Calcipex II has been widely used for root canal irrigation in endodontic treatment. It is a product of calcium oxide-based water soluble paste containing fine granular resin materials1). It was known that these granular materials were hardly dissolved in tissue and subsequently elicited foreign body granuloma by recruiting macrophages. Sometimes serious complications involving regional osteomyelitis and maxillary sinusitis were followed in long time after the endodontic treatment using Calcipex II materials2,3). And then the removed surgical specimen should be carefully examined to detect whether there exists Calcipex II material-related foreign body reaction or not. As the fine granular materials are too small in size, about 1 μm in diameter, and slightly translucent, it is difficult to find out the fine granular materials scattered throughout the granulomatous lesion even in the high magnification view. Here, we firstly found that the fine granular materials of Calcipex II showed bright birefringence under the polarizing microscope, and that the Calcipex II granules dispersed in chronic granulomatous lesion could be easily detected by their bright birefringence. The present study demonstrated a case of peri-implantitis involved with Calcipex II granule-related periapical granuloma, exhibiting numerous bright birefringence spots in the polarizing microscope observation.