Composite resins camphorquinone

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. 

When composite resins were first introduced, their polymerization involved free radical initiation by a combination of benzoyl peroxide with tertiary amine activator, de-hvered in two different pastes, known respectively as base and catalyst. Contemporary composites are visible light-activated one-paste systems and the principal photoinitiator used is camphorquinone [70,80], It is used in conjunction with a co-initiator, typically an amine [81], This latter compound does not absorb hght, but is necessary to react with the fight-activated camphorquinone molecule to generate free radicals and hence initiate the chain polymerization. 

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]. 

Modem composite resins are cured by application of visible light at 470 nm, which activates a photo-sensitive initiator such as camphorquinone. The camphorquinone readily dissociates to form free radicals when exposed to visible light, and these bring about a cure reaction, converting the highly viscous paste to a hard, durable solid material. Typical material properties of these materials are shown in O Table 56.3. 

The monomers that yielded homo- or copolymers were formulated into composites. Three comonomers, PBD, PBMD and p-dimethoxybenzene (DMOB), were combined individually with EBPADM, an ethoxylated bisphenol A dimethacrylate (Diacryl 101, Nouiy Chemicals), in various ratios to form the resin components of the composites. The initiator system used was 0.4 wt% camphorquinone (CQ) and 0.8 wt% ethyl 4-A, A -dimethylaminobenzoate (4-EDMAB). 

The most common restoratives comprise a mineral filler mixed with a vinyl monomer (often called a resin), which undergo photoinitiated free radical Chain polymerization. Typical components inclnde the adduct of bis-phenol A and glycidy methacrylate (bis-GMA) or nrethane dimethacrylate (UDMA), camphorquinone initiator (activated by a visible bine light sonrce of 480 nm) and a filler such as zirconia or borosilicate glass, which can comprise 70% by mass of the system and provides the strength . The whole is referred to as a composite . 

SCH 12] Schneider L.F.J., Cavalcante L.M., Prahl S.A. et al, Curing efficiency of dental resin composites formulated with camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide . Dental Materials, vol. 28, no. 4, pp. 392-397, 2012. 

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