Therapy-resistant foreign body giant cell granuloma at the periapex of a root-filled human tooth.

Although the primary etiological factor of periapical lesions is microbial, there are other independent factors that can adversely affect the outcome of endodontic treatment. In this communication, we present morphological evidence in support of the role of a foreign body reaction of periapical tissue to root-filling materials. The specimen consisted of a surgical biopsy of an asymptomatic periapical lesion which persisted after a decade of postendodontic follow-up. The biopsy was processed for correlated light and electron microscopy and was analyzed by various microtechniques. The unique feature of the lesion was the presence of vast numbers of large multinucleated cells and their cytoplasmic inclusion bodies. Morphologically, these multinucleated cells resembled foreign body giant cells. They contained characteristic birefringent cytoplasmic inclusions which on electron-probe X-ray microanalysis consistently revealed the presence of magnesium and silicon. The magnesium and silicon are presumably the remnants of a root-filling excess which protruded into the periapex and had been resorbed during the follow-up period. These observations strongly suggest that in the absence of microbial factors, root-filling materials which contain irritating substances can evoke a foreign body reaction at the periapex, leading to the development of asymptomatic periapical lesions that may remain refractory to endodontic therapy for long periods of time.