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(2))-implants. Titanium dioxide (TiO(2))- and ZrO(2)-particles were compared regarding their toxicity and intranuclear cell uptake as well as the adhesion of various anaerobic bacteria on Ti- and ZrO(2)-implants. METHODS: Cyto- and genotoxicity of TiO(2)-microparticles (TiO(2)-MPs) and TiO(2)-nanoparticles (TiO(2)-NPs) in periodontal ligament (PDL)-hTERT cells were determined with XTT test and DNA damage with comet assay. Particle sizes of TiO(2)- and ZrO(2)-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(2)-implants were investigated by cultivation and counting bacterial colonies. RESULTS: Particle size measurements revealed that 99% of the TiO(2)-NPs had a size below 100 nm and 88% of the TiO(2)-MPs sizes were between 50 and 200 nm. Following EC(50) values were found for particles (mg/l): 92 (TiO(2)-MPs) and 15 (TiO(2)-NPs). A significant increase in olive tail moment (OTM) was found for TiO(2)-NPs at a concentration of 1/10 EC(50). TiO(2)- and ZrO(2)-NPs had a higher intranuclear cell uptake efficiency, compared to corresponding TiO(2)- and ZrO(2)-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(2)-implants. CONCLUSION: Ti usually develops an oxide layer (TiO(2)). Particles released from Ti-implants should be TiO(2)-particles or Ti-particles coated with a TiO(2)-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(2)- and ZrO(2)-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(2)-implants is reduced, compared to Ti-implants. Therefore, ZrO(2)-implants might contribute to reduced biological complications (e.g. periimplantitis).