By PhD. M. Inokoshi.

INTRODUCTION

Kuraray Noritake Dental Inc. is a manufacturer with a long history and wealth of experience in the field of producing dental materials, including bonds, cements and ceramics. The all-ceramic restorations market, including that for zirconia products, has been growing rapidly around the world since the beginning of the 2000’s. In response to this trend, we have established an integrated production system that can be used to manufacture a wide range of dental zirconia products in-house, from powder to discs.

When we develop new zirconia products, we carefully analyze the characteristics of dental zirconia that are actually demanded by users in the clinical setting and, based on the results of our analysis, we craft new products with these clinically needed characteristics. In our first efforts we focused on developing a dental zirconia that would have a natural tooth color after sintering. We launched “KATANA™ Zirconia”, our first dental zirconia product to span all the VITA^* Classical A1-D4 shade Guide, in 2007. Following in 2013, using our original manufacturing method, we developed and launched “KATANA™ Zirconia” ML (Multi-Layered), a multi-layered zirconia product that produces smooth color gradations like those of natural teeth, avoiding sharp color transition between layers. Then, in 2015, we also released “KATANA™ Zirconia” UTML (Ultra Translucent Multi-Layered) and STML (Super Translucent Multi- Layered). These are highly translucent, multi-layered zirconia products that became other versions of our multi-layered zirconia family. We are one of the pioneering manufacturers of dental zirconia, and as such, we promise ourselves that we will keep on delivering excellent highly-esthetic dental zirconia products to the dental market now and into the future.

^*VITA is a trademark of VITA Zahnfabrik, Bad Sackingen, Germany.

Recent advancements in dental technology have made it possible to use zirconia as a prosthetic material across a wide variety of dental applications, from large-sized implants where great mechanical strength is required, to treatment in the anterior region, where esthetics are of the utmost importance. The material characteristics needed, however, differ from one treated case to another. Many dental zirconia suppliers respond to these therapeutic requirements by offering various types of dental zirconia that feature different levels of mechanical and esthetic properties. This requires dentists and dental technologists in clinical settings to select, from a wide range, the type of zirconia that will be more better appropriate to treat the case they are facing at any given moment. This means it is necessary for each clinic to keep in stock many types of dental zirconia materials with different characteristics, in order to meet the requirements of the wide variety of possible case parameters.

Several dental material manufacturers have responded to these circumstances by offering dental zirconia disc products that have combinations of multiple layers with different levels of translucency and mechanical strength. They claim these products make materials available that can be used to fabricate a wide range of restorations. These products, however, can have serious shortcomings. Some require laborious manufacturing work, tailored to the fabrication of the particular restoration. Others do not include the required high-strength zirconia layer that makes it possible to fabricate a bridge. These products, therefore, may provide no assurance of providing the mechanical strength recommended by ISO for the manufacture of certain restorations. A market need arose for dental zirconia products that could be used easily and safely for the fabrication of a wide range of restorations.

In response to this need, at Kuraray Noritake Dental Inc., we have developed and released “KATANA™ Zirconia” YML(YML), a new type of dental zirconia material that provides the blend of excellent performance variables provided by the “KATANA™ Zirconia” Multi-Layered series. With its well-balanced performance, the YML can be indicated for the fabrication of a wide range of restorations, from large sized ones requiring great mechanical strength to anterior crowns that require a high level of translucency In this paper, we would like to describe YML’s features and the technology behind it. We will also present comparative data collected by Masanao Inokoshi, a professor in the Department of Gerodontology and Oral Rehabilitation at Tokyo Medical and Dental University, Graduate School of Medical and Dental Sciences, on YML and a similar product from the competition.

FEATURES OF THIS PRODUCT AND THE TECHNOLOGY BEHIND IT

Short sintering time

YML can be baked satisfactorily in a short period of time, thanks to our innovative technology. In addition to the conventional sintering schedule of about 7 hours, and even the 90-minute schedule, we have also made it possible to shorten the sintering time further, to a remarkable 54 minutes^*.

^*The material is removed from the furnace at 800°C / 1472°F. Up to 3-unit bridges.

Excellent translucency and great mechanical strength

A YML disc consists of four layers: one Enamel and three Body layers. The top Enamel layer (35% of the total thickness: 750 MPa^*1) is composed of the same zirconia material as “KATANA™ Zirconia” STML, which is highly acclaimed for its excellent translucency. The three Body layers ((1): 1,000 MPa^*1, (2): 1,100 MPa^*1 and (3): 1,100 MPa^*1) that lie below the Enamel layer are made from a new type of zirconia material. Body layer (1) is an intermediate layer that has the desirable translucence of STML. It includes, however, a well-balanced combination of translucency and mechanical strength suitable for the treatment of cases, such as those requiring bridges, which demand these notable characteristics. Body layers (2) and (3) provide the high level of mechanical strength of “KATANA™ Zirconia” HTML suitable for the fabrication of large-sized restorations, along with an improved level of translucency. With its well-balanced combination of translucency and mechanical properties, provided by taking advantage of multiple zirconia ceramics, YML is a product that meets the demand for highly esthetic products. It is suitable for the fabrication of the whole range of restorations, from single crowns to bridges.

^*1 : According to ISO 6872: 2015, three-point bending test.

Multi-layer gradation

Kuraray Noritake Dental Inc. released our first multi-layered zirconia product in 2013. Subsequently, the company launched zirconia products very much appreciated for their smooth transition of color gradation, much like that of natural teeth. We use our own innovative pressing method to manufacture YML. It smooths the change of colors between layers, which provides the desirable feature of a very smooth and natural color transition.

Reduced deformation after sintering

In general, dental zirconia shrinks during the sintering process by about 20 percent in 2 dimensions (50 percent in volume). If shrinkage cannot be controlled adequately, it becomes difficult to fabricate restorations that fit precisely into complicated abutments or margin lines. The shrinkage of zirconia materials varies subtly from one production lot to another, even when the same raw material is used. We appropriate raw material control such as raw material crushing etc., using different sintering shrinkage rates for different production lots. In view of the fact that the sintering shrinkage of zirconia materials requires delicate control, it is not hard to understand that shrinkage control is even more difficult when different zirconia materials are combined into one disc. If the shrinkage rates of the layers of a zirconia disc differ, the restoration will necessarily be deformed during shrinkage. Many users voiced particular concerns about dimensional stability when they were asked about using zirconia discs (which require high precision) for the fabrication of implants. Kuraray Noritake Dental Inc. has an integrated production system that is used to manufacture zirconia products in-house, from the design and manufacture of zirconia powder as a raw material to final products, thus making it possible for us to control the shrinkage rate of zirconia with great accuracy. For this reason, we are able to use zirconia materials with stably controlled shrinkage rates to manufacture YML, even though it consists of multilayers made up of different zirconia materials. This minimizes deformation of restorations after shrinkage.

RESULTS OF A VERIFICATION OF THE PHYSICAL PROPERTIES OF YML AND A REVIEW OF ITS CLINICAL ADVANTAGES

To verify the physical properties of YML, the translucence, mechanical strength and crystalline structure of YML and ZirCAD Prime (Ivoclar Vivadent) were analyzed and compared with one another at the Tokyo Medical and Dental University. Among the physical properties examined, this paper focuses especially on data on the translucency and mechanical strength of each product.

Data on translucency:

Different alphabets indicate a definite difference between groups.

Data Courtesy of PhD. Masanao Inokoshi, Tokyo Medical and Dental University.

The translucency of ZirCAD Prime was significantly higher than that of YML, when a comparison was made at the Enamel layer. This is probably because Prime contains almost no pigment in the Enamel layer, in order to bring out the brightness (whiteness) of the zirconia itself. By contrast, YML contains some pigment, so the product can deliver an optimal level of brightness in the clinical setting. That is, it seems that the addition of pigments leads to a difference in translucency between YML and Prime.

Data collected at Kuraray Noritake Dental on the relative translucency of YML and Prime

Total light transmittance (%) (Illuminant: D65; test specimens with a diameter of 30 mm, and a thickness of 1 mm) Raw material in YML’s Enamel layer (no coloring agent): 49% Prime’s Enamel layer: 49%.

Regarding the layers lying beneath the Enamel, such as the Transition and Body layers, YML was found to be more translucent than Prime. It can be concluded that YML is sufficiently translucent even beneath the layers lying beyond the Enamel layer. This makes it possible to fabricate prostheses with natural tooth colors, when used in combination with an Enamel layer that is suitably adjusted to provide the optimum color.

Mechanical strength data as results of four-point bending test:

Different alphabets indicate a definite difference between groups.

Data Courtesy of PhD. Masanao Inokoshi, Tokyo Medical and Dental University.

The Enamel layer of YML had a significantly greater bending strength than that of Prime. On the other hand, when the bending strength of the Body layers was compared, Prime’s Body layer was the strongest. The three YML Body layers ((1), (2) and (3)) had bending strength values of more than 850 MPa^*2, and there were no significant differences in bending strength among Prime’s Body layer and YML’s Body layers ((1), (2) and (3)).

The results revealed that while YML has small differences in bending strength among the Enamel layer and the three Body layers, Prime has clearly different levels of bending strength between the Body layer and the other two layers. YML’s Body layers (including the intermediate layer) have such a high level of mechanical strength that it is quite feasible to use it to fabricate highly reliable prostheses.

^*2 : According to ISO 6872: 2015, four-point bending test.

LAYERED DESIGN CONCEPT

The guide for fabricating large restorations using YML states the requirement that at least 50% of the connector cross-section should be positioned in the bottom (lower part) of the disc. This means that generally you can meet the requirement of the guide by positioning the restoration at the center of the disc’s four layers. Guides or advices of restoration fabrication for using zirconia discs available in the market may sometimes be complicated to position the restoration as specified in the guide or to position the piece as specified by the guide, which makes it difficult to fabricate a highly esthetic restoration that makes use of the Enamel layer’s better translucency.

When we developed YML, Kuraray Noritake Dental kept in mind that the fabrication guide must be practical, as well as easy. That’s why YML was designed with a sufficiently thick Enamel layer that permits a high level of esthetics for any type of restoration that might be fabricated.

CONCLUSION

“KATANA™ Zirconia” YML is our new zirconia disc product, which features a well-balanced combination of mechanical strength and esthetics. It has been developed by using our innovative zirconia manufacturing technology, as well as bringing together the essence of the development and production technology of multi-layered zirconia discs. We hope YML will be one of the options of choice for zirconia materials available to dentists and dental technologists who need to use multiple zirconia materials for various applications or who have concerns about the mechanical strength and esthetic properties of the zirconia materials they are currently using.

YML LINEUP

How did experts think about the effectiveness of MDP through the years? You can read about it below.

“In particular, primers and composite cements that contain 10-methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) resulted in a relatively high bond strength and durability.”

N. Nagaoka et al: “Chemical interaction mechanism of 10-MDP with zirconia” Nature, Sci Rep. 2017; 7: 45563.

“For most zirconia-bonding techniques, the use of an “MDP-containing primer” also appeared to have a positive effect.”

B. van Meerbeek et al: “Meta-analyis of Bonding Effectiveness to Zirconia Ceramics” J. Dent. Res. 93(4), 2014, 329-334.

“Based on the direct interaction of the phosphate-ester group of MDP with the metal oxides at the zirconia surface, a relatively favourable bonding effectiveness was recorded.”

B. van Meerbeek et al: “Durable bonding to mechanically and/or chemically pre-treated dental zirconia”, J. Dent. 41 (2013) 170-179.

“Clinical data provide strong evidence that air-abrasion at a moderate pressure in combination with using phosphate monomer containing primers and/or luting resins provide long-term durable bonding to glass-infiltrated alumina and zirconia ceramic under the humid and stressful oral conditions.”

M. Kern: “Bonding to oxide ceramics-laboratory testing versus clinical outcome”, Dent. Mater. Vol. 31 (1), 2016, 8–14.

“A high and reliable resin bond to alumina and zirconia ceramics was also achieved with airborne particle abrasion and by using a phosphate monomer (MDP) containing resin composite luting cement.”

M. Özcan et al: “Effect of surface conditioning methods on the bond strength of luting cements to ceramics”, Dent. Mat. 19, 2003, 725-732.

“In the present study, the use of the MDP-containing bonding/silane agent resulted in significantly higher bond strengths before and after long-term storage and thermal cycling with two types of resin luting agents.”

M.B. Blatz et al: “In vitro evaluation of shear bond strengths of resin to densely-sintered highpurity zirconium-oxide ceramic after long-term storage and thermal cycling”, J. Prosth. Dent. 91, 2004, 356-362.

“Dental zirconia can no longer be considered unbondable to tooth tissue (…) This also indicates that Al2O3 sandblasting is best followed by a chemical pre-treatment with an MDP containing primer.”

M. Inokoshi et al: “Meta-analysis of Bonding Effectiveness to Zirconia Ceramics”, J. Dent. Res. 93(4): 329-334, 2014.

“Airborne-particle abrasion of zirconia surface is one of the most-investigated methods, provides good bond strength to zirconia when combined with phosphate ester monomer.”

M. Ferrari et al: “Effect of surface pre-treatments on the zirconia ceramic–resin cement microtensile bond strength”, Dent. Mat. 27, 2011, 1024-1030.

“The data of the present work confirm the assumption of another study [13], that MDP bonds chemically to zirconia ceramic.”

C.H.F. Hämmerle et al: “Effect of thermocycling on bond strength of luting cements to zirconia ceramic”, Dent. Mat. 22, 2006, 195-200.

“An acidic adhesive monomer such as MDP shows chemical bonding to zirconia-based ceramics. The phosphate ester group of the acidic monomer results in chemical bonding to metal oxides (MxOy, oxidized surface of base-metal alloys), zirconia-based ceramics and other ceramics.”

J.M. Powers et al: “Guide to Zirconia Bonding Essentials”, New York, NY: Kuraray America Inc, 2009, 1-13.

Article by Peter Schouten.

We've seen them all: composite fillings that function present clinically, but are too ‘visible’ to be called aesthetic. The much-used term 'white filling' is probably quite appropriate here. In comparison to the tooth structure, these restorations are too opaque, or sometimes too transparent.

How much better would it be if the composite helped to create a seamless transition between tooth structure and composite? The so-called 'blending'.

But what enables this 'blending’ of composite and tooth structure to occur? The secret lies in utilizing the right mix of different filler particles and resins which give CLEARFIL MAJESTY™ ES-2 its light-diffusing properties. By varying the proportion of light-diffusing particles and the amount of pigment, it's possible to create composites with differing light-scattering properties and opacities. The most opaque variants contain more light-diffusing particles and more pigment. The more translucent ones contain obviously less.

All CLEARFIL MAJESTY™ ES-2 variants have the same filler content. This is important, as it means that the mechanical properties of all the CLEARFIL MAJESTY™ ES-2 variants are the same. The more translucent variants contain more barium glass than the more opaque variants. A higher barium glass content can lead to a less workable composite. With CLEARFIL MAJESTY™ ES-2, this is not the case. Kuraray has mastered the silanization process to such an extent that all variants, whether translucent or opaque, have the same filler amount, without compromising on workability.

Light diffusion test

Light diffusion properties are easy to see if the thin composite slices are placed on a black and white paper background and then held a few millimeters above the paper. Composites with high diffusion properties make the black strip virtually invisible. They blend in more readily with their surroundings.

Since 2010, thanks to its increased translucency, KATANA™ HT has become paramount in fully meeting the ever more demanding aesthetics in restorations where a zirconia frame is used in combination with new generation ceramics CZR. Such ceramics feature an enhanced leucite balancing, which makes them stronger and more durable.

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Since 2013, ML-Multi Layer technology has made it possible to skip the infiltration phase through multi-layered dentine/enamel millable discs. Such Multi-layered discs allow CUT-BACK solutions that definitely improve the function-related result as the palatal part of the restoration can be manufactured by using KATANA™ ML Zirconia only. Thus, without limiting the aesthetic results (which are reached by enamel-ceramic LUSTER porcelain with “MICRO LAYERING technique”, the restoration benefits of the low abrasiveness of the functional-occlusal areas which is reached through simple and effective mechanical polishing without either surface staining or glasuring.

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.

Fig. 9.

New generation KATANA™ UTML and STML introduced in 2015 can be used for anterior restoration thanks to the cubic zirconia based products that have been made available to make it possible to conceive a bi-layer to mono-layer transition in most clinical situations.

Cubic zirconia features superior optical behavior. Although mechanically inferior in performance to conventional zirconia, KATANA™ UTML and STML are aging-resistant, while UTML offers the same translucency as lithium disilicate based solution.

“ZERO-CUTBACK technique” is one of the ideal techniques that can be achieved with cubic zirconia solution. They can perfectly replicate digital projects without any need for subsequent layering and can be easily painted and mechanically polished in the palatal area.

Fig. 10.

Fig. 11.

Fig. 12.

Fig. 13.

Fig. 14.

Fig. 15.

Kuraray Noritake Dental has also developed CZR FC Paste Stain with a wide range of coloring pastes specially designed for full anatomical solution of multi-layered zirconia. Their effectiveness is proven to be enhanced when used with “ULTRA MICRO LAYERING technique” on thin glasure or thin transparent ceramic mass.

Another advantage with STML and UTML products is the lower thickness, respectful of the latest micro-invasive dentistry standards and current market requests.

Fig. 16.

Excellent flexural strengths higer than 550/750 MPa allow restoration to feature micro-invasive thicknesses from 0.4 mm on, p.e. on laminates. Unlike PFZ, zirconia lower thicknesses ensure better results.

Fig. 17.

Fig. 18.

Fig. 19.

Fig. 20.

Fig. 21.

Fig. 22.

Above all, new generation zirconia makes the digital work-flow more efficient and performing, from the intra-oral impression to the final product which can be manufactured “model-free”.

Fig. 23.

Fig. 24.

Thus a new procedure standard is introduced, where simplified adhesive cementation through composite cements opens the the way to zirconia-based adhesive restoration techniques. Regarding adhesion, unlike glass-ceramic, zirconia is not etchable, yet it can be fixed through phosphate monomer MDP, i.e. Panavia™ V5

Fig. 29.

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Fig. 31.

Fig. 32.

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Fig. 35.

Dentist:

DANIELE RONDONI, MDT

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

By Univ.-Prof. Dr. Florian Beuer MME

There is still some confusion among dental practitioners about how to cement zirconia restorations. In general, all types of cements – adhesive or self-adhesive resin cements and conventional cements – are compatible with all types of zirconia. The actual choice should be based on the restoration design (retentive or non-retentive), the translucency of the zirconia and the clinical situation (feasibility of working field isolation).

When to use which type of cement

The use of adhesive resin cements is mandatory whenever the highest possible bond strength is required. This is the case with one-wing Maryland bridges and other types of restorations lacking micromechanical retention, and with two-piece implant abutments.

In some other situations where retention is not an issue, adhesive or self-adhesive resin cements may have a beneficial effect. The major reason is their more esthetic appearance compared to conventional cements, which offers advantages whenever a highly translucent restorative material is used (e.g. KATANA Zirconia UTML). An important precondition for adhesive luting, however, is a dry working field. Consequently, conventional cements are preferable in the context of placing crowns, bridges and other types of restorations with retentive designs whenever opaque zirconia framework materials are used and / or it is difficult to ensure a dry working field.

How to pre-treat the tooth and the restoration

The highest bond strength of adhesive resin cements to zirconia is obtained after sandblasting with alumina (particle size max. 50 µm, pressure approx. 1 bar). Hence, this procedure is highly recommended. Subsequent steps may be different depending on the cement system employed and should be carried out according to the manufacturer’s instructions for use. On the side of the tooth, enamel etching is important independent of the products used.

Which products to use

In each of the cement classes, there are many different products to choose from. My recommendation is to select a proven and easy-to-use luting material. Among those products achieving the same high bond strength, the solution requiring the fewest application steps seems preferable as it reduces the risk of application errors. At Charité – University Medicine Berlin, we count on PANAVIA cements, which are based on many years of expertise in developing products for adhesive luting of zirconia.

Dentist:

PROF. DR. FLORIAN BEUER

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

With CLEARFIL MAJESTY™ ES-2, the shade transition from composite to tooth is virtually invisible. The secret to this lies in light diffusion technology. How does this work?

Before we discuss the technology in detail, here are some more information about our CLEARFIL MAJESTY™ ES-2 composites. All CLEARFIL MAJESTY™ ES-2 composites are suitable for both anterior and posterior applications. The different variants within the ES-2 family are characterized by supreme handling and a long working time, and the fact that they do not slump during modeling. A key feature of these composites is the ease with which restorations blend into their surroundings. This results in durable and aesthetic restorations.

In CLEARFIL MAJESTY™ ES-2 composites, two types of fillers are used. Barium glass particles form the basis of the filler. Alongside this, advanced prepolymerized filler particles are added. The latter type is called light diffusion filler, since it is primarily these filler particles that achieve a light-scattering effect within the composite.

The way in which a restoration 'adjusts itself', to the shade of the tooth to be restored, is not the same for all composites. Most composite manufacturers make use of the so-called 'chameleon effect'. A composite that is sufficiently translucent allows light to pass through. Light is reflected off the walls of the cavity, whereby the composite restoration assumes the shade of the adjacent tooth structure.

In cavities that aren't too large with a sufficient amount of surrounding tooth structure, this chameleon effect works well enough. However, with larger cavities or in the absence of underlying tooth structure, as is often the case with anterior restorations, the aesthetic blending effect is limited. The brightness is far from satisfactory, and the restoration looks gray.

At Kuraray Noritake Dental Inc., we do things differently.

Besides the optimized translucency in CLEARFIL MAJESTY™ ES-2 composites, it's the light diffusion technology that makes the restoration blend seamlessly with the adjacent tooth structure. Thanks to the combination of these two parameters — translucency and light diffusion — the capabilities are far more extensive than with just translucency.

The different dental tissues have different opacities. Enamel is more translucent than dentin. However, the degree of translucency/opacity of both tissues is not always the same. Age, thickness of the structure and various intrinsic and extrinsic factors all play a role.

Depending on the desired end result, the most appropriate member(s) of the CLEARFIL MAJESTY™ ES-2 family is/are selected for the restoration.

In aesthetic restorations in which opacity differences need to be considered, a layering system is necessary. More uniform restorations are easily constructed with a composite that has broad shade and opacity coverage.

CLEARFIL MAJESTY™ ES-2 Premium for highly esthetic restorations.

CLEARFIL MAJESTY™ ES-2 Universal for routine aesthetic restorations involving few or no opacity differences.

By Kazunobu Yamada, RDT

With the new KATANA™ Zirconia YML it is extraordinarily easy to produce beautiful restorations. Brilliance and vitality may be added simply by applying CERABIEN™ ZR FC Paste Stain to the monolithic restoration after surface preparation.

A possible technique is demonstrated by Kazunobu Yamada, RDT, in this video.

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.”

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.

The introduction of universal composites, which are not only universal in terms of application range but also in terms of shade adaptation, effectively marks the dawn of a new type of composite. This prompts a reinterpretation of the term "universal composite."

CLEARFIL MAJESTY™ ES-2 is a nanohybrid composite family. Nowadays, nanohybrid composites are commonly used as universal composites. They have a high filler content, they are strong, and they have exceptionally good polishability characteristics¹.

The newest variant in the CLEARFIL MAJESTY™ ES-2 range is CLEARFIL MAJESTY™ ES-2 Universal shade concept. For this composite; we expand the definition of universal and include shade coverage.

Posteriorly, a single material in a single shade is sufficient to cover the entire VITA™ range. This means that no shade determination is required. For the anterior zone, we offer two shade variants: a lighter and a darker variant (UL and UD). The lighter variant is used in the A1-A2 range and the darker for shades from A3 onwards. There is sufficient overlap between UL and UD ensuring no specific shade determination is necessary.

Finally, for situations that require extra lightness and brightness, an additional UW shade is available.

What makes CLEARFIL MAJESTY™ ES-2 Universal unique in comparison to other universal or single-shade composites?
The difference with CLEARFIL MAJESTY™ ES-2 Universal, is that without using an additional opaque composite, sometimes called a blocker, a successful, superbly matching restoration can be constructed. Not only with smaller cavities, but also with larger class I and II restorations. And, when used anteriorly, even an extensive Class IV restoration can be successfully constructed using CLEARFIL MAJESTY™ ES-2 Universal. So, it is not only for those small class III or V lesions.

Why Kuraray Noritake Dental Inc. can do this where others cannot, is to a large extent, thanks to optimized light diffusion technology (LDT). By using this technology in composites with the right translucency, the light is scattered and reflected in such a way that the composite blends in with the surrounding tooth structure.

Where others use the widely-employed chameleon effect, Kuraray Noritake Dental Inc. adds an extra dimension in the form of LDT. With the chameleon effect, light passes through the material and is reflected off the walls of the cavity. The perceived shade of the restoration is therefore the shade of the cavity walls. If the cavity is too large, thus requiring a larger amount of filling material, the light has to travel further and a large proportion of the light is absorbed. With this, the brightness of the restoration is reduced and the shade of the cavity walls no longer accurately reflected.

Our LDT allows light to be scattered within the composite itself, in addition to being reflected off the cavity walls. As a result, CLEARFIL MAJESTYTM ES-2 Universal is a particularly forgiving composite. This feature will be familiar to those who have used CLEARFIL MAJESTY™ ES-2 family products before.

CLEARFIL MAJESTY™ ES-2 Universal is the result of sophisticated filler, matrix and silane technology. It offers a solution for all your routine composite work. A consistently superb restoration where shade determination is a thing of the past.

Reference

¹ Ilie, N., & Hickel, R. (2011). Resin composite restorative materials. Aust Dent J, 56 Suppl 1, 59-66. doi:10.1111/j.1834-7819.2010.01296.x