Physical properties of current dental nanohybrid and nanofill light-cured resin composites

ObjectivesThe purpose of this work was the detailed study of sorption characteristics of water or artificial saliva, the determination of flexural strength and the flexural modulus, and the study of the thermal stability of some current commercial dental light-cured nanocomposites containing nano-sized filler particles.MethodsThree nanohydrid dental composites (Tetric EvoCeram (TEC), Grandio (GR) and Protofill-nano (PR)) and two nanofill composites (Filtek Supreme Body (FSB) and the Filtek Supreme Translucent (FST)) were used in this work. The volumetric shrinkage due to polymerization was first determined. Also the sorption, solubility and volumetric increase were measured after storage of composites in water or artificial saliva for 30 days. The flexural strength and flexural modulus were measured using a three-point bending set-up according to the ISO-4049 specification, after immersion of samples in water or artificial saliva for 1 day or 30 days. Thermal analysis technique TGA method was used to investigate the thermal stability of composites.ResultsGR and TEC composites showed statistically no difference in volumetric shrinkage (%) which is lower than the other composites, which follow the order PR < FSB < FST. The amount of sorbed water and solubility is not statistically different than those in artificial saliva. In all the composites studied the amount of water, which is sorbed (% on composite) is not statistically different than the amount of water, which is desorbed and follows the order: GR < TEC < PR < FSB < FST. After immersion in water for 1 day the highest flexural strength showed the FSB and the lowest TEC. GR, PR and FST showed no statistically different flexural strength. The flexural modulus of composites after immersion for one day follows the order TEC < PR≤FST < FSB < GR.SignificanceAmong the composites studied, Grandio had the lowest polymer matrix content, consisting mainly of Bis-GMA. It showed the lowest polymerization shrinkage and water sorption and the highest flexural strength and flexural modulus after immersion in water or artificial saliva for 30 days. The water and artificial saliva generally showed the same effect on physical properties of the studied composites. Thermogravimetric analysis gave good information about the structure and the amount of organic polymer matrix of composites.