Light-cured composite resins

Rice SL, Bailey WF, Wayne SF, Burns JA Comparative in vitro sliding-wear study of conventional, microfilled and light cured composite resin and glass ionomer cement. J Dent Res 1984 63 1173-1175. 

First, cavities were cut in a set of teeth, and these were mounted in dental stone and tested to failure in compression. Lastly, two types of repair were prepared in teeth, namely horizontally or obliquely cut, and these were repaired with light-cured composite resin. These teeth were then mounted in dental stone and tested in compression. Results are shown in Table 1.1. They show that repairing the tooth brings the strength... 

Y.J. Park, K.H. Chai, H.R. Rawls, Development of a new photoinitiation system for dental light-cure composite resins. Dent. Mater. 15 (1999) 120-127. 

D. Sustersic, P. Cevc, N. Funuk, M.M. Pintar, Determination of curing time in visible-light-cured composite resins of different thickness by electron paramagnetic resonance, J. Mater. Sci. Mater. Med. 8 (1997) 507-510. 

Takeshige, F., Kinimoto, Y., Torii, M. Additional heat-curing of light-cured composite resin for inlay restoration. Adhes. Dent. 35, 59-66 (1995)... 

Resins are also used for permanent tooth-colored veneers on fixed prostheses, ie, crown and bridges. Compositions for this application include acryflcs, vinyl—acryflcs, and dimethacrylates, as well as silica- or quartz-microfilled composites. The resins are placed on the metallic substrates of the prostheses and cured by heat or light. These resins are inexpensive, easy to fabricate, and can be matched to the color of tooth stmcture. Acrylic facings do not chemically adhere to the metals and are retained only by curing the resin into mechanical undercuts designed into the metal substrate. They have relatively low mechanical strength and color stability, and poor abrasion and strain resistance they also deform more under the stress of mastication than porcelain veneers or facings. 

Composite resins can be cured using a variety of methods. Intraoral curing can be done by chemical means, where amine—peroxide initiators are blended in the material to start the free-radical reaction. Visible light in the blue (470—490 nm) spectmm is used to intraoraHy cure systems containing amine—quin one initiators (247). Ultraviolet systems were used in some early materials but are no longer available (248). Laboratory curing of indirect restorations can be done by the above methods as well as the additional appHcation of heat and pressure (249,250). 

G. Eliades, A. Kakaboura, G. Palaghias, Acid base reaction and fluoride release profiles in visible light-cured polyacid modified composite resin restorations. Dent. Mater. 14 (1998) 57-63. 

MPa, compressive strength 245-303 MPa, water sorption 0.5-0.7/cm ) considerably exceeded the minimum requirement of the specification for dental composite resins (37). If low concentrations are employed in the formulations especially with DEAPAA as accelerator, the cured composites are nearly colorless. No perceptible change occurs in the color of the specimens containing a UV absorber after 24 hours exposure to a UV light source. Because of the excellent overall physical properties, nearly colorless appearance and the potentially better biocompatibility, compositions using these accelerators should yield improved restoratives. 

Both types of composite resin should be apphed using the technique of incremental build-up in which layers not exceeding 2 mm are placed and light-cured prior to the placement of the next layer [44], This allows the layers to be fully cured all the way through, and layers will adhere to each other, so that this technique does not introduce any points of weakness to the material. Occasional claims of bulk cure being acceptable have been made, ie, where layers of 5 mm or so are cured in a single burst of light. However, the scientific evidence does not support such claims, and they should be treated with caution [1],... 

By contrast, most modem composites cure by a light-activated process. The typical photoinitiator system used is based on camphorquinone (Fig. 3.4) with an aromatic tertiary amine as accelerator [13]. These are sensitive to blue light at 468 nm, and irradiation causes homolytic decomposition of the camphorquinone to form free radicals, which then initiate the polymerization and associated hardening of the composite resin. 

The majority of the polymerization of a dental composite resin occurs very quickly, typically during the 20-40 s or so of light irradiation from the dental cure lamp. However, free radicals within the material do not terminate immediately the lamp switches off. Hence they are able to continue their propagation steps for some time after this initial cure, as growing polymer molecules containing free radical centres continue to incorporate extra monomer molecules [24]. Shrinkage, which is associated with polymerization, has been shown to continue for up to 24h after initial setting [25] in a process known as post-polymerization [26]. 

K. Fujita, T. Ikemi, N. Nishiyama, Effects of particle size of silica filler on polymerization conversion in a light-curing resin composite. Dent. Mater. 27 (2011) 1079-1085. 

K. Arakawa, Shrinkage forces dne to polymerization of light-cured dental composite resin in cavities, Polym. Test. 29 (2010) 1052-1056. 

G.K.P. Barros, F.H.B. Aguiar, AJ. Santos, J.R. Lovadine, Effect of different intensity light curing modes on microleakage to two resin composite restorations. Open Dent. 28 (2003) 642-646. 

B. Ozturk, A.N. Ozturk, A. Usumez, S. Usumez, F. Omer, Temperature rise during adhesive and resin composite photopolymerization with various light curing systems. Open Dent. 29 (2004) 325-332. 

J. Manhaart, K.-H. Kunzehnann, H.Y. Chen, R. Hickel, Mechanical properties and wear behaviour of light-cured packable composite resins, Dent. Mater. 16 (2000) 33-40. 

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