market, including that for zirconia, has been growing rapidly. Increasing market demand resulted in various dental manufacturers marketing different dental zirconia types that can be used in many dental prosthetic applications. Today, dental ceramists play a key role with the latest CAD/CAM technology to provide high performance zirconia prosthetics with more precision and aesthetics for treatment needs.

Zirconia is a polycrystalline ceramic. This means that it is entirely composed of crystals, with no glass phase. The presence of an entirely crystalline microstructure brought strength to zirconia and gave initial formulations an opaque appearance with low translucency. The translucency of zirconia is improved by changing the atomic arrangement within the crystals of zirconia (most commonly known as translucent or aesthetic zirconia). There are several key factors dental ceramists should know when selecting zirconia:

1. Type/brand of zirconia

During the industrial process of making dental zirconia (zirconium dioxide), Yttria (Y₂O₃) is added to make refined zirconia stable at room temperature. Yttria also contributes to increasing the translucency of zirconia, but also conversely reduces its strength. The most common method of classifying zirconia is by Yttria concentration (i.e., 3Y, 4Y & 5Y). Many dental manufacturers use/buy zirconia from one large industrial ceramic manufacturer. This classification helps to understand and describe the properties of zirconia where the primary powder source is the same. 3Y is the strongest and least translucent, whereas 5Y is the highest translucency and lowest strength.

Fig. 1. Kuraray Noritake Dental Inc. original KATANA™ Zirconia powder.

Most dental zirconia manufacturers purchase raw zirconia powder from a third party. Only a few manufacturers like Kuraray Noritake Dental Inc. use their own proprietary original zirconia powder formulations (Figure 1). The company can thereby more accurately control the chemical and physical make-up, not only with Yttria concentration, but also parameters like grain or particle size, as well as sintering temperature. Kuraray Noritake has KATANA™ as an umbrella brand with three different options of strength and translucency in multi-layered formulations: KATANA™ HTML PLUS, STML and UTML.

2. Strength of dental zirconia

The most common method of measuring ceramic strength is by evaluating its flexural strength. The flexural strength test applies a force on the top of a ceramic specimen, which causes the specimen to bend and fracture. The International Standards Organization (ISO) and the American Dental Association have developed a standard for measuring the flexural strength of dental ceramics. Two methodologies are commonly used today. In the 3-point bend method (Figure 2), a rectangular specimen is used, whereas in the biaxial flexural strength method (Figure 3), a circular specimen is incorporated. Both tests are acceptable, however, ceramics tend to produce higher values when tested with the biaxial method over the 3-point bend method.

Furthermore, even in a 3-point bending test, if the span length (see Figure 2) of the specimen is decreased, it can produce higher values of flexural strength of the same ceramic. It is critical to understand testing parameters when selecting or comparing different ceramic brands. All materials should be tested under the same conditions, and by using the same methodology.

3. Multi-chromatic vs multi-translucent

Kuraray Noritake was the first dental manufacturer to introduce multi-layered zirconia as a commercial product in 2013. Different concentrations of pigment-containing zirconia powder are utilized to make the zirconia discs and blocks multi-chromatic.

Multi-chromatic: KATANA™ Zirconia HTML PLUS/STML/UTML (Figure 4) were developed based on the concept of “lifelike appearance”, accurately and naturally mimicking the color and translucency of natural teeth. It has a top enamel layer, two transition layers, and a base body layer. The unique manufacturing technology from Kuraray Noritake allows each powder layer to seamlessly blend within a gradient profile that eliminates any demarcation lines between the different layers. The Yttria concentration remains similar in all layers; therefore, the strength of the zirconia does not deviate from layer to layer. The pigments (chroma) are adjusted in a way that produces different chroma among the layers, where the translucency stays the same.

Multi-translucent: KATANA™ Zirconia YML (Figure 5) is the latest KATANA™ multi-layered disc, with a well-balanced combination of color translucency and flexural strength gradation. It is also manufactured using multilayer technology, with different Yttria content in each layer.

Strength differs in each layer, providing enamel with 750 MPa, the transition-body with 1000 MPa, and the base layer with 1100 MPa flexural strength. These layers are perfectly harmonized with each other, since all fundamental production steps, including purification, refining of the zirconia raw material and the addition of essential components such as Yttria, are all processed in-house by Kuraray Noritake.

4. Cleaning zirconia

During trial-fitting, the zirconia restoration might become contaminated with salivary proteins, thereby reducing the bond strength. KATANA™ Cleaner (Figure 6) can be used to remove contamination. This can be easily achieved by rubbing KATANA™ Cleaner on the intaglio surface, and subsequently rinsing it with water. KATANA™ Cleaner has a high cleaning effect, due to the surface-active characteristic of MDP Salt.

5. Bonding to zirconia

There are several clinical situations where zirconia restorations benefit from resin bonding: restorations that are less strong or thin, lack retention, or rely on resin bonding, (ex. resin-bonded fixed partial prostheses, onlays, or laminate veneers). Prof. Markus Blatz, DMD, PhD, University of Pennsylvania School of Dental Medicine and his group introduced a three-step approach, known as the “APC Zirconia Bonding Technique”.

APC Step A: Air-particle abrasion, then application of P: Primer and finally Step C: Composite resin. MDP-based resin cemented restorations exhibit better margins long term. MDP has shown a very stable chemical bond to zirconia. Kuraray Noritake invented and introduced the Original MDP monomer in 1981. All Kuraray Noritake PANAVIA™ cement (Figure 7) brands contain this original MDP monomer.

Kuraray Noritake is known for its legacy of inventing groundbreaking technologies in both resin and ceramic technologies. The company is committed to inventing the best quality materials that dental ceramists and dentists can use to treat their patients with confidence.

Dentist:

DINESH SINHA, BDS, PHD

First published in: A Journal of Dental Technology | November/December 2021

The KATANA™ Zirconia Multi-Layered series from Kuraray Noritake Dental Inc. (Kuraray Noritake Dental) is popular among dental technicians and dentists around the world, as it offers great mechanical and optical properties. The available materials have different levels of translucency and strength, and a multi-layered structure that facilitates the creation of lifelike restorations.

Furthermore, they are very well processable, which results in a high milling accuracy and smooth margins. Together, these properties are highly valuable for every dental office, as they result in precisely fitting, durable and beautiful restorations that help you exceed your patients’ expectations.

Clinical long-term success of these zirconia restorations, however, is not only determined by the material choice and laboratory processing alone. The way clinical procedures such as cementation and intra-oral adjustments are carried out have a decisive impact as well. In order to support you in your striving for a long-lasting bond between the tooth and the restoration, and to facilitate intra-oral polishing, Kuraray Noritake Dental has developed a wide variety of in-office products designed to make your life easier and your practice even more successful.

Remove bond-strength compromising proteins

When proteins present in blood and saliva are deposited on the bonding surfaces of teeth or dental restorations, the bonding performance of dental adhesives and self-adhesive resin cements will be compromised. As it is impossible to keep these surfaces free of oral fluids at try-in, effective cleaning strategies are required. In tests comparing different methods and cleaning agents, sandblasting and the use of KATANA™ Cleaner have been highly successful in removing the proteins from the bonding surfaces¹.

As KATANA™ Cleaner is a biocompatible material (unlike other often strongly alkaline zirconia cleaners), it is suitable for intra- and extra-oral use. Hence, it is the perfect solution for cleaning your KATANA™ Zirconia restorations as well as prepared enamel and dentin before cementation. The product has a high cleaning effect and is easy to use: simply rub it in for ten seconds, rinse and dry.

Obtain a reliable bond with fewer components

Fewer components and fewer procedure steps, this is what an increasing number of dental practitioners strives for when it comes to cementing zirconia restorations. For all of them, PANAVIA™ SA Cement Universal is the solution.

The self-adhesive resin cement contains the proprietary long carbon-chain silane coupling agent (LCSi Monomer) developed by Kuraray Noritake Dental that delivers a strong, durable chemical bond to porcelain, lithium disilicate and composite resin without the need for a separate primer. The original MDP monomer, also present in the paste, allows for chemical reactiveness with zirconia, dentin and enamel.

Therefore, the product is indicated for a wide range of indications (including adhesion bridges) without the need for separate priming and bonding. Another important fact is that excess removal requires a significantly lower force compared to other cements. This was already the case for product’s predecessor PANAVIA™ SA Cement Plus, as reported by a researcher from Tufts University in Boston, Massachusetts². For specifically demanding cases, you may increase the bond strength of PANAVIA™ SA Cement Universal to tooth structure with the aid of CLEARFIL™ Universal Bond Quick.

Choose the proven and familiar multi-step system

For all those who would like to stick to multi-step procedures they have trusted for years, PANAVIA™ V5 is the go-to product. It is suitable for all restorations, including those that demand the highest possible bond strength. It is the strongest cement Kuraray Noritake Dental ever developed, and with five shades, it is the most aesthetic one, too. This allows you to cement all tooth-coloured restorations with confidence, no matter whether they have a retentive or non-retentive design. PANAVIA™ V5 is designed to work perfectly with KATANA™ Zirconia, and is indicated for cementing a wide range of indirect restorations, and also for post-and-core procedures and amalgam bonding.

Create antagonist-friendly surfaces

Studies have shown that surface roughness of a restoration has a larger impact on the wear of the antagonist than the hardness of the dental material. This means that for an antagonist-friendly behaviour, the restoration surfaces need to be perfectly polished. This task is easily accomplished with TWIST™ DIA for Zirconia, which may be used after intra-oral adjustments or in the context of maintenance measures.

The flexible polishing spirals with an innovative shape offer you various application benefits for excellent polishing results. TWIST™ DIA for Zirconia is highly suitable for occlusal surface polishing as the shape and contour of the zirconia restoration is maintained. As they are sterilizable, the spirals may be reused.

A winning team for reliable results

By using a restorative material, cleaning solution, cementation system and polishing spirals from Kuraray Noritake Dental, you will benefit from streamlined procedures and reliable results. The products are not only designed to work with each other, but also thoroughly tried and tested for combined use, so that you can carry out your procedures with utmost confidence.

References

1 Data source: Kuraray Noritake Dental Inc.
2 A. Roberta et. al., J Dent Res Vol #98 (Spec Iss A), #3624, Determination of Excess Removability of Self-adhesive Resin Cements

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.

Kuraray Noritake Dental’s commitment to digital technology goes well beyond the dental practice. We know that our customers are tech-savvy and eager to engage with other dental professionals who use our products. This is why we focus on providing a range of free virtual solutions so that you can stay connected with all of Kuraray Noritake Dental’s activities.

An ultra-convenient app

The official Kuraray Noritake Dental app is designed to inform you about the latest updates and product releases at your own pace and convenience. A range of product brochures is easily accessible, providing the tools for you to obtain the information you need instantly. An automatic push notification function means that you do not need to worry any more about missing out on the latest dental news.

New magazine articles and videos can be quickly viewed in the app, whereas other tools provide support for your daily practice. The KATANA™ Color Simulator allows you to conduct a virtual colour simulation of a prosthesis created with KATANA™ Zirconia, whereas the cementation guide provides step-by-step instructions for the correct use of PANAVIA™ V5 and PANAVIA™ SA Cement Universal for a range of indications.

Download the Kuraray Noritake Dental app to your smartphone or tablet, and utilise its benefits anytime, anywhere.

Let’s be social

One of the most common ways in which dentists get new ideas and inspiration these days is through social media. By following our Instagram page, you will have direct access to a continually updated and convenient library of tips, videos and snapshots of Kuraray Noritake Dental products in action.

Over at our Facebook page, we have been developing a space for dental professionals to come together and discuss their experiences and tips for using our solutions. Become part of this community, and engage with what Kuraray Noritake Dental users from around the world are sharing.

A newsroom packed with new information

Webinars, clinical cases, interviews, magazine releases, product news and more—there is only one place where all of these can be found in abundance, and that is the Kuraray Noritake Dental virtual newsroom.

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.

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