The widespread use of camphorquinone (CQ) as a photosensitizer (photoinitiator) in light-curing composite resins (especially dental restorative materials) is mainly closely related to its unique chemical properties and application advantages. The following are the specific reasons analyzed:
1. Matching visible light wavelength, suitable for clinical application
Absorption characteristics:
The absorption peak of camphorquinone is in the 468 nm blue light region, which is highly matched with the blue light (450-490 nm) emitted by dental light curing equipment (e.g. LED light curing lamps).
Traditional UV curing agents (e.g. benzene diphenyl ethers) require ultraviolet (UV) light to be excited, but UV is harmful to human tissue, while blue light is safer and penetrating for oral operations.
High photoinitiation efficiency:
CQ rapidly absorbs energy under blue light irradiation and generates active free radicals (through hydrogen capture reaction or synergistic effect with amine accelerators), which efficiently initiates the polymerization of resin monomers (e.g. Bis-GMA, UDMA).
2. Good biocompatibility and safety
Low cytotoxicity:
Camphor quinone itself and its photolysis products (e.g. camphor derivatives) have low toxicity and meet the biocompatibility standards for dental materials (e.g. ISO 10993).
Compared to other photoinitiators (e.g. TPO), CQ has lower residuals after curing and better long-term safety.
No irritating odor:
CQ has no obvious volatile or irritating odor, which is suitable for use in a closed oral environment to avoid patient discomfort.
3. Compatibility with resin systems
Solubility and stability:
CQ has high solubility (about 0.1-1 wt%) in resin matrix (e.g. methacrylate monomers) and is chemically stable at room temperature, not easy to spontaneous polymerization or degradation, prolonging the storage period of the material.
Color adaptability:
CQ itself is light yellow, but the color has little effect after the resin is cured, which is especially suitable for dental restorative materials for aesthetic requirements (such as composite resins need to match the natural tooth color).
4. Synergy and formulation flexibility
Synergy with amine accelerators:
Clinical formulations often use CQ in combination with tertiary amine accelerators (such as DMABEE, 4-EDMAB) to form a redox system:
Blue light excitation of CQ → CQ from the amine hydrogen atoms → generation of free radicals → initiation of resin polymerization.
This synergistic action significantly improves the initiation efficiency and allows for fast curing at low light intensities.
Adjustable curing depth:
By adjusting the CQ concentration and light intensity, the curing depth of the resin can be controlled (typically 2-4 mm) to meet the demand for layer-by-layer curing of dental restorations.
5. Proven technology and regulatory support
Historical application verification:
CQ has been used for dental resins since the 1970’s. It has accumulated a large amount of clinical data and its performance and safety have been widely recognized.
Both the American Dental Association (ADA) and ISO standards recommend CQ as the core initiator for light-curing resins.
Limitations of alternatives:
Other visible light initiators (e.g., TPO, Ivocerin) have higher initiation efficiencies but suffer from the following problems:
Color interference (e.g. TPO is yellow, which affects aesthetics);
Toxicity controversy (metabolites of some new initiators may have potential risks);
Cost and process complexity (resin formulations and equipment need to be adjusted).
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