camphorquinon

Camphorquinone, also spelled camphorquinon, is an organic photoinitiator widely used to initiate free-radical polymerization of methacrylate resins when exposed to visible blue light. It is derived from camphor and belongs to the class of bicyclic diketones. In dentistry, camphorquinone is the most common visible-light initiator in resin-based composites and related bonding agents.

Mechanism and use: When irradiated with blue light, camphorquinone absorbs photons and reaches an excited state. In the presence of a co-initiator, typically a tertiary amine, it forms initiating radicals that start the polymerization of methacrylate groups. The efficiency and depth of cure depend on the initiator concentration, the co-initiator system, and the light source. Camphorquinone is typically used at about 0.5–1.5% by weight in resin formulations.

Properties: Camphorquinone absorbs light in the blue region with a peak near 460–470 nm, aligning with common blue-light curing units. It imparts a yellow-brown tint to resins, which can affect esthetics in dental applications. It has limited water solubility and, like other radical initiators, its performance can be influenced by oxygen and temperature.

Synthesis and origin: Camphorquinone is derived from camphor through oxidation and functionalization steps that introduce the two carbonyl groups characteristic of the compound.

Safety and handling: In practice, camphorquinone is used within formulated dental materials and laboratory products. Residual camphorquinone in cured restorations can contribute to discoloration, and standard safety and handling practices apply during manufacture and handling of bulk materials. Alternatives and co-initiators are used to tailor curing speed, depth, and esthetic properties for specific applications.