A Comparative Evaluation of Surface Roughness and Immediate Colour stability of Two Nanocomposites After Polishing with Two Different Polishing Systems: An In Vitro study

AIMS AND OBJECTIVES : AIM : To compare the surface roughness and immediate colour stability of Tetric evo ceram and IPS Empress Direct after polishing with astropol and astrobrush. OBJECTIVES : To assess the surface roughness of the nanocomposites polished with two different polishing systems using atomic force microscopy and their immediate colour stability using spectrophotometry. METHODOLOGY : A total of sixty samples were prepared in the study . The commercially available composite materials used in this study were Tetric evo ceram and IPS Empress Direct .Orthodontic bands of thickness 0.006 inches were used to make cylindrical metallic moulds of the dimensions 10mm diameter and 6 mm height. The composite material was placed in increments of 2mm or less and packed into the cylindrical metallic mould using a teflon coated composite placement instrument .A transparent matrix strip was applied on top of each increment of composite with a constant pressure to extrude excess material ,to flatten the surface and to reduce voids at the surface. Each increment of composite were light cured for 40 seconds using LED light curing unit. of intensity 400 milli watts/ cm2 . Following complete curing of the composite, the metallic moulds were separated using a scalpel to obtain cylindrical composites of the specified dimensions. Colour stability of the flat surfaces were evaluated before polishing using spectrophotometer. The specimens were randomly divided into six groups of ten specimens each . Groups used in the study were as follows : Group- I - Unpolished Tetric evo ceram ,Group -II - Unpolished IPS Empress Direct,Group- III( a) – Tetric evo ceram polished with astropol. Group –III(b) - Tetric evo ceram polished with astrobrush , Group –IV(a)- IPS Empress Direct polished with astropol, Group – IV(b)- IPS Empress Direct polished with astrobrush. Each of the flat surfaces of the samples were polished unidirectionally ( four strokes each) for eight seconds each using the two different polishing systems, 1 .Astropol with its finishing grit, polishing grit and high gloss polishing grit respectively.2.Astrobrush at low speed using a micro motor hand piece. Immediate colour stability was evaluated after polishing using spectrophotometer. The cylindrical composite specimens were placed in normal saline before evaluating the flat surfaces for surface roughness using AFM. The data were statistically analyzed using one - way analysis of variance(ANOVA) ,Post hoc and Dunnett’s test. RESULTS AND OBSERVATIONS : The results showed that among the experimental groups the maximum root mean square value of 1.93±0.03 nm2 was observed for group IV(a) [ Tetric evo ceram polished with astropol ] when compared to Groups-III(a), III(b), IV(b), (P<0.05), is considered statistically significant. The minimum root mean square value of 0.22±0.02 nm2 was observed for Group- IV(b) [ IPS Empress Direct polished with Astrobrush] when compared to Groups - III (a), III (b), IV (a) , (P<0.05), is considered statistically significant. The results showed that there is very minimal changes in colour values of groups before and after polishing with the two different polishing systems , (P>0.05), is considered statistically insignificant. CONCLUSION : Superior polish was obtained when the composites were polished with astrobrush when compared to those polished with astropol. There was very minimal difference in the colour stability of the composites before and after polising using the two different polishing systems. Clinical Significance : The esthetics and longevity of composite restorations strongly depends on the quality of the surface finishing and polishing as well as its colour stability . The presence of irregularities or change in its colour can influence appearance, plaque retention, surface discoloration, gingival inflammation .In addition, the surface roughness of composites can reduce the hardness and increase the wear of these restorations, hence the importance of proper finishing and polishing as well as the colour stability of composite restorations