As a result of shaping, finishing, or removal of dental composite resin restorations, resin particles may become trapped and embedded in oral tissues. However, tissue reactions induced by entrapped composite resin particles have not been thoroughly examined. To assess the soft tissue inflammatory response to composite restorative materials, three commercial dental composite resin suspensions were implanted subcutaneously in rats. Implantation resulted in a granulomatous inflammatory reaction that persisted 8 weeks after placement. The lesion was characterized by an influx of lymphocytes and the presence of fibroblasts and epithelioid cells. Composite resin particles have the potential to cause persistent inflammation if they are entrapped in oral tissues.