Internal corrosion in dental composite wear: Its significance and simulation

The internal corrosion of dental resin composites is associated with water- sorption and leads to (1) interfacial debonding, (2) filler dissolution, (3 ) matrix cracking, and (4) subsurface damage. The last factor creates a con dition for "corrosive-wear" in which the damaged layer is worn with ease ex posing a new surface and perpetuating the cycle of corrosion and wear. Cent ral to the simulation of in vivo corrosive-wear is the recreation of the su bsurface damage layer. To produce this layer in water, artificial saliva, a nd in media of low pH is time-consuming, because the degradation process in these environments is extremely slow. In laboratory wear tests using aqueo us environments, the contact time of resin composites with water is too sho rt to cause significant internal degradation. Thus, data obtained from such tests represent abrasive and not corrosive-wear, and do not correlate well with in vivo wear data. In considering this limitation of the above media for accelerated wear tests, an alkaline medium has been used in this study to simulate corrosive-wear of eleven commercial composites. The procedure c onsists of exposing each material to 0.1 N NaOH at 60 degrees C for 2 weeks followed by abrasion in a tooth brushing machine. The medium choice is bas ed on the rationale that in vivo degradation arises from reaction with the OH-, and this reaction can be enhanced by raising the pH and the temperatur e of the medium. The warm NaOH solution satisfies both these conditions. Pa rameters examined to evaluate the resistance of each composite to corrosion and wear were (1) mass loss, (2) Si-loss, (3) degradation depth, and (4) w ear depth, respectively. A highly significant correlation has been observed among various corrosion and wear parameters. SEM examination indicated deg radation to be associated with interfacial separation, filler dissolution, matrix cracking, and subsurface damage. These features are characteristics of in vivo worn composite restorations. Time is of utmost importance in lab oratory evaluation of restorative materials. The ability of NaOH to meet th is expediency and to mimic the in vivo degradation process makes it a usefu l medium for corrosive-wear studies of dental composites. (C) 2000 John Wil ey & Sons, Inc.