Characterization of light-cured, dental-resin-based biocomposites Zuzanna Okulus, 1 Tomasz Buchwald, 2 Adam Voelkel 1 1 Institute of Chemical Technology and Engineering, Pozna n University of Technology, ul. Berdychowo 4, 60-965 Pozna n, Poland 2 Faculty of Technical Physics, Pozna n University of Technology, ul. Piotrowo 3, 60-965 Pozna n, Poland Correspondence to: Z. Okulus (E - mail: zuzanna.okulus@gmail.com) ABSTRACT: The dependence of the depth of cure (DOC) and degree of conversion (DC) on the depth of experimental and commer- cial materials were determined according to ISO 4049 procedure and with the use of Raman spectroscopy, respectively. Moreover, an attempt was made to find the correlation between the DOC and DC and the depth of the material. The hypothesis was that curing time recommended by the manufacturers is appropriate for curing both commercial and experimental materials to achieve compara- ble values of the examined properties. The impact of the filler characteristic was clearly observed. The longer curing time provides a deeper curing (DOC values) and higher reaction rate (DC); however, the dependence between the DC values and DOC values was not visible. Instead, a logarithmic trend in the relation of the DOC and curing time was clearly observed. The results of this study suggest that the experimental materials give some hope for potential clinical applications and should be further investigated. VC 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42812. KEYWORDS: photopolymerization; properties and characterization; resins Received 10 April 2015; accepted 5 August 2015 DOI: 10.1002/app.42812 INTRODUCTION Photopolymerizable resin-based composites (RBCs) are the most popular materials applied in dentistry. 1–5 Their application includes many areas, for example, restorations 1–5 or prostheses. 2 The main advantage of these polymeric products is a high aes- thetic level, enabling the imitation of the natural tooth appear- ance. 1,4–9 Other advantages of RBCs include their good longevity after application, 9 good mechanical properties, 1,7 bio- compatibility, ease of use, 4 and good price. 10 These polyphase composites consist of two main parts: an organic resin matrix and inorganic filler particles. 5,6,9,11 The most popular organic matrixes consist of methacrylic resins and, in particular, bisphenol A glycidyl methacrylate (Bis-GMA; Bowen’s resin: [4-2-hydroxyl- 3-methacryloxypropoxy phenyl] propane). 5,6,9,12 According to the high viscosity of this compound, some low-viscosity comonomers are added to the matrix. 5,9,12 Hydroxyethyl methacrylate, triethy- lene glycol dimethacrylate, urethane dimethacrylate, and ethoxy- lated bisphenol A dimethacrylate are the most frequently used methacrylic comonomers. 5,6,9,12 The organic matrix acts as a con- tinuous phase of the composite, whereas an inorganic filler is the dispersed phase, whose main task it is to improve the properties of the composite. The addition of the filler affects the mechanical, chemical, physical, and biological properties of the RBC and also reduces the cost of the final product. 9 One of the very important roles of the filler is to reduce the polymerization shrinkage, the main disadvantage of light-cured materials; this is the cause of gap formation, a reduction in the adhesion between the tooth and the restoration. 9,13,14 The most commonly used fillers are flu- oroaluminosilicate glasses and ceramics. 5,6,9 A significant portion of the organic matrix is the photoinitiator system, which is gener- ally 5% or less of the weight of the organic matrix. Most com- mercial solutions contain camphor quinone (CQ) as a main initiator combined with different aliphatic or aromatic amines, for example, 2-ethyl-dimethylbenzoate. 5,9,15–17 CQ absorbs blue light (maximum at 470 nm) and initiates the radical polymerization of the composite, whereas amine accelerates this process. 5,9,17 The source of visible blue light is light-emitting diodes in most cases. Formerly, halogen lamps were used; however, according to their better characteristics (less power, longer life, minimal heat genera- tion, greater efficacy, etc.), light-emitting-diode lamps replaced them. 18–20 Photopolymerization is a more appropriate solution for curing composites than chemically activated polymerization according to its faster reaction rate; however, it influences the irra- diated material properties. 21 There are several requirements for composite materials for den- tal applications, such as a natural appearance, 14,22 longevity, 23 harmlessness, and lack of toxicity. 14 However, it is well known that no polymerized material could react with 100% efficiency. From incompletely polymerized composites, some amount of toxic or harmful compounds can be leached out in the moist VC 2015 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2015, DOI: 10.1002/APP.42812 42812 (1 of 10)