Subsurface degradation of resin-based composites

Objectives. To determine the depth of a degraded subsurface layer produced in dental composites as a result of exposure to lactic acid or NaOH, by observing the penetration of AgNO3 solution. Methods. Specimens were prepared from four resin composites; Point 4 (Kerr), Premise (Kerr), Filtek Supreme (3M/ESPE), Ceram X (Dentsply), and two polyacid-modified resin composites; Dyract (Dentsply) and F2000 (3M/ESPE). The specimens were immersed in distilled water for 1 week, transferred to one of three aqueous media at 60 degrees C for 2 weeks; distilled water, 0.01 mol/L lactic acid or 0.1N NaOH, washed and immersed in 50% (w/w) aqueous silver nitrate for 10 days at 60 degrees C and placed in a photodeveloper solution. After reduction of the silver, specimens were embedded in epoxy resin, sectioned and polished, coated with carbon, and examined by backscattered mode scanning electron microscopy. The depth of silver penetration into the degraded area was measured from the SEM micrographs. Energy dispersive analysis X-ray (EDAX) was used to confirm the presence of silver. Results. NaOH produced the greatest depth of degradation and lactic acid the least. Premise showed the greatest depth of silver penetration when subjected to NaOH, and Filtek Supreme the second with peeling of the surface and cracking, whereas F2000 and Point 4 showed the least in NaOH and lactic acid. Significance. ANOVA and Tukey's test showed that the depth of silver penetration was material and solution dependent, and the differences were significant for most of the materials (P < 0.05). (c) 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.