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September 2009 | Dental Products Report New chemistry opening doors Enhanced properties allow composite resins to make great strides. The set-up“Ever since we started using composite resin, the search has been on to find one with the physical properties and handling characteristics of amalgam. Almost 30 years since the introduction of BIS-GMA-based composites we are still searching…but getting closer. Dr. Gary Radz discusses new chemistry in composite resins that may be the next step in the evolution of these dental materials…closing the “gap” on the search for the “tooth-colored dental amalgam replacement.”—Dr. Robert Lowe, Team Lead For more than three decades, composite resins have existed in dentistry. The introduction of composites to dentistry started a new era of esthetics in the dental profession. Over the past several years, dentistry has made great strides in improving composite resin to enhance the physical and esthetic properties. Today, many manufacturers offer dentists a wide choice of excellent materials. But the very basic chemistry of these composites remains the same. These composites may provide the best results of physical and esthetic properties we can obtain with this base chemistry. Septodont recently introduced a new composite, N’Durance. Basing this composite on new resin chemistry developed by Dr. Jeffery Stansbury and his team at the University of Colorado, Septodont has created a new dental composite resin system that addresses one of the biggest concerns dentistry has with composite resins, which is shrinkage. This new composite material is a non BIS-GMA formula, which uses a nano dimer conversion technology. Polymerization shrinkage has been a cause for concern in dentistry since the introduction of composites. Currently, most of the composite resins in the dental market show volumetric shrinkage of 2% to 3.5%. N’Durance demonstrates a shrinkage rate near 1.5%. This may not seem like much of a difference, but clinically this could mean the difference between microleakage and recurrent decay or sensitivity. Also by decreasing the shrinkage, you decrease the stress of the restoration on the tooth itself. Additionally, this new chemistry has a high monomer conversion. This material, when fully polymerized, will have 75% conversion. Other composite resins on the market have conversion rates that range from 40% to 70%. This higher conversion rate is important because it allows for improvement in the material’s physical properties. The new chemistry in N’Durance could open the door to the next generation of composite resins, allowing us to provide our patients with stronger, longer lasting esthetic composite restorations. 
Clinical case 1 An extremely low-shrinkage composite is very important in a Class I restoration. The high C factor present in this restoration makes it highly sensitive to shrinkage-related issues. This case demonstrates a common clinical situation: an old amalgam restoration with defective margins and recurrent decay that requires replacement (Fig. 1). It is also common for patients to want and request the restoration to be replaced with a tooth-colored material. The following technique demonstrates one way a practitioner could attempt to minimize the potential for post-operative sensitivity with a Class I composite resin. Following anesthesia, rubber dam is placed. Using an electric handpiece from NSK America and the #813 amalgam removing bur from Axis Dental, the old amalgam restoration is removed. A caries detection agent from Ultradent Products is used to find and ensure removal of all remaining decay. Lastly, the walls of the preparation are smoothed and refined with an 845KR diamond bur from Axis. The bonding process is completed using Kerr Dental’s Optibond SE self-etching bonding agent. Many practitioners find a lower incidence of sensitivity using a self-etching bonding system. CONTINUED ON NEXT PAGE
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