Introduction: The role of bacteria in the etiology of peri-implantitis has been reported in the literature. However, the influence of confounding factors on the disease remains unclear. The following case series discusses the presence of metal particles in diseased peri-implant mucosa. Case Series: Four patients with peri-implantitis underwent surgical peri-implant therapy and diode laser surface decontamination procedures. Peri-implant mucosa was excised under local anesthesia and samples were prepared for histology, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to evaluate peri-implant tissues and identify deposits of foreign materials. Histologic examination demonstrated cellular fibrous connective tissue, with or without overlying stratified squamous epithelium. An inflammatory infiltrate consisting of a mixture of acute and chronic inflammatory cells was observed. Numerous deposits of granular foreign material were scattered within the connective tissue immediately below the epithelium. The presence of metal particles was evident in the SEM and confirmed by EDS. The size of titanium particles ranged from 2 to 15 μm. Additional particles, such as aluminum, phosphorous, and sulfur, were also found in some of the samples. Conclusions: All four cases yielded peri-implant soft-tissue specimens containing particulate black foreign material. SEM and EDS examination of histologic specimens confirmed the presence titanium particles and other elements in the peri-implant tissues. Whether the presence of titanium particles in the surrounding tissue constitutes a biocompatibility issue is still a question that needs to be clearly evaluated.