An interview with Dr. Tomohiro Takagaki, DDS, PhD by Dr. Jorge Espigares, DDS, PhD

Due to its increased usability, one-step universal adhesives are becoming more popular and are the choice of many clinicians all around the world. Nonetheless, some studies have shown lower performance for one-step universal adhesives than previous generations.

Dr. Jorge Espigares, DDS, PhD, Planning and Development Department at Kuraray Noritake Dental Inc., interviewed Dr. Tomohiro Takagaki, DDS, PhD, lecturer and former assistant professor at Tokyo Medical and Dental University (TMDU), pioneer in the field adhesive dentistry, author of many publications, and currently lecturing at Asahi University, Japan.

Dr. Takagaki, in your opinion, what are the most important factors for a good and durable adhesion?

Dr. Takagaki: Good resin infiltration (penetration) and good polymerization are essential factors for good bonding. This is the basic concept for the formation of the hybrid layer. Additionally, there are other important factors such as low water sorption for bonding durability and the demineralization depth, which should be the same as the depth that the resin is capable of penetrating to.

Nowadays, the trend seems to be one-step universal adhesives. Do you believe that this reduction in steps has brought any limitations compared to previous generations?

Dr. Takagaki: Traditionally, one-bottle adhesives are too hydrophilic. This hydrophilicity also brings high water sorption, therefore the durability of the interface is compromised. At TMDU, we did not accept one-step bonding agents in clinical usage based on results we obtained in our research in that area.

Water sorption/solubility of different bonding agents.
Data provided by Tokyo Medical and Dental University.

What do you think of the new MDP-Amide chemistry (included in CLEARFIL™ Universal Bond Quick) for overcoming such limitations?

Dr. Takagaki: The MDP monomer has proved through research to be the best monomer for adhesion to tooth substrate. Nowadays, many manufacturers include MDP. Although the MDP purity and performance differs from Kuraray Noritake’s original one, in one-step bonding agents only MDP is not enough. The differential factor is the amide monomer that provides the desired high penetration and low water sorption.

You and your work at TMDU are very well known in the field of adhesive dentistry. Did your research show results that would support the above mentioned statements?

Dr. Takagaki: In our research results, we observed indeed a lower water sorption compared to previous one-step generations. Actually, we were surprised to see water sorption levels equivalent to the two step bonding agent gold standard: CLEARFIL™ SE BOND. (1. Graph). The amide monomer behaves as hydrophilic before the polymerization and as hydrophobic after, which is the desired situation for one bottle self-etching systems.

Would you recommend, therefore, the usage of universal bonding agents in daily practice?

Dr. Takagaki: Yes, but as mentioned, the MDP-amide chemistry is essential. It is noteworthy that another company is also using an amide monomer. However, our results at TMDU indicate that the performance in terms of penetration is not that good. Actually, we still saw lesion formation with that other company’s amide. Kuraray Noritake’s MDP-amide chemistry is the only one that avoids lesion formation (2. SEM images). In addition, CLEARFIL™ Universal Bond Quick releases fluoride that helps protecting the interface degradation and its “no waiting time” makes it ideal for challenging conditions as pediatric and/or geriatric patients.

Let’s get out of the laboratory, according to your clinical experience is there any extra advice that you could provide for a reliable adhesion?

Dr. Takagaki: One important point that sometimes is missed is to properly air-dry the solvent for at least 5 seconds after the bond application. I also recommend selective enamel etch for achieving aesthetic margins, even if all universal bonding agents allow self-etching. Finally, I would like to talk about simplicity. We dentists tend to shorten the necessary time and sometimes the rubbing time is not respected. With CLEARFIL™ Universal Bond Quick, our research showed not significant difference in bond strength with rubbing time (3. Graph). Therefore, it reduces the risk of error, allowing consistent results. I believe that simplicity is required so the fact that CLEARFIL™ Universal Bond Quick and PANAVIA™ SA Cement Universal can cover direct and indirect restorations, is ideal for daily practice. CLEARFIL™ Universal Bond Quick achieves what I am looking for in my practice: easy, quick and reliable.

Although the amount of available universal adhesives market is large, key properties like the ones above-mentioned may help in the complicated process of selecting a one-step adhesive that offers the best performance, simplicity, consistency and predictable results.

Bond strength upon rubbing time. Data courtesy of Tokyo Medical and Dental University.

Case by Dr. Hendrik Zellerhoff

Not all zirconia is created equal. This finding presented by Prof. Martin Rosentritt⁷ back in 2014 has lost none of its actuality and even appears to be increasingly relevant these days. This is because dental practitioners are spoilt for choice between various zirconia blanks, which differ widely in terms of quality, flexural strength, shade appearance, translucency and production complexity. Hence, each material has its own specific processing requirements and range of indications⁶. Profound knowledge of the available zirconia options is therefore an absolute prerequisite for long-term success of every full contour restoration produced in a time-efficient and economic procedure.

While in the early years of zirconia manufacturing in dentistry, the dental practitioner’s choice was limited to industrially milled zirconia frameworks hand-veneered by the dental technician, a wide range of material variants for chairside CAD/CAM production is nowadays available. Material-specific improvements are one of the reasons for the fact that every single zirconia has its specific indications and its own material parameters⁶. Zirconia milling blocks for monolithic restorations are in principle very well suited for the chairside production of single crowns for the anterior and specifically the load bearing posterior area. This is due to their stability and the reduced processing effort compared to hand- veneered crowns. However, the material in use needs to fulfil high demands with regard to strength, translucency, and shading – parameters that also need to be balanced against each other² (Fig. 1 to 4).

Fig. 1. Initial situation with multiple insufficient fillings.

Fig. 2. Crown milled from a KATANA™ Zirconia Block (Kuraray Noritake Dental Inc., Tokyo, Japan).

Fig. 3. Crown glazed after sintering, with fissures characterized using stains.

Fig. 4. Adhesively cemented crown with the appearance of a natural molar.

NOT ALL ZIRCONIA IS CREATED EQUAL

Due to their high flexural strength of more than 1,000 MPa, tetragonal zirconia variants (3Y-TZP) of the first and second generation are perfectly suited as framework materials. However, they lack the translucency required for monolithic use. It is theoretically possible to improve the translucency of 3Y-TZP materials by increasing the sintering temperature, however, this would result in restorations with insufficient strength. This is different for the third and fourth generations of cubic-tetragonal zirconia (5- TZP and 4-TZP). Due to the increased yttria content in the formulation, cubic crystals grow in the crystal microstructure. These cubic crystals have a larger volume, which leads to reduced scattering at the grain boundaries and improved light transmission. In addition, cubic crystal structures are more isotropic than tetragonal structures, so that incoming light is spread more evenly into all directions⁸. The combination of a high flexural strength and a high translucency in the fourth generation zirconia sets the stage for monolithic use of the material. This, in turn, eliminates the risk of chipping of the veneering porcelain.

PREMISES OF MONOLITHIC CHAIRSIDE RESTORATIONS

In order to ensure the desired long-term stability, intraoral functionality and aesthetics of a monolithic restoration on one hand and a time- and cost-efficient chairside workflow on the other, two factors are crucial. One is a proper functional occlusal adjustment of the restorations, the other is knowledge about the material parameters of the zirconia blocks in use.

Hardness and abrasion

Clinically, monolithic zirconia shows virtually no abrasion and an antagonist-friendly behaviour - provided that the occlusal surface is polished properly, is free of sharp edges and is covered with glaze. In order to leverage this effect and to avoid improper occlusal contacts as factors triggering parafunctions, the dental practitioner should carefully carry out an occlusal and functional analysis. This analysis should include an examination of the vertical dimension and of different jaw movement like protrusion, retrusion, laterotrusion and mediotrusion. Based on the results, a precise dynamic occlusal adjustment is possible. Any retrospective adjustment – even in case of minimal irregularities – is impossible or, more specifically, restricted to the glazing layer. If the surfaces, especially the cusps, are not polished to a high gloss, any wear of the glaze would lead to the exposure of a rough abrasive zirconia surface. Material-specific high-gloss polishing and glazing, however, effectively avoids abrasive wear of the antagonist^3,4,5.

Strength, translucency and shade

Under these premises, 5Y-TZP materials like KATANA™ Zirconia UTML (Ultra Translucent Multi Layered) with a flexural strength of 557 MP and a translucency of 43 percent are particularly well suited for the production of highly aesthetic anterior crown or veneer restorations. In the load-bearing posterior area, however, higher flexural strength values are necessary. Using 4Y-TZP materials like KATANA™ Zirconia Block (Super Translucent Multi Layered) with a flexural strength of 763 MPa provides more stability of the restoration, which is required for the posterior region. The product offers a translucency of 38 percent and is suitable for the chairside production of aesthetically and functionally demanding restorations with high stability even in case of a reduced wall thickness. Thanks to the colour gradient, light shines through in the incisal area in an enamel-like way, while in the cervical area, the level of translucency is similar to dentin. The imitation of a colour gradient found in natural teeth, which ensures that the restoration will blend in perfectly with the adjacent teeth, is obtained with a multi-layered, polychromatic structure with a smooth shade transition from the incisal to the cervical part. This feature eliminates the need for a time-consuming manual application of shades prior to sintering. A patient- specific post-sintering characterisation with stains is optional. As shade, form and effects are already visible during application, the dental practitioner gains full control over aesthetics at all times (Fig. 5 to 8).

Fig. 5. Comparison of flexural strength and translucency.

Fig. 6. Smooth shade transition from the enamel to the dentin and cervical area.

Fig. 7. Comparison of the translucency exhibited by different ceramics.

Fig. 8. Range of shades of KATANA™ Zirconia Single Unit Blocks.

KATANA™ ZIRCONIA BLOCK IN THE CEREC WORKFLOW

Reliable material properties are imperative for a smooth production workflow leading to a consistent high quality of the restorations. They are only obtained with industrially produced zirconia blanks, which offer a defect-free, homogeneous grain structure^1,10. At Kuraray Noritake Dental, the whole manufacturing process of zirconia products is carried out in-house, including the production of the raw materials. Therefore, it is possible to optimize the material parameters of KATANA™ Zirconia Blocks for chairside production and with high-speed sintering process. Using these components, the dental practitioner can reduce the time needed for the production of a monolithic zirconia restoration including scanning, milling and sintering to less than an hour.

Design

For this purpose, the teeth to be restored are prepared and captured together with the adjacent and antagonist teeth using an intraoral scanner (Omnicam or Primescan, Dentsply Sirona). The digital data set is then imported into the CEREC software. The software extracts the required information from the data and generates a design proposal for the restoration. Usually, this proposal may be accepted without major modifications. Due to the high mechanical properties of KATANA™ Zirconia, a wall thickness of 1.0 mm is sufficient for a posterior crown. This design has two positive effects: it optimizes the translucency of the restoration and supports a minimal preparation, which also facilitates clinical procedures in situations with limited space conditions. The shade and translucency of the restoration is also customizable via virtual positioning of the designed crown in the multi-layer block. This enables the dental practitioner to harmonize the brightness and translucency with the parameters of the adjacent teeth (Fig. 9 to 13).

Fig. 9. Initial situation with insufficient porcelain layer.

Fig. 10. Abutment teeth after preparation prior to digital impression taking.

Fig. 11. Restorations after polishing, occlusal and cervical characterization and glaze firing.

Fig. 12 - 13. Final restorations in place - occlusal and frontal view.

Sintering

The designed crown is milled from the KATANA™ Zirconia Block with the CEREC milling machine. Subsequently, finishing steps are carried out and the sintering process is started using the induction furnace CEREC SpeedFire. This furnace reaches a maximum heating rate of 300° C per minute. Neither pre-heating is required nor holding temperatures needed. As the material properties of KATANA™ Zirconia Block are optimally aligned with the CEREC SpeedFire programme, the user can be sure that the device adheres to all sintering parameters. This, in turn, is important for the growth of the crystals as well as phase transformation and stabilization9, which affect the natural shade results after sintering (Fig. 14 to 18).

Fig. 14 - 15. Labial and palatal view of the initial situation with restorations on the lateral incisor and canine.

Fig. 16. Varying shade and translucency gradient depending on the position of the restoration in the multi-layer block.

Fig. 17. Crowns with a natural colour gradient from the incisal to the cervical area merely glazed after sintering (without any additional adjustment).

Fig. 18. Natural aesthetic appearance of the KATANA™ Zirconia crowns even in the esthetic zone.

Individualisation and characterization

After sintering, dental practitioners may individualize or characterize KATANA™ Zirconia Block restorations if desired. This requires only a few simple work steps. The marginal ridges, mamelons, fissures or enamel cracks are imitated controllably using paste stains (CERABIEN™ ZR FC Paste Stain, Kuraray Noritake Dental), as the shade, shape and effects created are already visible during application. For the final glaze firing process with Glaze or Clear Glaze (Kuraray Noritake Dental), the SpeedFire induction furnace is used again (Fig. 19 to 25).

Fig. 19. Initial situation with secondary caries below the amalgam restoration on the maxillary left second premolar (tooth #25).

Fig. 20. Tooth prepared for a core build-up after caries excavation and proximal modification of the adjacent premolar (tooth #24).

Fig. 21. Crown milled from the block before …

Fig. 22. … and after sintering (at try-in).

Fig. 23. Fissures with age-specific characterization.

Fig. 24. Functional contact point created in consideration of the adjacent teeth.

Fig. 25. Final crown after glazing and adhesive cementation with PANAVIA™ V5 (Kuraray Noritake Dental).

Conditioning and placement of the restoration

Prior to restoration placement, the inner surface of the crown is sandblasted with Al2O3 (grain size: 50 μm, pressure: 1 bar) and treated with CLEARFIL™ Ceramic Primer Plus (Kuraray Noritake Dental), whereas PANAVIA™ V5 Tooth Primer (Kuraray Noritake Dental) is applied to the prepared tooth structure. Finally, PANAVIA™ V5 (Kuraray Noritake Dental) is applied for adhesive luting of the crown. The MDP monomer contained in the primer establishes a stable chemical bond and eliminates the need for additional conditioning. The fact that PANAVIA™ V5 is free of amines ensures long-term colour stability of the restoration.

CONCLUSION

With its combination of a high translucency and a high flexural strength, chairside dentists may use KATANA™ Zirconia Block for monolithic restorations with confidence. Restorations made of KATANA™ Zirconia offer the required long-term stability and fulfil the high aesthetic standards demanded from it to be able to serve as an alternative not only to cast metal and PFM crowns, but also to glass ceramic restorations. Due to the lack of a porcelain layer, the risk of chipping does not exist. Optimally aligned components enable dental practitioners to make use of a simplified and constantly monitored digital workflow that offers a high process reliability. Aesthetic functional restorations for the load-bearing posterior and the anterior area can be produced and placed within a single appointment. This is an important factor, which greatly affects patient satisfaction.

Dentist:

DR. HENDRIK ZELLERHOFF

References

1. Edelhoff D, Beuer F, Schweiger J, Brix O, Stimmelmayr M, Güth JF. CAD/CAM-generated high-density polymer restorations for the pretreatment of complex cases: a case report. Quintessence Int 2012;43:457–467.
2. Güth JF, Magne P. Optische Integration von CAD/CAM-Materialien. Int J Esthet Dent 2016;11:380–395.
3. Preis V, Behr M, Handel G, Schneider-Feyrer S, Hahnel S, Rosentritt M. Wear performance of dental ceramics after grinding and polishing treatments. J Mech Behav Biomed Mater 10 (2012); 13-22.
4. Preis V, Weiser F, Handel G, Rosentritt M. Wear performance of monolithic dental ceramics with different surface treatments. Quintessence Int 44 (2013);393-405.
5. Rosentritt M, Behr M, Strasser T, Preis V. Zirkonoxide als Implantatwerkstoff? Quintessenz 2018; 69 (12): 1420–1430.
6. Rosentritt M, Kieschnick A, Hahnel S, Stawarczyk B. Werkstoffkunde-Kompendium. Zirkonoxid. Berlin: Apple ibook; 2018.
7. Rosentritt M. Studie zum Verschleißverhalten von Zirkonoxid – Zirkonoxid ist nicht gleich Zirkonoxid. ZWR 2014;123(11):570-571.
8. Stawarczyk B, Keul C, Eichberger M, Figge D, Edelhoff D, Lümkemann N. Werkstoffkunde-Update: Zirkonoxid und seine Generationen – von verblendet bis monolithisch. Quintessenz Zahntech 2016;42(6):740–765.
9. Stawarczyk B, Özcan M, Hallmann L et al. The effect of zirconia sintering temperature on flexural strength, grain size, and contrast ratio. Clin Oral Investig 2013; 269–274.
10. Stober T, Bermejo JL, Rammelsberg P, Schmitter M. Enamel wear caused by monolithic zirconia crowns after 6 months of clinical use. J Oral Rehabil 2014;41:314–322.

PROVEN SCIENCE AND ARTISTRY LEAD TO QUALITY

Kuraray Noritake Dental enables the unique in-house production of raw materials. In contrast to our competitors, who source their raw materials externally (well known: Tosoh Cooperation), Kuraray Noritake Dental distinguishes itself by its unique in-house production of zirconia raw materials. Many years of expertise in manufacturing the company’s own powder have brought the material quality of KATANA™ to completely new dimensions, not only by controlling the degree of purity and particle sizes, but also by creating an optimal balance of binders, color pigments, stabilizers and other ingredients.

“WE CONTROL EVERY DETAIL.”

KATANA™ Zirconia STML NW with CERABIEN™ ZR FC Paste Stain
Sergio R. Arias DDS, MS Sung Bin Im, MDC, CDT

NEW SINTERING SCHEDULE

In addition to the new sintering programs, the traditional KATANA™ sintering programs can also be used, if desired.

Case by Daniel Vasquez, DDS

The dental practitioner’s time is the most valuable factor in the dental practice. Hence, it should be well spent, and saved wherever possible. In the context of placing direct posterior restorations, the universal composite CLEARFIL MAJESTY™ ES-2 Universal provides valuable support to anyone who would like to achieve this goal - being universally applicable, it allows users to spend less time on material selection. With its universal shade concept consisting of a single posterior shade and two anterior shade options, it eliminates the need for shade determination. This gives users more time to focus on fulfilling their patient’s needs. The following clinical case illustrates the use of the innovative material in the posterior region.

Fig. 1. Pre-operative situation with multiple carious lesions in the second premolar and both molars.

Fig. 2. Isolated working field.

Fig. 3. View of the quadrant after cavity preparation.

Fig. 4. Selective etching of the enamel with phosphoric acid gel.

Fig. 5. Dispensing of the universal adhesive CLEARFIL™ Universal Bond Quick into a mixing dish.

Fig. 6. Application of the universal adhesive to the enamel and dentin after etching, rinsing and air-drying.

Fig. 7. Lining up of the cavity floors with of a thin layer of flowable composite (CLEARFIL MAJESTY™ Flow).

Fig. 8. Immediate treatment outcome after the placement of several layers of CLEARFIL MAJESTY™ ES-2 Universal in the shade Universal.

FINAL SITUATION

Fig. 9. Post-operative image taken after rubber dam removal.

Dentist:

DANIEL VASQUEZ, DDS

The Function that becomes aesthetics

Italian dental technician, CDT Stefano Lograno, demonstrates how it is possible for the medical-technical prosthetic team to adopt a protocol from diagnostics to cementation, in which aesthetics can be functionally guided in a simple, predictable and standardized workflow following the criteria of the gnathological school of Vienna of Prof. Rudolf Slavicek.

Click here to read. Enjoy!

Start Reading: BOND | SPECIAL EDITION | 6/2021

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BOND | VOLUME 7 | 10/2020

Case by Dr. Matthieu Gilli

Fig. 1. A 25 years old female patient was dissatisfied with the aesthetics of the existing composite filling in tooth 21.

Fig. 2. Shade determination of the cervical and middle third of the tooth. By using small amounts of different shades of CLEARFIL MAJESTY™ ES-2 Premium Dentin.

Fig. 3. Contrast increase allows for:

- a better picture of dentinal structure
- dentin shade selection with more accuracy

Fig. 4. Two spheres of two different Premium Enamel shades are put at the incisal edge and the photo turned to black and white to optimise the evaluation of the translucency.

Fig. 5. To allow for the creation of a suitable palatal index, a large isolation field is necessary.

Fig. 6. Since the shape of the existing restoration is still correct the putty index can be made directly in the mouth.

Fig. 7. To improve both adhesion and optical integration, a bevel of 2 mm, 45° has been made as recommended by XU et al. (Eur J Oral Sci 2012).

Fig. 8. Selective enamel etching with 30% phosphoric acid for 30 sec. followed by rinsing and drying.

Fig. 9.

Left: Self-etch primer on dentin followed by bonding with CLEARFIL™ SE Bond.
Middle: 20 sec., 1000 mW/cm2 polymerisation of the bonding.
Right: Completed adhesive procedure with CLEARFIL™ SE Bond.

Fig. 10. Palatal shell made of A1E shade with the aid of the palatal putty index.

Fig. 11. Proximal matrix in place.

Fig. 12. Dentin replaced with CLEARFIL MAJESTY™ ES-2 PREMIUM A2D.

Fig. 13. To create the incisal halo, a small amount of A1D has been applied at the incisal edge.

Fig. 14. A tiny amount of CLEARFIL MAJESTY™ ES-2 Premium Translucent Blue is placed between the mamelons to create translucency.

Fig. 15. A white spot is created with a white opaque staining material to complete internal characterisation.

Fig. 16. A small amount of CLEARFIL MAJESTY™ ES-2 PREMIUM A1E is applied as a final covering layer.

Fig. 17. Secondary anatomy is marked with a pencil as a polishing area guide.

Fig. 18. 2 week follow-up.

FINAL SITUATION

Dentist:

DR. MATTHIEU GILLI

Dr. Matthieu Gilli graduated in 2014 as a dentist from the Université Catholique de Louvain, Brussels. Currently he is completing his PhD study in Service of conservative dentistry, at the same university.

Dr Max Andrup, a 2010 graduate of Umeå University, currently runs a private practice in the city of Hudiksvall in Sweden, where he maintains a passion for restorative dentistry with a biomimetic approach. In this interview, he discusses the future of restorative dentistry and explains why he relies on Kuraray Noritake Dental’s products for his daily workflow.

Dr Andrup, could you please tell us a bit about your dental career to this point?

For the first few years of my career, I pursued a residency as an oral and maxillofacial surgeon. For various reasons, I ended up buying my own practice instead, and I couldn’t be happier with that decision! It allows me to take my time with patients and focus on delivering high-quality treatment together with co-workers with whom I really enjoy working.

How did your passion for restorative dentistry develop?

I have always enjoyed bringing patients’ dentition back to a functional and aesthetic state. I’m not sure why exactly, but I started looking for dental accounts on social media to broaden my horizons and to see how others solved challenging clinical situations. This was a turning point for my career, as I found so much inspiration and learnt a great deal from what others shared.

Do you have a dental philosophy? If so, what are its guiding principles?

Knowing that many people don’t really like going to the dentist, my goal in my practice has always been not just to provide excellent oral care but also to offer a comfortable and relaxing experience. My ultimate goal is that no patient should feel anxious about his or her visit. The patients don’t necessarily have to look forward to their visits, but they shouldn’t be something over which they lose sleep.

When were you first introduced to Kuraray Noritake Dental's portfolio of products?

About three years ago, I found these Instagram accounts talking about gold standard adhesives and biomimetic restorative dentistry. This piqued my interest, and I started to read many scientific papers in order to understand why some adhesives worked better than others, why certain composites are preferable when replacing deep dentine, and so on. Products from one particular company kept coming up: Kuraray Noritake Dental. I had never worked with their products before but, convinced as a result of what I’d read and seen, I ordered a starter pack with CLEARFIL™ SE Protect adhesive, CLEARFIL MAJESTY™ Flow and CLEARFIL™ AP-X and haven’t looked back since!

Which Kuraray Noritake Dental products do you use on a daily basis in your workflow and why?

The one product I couldn’t survive without is the CLEARFIL™ SE Protect adhesive. It brings a level of research and clinical backing that gives me a feeling of confidence when conducting restorative dentistry. It contains the MDPB monomer, which results in lower levels of bond degradation. If you want to achieve a bond strength to dentine in the range of 40-50 MPa* it all starts with the right dentine bonding agent, and CLEARFIL™ SE Protect is just that.

*depending on testing method

What do you think will be trends, or points of emphasis, in restorative dentistry moving forward?

Unfortunately, I believe that the trend in the field of dentistry will continue to move towards simplification regarding bulk-fill restoratives and one-step adhesives. I can understand why-simple procedures are faster, and many clinicians have very limited time. The truth is, however, that developing a strong bond to dentine takes time, and you need to have an understanding of how the materials work to make the bond last.

In the past few years, new technologies have emerged that make it easier to study what happens in the bottom of a cavity when placing bulk-fill restoratives and, as expected, the contraction stress from the polymerisation process forms gaps in the cavity floor. This results in postoperative sensitivity and eventually a degraded bond. Getting a strong and durable bond to dentine starts with a gold standard adhesive like CLEARFIL™ SE Protect, but if you don’t respect the hybrid layer and place bulk fill over it, it will most likely fail.

By Prof. Dr. Florian Beuer

Zirconia has been the most popular all-ceramic material in dentistry for more than two decades. While the earlier generations of zirconia had to be veneered with porcelain to achieve acceptable aesthetics, recent developments showed higher translucency, allowing them to be used as full-contour restorations with partial veneering on the buccal aspects. However, the higher translucency was paid off by reduced mechanical stability.

In the past, we had to decide whether we want high stability or high translucency. With the introduction of the new KATANA™ Zirconia YML, both characteristics are combined in one disc. Analogue to previous multi-layer materials, the graded translucency is now combined with graded mechanical strength. The three apical layers (body 1 to body 3) consist of high strength zirconia with a flexural strength of 1000 MPa, while the enamel layer shows a flexural strength of 750 MPa. Thanks to this combination, aesthetics can be achieved much easier with higher buffers for mechanical stress. On the other hand, there is the potential to reduce thickness of the restoration and save tooth tissue during preparation.

At the KATANA™ Zirconia YML symposium (www.kuraraysymposium.info) on July 3^rd, we will look at the developments of zirconia in the last years and point out the significance of monolithic restorations, their strengths and the crucial issues in the treatment protocol. Join us!

Dentist:

PROF. DR. FLORIAN BEUER

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

Case by MDT Daniele Rondoni

Usually, the aesthetic potential of a dental ceramic material – specifically its translucency – may be increased only at the expense of a decreased flexural strength. The new KATANA™ Zirconia YML from Kuraray Noritake Dental Inc. is different. With its high flexural strength of 1,100 MPa in the lower half of the blank and high translucency in the upper body and incisal areas, it has a high aesthetic potential and an unlimited indication range, as shown using the following case example.

Fig. 1. KATANA™ Zirconia YML 4-unit and 6-unit bridges after milling and sintering. A natural vestibular surface texture plays a decisive role in the creation of aesthetic monolithic restorations.

Fig. 2. The two bridges on the model after ultra-micro layering with CERABIEN™ ZR FC Paste Stain Kuraray Noritake Dental Inc.).

Fig. 3. Stained and glazed restorations and their translucency in transmitted light.

FINAL SITUATION

Fig. 4. Buccal view of the 6-unit bridge cemented in the patient’s mouth.

Fig. 5. Buccal view of the 4-unit bridge cemented in the patient’s mouth.

With this new type of multi-layered zirconia, it is possible to produce aesthetic monolithic restorations suitable even for use in the anterior area. A high design flexibility is offered despite strength gradation, and the high translucency in the incisal area is responsible for a natural look after sintering. Ultra-micro layering and glazing on the monolithic surface will be sufficient to produce outcomes to our patients’ satisfaction.

Dentist:

DANIELE RONDONI, MDT

Born in Savona in 1961 where he lives and has worked in his own laboratory since 1982 with his collaborators. Graduated from the dental technician school IPSIA “P. Gaslini” in Genoa in 1979. He continued his education by attending relevant workshops for the “Italian dental school“ and broadened his professional experience in Switzerland, Germany and Japan. Since 2011 Kuraray Noritake Dental International Instructor.

The fact that different zirconia materials are used depending on the indication is both a blessing and a curse: Blessing because it allows dental technicians to achieve the best possible outcomes in every situation, and curse because the approach requires a extensive inventory and a lot of decisions. For those who prefer to take a more efficient route without compromising the outcomes, KATANA™ Zirconia YML is the new go-to solution. With its strong core and translucent outer layer, this new generation of multi-layered zirconia offers the properties needed for a broad indication range and easily obtained aesthetics.

KATANA™ Zirconia YML is the reinvention of the original multi-layer technology developed by Kuraray Noritake Dental Inc. (Kuraray Noritake Dental) more than a decade ago. It features new raw materials of different yttria concentrations integrated into the well-liked four-layer colour structure. The result is a disc with a well-balanced combination of chroma, translucency and flexural strength gradation.

As all body layers have a flexural strength of at least 1,000 MPa, the new zirconia fulfills the requirements for a broad range of indications even including monolithic long-span restorations. With its proven colour gradient and super-high translucency enamel layer, the aesthetic potiential is so high that it is often sufficient to opt for a monolithic design of the desired restorations and a time-saving finishing procedure such as polishing or ultra-micro layering with liquid ceramics (e.g. CERABIEN™ ZR FC Paste Stain).

The different layers in the blank are perfectly adjusted to each other through an in-house production procedure which ensures easy positioning of the restorations within the blank, a seamless multi-layer structure required for flawless aesthetics, a precise fit and predictable long-term behaviour.

The advanced fabrication and material composition comes with another advantage: A 54-minute high-speed sintering procedure is available for single-tooth restorations and bridges with up to three units. The optical and mechanical properties of the restorations are comparable to those after the alternative 90-minute or seven-hour sintering cycle.

KATANA™ Zirconia YML will be available July 1^st 2021. To celebrate the launch of the new member to our KATANA™ Zirconia family, we invite you to join us for a virtual kick-off symposium on July 3^rd, 2021 at 10:00 CET. We will show you how aesthetic outcomes are achieved with minimal effort, how design flexibility puts you in control and how the pace of procedures is accelerated without compromising quality.

Registration and further information: www.kuraraysymposium.info

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