REVIEW ARTICLE Dental Biomaterials Cure mechanisms in materials for use in esthetic dentistry Tae-Yub Kwon 1 , Rafat Bagheri 2 , Young K. Kim 3 , Kyo-Han Kim 1 & Michael F. Burrow 4 1 Department of Dental Biomaterials, Kyungpook National University, Jung-gu, Daegu, Korea 2 Dental Materials Department, Shiraz Dental School, Shiraz University of Medical Sciences, Shiraz, Iran 3 Department of Conservative Dentistry, Kyungpook National University, Jung-gu, Daegu, Korea 4 Faculty of Dentistry, Prince Philip Dental Hospital, The University of Hong Kong, Sai Ying Pun, Hong Kong, China Introduction Most resin-based dental materials used in esthetic den- tistry cure via radical chain polymerization. 1–3 An initia- tion system can be ‘‘activated’’ by various methods to generate a free radical that ‘‘initiates’’ the polymerization process. The reactive species (e.g. free radical) is added to a monomer molecule by opening the p-bond to form a new radical center, and the process is repeated as many more monomer molecules are added to continuously propagate the reactive center. 1 Polymer growth is termi- nated at some point by combination (the coupling of two radicals), or more rarely, by disproportionation (the transfer of a b-hydrogen from one propagating radical to the other). 1,4 In a chain polymerization reaction, the chain growth is usually rapid, immediately forming a high molecular weight polymer once a reactive center is pro- duced. 1 The term ‘‘cure’’ denotes the process in which monomers are converted to polymers. 2 In resin-based dental materials, the cure indicates various types of initia- tion systems and activation methods. The initiation process has a significant effect on the kinetics of polymer- ization and the polymer structure, thus affecting various properties of the network. 2,5,6 In dental resin materials, initiation systems can be acti- vated either chemically or by light irradiation. The light-cure concept seems straightforward to clinicians, as most restor- ative resin composites are supplied as single-component Keywords aryl sulfinic acid sodium salt, benzoyl peroxide, camphorquinone, polymerization, tertiary amine. Correspondence Dr Michael F. Burrow, Faculty of Dentistry, Prince Philip Dental Hospital, The University of Hong Kong, 34 Hospital Road, Sai Ying Pun, Hong Kong, SAR, China. Tel: +852-2859-0553 Fax: +852-2858-2532 Email: mfburr58@hku.hk Received 21 July 2011; accepted 21 October 2011. doi: 10.1111/j.2041-1626.2012.00114.x Abstract The current paper reviews the curing mechanisms found in resin-based materi- als used in dentistry. Historical aspects of dental products and the associated curing mechanisms are reviewed. In comparison with common industrial pro- cedures, curing methods employed for dental materials are relatively limited because of the need to polymerize quickly in the oral cavity at an ambient tem- perature. Heat-cure and self-cure dental resins utilize benzoyl peroxide initiator alone with a tertiary amine co-initiator. At present, most dental restorative composites use a camphorquinone–amine complex initiation, visible light-cure, one-component systems, although alternative photoinitiators have been researched and developed. A multiple curing mode in a dual-cure material is a complex combination of various initiation systems. The use of aryl sulfinic acid sodium salt to overcome adverse chemical interactions between simplified adhesives and self- or dual-cure composites is based on another self-cure poly- merization mechanism, sulfinic acid-initiated polymerization, proposed by Hagger in 1948. The sodium salt of aryl sulfinic acid reacts with an acidic monomer in simplified adhesives, and is believed to produce radicals. Clini- cally, it is important to try to optimize the degree of conversion of resin-based materials using proper manipulation and adequate light-curing techniques to ensure the best outcome for materials used to restore teeth. Journal of Investigative and Clinical Dentistry (2012), 3, 3–16 ª 2012 Blackwell Publishing Asia Pty Ltd 3