Physical Properties of Nanohybrid and Microhybrid Resin Composites Subjected to an Acidic Environment: A Laboratory Study

Abstract

SUMMARY Background: This study investigated the hardness and color stability of five resin composites subjected to different polishing methods following immersion in distilled water or lactic acid for up to three months. Methods and Materials: Three nanohybrid, Paradigm (3M ESPE), Estelite Sigma Quick (Tokuyama), Ice (SDI), and two microhybrid, Filtek P60 and Filtek Z250, composites were examined. Disc-shaped specimens (10×1.5 mm) were prepared and immersed in distilled water for 24 hours then polished using either silicon carbide paper, the Shofu polishing system or were left unpolished (control). The CIE values and microhardness were determined using a spectrophotometer and digital Vickers hardness tester, respectively (n=10) after one, 45, and 90 days of storage in distilled water or lactic acid. Data were analyzed using analysis of variance, Tukey test, and Pearson correlation coefficient. Results: Ice exhibited the greatest color change, yet Paradigm and Filtek P60 demonstrated the least. Overall, discoloration of tested materials was multifactorial and the effect of storage media depended on the material, polishing method and time interval. The greatest hardness was obtained for Paradigm and the lowest for Estelite. Hardness was found to be significantly higher in lactic acid after 45 days (p=0.014) and even higher after 90 days (p<0.001) compared with distilled water. Conclusions: An acidic environment did not adversely affect color stability or microhardness of the resin composites. There was a significantly mild reverse correlation between hardness and color change in both storage media.