Light curing

The majority of the commercial radiation-curable coating systems (high energy electron and light-cured coating systems) are clear or contain siflca... 

In 1919, Huldschinski (8) realized that uv light cured rickets and impacted on its etiology. The uv light and codHver oil were found to be usehil in the treatment of the disease, and irradiation of food produced the same effect as irradiation of the animal. The link between irradiation and plant materials led to the conclusion that ergosterol was an antirachitic substance, and an extensive effort was made to characterize the chemistry of irradiated ergosterol. 

Another development has been the advent of the dual-cure resin cements. These are hybrids of glass polyalkenoate cements and methacrylates that set both by an add-base cementation reaction and by vinyl polymerization (which may be initiated by light-curing). In these materials, the solvent is not water but a mixture of water and hydroxyethylmethacrylate which is capable of taking dimethacrylates and poly(acrylic add)-containing vinyl groups into solution. In the absence of light these materials set slowly and... 

In chemically-cured materials, one example of an initiator/activator system is hydrogen peroxide as initiator, ascorbic acid as activator and cupric sulphate as co-activator. In light-cured materials, camphorquinone is used as a visible-light photochemical initiator, sodium p-toluene-sulphinate as activator and ethyl 4-dimethylaminobenzoate as photoaccelerator. 

Minnesota Mining Manufacturing Company. (1989). Vitrabond Light Cure Glass Ionomer Cement Liner/Base. Report of Dental Products, 3M Health Care. 

Nicholson, J. W., Anstice, H. M. McLean, J. W. (1992). A preliminary report on the effect of storage in water on the properties of commercial light-cured glass-ionomer cements. British Dental Journal, 173, 98-101. 

Use of visible light is desirable if a portable light curing source is to be used because of the reduced eye hazard and the fact that these lamps do not contain mercury. However, at the present time there is no commercially available portable light source meeting the performance requirements. 

S.B. Mitra, In vitro fluoride release from a light-cured glass-ionomer liner/base, J. Dent. Res. 70 (1991) 75-78. 

H. Forss, Release of fluoride and other elements from light cured glass ionomers in neutral and acidic conditions, J. Dent. Res. 72 (1993) 1257-1262. 

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. 

During the early stages of the setting reaction, both water uptake and water loss can occur. The matrix is sensitive to water attack and can degrade. It is therefore desirable that the material set as soon as possible once placed in the mouth. Light-cured varnishes are often used to seal newly placed restorations... 

When a restoration is light cured, there is a relatively long time for the dentist to place the material and adapt the composite to the preparation. The dentist can then use a light source (470 nm, with an output of at least 300mW/cm2) to obtain complete cure of the material within 60 s [182]. 

With the light curing mechanism, there is a limitation to the penetration of the light. The dentist may have to place a restoration that is 6 + mm thick, whereas the light may penetrate only 2 mm [182]. Factors that affect this penetration are the translucence of the material, the color or shade used to match the tooth, the ability to place the light source close to the material being polymerized, and the intensity of the source. Under relatively ideal conditions, the mean depth of cure is approximately 4-5 mm. Thus, the dental application requires that the material be placed in layers. Due to the oxygen inhibition of the outside surface of the resin layers, additional layers can be laminated and cured with the appearance of uniformity of the final restoration. 

Manual shutter open. (Courtesy of Dymax Light Curing Systems.)... 

Photopolymerized hyaluronic Visible light cure Requires several minutes... 

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