Polymerization behavior of a light-cured resin using the laser speckle-correlation method

Tomomi Sato, DDS,(a) Masashi Miyazaki, DDS, PhD,(a,b) Akitomo Rikuta, DDS, PhD,(a,b) Hiroyasu Kurokawa, DDS, PhD,(a,b) and Toshiki Takamizawa, DDS, PhD(a)

(a)Department of Operative Dentistry, and (b)Division of Biomaterial Science, Dental Research Center, Nihon University School of Dentistry, Tokyo, Japan

Purpose: The aim of this study was to monitor the polymerization reaction of a light-cured resin using the laser speckle-correlation method.
Materials and Methods: The experimental apparatus comprised semiconductor lasers, a speckle analyzer and a computer-controlled data-acquisition system. The resin composite was condensed into a glass tube and irradiated using a curing unit with a light intensity of 100 or 600 mW/cm2. The speckle patterns obtained from the lateral surfaces and the underside of the specimen were monitored using a CCD camera connected to a personal computer. A simplified correlation value was obtained for each pair of adjacent speckle patterns. The images of the speckle patterns were analyzed using the phase-only correlation method. The speckle contrast was then obtained as a function of the time that elapsed while measurements were made.
Results: The speckle contrast decreased soon after light exposure commenced, then gradually increased after irradiation. The changes in speckle contrast corresponded to changes in the polymerization reaction of the light-cured resin. The speckle-contrast data obtained from the underside were lower than those from the lateral surfaces. This tendency was more pronounced when the specimen was irradiated with lower intensity light.
Conclusion: This approach has the potential to record accurately the polymerization characteristics of light-cured resins. (Int Chin J Dent 2004; 4: 45-50.)
Clinical Significance: These data suggest that the shrinkage characteristics of a light-cured resin were influenced by the light intensity of the curing unit.

Key Words: laser speckle, light-cured resin, light irradiation, polymerization.