SBIR-STTR Award

Recently, New Photonics LLC (NP) demonstrated that newly developed blue Light Emitting Diodes (LEDs) used in continuous mode can provide up to 4 mm depth of cure in Dental composite resin in about 2 minutes of exposure. Despite its many advantages, the commercial viability of this LED-based technology would be significantly enhanced if the time of exposure necessary for curing is reduced to a few seconds. The application proposes to investigate the use of LEDs in a pulsed mode as a source of optical radiation for curing Dental composite resins. The spectral output of the widely available blue-green LEDs peaks at the excitation maximum of the camphorquinone photoinitiators used in most Dental composites. The luminous output of the LEDs is entirely within the absorption band of the photoinitiators. Use of pulsed LEDs is an attractive option because it may allow for fine-tuning of the pulse timings to suitably match the photopolymerization dynamics thus reducing cure time to what is currently achieved with lasers. NP will develop a pulsed LED curing system and investigate the curing characteristics (depth of cure, degree of conversion of monomers to polymer, hardness, time of exposure, thermal load) of Dental resins cured using pulsed LEDs.

Thesaurus Terms:
biomedical equipment development, composite resin, dental material, light emission, photoactivation, physical process, visible light laser bioengineering /biomedical engineering

LED based curing lights are beginning to replace conventional halogen lamps as the first choice for dental photo-curing applications. The target of this proposal is to develop a new generation LED dental curing light. It will be the first curing light that is optimized according to the kinetic response of the dental composite, which plays a key role in determining the curing time, the quality of the cured resin, and the heat production. The proposed LED light cures the dental composite by a train of short-duration light pulses, where the time scale of the pulse width and pulse period is designed to match with the response time of the photo-initiation process. This 'resonant' curing mode yields the best quantum efficiency for photo-polymerization. Phase I study of this project leads to successful demonstration of the feasibility and advantages of the proposed pulsed LED light over conventional light curing units (LCUs). It was found that the pulsed LED light yields 10-12% more curing depth and better surface hardness than that obtained by a continuous wave (CW) light with same exposure energy. For phase II project, we will establish a simple but practical model to analyze the kinetic characteristics of the photo-polymerization process and use the model as a guide to help us further explore the potential of the pulsed LED light for dental composite curing. A Raman spectrometer will be utilized in combination with the pulsed LED for real time and in situ monitoring of the photo-polymerization process as to obtain the parameters used in the kinetic model. We will conduct a systematic study on the physical properties of the dental composite cured by both conventional LCUs and the proposed pulsed LED, which will be used to further optimize the pulse sequence. A novel automatic curing time control method employing fluorescence level monitoring at off-time of the pulse train will also be explored. Finally, we will develop a prototype pulsed LED photo-curing system capable of curing all dental polymer resins currently on the market in a time scale comparable to that can be obtained using laser radiation (typically 5-10 seconds) and with a high "quality" of cure in terms of depth of cure, hardness, shrinkage, shear bond strength, and temperature change in the resin