With so many different adhesives, cements, and restorative materials available on the dental market, it seems difficult to decide which products are best suited to fulfill the individual requirements. A direct comparison obtained through testing of all products in the dental office is simply impossible due to the great number of available solutions. Laboratory investigations provide information about specific product properties, but usually cannot create the overall picture. Moreover, the results of different tests are barely comparable due to variations in test conditions. Clinical study results are very useful as they shed light on clinical (long-term) performance of selected materials, but they are usually published years after a product’s launch. Hence, they are not available in the early stages. A great source of information are practice-based evaluations, as they support potential users in identifying high-quality dental materials.

One of the institutions conducting and publishing practice-based clinical evaluations and product performance tests is the US-based DENTAL ADVISOR. Once per year, the dental materials and equipment with the best performance receive a Top Product or Preferred Product Award. The list of winners is published online (www.dentaladvisor.com) and in the January-February issue of the DENTAL ADVISOR. In 2021, numerous products from Kuraray Noritake Dental Inc. were among the award winners.

Top Product Awards

CLEARFIL™ SE Protect received a Top Product Award in the category Direct Restoratives, Bonding Agent: Self-Etch. The self-etch adhesive is based on the formulation of the gold standard two-step self-etch adhesive CLEARFIL™ SE BOND but contains an extra MDPB monomer offering an antibacterial cavity-cleansing effect and fluoride for long-term fluoride release. The honoring of the DENTAL ADVISOR is based on a material test carried out by 13 DENTAL ADVISOR consultants and editors in their dental offices for six weeks. Due to its excellent performance, the antibacterial self-etch adhesive received a 98 percent clinical rating.

For the sixth year in a row, the Top Product Award in the category Direct Restoratives, Composite: Highly Filled Flowable went to CLEARFIL MAJESTY™ ES Flow.

The universal flowable composite that also became the Editor’s Choice comes in three different levels of flowability, from high to super low*. This enables the user to choose the right viscosity for every clinical situation – with the high flowability variant being the perfect choice for cavity lining and as a resin coat in IDS procedures, and the super low flowability option being specifically suited for direct veneer procedures and even for build-up of posterior cusps etc. The universal flowable composite was tested by 29 consultants of the DENTAL ADVISOR in more than 900 clinical applications. The evaluated properties – placement/handling, aesthetics, viscosity and polishability – were rated “excellent”. This led to a recommendation rate of 100 percent and a 98 percent overall clinical rating.

^{*DENTAL ADVISOR evaluated only the standard level of flowability (Low), because other two variants are not available in US.}

A product that earned recognition from the Dental Advisor for the seventh time already is TEETHMATE™ DESENSITIZER for hypersensitivity treatment.

The product that won a Top Product Award this year was designed to create hydroxyapatite (HAp), which is able to occlude open dentinal tubules and enamel cracks. This leads to a significant reduction of hypersensitivities when applied to exposed, mechanically treated or freshly prepared dentin. When used in the context of restorative treatment, TEETHMATE™ DESENSITIZER does not have a negative effect on the bond strength of dental adhesives or cements. A six-month clinical evaluation conducted by the DENTAL ADVISOR involving 27 patients with gingival recession-related hypersensitivity revealed that the use of the product is very effective in providing immediate and even long-term (six-months) hypersensitivity relief. This resulted in an excellent rating with a score of 96 percent.

In the category Self-Adhesive Cement, an additional Top Product Award went to PANAVIA™ SA Cement Plus. The dual-cure self-adhesive resin cement stands out due to its ease of use, favorable viscosity and an easy excess removal feature after tack-curing.

Preferred Products

Among the 2021 Preferred Products that also received an Editor’s Choice label is PANAVIA™ SA Cement Universal. The Top Product Award winning self-adhesive universal resin cement from 2020 contains the unique LCSi monomer. This monomer is a silane coupling agent, which has a unique long carbon chain in its molecule. This carbon chain establishes a durable, chemical bond with porcelain, lithium disilicate and composite resin without the need for a separate silane containing primer. The other key technology present in the formulation is the original MDP monomer, which ensures chemical reactiveness with zirconia, dentin and enamel. Together, the technologies ensure that PANAVIA™ SA Cement Universal produces a strong and durable bond with virtually every restorative material without the need for a separate primer. Its handling characteristics, aesthetics and gingival friendliness received very good to excellent ratings from 31 clinical evaluators, who used the cement in 516 applications. The result of the overall clinical rating was 96 percent.

Moreover, CLEARFIL™ Universal Bond Quick was honored as a Preferred Product by the Dental Advisor consultants for the second consecutive year.

The universal bonding agent may be applied using the self-etch technique or – together with K-ETCHANT syringe – in the selective enamel etch or total-etch technique. Containing our rapid bond technology – a combination of the original MDP monomer with innovative hydrophilic amide monomers – the adhesive works instantly and without the need for extended exposure times, application of multiple layers or extensive rubbing into the tooth structure. The fast and easy application procedure was one of the main reasons for the consultants of the DENTAL ADVISOR to select CLEARFIL™ Universal Bond Quick as a Preferred Product and Editor’s Choice with a 98 percent score in a clinical evaluation.

Finally, CLEARFIL™ CERAMIC PRIMER PLUS became a Preferred Product in 2019, 2020 and 2021, and an Editor’s Choice in 2021. It contains the original MDP monomer and a silane monomer, which ensure excellent bond strength to all kinds of restorative materials, i.e., to silica-based ceramics, zirconia, composites and even metals. Users benefit from procedural simplicity as the product is just applied and dried to the bonding surface after the recommended pretreatment. In a clinical evaluation, the product received a recommendation rate of 96 percent and a 96 percent overall score from the DENTAL ADVISOR consultants.

Conclusion

Most of the Kuraray Noritake Dental products that received an award this year are based on resin technologies, one of our key competencies. In the 1980s, we developed the original MDP monomer, a functional monomer, which is an essential component of any adhesive product we introduced down to the present day, including the award-winning CLEARFIL™ SE Protect, PANAVIA™ SA Cement Universal, CLEARFIL™ Universal Bond Quick and CLEARFIL™ CERAMIC PRIMER PLUS. This is only one of our many areas of expertise. We also provide users with preventive products and a whole range of restorative materials – from composite filling materials like CLEARFIL MAJESTY™ ES Flow to dental ceramics like KATANA™ Zirconia UTML, STML and HTML. We see the winning of the awards as a positive proof of a reliable product performance that supports dental practitioners in reaching their own goals.

Interview with Dr Imad Ghandour

In recent years, zirconia has emerged as the preferred choice for dentists who wish to perform restorative procedures with a reliable and metal-free material. With the recent development of multi-layered aesthetic high-translucency options, zirconia’s popularity has further increased. In comparison to the opaque whiteness of older generations of zirconia, these newer versions have an enhanced appearance and functionality that makes them suitable for natural-looking anterior restorations.

Kuraray Noritake Dental’s KATANA Zirconia disc range is made with a proprietary zirconia powder - processed in-house - that gives it its natural appearance. Suitable for zirconia prostheses, from single crown to full arch, it is an ideal option for restorations in both the anterior and posterior regions. We spoke with Dr Imad Ghandour, a prosthodontist with a strong scientific background and a private practice in Le Cannet in France, about his experiences with the KATANA Zirconia range in restorative procedures.

Dr Ghandour, when did you first start using zirconia as a material for your restorations?

In 1998, when I was still sintering manually, I began using zirconia alumina. It was nice to have an alternative to metal alloys that was much more aesthetic. From 2003, however, I started with VITA blocks, but only for frameworks - I would still build up with ceramics. Now, with so much of dentistry being digitally focused, there is a need for a material that can be milled without changing anything in the morphology of the teeth. Why? Because we need to be able to reproduce the treatment plan as accurately as possible. Simply put, the KATANA Zirconia range solves this need for me.

With respect to dentistry being digitally focused, how has this changed the role of the dentist regarding performing restorative procedures?

Well, it is clear that we have entered the age of digital dentistry. Around 80 per cent of restorations are conducted via CAD/CAM systems and without dentists even touching the materials themselves. There are great advances being made in the technologies that are available for everyday use in dental practices worldwide, and many of them can be used to assist dentists performing restorative procedures. It is important, though, to keep in mind that these technological advancements alone will not lead to better results - they should supplement the requisite hands-on skills and techniques that all dentists must first learn. With this base of fundamentals, we can then use digital dentistry to make restorative procedures more predictable and reproducible. Of course, to ensure the best results in restorative procedures, dentists also need to use the materials that have the best aesthetic and mechanical properties.

For how long have you been using Kuraray Noritake Dental’s KATANA Zirconia range, and what has your experience been?

I have been using KATANA Zirconia for a little bit more than one year. In that time, I have primarily used the KATANA Zirconia STML (Super Translucent Multi Layered) line and have been pleasantly surprised by how natural-looking the restorations I have made with the material are. For example, when I sinter a crown made of Katana Zirconia STML, I am amazed at how much the sintered material is reminiscent of a pearl - it truly brings to mind the idea of one’s teeth being one’s pearly whites.

When using KATANA, how do you ensure that you select the correct shade to achieve a natural look?

Firstly, no one - not a dentist nor a dental technician - can be absolutely certain that the shade and chroma of the restoration that is in one’s hand will be the same once it is in position in the oral cavity. This is due to the complexities of the oral environment - the pinkness of the gingivae, for one, can have a large impact on how the restoration appears, often making it seem far duller than it does in the light of a dental laboratory. This can cause dental practitioners to compensate and make prostheses that appear far brighter than they will when they are in place.

With a product like KATANA and its related glazing materials, however, I can create crowns and other restorations that have an optimal fluorescence and translucency and are able to maintain their shading better than any other ceramic material I have used. I am able to select a shade with the confidence that it will look exactly the same once placed inside the mouth, with its chroma remaining unabsorbed by the gingiva. Achieving a natural look, then, depends on choosing a shade that is as close to that of the surrounding dentition as possible. Since KATANA Zirconia UTML (Ultra Translucent Multi Layered) is available in 16 standard shades and a further four enamel shades, there is no shortage of options in this regard.

How does the multi-layered technology of KATANA Zirconia help you to achieve optimal and natural-looking aesthetic results?

Well, firstly, the layering of the material is designed to replicate the colour and translucency progression of natural teeth, which allows for restorations to blend in as much as possible. This multi-layered technology has also proved itself to be very handy when I am sintering crowns made of KATANA Zirconia. Simply put, if one sinters a crown quickly, it will be a little more opaque. If one sinters it at a higher temperature and quite slowly, it will be much more translucent. The multi-layered aspect of KATANA Zirconia is excellent in that it gives me the ability to make restorations more or less translucent depending on what is required.

With 40 years of success in the commercial dental products market, Kuraray Noritake Dental has firmly established its commitment to providing leading-edge solutions for adhesive dentistry. The 1983 introduction of the PANAVIA™ EX resin cement, which utilized Kuraray’s original MDP monomer technology, set the industry standard for adhesion and has continued to do so for over 30 years since. With PANAVIA™ V5, and PANAVIA™ SA Cement Universal which is the latest addition to PANAVIA™ family, Kuraray Noritake Dental presents a pair of resin cements designed for strong, durable bonding for zirconia-based and other restorations.

PANAVIA™ V5

PANAVIA™ V5 is a resin cement with exceptional procedural simplicity and predictability. It sets a new standard for adhesion to the KATANA™ Zirconia Block or other zirconia, allowing for self-cure dentine bond strengths equal to our gold-standard light-cure bonding agent, CLEARFIL™ SE BOND. PANAVIA™ V5 offers natural aesthetic stability in shading through its amine-free paste, which is available in five shades and has been scientifically proven to demonstrate a lower level of post-curing colour variance than other cements.

PANAVIA™ SA Cement Universal

PANAVIA™ SA Cement Universal is a forerunner in self-adhesive resin cements that adheres virtually to all materials including glass ceramics. The original silane coupling agent, LCSi monomer, incorporated in the paste creates a strong chemical bond to porcelain, lithium disilicate and composite resin. Available in an automix or handmix option, its high concentration of MDP monomer allows for increased chemical reactiveness with zirconia, which, combined with mechanical retention created by sandblasting, has been demonstrated as crucial for durable bonding to this material. Building upon the success of our PANAVIA™ SA Cement Plus, it offers a wide range of indications for adhesion and is suitable for crowns/bridges, inlays/onlays, posts, and even adhesion bridges.

By Peter Schouten, Technical Manager Kuraray Europe Benelux

Kuraray Noritake’s self-adhesive cement series, PANAVIA™ SA Cement Universal, has evolved through several stages of development since it was first introduced as “CLEARFIL™ SA Cement”. Over time, various improvements have been implemented, bringing us to our latest product: PANAVIA™ SA Cement Universal. Improvements include: strengthening of the bonding power to dental tissue, increasing the storage temperature to room temperature and extending the shelf life to three years. What remained the same - the easy removal of any excess cement, the moisture tolerance and the integration of the original MDP monomer.

The original MDP enables PANAVIA™ SA Cement Universal to be bonded to dental tissue as well as to metals and zirconia ceramics. Until recently, the chemical bonding of glass-based materials such as porcelain, glass ceramics, including lithium disilicate, and composite, was only possible with an additional silane-based primer.

With the introduction of PANAVIA™ SA Cement Universal the silanisation step has become redundant. Instead, the silane has been incorporated into the PANAVIA™ SA Cement Universal paste. As a result, there is only one single universal procedure, without the need for separate primers.

LCSi

Adding silane to the paste sounds easy. However, there are some limiting factors. For example, keeping silane in the form of γ-MPS (γ-methacryloxypropyltrimethoxysilane) active for a long time is a challenge. This is partly due to γ-MPS’ hydrophilic nature. Contact with water under acidic condition results in hydrolysis of alkoxy groups of silane. Therefore, it is best to use a more hydrophobic and thus stable silane and to avoid bringing it into contact with water and acid prematurely.

We have been using a long-chain silane (LCSi) for some time in a number of our superior composites, such as CLEARFIL™ MAJESTY™ Posterior and CLEARFIL™ MAJESTY™ ES Flow. However it’s the first time we have used it in a cement.

This unique silane has long hydrocarbon spacer (the hydrocarbon chain between the silanol group and the methacrylate group) which makes it more hydrophobic and stable than the small γ-MPS molecule. The reaction with the silica particles in the glass-based materials is expected to be also more orderly and faster. The result is a more optimally bonded surface with a greater resistance to hydrolysis.

A great deal of thought has gone into combatting the degradation of silanes in PANAVIA™ SA Cement Universal. It was decided to separate the more hydrophilic components from the hydrophobic ones so they only come together when the paste is mixed. This is why we are able to achieve a three-year shelf life, even when stored at room temperature.

Research

It’s not only in-house data that show comparable or even better bonding of PANAVIA™ SA Cement Universal to glass-based materials, than with its previous version, PANAVIA™ SA Cement Plus, in combination with CLEARFIL™ CERAMIC PRIMER PLUS. The first results from independent research are also strongly supporting this.

With PANAVIA™ SA Cement Universal, there is now a self-adhesive resin cement on the market that allows virtually all indirect materials to be bonded directly without the intervention of primers or bonding.

By Peter Schouten, Technical Manager Kuraray Europe Benelux

CLEARFIL MAJESTY™ ES-2 is the composite that allows intuitive creation of natural-looking restorations. The combination of its self-adaptive capacity, thanks to the use of light diffusion technology, its natural fluorescence, high filler content, fine workability and exceptional polishability provide outstanding aesthetic results.

CLEARFIL MAJESTY™ ES-2 is a forgiving composite. It blends seamlessly with the adjacent tooth structure. This is because CLEARFIL MAJESTY™ ES-2 incorporates light diffusing technology. This makes it possible to cover the entire VITA range using only VITA A shades.

In our endeavors to reproduce nature, we need to step away from the notion that artificial materials do all the work for us. Especially enamel is a difficult kind of tissue to replace with artificial materials like composite. When you replace natural enamel with translucent composite you almost never reach the desired goal! Why is this? The most determinant factor is the difference in value. Natural enamel increases in value in proportion to its thickness, while for (translucent) composite the value decreases.

In certain situations, for instance for the reproduction of the incisal edge of a central incisor, where a translucent zone is naturally present, the use of a more or less translucent composite is needed. However, it is often the opacity of a composite that we wish to harness in order to cover up underlying (irregular) discoloration. To do this, the use of a translucent composite is clearly not desirable. In this situation, the most opaque variant is your first choice of composite.

You've probably been there: applying anatomical layering techniques with a composite system, only to arrive at a somewhat disappointing result that looks too gray. This can be explained by the fact that, as a manufacturer - and we're certainly not alone here - we have created some confusion by giving composites names such as Dentin and, worse still, Enamel. These names suggest that these materials can be used as a replacement for natural dental tissue. Due to the totally different optical properties of each dental tissue and composite, this can only be achieved within a frequently too narrow spectrum. Therefore, when it comes to the use of the more translucent composite variants, I recommend a cautious approach. Only use such variants where transparency is required.

...it is often the opacity of a composite that we wish to harness in order to cover up underlying (irregular) discoloration. To do this, the use of a translucent composite is clearly not desirable. In this situation, the most opaque variant is your first choice of composite.

Kuraray Noritake Dental offers three basic opacities within the CLEARFIL MAJESTY™ family. These three variants enable you to create transparency where necessary, or indeed to avoid it in zones where greater coverage is required. The most opaque variant within the CLEARFIL MAJESTY™ ES-2 family is Premium Dentin. The semi-opaque variant Classic and the semi-translucent variant Premium Enamel.

The challenging class IV restoration as an example. The tendency exists to use dentin composite up to the dentin-enamel junction. Don't do this, but instead apply it right up to the outermost edge of the restoration. This means also covering the beveled enamel. Depending on the desired end result, you should only use the more translucent variants, Classic or Premium Enamel, in the incisal third.

Working with different variants of CLEARFIL MAJESTY™ ES-2 in one restoration where more than one variant end at the surface the transition from one type to the other is totally seamless. Since all three variants have virtually the same high filler percentages and filler type. During finishing you won't even notice the transition between the different variants. The polishability of all the variants is also identical.

All these qualities make CLEARFIL MAJESTY™ ES-2 your aesthetic composite for the effortless creation of natural-looking restorations. Both anterior and posterior.

In this interview, Dr Adham Elsayed, certified specialist in dental prosthodontics and implants and clinical and scientific manager at Kuraray Noritake Dental, details the benefits of the company’s new CLEARFIL MAJESTY™ ES-2 Universal composite and explains its application in the daily dental workflow.

Though dentists are becoming increasingly specialised, there’s a growing demand for products that can be used for all indications. How does CLEARFIL MAJESTY™ ES-2 Universal fit this model?

First, we need to explain the meaning of the term ‘universal’ in this context. Previously, there have been two types of composites that differ according to the area of application: anterior composites, used in Class III, IV and V restorations where the aesthetic outcome is the priority, and posterior composites, in which the mechanical properties like strength and wear rate are more important. Universal composites, then, are those that can be used for all types of restorations in the anterior as well as the posterior region.

Another way in which ‘universal’ can be considered is in relation to shade. In this case, the term is used to describe a restorative composite system that exists in fewer shades, one that can adapt to the tooth structure independent of the colour of the tooth. A major benefit of this type of composites is that it offers a simplified workflow.

CLEARFIL MAJESTY™ ES-2 Universal is essentially universal in both meanings: it is one system that can be used for posterior and anterior restorations, and it is also provided in only three shades—one for posterior, and two for anterior.

Universal products, whether they are luting cements, bonding agents or composites, are attractive to dentists as long as they offer simplification of the treatment procedure without compromising quality and durability.

How does CLEARFIL MAJESTY™ ES-2 Universal build upon the success of the CLEARFIL MAJESTY™ range?

The CLEARFIL MAJESTY™ family is very well established at this stage. It includes such products as CLEARFIL MAJESTY™ Posterior, one of the most popular posterior composites owing to its superior mechanical properties and minimal polymerisation shrinkage. CLEARFIL MAJESTY™ ES-2 is an extensive system that is highly beneficial thanks to its outstanding optical properties and ability to produce high-end aesthetics in the anterior region using Kuraray Noritake Dental’s multilayering technique. The three flowable alternatives of CLEARFIL MAJESTY™ ES Flow, with different consistencies, are also other successful members of the family.

Kuraray Noritake Dental now continues the success story of CLEARFIL MAJESTY™ with the latest innovative product that can change the definition of the universal composite. CLEARFIL MAJESTY™ ES-2 Universal incorporates several attributes from the well-established ES-2 and ES Flow, including Kuraray Noritake Dental’s light diffusion technology (LDT).

Speaking of LDT—how does this technology benefit the composite?

LDT allows the material to scatter and reflect light rays at many different angles, which, in turn, allows the composite restoration to diffuse light in a similar way to the surrounding tooth structure. Hence, it eliminates aesthetic problems like the visibility of restoration and preparation borders. Thanks to innovative LDT, optimal particle fillers and opacity, CLEARFIL MAJESTY™ ES-2 Universal blends seamlessly with the surrounding tooth structure and emulates natural teeth, eliminating the need for shade selection.

As you mentioned, CLEARFIL MAJESTY™ ES-2 Universal comes with one shade for posterior restorations and two for anterior restorations. Can such a reduced shade range still truly deliver aesthetic restorations?

CLEARFIL MAJESTY™ ES-2 Universal is not the first composite on the market with a reduced shade system. However, we can safely say that it is the first to focus on aesthetics and not just on reducing the number of shades.

We know from experience that using one-shade composite systems in the anterior region mostly leads to unsatisfying aesthetic results, even with the use of an opaquer composite to reduce shade-matching interference. This is due to the fact that trying to provide one shade for all posterior and anterior restorations, and for all tooth shades, compromises the aesthetic to a high extent. In other words, using a highly translucent material to try to match all restorations and shades will result in the interference of other objects in the mouth, such as the tongue, gingivae and so on.

Kuraray Noritake understood this fact well and solved the problem by introducing three shades with translucencies designed to match specific indications. It is important to note the simplicity of the workflow, since only one syringe per restoration is required. This makes CLEARFIL Majesty™ ES-2 Universal a true game-changer, as it provides the perfect match between simplicity and aesthetics.

What other advantages does this new composite deliver?

Other advantages include the superior mechanical properties for which the CLEARFIL MAJESTY™ family is already known, such as favourable wear properties, low shrinkage stress and high strength. It can be polished easily and retains its gloss. Moreover, the handling of the material is a huge advantage: this includes a long working time of about 270 seconds under ambient light. It is non-sticky and can be sculpted easily.

Which dental professionals would benefit most from this product?

The perfect match between simplicity and aesthetics offers the clinician several benefits. It delivers a very straightforward time-saving procedure without compromising aesthetic results. There is no need for exact shade selection, thereby excluding visible errors of non-matching shades, and there is also a reduced amount of material stock needed. Therefore, in my opinion, this should be the product of choice for most cases in everyday practice.

Advances and developments in dental materials are rapidly accelerating, and clinicians should integrate these innovations and make their daily practice more efficient with simplified workflows, time-saving procedures, fewer material selections and, accordingly, less technique sensitivity and less need for dental practice personnel to become acquainted with an abundance of materials.

No shade taking needed. Just one shade to cover all posterior cases. Even the larger Class I's and II's!

A guideline with regard to contemporary materials

The retention of the fixed prosthodontic restorations is a critical factor for the long-term success, as the loss of crown retention is one of the main reasons for failure of crowns and fixed dental prosthesis (FDP) ^{(1, 2)}. There are three main elements that need to be considered to achieve proper retention of the restorations; the tooth preparation, the restorative material and the luting agent.

TOOTH PREPARATION

During tooth preparation there are some important features to be considered, such as the height, angle and surface texture of the abutment tooth, in order to achieve an adequate retention and resistance form which provide stability of the restorations to resist dislodgment and subsequent loss ⁽³⁾. Retention form is responsible for counteracting tensile stresses, whereas resistance form counteracts shear stresses ⁽⁴⁾.

In order to achieve a sufficient retention and resistance form for full coverage crowns it is recommended that the height of the abutment tooth should be at least 4 mm and that the optimal convergence angle should range from 6 to 12 degrees with a maximum of 15 degrees ^{(1, 5-8)}.

RESTORATIVE MATERIAL

With the continuous introduction of new restorative materials to the dental market it is important to take into consideration the different mechanical properties of the various materials. The composition and the surface properties of the material have a decisive role in the ability to accomplish mechanical and/or chemical attachment to the restoration and therefore achieving required retention.

LUTING AGENT

The luting agent is the connection between the tooth and the restoration. Proper luting of indirect restoration is critical in achieving long-term success as it highly influences the retention of the restoration as well as tightly sealing the gap between the restoration and the tooth. Although there are several classifications for the definitive luting agents, they can be , however, classified into two main categories based on the ability to achieve chemical connection to different substrates; conventional (e.g. zinc phosphate, glass-ionomer and resin-modified glass-ionomer cements) and adhesives. Most commonly used and best documented adhesive luting agents are the adhesive composite resin cements.

Composite resin cements can be further classified according to the chemical composition into traditional full-adhesive resin cement and self-adhesive resin cements, both also differ in the bonding procedure. The full-adhesive resin cements require pre-treatment of the tooth structure and restorative material using separate adhesive systems. In this combination of the resin cement and the adhesive system, very durable chemical bonding can be reached.

To simplify the luting procedure and eliminate the need of using several components, the self-adhesive resin cements are a good choice for the daily busy practice, in which reliable bonding can be achieved in only one simple step of cement application, mostly without additional primers or bonding agents.

With the availability of different types of cements, the decision of choosing the suitable luting agent and method can be confusing for the practitioner. Especially with the wide use of contemporary restorative materials such as new generations of highly translucent zirconia as well as reinforced-composites, it is important to take into consideration that the properties of such materials differ highly from metal or earlier generations of zirconia. Subsequently the choice of the luting agent must be appropriate to achieve satisfying results and long-term success. Therefore, in this article, the authors aim to provide insights for the clinicians on choosing the correct luting agent that can help achieve satisfactory results for the dentist as well as the patients.

CONVENTIONAL CEMENTATION OR ADHESIVE LUTING?

The choice of whether to use a conventional cement or an adhesive resin cement depends on several factors, the key factors are:

1. Retention and resistance form of the abutment tooth.
2. Mechanical and optical properties of the restorative material (flexural strength and translucency).
3. Simplicity of the workflow and special requirements of the working environment.

1) RETENTION AND RESISTANCE FORM OF THE ABUTMENT TOOTH

Minimal-invasive restorations, such as resin-bonded FDP, labial and occlusal veneers and inlay-retained FDP are based on a non-retentive preparation form. In this case the only possible method to achieve retention is the adhesive luting ^(9-11).

Even though such preparations completely lack a retentive form, long-term success of the restorations is well-documented when using a durable resin cement (e.g. PANAVIA™ 21, Kuraray Noritake Dental Inc., Japan) and proper bonding procedure ^{(10, 11)}.

For full-coverage restorations (e.g. crowns and FDPs), the guidelines for tooth preparation discussed before (minimum height of 4 mm and maximum convergence of 15 degrees) need to be applied in order to achieve the retention and resistance form required to make cementation with a conventional luting agent acceptable.

However, in reality this retention form is hard to realize due to several factors.

In cases of severe loss of tooth substance, achieving a minimum height of the abutment tooth is only possible with building up the tooth using a core build-up material which in some cases can be considered time consuming especially when the required build-up is minor (for example 1-2 mm). Moreover, increasing the height through core build-up is sometimes not possible, as in cases with short clinical crowns and insufficient occlusal clearance that is essential to provide the minimum thickness required for the restorative material. In such cases surgical crown lengthening is necessary to increase the height of the tooth without compromising the occlusal space required, which can be time consuming for the clinician and undesirable for the patient as it involves a surgical procedure and extends the treatment process.

Concerning the convergence angle, several studies showed that in reality and in daily practice of the dentist, the preparation angle is much higher than 15 degrees ^{(5, 6, 12, 13)}. For instance, preparations from general practitioners were evaluated digitally and compared to clinical recommendations and it was found that the mean convergence angle was 26.7 degree with the distopalatal angle being 31.7 degree ⁽¹²⁾.

Based on the previous concerns, it can be concluded that achieving a proper retention form during daily practice is hard to realize and thus conventional cementation in such cases can present clinical problems especially on the long term. Therefore, adhesive luting can be recommended in these cases as an alternative to conventional cementation ^{(6, 14)}. For full-coverage restorations with preparation designs featuring at least some mechanical retention, the use of self-adhesive resin cements can be considerate a good alternative as it provides high clinical success rates ^{(9, 15)}.

Conclusion / Clinical Significance:

• For non-retentive minimal-invasive restorations, traditional full-adhesive luting is a must.
• For full-coverage restorations, full-adhesive or self-adhesive luting is recommended.
• In case a retentive preparation with minimum height of 4mm and convergence angle of 6-12 degrees, adhesive luting as well as conventional cementation can be used.

2) MECHANICAL AND OPTICAL PROPERTIES OF THE RESTORATIVE MATERIAL

Flexural strength and translucency of the restorative material are critical factors that influence the decision which luting agent to use.

a) Flexural strength

As a general guideline for all-ceramic restorations, ceramics with low and medium flexural strength under 350 MPa should be adhesively luted with composite resin cements, as these restorations rely on resin bonding for reinforcement and support ^{(9, 14, 16)}. This includes feldspathic-, glass-, hybrid-ceramics and composite.

Although discussions on conventional cementation versus adhesive luting for high-strength ceramics with flexure strength of more than 350 MPa have been going on for a long time ⁽⁹⁾, there are several studies showing an increased stability and strength of all types of ceramics, even lithium disilicate and zirconia, when they are adhesively luted ^{(9, 17-20)}.

It is also important to consider that the documented success of most conventional cements is mainly combined with restorations made of metal or early generations of zirconia. Nonetheless, the clinical success of new generations of high-translucent zirconia can be significantly influenced by the luting agent as these new generations have notably lower flexural strength ⁽⁹⁾. And therefore, attention has to be paid to minimal material thickness together with adhesive luting to ensure long-term clinical success and prevent fractures ⁽⁹⁾.

Conclusion / Clinical Significance:

• For glass-ceramic, hybrid-ceramics and composites, adhesive luting is a must.
• For lithium disilicate and zirconia restorations, adhesive luting is highly recommended.
• For metal restorations, adhesive luting as well as conventional cementation can be used.

b) Translucency

To meet the increasing esthetic demands of the patients, new materials and techniques are continuously introduced, aiming to provide the perfect esthetic restorations. This includes not only new restorative materials but also new modifications to the luting agents as well. Highly translucent ceramics can deliver superior esthetics and therefore their popularity and clinical applications expanded widely among clinicians. It is nevertheless very important for the clinician to apprehend that the final esthetic result is influenced by the complete restorative complex and not just by the restorative material, as the luting agent is a key factor in achieving the desired high esthetics ^(21-24).

For that reason, the choice of an opaque conventional cement for cementation of high-translucent restoration should not be recommended as it can negatively influence the final esthetic results. Therefore, composite resin cements are the material of choice, as they are available in different shades and translucencies for the clinician to be able to choose the suitable resin cement to achieve the desired esthetics based on the restorative material and thickness as well as the color of the underlying abutment. Some composite resin cements offer try-in paste so that the clinician and the patient can visualize the final results before luting and therefore better choose the appropriate shade of the resin cement.

Conclusion / Clinical Significance:

• For all translucent ceramic restorations, adhesive luting is highly recommended.
• For metal and opaque high-strength zirconia restorations, adhesive luting as well as conventional cementation can be used.

3) SIMPLICITY OF THE WORKFLOW AND SPECIAL REQUIREMENTS OF THE WORKING ENVIRONMENT

The process of adhesive luting with full-adhesive composite resin cements (e.g. PANAVIA™ V5, Kuraray Noritake Dental Inc.) requires separate etching and priming procedures usually using a self-etch adhesive system (e.g. PANAVIA™ V5 Tooth Primer, Kuraray Noritake Dental Inc.) as well as a primer for the restorative material such as a universal primer that can be used for different substrates including metal, ceramics and composites (e.g. CLEARFIL™ CERAMIC PRIMER PLUS, Kuraray Noritake Dental Inc.). These procedures are technique sensitive and intolerant to contaminations, therefore the luting process needs a dry oral environment avoiding any contamination, such as saliva or blood, preferably using rubber dam, as any contamination can compromise the bond strength. Therefore, inability to maintain dry field as in case of subgingival preparation margins is considered a contraindication for traditional full-adhesive luting. However, this method provides very durable bond strength, therefore it is the luting method of choice for minimal invasive non-retentive preparations, such as resin-bonded FDPs, labial and occlusal veneers and inlay-retained FDPs, in which the retention is mainly dependent on the adhesion ^(9-11).

Still, in everyday practice, clinicians seek efficiency and effectivity by using a simple but durable luting agent for the insertion of full-coverage restorations such as tooth-or implant-supported crowns and FDPs. Although the conventional cements are simple and fast in their use, they provide little or no adhesion at all and therefore they are not recommended in several cases ^{(6, 9, 14, 15, 19, 20)}. A simple but reliable method can be well accomplished by the use of self-adhesive resin cements (e.g. PANAVIA™ SA Cement Universal, Kuraray Noritake Dental Inc.) as they can be considered the best alternative for full-adhesive adhesive luting in less critical situations that do not rely entirely on adhesion ^{(9, 15)}. Furthermore, self-adhesive resin cements are not as technique sensitive and intolerant to contaminations as traditional full-adhesive resin cements.

Typically, a MDP phosphate monomer is integrated in the self-adhesive resin cement, which is required to chemically bond to different substrates, making it possible for the resin cement to chemically bond to non-precious metals and zirconia as well as tooth substance. However, regardless of the self-adhesive resin cement, the use of a separate silane coupling agent is still required when bonding to silica-based ceramics (e.g. leucite, lithium silicate and lithium disilicate), hybrid ceramics and composite restorations.

Recently, a unique self-adhesive resin cement (PANAVIA™ SA Cement Universal, Kuraray Noritake Dental Inc.) was introduced: through an innovative and distinctive production technology, a silane-coupling agent (long carbon chain silane (LCSi)) is integrated in the cement, and thus being the real universal adhesive system that completely eliminate the need for any other adhesive or primer when being used for all substrates including glass ceramics. So the luting process can be in this case truly shortened to one step.

Therefore, this unique cement combines several advantages of adhesive luting as well as the straightforward procedure of the conventional cementation without compromising the clinical success, regardless of the type of the restorative material.

As a conclusion, adhesive luting has more benefits over conventional cementation, regarding retention, esthetics, stabilization of the tooth and the restoration as well as preventing micro leakage ^{(6, 9, 14-17, 19, 20, 25, 26)} (Table 1). Moreover, there are no absolute contraindications for adhesive luting other than hypersensitivity to methacrylate monomers, as self-adhesive resin cements can be used in cases where full-adhesive resin cements are contraindicated, such as inability to avoid contamination (Table 2). As a result, adhesive luting can be generally used in every clinical situation, whereas conventional cementation is limited (Table 3).

Dentist(s):

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

Dr. Adham Elsayed
Clinical and Scientific manager, Kuraray Europe GmbH, Hattersheim, Germany.

References

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5. Edelhoff D, Özcan M. To what extent does the longevity of fixed dental prostheses depend on the function of the cement? Working Group 4 materials: cementation. Clin Oral Implants Res. 2007;18 Suppl 3:193-204.
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8. Uy JN, Neo JC, Chan SH. The effect of tooth and foundation restoration heights on the load fatigue performance of cast crowns. J Prosthet Dent. 2010;104(5):318-24.
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10. Chaar MS, Kern M. Five-year clinical outcome of posterior zirconia ceramic inlay-retained FDPs with a modified design. J Dent. 2015;43(12):1411-5.
11. Kern M, Passia N, Sasse M, Yazigi C. Ten-year outcome of zirconia ceramic cantilever resin-bonded fixed dental prostheses and the influence of the reasons for missing incisors. J Dent. 2017;65:51-5.
12. Guth JF, Wallbach J, Stimmelmayr M, Gernet W, Beuer F, Edelhoff D. Computer-aided evaluation of preparations for CAD/CAM-fabricated all-ceramic crowns. Clin Oral Investig. 2013;17(5):1389-95.
13. Nordlander J, Weir D, Stoffer W, Ochi S. The taper of clinical preparations for fixed prosthodontics. J Prosthet Dent. 1988;60(2):148-51.
14. Blatz MB. Long-term clinical success of all-ceramic posterior restorations. Quintessence Int. 2002;33(6):415-26.
15. Blatz MB, Phark JH, Ozer F, Mante FK, Saleh N, Bergler M, et al. In vitro comparative bond strength of contemporary self-adhesive resin cements to zirconium oxide ceramic with and without air-particle abrasion. Clin Oral Investig. 2010;14(2):187-92.
16. Kern M, Thompson VP, Beuer F, Edelhoff D, Frankenberger R, Kohal RJ, et al. All ceramics at a glance. 3rd English Edition ed: AG Keramik; 2017.
17. Attia A, Abdelaziz KM, Freitag S, Kern M. Fracture load of composite resin and feldspathic all-ceramic CAD/CAM crowns. J Prosthet Dent. 2006;95(2):117-23.
18. Borges GA, Caldas D, Taskonak B, Yan J, Sobrinho LC, de Oliveira WJ. Fracture loads of all-ceramic crowns under wet and dry fatigue conditions. J Prosthodont. 2009;18(8):649-55.
19. Campos F, Valandro LF, Feitosa SA, Kleverlaan CJ, Feilzer AJ, de Jager N, et al. Adhesive Cementation Promotes Higher Fatigue Resistance to Zirconia Crowns. Oper Dent. 2017;42(2):215-24.
20. Weigl P, Sander A, Wu Y, Felber R, Lauer HC, Rosentritt M. In-vitro performance and fracture strength of thin monolithic zirconia crowns. J Adv Prosthodont. 2018;10(2):79-84.
21. Calgaro PA, Furuse AY, Correr GM, Ornaghi BP, Gonzaga CC. Post-cementation colorimetric evaluation of the interaction between the thickness of ceramic veneers and the shade of resin cement. Am J Dent. 2014;27(4):191-4.
22. Chang J, Da Silva JD, Sakai M, Kristiansen J, Ishikawa-Nagai S. The optical effect of composite luting cement on all ceramic crowns. J Dent. 2009;37(12):937-43.
23. Turgut S, Bagis B. Effect of resin cement and ceramic thickness on final color of laminate veneers: an in vitro study. J Prosthet Dent. 2013;109(3):179-86.
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Zirconia ceramics are increasingly being used for dental prostheses. In the past, they were used as a substructure that was baked with porcelain; nowadays, monolithic zirconia prostheses have been made possible by the introduction of aesthetic zirconia ceramics varieties. They are used more and more, even as RBFDPs (Resin Bonded Fixed Dental Prosthesis).

There is currently quite a lot of discussion about zirconia. So much the better, because it keeps the dynamics of the subject alive. Is it possible to adhesively cement zirconia? Is it permissible to sandblast zirconia? Is it feasible to polish zirconia? Is wear of the antagonist an issue? And so on and so forth.

New dental technologies and materials have been developed in recent years to meet the demand for aesthetic, biocompatible and metal-free prostheses. Although porcelain has been used as an aesthetic dental material for more than hundred years, its restrictions are now well-known. It is the fragility of porcelain (low flexural strength and fracture toughness) in particular which restricts its application in areas where the exertion of massive force on the material is a factor. Zirconia has a high flexural strength and is therefore suitable for multiple dental applications.

Development

The first generation of zirconias used in dentistry belonged to the Partially Stabilised Zirconia (PSZ) class. This type of zirconia, stabilised with yttrium oxide, was composed of a mix of monoclinic, tetragonal and cubic crystals but is no longer used nowadays. The so-called Y-TZP variant was then used for many years, and still is. Its main characteristics are high flexural strength (> 1.000 MPa) and an opaque white appearance. For the most part, this variant is composed of tetragonal crystals of a few hundred nanometers. To keep the material stable at room temperature, approximately 3 mol% of yttrium oxide is added to the composition, which is why it is sometimes referred to as 3Y zirconia.

In order to improve its aesthetic properties, a start was made on the development of a new variety, so-called cubic zirconia. Cubic zirconia is characterised by a high translucence, meaning that a lower flexural strength must be accepted. Admittedly, the flexural strength of this variant is lower than that of the tetragonal variety, but still much higher than the flexural strength of lithium disilicate. It also contains more yttrium oxide; approximately 5 mol%.

Crystal phases

We currently know zirconia crystals in three varieties: monoclinic, tetragonal and cubic. In general, zirconia only exists in the monoclinic phase at room temperature. Monoclinic zirconia has low strength as well as low translucence. Tetragonal zirconia crystals are metastable and can only exist at room temperature after having been stabilised with yttrium oxide, among other metal oxides. The characteristics of tetragonal zirconia are that it is strong, but at the same time devoid of aesthetic
properties. Cubic crystals are stable and ensure improved translucence. Although prostheses made from cubic zirconia are not as strong as the tetragonal variety, they are highly aesthetic, and are even suitable for monolithic restorations in the aesthetic zones.

Multilayer

KATANA™ Zirconia ML, STML and UTML, as well as the latest KATANA™ Zirconia Block, are so-called multilayer zirconias. These products are built up of four layers with an ascending degree of translucency, ranging from the more opaque and coloured body layer (cervical), through two transitional layers, to the translucent incisal edge (occlusal/incisal). The invisible transition from one layer to another is achieved using a unique process. The secret is in the specific distribution of particles during the pre-sintered stage (continuous gap grading). In combination with the cold isostatic pressing method, this ensures material of an outstandingly high quality.

KATANA™ Zirconia Block

The use of KATANA™ Zirconia Block makes it possible to produce a complete monolithic zirconia prosthesis in a short time. This block was developed to be used within the CEREC workflow. After scanning, the prosthesis is ground for approximately 15 minutes and can then be sintered in the SpeedFire oven in just half an hour¹). KATANA™ Zirconia Block shares the properties of KATANA™ STML and can be used for the production of single-unit prostheses such as full crowns for both anterior and posterior applications.

Wear of the antagonist

The question of whether zirconia prostheses are harmful to the antagonist would seem to be justified; after all, this is a very hard material. Hardness, however, does not relate directly to the abrasive properties of a material. Smoothly polished zirconia is minimally abrasive, something which has been corroborated by multiple studies²). Glaze, porcelain, lithium disilicate and even enamel are all more abrasive for the antagonist.

CAD/CAM

Thanks to emerging digital solutions (CAD/CAM) combined with the possibility of executing fixed partial dentures (FPDs) in monolithic zirconia, a fully digital workflow - from scan to prosthesis - is now feasible.

Sandblasting

Sandblasting using alumina is the standard method for the roughening of zirconia. In order to reduce the decline from the tetragonal crystal stage to the monoclinic stage, it is recommended that sandblasting be carried out at a maximum pressure of 2.5 bar using 50 micron aluminium oxide particles as a maximum³). In practice, zirconia is also frequently sandblasted tribochemically, for example, by means of CoJet (3M). The results achieved with this method are variable. In the case of limited pressure (2.5 bar as a maximum) there is a risk that the energy will be insufficient to achieve an effective and complete fusion between the silica and the zirconia surface. It is therefore recommended that CLEARFIL™ Ceramic Primer Plus be used for adhesive connection with the sandblasted surface. The silane in this ceramic primer bonds chemically with the silica, while the MDP bonds with the areas of zirconia not covered by silica. The use of silane alone does not provide an adequate basis for a reliable result⁴). Sandblasting with alumina, however, followed by priming with CLEARFIL™ Ceramic Primer Plus, is a well-proven and reliable method to ensure effective bonding to zirconia⁵).

Not etchable, but certainly bondable

Zirconia is not – or is barely – etchable with the etching technology available (HF). In addition, it cannot be recommended that zirconia be treated with phosphoric acid, because of the bonding of phosphates to the surface of the zirconia, which will inhibit a chemical activation of the surface for some adhesive cementation systems. The question of whether an etching product should be used is a valid one; after all, chemical etching is not necessary to achieve surface roughness. Achieving surface roughness is, however, a logical option, and roughening by means of sandblasting would seem to be the most appropriate method for zirconia. Thereafter, chemical bonding is ensured using a phosphoric functional monomer, preferably MDP.

Adhesion principles

Three basic factors are required to achieve the effective bonding of different materials. In keeping with the principles of adhesion, these are: surface enlargement (micromechanical retention), chemical activity (adsorption and electrostatic bonding) and a high-energetic surface to guarantee proper adaptation.

Adhesive bonding

The best method of adhesive bonding for zirconia is the use of a composite cement containing MDP. Professor Mathias Kern published an article about bonding to zirconia using MDP as early as 1998. This study showed that sustainable resin bonding to zirconia can only be achieved using a composite cement with a special adhesive monomer. The monomer used was in fact MDP. In the meantime, many studies have been published about bonding to zirconia.

On the one hand, these studies concern bonding with phosphate monomers (MDP); on the other hand, attention has been paid to the modification of the zirconia surface to render it etchable. The simplest and most reliable method is to sandblast the surface at a low pressure using aluminium oxide, followed by priming with an MDP-containing primer⁶).

PETER SCHOUTEN,
Technical Manager Kuraray Europe Benelux

1) Depending on the method of grinding/milling.
2) Mörmann W.H. et al. Wear characteristics of current aesthetic dental restorative CAD/CAM materials: Two body wear, gloss retention, roughness and Martens hardness. Journal of the mech. Behavior of Biomedical Materials 20 (2013) 113-125, Janyavula S. et al. The wear of polished and glazed zirconia against enamel. J Prosthet Dent 2013; 109;22-29 Stawarczyk B. et al. Comparison of four monolithic zirconia materials with conventional ones: Contrast ratio, grain size, four-point flexural strength and two-body wear. Journal of the mech. Behavior of Biomedical Materials 59 (2016) 128-138 D’Arcangelo C. et al. Wear Evaluation of Prosthetic Materials Opposing Themselves. Oper Dent 2017 antagonistic surface roughness on the wear of human enamel and nanofilled composite resin artificial teeth. J Prosthet dent 2009; 101: 342-349.
3) Attia A. / Kern M. Effect of cleaning methods after reduced-pressure Air Abrasion on Bonding to Zirconia Ceramic J Adhes Dent 2011; 13: 561-567.
4) Pilo R. Effect of tribochemical treatments and silane reactivity on resin bonding to zirconia. Dent Mater (2017).
5) Kern M. Bonding to oxide ceramics - Laboratory testing versus clinical outcomes. Dent Mater (2014).
6) M. Kern et al., Bonding to zirconia ceramic: adhesion methods and their durability. Dent Mater 14: 64-71, Jan.1998.

Did you know that a complete removal of temporary cement from the abutment tooth with a rubber cup and pumice paste or an ultrasonic scaler is usually impossible? In most cases, some visibly undetectable residues remain on the surface. They will negatively affect the bonding performance of the permanent cementation system you selected. KATANA™ Cleaner is our answer to this problem! Applied after conventional temporary cement removal, it provides optimal conditions for permanent cementation.

All relevant details are revealed in this scientific report.