Filler-immobilization assisted designing of hydroxyapatite and silica/ hydroxyapatite filled acrylate based dental restorative composites: Comparative evaluation of quasi-static and dynamic mechanical properties

The comparative effect of filler combinations on the quasi-static and thermo-mechanical properties of light cured acrylate based restorative composites is addressed in the study. Two series of acrylate based restorative composites filled with hydroxyapatite (Hap) and silica/Hap combination were prepared. FTIR spectroscopy showed the filler-assisted functional interference with the chemical structure of the resin, whereas SEM–EDX revealed the state of micro-dispersion/distribution morphology of the filled composites. The silica/Hap combination filled (micro-hybrid) composites with 30 wt.-% filler showed highest compressive strength (CS) and composites with 20 wt.-% filler showed highest diametral tensile strength (DTS) as well as flexural strength (FS). Dynamic mechanical properties revealed reinforcement effectiveness correlated to extent of filler immobilization effects estimated from Kerner equation. Our study conceptually establishes the possibility of manipulating the mechanical and thermo-mechanical strength requirements, by catering to the extent of filler induced bulk hardening contributions, as characterized by immobilized volume fraction of the polymer chains. It was imperatively deduced that at very high amount of overall filler content (e.g. > 50 wt.-%) the reinforcement effectiveness is filler-controlled whereas the same extent of effectiveness may be obtained by manipulating the filler induced immobilization effects (e.g. < 20 wt. - %).