The effect of prolonged packing on the surface hardness of posterior composites

This study evaluated the effect of four different packing times on the Knoop Hardness Number of three composites (Surefil, Z100 and Spectrum TPH). Ten samples of each composite were prepared for each packing time and 10 readings were made on each sample to produce the KHN. Photomicrographs were made of 147 indentations to determine whether the indentations had routinely been made on porosity-free sites. Statistical analysis was made using two-way ANOVA and least square means. Generally, as the packing time increased, the KHN decreased,and although the indentations appeared to have been made in porosity-free composite, the potential effect of porosities was not discounted. Increasing the packing time for clinical composites may result in a lower KHN and increased clinical wear, which would further increase if also associated with porosities within the composite.