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TOKYO, Japan: Some companies mainly use basic technologies developed by others to improve their products and introduce new ones, whereas others conduct fundamental research and technology development in-house. Is this difference relevant for end users in the dental practice or dental laboratory? It is, because companies with a deep understanding of the underlying components, chemistry and technologies are able to solve existing problems and quickly and flexibly respond to market needs. This article describes the impact of several basic technologies developed by Kuraray Noritake Dental for cementing indirect restorations.
Adhesive cementation then and now
The possibility of milling dental restorations from different kinds of ceramics has created new opportunities in prosthodontics, enabling highly aesthetic restorations. What is often undervalued in this context is the role of adhesive cementation systems, which not only support the aesthetic appearance of the translucent, tooth-coloured restorations, but also pave the way for preparation and restoration designs that are less invasive. Early systems that provided for chemical adhesion between teeth and indirect restorations unfortunately resulted in compromised long-term behaviour and suffered from high technique sensitivity that resulted in extremely complex application procedures. Since then, the technology developed at Kuraray Noritake Dental has made significant contributions to improved long-term bonding performance of adhesive cementation systems and enabled simplified handling.
Optimising long-term bonding performance
In order to achieve long-term bonding to tooth structure (especially dentine), Kuraray Co., a parent company of Kuraray Noritake Dental, decided in the 1970s to focus on the development of a more powerful adhesive monomer. The company introduced the phosphate monomer Phenyl-P in 1976, and five years later, continued efforts to improve and refine its molecular structure led to the popular MDP monomer, which can establish a particularly strong and long-lasting bond to enamel, dentine, metal and zirconia.
The enduring value of the MDP monomer is evident from its use in every adhesive and adhesive cementation system from Kuraray Noritake Dental and its use by other manufacturers to optimise the bond strength and bond durability of their products. Compared with MDP synthesised elsewhere, the original MDP monomer stands out owing to an unmatched level of purity. Independent studies show that this level of purity has a positive effect on its bonding behaviour. By offering stability in a moist environment, the MDP monomer improves the consistency and performance of the products that contain it.
However, simply adding an adhesive monomer is not enough to ensure that adhesive resin cement systems deliver a strong bond with an outstanding marginal seal. Effective polymerisation of this monomer is also necessary, but is not always easily accomplished. In order to provide for effective light and dark polymerisation performance of PANAVIA V5, Kuraray Noritake Dental developed touch-cure technology. The key element of this technology is a newly developed, highly active polymerisation accelerator used in PANAVIA V5 Tooth Primer. The accelerator is able to coexist with the acidic MDP monomer, and it promotes polymerisation, starting from the interface between the tooth and the cement as soon as PANAVIA V5 Paste is applied to the already primed tooth surface. In PANAVIA Veneer LC—a light-polymerising resin cement system that works with the same primers—the polymerisation accelerator in PANAVIA V5 Tooth Primer shows the same mechanism of action. It contributes to the polymerisation of the adhesive interface, and PANAVIA Veneer LC Paste offers excellent ambient light stability and is polymerised by light.
This polymerisation of the adhesive interface was evaluated for PANAVIA F2.0, the predecessor of PANAVIA V5. The study showed that PANAVIA F2.0 offered better marginal sealing properties compared with other cement systems. This documented secure sealing of the interface leads to a lower incidence of marginal leakage and a very high polymerisation ratio even when self-polymerised (without light polymerisation or wherever the light is blocked by the restorative material) and hence to a particularly strong bond.
An additional benefit arising from the incorporation of the polymerisation accelerator is its function as a strong reductant. It neutralises sodium hypochlorite, which is commonly used as an irrigation solution during endodontic treatment, and thus eliminates its negative effect on the bond strength of the subsequently applied cement paste.
Simplifying glass-ceramic cementation
Adhesive resin cements were developed and introduced in the early 2000s in order to streamline cementation procedures by reducing the number of bottles and steps required. Most of these products, however, have a limited indication range. They work well on zirconia, metal, enamel and dentine, but are either not recommended or need an extra silane primer for glass-ceramic bonding. The MDP-containing PANAVIA SA Cement Universal, however, is different, owing to another proprietary technology from Kuraray Noritake Dental, the LCSi monomer, a long-chain silane coupling agent.
This monomer forms a strong chemical bond with resin composite, porcelain and silica ceramics (such as lithium disilicate), thereby eliminating the need for a separate silane component (a primer or adhesive). By leveraging the benefits of this technology, PANAVIA SA Cement Universal clearly sets itself apart from other self-adhesive resin cements as a true single-component cementation system, even for restorations made of glass-ceramics.
If desired, the strength of the product’s bond to tooth structure can be increased by use of the popular universal adhesive CLEARFIL Universal Bond Quick, which features rapid bond technology. This technology was developed by Kuraray Noritake Dental to solve problems related to the slow penetration of tooth structure—especially wet dentine—which is typical for universal adhesives. In order to provide proper penetration, these adhesives need to be actively rubbed into the tooth structure for a long time, otherwise users have to wait before light-polymerising the layer. Employing the original MDP monomer and hydrophilic amide monomers, the proprietary rapid bond technology provides for a high affinity to water, leading to rapid and deep penetration of wet dentine. As a consequence, application times are shortened and handling is simplified without negatively affecting the bonding performance.
Resin cements for every user and all typical clinical situations
Technologies developed by Kuraray Noritake Dental have contributed greatly to improved bonding performance of adhesive cementation systems and truly universal use of self-adhesive resin cements. The company therefore offers a streamlined portfolio of high-performance resin cements for every user and all typical clinical situations. Fewer components and fewer steps are necessary, and procedures are simplified, resulting in fewer errors and in aesthetic restorations that last. Apart from the technology-related benefits, the products mentioned offer many additional advantageous features. A detailed description can be found on Kuraray Noritake Dental’s website.