Photoinitiators in Dentistry: A Review

Abstract

Polymerization of Resin Based Composites (RBCs) initiated by a light curing unit activating photoinitiators. Different RBCs require different light energy levels for proper curing. Manufacturers are now producing RBCs with more than one initiator and not all of these will be properly polymerised with blue LED lights. An added problem is that manufacturers do not always indicate the type of photoinitiators in their materials. This review discusses the importance of matching the spectral output of LCUs to the absorption spectra of RBCs and the consequences of spectral mismatch. Resin based composites (RBCs) were first introduced in the 1960s and with development of effective and reliable dentine bonding systems2, have been used routinely as a filling material for both anterior and posterior teeth. The early RBCs were either chemically cured two component materials or photo-initiated materials that used UV initiators in the beginning and then transitioned to visible light initiators such as camphorquinine which was introduced in 1978.3 The first report of a light curing material was of an ultraviolet (UV) cured fissure sealant. However, due to the limited penetration depth of the UV light and the potential health hazards, this system was quickly abandoned. The advancement of science yielded light curing materials which contributed to a significant clinical progress over the UV and chemically cured RBCs. Additional advancements to direct RBC restoration materials included luting agents for ceramic restorations, pit and fissure sealants and resin modified glass ionomers. Polymerization in an RBC is initiated by a light curing unit (LCU); this technology is based on the use of photoreactive systems that absorb light irradiation from the LCUs at appropriate wavelength. Then the photoinitiators contained in the RBCs, absorb the incoming photons from the LCU and the monomers in the molecular structure become excited and in that active state, there is a change from monomers into a polymer network. The success of this technology hinges on matching the spectral emission of the LCU with the requirements of the photoinitiator system to convert the monomers into a polymer network. The amount of activated photo initiator depends on the concentration of photoinitiator in the material, the number of photons to which the material is exposed and the energy of the photons (wavelength), the latter depending on the curing light.The most common photoinitiator in dental materials today is camphorquinone, which has a peak activity around 470 nanometres. The factors affecting polymerization include filler type, size and loading, the thickness and shade of the restorative material, the effectiveness of light transmission (eg. light guide tips being free from debris and scratches), exposure time, distance of the light source from the restorative material and light intensity. It is important to note that the photoinitiator activation occurs at specific wavelengths, in other words, the optimum efficiency is obtained when the peak absorptivity ...

An Evaluation of the Light Output from 22 Contemporary Light Curing Units

“…Camphorquinone (CQ) is the traditional initiator used in most RBCs and it is mostly activated by blue light peaking at 468 nm wavelength. Several new photoinitiators have been developed as an alternative to CQ, e.g., trimethylbenzoyldiphenylphosphine oxide (TPO, ranging from 375 to 410 nm) and 1-phenyl-1,2-propanedione (PPD, maximum wavelength ≈ 410 nm) (12,13). Some broad-spectrum LED units include additional LED emitters that produce light at these lower wavelengths, which are in the 'violet' range, to make these LCUs compatible with a wider range of…”

Pilot Study Of Photoallergic Reactions To Non-steroidal Anti-inflammatory Agents, Chemicals Used In Dental Composites And Antiseptic Agents Among Dental Professionals

“…The concentration of CQ in dental resins varies significantly. An analysis of seven visible-lightcurable dental composite resins revealed that the concentration of CQ in the resin phase was between 0.17 and 1.03 wt% (12,13).…”

Photo-irradiation paradigm: Mapping a remarkable facile technique used for advanced drug, gene and cell delivery

“…This moiety contains domain bond (almost double bond or epoxide) that is irreversibly changed by irradiation in the presence of PIS. Acrylates [63], methacrylates [13], and cyano-acrylates [46] are commonly used photosensitive moieties, that can be covalently crosslinked with the excitation of free radical generating PIs. Similarly, fumarate moiety which is commonly used for the formulation of different injectable/implantable biomaterials is covalently crosslinked upon exposure to photo-irradiation [64].…”

“…Several light sources have been practically explored for the photo-formulation including ultraviolet (UV) lamps, visible light lamps, plasma arc lamps, light emitted diode, titanium-sapphire laser, and gamma irradiator [16,19,20,46,53,93]. The main differences associated with those sources are the generated light wavelength, intensity and the associated amount of entropy loss (heat evolved) [53].…”

“…The third classification system is according to the type of light used to induce photoinitiation where PIs have also been categorized into ultraviolet (UV), visible and laser PIs [46,55,56]. The only dissimilarity between them is the difference in the appropriate light wavelength range where absorption capability of the PIs occurs.…”