Investigation of foreign materials in gingival biopsies: a clinicopathologic, energy-dispersive x-ray microanalysis, and in vitro study

Foreign body gingivitis (FBG) has been previously described as a localized inflammatory reaction associated with the presence of foreign material in gingival tissues. However, among the gingival biopsies submitted to the Pacific Oral Pathology Laboratory (POPL) for diagnosis, we have identified foreign material in lesions that are markedly keratinized and described clinically as white plaques rather than inflamed lesions. Objectives To evaluate the clinical and histopathological features of 86 gingival biopsies containing foreign material retrieved from the POPL archives and to identify the composition of these particles by energy-dispersive x-ray spectroscopy (EDX). Further, primary human gingival fibroblasts (HGF) were stimulated with silica (SiO2) microparticles to investigate the production of COL-1, MMP2 and inflammatory cytokines. Findings Foreign material was most commonly found in women (61%), in the 6th or 7th decade of life, and the clinical lesions were most frequently described as white plaques involving posterior mandibular gingiva. Interestingly, histopathological examination identified verrucous hyperplasia in 60.5% of the cases and epithelial dysplasia in 28.5% of the cases. EDX microanalysis revealed that Si (94%) followed by Ca (85%) and Al (66%) were the most frequently detected elements in the foreign particles. Silica microparticles induced higher COL-1 expression and increased MMP-2 activity in HGF, and higher levels of pro-inflammatory cytokines such as IL-6, IL-8 and TGF-s in a microparticle-concentration-dependent manner. Conclusions Our study demonstrates that there is a strong association between the presence of foreign material in gingiva and clinically and microscopically demonstrable hyperkeratotic verrucous plaques. Moreover, we found that the most common element in the foreign material is Si which is usually found in the Earth's crust as silica. Our in vitro findings demonstrate the importance of silica-mediated effects on gingival fibroblasts, suggesting that the presence of silica in gingival biopsies could modulate the host inflammatory response and should be further investigated.