The silver sorption layer in dental composites: three year results

The purpose of this investigation was to observe the behaviour of a recently discovered silver sorption layer in seven dental composites for three years.

Rectangular block testpieces (3.0 x 2.5 x 2.5 mm) of seven resin composites were fabricated and the resin rich layer removed from one surface by grinding on silica carbide paper. The testpieces were immersed in aqueous AgNO3 (3 mol/l). After 26, 42, 90, 180, 360, 540, 720 and 1085 days, respectively, nine specimens of each material were removed to measure the depth of silver stain in the different composites.

The depth of silver stain continued to increase at a rate proportional to (time)0.5. After three years, five homogeneous subsets [HS] were distinguished for the resin rich surface [HS1] Occlusin (stain depth = 45.6 microns); [HS2] Clearfil (117.8 microns), [HS3] Heliomolar (145.6 microns), Concise (148.8 microns), P-30 (168.9 microns); [HS4] Silux (243.3 microns); [HS5] Profile-TLC (446.7 microns). For the ground surface, the materials were in similar subsets but the depth of stain was less. Different coloured layers were seen within the sorption layer in some materials.

The linear relationship between the depth of stain and (time)0.5 indicate that the mechanism controlling the sorption is Case 1 (Fickian) diffusion. The different depths in the individual materials may indicate differences in the segmental mobility of the polymer chains and free space within the resin phase of the composites. If the silver sorption layer marks the extent of water penetration, then the results show different depth distributions for individual composites.