Effect of light intensity on polymerisation of three composite resins.

The polymerisation ability of twelve light activation units, a mixture of new and old, was assessed by micro-hardness evaluation of samples of three composite resins cured with the lights. Light intensity was assessed using a commercially available band held dental radiometer. Intensity values were representative of the range of intensities that may be found in clinical practice. When a 2 mm thick sample of a microfilled composite was cured for 40s less than half of the light units evaluated produced an acceptable lower surface polymerisation. All but one of the light units tested produced a satisfactory lower surface cure with the monomodal and the hybrid composites. For the products tested material composition was an important factor in regard to the ability to cure a 2 mm thick increment of material with a 40s irradiation time. A significant correlation was found between lower surface hardness and light intensity. Standardising the area of the light sensing device of the hand held radiometer with respect to the diameter of the specimen to be cured improved the correlation between light intensity and lower surface micro-hardness.