Influence of zinc oxide on Aspergillus species: A possible cause of local, non-invasive aspergillosis of the maxillary sinus

Recently the appearance of radiopaque 'concrements' in the maxillary sinus was reported. These radiodense objects could be identified as root-filling material for teeth of the upper jaw containing zinc oxide. This suggested that excess root-filling material containing zinc oxide in the maxillary sinus could favour the formation of a local, non-invasive aspergillosis. To verify this hypothesis in vitro, we tested the influence of zinc oxide on Aspergillus fumigatus, A. flavus, A. terreus, A. nidulans, A. niger and A. niveus. A geometric series of zinc oxide diluted in 0.1 N H2SO4 was used. Czapek-Dox agar was inoculated with the six Aspergillus species. Circular cavities stamped into the centre of each agar plate were filled with an equal amount of the dilutions and all plates were then incubated for 7 days at 37 degrees C. Readings were taken on days 3, 5 and 7. Soluble zinc oxide promoted the growth of all the tested Aspergillus species, the effect diminishing with decreasing concentration. This effect could be observed on all days of measurement. Only with A. niger was stimulation of growth minimal, probably because this species already exhibits a high growth rate on Czapek-Dox agar. Therefore, overfilling of maxillary teeth with a zinc oxide-containing root-filling material may favour the formation of local aspergillosis.