Effect of light-tip distance on polymerization of resin composite

The inability to place a light tip in close approximation to a resin restoration may affect the resultant polymerization and clinical durability of the restoration. This research measured light intensity at the surface of a resin composite, as well as 2 mm within its bulk, as the tip-to-resin distance is moved from 0 to 10 mm. The polymerization of the resin composite at both locations was measured for the various tip distances using exposure durations of 10, 20, 40, and 60 seconds. Light intensity did not decrease with the inverse square of the tip distance. The polymerization on the surface was greatly dependent upon the duration of exposure. The extent of polymerization 2 mm below the surface was still dependent primarily upon exposure duration, but intensity had a significant affect. For exposure durations of 10, 20, and 40 seconds, a tip distance greater than 4 mm demonstrated a significant decrease in resin polymerization 2 mm below the resin composite surface.