Relative biocompatibility of microhybrid and nanohybrid lightactivated composite resins

Background. In vitro studies have revealed a direct association between resin content and cytotoxicity of composite resins; however, implantation studies in this regard are sparse. This study investigates the relationship between filler content of composite resins and biocompatibility. Methods. This research employed twelve 180‒200gr male Wistar rats, 1 nanohybrid (PrimeDent Inc.) and 1 microhybrid (Medental Inc.) composite resins containing 74% and 80‒90% filler content, respectively. The samples were assessed on the 2nd, 14th and 90th day of implantation. Four rats were allocated to each day in this experimental study. A section of 1.5mm long cured nanohybrid and microhybrid materials were implanted into the right and left upper and lower limbs of the rats, respectively. Eight samples were generated on each day of observation. Inflammation was graded according to the criteria suggested by Orstavik and Major. Pearson’s chisquared test was employed to determine the relationship between the tissue responses of the two materials. Statistical significance was set at P lt; 0.05. Results. The average grade of inflammation for the nanohybrid on the 2nd day of implantation was 3.3. The microhybrid resin had a score of 3.0 for cellular inflammation. On the 14th day, the microhybrid resin also exhibited a lower average grade for cellular inflammation. On the 90th day, the microhybrid resin had a higher grade of inflammation (0.9) compared to 0.3 recorded for nanohybrid. The composite resins with higher filler content elicited a significantly lower grade of inflammation irrespective of the duration (χ=20.000, df=8, P=0.010) while the composite resins with lower filler content elicited a significantly lower inflammatory response on the 90th day (χ=4.000, df=1, P=0.046). Conclusion. The composite resins with higher filler content generally elicited significantly lower grades of inflammation, and the composite resins with lower filler content exhibited significantly lower inflammatory response on the 90th day of implantation.