Evaluation of Surface Roughness and Discolouration of Various Composite Resins

Objective: To evaluate the surface roughness and colour stability of several composite resins after immersion in coffee solution. Method: Four types of composite resins (Z-250, P-60, Z-100 & A-110) (3M Co., St. Paul, MN, USA) were evaluated. Ten specimens (10mm diameter x 2mm thickness) were fabricated for each group and subjected to polishing with aluminium-oxide disc (Sof-LexTM, 3M Co., St. Paul, MN, USA). Each specimen was polished in a sequential manner from the coarsest to the finest disc. For Z-250, 10 additional specimens were fabricated and not subjected to polishing treatment (surfaces were as cured against the mylar strip). All specimens were immersed in coffee solution and incubated at 100% relative humidity at 37°C±1°C for 7 days. Specimens were analyzed for surface roughness using a profilometer prior to immersion in coffee solution and at day seven. A spectrophotometer was used to determine the initial colour and the colour change after 24 hours and 7 days of immersion. Independent samples t-test (to compare mylar-cured Z250 and polished Z250), one-way ANOVA (to compare between polished groups) and Scheffe's statistical tests were applied to the data (α=0.05). Results: Mylar-cured Z250 showed statistically lower mean surface roughness compared to polished Z250 before and after 7 days immersion but recorded statistically higher colour changes after 24 hours and 7 days immersion compared with polished Z250. When the polished groups were compared, A-110 showed the greatest colour changes after 24 hours and 7 days immersion and the highest surface roughness before and after 7 days immersion and the mean difference was statistically significant (p<.05) compared with Z-250, P-60 and Z100. Conclusion: Mylar-cured Z250 was significantly smoother than polished Z250 but discoloured more (p<.05) than polished Z250. Microfilled composite A-110 was significantly rougher and showed greater discolouration than hybrid composite Z-250, P-60 and Z100.