Raman scattering determination of the depth of cure of light-activated composites: influence of different clinically relevant parameters G. LELOUP*, P. E. HOLVOET*, S. BEBELMAN † & J. DEVAUX † *Department of Operative Dentistry, Universite´catholique de Louvain, Bruxelles, Belgium, and † Laboratoire de Physique et de Chimie des Hauts Polyme`res, Universite´catholique de Louvain, Louvain-la-Neuve, Belgium SUMMARY SUMMARY The purpose of this research was to determine the depth of cure of light-activated composites in relation with different clinically rele- vant parameters. A Raman spectroscopic method has been used. The measurement of cure is made on a relative basis by comparing the vibration band of the residual unpolymerized methacrylate C@C bond at 1640 cm –1 against the aromatic C@C stretching band at 1610 cm –1 used as an internal standard. The information gained draw attention to the import- ance of light transmission during the exposure. The influence of sample’s thickness on the depth of cure is illustrated by a second order polynomial regression. The shade and translucency of the resin composite also modify the light transmission and thus have a significant influence on the degree of conversion. Moreover the light-source intensity and the distance from the curing tip are important parameters of influence. A significant reduction of the depth of cure is observed for all sample thick- ness of resin composite tested when using a light device with an intensity of 300 mW cm –2 as well as using a distance from the curing tip higher than 20 mm. KEYWORDS KEYWORDS: depth of cure, resin composites, micro- Raman spectroscopy Introduction Dental practitioners are demanding a restorative material that can accommodate a wide range of appli- cations for both anterior and posterior restorations. The research of such an ideal dental restorative material, exhibiting appropriate physical and mechanical prop- erties as well as excellent aesthetics, has resulted in the introduction of light-cured polymer composites. These materials have one major drawback: the degree to which they cure is proportional to the amount of light to which they are exposed. So, they polymerize to a certain depth which varies with the penetration of a light beam in the bulk material. This decrement in cure has been termed ‘depth of cure’ and has significant influence on both the physical (Asmussen, 1982; Unterbrink & Muessner, 1995; Baharav et al., 1997; Ferracane et al., 1997) and biological (Caughman et al., 1991) properties of restorations. Because dental restorations need an optimal poly- merization level, investigators have studied the effect of different parameters on the depth of cure. They found that the depth of cure of light-activated composite resins depends on the material filler composition (Ruyter & Oysaed, 1982; Yearn, 1985), its shade and translucency (Swartz, Philips & Rhodes, 1983; Ferra- cane et al., 1986; Davidson-Kaban et al., 1997), the intensity of the light source (Yearn, 1985; Rueggeberg et al., 1994; Unterbrink & Muessner, 1995; Davidson- Kaban et al., 1997; Sakaguchi & Berge, 1998) or the distance from the curing tip (Swartz et al., 1983; Pires et al., 1993; Hansen & Asmussen, 1997). They usually employed methods like microhardness measurement, optical microscopy, scraping test or infrared spec- troscopy. In another paper (Pianelli et al., 1999), a micro-Raman technique was demonstrated to be more convenient and also more accurate than the popular Fourier-transform infra red spectroscopy (FT-IR) one. ª 2002 Blackwell Science Ltd 510 Journal of Oral Rehabilitation 2002 29; 510–515