The influence of the tilt angle and distance of the light guide to the sensor surface on the delivered radiant exposure was examined for three different LCUs (Celalux 2 [C2], Bluephase [BP] and Translux Powerblue [TPB]). The measurements were performed for 20 s each with five different tilt angles (α = 0°, 5°, 10°, 15°, 20°) and nine different distances (L = 1, 2, 3, 4, 5, 6, 7, 8, 9 mm).
For all LCUs, a distinct influence of the tilt angle on the delivered amount of fluence was found. At 0° tilt the C2 delivered a total light energy of 38.55 J/cm2. By increasing the tilt of the light guide the amount of energy applied significantly decreased. At 20° tilt a reduction by 31.2% of the original light fluence was recorded. However, the C2 was the most powerful LCU measured. Even under optimum measurement conditions, the BP delivered a fluence of only 14.8 J/cm2. At a tilt angle of 20°, though, the light sensor still registered 92.7% of the original output power. Under the same conditions, the TPB delivered 81.4%.
With increasing distance of the light guide exit face to the surface of the sensor all LCUs showed a significant loss in delivered light energy. At a distance of 2 mm the C2 showed a reduction by 46.7%, whereas total fluence of BP and TPB were reduced by 3.8% and 4.8%, respectively.
The choice of LCU and the application of an appropriate curing time are important for successful polymerization. Nevertheless, a perpendicular positioning of the light guide as close as possible to the surface of the composite increment is of essential importance in order to ensure sufficient delivery of light.