Composite resins cure lamps

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]. 

It is difficult to draw hard and fast conclusions concerning the relative merits of the various types of cure lamp on the market. All types seem capable of producing an acceptable degree of cure, and differences found in scientific studies probably do not translate into significant differences in clinical performance. In practice, the performance of aU cure lamps appears to give acceptable degrees of cure of commercial composite resins, and so any type of commercial dental cure lamp can safely be used for activating the cure of composites. 

Various types of cure lamp are available for use with composite resins, and all of them seem to give clinically acceptable degrees of cure. 

The conventional filler, Raysorb T-4000, is a commercial unreactive particulate glass that is widely used in conventional composite resins, and was also incorporated either untreated or silanated. In all cases, discs of material of dimensions 13 mm diameter X 1mm thickness were prepared and cured from each side with a conventional dental curing lamp through a glass microscope slide for 40 s. They were stored in water for 24 h, after which they were tested for net water uptake and biaxial flexure strength [23]. Results are shown in Table 4.4. 

For light-cured materials, the initiator system can be based on camphorquinone, so that cements can be cured with a conventional dental cure lamp emitting at a maximum wavelength around 470nm. Unlike formulations of composite resin, these materials cannot deploy amines as activators, because they would react with the carboxylic acid groups on the polymer, forming salts. Instead, a substance such as sodium p-toluene sulfinide is used as the activator. In addition, a photo-accelerator such as ethyl 4-NJ -dimethylamino benzoate is included [10]. 

The resin component is ethylene urethane dimethacrylate, UDMA [40], a substance of the type used in conunercial composite resins. It contains two carbon-carbon double bonds and these are capable of undergoing addition polymerization. This particular reaction is triggered by the photo-initiators present when the material is exposed to light from a dental cure lamp. The calcium hydroxide component effectively serves as filler and is completely enclosed in the polymeric UDMA matrix... 

On-aircraft repairs of composite using a rapid-cure resin system of composite component with UV light irradiation based on TRI patenP have been developed by the U.S. Air Force Research Laboratory. Alternating layers of the acrylate-based resin system and woven fiberglass (the widely used wet la)mp procedure) are applied to fill the hole and form a UV curable composition. The width of the patch can be up to 2 ft (0.6 m) and the depth as much as 0.2 in. (5 mm). The cure time using a 400 W UVA lamp is reported to be 20 min. Although it is essentially a depot repair, it can be done field when necessary to return an aircraft to service. Because of the necessity to cure relatively thick repair patches, Us-acylphosphine oxide was used as a photoinitiator. An example of the patented UV curable resin system used for the repairs is in Table 11.1. 

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