Factors Affecting the Energy Delivered to Simulated Class I and Class V Preparations(2)

e varies widely among brands of curing units, and the choice of light guide confounds the issue.^11-17 For example, for one light curing unit, researchers reported a 50% reduction in light intensity as the distance increased from 0 mm to 6 mm with use of a standard light guide. However, with use of a turbo light guide in the same light curing unit, the reduction in irradiance over the same distance (0 to 6 mm) was 77%.¹⁴ This finding is clinically relevant for Class II restorations, for which the distance from the end of the light guide to the gingival floor of a proximal box can easily be 6 mm or more.

 

Studies establishing the relationship between energy density received and qualities of the resultant resin curing have typically utilized ideal laboratory conditions, whereby the light curing unit was fixed at 90° directly above the resin, maximizing exposure of the restoration to the beam and minimizing the amount of light scattering at the surface.^3,5-11,13 However, in a clinical environment, there are substantial deviations from this ideal configuration, and the clinician may have difficulty achieving or consistently maintaining the orientation of the light guide end at 90° with respect to the restoration. Under these clinical conditions, it is unlikely that experimentally determined exposure times will deliver the intended total dose of light energy. Furthermore, operator error may cause the curing light to shift in position relative to the restoration. This could reduce the actual time that the resin is exposed to the light and the energy delivered to the restoration.

Many studies of the effects of different light curing units on resin polymerization have used hand-held dental curing radiometers to measure irradiance,^18-21 but other work has shown that these instruments are inaccurate.^22,23 In addition, these meters report only the irradiance at the tip-end of the curing light; they do not report the irradiance or energy actually received by the resin restora