relative biocompatibility of micro-hybrid and nano-hybrid light activated composite resins

background and aim: in vitro studies have revealed a direct association between resin content and cytotoxicity of resin composites; but implantation studies in this regard are sparse. this study investigates the relationship between filler content of composite resins and biocompatibility. materials and methods: this study was conducted using 18 male wistar rats (180-200g), 1 nano-hybrid (prime-dent inc.) and 1 micro-hybrid (medental inc.) composites 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 the experimental group, while two were allocated to the control group. a section of 1.5mm long cured nano-hybrid and micro-hybrid 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 & major. the average scores were calculated. result: the average grade of inflammation for the nano-hybrid on the 2nd day of implantation was 3.3. the micro-hybrid resin had a score of 3.0 for inflammation. on the 14th day, the micro-hybrid resin also had a lower average grade for cellular inflammation. on the 90th day, the micro-hybrid resin had a higher grade of inflammation (0.9) as against 0.3 recorded for nano-hybrid. conclusion: the resin composites with higher filler content elicited lower grade of inflammation in the first two weeks of implantation, but after three months the converse was the case.