News Feature

Transforming dentistry with ground-breaking technologies:

Direct restoration procedures simplified

Some companies mainly make use of basic technologies developed by others to improve their products and introduce new ones, while other companies conduct fundamental research and technology development inhouse. Is this difference relevant for someone who uses the resulting products in the dental practice or laboratory on a daily basis? It is – as companies developing everything from scratch usually have a deeper understanding of the products and their production procedures, which makes it easier for them to modify specific features, solve existing problems and respond to market needs. This article describes the impact of several basic technologies developed by Kuraray Noritake Dental Inc. on the workflow of creating direct composite restorations.

Direct restorations – from complex to simple

Adhesive restorative dentistry using high-performance dental adhesives and resin composites is currently one of the most popular way of treating teeth with carious lesions. Nowadays, a single-bottle universal adhesive and one or two shades and opacities of universal composite are usually enough to create beautiful and durable outcomes, provided that the right materials are selected.

This, however, has not always been the case. For a long time, the techniques used to create direct restorations have been quite complex: adhesives were technique-sensitive multi-bottle and multi-step systems with long application times. Composite filling materials, on the other hand, only produced lifelike outcomes when many different shades and opacities were combined in the right way. And even if the complex procedures were carried out correctly, the risk of microleakage, discolouration and eventually secondary caries was comparatively high. Kuraray Noritake Dental Inc. focused on solving these issues quite early, starting with the utilization of the Original MDP Monomer developed in 1981.

Optimizing the bonding performance

The Original MDP Monomer addressed the issue of limited long-term bonding performance of adhesive systems. MDP’s hydrophilic (phosphate) group forms a particularly strong and long-lasting chemical bond with calcium found in hydroxyapatite, the main component of enamel and dentin. The formed MDP-Ca salt provides the basis for a stable, strong and durable hybrid layer. In combination with the resin in the bonding agent a tight seal of the cavity after light-curing is the result. Down to the present day, MDP is an essential component of any adhesive product from Kuraray Noritake Dental Inc., and it is the key component that made CLEARFIL™ SE Bond become the Gold Standard self-etch adhesive system.

The Original MDP monomer creates a strong chemical bond to Enamel, Dentin, Metal Alloy and Zirconia.

However, convinced that dental adhesives should provide for more than just a strong and long-lasting bond, Kuraray Noritake Dental Inc. started to focus on solving another issue: the risk of demineralization and cavitation caused by bacteria remaining in the cavity. Based on its experience in developing other adhesive monomers, Kuraray Noritake Dental Inc. invented the MDPB monomer that has an antibacterial cavity cleansing effect. Different from antibacterial agents that might impair the bond strength of a subsequently applied adhesive, the MDPB monomer kills remaining bacteria without affecting the bonding performance. It is contained in the primer of the two-bottle self-etch adhesive CLEARFIL™ SE Protect and is immobilized by polymerization.

The bactericidal mechanism of MDPB is presumed to be similar to the well-known antibacterial agent CPC (Cetyl pyridinium chloride), which is in many toothpastes and mouth rinses.

While two-bottle self-etch adhesives has already simplified the adhesive procedure, single-bottle universal adhesives go the extra mile. It is a challenge to bring together ingredients distributed in multi step systems in one bottle without compromising the stability of the product. Current technology now makes this possible. To seal the surface as soon as possible after application, the penetration of the monomers into the dental tissue must be fast and efficient. However, the penetration is usually slowed down by monomers that need time to penetrate the tooth structure – especially wet dentin – and sometimes even need to be rubbed into it. That is why Kuraray Noritake Dental Inc. focused on developing the Rapid Bond Technology. It consists of the Original MDP Monomer combined with newly developed hydrophilic crosslinking amide monomers and is integrated in CLEARFIL™ Universal Bond Quick. The hydrophilic amide monomers provide for a rapid, deep and complete penetration of the dentin and form upon curing a densely cross-linked polymer network responsible for a strong and durable bond. Hence, waiting and rubbing times are eliminated and a tight and long-lasting seal of the cavity is established after light-curing.

Prepared dentin with smear layer.	Dentin bonded with CLEARFIL™ Universal Bond Quick.
Due to its hydrophilicity we need a very hydrophilic bonding to be able to optimally penetrate the dentin.	During curing CLEARFIL™ Universal Bond Quick creates a highly cross linked polymer network. As a result of this network, the bonding has a very low water absorption which gives a long lasting restoration.

Due to their hydrophilicity (water-affinity), the amide monomers of the Rapid Bond Technology penetrate dentin very well. After light-curing, the bond exhibits low water sorption and therefore high aging-resistance.

Optimizing direct restoratives

Combining multiple layers, shades and opacities: The use of highly complex layering techniques for the creation of lifelike composite restorations is luckily a thing of the past in many clinical situations. The reason: highly developed resin composites that blend seamlessly with the adjacent tooth structure. To provide for this favourable feature, Kuraray Noritake Dental Inc. has developed its proprietary Light Diffusion Technology (LDT). The technology is incorporated in special pre-polymerized fillers acting like millions of micro-prisms that transmit and refract light and colour from the surrounding tooth structure. Optimized in size, distribution and refractive index in relation to the matrix, the fillers offer unsurpassed natural blending.

The whole CLEARFIL MAJESTY™ composite line-up contains this proprietary filler technology. Its latest product – CLEARFIL MAJESTY™ ES-2 Universal – in which Kuraray Noritake Dental Inc. makes use of next level LDT allows for a single-shade technique with simplified shade selection: it is available in two shades for the anterior and a single shade for the posterior region, but blends in so nicely that it covers virtually every shade of the VITA classical A1-D4 shade guide.

Refracting and transmitting light in the right way for a great optical integration: light diffusion fillers of CLEARFIL MAJESTY™ ES-2 from Kuraray Noritake Dental Inc.

As a great optical appearance is not only dependent on optical integration and undetectable restoration margins, Kuraray Noritake Dental Inc. also developed fillers that provide for the rest – a natural surface gloss and long-term polish retention. The solution integrated in CLEARFIL MAJESTY™ ES Flow with its three levels of flowability is called Submicron Filler Technology, which consists of glossy submicron-sized fillers. These fillers are so small that light reflections show a natural effect even after wear. Kuraray Noritake Dental Inc.’s exceptional silane technology is used to join millions of those submicron fillers and keep them together over time. It allows for high filler loads in the low-viscosity composites and limits water uptake that would otherwise lead to degradation of the cured composite. The perfect balance between the glossy submicron fillers, light diffusion fillers, resin matrix and proprietary silane technology is responsible for a balanced combination of mechanical and optical properties.

Example of a single-shade restoration made of CLEARFIL MAJESTY™ ES-2 Universal.

Conclusion

Adhesive monomers, filler technologies and silane technology providing for a solid combination of fillers, clusters and resin matrix: Kuraray Noritake Dental Inc. clearly is a trusted expert in the field of adhesive restorations. The proprietary technologies developed during the past decades have definitely contributed to a better (long-term) performance of direct restorations, and to reliable and aesthetic outcomes more easily achieved.