Intranuclear cell uptake and toxicity of titanium dioxide and zirconia particles as well as bacterial adhesion on dental titanium- and zirconia-implants.

OBJECTIVE

Previous studies have shown that particles can be released from dental titanium (Ti)- and zirconia (ZrO)-implants. Titanium dioxide (TiO)- and ZrO-particles were compared regarding their toxicity and intranuclear cell uptake as well as the adhesion of various anaerobic bacteria on Ti- and ZrO-implants.

METHODS

Cyto- and genotoxicity of TiO-microparticles (TiO-MPs) and TiO-nanoparticles (TiO-NPs) in periodontal ligament (PDL)-hTERT cells were determined with XTT test and DNA damage with comet assay. Particle sizes of TiO- and ZrO-particles were measured with scanning electron microscope. Intranuclear uptake in PDL-hTERT cells was determined with laser scanning confocal microscopy. Adhesions of relevant anaerobic mouth bacteria Porphyromonas gingivalis, Prevotella intermedia and Aggregatibacter actinomycetemcomitans on Ti- and ZrO-implants were investigated by cultivation and counting bacterial colonies.

RESULTS

Particle size measurements revealed that 99% of the TiO-NPs had a size below 100 nm and 88% of the TiO-MPs sizes were between 50 and 200 nm. Following EC values were found for particles (mg/l): 92 (TiO-MPs) and 15 (TiO-NPs). A significant increase in olive tail moment (OTM) was found for TiO-NPs at a concentration of 1/10 EC. TiO- and ZrO-NPs had a higher intranuclear cell uptake efficiency, compared to corresponding TiO- and ZrO-MPs. All investigated particles could be detected in cell nucleus. Adhesion of all investigated bacterial species was significantly higher on Ti-implants, compared to ZrO-implants.

CONCLUSION

Ti usually develops an oxide layer (TiO). Particles released from Ti-implants should be TiO-particles or Ti-particles coated with a TiO-layer. Toxicity of released Ti-particles depends on their oxidation state and on their size (NP or MP). Particularly, NPs were more cyto- and genotoxic compared to the corresponding MPs. TiO- and ZrO-NPs showed a significant increase in the intranuclear cell uptake ratio at higher exposure concentration, compared to lower concentrations and consequently might lead to a higher potential of DNA damage. Adhesion of bacteria to ZrO-implants is reduced, compared to Ti-implants. Therefore, ZrO-implants might contribute to reduced biological complications (e.g. periimplantitis).