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Characteristics of Polymers and Polymerization Processes
Published in Manas Chanda, Plastics Technology Handbook, 2017
The dental resins are commonly based on the highly viscous bisphenol A glycidyl methacrylate (abbreviated as bis-GMA, also known as Bowen's monomer after the inventor) have been used for over four decades. Because of its high viscosity (1,369 Pa.s), bis-GMA is blended with diluent, lower molecular weight monomers, to provide a workable matrix resin for composites, for example, bisphenol-A dimethacrylate (bis-DMA), ethylene glycol dimethacrylate (EGDMA), and triethylene glycol dimethacrylate (TEGDMA). Camphorquinone (CQ) is traditionally used as photosensitizer for dental composites. It undergoes a redox reaction with a tertiary amine to produce radicals for free-radical polymerization of the acrylate resin. In a typical procedure, a mixture of bis-GMA and TEGDMA with 1 wt% of CQ and tertiary amine is photopolymerized using visible light device with an intensity of 900 mW/cm2. The photopolymerization of the dental resin is fast with most of the reaction taking place within 40 s, causing gelation and vitrification accompanied by shrinkage of about 8%. Shrinkage continues, as also stiffening, during post-polymerization at a much slower rate (see Table 1.22).
Biomaterials and Surface Modification
Published in Mohammad E. Khosroshahi, Applications of Biophotonics and Nanobiomaterials in Biomedical Engineering, 2017
On the other hand, the argon laser appeared as a suitable alternative polymerization source of composite resins, particularly for CQ, whose activation is initiated by a hue of blue light covering the range of 400–500 nm with broad peaks at about 468 and 480 nm, depending on the type of diluent (Kelsey et al. 1989, Cassoni et al. 2005). Furthermore, lasers such as argon laser with its inherent optical characteristics like low beam divergence, monochoromacity, collimation, coherency, absorption selectivity because of wavelength tunability, and fiber delivery capability can all make it to be practically a better candidate, which effectively can reduce curing time, provide a larger degree of conversion (DC) of monomers, and enhance physical properties of cured composites (Fleming and Mailet 1999, Conrado et al. 2004). The advantages of Bis-GMA over other small-sized monomers like methyl methacrylate, include less shrinkage, higher modulus, and reduced toxicity because of its lower volatility and diffusivity into the tissue. Furthermore, TEGDMA is added to Bis-GMA to achieve workable viscosity limits because the latter monomer possess very high viscosity because of the intermolecular hydrogen bonding (Sankarapandian and Shobha 1997).
Resin-Based Composites in Dentistry—A Review
Published in S. M. Sapuan, Y. Nukman, N. A. Abu Osman, R. A. Ilyas, Composites in Biomedical Applications, 2020
Z. Radzi, R. A. Diab, N. A. Yahya, M. A. G. Gonzalez
In 1956, the era of dental RBCs started when Bowen synthesized a new monomer, 2,2-bis[4-(2-hydroxy-3-methacrylyloxypropoxy)phenyl]propane, which is also known as Bis-GMA. It resembles an epoxy resin; however, the epoxy groups are replaced by methacrylate groups. It is prepared from bisphenol A and glycidyl methacrylate or diglycidyl ether of bisphenol A and methacrylic acid; therefore, it is a dimethacrylate (Bowen, 1959). Polymerization of the monomer occurs through carbon-carbon double bonds (C=C) of the two methacrylate groups. Bis-GMA is superior to methyl methacrylate because of its large molecular size and chemical structure, providing lower volatility, lower polymerization shrinkage, more rapid hardening, and production of stronger and stiffer resins.
Preparation of an experimental dental composite with different Bis-GMA/UDMA proportions
Published in Materials and Manufacturing Processes, 2023
Michał Krasowski, Sandra Ciesielska, Beata Śmielak, Karolina Kopacz, Kinga Bociong
When creating a dental composite, its composition should be composed such as to provide it with the best operational properties. The organic matrix used in resin dental composites often consist of monomers such as bisphenol A-glycidyldimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), ethoxylated bisphenol A dimethacrylate (Bis-EMA), and photoinitiators.[8,16,17] Bis-GMA is characterized by low polymerization shrinkage and appropriate adhesion to tooth tissues beneficial for the dental composite.[18] However, high viscosity and chain rigidity of Bis-GMA lead to quick gel upon photoactivation resulting in a low degree of conversion. Accordingly, to this monomer a diluent is added TEGDMA – low viscosity monomer.[16] The degree of conversion of the mixture increased, but it reduced the mechanical properties and increased the polymerization shrinkage.[1,19] UDMA is also used as a base polymer. It has a lower viscosity, when compared to Bis-GMA. Highly flexible urethane linkage can improve the toughness of resin composites based on this monomer. Research has shown that the microhardness and flexural strength of homopolymer UDMA is higher than Bis-GMA and for the elastic modulus the relationship is inverse EBis-GMA < ETEGDMA.[20,21] Bis-EMA is a monomer with a similar molecular weight to Bis-GMA; however, it has a lower viscosity. As a consequence, Bis-EMA has an increased degree of conversion and cross-linking in relation to Bis-GMA.[22] Research has shown that the presence of Bis-EMA in the Bis-GMA/TEGDMA/UDMA copolymer matrix reduces the amount of leakage TEGDMA from the polymerized composite.[23] In the presented study, matrix and composites were based on the mentioned above four monomers – Bis-GMA, UDMA, TEGMA, and Bis-EMA. However, research reported that residual unreacted Bis-GMA is hydrolyzed in human saliva to bisphenol A (BPA) and may pose a threat to human health.[24–27]