Nanocomposites Investigated: The Correlation Between Surface Character and Color

Objectives: This study evaluated the correlation between roughness parameters (R_a and R _max) and color coordinates (L* , a*, b*) of two nanohybrid composites ( Heritage 7, Ice) and one nanofilled composite ( Z350) following finishing alone and finishing and polishing
Methods: 70 specimens (8mmX8mmX2mm) of each composite were fabricated. One group of 10 specimens served as control. The remaining specimens of 10 per group were either finished sequentially with (a) diamonds (b) stones (c) carbides or finished and polished with (d) diamonds and Sof-lex discs (e) stones and Sof-lex discs, (f) carbides and Sof-lex discs. Following instrumentation the specimens were assessed using profilometry for surface roughness. Immediately following surface roughness measurements color was assessed using a spectrophotometer. Roughness and color data were assessed using a one-way analysis of variance (ANOVA) and post-hoc Bonferroni. Correlations between the color coordinates (L*a*b*) and ∆E and roughness parameters (R_max and R_a) were analyzed at a 0.05 level of significance
Results: There were no statistical changes in R_a measurements between finishing and finishing and polishing for Heritage 7 for any of the instrumentation regimes, however specimens finished with stones showed a dramatic change in R_max values (16.7) compared to control (6.4) and all the other finishing and finishing and polishing regimens. Samples of Ice finished with Stones and discs (R_a: 0.5, R_max; 3.6) were significantly smoother in terms of R_a and R_max compared to analogous specimens that were finished only (R_a: 1.8, R_max 26.3). There was no statistically significant improvement between finishing and finishing and polishing for the Z350 samples (R_a: 0.6 vs 0.5, R_max: 5.4 vs 3.0). There was a correlation between R_a and color parameters L* and a* and ∆E for the nanocomposites Heritage 7 and Ice. Green and white stones produced the most surface detriment in terms of surface roughness and color on the tested nanohybrids.

Conclusions: Green and white stones are inappropriate for the finishing of nanohybrid composites even when a subsequent polishing regimen is employed. The use of green and white stones produce unacceptably rough surfaces which may have a deleterious effect on the individual components of color of nanohybrids thus affecting the overall esthetic result.