Interview with Dr. Karim Nasr

Zirconia is a popular restorative material with highly beneficial mechanical and meanwhile also optical properties. Due to long processing times, especially sintering, the material was initially not suitable for single-visit dentistry. This changed with the availability of zirconia variants with shortened sintering times and special high-speed sintering furnaces.

We discussed with Dr. Karim Nasr, who is senior lecturer at the University of Toulouse in France and head of CAD/CAM postgraduate training, about his actual practice. His passion for CAD/CAM leads him to use CEREC since 2006 (former CEREC trainer) and to found also iAcademy, a training academy about digital dentistry. He shared his experience with us and we talked about his workflow and indication-specific material preferences as well as specific recommendations regarding the use of KATANA™ Zirconia Block in single-visit dentistry.

Dr. Nasr, which chairside CAD/CAM system do you currently use?

Karim Nasr: I am currently using a chairside CEREC Primescan AC system (Dentsply Sirona) combined with a MCXL milling machine (Dentsply Sirona) in my private practice. In my hospital practice and in the specialized esthetic dentistry consultation that I manage, we use a CEREC Primescan AC system combined with a CEREC Primemill milling machine (Dentsply Sirona).

Why did you opt for those components?

Karim Nasr: The choice of this entire system was guided by several criteria. Working on a proprietary chain certainly locks the possibilities of mixing the equipment, but brings real simplicity and fluidity of use. Moreover, the CEREC Software is certainly the most successful CAD software for a chairside use. It offers personalized and easily modifiable restorations in just a few steps. The simultaneous milling of the top (extrados) and bottom (intrados) surfaces without changing the burs ensures a very short milling time. Finally, a large number of materials are available and can be used with this system.

When did you start working with a chairside CAD/CAM system?

Karim Nasr: I discovered and started working with my first chairside system (CEREC 3) in 2005, shortly after graduating. At that time, everything was new in this field. The intraoral scanner, CAD software, milling unit and ceramic materials had just been introduced. All those components allowed us to deliver aesthetic dental treatments within a single treatment session for the first time.

How did the chairside CAD/CAM systems evolve over time?

Karim Nasr: Of course, with the advances in computer technology, the systems have become more efficient. While it was still necessary to powder the surfaces and possible to record one or two teeth in 2005, powder is no longer required in 2022 and complete arches can be scanned in less than two minutes with an accuracy of less than 20 μm. The design process is highly automated and very well assisted – artificial intelligence is used at all stages, making the work easier.

For what purposes do you use your system today?

Karim Nasr: In more than 15 years, the use of my system has evolved a lot. Nowadays, I reserve it for procedures that can be performed in a single session. This is of the greatest utility for my patients and it allows me to optimize my treatment time. For this reason, not only the milling time, but also the time needed for post-processing is crucial for the decision whether to use my chairside CAD/CAM system or to collaborate with a dental laboratory.

What kinds of materials do you process chairside?

Karim Nasr: I think I have tested all the materials available (at least in France), to be able to select the most suitable ones for daily procedures. Currently, I use different kinds of materials depending on the indications encountered: PMMA for temporary restorations, composites for inlays and onlays, glass-ceramics for onlays, overlays and crowns, and finally zirconia for crowns and bridges.

How do chairside CAD/CAM and zirconia go together?

Karim Nasr: In fact, quite simply. For me, a chairside equipment must be able to produce restorations in the same treatment session. Otherwise, it is a labside workflow. Thus, to use zirconia in chairside systems, the milling procedure must be fast and efficient, but above all, the post-processing (especially sintering) process must be fast. For short processing times, dry milling is recommended, as well as the use of a fast-sintering furnace (such as the CEREC SpeedFire from Dentsply Sirona).

What are the benefits of zirconia compared to other ceramic materials?

Karim Nasr: There are many of them. From a biomechanical point of view, the high mechanical strength of zirconia allows us to work with reduced wall thicknesses, which enables us to be more conservative in dental tissues or to choose any placement method (cementation or bonding). From a biological point of view, perfectly polished, zirconia is the most tolerant ceramic, as it is kind to antagonistic teeth and incredibly well tolerated by periodontal tissues. I prefer zirconia for my crowns on implants for this reason.

What was your first impression when you heard about KATANA™ Zirconia Block?

Karim Nasr: I caught a first glimpse of the new material during an event in 2018. KATANA™ Zirconia STML already existed in discs for laboratories and was well known for its aesthetic qualities. Its block version was highly anticipated. But the most amazing feature was the short sintering times announced (with the CEREC SpeedFire in particular). Testing it, I was immediately amazed by the quality of the ceramic and impressed that it is possible to obtain such an aesthetic result (translucency and shade gradation) within such a short time. This is aesthetic zirconia for everyone!

For which indications would you employ KATANA™ Zirconia Block?

Karim Nasr: I reserve the use of KATANA™ Zirconia Block for crowns and for 3-unit bridges. In some cases, I also use it to produce cantilever bridges with a single-retainer design to replace missing incisors (as described by M. Kern). I particularly like it in my cases where I employ a Biologically Oriented Preparation Technique (BOPT) or Vertiprep.

Are there any material features which are particularly interesting for you?

Karim Nasr: Its biomechanical qualities (which are those of zirconia, already mentioned above) already allow me to extend the indications of my chairside restorations. But, in my opinion, the most interesting property is the degree of translucency. Although it is translucent, KATANA™ Zirconia Block is slightly more opaque than glass-ceramics in their lowest degree of translucency. This allows me to use it on discoloured substrates with higher confidence and to avoid the gray effect without having to use an opaque resin cement.

Do you have any recommendations for an ideal processing of KATANA™ Zirconia Block?

Karim Nasr: The use of zirconia in chairside procedures requires certain precautions to be taken in order to achieve the expected results. I have carried out many tests to identify the mistakes not to be made.

First, dry milling is strongly recommended. Nevertheless, it is quite possible to mill in wet environment. However, in this case, it is fundamental to reserve a tank only for the milling of zirconia, never use any lubricant in water (ideally demineralized water), and to have the filters always clean, which means that they need to be cleaned after each milling procedure. After milling, it is important to remove all the powder of zirconia that may have remained on the surface. After dry milling, the restoration must be sprayed with air. The same is the case after the use of burs or polishers to finish the surface. After wet milling, a demineralized water and ultrasound bath may be indicated but is not mandatory.

(Very) fast sintering with CEREC SpeedFire, for example, gives very satisfactory results comparable to conventional slow sintering, which has also been confirmed by scientific literature. Without an appropriate furnace, it is impossible to perform restorations in the same treatment session. However, I do not use CEREC SpeedFire for staining, glazing or micro-layering, but rather a furnace that can be parameterized. Finally, I advise users to finish and glaze only what is necessary (occlusal grooves, vestibular surfaces if visible) and to polish the rest.

Do you have any tips on how to achieve optimal outcomes with KATANA™ Zirconia Block?

Karim Nasr: In anterior cases, I always recommend to perform shading and staining steps in the mouth because there is no better model than the patient himself. Micro-layering in anterior cases makes it possible to improve the aesthetic result with few steps. The 4.4.1. system, which has been specifically developed for KATANA™ Zirconia, makes micro-layering easy to achieve. For polishing, the use of “twist” polishers is recommended. They make it easier to polish all surfaces, especially the occlusal surfaces, both extra-orally and in the mouth. Just like their counterparts for composite, TWIST™ DIA for Zirconia for Zirconia polishers prove to be very effective.

Dr. Nasr, thank you very much.

DR. KARIM NASR

Stratos Chatzichristos just tested the brand-new Esthetic Colorant on restorations made of KATANA™ Zirconia. This is his verdict:

“For me, KATANA™ Zirconia plus Esthetic Colorant is a true killer combination that leaves nothing to be desired. I love to apply the dyeing liquids to my monolithic zirconia restorations to intensify characteristic features and create natural shade effects. Usually, those restorations just need a final layer of glaze to look amazing!”

Would you like to know more about Esthetic Colorant for KATANA Zirconia? Watch this short video explaining the product and highlighting its features and benefits:

Case by Aleksandra Łyżwińska, Warsaw, Poland.

ABSTRACT

Indirect overlays are the contemporary restoration standard for posterior teeth with extensive hard tissue loss. They provide for cuspal coverage, which decreases the likeliness of coronal and/or root fracture. At the same time and in contrast to crowns, overlay preparations minimize the removal of sound tooth structure especially in the cervical region, which is a critical factor.¹ Modern dental resin composites allow for direct cuspal coverage in a single-visit appointment. The results of in-vitro studies suggest that these direct overlays are a suitable alternative to their indirect counterparts in specific situations.^2-6 The following case report is used to describe the direct restoration procedure by means of a maxillary right molar with an extensive, deep MOD lesion.

INTRODUCTION

In the context of treating a tooth with an extensive carious lesion, a biomechanical risk assessment should be performed. The primary method of reducing the likeliness of tooth fracture is treatment with a restoration that provides cuspal coverage. The contemporary gold standard for biomechanically compromised teeth are adhesively cemented overlays as an alternative to crowns.¹ Another option that does not involve labwork is a direct overlay restoration.^2-6 The direct approach is especially suitable for long-term temporization, which may be required during orthodontic treatment, for example.

For those who are still hesitant, we have listed several good reasons to come. Those already planning to come should have a look at why it is worth visiting the Kuraray Noritake Dental booth in Hall 11.3 | Stand E010!

Why visit the International Dental Show 2023 in Cologne?

• Get yourself informed about the latest developments in dentistry
• Meet and chat with like-minded people
• Make investment decisions based on information and a comparison of different products presented at IDS
• Benefit from special trade fair offers
• Enjoy the beautiful city of Cologne

Why visit the Kuraray Noritake Dental booth?

• Learn more about diverse high-quality products we offer
• Obtain first-hand information on these products’ use in live demonstrations and lectures
• Cease the opportunity to experience our latest products yourself
• Engage in fruitful conversations with renowned speakers
• Let our warm-hearted staff answer product- and procedure-specific questions that have been preying on your mind
• Share your own ideas (e.g. about new developments) and demands with our team

We look forward to seeing you in Cologne!

Article by Peter Schouten.

I am frequently asked questions about the intraoral repair of porcelain chippings. To achieve success in repairs, it is essential to consider several important issues.

Perhaps the single most crucial issue to recognise is why the chipping occurred in the first place. For example, if loading stress is the leading cause, this should be considered during the repair.

Other issues to consider are removal of contamination, optimal roughening and chemical activation of the surface, and the prevention of contamination during the repair. Also, a rubber dam should be used to isolate the working field.

FUNDAMENTALS OF ADHESION

Adhesive procedures can be only successful by using the proper substances and methods. Different kinds of surfaces often need different treatments for success. However, the three basic fundamentals of adhesion must be respected to achieve the best results.

1) Mechanical retention through a roughened surface.

2) Chemical activation through chemically active substances.

3) High energetic bonding surface allowing for optimal interaction (wetting capacity) between the surface and the applied medium. Contamination will lower the bonding capacities and must be avoided or removed in any case.

TYPES OF FRACTURE

The most frequent fractures are porcelain only and those that include exposure of the substructure in PFZ or PFM prosthesis.

Many cases present with only limited chipping to the porcelain, for example, at the incisal edge. To achieve a durable repair in this instance, start by increasing the bonding/repair area using a fine diamond burr to create a large bevel. A fine grit burr is preferable over a medium or coarse version because a higher number of shallow grooves deliver a more optimal bonding surface than lesser deeper ones do. Additional roughening of the adherent surface by sandblasting with alumina (50 µm grain size, 2 bar pressure) is highly recommended to increase the surface area further.

When repairing porcelain chippings where the substructure is exposed, it is essential to be aware that multiple substrates are dealt with, indicating a need to adjust the repair protocol accordingly.

Clean the roughened fractured surface thoroughly. KATANA™ Cleaner is the product of choice. It is a safe and easy to use product with high cleaning power. It can be used both intra and extra orally on all kinds of dental substrates. After rinsing and thorough drying, the surface is ready for the next step, chemical activation.

CLEARFIL™ CERAMIC PRIMER PLUS contains both silane and MDP and effectively treats both silica-containing ceramics and metal oxides (zirconia) and metals. After application and thorough drying, the composite restoration can be carried out immediately without an extra bonding step. The composite of choice is a durable flowable, CLEARFIL MAJESTY™ ES Flow. It has high flexural strength, even higher than most paste-type composites. Besides that, it adapts to the surface better and easier. Quick and easy polishing and gloss retention are other highly valuated qualities of CLEARFIL MAJESTY™ ES Flow.

HINTS AND TIPS

• Isolate the working field by using rubber dam
• Bevel the chipping extensively using a fine diamond burr
• Roughen the adherent surface, preferably by sandblasting
• Clean the bonding area with KATANA™ Cleaner
• Apply CLEARFIL™ CERAMIC PRIMER PLUS to the entire bonding area (including exposed zirconia or metal) and dry thoroughly
• Cover exposed metal with a thin layer of CLEARFIL™ ST OPAQUER and light cure
• Repair with a strong flowable composite, such as CLEARFIL MAJESTY™ ES Flow

REPAIR OF PORCELAIN CHIPPINGS VIDEO

Why should you have Esthetic Colorant in your lab?

Esthetic Colorant for “KATANA™ Zirconia” is a set of easy-to-use shading liquids diffusing into the zirconia structure and enabling imitation of variety of internal shade structures.

It is an excellent choice for creating initial characteristics of the restoration before the sintering procedure, and by doing so laying groundwork for the final fast and easy individualization.

Check out the video to learn about the features of Esthetic Colorant and the resulting benefits.

Case by Dr. Yohei Sato, DMD, PhD, Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine, JAPAN and Dr. Keisuke Ihara, CDT, i- Dental Lab, JAPAN.

Fig. 1. The patient visited us with a chief complaint of a desire for improved esthetics of the maxillary right and left lateral incisors.

Fig. 2. A core fabricated from a diagnostic wax model was applied and the necessary clearances were determined.

Fig. 3. Since the teeth are microdonts, the preparation of each abutment was completed by simply exposing a fresh surface to be covered by the laminate veneers.

Fig. 4. A layer of porcelain was applied on the lithium disilicate glass substrate, to make a complete laminate veneer.

Fig. 5. After a trial fitting, the inner surface of the laminate veneer was cleaned with KATANA™ Cleaner. The inner surface was conditioned according to the prosthesis‘ IFU.

Fig. 6. Milling. CLEARFIL™ CERAMIC PRIMER PLUS was applied and dried to silane couple the restoration.

Fig. 7. After a trial fitting, KATANA™ Cleaner was applied to the abutment, and rubbed for more than 10 seconds. Then, it was washed off sufficiently (until the cleaner color had completely disappeared), and dried with compressed air.

Fig. 8. K-ETCHANT Syringe was applied and left for 10 seconds before water-washing and compressed air-drying.

Fig. 9. PANAVIA™ V5 Tooth Primer was applied and left for 20 seconds before compressed-air drying.

Fig. 10. PANAVIA™ Veneer LC Paste was applied to the inner surface of the laminate veneer.

Fig. 11. The laminate veneer was seated and the fit checked. Then, the excess cement was tack-cured (not more than 1 second at any one point) and removed. Finally, the restoration was light-cured and finished.

FINAL SITUATION

Fig. 12. This photo shows the laminate veneer restorations one month after placement. The morphology and color of the right and left lateral incisors have been improved, providing a good balance to the entire anterior dentition.

A discoloured abutment tooth, a metal post or tooth-coloured gum areas: It is not always possible to meet the target tooth or gum shade with a pre-shaded zirconia framework. Porcelain layering on a differently coloured base, however, is likely to deliver unexpected outcomes. The “CERABIEN™ ZR” Shade Base line-up has been developed and recently extended by Kuraray Noritake Dental Inc. for those who would like to avoid surprises and provide for a favourable framework colour, right from the start of porcelain layering. The five new opaque shades deliver approximately five times higher opacity than conventional “CERABIEN™ ZR” Shade Base porcelains, and can mask the base colour much more effectively for even more lifelike restorations.

The “CERABIEN™ ZR” Shade Base opaque shade line-up consists of three shades that reproduce tooth colour: Opaque White as a bleaching shade, Opaque Light as an A2 shade, and Opaque Dark as an A3.5 shade. They may be mixed or applied as delivered to the zirconia framework in thin layers to mask severely discoloured or metal areas. In most situations with a severely discoloured base, a precise matching of the target shade is achieved by applying an opaque shade as a first layer and a target-coloured “CERABIEN™ ZR” Shade Base as a second layer.

The other two new opaque shades – “CERABIEN™ ZR” Opaque Light Tissue and Opaque Dark Tissue – are used in a similar way to create a pink-opaque base in the gum areas of tooth-coloured zirconia frameworks (e.g. made of KATANA™ Zirconia Multi-Layered discs), which is perfect for reproducing gingival colour. Applied as a thin coating, the opaque tissue shades neutralise the tooth colour and their moderate reflection improves the colour effect of the subsequently applied tissue porcelains.

With their high masking ability, the new opaque shades make it even easier to adjust zirconia framework colours for highly aesthetic porcelain layering – no matter whether the base colour of a tissue or tooth area needs to be optimized.

100 years ago, the Association of the German Dental Industry (VDDI) organized its first dental show. Now, the show that became the world’s leading dental trade fair is just about to take place for the 40^th time – and Kuraray Noritake Dental Inc. is going to be part of it. At the company’s booth in Hall 11.3 (Stand E010), visitors are invited to discover new opportunities related to countless innovative products and their benefits – by chatting with the warm-hearted and knowledgeable team or by watching one of the lectures and hands-on demonstrations given by numerous internationally renowned experts.

Among the products worth a closer look are universal excellence solutions. These universally applicable, highly intuitive materials may be used to streamline clinical workflows by reducing the number of required components and work steps. Prominent examples are a universal composite with very few universal shades, a universal adhesive suitable for every etching technique and a universal resin cement working as a single-component solution even on silica-based ceramics.

Dental practitioners with a particular interest in prosthodontics should stop at the desk focusing on indirect restorative workflows. Here, they will find the PANAVIA™ family of resin cements and its three popular members, which are able to cover virtually every need. Moreover, CAD/CAM blocks for chairside processing and KATANA™ Cleaner, a cleaning solution providing for optimal bonding conditions on every surface will be presented here.

The bread and butter of many dental offices is placing direct restorations. However, the patient- and situation-specific demands may vary widely and may require very different types of materials – even within the class of composites. That is why Kuraray Noritake Dental offers various types of restoratives – all with excellent mechanical properties and innovative technologies such as Light Diffusion. They are part of the CLEARFIL MAJESTY™ series, showcased at the booth together with the well-known and researched CLEARFIL adhesives.

Minimally invasive restoration designs and excellent aesthetic despite a high degree of automation have found their way into dental technology. The materials required to realize these patient-centred concepts are found at a dedicated counter of the Kuraray Noritake booth. New in the portfolio: Esthetic Colorant that enables dental technicians to create characteristic shade effects on pre-sintered KATANA™ Zirconia!

A special highlight for dentists and dental technicians will be the lectures and hands-on demonstrations hosted by internationally renowned speakers. They will take place from Wednesday, March 15 to Saturday, March 18, 2023, at the Kuraray Noritake booth. The full programme and additional information about what to expect from Kuraray Noritake Dental in Cologne is available online at www.kuraraynoritake.eu. For those who are unable to attend in person, the presentations will also be broadcasted online.

A particularly chromatic cervical area, pronounced mamelons and translucencies in the incisal area: every natural tooth has its characteristic optical features stemming from its inner structure. Unfortunately, imitating these specific effects by merely adding stains or liquid ceramics to the surface of a monolithic restoration is quite hard to achieve. For this reason, Kuraray Noritake Dental Inc. introduces Esthetic Colorant for “KATANA™ Zirconia” – a set of easy-to-use shading liquids diffusing into the zirconia structure and enabling imitation of variety of internal shade structures. It is an excellent choice for creating initial characteristics of the restoration before the sintering procedure, and by doing so laying groundwork for the final fast and easy individualization.

Esthetic Colorant has been specifically developed for the “KATANA™ Zirconia” Multi-Layered Series to complement the effects obtained from the materials’ multi-layered colour structure. The system consists of twelve shading liquids, which have been optimised to maintain the original flexural strength of the “KATANA™ Zirconia” restoration. After milling, the liquids are applied to the clean surface of a monolithic or anatomically reduced restoration with a metal-free brush, preferably with our Liquid Brush Pen. The Esthetic Colorant then diffuses into the zirconia, and the desired inner shade effects are fixed and revealed after the final sintering procedure. Finishing can be accomplished through a variety of techniques including polishing, glazing and micro-layering.

The compact Esthetic Colorant line-up facilitates inventory management, while the typical effects of natural teeth can be reproduced in a predictable way. Using the new Liquid Brush Pen for Esthetic Colorant, the application procedure is streamlined, as the dental technician is given full control over the amount of shading liquid applied.