Objective: The objective was to compare the degradation characteristics of two composite resin materials that contain ZrO2/SiO2 filler particles of different size and morphology. Methods: The materials studied were: (S) Filtek Supreme and (Z) Filtek Z- 250. The filler in S is a combination of nano-sized (5- 20 nm) particles of clusters of ZrO2/SiO2 and SiO2. Z contains only ZrO2/SiO2 fillers of larger particle size (.01 to 3.5µ). The volume % of fillers in both resins is essentially the same around 60%. The composition of resin matrix of the two materials is also similar. Light cured discs (n=3) of each material were exposed to 0.1 NaOH at 60º C for two weeks. Degradation parameters were evaluated by (1) mass loss by gravimetry; (2) Si loss from solution analysis by ICP; (3) degradation depth by optical microscopy of polished sections of degraded discs; and (4) structural changes due to degradation by SEM. Details of the evaluation technique including the rational for the alkaline medium , have been reported before [ Sarkar, J. Biomed. Mater. Res. (Appl. Biomater.) 53,371,2000].
Results: The quantitative degradation parameters (mean ± standard deviation) are shown below.
| Material | Mass Loss (%) | Degradation Depth (micron) | Si. Loss (ppm/cm2) |
| S | 9.36 ± 0.15 | 194.37 ± 11.16 | 760.35 ± 26.86 |
| Z | 5.92 ± 0.36 | 92.67 ± 4.65 | 509.41 ± 18.18 |
All parameters associated with S were significantly ( p< .0002) higher than those of Z indicating its hydrolytic degradation resistance is inferior to that of Z. Surface and subsurface cracking were seen in both materials; however, cracking was more severe in S. The filler- matrix debonding due to NaOH exposure was evidenced in Z but not resolved in S.
Conclusion: The enhanced degradation of S is attributed to reduced filler size that increases the matrix-filler interface, the main diffusion path for hydroxyl ions.