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What if Kuraray Noritake Dental had not developed the MDP monomer?

What would the quality of adhesive dentistry be if Kuraray Noritake had not developed the MDP monomer? MDP has proved to be a very effective functional monomer for creating durable bonding to enamel, dentine and metals. The best-known products containing MDP are CLEARFIL™ SE BOND and PANAVIA™.

Structure of Adhesive monomer MDP

Adhesion to various substrates is possible Thanks to MDP (methacryloyloxydecyl dihydrogen phosphate), which has been shown to create a long term, durable and stable bond to both dental tissue and metal oxides. Research conducted over the past few decades has demonstrated the effectiveness of MDP. The first Kuraray Noritake Dental product to contain MDP was PANAVIA EX. Various other adhesive and cementation systems followed. Our latest products, PANAVIA™ V5 and CLEARFIL™ Universal Bond, also rely to a large extent on the performance of the original MDP monomer. MDP has the following structure:

1. terminal double bond group for polymerisation
2. hydrophobic alkylene group to maintain a delicate balance between hydrophobic and hydrophilic properties and
3. hydrophilic phosphate group for performance of the acid demineralisation and chemical bonding to tooth structure.

Fig. 1. The chemical structure of adhesive monomer (MDP).

History

In the years between 1978 and the late 1990s, it became possible to increase the bond strength to dentine to more than the intrinsic strength of the dentine itself. MDP played a major role in these developments. The solid ionic bond with calcium from the HAp in dental tissue means that such failures as occur are cohesive in the dentine rather than being failures of the adhesive. Apart from in vitro studies confirming this bond strength, the long term clinical durability recorded over 13 years is also impressive.

Research

Research from Yaun et al., 2007, shows that defects along the interface are largely responsible for degradation of the hybrid layer. CLEARFIL™ SE BOND exhibited no such defects. So it was expected that SE BOND would also prove to have a stable connection to dental tissue. Recently, Peumans et al. From Leuven University, Belgium found CLEARFIL™ SE BOND to still have excellent clinical effectiveness after 13 years.

In their publication in the Journal of Dental Research 83, 2004, Yoshida et al. concluded that the choice of the adhesive monomer played a significant role in the effectiveness of the adhesive. They found MDP to be the best and fastest in tests for chemical adhesion (ionic bonding) and stability in a moist environment (insoluble) – better and more stable than 4-MET and Phenyl-P, in that order.

After 35 years, MDP is still in a class of its own. To date, no manufacturer has been able to develop an adhesive monomer with better adhesion properties combined with durable bond strength. Many attempts have been made, but none have succeeded. In the meantime, Kuraray’s patent on MDP has expired. This has opened up the market for other manufacturers to synthesise their own MDP. Only a few non-dental chemical companies are supplying MDP to other manufacturers of adhesive systems, and the synthesis of high-purity MDP remains extremely difficult.

More recently, Kumiko Yoshihara et al. published ‘Functional monomer impurity affects adhesive performance’, in Dental Materials 31 (2015) 1493-1501. They concluded that the three MDP’s they studied exhibited different levels of purity. Differences in the resultant hybrid layers were observed in all three MDP versions: both impurities and the presence of dimers had an effect on the etching efficacy of the HAp, and also on the intensity of nano-layer presence and the immediate bond strength.

μTBS of MDP’s from different origin

Yoshihara Ket al. Functional monomer impurity affects adhesive performance Dent Mater 31, 1493-1501, 2015.

Fig. 2.

Explanation

The three 10-MDP’s studied in this study clearly revealed a different purity. Differences in the ultrastructure of the resultant hybrid layers were observed for the three 10-MDP versions. Both the impurities and the presence of dimers affected the etching efficacy of HAp, the intensity of nano layering and the ïmmediate’ bond strength.

“The purity of 10-MDP present in commercial dental primers, adhesives and cements can be expected to influence bonding performance.”

Case by Dr. Salvatore Scolavino

The establishing of a stable occlusal relationship is one of the biggest challenges dental practitioners are facing when restoring posterior teeth with resin composite, but it is a task with a decisive impact on the integrity of the masticatory apparatus. A poor static and dynamic occlusion may have a negative effect on the restored tooth, the periodontal apparatus, and also on the opposing dentition.¹ Ideally, the occlusal anatomy of direct restorations is designed in a way that occlusal forces are directed along the long axis of the tooth, which is achieved when each cusp tip in occlusal contact touches a flat surface. Horizontally directed forces, on the other hand, should be avoided, as they tend to cause tipping and increase the risk of cuspal fracture, tooth mobility etc.

In cases concerning improper occlusal relationship involving tipping of restored teeth, it may be possible to stabilize the situation by replacing the restoration and re-establishing a proper occlusion. If carried out correctly and early enough, this restorative approach may be a way around orthodontic treatment. The following clinical case is used to demonstrate how to create a functional occlusal surface right away – without larger adjustments. The whole restorative procedure is simplified by the use of a universal composite with a single posterior shade that eliminates the need for shade determination and shade selection, while it produces lifelike treatment outcomes.

Case description

This patient presented with direct composite restorations in the mandibular left first and second molar that were lacking an elaborated occlusal morphology (Fig. 1). The second molar appeared to be tipped mesially towards the first molar (Figs. 2 and 3), which resulted in improper occlusal relationships and a decreased position of the mesial marginal ridge. In order to verify the clinical and radiographic observation of an improper occlusal relationship, the occlusal contacts were recorded with articulating paper (Fig. 4). As expected, there was an uneven distribution of occlusal contacts, which were exclusively located in the distobuccal area on the second molar, and not matching the tooth-restoration interface on both molars.

Fig. 1. Pre-operative clinical situation: Occlusal view.

Fig. 2. Pre-operative clinical situation: Lateral view revealing the tipping of the second molar.

Fig. 3. Pre-operative bite-wing radiograph confirming the tipping issue.

Fig. 4. Checking of the occlusal contacts.

Planned approach

As orthodontic treatment was not an option, it was decided to replace the composite restorations, thereby treating the Class I cavity of the second molar as if it were a Class II cavity. This would allow us to increase the height of the mesial marginal ridge and establish the proper occlusion.

Preliminary measures

Once the rubber dam was placed (Fig. 5), the existing composite restorations were removed and the cavity slightly extended with a diamond chamfer bur (Fig. 6). The result of this procedure is shown in Figure 7. In order to provide an anatomical build-up of the mesial wall, a sectional matrix was mounted with the aid of a wooden wedge and a separator ring (Fig. 8).

Fig. 5. Isolation with rubber dam, held in place with a clamp and a wedge.

Fig. 6. Tooth preparation with a diamond chamfer bur.

Fig. 7. Appearance of the teeth after preparation.

Fig. 8. Sectional matrix, wedge and separator ring in place.

Adhesive procedure

After selective etching of the enamel (K-ETCHANT GEL, Kuraray Noritake Dental Inc.) (Fig. 9), the enamel bonding surfaces had a chalky-white appearance, which indicates properties that are favourable for bonding (Fig. 10). The adhesive procedure was performed with CLEARFIL™ SE BOND 2 (Kuraray Noritake Dental; Fig. 11). In the first step, the primer of the system was applied and actively rubbed into the surface for 40 seconds, and air-dried. Subsequently, the bond was used in the same manner. After complete evaporation of the solvent, the bonding surface was light-cured for 40 seconds to ensure proper polymerisation. The cavity floor was then covered with a 1 mm thick layer of flowable composite (CLEARFIL MAJESTY™ ES FLOW SUPER LOW A3, Kuraray Noritake Dental).

Fig. 9. Selective etching of the enamel.

Fig. 10. Chalky-white enamel surfaces.

Fig. 11. Glossy appearance of the bonding surfaces after application of the tooth primer and bond.

Restoration procedure

Before starting to elevate the mesial wall of the second molar using the centripetal build-up technique² (Fig. 12), we analyzed the height of the marginal ridge and anatomical details of the contralateral tooth, while the adjacent molar provided orientation as well. In general, knowledge not only about the tooth’s typical anatomy, but also about the patient-specific anatomical details of the adjacent and contralateral teeth as well as the antagonist is very useful for designing the occlusal anatomy. In addition, remaining anatomical structures should be read and used. In this particular case, the restorations were completed with CLEARFIL MAJESTY™ ES-2 Universal composite (Kuraray Noritake Dental) in the posterior shade U, using the cusp-by-cusp technique (Figs. 13 to 15). In most areas, it was possible to follow the inclination of the remaining cusps and the orientation of the grooves to produce an ideal surface anatomy. For those who would like to speed up the procedure, the simultaneous modeling technique³ may be an option. In this technique, the cusps are built up simultaneously from separate increments, which remain out of contact to each other until light-cured in a single curing cycle.

Fig. 12. Mesial wall built up with composite.

Fig. 13. Application of the first increment for cusp build-up. It is useful to limit the size of the increments for controllability.

Fig. 14. Cusp-by-cusp build-up completed on the second molar.

Fig. 15. Molars with restored occlusal surfaces.

In order to improve the already great optical integration of the restorations, some stain (Dark Brown, CHROMA ZONE™ COLOR STAIN, Kuraray Noritake Dental) was applied to the fissures. A multi-blade ball shaped bur and an Arkansas Flame abrasive stone were used for finishing. Final polishing was accomplished with the TWIST™ DIA system (EVE). The immediate treatment outcome is shown in Figure 16. The patient was released after rubber dam removal, checking the static and dynamic occlusion, and conducting a control radiograph (Fig. 17). The optical integration was even better at the recall after one month due to the rehydration of the surrounding tissues (Fig. 18), while the functional integration was excellent and no occlusal adjustments were required.

Fig. 16. Immediate treatment outcome with a nice optical integration of the restorations providing for a stable occlusal relationship.

Fig. 17. Control radiograph taken after the direct restoration procedure.

FINAL SITUATION

Fig. 18. Treatment outcome at recall after 30 days.

Conclusion

The presented case example reveals how important it is to strive for occlusal stability when restoring posterior teeth with composite. Furthermore, it demonstrates how it is possible to re-establish a stable occlusal relationship, even if some tipping has already occurred. In order to get it right the first time, it is essential to make use of the remaining anatomical structures, which guide the way toward an occlusal surface that ensures a favourable distribution of occlusal forces, and therefore provides optimal conditions for a long life of the freshly restored teeth. The combined use of the presented restorative techniques with innovative materials like CLEARFIL MAJESTY™ ES-2 Universal will make the procedures simpler and even more efficient.

References

1 Sandhu S, Lal J, Singh R, Sandhu R, Sra J. Significance of establishing occlusal anatomy in operative dentistry. Saint Int Dent J 2016;2:7-10.
2 Bichacho N. The centripetal build-up for composite resin posterior restorations. Pract Periodontics Aesthet Dent. 1994 Apr;6(3):17-23.
3 Scolavino S, Paolone G, Orsini G, Devoto W, Putignano A. The Simultaneous Modeling Technique: closing gaps in posteriors. Int J Esthet Dent. 2016 Spring;11(1):58-81.

Dentist:

DR. SALVATORE SCOLAVINO

Dr. Salvatore Scolavino, graduated with honors in Dentistry and Dental Prosthesis from the University of Naples. Dr. Salvatore is a specialist in aesthetics and direct and indirect anterior and posterior adhesive restorations. His focus lies with Conservation, Endodontics and Prosthetics in particular. He is an active member of prestigious academies and scientific societies: AIC -Italian Academy of Conservation, IAED -Italian Academy of Esthetic Dentistry and SIDOC (Italian Society of Conservative Dentistry. Since 2004, he has private practice Nola, Italy.

Dr. Scolavino is a founder of werestoreit.it, an inspiring site that offers abundance and variety of aesthetic clinical cases. Author of the book published by Quintessence Publishing „Direct Restorations in the posterior regions“, author of scientific publications in national and international journals, he is speaker at courses and conferences in Italy and abroad.

By Kazunobu Yamada, RDT

Are you looking for a convenient finishing technique that allows you to successfully start using KATANA™ Zirconia YML for the production of life-like restorations?

In this video, Kazunobu Yamada, RDT, demonstrates how texturing and polishing of the lingual surface and texturing, pre-polishing and glazing of the labial surface of an anterior crown will deliver impressive outcomes.

Case by Marco Valenti, DDS and Angelo Canale, CDT

When dental zirconia evolved into a highly aesthetic material suitable for the production of restorations with a monolithic design or minimal labial cutback, the amount of hand work (ceramic layering) was reduced. At the same time, however, every dental laboratory needed to have more blanks available, and the need for an indication-specific material selection complicated the planning process.

Some dental technicians love to play with different blanks and with a combination of automated and manual work steps to exactly meet the patient and indication-specific needs. Others, however, would like to take a faster and more standardized path to beauty. For the latter group, Kuraray Noritake Inc. has just introduced a true allrounder. KATANA™ Zirconia YML is based on newly developed raw materials with different yttria content integrated into the company’s multi-layer colour structure. As a consequence, KATANA™ Zirconia YML offers colour, translucency and strength gradation throughout the blank, resulting in an unlimited indication range.

That sounds promising, but does it really work in the laboratory and clinical environment? Are there any hidden challenges with regard to designing and manufacturing? And how beautiful are the outcomes? In order to assess the material’s properties in real life and to see how it performs in our hands, we decided to select a complex case and run a clinical test.

INITIAL SITUATION AND TREATMENT PLAN

This female patient was concerned about the aesthetics of her maxillary anterior teeth (Figs. 1 and 2). Several porcelain-fused-to-metal crowns in the anterior (both central incisors) and posterior region (three premolars) had unsightly dark margins and an unnaturally opaque core. The adjacent natural teeth appeared more translucent and their look was compromised by several composite restorations with discoloured margins. A missing right first molar had caused second molar to drift mesially (Fig. 3). In addition, the left canine was missing, but the space had been closed (Fig. 4). Figure 5 provides an occlusal view of the pre-operative situation.

Fig. 1. Facial view of the pre-operative clinical situation.

Fig. 2. Frontal intraoral view of the patient’s teeth.

Fig. 3. Lateral view of the upper and lower right quadrant.

Fig. 4. Lateral view of the upper and lower left quadrant.

Fig. 5. Occlusal view of the maxillary teeth.

All restorations in the maxilla needed to be replaced, and the patient set great value on a long-lasting aesthetic improvement of the situation. Hence, an all-ceramic material needed to be selected. An orthodontic correction of the malocclusion prior to restorative treatment was not an option, so that the restorations needed to be adjusted to the existing clinical situation. In order to provide for a smooth optical integration, we decided to use a single material for all restorations from the incisors up to the second premolars. This was a great chance to put the new KATANA™ Zirconia YML to a test! It was planned to use the material monolithically with zero cutback and to just paint on an ultra-thin layer of liquid ceramics (CERABIEN™ ZR FC Paste Stain).

CLINICAL PROCEDURE

The old restorations were removed and tooth preparation was carried out (Fig. 6). A minimally-invasive structure removal is supported by the fact that KATANA™ Zirconia YML has a minimum wall thickness of just 0.4 mm in the anterior and 0.5 mm in the posterior region. Then, a digital impression was taken with 3Shape TRIOS 3 (Fig. 7). The acquired data was matched with photographs of the patient’s face to design a virtual wax-up (Fig. 8) and mill a temporary restoration in the dental laboratory. The placement of this temporary allowed for an aesthetic and functional assessment as well as a clinical test drive of the planned definitive restorations (Fig. 9). In this set-up, the left first premolar took over the function and shape of the missing canine. The fact that the gingival margin was slightly higher in the region of the right compared to the left central incisor did not bother the patient, so that an alignment (gingivectomy) was not necessary.

Fig. 6. Situation after tooth preparation with a heavily discoloured central incisor.

Fig. 7. Digital impression taken after tooth preparation.

Fig. 8. Smile design for the production of the temporary.

Fig. 9. Temporary restoration in place.

PRODUCTION OF THE FINAL RESTORATIONS

After successful completion of the test drive, a digital impression was taken with the temporary in place (Fig. 10). Based on this impression and the information acquired during the test drive, four full-contour crowns, two partial crowns and one bridge were designed (Fig. 11 to 13). The bridge in the region of the right first premolar to first molar had a small cantilever pontic to fill the reduced space of the missing first molar.

The restorations were milled from KATANA™ Zirconia YML. Despite the varying levels of flexural strength within the blank, virtual positioning of the restorations in the disc is extraordinarily easy. For the restorations produced in this case, it is only necessary to respect the minimum wall thickness and connector cross section recommended by the manufacturer. When long-span restorations (with more than three units) are planned, half of the connector cross sectional area needs to be positioned in the lower half of the blank. This is the case if a restoration is placed in the middle of the disc, independent of its size.

Fig. 10. Digital impression taken with the temporary restoration in place.

Fig. 11. Computer-aided design of the final restorations.

Fig. 12. Aesthetic assessment of the virtual design.

Fig. 13. Functional assessment of the virtual design.

FINISHING

Figures 14 and 15 show the sintered restorations on the resin models after the addition of individual textural features with hand instruments. A seamless multi-layer structure without transition lines and with a warm body area is obtained. For an even more natural appearance, some individual effects and glaze were added using the CERABIEN™ ZR FC Paste Stain kit from Kuraray Noritake Dental Inc. (Fig. 16 to 19).

Fig. 14. Frontal view of the restorations on the resin models.

Fig. 15. Occlusal view of the restorations.

Fig. 16. Frontal view of the final restorations.

Fig. 17. Lateral view showing the bridge and the anterior crowns in the first quadrant.

Fig. 18. Lateral view showing the crowns in the second quadrant.

Fig. 19. Occlusal view of the lifelike restorations.

TREATMENT OUTCOME

The restorations were placed with the adhesive cementation system PANAVIA™ V5 (Kuraray Noritake Dental Inc.). Figure 20 shows the treatment outcome immediately after cementation. The material masks the discolouration of the underlying tooth structure very well and offers a nice translucency in the incisal area.

FINAL SITUATION

Fig. 20. Treatment outcome.

A TRUE ALLROUNDER

Our test project confirmed that KATANA™ Zirconia YML is a high-quality material with a great aesthetic potential and no limits with regard to the indication range. It is surprisingly easy to design and position the restorations in the virtual blank and after milling, the surfaces are smooth, the margins are sharp and stable, and the fit is accurate. Micro-layering with paste stain is often sufficient for lively outcomes. This makes the new KATANA™ Zirconia YML the material of choice for anyone placing great value on a high level of automation, the standardization of laboratory workflows and efficient and easy procedures.

Dentists:

We are pleased to share with you short training videos for CERABIEN™ ZR (CZR) porcelain.

Check out the below working steps and learn more about how to achieve outstanding aesthetics using this tried and proven material.

It is strong, it is pre-shaded like natural teeth, and it is reliable: KATANA™ Zirconia HTML, the highest strength version among KATANA™ multi-layered zirconia series. Now, Kuraray Noritake Dental Inc. has carefully optimized the product to further improve its optical properties and to harmonize the sintering schedules with all other materials of the KATANA™ Zirconia Multi-Layered Series.

The new KATANA™ Zirconia HTML Plus offers all popular properties of its predecessor, including the multi-layered colour structure and uniform strength distribution throughout the blank. It is suitable for a variety of indications including long-span bridges with a minimum wall thickness of just 0.4 mm in the anterior and 0.5 mm in the posterior region. This allows for minimally invasive preparations, while the user may choose between a monolithic, cut-back or framework design combined with the preferred finishing technique.

The PLUS refers to additional benefits like the material’s improved optical properties: KATANA™ Zirconia HTML Plus offers an increased translucency of 45 percent (compared to 43 percent KATANA™ Zirconia HTML) and an even more natural shade appearance of the manufactured restorations. “As the colour of the restorations appears deeper, more vivid and more saturated, and the translucency is closer to that of natural teeth, a great optical integration is achieved straight away. This leads to a reduced finishing effort”, says Mathias Fernandez Y Lombardi, EU Scientific Manager Dental Ceramics & CAD/CAM Materials at Kuraray Noritake Dental. At the same time, the high flexural strength (1,150 MPa) is maintained, providing for an unlimited range of indications.

Like its predecessor and all other materials of the KATANA™ Zirconia Multi-Layered Series, KATANA™ Zirconia HTML Plus is the result of an in-house development, powder compilation and blank production process that is able to control every detail. This enabled our specialists to achieve a precise alignment of the desired properties, while maintaining a high blank quality that leads to the accurate milling results with smooth surfaces and regular edges users of KATANA™ Zirconia HTML are familiar with.

The unique powder composition and specific in-house blank production procedure also allowed us to streamline the sintering protocols. For single-tooth restorations and bridges with up to three units, three different protocols are available: a 54-minute high-speed sintering programme specifically developed for remake and rush cases, a 90-minute schedule and the traditional seven-hour sintering programme. The latter is also suitable for long-span restorations.

These three options and identical schedules are available for KATANA™ Zirconia HTML Plus, KATANA™ Zirconia UTML, KATANA™ Zirconia STML and the new KATANA™ Zirconia YML with additional flexural strength and technical translucency gradation. With this feature, it becomes extraordinarily easy to standardize procedures despite an indication-specific selection of the best-suited KATANA™ Multi-Layered Zirconia.

Mathias Fernandez Y Lombardi concludes: “KATANA™ Zirconia HTML Plus is completely in line with our philosophy of developing products that support their users in streamlining and simplifying procedures without limiting choices. Users may choose from a whole range of highly specialized or universal zirconia solutions, may opt for their preferred design and finishing technique, and can select the sintering protocol that suits their individual needs. At the same time, the manual effort is reduced and the risk of starting the wrong sintering programme is eliminated.”

One for all: With KATANA™ Zirconia YML (yttria multi-layered), Kuraray Noritake Dental Inc. has launched a true allrounder covering traditional and new zirconia indications. At the KATANA™ Zirconia YML Virtual Kick-Off Symposium on July 3, 2021, professionals from the clinical and technical field as well as scientific experts from Kuraray Noritake Inc. provided insights into the properties and benefits of the innovation. We had a conversation with three of them about the specific features of KATANA™ Zirconia YML and its potential role in the dental practice and laboratory. Mathias Fernandez Y Lombardi, EU Scientific Manager Dental Ceramics & CAD/CAM Materials, provided insights from inside the company, while Prof. Dr. Florian Beuer MME, Charité – Universitätsmedizin Berlin and MDT Nondas Vlachopoulos, owner of the dental laboratory AestheticLab in Athens, shared their external perspectives.

Prof. Dr. Florian Beuer MME and Mathias Fernandez Y Lombardi during the conversation at the Kick-Off Symposium in Munich.

MDT Nondas Vlachopoulos virtually attended the meeting.

What are the most important features and benefits of the new KATANA™ Zirconia YML?

Mathias Fernandez Y Lombardi: KATANA™ Zirconia YML is a 5^th generation zirconia featuring next-generation multi-layered technology: it offers colour, translucency and flexural strength gradation in one disc – for a virtually unlimited indication range. As it may be used as the only zirconia or even ceramic CAD/CAM material in a laboratory or milling centre, it is designed for everyone who would like to simplify and standardize laboratory procedures. It may be sintered within 54 minutes, offers a high accuracy of fit and may be finished using time-saving techniques.

The new discs presented at the KATANA™ Zirconia YML Virtual Kick-Off Symposium.

Multi-layered structure of KATANA™ Zirconia YML.

What are the benefits of using a single zirconia for every indication from the dental technician’s perspective?

Nondas Vlachopoulos: The use of a universal zirconia solution with a high aesthetic potential and well-aligned mechanical properties allows dental technicians to reduce their inventory and streamline their procedures – from designing to finishing. Nowadays, we all know that, in order to optimize the outcomes, it is essential that we develop a deep understanding of a material’s properties, respect its design parameters (like minimum wall thicknesses) and adhere to the sintering protocols. It is much easier to accomplish this for a single material than for many different ceramics, and the potential for errors is minimized with a single-material approach. With KATANA™ Zirconia YML, this approach enables us to produce very different outcomes depending on where the restoration is placed in the multi-layered blank.

What are the benefits of using KATANA™ Zirconia YML as the only ceramic material from the dental practitioner’s perspective?

Florian Beuer: To my mind, the most important benefit of using a single zirconia every time lies in a simplified documentation. When different ceramic materials are used in the dental laboratory, we need to keep track of the material selected in every single case. Only in this way, it is possible to make the right cementation decisions (regarding cement selection and the appropriate pre-treatment of the restoration). In addition, when it comes to failure of the restoration, we need to know which material was used to prove that it has been processed correctly and is suitable for the actual indication. This is much easier when a single material is used every time. Zirconia is predestined for this approach as it is forgiving, supports minimally invasive preparations and – in case of KATANA™ Zirconia YML – almost everything can be done with it.

What are the secrets of KATANA™ Zirconia YML that allow for excellent treatment outcomes despite the one-for-all approach?

Mathias Fernandez Y Lombardi: KATANA™ Zirconia YML is based on a completely new, seamless multi-layer technology combining different, newly developed raw materials with varying yttria concentrations in a single blank. The inhouse development of the powders and their precise adjustment of each other in terms of properties like shrinkage and coefficients of thermal expansion are prerequisites for a smooth transition from one layer to the next. Only if the layers are very well integrated, it will be possible to reliably produce even long-span restorations with a delicate design, perfect fit and flawless aesthetics (without transition lines). The aesthetic properties were also optimized by integrating clinical instead of purely technical translucency.

Please explain the term clinical translucency.

Mathias Fernandez Y Lombardi: Usually, translucency of dental materials like zirconia is measured in its white, pre-shaded state. This so-called technical translucency value is increased by adding yttria to the formulation, which makes the zirconia itself appear brighter (increasing the whiteness). The translucency of the final restoration, however, is also affected by pigments and other additives in the formulation. Consequently, monolithic restorations made of different materials with the same technical translucency value may vary widely in terms of their actual, clinical translucency, which affect the overall aesthetic potential. The formulation of KATANA™ Zirconia YML has been optimized by carefully selecting and combining the right additives to obtain a natural, tooth-like translucency.

Translucency and shade appearance of KATANA™ Zirconia YML (left column) compared to various other 5^th generation zirconia materials.

Nondas Vlachopoulos, is this measure of optimizing the clinical translucency a key feature enabling the one-for-all approach of KATANA™ Zirconia YML?

Nondas Vlachopoulos: The positive effect attributed to this measure is noticeable, as KATANA™ Zirconia YML has a particularly warm and natural appearance especially in the body area some other materials with flexural strength gradation are lacking. This leads to an exact colour match with the VITA classical A1-D4 shade guide, and reduces the need for manual shade adjustments. This is important for a one-for-all approach, as the material should be a perfect basis for the production of monolithic restorations, which are not covered by a thick porcelain layer able to mask any imperfections. However, there is another key feature that facilitates the zirconia’s use for virtually every indication: Its exceptional design flexibility. It enables users to control the translucency and overall aesthetics by positioning the restoration quite freely within the blank. For restorations with up to three units, there is a complete freedom of placement. Larger restorations with four or more units need to be positioned in a way that at least 50% of the connector cross-section is in the bottom half of the disc. This is easily accomplished and gives us optimal options to exploit the various properties of each layer depending on the aesthetics and strength needed in each specific case.

Positioning guidelines for KATANA™ Zirconia YML.

What is the recommended finishing procedure?

Mathias Fernandez Y Lombardi: In principle, all designs and finishing options are available for KATANA™ Zirconia YML – from a monolithic design individualized with liquid ceramics to microlayering after a minimal vestibular cutback or even full ceramic layering on frameworks. As the aesthetic potential of the zirconia is already high, however, we believe that in most cases, the first option is absolutely sufficient. In this case, a monolithic restoration is milled and the surface subsequently treated with our liquid ceramic system CERABIEN™ ZR FC Paste Stain. The pastes are easily applied in ultra-thin layers, very well controllable and wear resistant.

Anterior and posterior crown made of KATANA™ Zirconia YML after sintering (left part) and after sintering and finishing with CERABIEN™ ZR FC PASTE STAIN (right part).

Nondas Vlachopoulos, what is your preferred finishing procedure for restorations made of KATANA™ Zirconia YML?

Nondas Vlachopoulos: In the posterior area, I often opt for monolithic restorations individualized with CERABIEN™ ZR FC Paste Stain. The technique leads to beautiful outcomes a large majority of patients would love to see even in the anterior region. However, as orders for the production of anterior restorations coming my way are usually placed by clinicians and patients with the highest possible aesthetic demands, I often go for a framework design and full porcelain layering with CERABIEN ZR Porcelains. The materials (like EX-3 portfolio for metal frameworks) are based on synthetic feldspathic porcelain with a structure and particle distribution very similar to natural dentin and enamel. All in all, I like the fact that I can select the most suitable finishing technique for every individual case, and I believe that it is often possible to reduce the finishing effort to a minimum.

Clinical translucency, design flexibility, mechanical properties: Apparently, the differences between the available zirconia materials – even of the 5^th generation – are huge. How can users ensure that the material they select is of high quality and offers favourable mechanical as well as optical properties?

Florian Beuer: When the first-generation zirconia materials appeared on the dental market, laboratory testing revealed that there are huge differences in quality between materials of different manufacturers. Although independent studies comparing the properties and behaviour of 5^th generation zirconia are still scarce, it may be assumed that differences do exist. My recommendation is to select a several materials from well-known manufacturers supporting clinical studies, compare the study results already available, and test the selected options in the laboratory setting. Directly comparing design concepts, the processing quality and final appearance will most likely reveal which material is a dental technician’s favourite. I am sure that KATANA™ Zirconia YML is among the materials worth being tested.

Thank you for this insightful conversation.

A while ago Mr. Takuro Nagura of Kuraray Noritake Dental put in an appearance at the Mardent Dental Trade event in Breda to provide some practice-oriented information to the attending dental technicians about the application of CERABIEN ZR FC Paste Stain in combination with KATANA™ Zirconia. The result was a fruitful afternoon, filled with questions, insights and tips.

Those in attendance were all dental technicians with ample experience of working with KATANA™ Zirconia. Mr. Takuro Nagura was therefore able to enjoy the experience of being surrounded by a group of enthusiastic KATANA™ fans, all of whom also use Noritake porcelain and PANAVIA™ V5 to their full satisfaction. The excellent aesthetics, perfect fit and ease of use were frequently-heard endorsements in favour of the use of Kuraray Noritake Dental products.

The session began with an introductory presentation, with an in-depth focus on the technical properties of the materials, instructions for baking, shade taking and staining techniques. Then it was time for the group to get started themselves. A KATANA™ Zirconia UTML molar and front crown had been prepared for each participant, and these were then characterised by means of CERABIEN ZR FC Paste Stain. The shades A+, Grayish Blue and Reddish Brown were used as starting points.

The entire front crown was first treated with glaze, after which external stain was applied; first in a horizontal direction, whereby dentine A+ was used cervically and enamel Greyish Blue incisal. Finally, dentine A+ was also applied vertically to emphasize the marmelon structure. Mr. Nagura offered the useful tip of first scratching in the eventual necessary crack lines with a sharp instrument such as a needle, and then colouring them in with external stain.

Glaze was initially applied to the full surface of the molar too, after which external stain was applied horizontally. A+ was used for the cervical and occlusal plane, with enamel Greyish Blue for the occlusal cusps. A+ was then applied to the vertical lines, and the fissures were finally coloured in using Reddish Brown.

Examples of staining with fc paste stain

Case by Dt Giuliano Moustakis

When producing restorations for the upper anterior region, the first thing that comes to a dental technician’s mind is the selection of a material that matches the colour and translucency of the patient’s natural teeth. The aim behind this action is to provide a perfect optical integration of the restorations to be produced. In order to achieve this optical integration, however, dental technicians need to focus on the surface morphology as well. The following clinical case is used to demonstrate how restorations with the right colour, translucency and texture are able to create a stunning, natural smile, even in complex cases.

The female patient had a periodontally compromised dentition with a missing maxillary lateral incisor and mandibular prognathism. Spacing was present in both jaws, but the patient decided not to undergo orthodontic treatment due to the challenging periodontal situation and the associated risk of losing additional teeth. Instead, a cosmetic camouflage was planned. As the existing direct restorations on the upper central incisors were in need of replacement, the restoration of choice was an all-ceramic, five-unit bridge. Knowing that this situation would best be solved with a material that offers high flexural strength in the body area (strictly mandatory for five-unit bridges) and high translucency in the enamel part (required to imitate nature in the anterior region), the new KATANA™ Zirconia YML was selected. Thanks to its multi-layer structure with colour, translucency and flexural strength gradation (achieved through yttria content gradation), this material offers exactly the desired properties. We decided to use it with a slight vestibular cutback and microlayering with CERABIEN™ ZR (CZR) porcelain.

Fig. 1 Pre-operative clinical situation with a Class III Malocclusion, a missing lateral incisor, spacing and periodontally compromised teeth in both jaws.

Fig. 2 Lateral view of the pre-operative situation.

Fig. 3 Shade determination in the dental office.

Fig. 4 Maxillary central and lateral incisors and right canine after tooth preparation.

Fig. 5 Printed models of both jaws based on an intraoral scan. This view reveals the discrepancy between the upper and lower jaws that needs to be camouflaged.

Fig. 6 Vestibular and incisal reduction and surface texturing on the pre-sintered restorations made of KATANA™ Zirconia YML. Integration of mamelon structures with a round-end straight carbide bur.

Fig. 7 Integration of horizontal growth grooves with a coneshaped instrument (Panther Stone 040).

Fig. 8 Translucency of the reduced bridge after sintering.

Fig. 9 KATANA™ Zirconia YML structure on the model after sintering.

Fig. 10 Silicone index revealing the space generated in the cutback procedure.

Fig. 11 Evaluation of the camouflage effect.

Fig. 12 Try-in of the zirconia structure.

Fig. 13 Sandblasted bridge ready for microlayering.

Fig. 14 Bridge after the application of internal stains and a single layer of CERABIEN™ ZR Body (A3B) and CERABIEN™ ZR Luster Porcelain (LT1, LT Royal Blue, LTx and LT Coral mixed with Incisal Aureola).

Fig. 15 Chromatic map of the microlayering procedure.

Fig. 16 Palatal view of the restoration.

Fig. 17 Bridge after the first bake and the addition of LT1.

Fig. 18 Finished restoration. In order to optimize the look of tooth and gingiva parts, a final layer of CERABIEN™ ZR FC Paste Stain and Glaze was added.

Fig. 19 Palatal view of the restoration after finishing.

Fig. 20 Try-in of the bridge for aesthetic and functional evaluation.

FINAL SITUATION

Fig. 21 Treatment outcome.

CONCLUSION

This clinical case shows that KATANA™ Zirconia is an innovative material with high aesthetic potential. Despite flexural strength gradation, there are no severe design restrictions that limit the indication range. Instead, it is easy to design and produce even long-span bridges. Furthermore, due to the material’s high aesthetic potential, a monolithic design with zero cutback and paste staining with liquid ceramics is often an option. If users want to add a porcelain layer, a simplified and time-efficient microlayering approach is highly recommended. In any case, a natural surface morphology should be integrated, as it is essential for an aesthetic outcome.

Dentist:

DT GIULIANO MOUSTAKIS

Using different zirconia materials depending on the indication and on patient-specific needs allows for the best possible outcomes, yet comes with the danger of mixing up processing protocols. Kuraray Noritake Dental Inc. (Kuraray Noritake Dental) eliminates this problem by offering a complete portfolio of KATANA™ Zirconia Multi-Layered materials with harmonized sintering schedules. The latest member of the KATANA™ Zirconia Multi-Layered Series, KATANA™ Zirconia HTML Plus, is available since September 1, 2021. In addition to the aligned sintering schedules, it offers an increased translucency and optimized colour without compromising its flexural strength.

KATANA™ Zirconia HTML Plus is based on its tried and proven predecessor KATANA™ Zirconia HTML and also offers a multi-layered colour structure and uniform strength distribution throughout the blank. It is suitable for a variety of indications including long-span bridges with a minimum wall thickness of just 0.4 mm in the anterior and 0.5 mm in the posterior region. This allows for minimally invasive preparations, while the user may choose between a monolithic, cut-back or framework design combined with the preferred finishing technique.

Careful in-house optimizations in the material composition and structure have paved the way for an increased translucency of 45 percent (compared to 43 percent KATANA™ Zirconia HTML) and an even more natural shade appearance of the manufactured restorations. The colour appears more vivid and more saturated, which leads to an improved optical integration with the adjacent teeth and gums. At the same time, the high flexural strength (1,150 MPa) is maintained, ensuring an unlimited range of indications.

When it comes to sintering, three options are available for single-tooth restorations and bridges with up to three units: a 54-minute high-speed sintering programme especifically valuable for remake and rush cases, a 90-minute programme and the traditional seven-hour sintering programme suitable for long-span restorations as well.

All three options and identical schedules are also available for the other materials of the portfolio: KATANA™ Zirconia UTML, KATANA™ Zirconia STML and the new KATANA™ Zirconia YML (yttria multi-layered) with additional flexural strength and translucency gradation. Due to this feature, standardizing manufacturing procedures for a minimized risk of errors and consistent outcomes becomes extraordinarily easy. More information about KATANA™ Zirconia HTML Plus and the whole product family is available at our website.